EVOLUTION-MANAGER

Edit File: xla_compilation_cache.h

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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==============================================================================*/

#ifndef TENSORFLOW_COMPILER_JIT_XLA_COMPILATION_CACHE_H_
#define TENSORFLOW_COMPILER_JIT_XLA_COMPILATION_CACHE_H_

#include "absl/container/flat_hash_map.h"
#include "absl/container/inlined_vector.h"
#include "absl/types/optional.h"
#include "absl/types/span.h"
#include "tensorflow/compiler/tf2xla/xla_compiler.h"
#include "tensorflow/compiler/tf2xla/xla_context.h"
#include "tensorflow/compiler/xla/client/local_client.h"
#include "tensorflow/compiler/xla/statusor.h"
#include "tensorflow/core/common_runtime/device.h"
#include "tensorflow/core/common_runtime/device_mgr.h"
#include "tensorflow/core/framework/graph.pb.h"
#include "tensorflow/core/framework/op_kernel.h"
#include "tensorflow/core/lib/core/threadpool.h"
#include "tensorflow/core/platform/mutex.h"
#include "tensorflow/core/platform/thread_annotations.h"

namespace tensorflow {

// The XlaCompilationCache class caches the results of the XlaCompiler class,
// which converts a Tensorflow graph into a compiled XLA compilation.
//
// Since XLA computations must have static shapes, the cache generates a new
// XLA computation for each new set of input shapes.
//
// Currently no cache eviction policy is implemented and the cache grows without
// bound.
class XlaCompilationCache : public ResourceBase {
 public:
  XlaCompilationCache(xla::LocalClient* client, DeviceType device_type);
  ~XlaCompilationCache() override;

enum class CompileMode {
    kLazy,
    kStrict,
  };

// Compiles a function into a XlaCompiler::CompilationResult that can be used
  // to execute an XLA Computation. Compilation results are cached.
  // `function` is the name of a Tensorflow function to compile.
  // `args` is a description of the arguments to the computation.
  //
  // `compile_mode` controls the behavior of the compilation cache on a cache
  // miss.  If `compile_mode` is `kLazy` then, based on some profitability
  // heuristics, the compilation cache may decide not to compile the cluster at
  // this time.  In this case it returns null into both `out_compilation_result`
  // and `out_executable`.  If `compile_mode` is `kStrict` then the compilation
  // cache always attempts the compilation on a cache miss.
  //
  // The result of compilation is written to `*out_compilation_result`, which
  // must be non-null. If `out_executable` is non-null, also builds an
  // xla::LocalExecutable and sets `out_executable` to point to it. The
  // resulting executable pointer may be null if the computation has no
  // non-constant outputs.
  Status Compile(const XlaCompiler::Options& options,
                 const NameAttrList& function,
                 absl::Span<const XlaCompiler::Argument> args,
                 const XlaCompiler::CompileOptions& compile_options,
                 CompileMode compile_mode,
                 const XlaCompiler::CompilationResult** out_compilation_result,
                 xla::LocalExecutable** out_executable);

// As above, but calls XlaCompiler::CompileSingleOp instead of
  // XlaCompiler::CompileFunction. If MLIR bridge is enabled through ConfigProto
  // in OpKernelContext, then uses MLIR bridge for compilation instead of
  // XlaCompiler, if possible.
  Status CompileSingleOp(
      const XlaCompiler::Options& options,
      absl::Span<const XlaCompiler::Argument> args, OpKernelContext* ctx,
      const XlaCompiler::CompileOptions& compile_options,
      const XlaCompiler::CompilationResult** out_compilation_result,
      xla::LocalExecutable** out_executable);

xla::LocalClient* client() const { return client_; }
  const DeviceType& device_type() const { return device_type_; }

string DebugString() const override;

// Describes the types, shapes and any compile-time constant arguments
  // to a kernel. Key that uniquely identifies a compilation output.
  struct Signature {
    string name;

// List of Tensor types & shapes for compile-time constant arguments to the
    // compilation, ordered by argument number.
    absl::InlinedVector<std::pair<DataType, absl::InlinedVector<int64, 4>>, 4>
        arg_shapes;

// List of Tensor values for compile-time constant arguments to the
    // compilation, ordered by argument number. Tensors must be in host memory.
    absl::InlinedVector<Tensor, 4> arg_values;

bool operator==(const Signature& other) const;

struct Hash {
      uint64 operator()(const Signature& signature) const;
    };

// Returns a human-readable description of the signature.
    string HumanString() const;
  };

// Builds the signature for a compilation.
  static xla::StatusOr<Signature> BuildSignature(
      const NameAttrList& function,
      absl::Span<const XlaCompiler::Argument> args);

private:
  // Common implementation of Compile and CompileSingleOp.
  Status CompileImpl(
      const XlaCompiler::Options& options, const NameAttrList& function,
      absl::Span<const XlaCompiler::Argument> args,
      const std::function<Status(XlaCompiler* compiler,
                                 XlaCompiler::CompilationResult*)>& compile_fn,
      absl::optional<int64> compile_threshold,
      const XlaCompiler::CompilationResult** out_compilation_result,
      xla::LocalExecutable** out_executable);

// Takes `result` which has been compiled from a Tensorflow subgraph to a
  // XLA computation already, and generates an XLA LocalExecutable `executable`.
  Status BuildExecutable(const XlaCompiler::Options& options,
                         const XlaCompiler::CompilationResult& result,
                         std::unique_ptr<xla::LocalExecutable>* executable);

xla::LocalClient* const client_;
  const DeviceType device_type_;

// The value associated with a cache entry.
  struct Entry {
    mutex mu;

// Have we tried compiling this entry?
    bool compiled = false;

// The number of times a compilation with this signature has been requested.
    int64 request_count = 0;

// Did compilation succeed?
    Status compilation_status TF_GUARDED_BY(mu);

// Output of the XlaCompiler.
    XlaCompiler::CompilationResult compilation_result TF_GUARDED_BY(mu);

// The XLA executable compiled from <computation>. May be null if no
    // executable has been built.
    std::unique_ptr<xla::LocalExecutable> executable TF_GUARDED_BY(mu);
  };

mutex compile_cache_mu_;
  absl::flat_hash_map<Signature, std::unique_ptr<Entry>, Signature::Hash> cache_
      TF_GUARDED_BY(compile_cache_mu_);

struct ClusterCompileStats {
    // Number of times the cluster has been (re-)compiled.
    int64 compile_count = 0;

// The number of times this cluster has been executed.
    int64 execution_count = 0;

// Cumulative time spent compiling the cluster.
    int64 cumulative_compile_time_us = 0;

// True if we have decided that this cluster is too dynamic (i.e. its shapes
    // change too frequently) to profitably JIT compile.  Once a cluster is
    // tagged megamorphic, it stays megamorphic forever.
    bool is_megamorphic = false;
  };

mutex cluster_compile_stats_mu_;

// Maps cluster names to compilation statistics for said cluster.
  absl::flat_hash_map<string, ClusterCompileStats> cluster_compile_stats_
      TF_GUARDED_BY(cluster_compile_stats_mu_);

// The number of times a lazy compilation must be requested for a specific
  // signature before  we attempt to compile it.
  static constexpr int64 kDefaultCompilationThreshold = 2;

TF_DISALLOW_COPY_AND_ASSIGN(XlaCompilationCache);
};

}  // namespace tensorflow

#endif  // TENSORFLOW_COMPILER_JIT_XLA_COMPILATION_CACHE_H_