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https://github.com/KhronosGroup/SPIRV-Tools
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5d602abd66
Adds a pass that looks for redundant instruction in a function, and removes them. The algorithm is a hash table based value numbering algorithm that traverses the dominator tree. This pass removes completely redundant instructions, not partially redundant ones.
65 lines
2.5 KiB
C++
65 lines
2.5 KiB
C++
// Copyright (c) 2017 Google Inc.
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//
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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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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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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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#ifndef LIBSPIRV_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_
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#define LIBSPIRV_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_
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#include "ir_context.h"
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#include "pass.h"
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#include "value_number_table.h"
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namespace spvtools {
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namespace opt {
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// This pass implements local redundancy elimination. Its goal is to reduce the
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// number of times the same value is computed. It works on each basic block
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// independently, ie local. For each instruction in a basic block, it gets the
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// value number for the result id, |id|, of the instruction. If that value
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// number has already been computed in the basic block, it tries to replace the
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// uses of |id| by the id that already contains the same value. Then the
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// current instruction is deleted.
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class LocalRedundancyEliminationPass : public Pass {
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public:
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const char* name() const override { return "local-redundancy-elimination"; }
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Status Process(ir::IRContext*) override;
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virtual ir::IRContext::Analysis GetPreservedAnalyses() override {
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return ir::IRContext::kAnalysisDefUse |
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ir::IRContext::kAnalysisInstrToBlockMapping |
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ir::IRContext::kAnalysisDecorations |
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ir::IRContext::kAnalysisCombinators | ir::IRContext::kAnalysisCFG |
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ir::IRContext::kAnalysisDominatorAnalysis;
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}
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protected:
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// Deletes instructions in |block| whose value is in |value_to_ids| or is
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// computed earlier in |block|.
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//
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// |vnTable| must have computed a value number for every result id defined
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// in |bb|.
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//
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// |value_to_ids| is a map from value number to ids. If {vn, id} is in
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// |value_to_ids| then vn is the value number of id, and the definition of id
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// dominates |bb|.
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//
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// Returns true if the module is changed.
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bool EliminateRedundanciesInBB(ir::BasicBlock* block,
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const ValueNumberTable& vnTable,
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std::map<uint32_t, uint32_t>* value_to_ids);
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};
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} // namespace opt
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} // namespace spvtools
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#endif // LIBSPIRV_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_
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