79 lines
3.0 KiB
C
79 lines
3.0 KiB
C
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/* Copyright 2017 The OpenXLA Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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==============================================================================*/
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#ifndef XLA_SERVICE_HLO_DCE_H_
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#define XLA_SERVICE_HLO_DCE_H_
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#include "absl/container/flat_hash_map.h"
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#include "absl/container/flat_hash_set.h"
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#include "absl/strings/string_view.h"
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#include "xla/hlo/ir/hlo_computation.h"
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#include "xla/hlo/ir/hlo_instruction.h"
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#include "xla/hlo/ir/hlo_module.h"
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#include "xla/service/hlo_pass_interface.h"
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#include "xla/status.h"
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#include "xla/statusor.h"
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namespace xla {
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// HLO pass which removes dead instructions from each computation in the module
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// and removes dead computations from the module.
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//
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// An instruction is dead if it is not reachable from the root. A computation is
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// dead if it is not the entry computation of the module and it is not reachable
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// from the entry computation.
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//
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// This pass does not remove dead parameter instructions, as parameter
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// instructions cannot be deleted.
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class HloDCE : public HloModulePass {
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public:
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HloDCE() : remove_cross_partition_collective_ops_(false) {}
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explicit HloDCE(bool remove_cross_partition_collective_ops)
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: remove_cross_partition_collective_ops_(
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remove_cross_partition_collective_ops) {}
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~HloDCE() override {}
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absl::string_view name() const override { return "dce"; }
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// Run DCE on a computation.
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static StatusOr<bool> RunOnComputation(
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HloComputation* computation, bool remove_cross_partition_collective_ops);
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// Run the pass on the given module. Returns whether the module was changed
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// (instructions were removed).
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using HloPassInterface::Run;
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StatusOr<bool> Run(
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HloModule* module,
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const absl::flat_hash_set<absl::string_view>& execution_threads) override;
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private:
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// Finds all computations that are not called by any instruction and removes
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// them from the module. Returns whether any dead code was removed.
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StatusOr<bool> RecursivelyRemoveDeadComputations(HloModule* module);
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// Given a dead computation, decrements the ref count of all its called
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// computations and checks if any of the subcomputations become dead after the
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// removal. Returns whether all dead computations were successfully removed
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// from the module.
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Status RecursivelyRemoveDeadComputation(
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HloModule* module, HloComputation* computation,
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absl::flat_hash_map<HloComputation*, int>& live_call_counts);
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bool remove_cross_partition_collective_ops_;
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};
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} // namespace xla
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#endif // XLA_SERVICE_HLO_DCE_H_
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