/* Copyright 2017 The OpenXLA Authors.

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 XLA_HLO_PASS_HLO_PASS_INTERFACE_H_
#define XLA_HLO_PASS_HLO_PASS_INTERFACE_H_

#include <cstdint>
#include <memory>
#include <string>

#include "absl/base/attributes.h"
#include "absl/container/flat_hash_set.h"
#include "absl/log/log.h"
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/string_view.h"
#include "xla/hlo/ir/hlo_computation.h"
#include "xla/hlo/ir/hlo_module.h"
#include "xla/shape.h"
#include "xla/shape_util.h"
#include "xla/status_macros.h"
#include "xla/tsl/platform/statusor.h"
#include "xla/types.h"
#include "xla/util.h"

namespace xla {

// Base class for HLO passes. These are used with the HloPassPipeline to
// organize a sequence of passes. An HLO pass should not extend this class
// directly; it should extend HloModulePass.
class HloPassInterface {
 public:
  // Struct that holds states of pass runs across multiple iterations.
  struct RunState {
    // The current iteration number.
    int iteration = 0;
    // Set of all changed computations from all pass runs using this state.
    absl::flat_hash_set<HloComputation*> changed;
    // Set of changed computation from previous iteration.
    absl::flat_hash_set<HloComputation*> changed_last_iteration;
    // Set of changed computation from current iteration.
    absl::flat_hash_set<HloComputation*> changed_this_iteration;

    RunState() = default;
    explicit RunState(HloModule* module)
        : changed_last_iteration(module->computations().begin(),
                                 module->computations().end()) {}

    // Transition to the next iteration.
    //
    // Depending on the pass implementation, one iteration includes all the work
    // done between two IncrementIteration calls, there can be arbitrary number
    // of passes that ran arbitrary times with this state.
    void IncrementIteration() {
      using std::swap;
      changed.insert(changed_this_iteration.begin(),
                     changed_this_iteration.end());
      swap(changed_last_iteration, changed_this_iteration);
      changed_this_iteration.clear();
      ++iteration;
    }
  };
  virtual ~HloPassInterface() = default;
  virtual absl::string_view name() const = 0;

  // Run the pass on the given HLO module with specified execution_threads.
  // Empty execution_threads list means all execution_threads are included.
  // Returns whether it modified the module.
  absl::StatusOr<bool> Run(
      HloModule* module,
      const absl::flat_hash_set<absl::string_view>& execution_threads = {});

  // Same as above, except that this API allows the pass to return a *different*
  // module, rather than modifying the module in-place.
  // TODO(b/454418238): Remove this function (and the corresponding RunImpl).
  ABSL_DEPRECATED(
      "This interface exists for passes which create an entire new HloModule "
      "instead of updating the existing one in place. This is not the norm and "
      "should not be done.")
  absl::StatusOr<bool> Run(
      std::unique_ptr<HloModule>& module_ptr,
      const absl::flat_hash_set<absl::string_view>& execution_threads = {});

  // Run the pass on computation on changed computations from last iteration in
  // given HLO module for specified execution_threads, with caller provided
  // RunState which holds the state information across multiple iterations.
  //
  // NOTE: This is a temporary default implementation that conservatively treats
  // all computations as changed. Eventually all passes should override this
  // method instead of Run() and Run() will call into this method instead.
  virtual absl::Status RunOnChangedComputations(
      HloModule* module, RunState* run_state,
      const absl::flat_hash_set<absl::string_view>& execution_threads) {
    TF_ASSIGN_OR_RETURN(bool changed, Run(module, execution_threads));
    if (changed) {
      auto computations = module->computations(execution_threads);
      run_state->changed_this_iteration.insert(computations.begin(),
                                               computations.end());
    }
    return absl::OkStatus();
  }

  virtual bool IsPassPipeline() const { return false; }

  // If an HloPassMetadata has previously been created, it adds a (key, value)
  // pair metric if none was already set or updates the existing value.
  // If an HloPassMetadata doesn't exist, it simply returns.
  static void SetKVMetric(HloModule* module, const std::string& key,
                          int64_t value) {
    auto status = module->metadata()->set_key_value_metric(key, value);
    if (!status.ok()) {
      // Only logging since this should not crash the application.
      // It usually means the pass was invoked on its own.
      LOG(WARNING) << "Failed to set stat: " << status;
    }
  }

 protected:
  virtual absl::StatusOr<bool> RunImpl(
      HloModule* module,
      const absl::flat_hash_set<absl::string_view>& execution_threads) = 0;

  // TODO(b/454418238): Remove this function.
  virtual absl::StatusOr<bool> RunImpl(
      std::unique_ptr<HloModule>& module_ptr,
      const absl::flat_hash_set<absl::string_view>& execution_threads) {
    return RunImpl(module_ptr.get(), execution_threads);
  }
};

// Base class for passes which are module-scoped.
class HloModulePass : public HloPassInterface {
 public:
  // Update the layout of a Shape to one that is supported by a given backend.
  // One can call this function after modifying the Shape in case that modifying
  // the Shape requires changes to the layout for the given Backend.
  //
  // TODO(b/129084868): Make this Backend dependent instead of requiring
  // deriving from the pass and overriding this function.
  virtual void UpdateLayout(Shape* shape) {
    // CPU/GPU backends require shapes of subbyte types to be packed.
    ShapeUtil::UpdateElementSizeInBits(shape, /*pack_subbyte_types=*/true);
  }
};

}  // namespace xla

#endif  // XLA_HLO_PASS_HLO_PASS_INTERFACE_H_