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_DEAD_VARIABLE_ELIMINATION_H_
16#define SOURCE_OPT_DEAD_VARIABLE_ELIMINATION_H_
17
18#include <climits>
19#include <unordered_map>
20
21#include "source/opt/decoration_manager.h"
22#include "source/opt/mem_pass.h"
23
24namespace spvtools {
25namespace opt {
26
27class DeadVariableElimination : public MemPass {
28 public:
29 const char* name() const override { return "eliminate-dead-variables"; }
30 Status Process() override;
31
32 IRContext::Analysis GetPreservedAnalyses() override {
33 return IRContext::kAnalysisDefUse | IRContext::kAnalysisConstants |
34 IRContext::kAnalysisTypes;
35 }
36
37 private:
38 // Deletes the OpVariable instruction who result id is |result_id|.
39 void DeleteVariable(uint32_t result_id);
40
41 // Keeps track of the number of references of an id. Once that value is 0, it
42 // is safe to remove the corresponding instruction.
43 //
44 // Note that the special value kMustKeep is used to indicate that the
45 // instruction cannot be deleted for reasons other that is being explicitly
46 // referenced.
47 std::unordered_map<uint32_t, size_t> reference_count_;
48
49 // Special value used to indicate that an id cannot be safely deleted.
50 enum { kMustKeep = INT_MAX };
51};
52
53} // namespace opt
54} // namespace spvtools
55
56#endif // SOURCE_OPT_DEAD_VARIABLE_ELIMINATION_H_
57