1// Copyright (c) 2018 Google LLC.
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_VECTOR_DCE_H_
16#define SOURCE_OPT_VECTOR_DCE_H_
17
18#include <unordered_map>
19#include <vector>
20
21#include "source/opt/mem_pass.h"
22#include "source/util/bit_vector.h"
23
24namespace spvtools {
25namespace opt {
26
27class VectorDCE : public MemPass {
28 private:
29 using LiveComponentMap = std::unordered_map<uint32_t, utils::BitVector>;
30
31 // According to the SPEC the maximum size for a vector is 16. See the data
32 // rules in the universal validation rules (section 2.16.1).
33 enum { kMaxVectorSize = 16 };
34
35 struct WorkListItem {
36 WorkListItem() : instruction(nullptr), components(kMaxVectorSize) {}
37
38 Instruction* instruction;
39 utils::BitVector components;
40 };
41
42 public:
43 VectorDCE() : all_components_live_(kMaxVectorSize) {
44 for (uint32_t i = 0; i < kMaxVectorSize; i++) {
45 all_components_live_.Set(i);
46 }
47 }
48
49 const char* name() const override { return "vector-dce"; }
50 Status Process() override;
51
52 IRContext::Analysis GetPreservedAnalyses() override {
53 return IRContext::kAnalysisDefUse | IRContext::kAnalysisCFG |
54 IRContext::kAnalysisInstrToBlockMapping |
55 IRContext::kAnalysisLoopAnalysis | IRContext::kAnalysisDecorations |
56 IRContext::kAnalysisDominatorAnalysis | IRContext::kAnalysisNameMap |
57 IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
58 }
59
60 private:
61 // Runs the vector dce pass on |function|. Returns true if |function| was
62 // modified.
63 bool VectorDCEFunction(Function* function);
64
65 // Identifies the live components of the vectors that are results of
66 // instructions in |function|. The results are stored in |live_components|.
67 void FindLiveComponents(Function* function,
68 LiveComponentMap* live_components);
69
70 // Rewrites instructions in |function| that are dead or partially dead. If an
71 // instruction does not have an entry in |live_components|, then it is not
72 // changed. Returns true if |function| was modified.
73 bool RewriteInstructions(Function* function,
74 const LiveComponentMap& live_components);
75
76 // Rewrites the OpCompositeInsert instruction |current_inst| to avoid
77 // unnecessary computes given that the only components of the result that are
78 // live are |live_components|.
79 //
80 // If the value being inserted is not live, then the result of |current_inst|
81 // is replaced by the composite input to |current_inst|.
82 //
83 // If the composite input to |current_inst| is not live, then it is replaced
84 // by and OpUndef in |current_inst|.
85 bool RewriteInsertInstruction(Instruction* current_inst,
86 const utils::BitVector& live_components);
87
88 // Returns true if the result of |inst| is a vector or a scalar.
89 bool HasVectorOrScalarResult(const Instruction* inst) const;
90
91 // Returns true if the result of |inst| is a scalar.
92 bool HasVectorResult(const Instruction* inst) const;
93
94 // Returns true if the result of |inst| is a vector.
95 bool HasScalarResult(const Instruction* inst) const;
96
97 // Adds |work_item| to |work_list| if it is not already live according to
98 // |live_components|. |live_components| is updated to indicate that
99 // |work_item| is now live.
100 void AddItemToWorkListIfNeeded(WorkListItem work_item,
101 LiveComponentMap* live_components,
102 std::vector<WorkListItem>* work_list);
103
104 // Marks the components |live_elements| of the uses in |current_inst| as live
105 // according to |live_components|. If they were not live before, then they are
106 // added to |work_list|.
107 void MarkUsesAsLive(Instruction* current_inst,
108 const utils::BitVector& live_elements,
109 LiveComponentMap* live_components,
110 std::vector<WorkListItem>* work_list);
111
112 // Marks the uses in the OpVectorShuffle instruction in |current_item| as live
113 // based on the live components in |current_item|. If anything becomes live
114 // they are added to |work_list| and |live_components| is updated
115 // accordingly.
116 void MarkVectorShuffleUsesAsLive(const WorkListItem& current_item,
117 VectorDCE::LiveComponentMap* live_components,
118 std::vector<WorkListItem>* work_list);
119
120 // Marks the uses in the OpCompositeInsert instruction in |current_item| as
121 // live based on the live components in |current_item|. If anything becomes
122 // live they are added to |work_list| and |live_components| is updated
123 // accordingly.
124 void MarkInsertUsesAsLive(const WorkListItem& current_item,
125 LiveComponentMap* live_components,
126 std::vector<WorkListItem>* work_list);
127
128 // Marks the uses in the OpCompositeExtract instruction |current_inst| as
129 // live. If anything becomes live they are added to |work_list| and
130 // |live_components| is updated accordingly.
131 void MarkExtractUseAsLive(const Instruction* current_inst,
132 const utils::BitVector& live_elements,
133 LiveComponentMap* live_components,
134 std::vector<WorkListItem>* work_list);
135
136 // Marks the uses in the OpCompositeConstruct instruction |current_inst| as
137 // live. If anything becomes live they are added to |work_list| and
138 // |live_components| is updated accordingly.
139 void MarkCompositeContructUsesAsLive(WorkListItem work_item,
140 LiveComponentMap* live_components,
141 std::vector<WorkListItem>* work_list);
142
143 // A BitVector that can always be used to say that all components of a vector
144 // are live.
145 utils::BitVector all_components_live_;
146};
147
148} // namespace opt
149} // namespace spvtools
150
151#endif // SOURCE_OPT_VECTOR_DCE_H_
152