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 
24 namespace spvtools {
25 namespace opt {
26 
27 class DeadVariableElimination : public MemPass {
28  public:
name()29   const char* name() const override { return "eliminate-dead-variables"; }
30   Status Process() override;
31 
GetPreservedAnalyses()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