EVOLUTION-MANAGER

Edit File: compress.js

/***********************************************************************

A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS

-------------------------------- (C) ---------------------------------

Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

Distributed under the BSD license:

Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

* Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

* Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

***********************************************************************/

"use strict";

Compressor.prototype = new TreeTransformer;
merge(Compressor.prototype, {
    option: function(key) { return this.options[key] },
    exposed: function(def) {
        if (def.global) for (var i = 0; i < def.orig.length; i++)
            if (!this.toplevel[def.orig[i] instanceof AST_SymbolDefun ? "funcs" : "vars"])
                return true;
        return false;
    },
    compress: function(node) {
        node = node.resolve_defines(this);
        if (this.option("expression")) {
            node.process_expression(true);
        }
        var passes = +this.options.passes || 1;
        var min_count = 1 / 0;
        var stopping = false;
        var mangle = { ie8: this.option("ie8") };
        for (var pass = 0; pass < passes; pass++) {
            node.figure_out_scope(mangle);
            if (pass > 0 || this.option("reduce_vars"))
                node.reset_opt_flags(this);
            node = node.transform(this);
            if (passes > 1) {
                var count = 0;
                node.walk(new TreeWalker(function() {
                    count++;
                }));
                AST_Node.info("pass " + pass + ": last_count: " + min_count + ", count: " + count);
                if (count < min_count) {
                    min_count = count;
                    stopping = false;
                } else if (stopping) {
                    break;
                } else {
                    stopping = true;
                }
            }
        }
        if (this.option("expression")) {
            node.process_expression(false);
        }
        return node;
    },
    before: function(node, descend, in_list) {
        if (node._squeezed) return node;
        var is_scope = node instanceof AST_Scope;
        if (is_scope) {
            node.hoist_properties(this);
            node.hoist_declarations(this);
            node.process_boolean_returns(this);
        }
        // Before https://github.com/mishoo/UglifyJS/pull/1602 AST_Node.optimize()
        // would call AST_Node.transform() if a different instance of AST_Node is
        // produced after OPT().
        // This corrupts TreeWalker.stack, which cause AST look-ups to malfunction.
        // Migrate and defer all children's AST_Node.transform() to below, which
        // will now happen after this parent AST_Node has been properly substituted
        // thus gives a consistent AST snapshot.
        descend(node, this);
        // Existing code relies on how AST_Node.optimize() worked, and omitting the
        // following replacement call would result in degraded efficiency of both
        // output and performance.
        descend(node, this);
        var opt = node.optimize(this);
        if (is_scope && opt === node) {
            opt.drop_unused(this);
            descend(opt, this);
        }
        if (opt === node) opt._squeezed = true;
        return opt;
    }
});

(function(OPT) {
    OPT(AST_Node, function(self, compressor) {
        return self;
    });

AST_Node.DEFMETHOD("equivalent_to", function(node) {
        return this.TYPE == node.TYPE && this.print_to_string() == node.print_to_string();
    });

AST_Scope.DEFMETHOD("process_expression", function(insert, transform) {
        var self = this;
        var tt = new TreeTransformer(function(node) {
            if (insert && node instanceof AST_SimpleStatement) {
                return make_node(AST_Return, node, {
                    value: node.body
                });
            }
            if (!insert && node instanceof AST_Return) {
                return transform ? transform(node) : make_node(AST_SimpleStatement, node, {
                    body: node.value || make_node(AST_UnaryPrefix, node, {
                        operator: "void",
                        expression: make_node(AST_Number, node, {
                            value: 0
                        })
                    })
                });
            }
            if (node instanceof AST_Lambda && node !== self) {
                return node;
            }
            if (node instanceof AST_Block) {
                var index = node.body.length - 1;
                if (index >= 0) {
                    node.body[index] = node.body[index].transform(tt);
                }
            } else if (node instanceof AST_If) {
                node.body = node.body.transform(tt);
                if (node.alternative) {
                    node.alternative = node.alternative.transform(tt);
                }
            } else if (node instanceof AST_With) {
                node.body = node.body.transform(tt);
            }
            return node;
        });
        self.transform(tt);
    });

function is_read_only_fn(value, name) {
        if (value instanceof AST_Boolean) return native_fns.Boolean[name];
        if (value instanceof AST_Number) return native_fns.Number[name];
        if (value instanceof AST_String) return native_fns.String[name];
        if (name == "valueOf") return false;
        if (value instanceof AST_Array) return native_fns.Array[name];
        if (value instanceof AST_Function) return native_fns.Function[name];
        if (value instanceof AST_Object) return native_fns.Object[name];
        if (value instanceof AST_RegExp) return native_fns.RegExp[name] && !value.value.global;
    }

function is_arguments(def) {
        if (def.name != "arguments") return false;
        var orig = def.orig;
        return orig.length == 1 && orig[0] instanceof AST_SymbolFunarg;
    }

(function(def) {
        def(AST_Node, noop);

function push(tw) {
            tw.safe_ids = Object.create(tw.safe_ids);
        }

function pop(tw) {
            tw.safe_ids = Object.getPrototypeOf(tw.safe_ids);
        }

function mark(tw, def, safe) {
            tw.safe_ids[def.id] = safe;
        }

function add_assign(tw, def, node) {
            if (def.fixed === false) return;
            tw.assigns.add(def.id, node);
        }

function set_assign(tw, def, node) {
            if (def.fixed === false) return;
            var assigns = tw.assigns.get(def.id);
            if (assigns) assigns.forEach(function(node) {
                node.assigns = assigns;
            });
            tw.assigns.set(def.id, def.assigns = [ node ]);
        }

function ref_once(tw, compressor, def) {
            return compressor.option("unused")
                && !def.scope.pinned()
                && def.references.length - def.recursive_refs == 1;
        }

function is_immutable(value) {
            if (!value) return false;
            return value.is_constant()
                || value instanceof AST_Lambda
                || value instanceof AST_This;
        }

function mark_assignment_to_arguments(node) {
            if (!(node instanceof AST_Sub)) return;
            var expr = node.expression;
            if (!(expr instanceof AST_SymbolRef)) return;
            var def = expr.definition();
            if (is_arguments(def) && node.property instanceof AST_Number) def.reassigned = true;
        }

AST_Toplevel.DEFMETHOD("reset_opt_flags", function(compressor) {
        var tw = new TreeWalker(compressor.option("reduce_vars") ? function(node, descend) {
            reset_flags(node);
            return node.reduce_vars(tw, descend, compressor);
        } : reset_flags);
        // Assignment chains
        tw.assigns = new Dictionary();
        // Flow control for visiting `AST_Defun`s
        tw.defun_ids = Object.create(null);
        tw.defun_visited = Object.create(null);
        // Record the loop body in which `AST_SymbolDeclaration` is first encountered
        tw.in_loop = null;
        tw.loop_ids = Object.create(null);
        // Stack of look-up tables to keep track of whether a `SymbolDef` has been
        // properly assigned before use:
        // - `push()` & `pop()` when visiting conditional branches
        // - backup & restore via `save_ids` when visiting out-of-order sections
        tw.safe_ids = Object.create(null);
        this.walk(tw);

function reset_flags(node) {
            node._squeezed = false;
            node._optimized = false;
            if (node instanceof AST_Scope) delete node._var_names;
        }
    });

AST_Symbol.DEFMETHOD("fixed_value", function() {
        var fixed = this.definition().fixed;
        if (!fixed) return fixed;
        if (this.fixed) fixed = this.fixed;
        return fixed instanceof AST_Node ? fixed : fixed();
    });

AST_SymbolRef.DEFMETHOD("is_immutable", function() {
        var def = this.definition();
        if (def.orig.length != 1) return false;
        var sym = def.orig[0];
        return sym instanceof AST_SymbolLambda && def.scope.name === sym;
    });

function make_sequence(orig, expressions) {
        if (expressions.length == 1) return expressions[0];
        return make_node(AST_Sequence, orig, {
            expressions: expressions.reduce(merge_sequence, [])
        });
    }

function needs_unbinding(compressor, val) {
        return val instanceof AST_PropAccess
            || is_undeclared_ref(val) && val.name == "eval";
    }

// we shouldn't compress (1,func)(something) to
    // func(something) because that changes the meaning of
    // the func (becomes lexical instead of global).
    function maintain_this_binding(compressor, parent, orig, val) {
        if (parent instanceof AST_UnaryPrefix && parent.operator == "delete"
            || parent.TYPE == "Call" && parent.expression === orig && needs_unbinding(compressor, val)) {
            return make_sequence(orig, [ make_node(AST_Number, orig, { value: 0 }), val ]);
        }
        return val;
    }

function as_statement_array(thing) {
        if (thing === null) return [];
        if (thing instanceof AST_BlockStatement) return thing.body;
        if (thing instanceof AST_EmptyStatement) return [];
        if (thing instanceof AST_Statement) return [ thing ];
        throw new Error("Can't convert thing to statement array");
    }

function is_empty(thing) {
        if (thing === null) return true;
        if (thing instanceof AST_EmptyStatement) return true;
        if (thing instanceof AST_BlockStatement) return thing.body.length == 0;
        return false;
    }

function loop_body(x) {
        if (x instanceof AST_IterationStatement) {
            return x.body instanceof AST_BlockStatement ? x.body : x;
        }
        return x;
    }

function root_expr(prop) {
        while (prop instanceof AST_PropAccess) prop = prop.expression;
        return prop;
    }

function is_iife_call(node) {
        if (node.TYPE != "Call") return false;
        return node.expression instanceof AST_Function || is_iife_call(node.expression);
    }

function is_undeclared_ref(node) {
        return node instanceof AST_SymbolRef && node.definition().undeclared;
    }

function get_rvalue(expr) {
        return expr[expr instanceof AST_Assign ? "right" : "value"];
    }

var global_names = makePredicate("Array Boolean clearInterval clearTimeout console Date decodeURI decodeURIComponent encodeURI encodeURIComponent Error escape eval EvalError Function isFinite isNaN JSON Math Number parseFloat parseInt RangeError ReferenceError RegExp Object setInterval setTimeout String SyntaxError TypeError unescape URIError");
    AST_SymbolRef.DEFMETHOD("is_declared", function(compressor) {
        return this.defined
            || !this.definition().undeclared
            || compressor.option("unsafe") && global_names[this.name];
    });

var identifier_atom = makePredicate("Infinity NaN undefined");
    function is_identifier_atom(node) {
        return node instanceof AST_Infinity
            || node instanceof AST_NaN
            || node instanceof AST_Undefined;
    }

// Search from right to left for assignment-like expressions:
        // - `var a = x;`
        // - `a = x;`
        // - `++a`
        // For each candidate, scan from left to right for first usage, then try
        // to fold assignment into the site for compression.
        // Will not attempt to collapse assignments into or past code blocks
        // which are not sequentially executed, e.g. loops and conditionals.
        function collapse(statements, compressor) {
            if (scope.pinned()) return statements;
            var args;
            var assignments = Object.create(null);
            var candidates = [];
            var declare_only = Object.create(null);
            var force_single;
            var stat_index = statements.length;
            var scanner = new TreeTransformer(function(node, descend) {
                if (abort) return node;
                // Skip nodes before `candidate` as quickly as possible
                if (!hit) {
                    if (node !== hit_stack[hit_index]) return node;
                    hit_index++;
                    if (hit_index < hit_stack.length) return handle_custom_scan_order(node, scanner);
                    hit = true;
                    stop_after = (value_def ? find_stop_value : find_stop)(node, 0);
                    if (stop_after === node) abort = true;
                    return node;
                }
                // Stop immediately if these node types are encountered
                var parent = scanner.parent();
                if (should_stop(node, parent)) {
                    abort = true;
                    return node;
                }
                // Stop only if candidate is found within conditional branches
                if (!stop_if_hit && in_conditional(node, parent)) {
                    stop_if_hit = parent;
                }
                // Skip transient nodes caused by single-use variable replacement
                if (node.single_use && parent instanceof AST_VarDef && parent.value === node) return node;
                // Replace variable with assignment when found
                var hit_rhs;
                if (!(node instanceof AST_SymbolDeclaration)
                    && (scan_lhs && lhs.equivalent_to(node)
                        || scan_rhs && (hit_rhs = scan_rhs(node, this)))) {
                    if (!can_replace || stop_if_hit && (hit_rhs || !lhs_local || !replace_all)) {
                        if (!hit_rhs || !value_def) abort = true;
                        return node;
                    }
                    if (is_lhs(node, parent)) {
                        if (value_def && !hit_rhs) {
                            assign_used = true;
                            replaced++;
                        }
                        return node;
                    } else if (value_def) {
                        if (!hit_rhs) replaced++;
                        return node;
                    } else {
                        replaced++;
                    }
                    CHANGED = abort = true;
                    AST_Node.info("Collapsing {name} [{file}:{line},{col}]", {
                        name: node.print_to_string(),
                        file: node.start.file,
                        line: node.start.line,
                        col: node.start.col
                    });
                    if (candidate instanceof AST_UnaryPostfix) {
                        delete candidate.expression.fixed;
                        return make_node(AST_UnaryPrefix, candidate, candidate);
                    }
                    if (candidate instanceof AST_VarDef) {
                        var def = candidate.name.definition();
                        if (def.references.length - def.replaced == 1 && !compressor.exposed(def)) {
                            def.replaced++;
                            return maintain_this_binding(compressor, parent, node, candidate.value);
                        }
                        return make_node(AST_Assign, candidate, {
                            operator: "=",
                            left: make_node(AST_SymbolRef, candidate.name, candidate.name),
                            right: candidate.value
                        });
                    }
                    candidate.write_only = false;
                    return candidate;
                }
                // These node types have child nodes that execute sequentially,
                // but are otherwise not safe to scan into or beyond them.
                if (is_last_node(node, parent) || may_throw(node)) {
                    stop_after = node;
                    if (node instanceof AST_Scope) abort = true;
                }
                // Scan but don't replace inside getter/setter
                if (node instanceof AST_Accessor) {
                    var replace = can_replace;
                    can_replace = false;
                    descend(node, scanner);
                    can_replace = replace;
                    return node;
                }
                return handle_custom_scan_order(node, scanner);
            }, function(node) {
                if (abort) return;
                if (stop_after === node) abort = true;
                if (stop_if_hit === node) stop_if_hit = null;
            });
            var multi_replacer = new TreeTransformer(function(node) {
                if (abort) return node;
                // Skip nodes before `candidate` as quickly as possible
                if (!hit) {
                    if (node !== hit_stack[hit_index]) return node;
                    hit_index++;
                    switch (hit_stack.length - hit_index) {
                      case 0:
                        hit = true;
                        if (assign_used) return node;
                        if (node instanceof AST_VarDef) return node;
                        def.replaced++;
                        var parent = multi_replacer.parent();
                        if (parent instanceof AST_Sequence && parent.tail_node() !== node) {
                            value_def.replaced++;
                            return List.skip;
                        }
                        return get_rvalue(candidate);
                      case 1:
                        if (!assign_used && node.body === candidate) {
                            hit = true;
                            def.replaced++;
                            value_def.replaced++;
                            return null;
                        }
                      default:
                        return;
                    }
                }
                // Replace variable when found
                if (node instanceof AST_SymbolRef
                    && node.name == def.name) {
                    if (!--replaced) abort = true;
                    if (is_lhs(node, multi_replacer.parent())) return node;
                    def.replaced++;
                    value_def.replaced--;
                    return get_rvalue(candidate).clone();
                }
                // Skip (non-executed) functions and (leading) default case in switch statements
                if (node instanceof AST_Default || node instanceof AST_Scope) return node;
            }, patch_sequence);
            while (--stat_index >= 0) {
                // Treat parameters as collapsible in IIFE, i.e.
                //   function(a, b){ ... }(x());
                // would be translated into equivalent assignments:
                //   var a = x(), b = undefined;
                if (stat_index == 0 && compressor.option("unused")) extract_args();
                // Find collapsible assignments
                var hit_stack = [];
                extract_candidates(statements[stat_index]);
                while (candidates.length > 0) {
                    hit_stack = candidates.pop();
                    var hit_index = 0;
                    var candidate = hit_stack[hit_stack.length - 1];
                    var value_def = null;
                    var stop_after = null;
                    var stop_if_hit = null;
                    var lhs = get_lhs(candidate);
                    var side_effects = lhs && lhs.has_side_effects(compressor);
                    var scan_lhs = lhs && !side_effects && !is_lhs_read_only(lhs, compressor);
                    var scan_rhs = foldable(get_rhs(candidate));
                    if (!scan_lhs && !scan_rhs) continue;
                    var modify_toplevel = false;
                    // Locate symbols which may execute code outside of scanning range
                    var lvalues = get_lvalues(candidate);
                    var lhs_local = is_lhs_local(lhs);
                    if (!side_effects) side_effects = value_has_side_effects(candidate);
                    var replace_all = replace_all_symbols(candidate);
                    var may_throw = candidate.may_throw(compressor) ? in_try ? function(node) {
                        return node.has_side_effects(compressor);
                    } : side_effects_external : return_false;
                    var funarg = candidate.name instanceof AST_SymbolFunarg;
                    var hit = funarg;
                    var abort = false;
                    var replaced = 0;
                    var assign_used = false;
                    var can_replace = !args || !hit;
                    if (!can_replace) {
                        for (var j = compressor.self().argnames.lastIndexOf(candidate.name) + 1; !abort && j < args.length; j++) {
                            args[j].transform(scanner);
                        }
                        can_replace = true;
                    }
                    for (var i = stat_index; !abort && i < statements.length; i++) {
                        statements[i].transform(scanner);
                    }
                    if (value_def) {
                        var def = lhs.definition();
                        var referenced = def.references.length - def.replaced;
                        if (candidate instanceof AST_Assign) referenced--;
                        if (replaced && referenced == replaced) {
                            abort = false;
                        } else {
                            candidates.push(hit_stack);
                            force_single = true;
                            continue;
                        }
                        if (replaced) {
                            hit_index = 0;
                            hit = funarg;
                            for (var i = stat_index; !abort && i < statements.length; i++) {
                                if (!statements[i].transform(multi_replacer)) statements.splice(i--, 1);
                            }
                            if (candidate instanceof AST_VarDef) {
                                replaced = !compressor.exposed(def) && def.references.length == def.replaced;
                            }
                            value_def.single_use = false;
                        }
                    }
                    if (replaced && !remove_candidate(candidate)) statements.splice(stat_index, 1);
                }
            }

function in_conditional(node, parent) {
                if (parent instanceof AST_Binary) return lazy_op[parent.operator] && parent.left !== node;
                if (parent instanceof AST_Case) return parent.expression !== node;
                if (parent instanceof AST_Conditional) return parent.condition !== node;
                return parent instanceof AST_If && parent.condition !== node;
            }

function find_stop(node, level) {
                var parent = scanner.parent(level);
                if (parent instanceof AST_Array) return node;
                if (parent instanceof AST_Assign) return node;
                if (parent instanceof AST_Binary) return node;
                if (parent instanceof AST_Call) return node;
                if (parent instanceof AST_Case) return node;
                if (parent instanceof AST_Conditional) return node;
                if (parent instanceof AST_Definitions) return find_stop_unused(parent, level + 1);
                if (parent instanceof AST_Exit) return node;
                if (parent instanceof AST_If) return node;
                if (parent instanceof AST_IterationStatement) return node;
                if (parent instanceof AST_ObjectKeyVal) return node;
                if (parent instanceof AST_PropAccess) return node;
                if (parent instanceof AST_Sequence) {
                    return (parent.tail_node() === node ? find_stop : find_stop_unused)(parent, level + 1);
                }
                if (parent instanceof AST_SimpleStatement) return find_stop_unused(parent, level + 1);
                if (parent instanceof AST_Switch) return node;
                if (parent instanceof AST_Unary) return node;
                if (parent instanceof AST_VarDef) return node;
                return null;
            }

function mangleable_var(value) {
                if (force_single) {
                    force_single = false;
                    return;
                }
                if (!(value instanceof AST_SymbolRef)) return;
                var def = value.definition();
                if (def.undeclared) return;
                if (is_arguments(def)) return;
                return value_def = def;
            }

function get_rhs(expr) {
                return candidate instanceof AST_Assign && candidate.operator == "=" && candidate.right;
            }

function rhs_exact_match(node) {
                    return expr.equivalent_to(node);
                }
            }

function patch_sequence(node) {
                if (node instanceof AST_Sequence) switch (node.expressions.length) {
                    case 0: return null;
                    case 1: return node.expressions[0];
                }
            }

function is_lhs_local(lhs) {
                var sym = root_expr(lhs);
                return sym instanceof AST_SymbolRef
                    && sym.definition().scope === scope
                    && !(in_loop
                        && (lvalues.has(sym.name) && lvalues.get(sym.name)[0] !== lhs
                            || candidate instanceof AST_Unary
                            || candidate instanceof AST_Assign && candidate.operator != "="));
            }

function value_has_side_effects(expr) {
                if (expr instanceof AST_Unary) return false;
                return get_rvalue(expr).has_side_effects(compressor);
            }

function symbol_in_lvalues(sym, parent) {
                var lvalue = lvalues.get(sym.name);
                if (!lvalue || all(lvalue, function(lhs) {
                    return !lhs;
                })) return;
                if (lvalue[0] !== lhs) return true;
                scan_rhs = false;
            }

function may_modify(sym) {
                var def = sym.definition();
                if (def.orig.length == 1 && def.orig[0] instanceof AST_SymbolDefun) return false;
                if (def.scope !== scope) return true;
                if (modify_toplevel && compressor.exposed(def)) return true;
                return !all(def.references, function(ref) {
                    return ref.scope.resolve() === scope;
                });
            }

function side_effects_external(node, lhs) {
                if (node instanceof AST_Assign) return side_effects_external(node.left, true);
                if (node instanceof AST_Unary) return side_effects_external(node.expression, true);
                if (node instanceof AST_VarDef) return node.value && side_effects_external(node.value);
                if (lhs) {
                    if (node instanceof AST_Dot) return side_effects_external(node.expression, true);
                    if (node instanceof AST_Sub) return side_effects_external(node.expression, true);
                    if (node instanceof AST_SymbolRef) return node.definition().scope !== scope;
                }
                return false;
            }
        }

function handle_if_return(statements, compressor) {
            var self = compressor.self();
            var parent = compressor.parent();
            var in_lambda = self instanceof AST_Lambda;
            var in_iife = in_lambda && parent && parent.TYPE == "Call";
            var multiple_if_returns = has_multiple_if_returns(statements);
            for (var i = statements.length; --i >= 0;) {
                var stat = statements[i];
                var j = next_index(i);
                var next = statements[j];

if (in_lambda && !next && stat instanceof AST_Return) {
                    if (!stat.value) {
                        CHANGED = true;
                        statements.splice(i, 1);
                        continue;
                    }
                    if (stat.value instanceof AST_UnaryPrefix && stat.value.operator == "void") {
                        CHANGED = true;
                        statements[i] = make_node(AST_SimpleStatement, stat, {
                            body: stat.value.expression
                        });
                        continue;
                    }
                }

if (stat instanceof AST_If) {
                    var ab = aborts(stat.body);
                    if (can_merge_flow(ab)) {
                        if (ab.label) remove(ab.label.thedef.references, ab);
                        CHANGED = true;
                        stat = stat.clone();
                        stat.condition = stat.condition.negate(compressor);
                        var body = as_statement_array_with_return(stat.body, ab);
                        stat.body = make_node(AST_BlockStatement, stat, {
                            body: as_statement_array(stat.alternative).concat(extract_functions())
                        });
                        stat.alternative = make_node(AST_BlockStatement, stat, {
                            body: body
                        });
                        statements[i] = stat;
                        statements[i] = stat.transform(compressor);
                        continue;
                    }

if (ab && !stat.alternative && stat.body instanceof AST_BlockStatement && next instanceof AST_Jump) {
                        var negated = stat.condition.negate(compressor);
                        if (negated.print_to_string().length <= stat.condition.print_to_string().length) {
                            CHANGED = true;
                            stat = stat.clone();
                            stat.condition = negated;
                            statements[j] = stat.body;
                            stat.body = next;
                            statements[i] = stat;
                            statements[i] = stat.transform(compressor);
                            continue;
                        }
                    }

if (compressor.option("typeofs")) {
                        if (ab && !alt) {
                            mark_locally_defined(stat.condition, null, make_node(AST_BlockStatement, self, {
                                body: statements.slice(i + 1)
                            }));
                        }
                        if (!ab && alt) {
                            mark_locally_defined(stat.condition, make_node(AST_BlockStatement, self, {
                                body: statements.slice(i + 1)
                            }));
                        }
                    }
                }

if (stat instanceof AST_If && stat.body instanceof AST_Return) {
                    var value = stat.body.value;
                    var in_bool = stat.body.in_bool || next instanceof AST_Return && next.in_bool;
                    //---
                    // pretty silly case, but:
                    // if (foo()) return; return; => foo(); return;
                    if (!value && !stat.alternative
                        && (in_lambda && !next || next instanceof AST_Return && !next.value)) {
                        CHANGED = true;
                        statements[i] = make_node(AST_SimpleStatement, stat.condition, {
                            body: stat.condition
                        });
                        continue;
                    }
                    //---
                    // if (foo()) return x; return y; => return foo() ? x : y;
                    if ((in_bool || value) && !stat.alternative && next instanceof AST_Return) {
                        CHANGED = true;
                        stat = stat.clone();
                        stat.alternative = next;
                        statements.splice(i, 1, stat.transform(compressor));
                        statements.splice(j, 1);
                        continue;
                    }
                    //---
                    // if (foo()) return x; [ return ; ] => return foo() ? x : undefined;
                    if (!stat.alternative && !next && in_lambda && (in_bool || value && multiple_if_returns)) {
                        CHANGED = true;
                        stat = stat.clone();
                        stat.alternative = make_node(AST_Return, stat, {
                            value: null
                        });
                        statements.splice(i, 1, stat.transform(compressor));
                        continue;
                    }
                    //---
                    // if (a) return b; if (c) return d; e; => return a ? b : c ? d : void e;
                    //
                    // if sequences is not enabled, this can lead to an endless loop (issue #866).
                    // however, with sequences on this helps producing slightly better output for
                    // the example code.
                    var prev = statements[prev_index(i)];
                    if (compressor.option("sequences") && in_lambda && !stat.alternative
                        && (!prev && in_iife || prev instanceof AST_If && prev.body instanceof AST_Return)
                        && next_index(j) == statements.length && next instanceof AST_SimpleStatement) {
                        CHANGED = true;
                        stat = stat.clone();
                        stat.alternative = make_node(AST_BlockStatement, next, {
                            body: [
                                next,
                                make_node(AST_Return, next, {
                                    value: null
                                })
                            ]
                        });
                        statements.splice(i, 1, stat.transform(compressor));
                        statements.splice(j, 1);
                        continue;
                    }
                }
            }

function is_return_void(value) {
                return !value || value instanceof AST_UnaryPrefix && value.operator == "void";
            }

function can_merge_flow(ab) {
                if (!ab) return false;
                var lct = ab instanceof AST_LoopControl ? compressor.loopcontrol_target(ab) : null;
                return ab instanceof AST_Return && in_lambda && is_return_void(ab.value)
                    || ab instanceof AST_Continue && self === loop_body(lct)
                    || ab instanceof AST_Break && lct instanceof AST_BlockStatement && self === lct;
            }

function declarations_only(node) {
            return all(node.definitions, function(var_def) {
                return !var_def.value;
            });
        }

function merge_conditional_assignments(var_def, exprs, keep) {
            if (!compressor.option("conditionals")) return;
            var trimmed = false;
            var def = var_def.name.definition();
            while (exprs.length > keep) {
                var cond = to_conditional_assignment(compressor, def, var_def.value, exprs[0]);
                if (!cond) break;
                var_def.value = cond;
                exprs.shift();
                trimmed = true;
            }
            return trimmed;
        }

function join_assigns_expr(value) {
                var exprs = join_assigns(prev, value, 1);
                if (!exprs) return value;
                CHANGED = true;
                var tail = value.tail_node();
                if (exprs[exprs.length - 1] !== tail) exprs.push(tail.left);
                return make_sequence(value, exprs);
            }

function is_undefined(node, compressor) {
        return node.is_undefined
            || node instanceof AST_Undefined
            || node instanceof AST_UnaryPrefix
                && node.operator == "void"
                && !node.expression.has_side_effects(compressor);
    }

// is_truthy()
    // return true if `!!node === true`
    (function(def) {
        def(AST_Node, return_false);
        def(AST_Array, return_true);
        def(AST_Assign, function() {
            return this.operator == "=" && this.right.is_truthy();
        });
        def(AST_Lambda, return_true);
        def(AST_Object, return_true);
        def(AST_RegExp, return_true);
        def(AST_Sequence, function() {
            return this.tail_node().is_truthy();
        });
        def(AST_SymbolRef, function() {
            var fixed = this.fixed_value();
            if (!fixed) return false;
            this.is_truthy = return_false;
            var result = fixed.is_truthy();
            delete this.is_truthy;
            return result;
        });
    })(function(node, func) {
        node.DEFMETHOD("is_truthy", func);
    });

// is_negative_zero()
    // return true if the node may represent -0
    (function(def) {
        def(AST_Node, return_true);
        def(AST_Array, return_false);
        function binary(op, left, right) {
            switch (op) {
              case "-":
                return left.is_negative_zero()
                    && (!(right instanceof AST_Constant) || right.value == 0);
              case "&&":
              case "||":
                return left.is_negative_zero() || right.is_negative_zero();
              case "*":
              case "/":
              case "%":
                return true;
              default:
                return false;
            }
        }
        def(AST_Assign, function() {
            var op = this.operator;
            if (op == "=") return this.right.is_negative_zero();
            return binary(op.slice(0, -1), this.left, this.right);
        });
        def(AST_Binary, function() {
            return binary(this.operator, this.left, this.right);
        });
        def(AST_Constant, function() {
            return this.value == 0 && 1 / this.value < 0;
        });
        def(AST_Lambda, return_false);
        def(AST_Object, return_false);
        def(AST_RegExp, return_false);
        def(AST_Sequence, function() {
            return this.tail_node().is_negative_zero();
        });
        def(AST_SymbolRef, function() {
            var fixed = this.fixed_value();
            if (!fixed) return true;
            this.is_negative_zero = return_true;
            var result = fixed.is_negative_zero();
            delete this.is_negative_zero;
            return result;
        });
        def(AST_UnaryPrefix, function() {
            return this.operator == "+" && this.expression.is_negative_zero()
                || this.operator == "-";
        });
    })(function(node, func) {
        node.DEFMETHOD("is_negative_zero", func);
    });

// may_throw_on_access()
    // returns true if this node may be null, undefined or contain `AST_Accessor`
    (function(def) {
        AST_Node.DEFMETHOD("may_throw_on_access", function(compressor) {
            return !compressor.option("pure_getters") || this._dot_throw(compressor);
        });
        function is_strict(compressor) {
            return /strict/.test(compressor.option("pure_getters"));
        }
        def(AST_Node, is_strict);
        def(AST_Array, return_false);
        def(AST_Assign, function(compressor) {
            if (this.operator != "=") return false;
            var rhs = this.right;
            if (!rhs._dot_throw(compressor)) return false;
            var sym = this.left;
            if (!(sym instanceof AST_SymbolRef)) return true;
            if (rhs instanceof AST_Binary && rhs.operator == "||" && sym.name == rhs.left.name) {
                return rhs.right._dot_throw(compressor);
            }
            return true;
        });
        def(AST_Binary, function(compressor) {
            switch (this.operator) {
              case "&&":
                return this.left._dot_throw(compressor) || this.right._dot_throw(compressor);
              case "||":
                return this.right._dot_throw(compressor);
              default:
                return false;
            }
        });
        def(AST_Conditional, function(compressor) {
            return this.consequent._dot_throw(compressor) || this.alternative._dot_throw(compressor);
        });
        def(AST_Constant, return_false);
        def(AST_Dot, function(compressor) {
            if (!is_strict(compressor)) return false;
            var exp = this.expression;
            if (exp instanceof AST_SymbolRef) exp = exp.fixed_value();
            return !(exp instanceof AST_Lambda && this.property == "prototype");
        });
        def(AST_Lambda, return_false);
        def(AST_Null, return_true);
        def(AST_Object, function(compressor) {
            if (!is_strict(compressor)) return false;
            for (var i = this.properties.length; --i >=0;)
                if (this.properties[i].value instanceof AST_Accessor) return true;
            return false;
        });
        def(AST_Sequence, function(compressor) {
            return this.tail_node()._dot_throw(compressor);
        });
        def(AST_SymbolRef, function(compressor) {
            if (this.is_undefined) return true;
            if (!is_strict(compressor)) return false;
            if (is_undeclared_ref(this) && this.is_declared(compressor)) return false;
            if (this.is_immutable()) return false;
            if (is_arguments(this.definition())) return false;
            var fixed = this.fixed_value();
            if (!fixed) return true;
            this._dot_throw = return_true;
            var result = fixed._dot_throw(compressor);
            delete this._dot_throw;
            return result;
        });
        def(AST_UnaryPrefix, function() {
            return this.operator == "void";
        });
        def(AST_UnaryPostfix, return_false);
        def(AST_Undefined, return_true);
    })(function(node, func) {
        node.DEFMETHOD("_dot_throw", func);
    });

/* -----[ boolean/negation helpers ]----- */

// methods to determine whether an expression has a boolean result type
    (function(def) {
        def(AST_Node, return_false);
        def(AST_Assign, function(compressor) {
            return this.operator == "=" && this.right.is_boolean(compressor);
        });
        var binary = makePredicate("in instanceof == != === !== < <= >= >");
        def(AST_Binary, function(compressor) {
            return binary[this.operator] || lazy_op[this.operator]
                && this.left.is_boolean(compressor)
                && this.right.is_boolean(compressor);
        });
        def(AST_Boolean, return_true);
        var fn = makePredicate("every hasOwnProperty isPrototypeOf propertyIsEnumerable some");
        def(AST_Call, function(compressor) {
            if (!compressor.option("unsafe")) return false;
            var exp = this.expression;
            return exp instanceof AST_Dot && (fn[exp.property]
                || exp.property == "test" && exp.expression instanceof AST_RegExp);
        });
        def(AST_Conditional, function(compressor) {
            return this.consequent.is_boolean(compressor) && this.alternative.is_boolean(compressor);
        });
        def(AST_New, return_false);
        def(AST_Sequence, function(compressor) {
            return this.tail_node().is_boolean(compressor);
        });
        def(AST_SymbolRef, function(compressor) {
            var fixed = this.fixed_value();
            if (!fixed) return false;
            this.is_boolean = return_false;
            var result = fixed.is_boolean(compressor);
            delete this.is_boolean;
            return result;
        });
        var unary = makePredicate("! delete");
        def(AST_UnaryPrefix, function() {
            return unary[this.operator];
        });
    })(function(node, func) {
        node.DEFMETHOD("is_boolean", func);
    });

// methods to determine if an expression has a numeric result type
    (function(def) {
        def(AST_Node, return_false);
        var binary = makePredicate("- * / % & | ^ << >> >>>");
        def(AST_Assign, function(compressor) {
            return binary[this.operator.slice(0, -1)]
                || this.operator == "=" && this.right.is_number(compressor);
        });
        def(AST_Binary, function(compressor) {
            if (binary[this.operator]) return true;
            if (this.operator != "+") return false;
            return (this.left.is_boolean(compressor) || this.left.is_number(compressor))
                && (this.right.is_boolean(compressor) || this.right.is_number(compressor));
        });
        var fn = makePredicate([
            "charCodeAt",
            "getDate",
            "getDay",
            "getFullYear",
            "getHours",
            "getMilliseconds",
            "getMinutes",
            "getMonth",
            "getSeconds",
            "getTime",
            "getTimezoneOffset",
            "getUTCDate",
            "getUTCDay",
            "getUTCFullYear",
            "getUTCHours",
            "getUTCMilliseconds",
            "getUTCMinutes",
            "getUTCMonth",
            "getUTCSeconds",
            "getYear",
            "indexOf",
            "lastIndexOf",
            "localeCompare",
            "push",
            "search",
            "setDate",
            "setFullYear",
            "setHours",
            "setMilliseconds",
            "setMinutes",
            "setMonth",
            "setSeconds",
            "setTime",
            "setUTCDate",
            "setUTCFullYear",
            "setUTCHours",
            "setUTCMilliseconds",
            "setUTCMinutes",
            "setUTCMonth",
            "setUTCSeconds",
            "setYear",
            "toExponential",
            "toFixed",
            "toPrecision",
        ]);
        def(AST_Call, function(compressor) {
            if (!compressor.option("unsafe")) return false;
            var exp = this.expression;
            return exp instanceof AST_Dot && (fn[exp.property]
                || is_undeclared_ref(exp.expression) && exp.expression.name == "Math");
        });
        def(AST_Conditional, function(compressor) {
            return this.consequent.is_number(compressor) && this.alternative.is_number(compressor);
        });
        def(AST_New, return_false);
        def(AST_Number, return_true);
        def(AST_Sequence, function(compressor) {
            return this.tail_node().is_number(compressor);
        });
        def(AST_SymbolRef, function(compressor) {
            var fixed = this.fixed_value();
            if (!fixed) return false;
            this.is_number = return_false;
            var result = fixed.is_number(compressor);
            delete this.is_number;
            return result;
        });
        var unary = makePredicate("+ - ~ ++ --");
        def(AST_Unary, function() {
            return unary[this.operator];
        });
    })(function(node, func) {
        node.DEFMETHOD("is_number", func);
    });

// methods to determine if an expression has a string result type
    (function(def) {
        def(AST_Node, return_false);
        def(AST_Assign, function(compressor) {
            return (this.operator == "=" || this.operator == "+=") && this.right.is_string(compressor);
        });
        def(AST_Binary, function(compressor) {
            return this.operator == "+" &&
                (this.left.is_string(compressor) || this.right.is_string(compressor));
        });
        var fn = makePredicate([
            "charAt",
            "substr",
            "substring",
            "toLowerCase",
            "toString",
            "toUpperCase",
            "trim",
        ]);
        def(AST_Call, function(compressor) {
            if (!compressor.option("unsafe")) return false;
            var exp = this.expression;
            return exp instanceof AST_Dot && fn[exp.property];
        });
        def(AST_Conditional, function(compressor) {
            return this.consequent.is_string(compressor) && this.alternative.is_string(compressor);
        });
        def(AST_Sequence, function(compressor) {
            return this.tail_node().is_string(compressor);
        });
        def(AST_String, return_true);
        def(AST_SymbolRef, function(compressor) {
            var fixed = this.fixed_value();
            if (!fixed) return false;
            this.is_string = return_false;
            var result = fixed.is_string(compressor);
            delete this.is_string;
            return result;
        });
        def(AST_UnaryPrefix, function() {
            return this.operator == "typeof";
        });
    })(function(node, func) {
        node.DEFMETHOD("is_string", func);
    });

var lazy_op = makePredicate("&& ||");
    var unary_arithmetic = makePredicate("++ --");
    var unary_side_effects = makePredicate("delete ++ --");

function is_lhs(node, parent) {
        if (parent instanceof AST_Unary && unary_side_effects[parent.operator]) return parent.expression;
        if (parent instanceof AST_Assign && parent.left === node) return node;
    }

function warn(node) {
            AST_Node.warn("global_defs " + node.print_to_string() + " redefined [{file}:{line},{col}]", node.start);
        }

AST_Toplevel.DEFMETHOD("resolve_defines", function(compressor) {
            if (!compressor.option("global_defs")) return this;
            this.figure_out_scope({ ie8: compressor.option("ie8") });
            return this.transform(new TreeTransformer(function(node) {
                var def = node._find_defs(compressor, "");
                if (!def) return;
                var level = 0, child = node, parent;
                while (parent = this.parent(level++)) {
                    if (!(parent instanceof AST_PropAccess)) break;
                    if (parent.expression !== child) break;
                    child = parent;
                }
                if (is_lhs(child, parent)) {
                    warn(node);
                    return;
                }
                return def;
            }));
        });
        def(AST_Node, noop);
        def(AST_Dot, function(compressor, suffix) {
            return this.expression._find_defs(compressor, "." + this.property + suffix);
        });
        def(AST_SymbolDeclaration, function(compressor) {
            if (!this.global()) return;
            if (HOP(compressor.option("global_defs"), this.name)) warn(this);
        });
        def(AST_SymbolRef, function(compressor, suffix) {
            if (!this.global()) return;
            var defines = compressor.option("global_defs");
            var name = this.name + suffix;
            if (HOP(defines, name)) return to_node(defines[name], this);
        });
    })(function(node, func) {
        node.DEFMETHOD("_find_defs", func);
    });

function best_of_expression(ast1, ast2, threshold) {
        var delta = ast2.print_to_string().length - ast1.print_to_string().length;
        return delta < (threshold || 0) ? ast2 : ast1;
    }

function best_of_statement(ast1, ast2, threshold) {
        return best_of_expression(make_node(AST_SimpleStatement, ast1, {
            body: ast1
        }), make_node(AST_SimpleStatement, ast2, {
            body: ast2
        }), threshold).body;
    }

function best_of(compressor, ast1, ast2, threshold) {
        return (first_in_statement(compressor) ? best_of_statement : best_of_expression)(ast1, ast2, threshold);
    }

function convert_to_predicate(obj) {
        var map = Object.create(null);
        Object.keys(obj).forEach(function(key) {
            map[key] = makePredicate(obj[key]);
        });
        return map;
    }

AST_Lambda.DEFMETHOD("first_statement", function() {
        var body = this.body;
        for (var i = 0; i < body.length; i++) {
            var stat = body[i];
            if (!(stat instanceof AST_Directive)) return stat;
        }
    });

function try_evaluate(compressor, node) {
        var ev = node.evaluate(compressor);
        if (ev === node) return node;
        ev = make_node_from_constant(ev, node).optimize(compressor);
        return best_of(compressor, node, ev, compressor.eval_threshold);
    }

var object_fns = [
        "constructor",
        "toString",
        "valueOf",
    ];
    var native_fns = convert_to_predicate({
        Array: [
            "indexOf",
            "join",
            "lastIndexOf",
            "slice",
        ].concat(object_fns),
        Boolean: object_fns,
        Function: object_fns,
        Number: [
            "toExponential",
            "toFixed",
            "toPrecision",
        ].concat(object_fns),
        Object: object_fns,
        RegExp: [
            "exec",
            "test",
        ].concat(object_fns),
        String: [
            "charAt",
            "charCodeAt",
            "concat",
            "indexOf",
            "italics",
            "lastIndexOf",
            "match",
            "replace",
            "search",
            "slice",
            "split",
            "substr",
            "substring",
            "toLowerCase",
            "toUpperCase",
            "trim",
        ].concat(object_fns),
    });
    var static_fns = convert_to_predicate({
        Array: [
            "isArray",
        ],
        Math: [
            "abs",
            "acos",
            "asin",
            "atan",
            "ceil",
            "cos",
            "exp",
            "floor",
            "log",
            "round",
            "sin",
            "sqrt",
            "tan",
            "atan2",
            "pow",
            "max",
            "min",
        ],
        Number: [
            "isFinite",
            "isNaN",
        ],
        Object: [
            "create",
            "getOwnPropertyDescriptor",
            "getOwnPropertyNames",
            "getPrototypeOf",
            "isExtensible",
            "isFrozen",
            "isSealed",
            "keys",
        ],
        String: [
            "fromCharCode",
        ],
    });

// methods to evaluate a constant expression
    (function(def) {
        // If the node has been successfully reduced to a constant,
        // then its value is returned; otherwise the element itself
        // is returned.
        //
        // They can be distinguished as constant value is never a
        // descendant of AST_Node.
        //
        // When `ignore_side_effects` is `true`, inspect the constant value
        // produced without worrying about any side effects caused by said
        // expression.
        AST_Node.DEFMETHOD("evaluate", function(compressor, ignore_side_effects) {
            if (!compressor.option("evaluate")) return this;
            var cached = [];
            var val = this._eval(compressor, ignore_side_effects, cached, 1);
            cached.forEach(function(node) {
                delete node._eval;
            });
            if (ignore_side_effects) return val;
            if (!val || val instanceof RegExp) return val;
            if (typeof val == "function" || typeof val == "object") return this;
            return val;
        });
        var unaryPrefix = makePredicate("! ~ - + void");
        AST_Node.DEFMETHOD("is_constant", function() {
            // Accomodate when compress option evaluate=false
            // as well as the common constant expressions !0 and -1
            if (this instanceof AST_Constant) {
                return !(this instanceof AST_RegExp);
            } else {
                return this instanceof AST_UnaryPrefix
                    && this.expression instanceof AST_Constant
                    && unaryPrefix[this.operator];
            }
        });
        function modified(sym) {
            if (!(sym instanceof AST_SymbolRef)) return;
            sym.definition().references.forEach(function(node) {
                delete node._eval;
            });
        }
        def(AST_Statement, function() {
            throw new Error(string_template("Cannot evaluate a statement [{file}:{line},{col}]", this.start));
        });
        def(AST_Accessor, return_this);
        def(AST_Node, return_this);
        def(AST_Constant, function() {
            return this.value;
        });
        def(AST_Assign, function(compressor, ignore_side_effects, cached, depth) {
            if (!ignore_side_effects) return this;
            if (this.operator != "=") return this;
            var node = this.right;
            var value = node._eval(compressor, ignore_side_effects, cached, depth);
            modified(this.left);
            return value === node ? this : value;
        });
        def(AST_Sequence, function(compressor, ignore_side_effects, cached, depth) {
            if (!ignore_side_effects) return this;
            var tail = this.tail_node();
            this.walk(new TreeWalker(function(node) {
                if (node === tail) return true;
                if (node instanceof AST_Assign) modified(node.left);
                if (node instanceof AST_Unary && unary_arithmetic[node.operator]) modified(node.expression);
            }));
            var value = tail._eval(compressor, ignore_side_effects, cached, depth);
            return value === tail ? this : value;
        });
        def(AST_Lambda, function(compressor) {
            if (compressor.option("unsafe")) {
                var fn = function() {};
                fn.node = this;
                fn.toString = function() {
                    return "function(){}";
                };
                return fn;
            }
            return this;
        });
        def(AST_Array, function(compressor, ignore_side_effects, cached, depth) {
            if (compressor.option("unsafe")) {
                var elements = [];
                for (var i = 0; i < this.elements.length; i++) {
                    var element = this.elements[i];
                    var value = element._eval(compressor, ignore_side_effects, cached, depth);
                    if (element === value) return this;
                    elements.push(value);
                }
                return elements;
            }
            return this;
        });
        def(AST_Object, function(compressor, ignore_side_effects, cached, depth) {
            if (compressor.option("unsafe")) {
                var val = {};
                for (var i = 0; i < this.properties.length; i++) {
                    var prop = this.properties[i];
                    var key = prop.key;
                    if (key instanceof AST_Symbol) {
                        key = key.name;
                    } else if (key instanceof AST_Node) {
                        key = key._eval(compressor, ignore_side_effects, cached, depth);
                        if (key === prop.key) return this;
                    }
                    if (typeof Object.prototype[key] === 'function') {
                        return this;
                    }
                    if (prop.value instanceof AST_Function) continue;
                    val[key] = prop.value._eval(compressor, ignore_side_effects, cached, depth);
                    if (val[key] === prop.value) return this;
                }
                return val;
            }
            return this;
        });
        var non_converting_unary = makePredicate("! typeof void");
        def(AST_UnaryPrefix, function(compressor, ignore_side_effects, cached, depth) {
            var e = this.expression;
            var op = this.operator;
            // Function would be evaluated to an array and so typeof would
            // incorrectly return 'object'. Hence making is a special case.
            if (compressor.option("typeofs")
                && op == "typeof"
                && (e instanceof AST_Lambda
                    || e instanceof AST_SymbolRef
                        && e.fixed_value() instanceof AST_Lambda)) {
                return typeof function(){};
            }
            if (!non_converting_unary[op]) depth++;
            var v = e._eval(compressor, ignore_side_effects, cached, depth);
            if (v === e) {
                if (ignore_side_effects && op == "void") return;
                return this;
            }
            switch (op) {
              case "!": return !v;
              case "typeof":
                // typeof <RegExp> returns "object" or "function" on different platforms
                // so cannot evaluate reliably
                if (v instanceof RegExp) return this;
                return typeof v;
              case "void": return;
              case "~": return ~v;
              case "-": return -v;
              case "+": return +v;
              case "++":
              case "--":
                if (!(e instanceof AST_SymbolRef)) return this;
                var refs = e.definition().references;
                if (!ignore_side_effects && refs[refs.length - 1] !== e) return this;
                if (HOP(e, "_eval")) v = +(op[0] + 1) + +v;
                modified(e);
                return v;
            }
            return this;
        });
        def(AST_UnaryPostfix, function(compressor, ignore_side_effects, cached, depth) {
            var e = this.expression;
            if (!e.fixed) return this;
            var refs = e.definition().references;
            if (!ignore_side_effects && refs[refs.length - 1] !== e) return this;
            var v = e._eval(compressor, ignore_side_effects, cached, depth + 1);
            modified(e);
            return v === e ? this : +v;
        });
        var non_converting_binary = makePredicate("&& || === !==");
        def(AST_Binary, function(compressor, ignore_side_effects, cached, depth) {
            if (!non_converting_binary[this.operator]) depth++;
            var left = this.left._eval(compressor, ignore_side_effects, cached, depth);
            if (left === this.left) return this;
            if (this.operator == (left ? "||" : "&&")) return left;
            var right = this.right._eval(compressor, ignore_side_effects, cached, depth);
            if (right === this.right) return this;
            var result;
            switch (this.operator) {
              case "&&" : result = left &&  right; break;
              case "||" : result = left ||  right; break;
              case "|"  : result = left |   right; break;
              case "&"  : result = left &   right; break;
              case "^"  : result = left ^   right; break;
              case "+"  : result = left +   right; break;
              case "*"  : result = left *   right; break;
              case "/"  : result = left /   right; break;
              case "%"  : result = left %   right; break;
              case "-"  : result = left -   right; break;
              case "<<" : result = left <<  right; break;
              case ">>" : result = left >>  right; break;
              case ">>>": result = left >>> right; break;
              case "==" : result = left ==  right; break;
              case "===": result = left === right; break;
              case "!=" : result = left !=  right; break;
              case "!==": result = left !== right; break;
              case "<"  : result = left <   right; break;
              case "<=" : result = left <=  right; break;
              case ">"  : result = left >   right; break;
              case ">=" : result = left >=  right; break;
              default   : return this;
            }
            if (isNaN(result)) return compressor.find_parent(AST_With) ? this : result;
            if (compressor.option("unsafe_math")
                && !ignore_side_effects
                && result
                && typeof result == "number"
                && (this.operator == "+" || this.operator == "-")) {
                var digits = Math.max(0, decimals(left), decimals(right));
                // 53-bit significand => 15.95 decimal places
                if (digits < 16) return +result.toFixed(digits);
            }
            return result;

// method to negate an expression
    (function(def) {
        function basic_negation(exp) {
            return make_node(AST_UnaryPrefix, exp, {
                operator: "!",
                expression: exp
            });
        }
        function best(orig, alt, first_in_statement) {
            var negated = basic_negation(orig);
            if (first_in_statement) {
                var stat = make_node(AST_SimpleStatement, alt, {
                    body: alt
                });
                return best_of_expression(negated, stat) === stat ? alt : negated;
            }
            return best_of_expression(negated, alt);
        }
        def(AST_Node, function() {
            return basic_negation(this);
        });
        def(AST_Statement, function() {
            throw new Error("Cannot negate a statement");
        });
        def(AST_Function, function() {
            return basic_negation(this);
        });
        def(AST_UnaryPrefix, function() {
            if (this.operator == "!")
                return this.expression;
            return basic_negation(this);
        });
        def(AST_Sequence, function(compressor) {
            var expressions = this.expressions.slice();
            expressions.push(expressions.pop().negate(compressor));
            return make_sequence(this, expressions);
        });
        def(AST_Conditional, function(compressor, first_in_statement) {
            var self = this.clone();
            self.consequent = self.consequent.negate(compressor);
            self.alternative = self.alternative.negate(compressor);
            return best(this, self, first_in_statement);
        });
        def(AST_Binary, function(compressor, first_in_statement) {
            var self = this.clone(), op = this.operator;
            if (compressor.option("unsafe_comps")) {
                switch (op) {
                  case "<=" : self.operator = ">"  ; return self;
                  case "<"  : self.operator = ">=" ; return self;
                  case ">=" : self.operator = "<"  ; return self;
                  case ">"  : self.operator = "<=" ; return self;
                }
            }
            switch (op) {
              case "==" : self.operator = "!="; return self;
              case "!=" : self.operator = "=="; return self;
              case "===": self.operator = "!=="; return self;
              case "!==": self.operator = "==="; return self;
              case "&&":
                self.operator = "||";
                self.left = self.left.negate(compressor, first_in_statement);
                self.right = self.right.negate(compressor);
                return best(this, self, first_in_statement);
              case "||":
                self.operator = "&&";
                self.left = self.left.negate(compressor, first_in_statement);
                self.right = self.right.negate(compressor);
                return best(this, self, first_in_statement);
            }
            return basic_negation(this);
        });
    })(function(node, func) {
        node.DEFMETHOD("negate", function(compressor, first_in_statement) {
            return func.call(this, compressor, first_in_statement);
        });
    });

// determine if expression has side effects
    (function(def) {
        function any(list, compressor) {
            for (var i = list.length; --i >= 0;)
                if (list[i].has_side_effects(compressor))
                    return true;
            return false;
        }
        def(AST_Node, return_true);
        def(AST_Array, function(compressor) {
            return any(this.elements, compressor);
        });
        def(AST_Assign, return_true);
        def(AST_Binary, function(compressor) {
            return this.left.has_side_effects(compressor)
                || this.right.has_side_effects(compressor);
        });
        def(AST_Block, function(compressor) {
            return any(this.body, compressor);
        });
        def(AST_Call, function(compressor) {
            if (!this.is_expr_pure(compressor)
                && (!this.is_call_pure(compressor) || this.expression.has_side_effects(compressor))) {
                return true;
            }
            return any(this.args, compressor);
        });
        def(AST_Case, function(compressor) {
            return this.expression.has_side_effects(compressor)
                || any(this.body, compressor);
        });
        def(AST_Conditional, function(compressor) {
            return this.condition.has_side_effects(compressor)
                || this.consequent.has_side_effects(compressor)
                || this.alternative.has_side_effects(compressor);
        });
        def(AST_Constant, return_false);
        def(AST_Definitions, function(compressor) {
            return any(this.definitions, compressor);
        });
        def(AST_Dot, function(compressor) {
            return this.expression.may_throw_on_access(compressor)
                || this.expression.has_side_effects(compressor);
        });
        def(AST_EmptyStatement, return_false);
        def(AST_If, function(compressor) {
            return this.condition.has_side_effects(compressor)
                || this.body && this.body.has_side_effects(compressor)
                || this.alternative && this.alternative.has_side_effects(compressor);
        });
        def(AST_LabeledStatement, function(compressor) {
            return this.body.has_side_effects(compressor);
        });
        def(AST_Lambda, return_false);
        def(AST_Object, function(compressor) {
            return any(this.properties, compressor);
        });
        def(AST_ObjectProperty, function(compressor) {
            return this.value.has_side_effects(compressor);
        });
        def(AST_Sub, function(compressor) {
            return this.expression.may_throw_on_access(compressor)
                || this.expression.has_side_effects(compressor)
                || this.property.has_side_effects(compressor);
        });
        def(AST_Sequence, function(compressor) {
            return any(this.expressions, compressor);
        });
        def(AST_SimpleStatement, function(compressor) {
            return this.body.has_side_effects(compressor);
        });
        def(AST_Switch, function(compressor) {
            return this.expression.has_side_effects(compressor)
                || any(this.body, compressor);
        });
        def(AST_SymbolDeclaration, return_false);
        def(AST_SymbolRef, function(compressor) {
            return !this.is_declared(compressor);
        });
        def(AST_This, return_false);
        def(AST_Try, function(compressor) {
            return any(this.body, compressor)
                || this.bcatch && this.bcatch.has_side_effects(compressor)
                || this.bfinally && this.bfinally.has_side_effects(compressor);
        });
        def(AST_Unary, function(compressor) {
            return unary_side_effects[this.operator]
                || this.expression.has_side_effects(compressor);
        });
        def(AST_VarDef, function(compressor) {
            return this.value;
        });
    })(function(node, func) {
        node.DEFMETHOD("has_side_effects", func);
    });

// determine if expression may throw
    (function(def) {
        def(AST_Node, return_true);

def(AST_Constant, return_false);
        def(AST_EmptyStatement, return_false);
        def(AST_Lambda, return_false);
        def(AST_SymbolDeclaration, return_false);
        def(AST_This, return_false);

function any(list, compressor) {
            for (var i = list.length; --i >= 0;)
                if (list[i].may_throw(compressor))
                    return true;
            return false;
        }

def(AST_Array, function(compressor) {
            return any(this.elements, compressor);
        });
        def(AST_Assign, function(compressor) {
            if (this.right.may_throw(compressor)) return true;
            if (!compressor.has_directive("use strict")
                && this.operator == "="
                && this.left instanceof AST_SymbolRef) {
                return false;
            }
            return this.left.may_throw(compressor);
        });
        def(AST_Binary, function(compressor) {
            return this.left.may_throw(compressor)
                || this.right.may_throw(compressor);
        });
        def(AST_Block, function(compressor) {
            return any(this.body, compressor);
        });
        def(AST_Call, function(compressor) {
            if (any(this.args, compressor)) return true;
            if (this.is_expr_pure(compressor)) return false;
            if (this.expression.may_throw(compressor)) return true;
            return !(this.expression instanceof AST_Lambda)
                || any(this.expression.body, compressor);
        });
        def(AST_Case, function(compressor) {
            return this.expression.may_throw(compressor)
                || any(this.body, compressor);
        });
        def(AST_Conditional, function(compressor) {
            return this.condition.may_throw(compressor)
                || this.consequent.may_throw(compressor)
                || this.alternative.may_throw(compressor);
        });
        def(AST_Definitions, function(compressor) {
            return any(this.definitions, compressor);
        });
        def(AST_Dot, function(compressor) {
            return this.expression.may_throw_on_access(compressor)
                || this.expression.may_throw(compressor);
        });
        def(AST_If, function(compressor) {
            return this.condition.may_throw(compressor)
                || this.body && this.body.may_throw(compressor)
                || this.alternative && this.alternative.may_throw(compressor);
        });
        def(AST_LabeledStatement, function(compressor) {
            return this.body.may_throw(compressor);
        });
        def(AST_Object, function(compressor) {
            return any(this.properties, compressor);
        });
        def(AST_ObjectProperty, function(compressor) {
            return this.value.may_throw(compressor);
        });
        def(AST_Return, function(compressor) {
            return this.value && this.value.may_throw(compressor);
        });
        def(AST_Sequence, function(compressor) {
            return any(this.expressions, compressor);
        });
        def(AST_SimpleStatement, function(compressor) {
            return this.body.may_throw(compressor);
        });
        def(AST_Sub, function(compressor) {
            return this.expression.may_throw_on_access(compressor)
                || this.expression.may_throw(compressor)
                || this.property.may_throw(compressor);
        });
        def(AST_Switch, function(compressor) {
            return this.expression.may_throw(compressor)
                || any(this.body, compressor);
        });
        def(AST_SymbolRef, function(compressor) {
            return !this.is_declared(compressor);
        });
        def(AST_Try, function(compressor) {
            return (this.bcatch ? this.bcatch.may_throw(compressor) : any(this.body, compressor))
                || this.bfinally && this.bfinally.may_throw(compressor);
        });
        def(AST_Unary, function(compressor) {
            if (this.operator == "typeof" && this.expression instanceof AST_SymbolRef)
                return false;
            return this.expression.may_throw(compressor);
        });
        def(AST_VarDef, function(compressor) {
            if (!this.value) return false;
            return this.value.may_throw(compressor);
        });
    })(function(node, func) {
        node.DEFMETHOD("may_throw", func);
    });

// determine if expression is constant
    (function(def) {
        function all(list) {
            for (var i = list.length; --i >= 0;)
                if (!list[i].is_constant_expression())
                    return false;
            return true;
        }
        def(AST_Node, return_false);
        def(AST_Array, function() {
            return all(this.elements);
        });
        def(AST_Binary, function() {
            return this.left.is_constant_expression() && this.right.is_constant_expression();
        });
        def(AST_Constant, return_true);
        def(AST_Lambda, function(scope) {
            var self = this;
            var result = true;
            var scopes = [];
            self.walk(new TreeWalker(function(node, descend) {
                if (!result) return true;
                if (node instanceof AST_Catch) {
                    scopes.push(node.argname.scope);
                    descend();
                    scopes.pop();
                    return true;
                }
                if (node instanceof AST_Scope) {
                    if (node === self) return;
                    scopes.push(node);
                    descend();
                    scopes.pop();
                    return true;
                }
                if (node instanceof AST_SymbolRef) {
                    if (self.inlined) {
                        result = false;
                        return true;
                    }
                    if (self.variables.has(node.name)) return true;
                    var def = node.definition();
                    if (member(def.scope, scopes)) return true;
                    if (scope) {
                        var scope_def = scope.find_variable(node);
                        if (def.undeclared ? !scope_def : scope_def === def) {
                            result = "f";
                            return true;
                        }
                    }
                    result = false;
                    return true;
                }
            }));
            return result;
        });
        def(AST_Object, function() {
            return all(this.properties);
        });
        def(AST_ObjectProperty, function() {
            return this.value.is_constant_expression();
        });
        def(AST_Unary, function() {
            return this.expression.is_constant_expression();
        });
    })(function(node, func) {
        node.DEFMETHOD("is_constant_expression", func);
    });

// tell me if a statement aborts
    function aborts(thing) {
        return thing && thing.aborts();
    }
    (function(def) {
        def(AST_Statement, return_null);
        def(AST_Jump, return_this);
        function block_aborts() {
            var n = this.body.length;
            return n > 0 && aborts(this.body[n - 1]);
        }
        def(AST_BlockStatement, block_aborts);
        def(AST_SwitchBranch, block_aborts);
        def(AST_If, function() {
            return this.alternative && aborts(this.body) && aborts(this.alternative) && this;
        });
    })(function(node, func) {
        node.DEFMETHOD("aborts", func);
    });

/* -----[ optimizers ]----- */

var directives = makePredicate(["use asm", "use strict"]);
    OPT(AST_Directive, function(self, compressor) {
        if (compressor.option("directives")
            && (!directives[self.value] || compressor.has_directive(self.value) !== self)) {
            return make_node(AST_EmptyStatement, self);
        }
        return self;
    });

OPT(AST_Debugger, function(self, compressor) {
        if (compressor.option("drop_debugger"))
            return make_node(AST_EmptyStatement, self);
        return self;
    });

OPT(AST_LabeledStatement, function(self, compressor) {
        if (compressor.option("dead_code")
            && self.body instanceof AST_Break
            && compressor.loopcontrol_target(self.body) === self.body) {
            return make_node(AST_EmptyStatement, self);
        }
        return compressor.option("unused") && self.label.references.length == 0 ? self.body : self;
    });

OPT(AST_Block, function(self, compressor) {
        self.body = tighten_body(self.body, compressor);
        return self;
    });

OPT(AST_BlockStatement, function(self, compressor) {
        self.body = tighten_body(self.body, compressor);
        switch (self.body.length) {
          case 1: return self.body[0];
          case 0: return make_node(AST_EmptyStatement, self);
        }
        return self;
    });

OPT(AST_Function, function(self, compressor) {
        self.body = tighten_body(self.body, compressor);
        if (compressor.option("inline")) for (var i = 0; i < self.body.length; i++) {
            var stat = self.body[i];
            if (stat instanceof AST_Directive) continue;
            if (stat instanceof AST_Return) {
                var call = stat.value;
                if (!call || call.TYPE != "Call") break;
                if (call.is_expr_pure(compressor)) break;
                var fn = call.expression;
                if (fn instanceof AST_SymbolRef) {
                    if (self.name && self.name.definition() === fn.definition()) break;
                    fn = fn.fixed_value();
                }
                if (!(fn instanceof AST_Lambda)) break;
                if (fn.uses_arguments) break;
                if (fn === call.expression) {
                    if (fn.parent_scope !== self) break;
                    if (!all(fn.enclosed, function(def) {
                        return def.scope !== self;
                    })) break;
                }
                if (fn.contains_this()) break;
                var len = fn.argnames.length;
                if (len > 0 && compressor.option("inline") < 2) break;
                if (len > self.argnames.length) break;
                for (var j = 0; j < len; j++) {
                    var arg = call.args[j];
                    if (!(arg instanceof AST_SymbolRef)) break;
                    if (arg.definition() !== self.argnames[j].definition()) break;
                }
                if (j < len) break;
                for (; j < call.args.length; j++) {
                    if (call.args[j].has_side_effects(compressor)) break;
                }
                if (j < call.args.length) break;
                if (len < self.argnames.length && !compressor.drop_fargs(self, compressor.parent())) {
                    if (!compressor.drop_fargs(fn, call)) break;
                    do {
                        var argname = make_node(AST_SymbolFunarg, fn, {
                            name: fn.make_var_name("argument_" + len),
                            scope: fn
                        });
                        fn.argnames.push(argname);
                        fn.enclosed.push(fn.def_variable(argname));
                    } while (++len < self.argnames.length);
                }
                return call.expression;
            }
            break;
        }
        return self;
    });

AST_Scope.DEFMETHOD("drop_unused", function(compressor) {
        if (!compressor.option("unused")) return;
        if (compressor.has_directive("use asm")) return;
        var self = this;
        if (self.pinned()) return;
        var drop_funcs = !(self instanceof AST_Toplevel) || compressor.toplevel.funcs;
        var drop_vars = !(self instanceof AST_Toplevel) || compressor.toplevel.vars;
        var assign_as_unused = /keep_assign/.test(compressor.option("unused")) ? return_false : function(node, props) {
            var sym;
            if (node instanceof AST_Assign) {
                if (node.write_only || node.operator == "=") sym = node.left;
            } else if (node instanceof AST_Unary) {
                if (node.write_only) sym = node.expression;
            }
            if (/strict/.test(compressor.option("pure_getters"))) {
                while (sym instanceof AST_PropAccess && !sym.expression.may_throw_on_access(compressor)) {
                    if (sym instanceof AST_Sub) props.unshift(sym.property);
                    sym = sym.expression;
                }
            }
            if (!(sym instanceof AST_SymbolRef)) return;
            if (compressor.exposed(sym.definition())) return;
            if (!all(sym.definition().orig, function(sym) {
                return !(sym instanceof AST_SymbolLambda);
            })) return;
            return sym;
        };
        var chained = Object.create(null);
        var in_use = [];
        var in_use_ids = Object.create(null); // avoid expensive linear scans of in_use
        var value_read = Object.create(null);
        var value_modified = Object.create(null);
        if (self instanceof AST_Toplevel && compressor.top_retain) {
            self.variables.each(function(def) {
                if (compressor.top_retain(def) && !(def.id in in_use_ids)) {
                    in_use_ids[def.id] = true;
                    in_use.push(def);
                }
            });
        }
        var assign_in_use = new Dictionary();
        var var_defs_by_id = new Dictionary();
        var initializations = new Dictionary();
        // pass 1: find out which symbols are directly used in
        // this scope (not in nested scopes).
        var scope = this;
        var tw = new TreeWalker(function(node, descend) {
            if (node instanceof AST_Lambda && node.uses_arguments && !tw.has_directive("use strict")) {
                node.argnames.forEach(function(argname) {
                    var def = argname.definition();
                    if (!(def.id in in_use_ids)) {
                        in_use_ids[def.id] = true;
                        in_use.push(def);
                    }
                });
            }
            if (node === self) return;
            if (node instanceof AST_Defun) {
                var node_def = node.name.definition();
                if (!drop_funcs && scope === self) {
                    if (!(node_def.id in in_use_ids)) {
                        in_use_ids[node_def.id] = true;
                        in_use.push(node_def);
                    }
                }
                initializations.add(node_def.id, node);
                return true; // don't go in nested scopes
            }
            if (node instanceof AST_SymbolFunarg && scope === self) {
                var_defs_by_id.add(node.definition().id, node);
            }
            if (node instanceof AST_Definitions && scope === self) {
                node.definitions.forEach(function(def) {
                    var node_def = def.name.definition();
                    var_defs_by_id.add(node_def.id, def);
                    if (!drop_vars) {
                        if (!(node_def.id in in_use_ids)) {
                            in_use_ids[node_def.id] = true;
                            in_use.push(node_def);
                        }
                    }
                    if (def.value) {
                        if (def.value.has_side_effects(compressor)) {
                            def.value.walk(tw);
                        } else {
                            initializations.add(node_def.id, def.value);
                        }
                        match_assigns(node_def, def);
                    }
                });
                return true;
            }
            return scan_ref_scoped(node, descend, true);
        });
        self.walk(tw);
        // pass 2: for every used symbol we need to walk its
        // initialization code to figure out if it uses other
        // symbols (that may not be in_use).
        tw = new TreeWalker(scan_ref_scoped);
        for (var i = 0; i < in_use.length; i++) {
            var init = initializations.get(in_use[i].id);
            if (init) init.forEach(function(init) {
                init.walk(tw);
            });
        }
        var drop_fn_name = compressor.option("keep_fnames") ? return_false : compressor.option("ie8") ? function(def) {
            return !compressor.exposed(def) && def.references.length == def.replaced;
        } : function(def) {
            // any declarations with same name will overshadow
            // name of this anonymous function and can therefore
            // never be used anywhere
            return !(def.id in in_use_ids) || def.orig.length > 1;
        };
        // pass 3: we should drop declarations not in_use
        var unused_fn_names = [];
        var calls_to_drop_args = [];
        var fns_with_marked_args = [];
        var tt = new TreeTransformer(function(node, descend, in_list) {
            var parent = tt.parent();
            if (drop_vars) {
                var props = [], sym = assign_as_unused(node, props);
                if (sym) {
                    var def = sym.definition();
                    var in_use = def.id in in_use_ids;
                    var value;
                    if (node instanceof AST_Assign) {
                        if (!in_use || node.left === sym && indexOf_assign(def, node) < 0) {
                            value = get_rhs(node);
                            if (node.write_only === true) {
                                value = value.drop_side_effect_free(compressor) || make_node(AST_Number, node, {
                                    value: 0
                                });
                            }
                        }
                    } else if (!in_use || node.expression === sym && indexOf_assign(def, node) < 0) {
                        value = make_node(AST_Number, node, {
                            value: 0
                        });
                    }
                    if (value) {
                        if (parent instanceof AST_Sequence && parent.tail_node() !== node) {
                            value = value.drop_side_effect_free(compressor);
                        }
                        if (value) props.push(value);
                        switch (props.length) {
                          case 0:
                            return List.skip;
                          case 1:
                            return maintain_this_binding(compressor, parent, node, props[0].transform(tt));
                          default:
                            return make_sequence(node, props.map(function(prop) {
                                return prop.transform(tt);
                            }));
                        }
                    }
                }
            }
            if (node instanceof AST_Call) calls_to_drop_args.push(node);
            if (scope !== self) return;
            if (node instanceof AST_Lambda) {
                if (drop_funcs && node !== self && node instanceof AST_Defun) {
                    var def = node.name.definition();
                    if (!(def.id in in_use_ids)) {
                        log(node.name, "Dropping unused function {name} [{file}:{line},{col}]", template(node.name));
                        def.eliminated++;
                        return in_list ? List.skip : make_node(AST_EmptyStatement, node);
                    }
                }
                if (node instanceof AST_Function && node.name && drop_fn_name(node.name.definition())) {
                    unused_fn_names.push(node);
                }
                if (!(node instanceof AST_Accessor)) {
                    var trim = compressor.drop_fargs(node, parent);
                    for (var a = node.argnames, i = a.length; --i >= 0;) {
                        var sym = a[i];
                        if (!(sym.definition().id in in_use_ids)) {
                            sym.__unused = true;
                            if (trim) {
                                log(sym, "Dropping unused function argument {name} [{file}:{line},{col}]", template(sym));
                                a.pop();
                            }
                        } else {
                            trim = false;
                        }
                    }
                    fns_with_marked_args.push(node);
                }
            }
            if (node instanceof AST_Definitions && !(parent instanceof AST_ForIn && parent.init === node)) {
                // place uninitialized names at the start
                var body = [], head = [], tail = [];
                // for unused names whose initialization has
                // side effects, we can cascade the init. code
                // into the next one, or next statement.
                var side_effects = [];
                var duplicated = 0;
                node.definitions.forEach(function(def) {
                    if (def.value) def.value = def.value.transform(tt);
                    var sym = def.name.definition();
                    if (!drop_vars || sym.id in in_use_ids) {
                        if (def.value && indexOf_assign(sym, def) < 0) {
                            def.value = def.value.drop_side_effect_free(compressor);
                        }
                        var var_defs = var_defs_by_id.get(sym.id);
                        if (!def.value) {
                            if (var_defs.length > 1) {
                                AST_Node.warn("Dropping duplicated declaration of variable {name} [{file}:{line},{col}]", template(def.name));
                                remove(var_defs, def);
                                sym.eliminated++;
                            } else {
                                head.push(def);
                            }
                        } else if (compressor.option("functions")
                            && !compressor.option("ie8")
                            && var_defs.length == 1
                            && def.value === def.name.fixed_value()
                            && def.value instanceof AST_Function
                            && !(def.value.name && def.value.name.definition().assignments)
                            && can_rename(def.value, def.name.name)
                            && (!compressor.has_directive("use strict") || parent instanceof AST_Scope)) {
                            AST_Node.warn("Declaring {name} as function [{file}:{line},{col}]", template(def.name));
                            var defun = make_node(AST_Defun, def, def.value);
                            defun.name = make_node(AST_SymbolDefun, def.name, def.name);
                            var name_def = def.name.scope.resolve().def_function(defun.name);
                            if (def.value.name) {
                                var old_def = def.value.name.definition();
                                def.value.walk(new TreeWalker(function(node) {
                                    if (node instanceof AST_SymbolRef && node.definition() === old_def) {
                                        node.name = name_def.name;
                                        node.thedef = name_def;
                                        node.reference({});
                                    }
                                }));
                            }
                            body.push(defun);
                        } else {
                            if (var_defs.length > 1 && sym.orig.indexOf(def.name) > sym.eliminated) {
                                remove(var_defs, def);
                                duplicated++;
                            }
                            if (side_effects.length > 0) {
                                if (tail.length > 0) {
                                    side_effects.push(def.value);
                                    def.value = make_sequence(def.value, side_effects);
                                } else {
                                    body.push(make_node(AST_SimpleStatement, node, {
                                        body: make_sequence(node, side_effects)
                                    }));
                                }
                                side_effects = [];
                            }
                            tail.push(def);
                        }
                    } else if (sym.orig[0] instanceof AST_SymbolCatch) {
                        var value = def.value && def.value.drop_side_effect_free(compressor);
                        if (value) side_effects.push(value);
                        var var_defs = var_defs_by_id.get(sym.id);
                        if (var_defs.length > 1) {
                            AST_Node.warn("Dropping duplicated declaration of variable {name} [{file}:{line},{col}]", template(def.name));
                            remove(var_defs, def);
                            sym.eliminated++;
                        } else {
                            def.value = null;
                            head.push(def);
                        }
                    } else {
                        var value = def.value && !def.value.single_use && def.value.drop_side_effect_free(compressor);
                        if (value) {
                            AST_Node.warn("Side effects in initialization of unused variable {name} [{file}:{line},{col}]", template(def.name));
                            side_effects.push(value);
                        } else {
                            log(def.name, "Dropping unused variable {name} [{file}:{line},{col}]", template(def.name));
                        }
                        sym.eliminated++;
                    }

function log(sym, text, props) {
            AST_Node[sym.unreferenced() ? "warn" : "info"](text, props);
        }

function template(sym) {
            return {
                name: sym.name,
                file: sym.start.file,
                line: sym.start.line,
                col : sym.start.col
            };
        }

function indexOf_assign(def, node) {
            if (!def.fixed) return;
            if (!def.assigns) return;
            var assigns = assign_in_use.get(def.id);
            if (!assigns) return;
            if (assigns.length != def.assigns.length) return;
            var index = assigns.indexOf(node);
            if (index >= 0 || !chained[def.id] || node.assigns && all(node.assigns, function(assign) {
                return assign.write_only || assign.operator == "=" || assign instanceof AST_VarDef;
            })) return index;
        }

function get_rhs(assign) {
            var rhs = assign.right;
            if (!assign.write_only) return rhs;
            if (!(rhs instanceof AST_Binary && lazy_op[rhs.operator])) return rhs;
            var sym = assign.left;
            if (!(sym instanceof AST_SymbolRef) || sym.name != rhs.left.name) return rhs;
            return rhs.right.has_side_effects(compressor) ? rhs : rhs.right;
        }

AST_Scope.DEFMETHOD("hoist_declarations", function(compressor) {
        if (compressor.has_directive("use asm")) return;
        var hoist_funs = compressor.option("hoist_funs");
        var hoist_vars = compressor.option("hoist_vars");
        var self = this;
        if (hoist_vars) {
            // let's count var_decl first, we seem to waste a lot of
            // space if we hoist `var` when there's only one.
            var var_decl = 0;
            self.walk(new TreeWalker(function(node) {
                if (var_decl > 1) return true;
                if (node instanceof AST_Scope && node !== self) return true;
                if (node instanceof AST_Var) {
                    var_decl++;
                    return true;
                }
            }));
            if (var_decl <= 1) hoist_vars = false;
        }
        if (!hoist_funs && !hoist_vars) return;
        var dirs = [];
        var hoisted = [];
        var vars = new Dictionary(), vars_found = 0;
        var tt = new TreeTransformer(function(node) {
            if (node === self) return;
            if (node instanceof AST_Directive) {
                dirs.push(node);
                return make_node(AST_EmptyStatement, node);
            }
            if (hoist_funs && node instanceof AST_Defun
                && (tt.parent() === self || !compressor.has_directive("use strict"))) {
                hoisted.push(node);
                return make_node(AST_EmptyStatement, node);
            }
            if (hoist_vars && node instanceof AST_Var) {
                node.definitions.forEach(function(def) {
                    vars.set(def.name.name, def);
                    ++vars_found;
                });
                var seq = node.to_assignments(compressor);
                var p = tt.parent();
                if (p instanceof AST_ForIn && p.init === node) {
                    if (seq) return seq;
                    var def = node.definitions[0].name;
                    return make_node(AST_SymbolRef, def, def);
                }
                if (p instanceof AST_For && p.init === node) return seq;
                if (!seq) return make_node(AST_EmptyStatement, node);
                return make_node(AST_SimpleStatement, node, {
                    body: seq
                });
            }
            if (node instanceof AST_Scope) return node;
        });
        self.transform(tt);
        if (vars_found > 0) {
            // collect only vars which don't show up in self's arguments list
            var defs = [];
            vars.each(function(def, name) {
                if (self instanceof AST_Lambda
                    && !all(self.argnames, function(argname) {
                        return argname.name != name;
                    })) {
                    vars.del(name);
                } else {
                    def = def.clone();
                    def.value = null;
                    defs.push(def);
                    vars.set(name, def);
                }
            });
            if (defs.length > 0) {
                // try to merge in assignments
                for (var i = 0; i < self.body.length;) {
                    if (self.body[i] instanceof AST_SimpleStatement) {
                        var expr = self.body[i].body, sym, assign;
                        if (expr instanceof AST_Assign
                            && expr.operator == "="
                            && (sym = expr.left) instanceof AST_Symbol
                            && vars.has(sym.name))
                        {
                            var def = vars.get(sym.name);
                            if (def.value) break;
                            def.value = expr.right;
                            remove(defs, def);
                            defs.push(def);
                            self.body.splice(i, 1);
                            continue;
                        }
                        if (expr instanceof AST_Sequence
                            && (assign = expr.expressions[0]) instanceof AST_Assign
                            && assign.operator == "="
                            && (sym = assign.left) instanceof AST_Symbol
                            && vars.has(sym.name))
                        {
                            var def = vars.get(sym.name);
                            if (def.value) break;
                            def.value = assign.right;
                            remove(defs, def);
                            defs.push(def);
                            self.body[i].body = make_sequence(expr, expr.expressions.slice(1));
                            continue;
                        }
                    }
                    if (self.body[i] instanceof AST_EmptyStatement) {
                        self.body.splice(i, 1);
                        continue;
                    }
                    if (self.body[i] instanceof AST_BlockStatement) {
                        var tmp = [ i, 1 ].concat(self.body[i].body);
                        self.body.splice.apply(self.body, tmp);
                        continue;
                    }
                    break;
                }
                defs = make_node(AST_Var, self, {
                    definitions: defs
                });
                hoisted.push(defs);
            }
        }
        self.body = dirs.concat(hoisted, self.body);
    });

function all_bool(def, bool_returns, compressor) {
        return def.bool_fn + (bool_returns[def.id] || 0) === def.references.length - def.replaced
            && !compressor.exposed(def);
    }

AST_Scope.DEFMETHOD("process_boolean_returns", noop);
    AST_Defun.DEFMETHOD("process_boolean_returns", function(compressor) {
        if (!compressor.option("booleans")) return;
        var bool_returns = map_bool_returns(this);
        if (!all_bool(this.name.definition(), bool_returns, compressor)) return;
        process_boolean_returns(this, compressor);
    });
    AST_Function.DEFMETHOD("process_boolean_returns", function(compressor) {
        if (!compressor.option("booleans")) return;
        var bool_returns = map_bool_returns(this);
        if (this.name && !all_bool(this.name.definition(), bool_returns, compressor)) return;
        var parent = compressor.parent();
        if (parent instanceof AST_Assign) {
            if (parent.operator != "=") return;
            var sym = parent.left;
            if (!(sym instanceof AST_SymbolRef)) return;
            if (!all_bool(sym.definition(), bool_returns, compressor)) return;
        } else if (parent instanceof AST_Call && parent.expression !== this) {
            var exp = parent.expression;
            if (exp instanceof AST_SymbolRef) exp = exp.fixed_value();
            if (!(exp instanceof AST_Lambda)) return;
            if (exp.uses_arguments || exp.pinned()) return;
            var sym = exp.argnames[parent.args.indexOf(this)];
            if (sym && !all_bool(sym.definition(), bool_returns, compressor)) return;
        } else if (parent.TYPE == "Call") {
            compressor.pop();
            var in_bool = compressor.in_boolean_context();
            compressor.push(this);
            if (!in_bool) return;
        } else return;
        process_boolean_returns(this, compressor);
    });

AST_Scope.DEFMETHOD("var_names", function() {
        var var_names = this._var_names;
        if (!var_names) {
            this._var_names = var_names = Object.create(null);
            this.enclosed.forEach(function(def) {
                var_names[def.name] = true;
            });
            this.variables.each(function(def, name) {
                var_names[name] = true;
            });
        }
        return var_names;
    });

AST_Scope.DEFMETHOD("make_var_name", function(prefix) {
        var var_names = this.var_names();
        prefix = prefix.replace(/(?:^[^a-z_$]|[^a-z0-9_$])/ig, "_");
        var name = prefix;
        for (var i = 0; var_names[name]; i++) name = prefix + "$" + i;
        var_names[name] = true;
        return name;
    });

AST_Scope.DEFMETHOD("hoist_properties", function(compressor) {
        if (!compressor.option("hoist_props") || compressor.has_directive("use asm")) return;
        var self = this;
        var top_retain = self instanceof AST_Toplevel && compressor.top_retain || return_false;
        var defs_by_id = Object.create(null);
        self.transform(new TreeTransformer(function(node, descend) {
            if (node instanceof AST_Assign) {
                if (node.operator != "=") return;
                if (!node.write_only) return;
                if (node.left.scope !== self) return;
                if (!can_hoist(node.left, node.right, 1)) return;
                descend(node, this);
                var defs = new Dictionary();
                var assignments = [];
                var decls = [];
                node.right.properties.forEach(function(prop) {
                    var decl = make_sym(node.left, prop.key);
                    decls.push(make_node(AST_VarDef, node, {
                        name: decl,
                        value: null
                    }));
                    var sym = make_node(AST_SymbolRef, node, {
                        name: decl.name,
                        scope: self,
                        thedef: decl.definition()
                    });
                    sym.reference({});
                    assignments.push(make_node(AST_Assign, node, {
                        operator: "=",
                        left: sym,
                        right: prop.value
                    }));
                });
                defs_by_id[node.left.definition().id] = defs;
                self.body.splice(self.body.indexOf(this.stack[1]) + 1, 0, make_node(AST_Var, node, {
                    definitions: decls
                }));
                return make_sequence(node, assignments);
            }
            if (node instanceof AST_Scope) return node === self ? undefined : node;
            if (node instanceof AST_VarDef) {
                if (!can_hoist(node.name, node.value, 0)) return;
                descend(node, this);
                var defs = new Dictionary();
                var var_defs = [];
                node.value.properties.forEach(function(prop) {
                    var_defs.push(make_node(AST_VarDef, node, {
                        name: make_sym(node.name, prop.key),
                        value: prop.value
                    }));
                });
                defs_by_id[node.name.definition().id] = defs;
                return List.splice(var_defs);
            }

function can_hoist(sym, right, count) {
            var def = sym.definition();
            if (def.assignments != count) return;
            if (def.direct_access) return;
            if (def.escaped.depth == 1) return;
            if (def.references.length - def.replaced == count) return;
            if (def.single_use) return;
            if (top_retain(def)) return;
            if (sym.fixed_value() !== right) return;
            return right instanceof AST_Object
                && right.properties.length > 0
                && all(right.properties, function(prop) {
                    return prop instanceof AST_ObjectKeyVal;
                });
        }
    });

function safe_to_drop(fn, compressor) {
        if (!fn.name || !compressor.option("ie8")) return true;
        var def = fn.name.definition();
        if (compressor.exposed(def)) return false;
        return all(def.references, function(sym) {
            return !(sym instanceof AST_SymbolRef);
        });
    }

// drop_side_effect_free()
    // remove side-effect-free parts which only affects return value
    (function(def) {
        // Drop side-effect-free elements from an array of expressions.
        // Returns an array of expressions with side-effects or null
        // if all elements were dropped. Note: original array may be
        // returned if nothing changed.
        function trim(nodes, compressor, first_in_statement) {
            var len = nodes.length;
            if (!len) return null;
            var ret = [], changed = false;
            for (var i = 0; i < len; i++) {
                var node = nodes[i].drop_side_effect_free(compressor, first_in_statement);
                changed |= node !== nodes[i];
                if (node) {
                    ret.push(node);
                    first_in_statement = false;
                }
            }
            return changed ? ret.length ? ret : null : nodes;
        }

def(AST_Node, return_this);
        def(AST_Accessor, return_null);
        def(AST_Array, function(compressor, first_in_statement) {
            var values = trim(this.elements, compressor, first_in_statement);
            return values && make_sequence(this, values);
        });
        def(AST_Assign, function(compressor) {
            var left = this.left;
            if (left instanceof AST_PropAccess) {
                var expr = left.expression;
                if (expr instanceof AST_Assign && expr.operator == "=" && !expr.may_throw_on_access(compressor)) {
                    expr.write_only = "p";
                }
                if (compressor.has_directive("use strict") && expr.is_constant()) return this;
            }
            if (left.has_side_effects(compressor)) return this;
            this.write_only = true;
            if (root_expr(left).is_constant_expression(compressor.find_parent(AST_Scope))) {
                return this.right.drop_side_effect_free(compressor);
            }
            return this;
        });
        def(AST_Binary, function(compressor, first_in_statement) {
            var right = this.right.drop_side_effect_free(compressor, first_in_statement);
            if (!right) return this.left.drop_side_effect_free(compressor, first_in_statement);
            if (lazy_op[this.operator] && !(right instanceof AST_Function)) {
                var node = this;
                if (right !== node.right) {
                    node = this.clone();
                    node.right = right.drop_side_effect_free(compressor);
                }
                return (first_in_statement ? best_of_statement : best_of_expression)(node, make_node(AST_Binary, this, {
                    operator: node.operator == "&&" ? "||" : "&&",
                    left: node.left.negate(compressor, first_in_statement),
                    right: node.right
                }));
            } else {
                var left = this.left.drop_side_effect_free(compressor, first_in_statement);
                if (!left) return right;
                return make_sequence(this, [ left, right.drop_side_effect_free(compressor) ]);
            }
        });
        def(AST_Call, function(compressor, first_in_statement) {
            if (!this.is_expr_pure(compressor)) {
                var exp = this.expression;
                if (this.is_call_pure(compressor)) {
                    var exprs = this.args.slice();
                    exprs.unshift(exp.expression);
                    exprs = trim(exprs, compressor, first_in_statement);
                    return exprs && make_sequence(this, exprs);
                }
                if (exp instanceof AST_Function) {
                    if (exp.name) {
                        var def = exp.name.definition();
                        if (def.references.length > def.replaced) return this;
                    }
                    exp.process_expression(false, function(node) {
                        var value = node.value && node.value.drop_side_effect_free(compressor, true);
                        return value ? make_node(AST_SimpleStatement, node, {
                            body: value
                        }) : make_node(AST_EmptyStatement, node);
                    });
                    scan_local_returns(exp, function(node) {
                        if (node.value) node.value = node.value.drop_side_effect_free(compressor);
                    });
                    // always shallow clone to ensure stripping of negated IIFEs
                    return this.clone();
                }
                return this;
            }
            if (this.pure) AST_Node.warn("Dropping __PURE__ call [{file}:{line},{col}]", this.start);
            var args = trim(this.args, compressor, first_in_statement);
            return args && make_sequence(this, args);
        });
        def(AST_Conditional, function(compressor) {
            var consequent = this.consequent.drop_side_effect_free(compressor);
            var alternative = this.alternative.drop_side_effect_free(compressor);
            if (consequent === this.consequent && alternative === this.alternative) return this;
            var exprs;
            if (compressor.option("ie8")) {
                exprs = [];
                if (consequent instanceof AST_Function) {
                    exprs.push(consequent);
                    consequent = null;
                }
                if (alternative instanceof AST_Function) {
                    exprs.push(alternative);
                    alternative = null;
                }
            }
            var node;
            if (!consequent) {
                node = alternative ? make_node(AST_Binary, this, {
                    operator: "||",
                    left: this.condition,
                    right: alternative
                }) : this.condition.drop_side_effect_free(compressor);
            } else if (!alternative) {
                node = make_node(AST_Binary, this, {
                    operator: "&&",
                    left: this.condition,
                    right: consequent
                });
            } else {
                node = this.clone();
                node.consequent = consequent;
                node.alternative = alternative;
            }
            if (!compressor.option("ie8")) return node;
            if (node) exprs.push(node);
            return exprs.length == 0 ? null : make_sequence(this, exprs);
        });
        def(AST_Constant, return_null);
        def(AST_Dot, function(compressor, first_in_statement) {
            var expr = this.expression;
            if (expr.may_throw_on_access(compressor)) return this;
            return expr.drop_side_effect_free(compressor, first_in_statement);
        });
        def(AST_Function, function(compressor) {
            return safe_to_drop(this, compressor) ? null : this;
        });
        def(AST_Object, function(compressor, first_in_statement) {
            var values = trim(this.properties, compressor, first_in_statement);
            return values && make_sequence(this, values);
        });
        def(AST_ObjectProperty, function(compressor, first_in_statement) {
            return this.value.drop_side_effect_free(compressor, first_in_statement);
        });
        def(AST_Sequence, function(compressor, first_in_statement) {
            var expressions = trim(this.expressions, compressor, first_in_statement);
            if (!expressions) return null;
            var end = expressions.length - 1;
            var assign, cond, lhs;
            if (compressor.option("conditionals")
                && end > 0
                && (assign = expressions[end - 1]) instanceof AST_Assign
                && assign.operator == "="
                && (lhs = assign.left) instanceof AST_SymbolRef
                && (cond = to_conditional_assignment(compressor, lhs.definition(), assign.right, expressions[end]))) {
                assign = assign.clone();
                assign.right = cond;
                expressions = expressions.slice(0, -2);
                expressions.push(assign);
            }
            return expressions === this.expressions ? this : make_sequence(this, expressions);
        });
        def(AST_Sub, function(compressor, first_in_statement) {
            if (this.expression.may_throw_on_access(compressor)) return this;
            var expression = this.expression.drop_side_effect_free(compressor, first_in_statement);
            if (!expression) return this.property.drop_side_effect_free(compressor, first_in_statement);
            var property = this.property.drop_side_effect_free(compressor);
            if (!property) return expression;
            return make_sequence(this, [ expression, property ]);
        });
        def(AST_SymbolRef, function(compressor) {
            if (!this.is_declared(compressor)) return this;
            this.definition().replaced++;
            return null;
        });
        def(AST_This, return_null);
        def(AST_Unary, function(compressor, first_in_statement) {
            if (unary_side_effects[this.operator]) {
                this.write_only = !this.expression.has_side_effects(compressor);
                return this;
            }
            if (this.operator == "typeof" && this.expression instanceof AST_SymbolRef) {
                this.expression.definition().replaced++;
                return null;
            }
            var expression = this.expression.drop_side_effect_free(compressor, first_in_statement);
            if (first_in_statement && expression && is_iife_call(expression)) {
                if (expression === this.expression && this.operator == "!") return this;
                return expression.negate(compressor, first_in_statement);
            }
            return expression;
        });
    })(function(node, func) {
        node.DEFMETHOD("drop_side_effect_free", func);
    });

OPT(AST_SimpleStatement, function(self, compressor) {
        if (compressor.option("side_effects")) {
            var body = self.body;
            var node = body.drop_side_effect_free(compressor, true);
            if (!node) {
                AST_Node.warn("Dropping side-effect-free statement [{file}:{line},{col}]", self.start);
                return make_node(AST_EmptyStatement, self);
            }
            if (node !== body) {
                return make_node(AST_SimpleStatement, self, { body: node });
            }
        }
        return self;
    });

OPT(AST_While, function(self, compressor) {
        return compressor.option("loops") ? make_node(AST_For, self, self).optimize(compressor) : self;
    });

OPT(AST_Do, function(self, compressor) {
        if (!compressor.option("loops")) return self;
        var cond = self.condition.is_truthy() || self.condition.evaluate(compressor, true);
        if (!(cond instanceof AST_Node)) {
            if (cond) return make_node(AST_For, self, {
                body: make_node(AST_BlockStatement, self.body, {
                    body: [
                        self.body,
                        make_node(AST_SimpleStatement, self.condition, {
                            body: self.condition
                        })
                    ]
                })
            }).optimize(compressor);
            if (!has_break_or_continue(self, compressor.parent())) {
                return make_node(AST_BlockStatement, self.body, {
                    body: [
                        self.body,
                        make_node(AST_SimpleStatement, self.condition, {
                            body: self.condition
                        })
                    ]
                }).optimize(compressor);
            }
        }
        if (self.body instanceof AST_SimpleStatement) return make_node(AST_For, self, {
            condition: make_sequence(self.condition, [
                self.body.body,
                self.condition
            ]),
            body: make_node(AST_EmptyStatement, self)
        }).optimize(compressor);
        return self;
    });

function first_statement(body) {
            return body instanceof AST_BlockStatement ? body.body[0] : body;
        }

function external_target(node) {
            return compressor.loopcontrol_target(node) !== compressor.self();
        }

OPT(AST_For, function(self, compressor) {
        if (!compressor.option("loops")) return self;
        if (compressor.option("side_effects")) {
            if (self.init) self.init = self.init.drop_side_effect_free(compressor);
            if (self.step) self.step = self.step.drop_side_effect_free(compressor);
        }
        if (self.condition) {
            var cond = self.condition.evaluate(compressor);
            if (cond instanceof AST_Node) {
                cond = self.condition.is_truthy() || self.condition.evaluate(compressor, true);
            } else if (cond) {
                self.condition = null;
            } else if (!compressor.option("dead_code")) {
                var orig = self.condition;
                self.condition = make_node_from_constant(cond, self.condition);
                self.condition = best_of_expression(self.condition.transform(compressor), orig);
            }
            if (!cond) {
                if (compressor.option("dead_code")) {
                    var body = [];
                    extract_declarations_from_unreachable_code(self.body, body);
                    if (self.init instanceof AST_Statement) {
                        body.push(self.init);
                    } else if (self.init) {
                        body.push(make_node(AST_SimpleStatement, self.init, {
                            body: self.init
                        }));
                    }
                    body.push(make_node(AST_SimpleStatement, self.condition, {
                        body: self.condition
                    }));
                    return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
                }
            } else if (self.condition && !(cond instanceof AST_Node)) {
                self.body = make_node(AST_BlockStatement, self.body, {
                    body: [
                        make_node(AST_SimpleStatement, self.condition, {
                            body: self.condition
                        }),
                        self.body
                    ]
                });
                self.condition = null;
            }
        }
        return if_break_in_loop(self, compressor);
    });

function negate(node) {
            if (!(node instanceof AST_Binary)) return;
            switch (node.operator) {
              case "==":
                node = node.clone();
                node.operator = "!=";
                return node;
              case "!=":
                node = node.clone();
                node.operator = "==";
                return node;
            }
        }
    }

OPT(AST_If, function(self, compressor) {
        if (is_empty(self.alternative)) self.alternative = null;

if (!compressor.option("conditionals")) return self;
        // if condition can be statically determined, warn and drop
        // one of the blocks.  note, statically determined implies
        // “has no side effects”; also it doesn't work for cases like
        // `x && true`, though it probably should.
        var cond = self.condition.evaluate(compressor);
        if (!compressor.option("dead_code") && !(cond instanceof AST_Node)) {
            var orig = self.condition;
            self.condition = make_node_from_constant(cond, orig);
            self.condition = best_of_expression(self.condition.transform(compressor), orig);
        }
        if (compressor.option("dead_code")) {
            if (cond instanceof AST_Node) {
                cond = self.condition.is_truthy() || self.condition.evaluate(compressor, true);
            }
            if (!cond) {
                AST_Node.warn("Condition always false [{file}:{line},{col}]", self.condition.start);
                var body = [];
                extract_declarations_from_unreachable_code(self.body, body);
                body.push(make_node(AST_SimpleStatement, self.condition, {
                    body: self.condition
                }));
                if (self.alternative) body.push(self.alternative);
                return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
            } else if (!(cond instanceof AST_Node)) {
                AST_Node.warn("Condition always true [{file}:{line},{col}]", self.condition.start);
                var body = [];
                if (self.alternative) extract_declarations_from_unreachable_code(self.alternative, body);
                body.push(make_node(AST_SimpleStatement, self.condition, {
                    body: self.condition
                }));
                body.push(self.body);
                return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
            }
        }
        var negated = self.condition.negate(compressor);
        var self_condition_length = self.condition.print_to_string().length;
        var negated_length = negated.print_to_string().length;
        var negated_is_best = negated_length < self_condition_length;
        if (self.alternative && negated_is_best) {
            negated_is_best = false; // because we already do the switch here.
            // no need to swap values of self_condition_length and negated_length
            // here because they are only used in an equality comparison later on.
            self.condition = negated;
            var tmp = self.body;
            self.body = self.alternative || make_node(AST_EmptyStatement, self);
            self.alternative = tmp;
        }
        var body = [], var_defs = [], refs = [];
        var body_exprs = sequencesize(self.body, body, var_defs, refs);
        var alt_exprs = sequencesize(self.alternative, body, var_defs, refs);
        if (body_exprs && alt_exprs) {
            if (var_defs.length > 0) body.push(make_node(AST_Var, self, {
                definitions: var_defs
            }));
            if (body_exprs.length == 0) {
                body.push(make_node(AST_SimpleStatement, self.condition, {
                    body: alt_exprs.length > 0 ? make_node(AST_Binary, self, {
                        operator : "||",
                        left     : self.condition,
                        right    : make_sequence(self.alternative, alt_exprs)
                    }).transform(compressor) : self.condition.clone()
                }).optimize(compressor));
            } else if (alt_exprs.length == 0) {
                if (self_condition_length === negated_length && !negated_is_best
                    && self.condition instanceof AST_Binary && self.condition.operator == "||") {
                    // although the code length of self.condition and negated are the same,
                    // negated does not require additional surrounding parentheses.
                    // see https://github.com/mishoo/UglifyJS/issues/979
                    negated_is_best = true;
                }
                body.push(make_node(AST_SimpleStatement, self, {
                    body: make_node(AST_Binary, self, {
                        operator : negated_is_best ? "||" : "&&",
                        left     : negated_is_best ? negated : self.condition,
                        right    : make_sequence(self.body, body_exprs)
                    }).transform(compressor)
                }).optimize(compressor));
            } else {
                body.push(make_node(AST_SimpleStatement, self, {
                    body: make_node(AST_Conditional, self, {
                        condition   : self.condition,
                        consequent  : make_sequence(self.body, body_exprs),
                        alternative : make_sequence(self.alternative, alt_exprs)
                    })
                }).optimize(compressor));
            }
            refs.forEach(function(ref) {
                ref.definition().references.push(ref);
            });
            return make_node(AST_BlockStatement, self, {
                body: body
            }).optimize(compressor);
        }
        if (is_empty(self.body)) {
            self = make_node(AST_If, self, {
                condition: negated,
                body: self.alternative,
                alternative: null
            });
        }
        if (self.body instanceof AST_Exit
            && self.alternative instanceof AST_Exit
            && self.body.TYPE == self.alternative.TYPE) {
            var exit = make_node(self.body.CTOR, self, {
                value: make_node(AST_Conditional, self, {
                    condition   : self.condition,
                    consequent  : self.body.value || make_node(AST_Undefined, self.body).transform(compressor),
                    alternative : self.alternative.value || make_node(AST_Undefined, self.alternative).transform(compressor)
                })
            });
            if (exit instanceof AST_Return) {
                exit.in_bool = self.body.in_bool || self.alternative.in_bool;
            }
            return exit;
        }
        if (self.body instanceof AST_If
            && !self.body.alternative
            && !self.alternative) {
            self = make_node(AST_If, self, {
                condition: make_node(AST_Binary, self.condition, {
                    operator: "&&",
                    left: self.condition,
                    right: self.body.condition
                }),
                body: self.body.body,
                alternative: null
            });
        }
        if (aborts(self.body)) {
            if (self.alternative) {
                var alt = self.alternative;
                self.alternative = null;
                return make_node(AST_BlockStatement, self, {
                    body: [ self, alt ]
                }).optimize(compressor);
            }
        }
        if (aborts(self.alternative)) {
            var body = self.body;
            self.body = self.alternative;
            self.condition = negated_is_best ? negated : self.condition.negate(compressor);
            self.alternative = null;
            return make_node(AST_BlockStatement, self, {
                body: [ self, body ]
            }).optimize(compressor);
        }
        if (compressor.option("typeofs")) mark_locally_defined(self.condition, self.body, self.alternative);
        return self;

OPT(AST_Switch, function(self, compressor) {
        if (!compressor.option("switches")) return self;
        var branch;
        var value = self.expression.evaluate(compressor);
        if (!(value instanceof AST_Node)) {
            var orig = self.expression;
            self.expression = make_node_from_constant(value, orig);
            self.expression = best_of_expression(self.expression.transform(compressor), orig);
        }
        if (!compressor.option("dead_code")) return self;
        if (value instanceof AST_Node) {
            value = self.expression.evaluate(compressor, true);
        }
        var decl = [];
        var body = [];
        var default_branch;
        var exact_match;
        for (var i = 0, len = self.body.length; i < len && !exact_match; i++) {
            branch = self.body[i];
            if (branch instanceof AST_Default) {
                var prev = body[body.length - 1];
                if (default_branch || is_break(branch.body[0], compressor) && (!prev || aborts(prev))) {
                    eliminate_branch(branch, prev);
                    continue;
                } else {
                    default_branch = branch;
                }
            } else if (!(value instanceof AST_Node)) {
                var exp = branch.expression.evaluate(compressor);
                if (!(exp instanceof AST_Node) && exp !== value) {
                    eliminate_branch(branch, body[body.length - 1]);
                    continue;
                }
                if (exp instanceof AST_Node) exp = branch.expression.evaluate(compressor, true);
                if (exp === value) {
                    exact_match = branch;
                    if (default_branch) {
                        var default_index = body.indexOf(default_branch);
                        body.splice(default_index, 1);
                        eliminate_branch(default_branch, body[default_index - 1]);
                        default_branch = null;
                    }
                }
            }
            if (aborts(branch)) {
                var prev = body[body.length - 1];
                if (aborts(prev) && prev.body.length == branch.body.length
                    && make_node(AST_BlockStatement, prev, prev).equivalent_to(make_node(AST_BlockStatement, branch, branch))) {
                    prev.body = [];
                }
            }
            body.push(branch);
        }
        while (i < len) eliminate_branch(self.body[i++], body[body.length - 1]);
        while (branch = body[body.length - 1]) {
            var stat = branch.body[branch.body.length - 1];
            if (is_break(stat, compressor)) branch.body.pop();
            if (branch === default_branch) {
                if (!has_declarations_only(branch)) break;
            } else if (branch.expression.has_side_effects(compressor)) {
                break;
            } else if (default_branch) {
                if (!has_declarations_only(default_branch)) break;
                if (body[body.length - 2] !== default_branch) break;
                default_branch.body = default_branch.body.concat(branch.body);
                branch.body = [];
            } else if (!has_declarations_only(branch)) break;
            eliminate_branch(branch);
            if (body.pop() === default_branch) default_branch = null;
        }
        if (body.length == 0) {
            return make_node(AST_BlockStatement, self, {
                body: decl.concat(make_node(AST_SimpleStatement, self.expression, {
                    body: self.expression
                }))
            }).optimize(compressor);
        }
        body[0].body = decl.concat(body[0].body);
        self.body = body;
        if (body.length == 1 && (body[0] === exact_match || body[0] === default_branch)) {
            var has_break = false;
            var tw = new TreeWalker(function(node) {
                if (has_break
                    || node instanceof AST_Lambda
                    || node instanceof AST_SimpleStatement) return true;
                if (is_break(node, tw)) has_break = true;
            });
            self.walk(tw);
            if (!has_break) {
                var statements = body[0].body.slice();
                var exp = body[0].expression;
                if (exp) statements.unshift(make_node(AST_SimpleStatement, exp, {
                    body: exp
                }));
                statements.unshift(make_node(AST_SimpleStatement, self.expression, {
                    body:self.expression
                }));
                return make_node(AST_BlockStatement, self, {
                    body: statements
                }).optimize(compressor);
            }
        }
        return self;

function is_break(node, tw) {
            return node instanceof AST_Break && tw.loopcontrol_target(node) === self;
        }

OPT(AST_Try, function(self, compressor) {
        self.body = tighten_body(self.body, compressor);
        if (compressor.option("dead_code")) {
            if (has_declarations_only(self)) {
                var body = [];
                if (self.bcatch) {
                    extract_declarations_from_unreachable_code(self.bcatch, body);
                    body.forEach(function(stat) {
                        if (!(stat instanceof AST_Definitions)) return;
                        stat.definitions.forEach(function(var_def) {
                            var def = var_def.name.definition().redefined();
                            if (!def) return;
                            var_def.name = var_def.name.clone();
                            var_def.name.thedef = def;
                        });
                    });
                }
                [].unshift.apply(body, self.body);
                if (self.bfinally) [].push.apply(body, self.bfinally.body);
                return make_node(AST_BlockStatement, self, {
                    body: body
                }).optimize(compressor);
            }
            if (self.bfinally && has_declarations_only(self.bfinally)) {
                var body = self.body.concat(self.bfinally.body);
                if (!self.bcatch) return make_node(AST_BlockStatement, self, {
                    body: body
                }).optimize(compressor);
                self.body = body;
                self.bfinally = null;
            }
        }
        return self;
    });

AST_Definitions.DEFMETHOD("remove_initializers", function() {
        this.definitions.forEach(function(def) {
            def.value = null;
        });
    });

AST_Definitions.DEFMETHOD("to_assignments", function(compressor) {
        var reduce_vars = compressor.option("reduce_vars");
        var assignments = this.definitions.reduce(function(a, def) {
            if (def.value) {
                var name = make_node(AST_SymbolRef, def.name, def.name);
                a.push(make_node(AST_Assign, def, {
                    operator : "=",
                    left     : name,
                    right    : def.value
                }));
                if (reduce_vars) name.definition().fixed = false;
            }
            def = def.name.definition();
            def.eliminated++;
            def.replaced--;
            return a;
        }, []);
        if (assignments.length == 0) return null;
        return make_sequence(this, assignments);
    });

OPT(AST_Definitions, function(self, compressor) {
        return self.definitions.length ? self : make_node(AST_EmptyStatement, self);
    });

function lift_sequence_in_expression(node, compressor) {
        var exp = node.expression;
        if (!(exp instanceof AST_Sequence)) return node;
        var x = exp.expressions.slice();
        var e = node.clone();
        e.expression = x.pop();
        x.push(e);
        return make_sequence(node, x);
    }

OPT(AST_Call, function(self, compressor) {
        var exp = self.expression;
        if (compressor.option("sequences")) {
            if (exp instanceof AST_PropAccess) {
                var seq = lift_sequence_in_expression(exp, compressor);
                if (seq !== exp) {
                    var call = self.clone();
                    call.expression = seq.expressions.pop();
                    seq.expressions.push(call);
                    return seq.optimize(compressor);
                }
            } else if (!needs_unbinding(compressor, exp.tail_node())) {
                var seq = lift_sequence_in_expression(self, compressor);
                if (seq !== self) return seq.optimize(compressor);
            }
        }
        if (compressor.option("unused")) drop_unused_call_args(self, compressor);
        if (compressor.option("unsafe")) {
            if (is_undeclared_ref(exp)) switch (exp.name) {
              case "Array":
                if (self.args.length == 1) {
                    var first = self.args[0];
                    if (first instanceof AST_Number) try {
                        var length = first.value;
                        if (length > 6) break;
                        var elements = Array(length);
                        for (var i = 0; i < length; i++) elements[i] = make_node(AST_Hole, self);
                        return make_node(AST_Array, self, {
                            elements: elements
                        });
                    } catch (ex) {
                        AST_Node.warn("Invalid array length: {length} [{file}:{line},{col}]", {
                            length: length,
                            file: self.start.file,
                            line: self.start.line,
                            col: self.start.col
                        });
                        break;
                    }
                    if (!first.is_boolean(compressor) && !first.is_string(compressor)) break;
                }
                return make_node(AST_Array, self, {
                    elements: self.args
                });
              case "Object":
                if (self.args.length == 0) {
                    return make_node(AST_Object, self, {
                        properties: []
                    });
                }
                break;
              case "String":
                if (self.args.length == 0) return make_node(AST_String, self, {
                    value: ""
                });
                if (self.args.length <= 1) return make_node(AST_Binary, self, {
                    left: self.args[0],
                    operator: "+",
                    right: make_node(AST_String, self, { value: "" })
                }).optimize(compressor);
                break;
              case "Number":
                if (self.args.length == 0) return make_node(AST_Number, self, {
                    value: 0
                });
                if (self.args.length == 1) return make_node(AST_UnaryPrefix, self, {
                    expression: self.args[0],
                    operator: "+"
                }).optimize(compressor);
              case "Boolean":
                if (self.args.length == 0) return make_node(AST_False, self);
                if (self.args.length == 1) return make_node(AST_UnaryPrefix, self, {
                    expression: make_node(AST_UnaryPrefix, self, {
                        expression: self.args[0],
                        operator: "!"
                    }),
                    operator: "!"
                }).optimize(compressor);
                break;
              case "RegExp":
                var params = [];
                if (all(self.args, function(arg) {
                    var value = arg.evaluate(compressor);
                    params.unshift(value);
                    return arg !== value;
                })) {
                    try {
                        return best_of(compressor, self, make_node(AST_RegExp, self, {
                            value: RegExp.apply(RegExp, params),
                        }));
                    } catch (ex) {
                        AST_Node.warn("Error converting {expr} [{file}:{line},{col}]", {
                            expr: self.print_to_string(),
                            file: self.start.file,
                            line: self.start.line,
                            col: self.start.col
                        });
                    }
                }
                break;
            } else if (exp instanceof AST_Dot) switch(exp.property) {
              case "toString":
                if (self.args.length == 0 && !exp.expression.may_throw_on_access(compressor)) {
                    return make_node(AST_Binary, self, {
                        left: make_node(AST_String, self, { value: "" }),
                        operator: "+",
                        right: exp.expression
                    }).optimize(compressor);
                }
                break;
              case "join":
                if (exp.expression instanceof AST_Array) EXIT: {
                    var separator;
                    if (self.args.length > 0) {
                        separator = self.args[0].evaluate(compressor);
                        if (separator === self.args[0]) break EXIT; // not a constant
                    }
                    var elements = [];
                    var consts = [];
                    exp.expression.elements.forEach(function(el) {
                        var value = el.evaluate(compressor);
                        if (value !== el) {
                            consts.push(value);
                        } else {
                            if (consts.length > 0) {
                                elements.push(make_node(AST_String, self, {
                                    value: consts.join(separator)
                                }));
                                consts.length = 0;
                            }
                            elements.push(el);
                        }
                    });
                    if (consts.length > 0) {
                        elements.push(make_node(AST_String, self, {
                            value: consts.join(separator)
                        }));
                    }
                    if (elements.length == 0) return make_node(AST_String, self, { value: "" });
                    if (elements.length == 1) {
                        if (elements[0].is_string(compressor)) {
                            return elements[0];
                        }
                        return make_node(AST_Binary, elements[0], {
                            operator : "+",
                            left     : make_node(AST_String, self, { value: "" }),
                            right    : elements[0]
                        });
                    }
                    if (separator == "") {
                        var first;
                        if (elements[0].is_string(compressor)
                            || elements[1].is_string(compressor)) {
                            first = elements.shift();
                        } else {
                            first = make_node(AST_String, self, { value: "" });
                        }
                        return elements.reduce(function(prev, el) {
                            return make_node(AST_Binary, el, {
                                operator : "+",
                                left     : prev,
                                right    : el
                            });
                        }, first).optimize(compressor);
                    }
                    // need this awkward cloning to not affect original element
                    // best_of will decide which one to get through.
                    var node = self.clone();
                    node.expression = node.expression.clone();
                    node.expression.expression = node.expression.expression.clone();
                    node.expression.expression.elements = elements;
                    return best_of(compressor, self, node);
                }
                break;
              case "charAt":
                if (self.args.length < 2) {
                    var node = make_node(AST_Sub, self, {
                        expression: exp.expression,
                        property: self.args.length ? make_node(AST_Binary, self.args[0], {
                            operator: "|",
                            left: make_node(AST_Number, self, {
                                value: 0
                            }),
                            right: self.args[0]
                        }) : make_node(AST_Number, self, {
                            value: 0
                        })
                    });
                    node.is_string = return_true;
                    return node.optimize(compressor);
                }
                break;
              case "apply":
                if (self.args.length == 2 && self.args[1] instanceof AST_Array) {
                    var args = self.args[1].elements.slice();
                    args.unshift(self.args[0]);
                    return make_node(AST_Call, self, {
                        expression: make_node(AST_Dot, exp, {
                            expression: exp.expression,
                            property: "call"
                        }),
                        args: args
                    }).optimize(compressor);
                }
                break;
              case "call":
                var func = exp.expression;
                if (func instanceof AST_SymbolRef) {
                    func = func.fixed_value();
                }
                if (func instanceof AST_Lambda && !func.contains_this()) {
                    return (self.args.length ? make_sequence(this, [
                        self.args[0],
                        make_node(AST_Call, self, {
                            expression: exp.expression,
                            args: self.args.slice(1)
                        })
                    ]) : make_node(AST_Call, self, {
                        expression: exp.expression,
                        args: []
                    })).optimize(compressor);
                }
                break;
            }
        }
        if (compressor.option("unsafe_Function")
            && is_undeclared_ref(exp)
            && exp.name == "Function") {
            // new Function() => function(){}
            if (self.args.length == 0) return make_node(AST_Function, self, {
                argnames: [],
                body: []
            });
            if (all(self.args, function(x) {
                return x instanceof AST_String;
            })) {
                // quite a corner-case, but we can handle it:
                //   https://github.com/mishoo/UglifyJS/issues/203
                // if the code argument is a constant, then we can minify it.
                try {
                    var code = "n(function(" + self.args.slice(0, -1).map(function(arg) {
                        return arg.value;
                    }).join(",") + "){" + self.args[self.args.length - 1].value + "})";
                    var ast = parse(code);
                    var mangle = { ie8: compressor.option("ie8") };
                    ast.figure_out_scope(mangle);
                    var comp = new Compressor(compressor.options);
                    ast = ast.transform(comp);
                    ast.figure_out_scope(mangle);
                    ast.compute_char_frequency(mangle);
                    ast.mangle_names(mangle);
                    var fun;
                    ast.walk(new TreeWalker(function(node) {
                        if (fun) return true;
                        if (node instanceof AST_Lambda) {
                            fun = node;
                            return true;
                        }
                    }));
                    var code = OutputStream();
                    AST_BlockStatement.prototype._codegen.call(fun, fun, code);
                    self.args = [
                        make_node(AST_String, self, {
                            value: fun.argnames.map(function(arg) {
                                return arg.print_to_string();
                            }).join(",")
                        }),
                        make_node(AST_String, self.args[self.args.length - 1], {
                            value: code.get().replace(/^\{|\}$/g, "")
                        })
                    ];
                    return self;
                } catch (ex) {
                    if (ex instanceof JS_Parse_Error) {
                        AST_Node.warn("Error parsing code passed to new Function [{file}:{line},{col}]", self.args[self.args.length - 1].start);
                        AST_Node.warn(ex.toString());
                    } else {
                        throw ex;
                    }
                }
            }
        }
        var fn = exp instanceof AST_SymbolRef ? exp.fixed_value() : exp;
        var is_func = fn instanceof AST_Lambda;
        var stat = is_func && fn.first_statement();
        var can_inline = compressor.option("inline") && !self.is_expr_pure(compressor);
        if (can_inline && stat instanceof AST_Return) {
            var value = stat.value;
            if (exp === fn && (!value || value.is_constant_expression())) {
                var args = self.args.concat(value || make_node(AST_Undefined, self));
                return make_sequence(self, args).optimize(compressor);
            }
        }
        if (is_func) {
            var def, value, var_assigned = false;
            if (can_inline
                && !fn.uses_arguments
                && !fn.pinned()
                && !(fn.name && fn instanceof AST_Function)
                && (value = can_flatten_body(stat))
                && (exp === fn
                    || !recursive_ref(compressor, def = exp.definition()) && fn.is_constant_expression(exp.scope))
                && !fn.contains_this()) {
                if (can_substitute_directly()) {
                    var args = self.args.slice();
                    args.push(value.clone(true).transform(new TreeTransformer(function(node) {
                        if (node instanceof AST_SymbolRef) {
                            var def = node.definition();
                            if (fn.variables.get(node.name) !== def) {
                                if (exp !== fn) def.references.push(node);
                                return node;
                            }
                            var index = resolve_index(def);
                            var arg = args[index];
                            if (!arg) return make_node(AST_Undefined, self);
                            args[index] = null;
                            var parent = this.parent();
                            return parent ? maintain_this_binding(compressor, parent, node, arg) : arg;
                        }
                    })));
                    var node = make_sequence(self, args.filter(function(arg) {
                        return arg;
                    })).optimize(compressor);
                    node = maintain_this_binding(compressor, compressor.parent(), compressor.self(), node);
                    if (best_of(compressor, self, node) === node) return node;
                }
                var scope, in_loop, level = -1;
                if ((exp === fn || compressor.option("unused") && def.references.length - def.replaced == 1)
                    && can_inject_symbols()) {
                    fn._squeezed = true;
                    if (exp !== fn) fn.parent_scope = exp.scope;
                    var node = make_sequence(self, flatten_fn()).optimize(compressor);
                    return maintain_this_binding(compressor, compressor.parent(), compressor.self(), node);
                }
            }
            if (compressor.option("side_effects")
                && all(fn.body, is_empty)
                && (fn !== exp || safe_to_drop(fn, compressor))) {
                var args = self.args.concat(make_node(AST_Undefined, self));
                return make_sequence(self, args).optimize(compressor);
            }
        }
        if (compressor.option("drop_console")) {
            if (exp instanceof AST_PropAccess) {
                var name = exp.expression;
                while (name.expression) {
                    name = name.expression;
                }
                if (is_undeclared_ref(name) && name.name == "console") {
                    return make_node(AST_Undefined, self).optimize(compressor);
                }
            }
        }
        if (compressor.option("negate_iife")
            && compressor.parent() instanceof AST_SimpleStatement
            && is_iife_call(self)) {
            return self.negate(compressor, true);
        }
        return try_evaluate(compressor, self);

function resolve_index(def) {
            for (var i = fn.argnames.length; --i >= 0;) {
                if (fn.argnames[i].definition() === def) return i;
            }
        }

function var_exists(defined, name) {
            return defined[name] || identifier_atom[name] || scope.var_names()[name];
        }

function can_inject_args(catches, used, safe_to_inject) {
            for (var i = 0; i < fn.argnames.length; i++) {
                var arg = fn.argnames[i];
                if (arg.__unused) continue;
                if (!safe_to_inject || var_exists(catches, arg.name)) return false;
                used[arg.name] = true;
                if (in_loop) in_loop.push(arg.definition());
            }
            return true;
        }

OPT(AST_New, function(self, compressor) {
        if (compressor.option("sequences")) {
            var seq = lift_sequence_in_expression(self, compressor);
            if (seq !== self) return seq.optimize(compressor);
        }
        if (compressor.option("unsafe")) {
            var exp = self.expression;
            if (is_undeclared_ref(exp)) {
                switch (exp.name) {
                  case "Object":
                  case "RegExp":
                  case "Function":
                  case "Error":
                  case "Array":
                    return make_node(AST_Call, self, self).transform(compressor);
                }
            }
        }
        return self;
    });

// (a = b, x && a = c) => a = x ? c : b
    // (a = b, x || a = c) => a = x ? b : c
    function to_conditional_assignment(compressor, def, value, node) {
        if (!(node instanceof AST_Binary)) return;
        if (!lazy_op[node.operator]) return;
        if (!(node.right instanceof AST_Assign)) return;
        if (node.right.operator != "=") return;
        if (!(node.right.left instanceof AST_SymbolRef)) return;
        if (node.right.left.definition() !== def) return;
        if (value.has_side_effects(compressor)) return;
        if (!safe_from_assignment(node.left)) return;
        if (!safe_from_assignment(node.right.right)) return;
        def.replaced++;
        return node.operator == "&&" ? make_node(AST_Conditional, node, {
            condition: node.left,
            consequent: node.right.right,
            alternative: value
        }) : make_node(AST_Conditional, node, {
            condition: node.left,
            consequent: value,
            alternative: node.right.right
        });

function safe_from_assignment(node) {
            if (node.has_side_effects(compressor)) return;
            var hit = false;
            node.walk(new TreeWalker(function(node) {
                if (hit) return true;
                if (node instanceof AST_SymbolRef && node.definition() === def) return hit = true;
            }));
            return !hit;
        }
    }

OPT(AST_Sequence, function(self, compressor) {
        var expressions = filter_for_side_effects();
        var end = expressions.length - 1;
        merge_conditional_assignments();
        trim_right_for_undefined();
        if (end == 0) {
            self = maintain_this_binding(compressor, compressor.parent(), compressor.self(), expressions[0]);
            if (!(self instanceof AST_Sequence)) self = self.optimize(compressor);
            return self;
        }
        self.expressions = expressions;
        return self;

function merge_conditional_assignments() {
            if (!compressor.option("conditionals")) return;
            for (var i = 1; i < end; i++) {
                var assign = expressions[i - 1];
                if (!(assign instanceof AST_Assign)) continue;
                if (assign.operator != "=") continue;
                if (!(assign.left instanceof AST_SymbolRef)) continue;
                var def = assign.left.definition();
                var cond = to_conditional_assignment(compressor, def, assign.right, expressions[i]);
                if (!cond) continue;
                assign.right = cond;
                expressions.splice(i, 1);
                end--;
            }
        }
    });

OPT(AST_UnaryPostfix, function(self, compressor) {
        if (compressor.option("sequences")) {
            var seq = lift_sequence_in_expression(self, compressor);
            if (seq !== self) return seq.optimize(compressor);
        }
        return self;
    });

AST_Binary.DEFMETHOD("lift_sequences", function(compressor) {
        if (this.left instanceof AST_PropAccess) {
            if (!(this.left.expression instanceof AST_Sequence)) return this;
            var x = this.left.expression.expressions.slice();
            var e = this.clone();
            e.left = e.left.clone();
            e.left.expression = x.pop();
            x.push(e);
            return make_sequence(this, x);
        }
        if (this.left instanceof AST_Sequence) {
            var x = this.left.expressions.slice();
            var e = this.clone();
            e.left = x.pop();
            x.push(e);
            return make_sequence(this, x);
        }
        if (this.right instanceof AST_Sequence) {
            if (this.left.has_side_effects(compressor)) return this;
            var assign = this.operator == "=" && this.left instanceof AST_SymbolRef;
            var x = this.right.expressions;
            var last = x.length - 1;
            for (var i = 0; i < last; i++) {
                if (!assign && x[i].has_side_effects(compressor)) break;
            }
            if (i == last) {
                x = x.slice();
                var e = this.clone();
                e.right = x.pop();
                x.push(e);
                return make_sequence(this, x);
            }
            if (i > 0) {
                var e = this.clone();
                e.right = make_sequence(this.right, x.slice(i));
                x = x.slice(0, i);
                x.push(e);
                return make_sequence(this, x);
            }
        }
        return this;
    });

var indexFns = makePredicate("indexOf lastIndexOf");
    var commutativeOperators = makePredicate("== === != !== * & | ^");
    function is_object(node) {
        return node instanceof AST_Array
            || node instanceof AST_Lambda
            || node instanceof AST_Object;
    }

OPT(AST_Binary, function(self, compressor) {
        function reversible() {
            return self.left.is_constant()
                || self.right.is_constant()
                || !self.left.has_side_effects(compressor)
                    && !self.right.has_side_effects(compressor);
        }
        function reverse(op) {
            if (reversible()) {
                if (op) self.operator = op;
                var tmp = self.left;
                self.left = self.right;
                self.right = tmp;
            }
        }
        function swap_chain() {
            var rhs = self.right;
            self.left = make_node(AST_Binary, self, {
                operator: self.operator,
                left: self.left,
                right: rhs.left,
                start: self.left.start,
                end: rhs.left.end
            });
            self.right = rhs.right;
            self.left = self.left.transform(compressor);
        }
        if (commutativeOperators[self.operator]
            && self.right.is_constant()
            && !self.left.is_constant()
            && !(self.left instanceof AST_Binary
                && PRECEDENCE[self.left.operator] >= PRECEDENCE[self.operator])) {
            // if right is a constant, whatever side effects the
            // left side might have could not influence the
            // result.  hence, force switch.
            reverse();
        }
        if (compressor.option("sequences")) {
            var seq = self.lift_sequences(compressor);
            if (seq !== self) return seq.optimize(compressor);
        }
        if (compressor.option("assignments") && lazy_op[self.operator]) {
            var assign = self.right;
            // a || (a = x) => a = a || x
            // a && (a = x) => a = a && x
            if (self.left instanceof AST_SymbolRef
                && assign instanceof AST_Assign
                && assign.operator == "="
                && self.left.equivalent_to(assign.left)) {
                self.right = assign.right;
                assign.right = self;
                return assign;
            }
        }
        if (compressor.option("comparisons")) switch (self.operator) {
          case "===":
          case "!==":
            if (is_undefined(self.left, compressor) && self.right.is_defined(compressor)) {
                AST_Node.warn("Expression always defined [{file}:{line},{col}]", self.start);
                return make_sequence(self, [
                    self.right,
                    make_node(self.operator == "===" ? AST_False : AST_True, self)
                ]).optimize(compressor);
            }
            var is_strict_comparison = true;
            if ((self.left.is_string(compressor) && self.right.is_string(compressor)) ||
                (self.left.is_number(compressor) && self.right.is_number(compressor)) ||
                (self.left.is_boolean(compressor) && self.right.is_boolean(compressor)) ||
                can_self_compare(self.left) && self.left.equivalent_to(self.right)) {
                self.operator = self.operator.slice(0, 2);
            }
            // XXX: intentionally falling down to the next case
          case "==":
          case "!=":
            // void 0 == x => null == x
            if (!is_strict_comparison && is_undefined(self.left, compressor)) {
                self.left = make_node(AST_Null, self.left);
            }
            // "undefined" == typeof x => undefined === x
            else if (compressor.option("typeofs")
                && self.left instanceof AST_String
                && self.left.value == "undefined"
                && self.right instanceof AST_UnaryPrefix
                && self.right.operator == "typeof") {
                var expr = self.right.expression;
                if (expr instanceof AST_SymbolRef ? expr.is_declared(compressor)
                    : !(expr instanceof AST_PropAccess && compressor.option("ie8"))) {
                    self.right = expr;
                    self.left = make_node(AST_Undefined, self.left).optimize(compressor);
                    if (self.operator.length == 2) self.operator += "=";
                }
            }
            // obj !== obj => false
            else if (self.left instanceof AST_SymbolRef
                && self.right instanceof AST_SymbolRef
                && self.left.definition() === self.right.definition()
                && is_object(self.left.fixed_value())) {
                return make_node(self.operator[0] == "=" ? AST_True : AST_False, self);
            }
            break;
          case "&&":
          case "||":
            // void 0 !== x && null !== x => null != x
            // void 0 === x || null === x => null == x
            var lhs = self.left;
            if (lhs.operator == self.operator) {
                lhs = lhs.right;
            }
            if (lhs instanceof AST_Binary
                && lhs.operator == (self.operator == "&&" ? "!==" : "===")
                && self.right instanceof AST_Binary
                && lhs.operator == self.right.operator
                && (is_undefined(lhs.left, compressor) && self.right.left instanceof AST_Null
                    || lhs.left instanceof AST_Null && is_undefined(self.right.left, compressor))
                && !lhs.right.has_side_effects(compressor)
                && lhs.right.equivalent_to(self.right.right)) {
                var combined = make_node(AST_Binary, self, {
                    operator: lhs.operator.slice(0, -1),
                    left: make_node(AST_Null, self),
                    right: lhs.right
                });
                if (lhs !== self.left) {
                    combined = make_node(AST_Binary, self, {
                        operator: self.operator,
                        left: self.left.left,
                        right: combined
                    });
                }
                return combined;
            }
            break;
        }
        var in_bool = compressor.option("booleans") && compressor.in_boolean_context();
        if (in_bool) switch (self.operator) {
          case "+":
            var ll = self.left.evaluate(compressor);
            var rr = self.right.evaluate(compressor);
            if (ll && typeof ll == "string") {
                AST_Node.warn("+ in boolean context always true [{file}:{line},{col}]", self.start);
                return make_sequence(self, [
                    self.right,
                    make_node(AST_True, self)
                ]).optimize(compressor);
            }
            if (rr && typeof rr == "string") {
                AST_Node.warn("+ in boolean context always true [{file}:{line},{col}]", self.start);
                return make_sequence(self, [
                    self.left,
                    make_node(AST_True, self)
                ]).optimize(compressor);
            }
            break;
          case "==":
            if (self.left instanceof AST_String && self.left.value == "" && self.right.is_string(compressor)) {
                return make_node(AST_UnaryPrefix, self, {
                    operator: "!",
                    expression: self.right
                }).optimize(compressor);
            }
            break;
          case "!=":
            if (self.left instanceof AST_String && self.left.value == "" && self.right.is_string(compressor)) {
                return self.right.optimize(compressor);
            }
            break;
        }
        var parent = compressor.parent();
        if (compressor.option("comparisons") && self.is_boolean(compressor)) {
            if (!(parent instanceof AST_Binary) || parent instanceof AST_Assign) {
                var negated = make_node(AST_UnaryPrefix, self, {
                    operator: "!",
                    expression: self.negate(compressor, first_in_statement(compressor))
                });
                self = best_of(compressor, self, negated);
            }
            switch (self.operator) {
              case ">": reverse("<"); break;
              case ">=": reverse("<="); break;
            }
        }
        // x && (y && z) => x && y && z
        // x || (y || z) => x || y || z
        if (compressor.option("conditionals")
            && lazy_op[self.operator]
            && self.right instanceof AST_Binary
            && self.operator == self.right.operator) {
            swap_chain();
        }
        if (compressor.option("strings") && self.operator == "+") {
            // "foo" + 42 + "" => "foo" + 42
            if (self.right instanceof AST_String
                && self.right.value == ""
                && self.left.is_string(compressor)) {
                return self.left.optimize(compressor);
            }
            // "" + ("foo" + 42) => "foo" + 42
            if (self.left instanceof AST_String
                && self.left.value == ""
                && self.right.is_string(compressor)) {
                return self.right.optimize(compressor);
            }
            // "" + 42 + "foo" => 42 + "foo"
            if (self.left instanceof AST_Binary
                && self.left.operator == "+"
                && self.left.left instanceof AST_String
                && self.left.left.value == ""
                && self.right.is_string(compressor)) {
                self.left = self.left.right;
                return self.optimize(compressor);
            }
            // "x" + (y + "z") => "x" + y + "z"
            // x + ("y" + z) => x + "y" + z
            if (self.right instanceof AST_Binary
                && self.operator == self.right.operator
                && (self.left.is_string(compressor) && self.right.is_string(compressor)
                    || self.right.left.is_string(compressor)
                        && (self.left.is_constant() || !self.right.right.has_side_effects(compressor)))) {
                swap_chain();
            }
        }
        if (compressor.option("evaluate")) {
            var associative = true;
            switch (self.operator) {
              case "&&":
                var ll = fuzzy_eval(self.left);
                if (!ll) {
                    AST_Node.warn("Condition left of && always false [{file}:{line},{col}]", self.start);
                    return maintain_this_binding(compressor, parent, compressor.self(), self.left).optimize(compressor);
                } else if (!(ll instanceof AST_Node)) {
                    AST_Node.warn("Condition left of && always true [{file}:{line},{col}]", self.start);
                    return make_sequence(self, [ self.left, self.right ]).optimize(compressor);
                }
                var rr = self.right.evaluate(compressor);
                if (!rr) {
                    if (in_bool) {
                        AST_Node.warn("Boolean && always false [{file}:{line},{col}]", self.start);
                        return make_sequence(self, [
                            self.left,
                            make_node(AST_False, self)
                        ]).optimize(compressor);
                    } else self.falsy = true;
                } else if (!(rr instanceof AST_Node)) {
                    if (in_bool || parent.operator == "&&" && parent.left === compressor.self()) {
                        AST_Node.warn("Dropping side-effect-free && [{file}:{line},{col}]", self.start);
                        return self.left.optimize(compressor);
                    }
                }
                // (x || false) && y => x ? y : false
                if (self.left.operator == "||") {
                    var lr = self.left.right.evaluate(compressor, true);
                    if (!lr) return make_node(AST_Conditional, self, {
                        condition: self.left.left,
                        consequent: self.right,
                        alternative: self.left.right
                    }).optimize(compressor);
                }
                break;
              case "||":
                var ll = fuzzy_eval(self.left);
                if (!ll) {
                    AST_Node.warn("Condition left of || always false [{file}:{line},{col}]", self.start);
                    return make_sequence(self, [ self.left, self.right ]).optimize(compressor);
                } else if (!(ll instanceof AST_Node)) {
                    AST_Node.warn("Condition left of || always true [{file}:{line},{col}]", self.start);
                    return maintain_this_binding(compressor, parent, compressor.self(), self.left).optimize(compressor);
                }
                var rr = self.right.evaluate(compressor);
                if (!rr) {
                    if (in_bool || parent.operator == "||" && parent.left === compressor.self()) {
                        AST_Node.warn("Dropping side-effect-free || [{file}:{line},{col}]", self.start);
                        return self.left.optimize(compressor);
                    }
                } else if (!(rr instanceof AST_Node)) {
                    if (in_bool) {
                        AST_Node.warn("Boolean || always true [{file}:{line},{col}]", self.start);
                        return make_sequence(self, [
                            self.left,
                            make_node(AST_True, self)
                        ]).optimize(compressor);
                    } else self.truthy = true;
                }
                // x && true || y => x ? true : y
                if (self.left.operator == "&&") {
                    var lr = self.left.right.is_truthy() || self.left.right.evaluate(compressor, true);
                    if (lr && !(lr instanceof AST_Node)) return make_node(AST_Conditional, self, {
                        condition: self.left.left,
                        consequent: self.left.right,
                        alternative: self.right
                    }).optimize(compressor);
                }
                break;
              case "+":
                // "foo" + ("bar" + x) => "foobar" + x
                if (self.left instanceof AST_Constant
                    && self.right instanceof AST_Binary
                    && self.right.operator == "+"
                    && self.right.left instanceof AST_Constant
                    && self.right.is_string(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "+",
                        left: make_node(AST_String, self.left, {
                            value: "" + self.left.value + self.right.left.value,
                            start: self.left.start,
                            end: self.right.left.end
                        }),
                        right: self.right.right
                    });
                }
                // (x + "foo") + "bar" => x + "foobar"
                if (self.right instanceof AST_Constant
                    && self.left instanceof AST_Binary
                    && self.left.operator == "+"
                    && self.left.right instanceof AST_Constant
                    && self.left.is_string(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "+",
                        left: self.left.left,
                        right: make_node(AST_String, self.right, {
                            value: "" + self.left.right.value + self.right.value,
                            start: self.left.right.start,
                            end: self.right.end
                        })
                    });
                }
                // (x + "foo") + ("bar" + y) => (x + "foobar") + y
                if (self.left instanceof AST_Binary
                    && self.left.operator == "+"
                    && self.left.is_string(compressor)
                    && self.left.right instanceof AST_Constant
                    && self.right instanceof AST_Binary
                    && self.right.operator == "+"
                    && self.right.left instanceof AST_Constant
                    && self.right.is_string(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "+",
                        left: make_node(AST_Binary, self.left, {
                            operator: "+",
                            left: self.left.left,
                            right: make_node(AST_String, self.left.right, {
                                value: "" + self.left.right.value + self.right.left.value,
                                start: self.left.right.start,
                                end: self.right.left.end
                            })
                        }),
                        right: self.right.right
                    });
                }
                // a + -b => a - b
                if (self.right instanceof AST_UnaryPrefix
                    && self.right.operator == "-"
                    && self.left.is_number(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "-",
                        left: self.left,
                        right: self.right.expression
                    });
                    break;
                }
                // -a + b => b - a
                if (self.left instanceof AST_UnaryPrefix
                    && self.left.operator == "-"
                    && reversible()
                    && self.right.is_number(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "-",
                        left: self.right,
                        right: self.left.expression
                    });
                    break;
                }
                // (a + b) + 3 => 3 + (a + b)
                if (compressor.option("unsafe_math")
                    && self.left instanceof AST_Binary
                    && PRECEDENCE[self.left.operator] == PRECEDENCE[self.operator]
                    && self.right.is_constant()
                    && (self.right.is_boolean(compressor) || self.right.is_number(compressor))
                    && self.left.is_number(compressor)
                    && !self.left.right.is_constant()
                    && (self.left.left.is_boolean(compressor) || self.left.left.is_number(compressor))) {
                    self = make_node(AST_Binary, self, {
                        operator: self.left.operator,
                        left: make_node(AST_Binary, self, {
                            operator: self.operator,
                            left: self.right,
                            right: self.left.left
                        }),
                        right: self.left.right
                    });
                    break;
                }
              case "-":
                // a - -b => a + b
                if (self.right instanceof AST_UnaryPrefix
                    && self.right.operator == "-"
                    && self.left.is_number(compressor)
                    && self.right.expression.is_number(compressor)) {
                    self = make_node(AST_Binary, self, {
                        operator: "+",
                        left: self.left,
                        right: self.right.expression
                    });
                    break;
                }
              case "*":
              case "/":
                associative = compressor.option("unsafe_math");
                // +a - b => a - b
                // a - +b => a - b
                if (self.operator != "+") {
                    if (self.left instanceof AST_UnaryPrefix && self.left.operator == "+") {
                        self.left = self.left.expression;
                    }
                    if (self.right instanceof AST_UnaryPrefix && self.right.operator == "+") {
                        self.right = self.right.expression;
                    }
                }
              case "&":
              case "|":
              case "^":
                // a + +b => +b + a
                if (self.operator != "-"
                    && self.operator != "/"
                    && (self.left.is_boolean(compressor) || self.left.is_number(compressor))
                    && (self.right.is_boolean(compressor) || self.right.is_number(compressor))
                    && reversible()
                    && !(self.left instanceof AST_Binary
                        && self.left.operator != self.operator
                        && PRECEDENCE[self.left.operator] >= PRECEDENCE[self.operator])) {
                    var reversed = make_node(AST_Binary, self, {
                        operator: self.operator,
                        left: self.right,
                        right: self.left
                    });
                    if (self.right instanceof AST_Constant
                        && !(self.left instanceof AST_Constant)) {
                        self = best_of(compressor, reversed, self);
                    } else {
                        self = best_of(compressor, self, reversed);
                    }
                }
                if (!associative || !self.is_number(compressor)) break;
                // a + (b + c) => (a + b) + c
                if (self.right instanceof AST_Binary
                    && self.right.operator != "%"
                    && PRECEDENCE[self.right.operator] == PRECEDENCE[self.operator]
                    && self.right.is_number(compressor)
                    && (self.operator != "+"
                        || self.right.left.is_boolean(compressor)
                        || self.right.left.is_number(compressor))
                    && (self.operator != "-" || !self.left.is_negative_zero())
                    && (self.right.left.is_constant_expression()
                        || !self.right.right.has_side_effects(compressor))) {
                    self = make_node(AST_Binary, self, {
                        operator: align(self.operator, self.right.operator),
                        left: make_node(AST_Binary, self.left, {
                            operator: self.operator,
                            left: self.left,
                            right: self.right.left,
                            start: self.left.start,
                            end: self.right.left.end
                        }),
                        right: self.right.right
                    });
                    if (self.operator == "+"
                        && !self.right.is_boolean(compressor)
                        && !self.right.is_number(compressor)) {
                        self.right = make_node(AST_UnaryPrefix, self.right, {
                            operator: "+",
                            expression: self.right
                        });
                    }
                }
                // (2 * n) * 3 => 6 * n
                // (n + 2) + 3 => n + 5
                if (self.right instanceof AST_Constant
                    && self.left instanceof AST_Binary
                    && self.left.operator != "%"
                    && PRECEDENCE[self.left.operator] == PRECEDENCE[self.operator]
                    && self.left.is_number(compressor)) {
                    if (self.left.left instanceof AST_Constant) {
                        var lhs = make_binary(self.left, self.operator, self.left.left, self.right, self.left.left.start, self.right.end);
                        self = make_binary(self, self.left.operator, lhs, self.left.right);
                    } else if (self.left.right instanceof AST_Constant) {
                        var rhs = make_binary(self.left, align(self.left.operator, self.operator), self.left.right, self.right, self.left.right.start, self.right.end);
                        if (self.left.operator != "-"
                            || !self.right.value
                            || rhs.evaluate(compressor)
                            || !self.left.left.is_negative_zero()) {
                            self = make_binary(self, self.left.operator, self.left.left, rhs);
                        }
                    }
                }
                break;
            }
            if (self.left instanceof AST_Number && !self.right.is_constant()) switch (self.operator) {
              // 0 + n => n
              case "+":
                if (self.left.value == 0) {
                    if (self.right.is_boolean(compressor)) return make_node(AST_UnaryPrefix, self, {
                        operator: "+",
                        expression: self.right
                    }).optimize(compressor);
                    if (self.right.is_number(compressor) && !self.right.is_negative_zero()) return self.right;
                }
                break;
              // 1 * n => n
              case "*":
                if (self.left.value == 1) {
                    return self.right.is_number(compressor) ? self.right : make_node(AST_UnaryPrefix, self, {
                        operator: "+",
                        expression: self.right
                    }).optimize(compressor);
                }
                break;
            }
            if (self.right instanceof AST_Number && !self.left.is_constant()) switch (self.operator) {
              // n + 0 => n
              case "+":
                if (self.right.value == 0) {
                    if (self.left.is_boolean(compressor)) return make_node(AST_UnaryPrefix, self, {
                        operator: "+",
                        expression: self.left
                    }).optimize(compressor);
                    if (self.left.is_number(compressor) && !self.left.is_negative_zero()) return self.left;
                }
                break;
              // n - 0 => n
              case "-":
                if (self.right.value == 0) {
                    return self.left.is_number(compressor) ? self.left : make_node(AST_UnaryPrefix, self, {
                        operator: "+",
                        expression: self.left
                    }).optimize(compressor);
                }
                break;
              // n / 1 => n
              case "/":
                if (self.right.value == 1) {
                    return self.left.is_number(compressor) ? self.left : make_node(AST_UnaryPrefix, self, {
                        operator: "+",
                        expression: self.left
                    }).optimize(compressor);
                }
                break;
            }
        }
        if (compressor.option("typeofs")) switch (self.operator) {
          case "&&":
            mark_locally_defined(self.left, self.right, null);
            break;
          case "||":
            mark_locally_defined(self.left, null, self.right);
            break;
        }
        if (compressor.option("unsafe")) {
            var indexRight = is_indexFn(self.right);
            if (in_bool
                && indexRight
                && (self.operator == "==" || self.operator == "!=")
                && self.left instanceof AST_Number
                && self.left.value == 0) {
                return (self.operator == "==" ? make_node(AST_UnaryPrefix, self, {
                    operator: "!",
                    expression: self.right
                }) : self.right).optimize(compressor);
            }
            var indexLeft = is_indexFn(self.left);
            if (compressor.option("comparisons") && is_indexOf_match_pattern()) {
                var node = make_node(AST_UnaryPrefix, self, {
                    operator: "!",
                    expression: make_node(AST_UnaryPrefix, self, {
                        operator: "~",
                        expression: indexLeft ? self.left : self.right
                    })
                });
                switch (self.operator) {
                  case "<":
                    if (indexLeft) break;
                  case "<=":
                  case "!=":
                    node = make_node(AST_UnaryPrefix, self, {
                        operator: "!",
                        expression: node
                    });
                    break;
                }
                return node.optimize(compressor);
            }
        }
        return try_evaluate(compressor, self);

function can_self_compare(node) {
            if (node instanceof AST_Dot) return can_self_compare(node.expression);
            if (node instanceof AST_Sub) return can_self_compare(node.expression) && can_self_compare(node.property);
            if (node instanceof AST_Symbol) return true;
            return !node.has_side_effects(compressor);
        }

function align(ref, op) {
            switch (ref) {
              case "-":
                return op == "+" ? "-" : "+";
              case "/":
                return op == "*" ? "/" : "*";
              default:
                return op;
            }
        }

function fuzzy_eval(node) {
            if (node.truthy) return true;
            if (node.falsy) return false;
            if (node.is_truthy()) return true;
            return node.evaluate(compressor, true);
        }

function is_indexFn(node) {
            return node instanceof AST_Call
                && node.expression instanceof AST_Dot
                && indexFns[node.expression.property];
        }

function is_indexOf_match_pattern() {
            switch (self.operator) {
              case "<=":
                // 0 <= array.indexOf(string) => !!~array.indexOf(string)
                return indexRight && self.left instanceof AST_Number && self.left.value == 0;
              case "<":
                // array.indexOf(string) < 0 => !~array.indexOf(string)
                if (indexLeft && self.right instanceof AST_Number && self.right.value == 0) return true;
                // -1 < array.indexOf(string) => !!~array.indexOf(string)
              case "==":
              case "!=":
                // -1 == array.indexOf(string) => !~array.indexOf(string)
                // -1 != array.indexOf(string) => !!~array.indexOf(string)
                if (!indexRight) return false;
                return self.left instanceof AST_Number && self.left.value == -1
                    || self.left instanceof AST_UnaryPrefix && self.left.operator == "-"
                        && self.left.expression instanceof AST_Number && self.left.expression.value == 1;
            }
        }
    });

OPT(AST_SymbolRef, function(self, compressor) {
        if (!compressor.option("ie8")
            && is_undeclared_ref(self)
            // testing against `self.scope.uses_with` is an optimization
            && !(self.scope.uses_with && compressor.find_parent(AST_With))) {
            switch (self.name) {
              case "undefined":
                return make_node(AST_Undefined, self).optimize(compressor);
              case "NaN":
                return make_node(AST_NaN, self).optimize(compressor);
              case "Infinity":
                return make_node(AST_Infinity, self).optimize(compressor);
            }
        }
        var parent = compressor.parent();
        if (compressor.option("reduce_vars") && is_lhs(compressor.self(), parent) !== compressor.self()) {
            var def = self.definition();
            var fixed = self.fixed_value();
            var single_use = def.single_use && !(parent instanceof AST_Call && parent.is_expr_pure(compressor));
            if (single_use) {
                if (fixed instanceof AST_Lambda) {
                    if ((def.scope !== self.scope || def.in_loop)
                        && (!compressor.option("reduce_funcs") || def.escaped.depth == 1 || fixed.inlined)) {
                        single_use = false;
                    } else if (recursive_ref(compressor, def)) {
                        single_use = false;
                    } else if (def.scope !== self.scope || def.orig[0] instanceof AST_SymbolFunarg) {
                        single_use = fixed.is_constant_expression(self.scope);
                        if (single_use == "f") {
                            var scope = self.scope;
                            do if (scope instanceof AST_Defun || scope instanceof AST_Function) {
                                scope.inlined = true;
                            } while (scope = scope.parent_scope);
                        }
                    }
                    if (single_use) fixed.parent_scope = self.scope;
                } else if (!fixed || !fixed.is_constant_expression()) {
                    single_use = false;
                }
            }
            if (single_use) {
                def.single_use = false;
                fixed._squeezed = true;
                fixed.single_use = true;
                if (fixed instanceof AST_Defun) {
                    fixed = make_node(AST_Function, fixed, fixed);
                    fixed.name = make_node(AST_SymbolLambda, fixed.name, fixed.name);
                }
                if (fixed instanceof AST_Lambda) {
                    var scope = self.scope;
                    fixed.enclosed.forEach(function(def) {
                        if (fixed.variables.has(def.name)) return;
                        if (scope.var_names()[def.name]) return;
                        scope.enclosed.push(def);
                        scope.var_names()[def.name] = true;
                    });
                }
                var value;
                if (def.recursive_refs > 0) {
                    value = fixed.clone(true);
                    var defun_def = value.name.definition();
                    var lambda_def = value.variables.get(value.name.name);
                    var name = lambda_def && lambda_def.orig[0];
                    if (!(name instanceof AST_SymbolLambda)) {
                        name = make_node(AST_SymbolLambda, value.name, value.name);
                        name.scope = value;
                        value.name = name;
                        lambda_def = value.def_function(name);
                        lambda_def.recursive_refs = def.recursive_refs;
                    }
                    value.walk(new TreeWalker(function(node) {
                        if (!(node instanceof AST_SymbolRef)) return;
                        var def = node.definition();
                        if (def === defun_def) {
                            node.thedef = lambda_def;
                            lambda_def.references.push(node);
                        } else {
                            def.single_use = false;
                            var fn = node.fixed_value();
                            if (!(fn instanceof AST_Lambda)) return;
                            if (!fn.name) return;
                            if (fn.name.definition() !== def) return;
                            if (def.scope !== fn.name.scope) return;
                            if (fixed.variables.get(fn.name.name) !== def) return;
                            fn.name = fn.name.clone();
                            var value_def = value.variables.get(fn.name.name) || value.def_function(fn.name);
                            node.thedef = value_def;
                            value_def.references.push(node);
                        }
                    }));
                } else {
                    value = fixed.optimize(compressor);
                }
                def.replaced++;
                return value;
            }
            if (fixed && def.should_replace === undefined) {
                var init;
                if (fixed instanceof AST_This) {
                    if (!(def.orig[0] instanceof AST_SymbolFunarg) && same_scope(def)) {
                        init = fixed;
                    }
                } else {
                    var ev = fixed.evaluate(compressor, true);
                    if (ev !== fixed
                        && typeof ev != "function"
                        && (typeof ev != "object"
                            || ev instanceof RegExp
                                && compressor.option("unsafe_regexp")
                                && !def.cross_loop && same_scope(def))) {
                        init = make_node_from_constant(ev, fixed);
                    }
                }
                if (init) {
                    var value_length = init.optimize(compressor).print_to_string().length;
                    var fn;
                    if (has_symbol_ref(fixed)) {
                        fn = function() {
                            var result = init.optimize(compressor);
                            return result === init ? result.clone(true) : result;
                        };
                    } else {
                        value_length = Math.min(value_length, fixed.print_to_string().length);
                        fn = function() {
                            var result = best_of_expression(init.optimize(compressor), fixed);
                            return result === init || result === fixed ? result.clone(true) : result;
                        };
                    }
                    var name_length = def.name.length;
                    if (compressor.option("unused") && !compressor.exposed(def)) {
                        var referenced = def.references.length - def.replaced;
                        name_length += (name_length + 2 + value_length) / (referenced - def.assignments);
                    }
                    var delta = value_length - Math.floor(name_length);
                    def.should_replace = delta < compressor.eval_threshold ? fn : false;
                } else {
                    def.should_replace = false;
                }
            }
            if (def.should_replace) {
                var value = def.should_replace();
                def.replaced++;
                return value;
            }
        }
        return self;

function same_scope(def) {
            var scope = def.scope.resolve();
            return all(def.references, function(ref) {
                return scope === ref.scope.resolve();
            });
        }

function has_symbol_ref(value) {
            var found;
            value.walk(new TreeWalker(function(node) {
                if (node instanceof AST_SymbolRef) found = true;
                if (found) return true;
            }));
            return found;
        }
    });

function is_atomic(lhs, self) {
        return lhs instanceof AST_SymbolRef || lhs.TYPE === self.TYPE;
    }

OPT(AST_Undefined, function(self, compressor) {
        if (compressor.option("unsafe_undefined")) {
            var undef = find_variable(compressor, "undefined");
            if (undef) {
                var ref = make_node(AST_SymbolRef, self, {
                    name   : "undefined",
                    scope  : undef.scope,
                    thedef : undef
                });
                ref.is_undefined = true;
                return ref;
            }
        }
        var lhs = is_lhs(compressor.self(), compressor.parent());
        if (lhs && is_atomic(lhs, self)) return self;
        return make_node(AST_UnaryPrefix, self, {
            operator: "void",
            expression: make_node(AST_Number, self, {
                value: 0
            })
        });
    });

OPT(AST_Infinity, function(self, compressor) {
        var lhs = is_lhs(compressor.self(), compressor.parent());
        if (lhs && is_atomic(lhs, self)) return self;
        if (compressor.option("keep_infinity")
            && !(lhs && !is_atomic(lhs, self))
            && !find_variable(compressor, "Infinity"))
            return self;
        return make_node(AST_Binary, self, {
            operator: "/",
            left: make_node(AST_Number, self, {
                value: 1
            }),
            right: make_node(AST_Number, self, {
                value: 0
            })
        });
    });

OPT(AST_NaN, function(self, compressor) {
        var lhs = is_lhs(compressor.self(), compressor.parent());
        if (lhs && !is_atomic(lhs, self)
            || find_variable(compressor, "NaN")) {
            return make_node(AST_Binary, self, {
                operator: "/",
                left: make_node(AST_Number, self, {
                    value: 0
                }),
                right: make_node(AST_Number, self, {
                    value: 0
                })
            });
        }
        return self;
    });

function strip_assignment() {
            return (self.operator != "=" ? make_node(AST_Binary, self, {
                operator: self.operator.slice(0, -1),
                left: self.left,
                right: self.right
            }) : maintain_this_binding(compressor, compressor.parent(), self, self.right)).optimize(compressor);
        }
    });

OPT(AST_Conditional, function(self, compressor) {
        if (!compressor.option("conditionals")) return self;
        // This looks like lift_sequences(), should probably be under "sequences"
        if (self.condition instanceof AST_Sequence) {
            var expressions = self.condition.expressions.slice();
            self.condition = expressions.pop();
            expressions.push(self);
            return make_sequence(self, expressions);
        }
        var condition = self.condition.is_truthy() || self.condition.evaluate(compressor, true);
        if (!condition) {
            AST_Node.warn("Condition always false [{file}:{line},{col}]", self.start);
            return make_sequence(self, [ self.condition, self.alternative ]).optimize(compressor);
        } else if (!(condition instanceof AST_Node)) {
            AST_Node.warn("Condition always true [{file}:{line},{col}]", self.start);
            return make_sequence(self, [ self.condition, self.consequent ]).optimize(compressor);
        }
        var negated = condition.negate(compressor, first_in_statement(compressor));
        if (best_of(compressor, condition, negated) === negated) {
            self = make_node(AST_Conditional, self, {
                condition: negated,
                consequent: self.alternative,
                alternative: self.consequent
            });
            negated = condition;
            condition = self.condition;
        }
        var consequent = self.consequent;
        var alternative = self.alternative;
        // x ? x : y => x || y
        if (condition instanceof AST_SymbolRef
            && consequent instanceof AST_SymbolRef
            && condition.definition() === consequent.definition()) {
            return make_node(AST_Binary, self, {
                operator: "||",
                left: condition,
                right: alternative
            });
        }
        // if (foo) exp = something; else exp = something_else;
        //                   |
        //                   v
        // exp = foo ? something : something_else;
        var seq_tail = consequent.tail_node();
        if (seq_tail instanceof AST_Assign) {
            var is_eq = seq_tail.operator == "=";
            var alt_tail = is_eq ? alternative.tail_node() : alternative;
            if ((is_eq || consequent === seq_tail)
                && alt_tail instanceof AST_Assign
                && seq_tail.operator == alt_tail.operator
                && seq_tail.left.equivalent_to(alt_tail.left)
                && (is_eq && seq_tail.left instanceof AST_SymbolRef
                    || !condition.has_side_effects(compressor)
                        && can_shift_lhs_of_tail(consequent)
                        && can_shift_lhs_of_tail(alternative))) {
                return make_node(AST_Assign, self, {
                    operator: seq_tail.operator,
                    left: seq_tail.left,
                    right: make_node(AST_Conditional, self, {
                        condition: condition,
                        consequent: pop_lhs(consequent),
                        alternative: pop_lhs(alternative)
                    })
                });
            }
        }
        // x ? y : y => x, y
        if (consequent.equivalent_to(alternative)) return make_sequence(self, [
            condition,
            consequent
        ]).optimize(compressor);
        if (consequent instanceof AST_Call
            && alternative.TYPE === consequent.TYPE
            && consequent.args.length == alternative.args.length) {
            var arg_index = arg_diff();
            // x ? y(a) : z(a) => (x ? y : z)(a)
            if (arg_index == -1
                && !(consequent.expression instanceof AST_PropAccess)
                && !(alternative.expression instanceof AST_PropAccess)) {
                var node = consequent.clone();
                node.expression = make_node(AST_Conditional, self, {
                    condition: condition,
                    consequent: consequent.expression,
                    alternative: alternative.expression
                });
                return node;
            }
            // x ? y(a) : y(b) => y(x ? a : b)
            if (arg_index >= 0
                && consequent.expression.equivalent_to(alternative.expression)
                && !condition.has_side_effects(compressor)
                && !consequent.expression.has_side_effects(compressor)) {
                var node = consequent.clone();
                node.args[arg_index] = make_node(AST_Conditional, self, {
                    condition: condition,
                    consequent: consequent.args[arg_index],
                    alternative: alternative.args[arg_index]
                });
                return node;
            }
        }
        // x ? (y ? a : b) : b => x && y ? a : b
        if (consequent instanceof AST_Conditional
            && consequent.alternative.equivalent_to(alternative)) {
            return make_node(AST_Conditional, self, {
                condition: make_node(AST_Binary, self, {
                    left: condition,
                    operator: "&&",
                    right: consequent.condition
                }),
                consequent: consequent.consequent,
                alternative: alternative
            });
        }
        // x ? (y ? a : b) : a => !x || y ? a : b
        if (consequent instanceof AST_Conditional
            && consequent.consequent.equivalent_to(alternative)) {
            return make_node(AST_Conditional, self, {
                condition: make_node(AST_Binary, self, {
                    left: negated,
                    operator: "||",
                    right: consequent.condition
                }),
                consequent: alternative,
                alternative: consequent.alternative
            });
        }
        // x ? a : (y ? a : b) => x || y ? a : b
        if (alternative instanceof AST_Conditional
            && consequent.equivalent_to(alternative.consequent)) {
            return make_node(AST_Conditional, self, {
                condition: make_node(AST_Binary, self, {
                    left: condition,
                    operator: "||",
                    right: alternative.condition
                }),
                consequent: consequent,
                alternative: alternative.alternative
            });
        }
        // x ? b : (y ? a : b) => !x && y ? a : b
        if (alternative instanceof AST_Conditional
            && consequent.equivalent_to(alternative.alternative)) {
            return make_node(AST_Conditional, self, {
                condition: make_node(AST_Binary, self, {
                    left: negated,
                    operator: "&&",
                    right: alternative.condition
                }),
                consequent: alternative.consequent,
                alternative: consequent
            });
        }
        // x ? (a, c) : (b, c) => x ? a : b, c
        if ((consequent instanceof AST_Sequence || alternative instanceof AST_Sequence)
            && consequent.tail_node().equivalent_to(alternative.tail_node())) {
            return make_sequence(self, [
                make_node(AST_Conditional, self, {
                    condition: condition,
                    consequent: pop_seq(consequent),
                    alternative: pop_seq(alternative)
                }),
                consequent.tail_node()
            ]).optimize(compressor);
        }
        // x ? y && a : a => (!x || y) && a
        if (consequent instanceof AST_Binary
            && consequent.operator == "&&"
            && consequent.right.equivalent_to(alternative)) {
            return make_node(AST_Binary, self, {
                operator: "&&",
                left: make_node(AST_Binary, self, {
                    operator: "||",
                    left: negated,
                    right: consequent.left
                }),
                right: alternative
            }).optimize(compressor);
        }
        // x ? y || a : a => x && y || a
        if (consequent instanceof AST_Binary
            && consequent.operator == "||"
            && consequent.right.equivalent_to(alternative)) {
            return make_node(AST_Binary, self, {
                operator: "||",
                left: make_node(AST_Binary, self, {
                    operator: "&&",
                    left: condition,
                    right: consequent.left
                }),
                right: alternative
            }).optimize(compressor);
        }
        // x ? a : y && a => (x || y) && a
        if (alternative instanceof AST_Binary
            && alternative.operator == "&&"
            && alternative.right.equivalent_to(consequent)) {
            return make_node(AST_Binary, self, {
                operator: "&&",
                left: make_node(AST_Binary, self, {
                    operator: "||",
                    left: condition,
                    right: alternative.left
                }),
                right: consequent
            }).optimize(compressor);
        }
        // x ? a : y || a => !x && y || a
        if (alternative instanceof AST_Binary
            && alternative.operator == "||"
            && alternative.right.equivalent_to(consequent)) {
            return make_node(AST_Binary, self, {
                operator: "||",
                left: make_node(AST_Binary, self, {
                    operator: "&&",
                    left: negated,
                    right: alternative.left
                }),
                right: consequent
            }).optimize(compressor);
        }
        var in_bool = compressor.option("booleans") && compressor.in_boolean_context();
        if (is_true(consequent)) {
            if (is_false(alternative)) {
                // c ? true : false => !!c
                return booleanize(condition);
            }
            // c ? true : x => !!c || x
            return make_node(AST_Binary, self, {
                operator: "||",
                left: booleanize(condition),
                right: alternative
            });
        }
        if (is_false(consequent)) {
            if (is_true(alternative)) {
                // c ? false : true => !c
                return booleanize(condition.negate(compressor));
            }
            // c ? false : x => !c && x
            return make_node(AST_Binary, self, {
                operator: "&&",
                left: booleanize(condition.negate(compressor)),
                right: alternative
            });
        }
        if (is_true(alternative)) {
            // c ? x : true => !c || x
            return make_node(AST_Binary, self, {
                operator: "||",
                left: booleanize(condition.negate(compressor)),
                right: consequent
            });
        }
        if (is_false(alternative)) {
            // c ? x : false => !!c && x
            return make_node(AST_Binary, self, {
                operator: "&&",
                left: booleanize(condition),
                right: consequent
            });
        }
        if (compressor.option("typeofs")) mark_locally_defined(condition, consequent, alternative);
        return self;

function booleanize(node) {
            if (node.is_boolean(compressor)) return node;
            // !!expression
            return make_node(AST_UnaryPrefix, node, {
                operator: "!",
                expression: node.negate(compressor)
            });
        }

// AST_True or !0
        function is_true(node) {
            return node instanceof AST_True
                || in_bool
                    && node instanceof AST_Constant
                    && node.value
                || (node instanceof AST_UnaryPrefix
                    && node.operator == "!"
                    && node.expression instanceof AST_Constant
                    && !node.expression.value);
        }
        // AST_False or !1 or void 0
        function is_false(node) {
            return node instanceof AST_False
                || in_bool
                    && (node instanceof AST_Constant
                            && !node.value
                        || node instanceof AST_UnaryPrefix
                            && node.operator == "void"
                            && !node.expression.has_side_effects(compressor))
                || (node instanceof AST_UnaryPrefix
                    && node.operator == "!"
                    && node.expression instanceof AST_Constant
                    && node.expression.value);
        }

function can_shift_lhs_of_tail(node) {
            return node === node.tail_node() || all(node.expressions.slice(0, -1), function(expr) {
                return !expr.has_side_effects(compressor);
            });
        }

function pop_lhs(node) {
            if (!(node instanceof AST_Sequence)) return node.right;
            var exprs = node.expressions.slice();
            exprs.push(exprs.pop().right);
            return make_sequence(node, exprs);
        }

function pop_seq(node) {
            if (!(node instanceof AST_Sequence)) return make_node(AST_Number, node, {
                value: 0
            });
            return make_sequence(node, node.expressions.slice(0, -1));
        }
    });

OPT(AST_Boolean, function(self, compressor) {
        if (!compressor.option("booleans")) return self;
        if (compressor.in_boolean_context()) return make_node(AST_Number, self, {
            value: +self.value
        });
        var p = compressor.parent();
        if (p instanceof AST_Binary && (p.operator == "==" || p.operator == "!=")) {
            AST_Node.warn("Non-strict equality against boolean: {operator} {value} [{file}:{line},{col}]", {
                operator : p.operator,
                value    : self.value,
                file     : p.start.file,
                line     : p.start.line,
                col      : p.start.col,
            });
            return make_node(AST_Number, self, {
                value: +self.value
            });
        }
        return make_node(AST_UnaryPrefix, self, {
            operator: "!",
            expression: make_node(AST_Number, self, {
                value: 1 - self.value
            })
        });
    });

function safe_to_flatten(value, compressor) {
        if (value instanceof AST_SymbolRef) {
            value = value.fixed_value();
        }
        if (!value) return false;
        if (!(value instanceof AST_Lambda)) return true;
        var parent = compressor.parent();
        if (parent.TYPE != "Call") return true;
        if (parent.expression !== compressor.self()) return true;
        return !value.contains_this();
    }

OPT(AST_Sub, function(self, compressor) {
        var expr = self.expression;
        var prop = self.property;
        if (compressor.option("properties")) {
            var key = prop.evaluate(compressor);
            if (key !== prop) {
                if (typeof key == "string") {
                    if (key == "undefined") {
                        key = undefined;
                    } else {
                        var value = parseFloat(key);
                        if (value.toString() == key) {
                            key = value;
                        }
                    }
                }
                prop = self.property = best_of_expression(prop, make_node_from_constant(key, prop).transform(compressor));
                var property = "" + key;
                if (is_identifier_string(property)
                    && property.length <= prop.print_to_string().length + 1) {
                    return make_node(AST_Dot, self, {
                        expression: expr,
                        property: property
                    }).optimize(compressor);
                }
            }
        }
        var parent = compressor.parent();
        var def, fn, fn_parent;
        if (compressor.option("arguments")
            && expr instanceof AST_SymbolRef
            && is_arguments(def = expr.definition())
            && prop instanceof AST_Number
            && (fn = expr.scope) === find_lambda()) {
            var index = prop.value;
            if (parent instanceof AST_UnaryPrefix && parent.operator == "delete") {
                if (!def.deleted) def.deleted = [];
                def.deleted[index] = true;
            }
            var argname = fn.argnames[index];
            if (def.deleted && def.deleted[index]) {
                argname = null;
            } else if (argname && compressor.has_directive("use strict")) {
                var arg_def = argname.definition();
                if (!compressor.option("reduce_vars")
                    || def.reassigned
                    || arg_def.assignments
                    || arg_def.orig.length > 1) {
                    argname = null;
                }
            } else if (!argname && index < fn.argnames.length + 5 && compressor.drop_fargs(fn, fn_parent)) {
                while (index >= fn.argnames.length) {
                    argname = make_node(AST_SymbolFunarg, fn, {
                        name: fn.make_var_name("argument_" + fn.argnames.length),
                        scope: fn
                    });
                    fn.argnames.push(argname);
                    fn.enclosed.push(fn.def_variable(argname));
                }
            }
            if (argname && find_if(function(node) {
                return node.name === argname.name;
            }, fn.argnames) === argname) {
                def.reassigned = false;
                var sym = make_node(AST_SymbolRef, self, argname);
                sym.reference({});
                delete argname.__unused;
                return sym;
            }
        }
        if (is_lhs(compressor.self(), parent)) return self;
        if (compressor.option("sequences") && compressor.parent().TYPE != "Call") {
            var seq = lift_sequence_in_expression(self, compressor);
            if (seq !== self) return seq.optimize(compressor);
        }
        if (key !== prop) {
            var sub = self.flatten_object(property, compressor);
            if (sub) {
                expr = self.expression = sub.expression;
                prop = self.property = sub.property;
            }
        }
        if (compressor.option("properties") && compressor.option("side_effects")
            && prop instanceof AST_Number && expr instanceof AST_Array) {
            var index = prop.value;
            var elements = expr.elements;
            var retValue = elements[index];
            if (safe_to_flatten(retValue, compressor)) {
                var flatten = true;
                var values = [];
                for (var i = elements.length; --i > index;) {
                    var value = elements[i].drop_side_effect_free(compressor);
                    if (value) {
                        values.unshift(value);
                        if (flatten && value.has_side_effects(compressor)) flatten = false;
                    }
                }
                retValue = retValue instanceof AST_Hole ? make_node(AST_Undefined, retValue) : retValue;
                if (!flatten) values.unshift(retValue);
                while (--i >= 0) {
                    var value = elements[i].drop_side_effect_free(compressor);
                    if (value) values.unshift(value);
                    else index--;
                }
                if (flatten) {
                    values.push(retValue);
                    return make_sequence(self, values).optimize(compressor);
                } else return make_node(AST_Sub, self, {
                    expression: make_node(AST_Array, expr, {
                        elements: values
                    }),
                    property: make_node(AST_Number, prop, {
                        value: index
                    })
                });
            }
        }
        return try_evaluate(compressor, self);

AST_Scope.DEFMETHOD("contains_this", function() {
        var result;
        var self = this;
        self.walk(new TreeWalker(function(node) {
            if (result) return true;
            if (node instanceof AST_This) return result = true;
            if (node !== self && node instanceof AST_Scope) return true;
        }));
        return result;
    });

AST_PropAccess.DEFMETHOD("flatten_object", function(key, compressor) {
        if (!compressor.option("properties")) return;
        var expr = this.expression;
        if (expr instanceof AST_Object) {
            var props = expr.properties;
            for (var i = props.length; --i >= 0;) {
                var prop = props[i];
                if ("" + prop.key == key) {
                    if (!all(props, function(prop) {
                        return prop instanceof AST_ObjectKeyVal;
                    })) break;
                    if (!safe_to_flatten(prop.value, compressor)) break;
                    return make_node(AST_Sub, this, {
                        expression: make_node(AST_Array, expr, {
                            elements: props.map(function(prop) {
                                return prop.value;
                            })
                        }),
                        property: make_node(AST_Number, this, {
                            value: i
                        })
                    });
                }
            }
        }
    });

OPT(AST_Dot, function(self, compressor) {
        if (self.property == "arguments" || self.property == "caller") {
            AST_Node.warn("Function.prototype.{prop} not supported [{file}:{line},{col}]", {
                prop: self.property,
                file: self.start.file,
                line: self.start.line,
                col: self.start.col
            });
        }
        if (is_lhs(compressor.self(), compressor.parent())) return self;
        if (compressor.option("sequences") && compressor.parent().TYPE != "Call") {
            var seq = lift_sequence_in_expression(self, compressor);
            if (seq !== self) return seq.optimize(compressor);
        }
        if (compressor.option("unsafe_proto")
            && self.expression instanceof AST_Dot
            && self.expression.property == "prototype") {
            var exp = self.expression.expression;
            if (is_undeclared_ref(exp)) switch (exp.name) {
              case "Array":
                self.expression = make_node(AST_Array, self.expression, {
                    elements: []
                });
                break;
              case "Function":
                self.expression = make_node(AST_Function, self.expression, {
                    argnames: [],
                    body: []
                });
                break;
              case "Number":
                self.expression = make_node(AST_Number, self.expression, {
                    value: 0
                });
                break;
              case "Object":
                self.expression = make_node(AST_Object, self.expression, {
                    properties: []
                });
                break;
              case "RegExp":
                self.expression = make_node(AST_RegExp, self.expression, {
                    value: /t/
                });
                break;
              case "String":
                self.expression = make_node(AST_String, self.expression, {
                    value: ""
                });
                break;
            }
        }
        var sub = self.flatten_object(self.property, compressor);
        if (sub) return sub.optimize(compressor);
        return try_evaluate(compressor, self);
    });

OPT(AST_Object, function(self, compressor) {
        if (!compressor.option("objects") || compressor.has_directive("use strict")) return self;
        var keys = new Dictionary();
        var values = [];
        self.properties.forEach(function(prop) {
            if (typeof prop.key != "string") {
                flush();
                values.push(prop);
                return;
            }
            if (prop.value.has_side_effects(compressor)) {
                flush();
            }
            keys.add(prop.key, prop.value);
        });
        flush();
        if (self.properties.length != values.length) {
            return make_node(AST_Object, self, {
                properties: values
            });
        }
        return self;

OPT(AST_Return, function(self, compressor) {
        if (self.value && is_undefined(self.value, compressor)) {
            self.value = null;
        }
        return self;
    });
})(function(node, optimizer) {
    node.DEFMETHOD("optimize", function(compressor) {
        var self = this;
        if (self._optimized) return self;
        if (compressor.has_directive("use asm")) return self;
        var opt = optimizer(self, compressor);
        opt._optimized = true;
        return opt;
    });
});