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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:
name()36   const char* name() const override { return "local-redundancy-elimination"; }
37   Status Process() override;
38 
GetPreservedAnalyses()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 | IRContext::kAnalysisConstants |
45            IRContext::kAnalysisTypes;
46   }
47 
48  protected:
49   // Deletes instructions in |block| whose value is in |value_to_ids| or is
50   // computed earlier in |block|.
51   //
52   // |vnTable| must have computed a value number for every result id defined
53   // in |bb|.
54   //
55   // |value_to_ids| is a map from value number to ids.  If {vn, id} is in
56   // |value_to_ids| then vn is the value number of id, and the definition of id
57   // dominates |bb|.
58   //
59   // Returns true if the module is changed.
60   bool EliminateRedundanciesInBB(BasicBlock* block,
61                                  const ValueNumberTable& vnTable,
62                                  std::map<uint32_t, uint32_t>* value_to_ids);
63 };
64 
65 }  // namespace opt
66 }  // namespace spvtools
67 
68 #endif  // SOURCE_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_
69