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
24namespace spvtools {
25namespace 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.
34class 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 | 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