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      1 // Copyright (c) 2017 Google Inc.
      2 //
      3 // Licensed under the Apache License, Version 2.0 (the "License");
      4 // you may not use this file except in compliance with the License.
      5 // You may obtain a copy of the License at
      6 //
      7 //     http://www.apache.org/licenses/LICENSE-2.0
      8 //
      9 // Unless required by applicable law or agreed to in writing, software
     10 // distributed under the License is distributed on an "AS IS" BASIS,
     11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     12 // See the License for the specific language governing permissions and
     13 // limitations under the License.
     14 
     15 #ifndef SOURCE_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_
     16 #define SOURCE_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_
     17 
     18 #include <map>
     19 
     20 #include "source/opt/ir_context.h"
     21 #include "source/opt/pass.h"
     22 #include "source/opt/value_number_table.h"
     23 
     24 namespace spvtools {
     25 namespace opt {
     26 
     27 // This pass implements local redundancy elimination. Its goal is to reduce the
     28 // number of times the same value is computed. It works on each basic block
     29 // independently, ie local. For each instruction in a basic block, it gets the
     30 // value number for the result id, |id|, of the instruction. If that value
     31 // number has already been computed in the basic block, it tries to replace the
     32 // uses of |id| by the id that already contains the same value. Then the
     33 // current instruction is deleted.
     34 class LocalRedundancyEliminationPass : public Pass {
     35  public:
     36   const char* name() const override { return "local-redundancy-elimination"; }
     37   Status Process() override;
     38 
     39   IRContext::Analysis GetPreservedAnalyses() override {
     40     return IRContext::kAnalysisDefUse |
     41            IRContext::kAnalysisInstrToBlockMapping |
     42            IRContext::kAnalysisDecorations | IRContext::kAnalysisCombinators |
     43            IRContext::kAnalysisCFG | IRContext::kAnalysisDominatorAnalysis |
     44            IRContext::kAnalysisNameMap;
     45   }
     46 
     47  protected:
     48   // Deletes instructions in |block| whose value is in |value_to_ids| or is
     49   // computed earlier in |block|.
     50   //
     51   // |vnTable| must have computed a value number for every result id defined
     52   // in |bb|.
     53   //
     54   // |value_to_ids| is a map from value number to ids.  If {vn, id} is in
     55   // |value_to_ids| then vn is the value number of id, and the definition of id
     56   // dominates |bb|.
     57   //
     58   // Returns true if the module is changed.
     59   bool EliminateRedundanciesInBB(BasicBlock* block,
     60                                  const ValueNumberTable& vnTable,
     61                                  std::map<uint32_t, uint32_t>* value_to_ids);
     62 };
     63 
     64 }  // namespace opt
     65 }  // namespace spvtools
     66 
     67 #endif  // SOURCE_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_
     68