1 // Copyright (c) 2020 Vasyl Teliman
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 #include "source/fuzz/fuzzer_pass_wrap_regions_in_selections.h"
16
17 #include "source/fuzz/fuzzer_context.h"
18 #include "source/fuzz/instruction_descriptor.h"
19 #include "source/fuzz/transformation_split_block.h"
20 #include "source/fuzz/transformation_wrap_region_in_selection.h"
21
22 namespace spvtools {
23 namespace fuzz {
24
FuzzerPassWrapRegionsInSelections(opt::IRContext * ir_context,TransformationContext * transformation_context,FuzzerContext * fuzzer_context,protobufs::TransformationSequence * transformations,bool ignore_inapplicable_transformations)25 FuzzerPassWrapRegionsInSelections::FuzzerPassWrapRegionsInSelections(
26 opt::IRContext* ir_context, TransformationContext* transformation_context,
27 FuzzerContext* fuzzer_context,
28 protobufs::TransformationSequence* transformations,
29 bool ignore_inapplicable_transformations)
30 : FuzzerPass(ir_context, transformation_context, fuzzer_context,
31 transformations, ignore_inapplicable_transformations) {}
32
Apply()33 void FuzzerPassWrapRegionsInSelections::Apply() {
34 for (auto& function : *GetIRContext()->module()) {
35 if (!GetFuzzerContext()->ChoosePercentage(
36 GetFuzzerContext()->GetChanceOfWrappingRegionInSelection())) {
37 continue;
38 }
39
40 // It is easier to select an element at random from a vector than from an
41 // instruction list.
42 std::vector<opt::BasicBlock*> header_block_candidates;
43 for (auto& block : function) {
44 header_block_candidates.push_back(&block);
45 }
46
47 if (header_block_candidates.empty()) {
48 continue;
49 }
50
51 // Try to get a header block candidate that will increase the chances of the
52 // transformation being applicable.
53 auto* header_block_candidate = MaybeGetHeaderBlockCandidate(
54 header_block_candidates[GetFuzzerContext()->RandomIndex(
55 header_block_candidates)]);
56 if (!header_block_candidate) {
57 continue;
58 }
59
60 std::vector<opt::BasicBlock*> merge_block_candidates;
61 for (auto& block : function) {
62 if (GetIRContext()->GetDominatorAnalysis(&function)->StrictlyDominates(
63 header_block_candidate, &block) &&
64 GetIRContext()
65 ->GetPostDominatorAnalysis(&function)
66 ->StrictlyDominates(&block, header_block_candidate)) {
67 merge_block_candidates.push_back(&block);
68 }
69 }
70
71 if (merge_block_candidates.empty()) {
72 continue;
73 }
74
75 // Try to get a merge block candidate that will increase the chances of the
76 // transformation being applicable.
77 auto* merge_block_candidate = MaybeGetMergeBlockCandidate(
78 merge_block_candidates[GetFuzzerContext()->RandomIndex(
79 merge_block_candidates)]);
80 if (!merge_block_candidate) {
81 continue;
82 }
83
84 if (!TransformationWrapRegionInSelection::IsApplicableToBlockRange(
85 GetIRContext(), header_block_candidate->id(),
86 merge_block_candidate->id())) {
87 continue;
88 }
89
90 // This boolean constant will be used as a condition for the
91 // OpBranchConditional instruction. We mark it as irrelevant to be able to
92 // replace it with a more interesting value later.
93 auto branch_condition = GetFuzzerContext()->ChooseEven();
94 FindOrCreateBoolConstant(branch_condition, true);
95
96 ApplyTransformation(TransformationWrapRegionInSelection(
97 header_block_candidate->id(), merge_block_candidate->id(),
98 branch_condition));
99 }
100 }
101
102 opt::BasicBlock*
MaybeGetHeaderBlockCandidate(opt::BasicBlock * header_block_candidate)103 FuzzerPassWrapRegionsInSelections::MaybeGetHeaderBlockCandidate(
104 opt::BasicBlock* header_block_candidate) {
105 // Try to create a preheader if |header_block_candidate| is a loop header.
106 if (header_block_candidate->IsLoopHeader()) {
107 // GetOrCreateSimpleLoopPreheader only supports reachable blocks.
108 return GetIRContext()->cfg()->preds(header_block_candidate->id()).size() ==
109 1
110 ? nullptr
111 : GetOrCreateSimpleLoopPreheader(header_block_candidate->id());
112 }
113
114 // Try to split |header_block_candidate| if it's already a header block.
115 if (header_block_candidate->GetMergeInst()) {
116 SplitBlockAfterOpPhiOrOpVariable(header_block_candidate->id());
117 }
118
119 return header_block_candidate;
120 }
121
MaybeGetMergeBlockCandidate(opt::BasicBlock * merge_block_candidate)122 opt::BasicBlock* FuzzerPassWrapRegionsInSelections::MaybeGetMergeBlockCandidate(
123 opt::BasicBlock* merge_block_candidate) {
124 // If |merge_block_candidate| is a merge block of some construct, try to split
125 // it and return a newly created block.
126 if (GetIRContext()->GetStructuredCFGAnalysis()->IsMergeBlock(
127 merge_block_candidate->id())) {
128 // We can't split a merge block if it's also a loop header.
129 return merge_block_candidate->IsLoopHeader()
130 ? nullptr
131 : SplitBlockAfterOpPhiOrOpVariable(merge_block_candidate->id());
132 }
133
134 return merge_block_candidate;
135 }
136
137 } // namespace fuzz
138 } // namespace spvtools
139