path: root/tensorflow/compiler/xla/service/hlo_module.h

/* Copyright 2017 The TensorFlow Authors. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/

#ifndef TENSORFLOW_COMPILER_XLA_SERVICE_HLO_MODULE_H_
#define TENSORFLOW_COMPILER_XLA_SERVICE_HLO_MODULE_H_

#include <atomic>
#include <list>
#include <memory>
#include <random>
#include <string>
#include <unordered_map>
#include <vector>

#include "absl/strings/string_view.h"
#include "absl/types/optional.h"
#include "absl/types/span.h"
#include "tensorflow/compiler/xla/iterator_util.h"
#include "tensorflow/compiler/xla/service/hlo.pb.h"
#include "tensorflow/compiler/xla/service/hlo_clone_context.h"
#include "tensorflow/compiler/xla/service/hlo_computation.h"
#include "tensorflow/compiler/xla/service/hlo_instruction.h"
#include "tensorflow/compiler/xla/service/hlo_module_config.h"
#include "tensorflow/compiler/xla/service/hlo_schedule.h"
#include "tensorflow/compiler/xla/service/name_uniquer.h"
#include "tensorflow/compiler/xla/types.h"
#include "tensorflow/core/lib/gtl/iterator_range.h"
#include "tensorflow/core/platform/logging.h"
#include "tensorflow/core/platform/mutex.h"

namespace xla {

// Describes a compilation unit at the HLO level.
//
// HloModule is the top-level unit in the HLO IR.  It corresponds to a whole
// "program".  Running a module, from beginning to end, is the only way to run
// an XLA program.
//
// A module contains one "entry computation"; this HloComputation is like main()
// in a C program.  The result of running the module is the result of running
// this computation.
//
// A module also contains some number of "nested computations".  Each nested
// computation is attached to an HloInstruction within some other computation.
// The meaning of the nested computation depends on the instruction it's
// attached to.
class HloModule {
 public:
  // Constructor without a versioned computation handle. This constructor should
  // only be used for HloModules used outside of the XLA service (eg
  // tests). The versioned handle is used by the service in the compilation
  // cache. A default configuration is created for this module.
  explicit HloModule(const string& name, const HloModuleConfig& config);
  virtual ~HloModule() {}

  // Adds an entry computation to the module. A module can only have one entry
  // computation. Returns a pointer to the newly added computation.
  HloComputation* AddEntryComputation(
      std::unique_ptr<HloComputation> computation);

  // Adds an embedded computation to the module.
  HloComputation* AddEmbeddedComputation(
      std::unique_ptr<HloComputation> computation);

  // Removes an embedded computation.
  Status RemoveEmbeddedComputation(HloComputation* to_remove);

  // Replaces all uses of computations that are keys of 'replacements' with
  // the corresponding values in 'replacements'. Replaces the entry computation,
  // if applicable.
  //
  // This function iterates over all instructions in the module to find
  // computations to replace. We could speed it up by keeping track of users of
  // computations.
  void ReplaceComputations(
      const std::unordered_map<HloComputation*, HloComputation*>& replacements);

  const string& name() const { return name_; }
  void set_name(string name) { name_ = std::move(name); }

  // Returns a deep copy of this module including all computations.
  std::unique_ptr<HloModule> Clone(const string& suffix = "clone") const;

  // Performs a deep clone of the computation, by recursively cloning all
  // the called computations as well. If the clone context is specified, it
  // will be populated with the cloned object mappings.
  HloComputation* DeepCloneComputation(HloComputation* computation,
                                       HloCloneContext* context = nullptr);

  // Return a pointer to the entry computation of the module..
  const HloComputation* entry_computation() const {
    CHECK_NE(nullptr, entry_computation_);
    return entry_computation_;
  }
  HloComputation* entry_computation() {
    CHECK_NE(nullptr, entry_computation_);
    return entry_computation_;
  }

  // Creates the ComputationLayout which describes the current status of the HLO
  // module entry computation.
  ComputationLayout compute_computation_layout() const {
    return ComputationLayout(entry_computation()->ComputeProgramShape(),
                             /*ignore_layouts=*/false);
  }

  ComputationLayout* mutable_entry_computation_layout() {
    return config_.mutable_entry_computation_layout();
  }

  const ComputationLayout& entry_computation_layout() const {
    return config_.entry_computation_layout();
  }

  // Gets the computations in this module.
  //
  // Returns a view of HloComputation*s, so you can iterate over this in the
  // natural way:
  //
  //   for (HloComputation* c : module->computations()) { ... }
  //
  tensorflow::gtl::iterator_range<UnwrappingIterator<
      std::vector<std::unique_ptr<HloComputation>>::const_iterator>>
  computations() const {
    return {MakeUnwrappingIterator(computations_.begin()),
            MakeUnwrappingIterator(computations_.end())};
  }
  tensorflow::gtl::iterator_range<UnwrappingIterator<
      std::vector<std::unique_ptr<HloComputation>>::iterator>>
  computations() {
    return {MakeUnwrappingIterator(computations_.begin()),
            MakeUnwrappingIterator(computations_.end())};
  }

  // Returns the computation in this module that has the name `name`.  Returns
  // null if there is no such computation.
  HloComputation* GetComputationWithName(absl::string_view name);

  // Gets the number of computations in this module.
  int64 computation_count() const { return computations_.size(); }

  // Gets the number of instructions in this module.
  int64 instruction_count() const;

  // Compute and return a post order of all computations in the module. The sort
  // is defined like so: if computation A has an instruction which calls
  // computation B, then A will appear after B in the sort.
  std::vector<HloComputation*> MakeComputationPostOrder() const;

  // Gets the computations in this module which aren't for fusion nodes.
  //
  // Postcondition: All computations in the returned list have
  // !IsFusionComputation().
  //
  // Note: Callers can and do rely on the return value here being a *snapshot*
  // of the module's non-fusion computations -- that is, it's OK to add or
  // remove computations from a module while iterating over
  // MakeNonfusionComputations().
  std::vector<HloComputation*> MakeNonfusionComputations() const;

  const HloModuleConfig& config() const { return config_; }

  // Return a string representation of the module.
  //
  // (We express the default options using an overload rather than a default
  // param because gdb ignores default params, but does resolve overloads.)
  string ToString() const { return ToString(HloPrintOptions()); }
  string ToString(const HloPrintOptions& options) const;

  // Convert an HloModule to or from a proto.
  HloModuleProto ToProto() const;
  static StatusOr<std::unique_ptr<HloModule>> CreateFromProto(
      const HloModuleProto& proto, const HloModuleConfig& module_config);

  // Creates and returns an HloModuleConfig with an appropriate program shape
  // for the HLO module in the given proto.
  static StatusOr<HloModuleConfig> CreateModuleConfigFromProto(
      const HloModuleProto& module, const DebugOptions& debug_options);

  // Outlines the given expression from the given computation.
  // instructions_to_outline contains the instructions that form the expression.
  //
  // Precondition: instructions in instructions_to_outline are in topological
  // order (root of outlined instructions last). TODO(jingyue): takes a set of
  // instructions and topologically sorts them.
  HloInstruction* OutlineExpressionFromComputation(
      absl::Span<HloInstruction* const> instructions_to_outline,
      const string& outlined_computation_name, HloComputation* computation);

  // Returns a randomly generated uint64.
  uint64 RandomNew64() const;

  // Returns the NameUniquer for uniquing instruction names in this module.
  NameUniquer& instruction_name_uniquer() { return instruction_name_uniquer_; }

  // Assign a new unique dense id for an instruction
  int NewUniqueInstructionId() {
    int result = next_unique_id_;
    next_unique_id_++;
    return result;
  }

  // Returns the number of unique intruction ids given out.  All ids up to
  // this point are guaranteed to be in the range [0..NumUniqueInstructionIds())
  int NumUniqueInstructionIds() const { return next_unique_id_; }

  // Returns an id that is unique to this module across all modules created over
  // the lifetime of this process.
  int unique_id() const { return unique_id_; }

  // Returns a non-const version of the passed-in const HloInstruction*. This is
  // safe on the argument that if you have a non-const module, then you can
  // access all instructions in the module as non-const.
  //
  // Returns an error if the passed-in instruction is not from this module,
  // except that it is allowed to pass in a null pointer.
  //
  // TODO(b/78350259): Eliminate const laundering. The argument above is not
  // reliable since at any time someone could add or discover a way for a
  // non-const module to transitively contain a const HloInstruction. The
  // reliable way to do this would be to create a const laundering map from a
  // module, mapping each encountered HloInstruction to its non-const version
  // and then look up each instruction in need of laundering in that map, but
  // this is much more expensive and complicated. This returns a Status instead
  // of doing a CHECK-failure in part to make it strongly apparent that this is
  // something that can fail.
  StatusOr<HloInstruction*> LaunderConstInstructionFromModule(
      const HloInstruction* hlo);

  // Sets the schedule of the module to the given schedule.
  Status set_schedule(HloSchedule schedule);

  // Clears the schedule of the module.
  void clear_schedule() { schedule_.reset(); }

  // Returns true if the module has a schedule set.
  bool has_schedule() const { return schedule_.has_value(); }

  // Returns the schedue of the module. CHECK fails if no schedule is set.
  const HloSchedule& schedule() const { return *schedule_; }
  HloSchedule& schedule() { return *schedule_; }

 private:
  HloComputation* AddComputationInternal(
      std::unique_ptr<HloComputation> computation, bool is_entry,
      bool uniquify_identifiers);

  string name_;
  HloModuleConfig config_;
  HloComputation* entry_computation_ = nullptr;
  std::vector<std::unique_ptr<HloComputation>> computations_;

  // Random number generator engine to use when generating random numbers per
  // HloModule compilation.
  // TODO(b/25995601): Replace with better seed setting or dev/random for
  // where we don't need deterministic execution.
  mutable std::mt19937_64 rng_{42};
  mutable tensorflow::mutex rng_mutex_;

  // Unique name generator for computation and instruction names, which are
  // unique per module.
  NameUniquer computation_name_uniquer_{/*separator=*/"."};
  NameUniquer instruction_name_uniquer_{/*separator=*/"."};
  int next_unique_id_ = 0;

  // Used to keep track of the next unique module id that should be assigned.
  static std::atomic<int> next_unique_module_id_;
  // A unique id to label modules with.
  int unique_id_;

  // The HloSchedule of the module. The schedule if it exists contains a
  // sequential order of instructions for each non-fusion computation in the
  // module.
  absl::optional<HloSchedule> schedule_;
};

}  // namespace xla

#endif  // TENSORFLOW_COMPILER_XLA_SERVICE_HLO_MODULE_H_