1 // Copyright (c) 2019 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 #include "source/fuzz/fuzzer_pass_add_dead_blocks.h"
16
17 #include <algorithm>
18
19 #include "source/fuzz/fuzzer_util.h"
20 #include "source/fuzz/transformation_add_dead_block.h"
21
22 namespace spvtools {
23 namespace fuzz {
24
25 namespace {
26
27 const size_t kMaxTransformationsInOnePass = 100U;
28
29 } // namespace
30
FuzzerPassAddDeadBlocks(opt::IRContext * ir_context,TransformationContext * transformation_context,FuzzerContext * fuzzer_context,protobufs::TransformationSequence * transformations,bool ignore_inapplicable_transformations)31 FuzzerPassAddDeadBlocks::FuzzerPassAddDeadBlocks(
32 opt::IRContext* ir_context, TransformationContext* transformation_context,
33 FuzzerContext* fuzzer_context,
34 protobufs::TransformationSequence* transformations,
35 bool ignore_inapplicable_transformations)
36 : FuzzerPass(ir_context, transformation_context, fuzzer_context,
37 transformations, ignore_inapplicable_transformations) {}
38
Apply()39 void FuzzerPassAddDeadBlocks::Apply() {
40 // We iterate over all blocks in the module collecting up those at which we
41 // might add a branch to a new dead block. We then loop over all such
42 // candidates and actually apply transformations. This separation is to
43 // avoid modifying the module as we traverse it.
44 std::vector<TransformationAddDeadBlock> candidate_transformations;
45 for (auto& function : *GetIRContext()->module()) {
46 for (auto& block : function) {
47 if (!GetFuzzerContext()->ChoosePercentage(
48 GetFuzzerContext()->GetChanceOfAddingDeadBlock())) {
49 continue;
50 }
51
52 // Make sure the module contains a boolean constant equal to
53 // |condition_value|.
54 bool condition_value = GetFuzzerContext()->ChooseEven();
55 FindOrCreateBoolConstant(condition_value, false);
56
57 // We speculatively create a transformation, and then apply it (below) if
58 // it turns out to be applicable. This avoids duplicating the logic for
59 // applicability checking.
60 //
61 // It means that fresh ids for transformations that turn out not to be
62 // applicable end up being unused.
63 candidate_transformations.emplace_back(TransformationAddDeadBlock(
64 GetFuzzerContext()->GetFreshId(), block.id(), condition_value));
65 }
66 }
67 // Applying transformations can be expensive as each transformation requires
68 // dominator information and also invalidates dominator information. We thus
69 // limit the number of transformations that one application of this fuzzer
70 // pass can apply. We choose to do this after identifying all the
71 // transformations that we *might* want to apply, rather than breaking the
72 // above loops once the limit is reached, to avoid biasing towards
73 // transformations that target early parts of the module.
74 GetFuzzerContext()->Shuffle(&candidate_transformations);
75 for (size_t i = 0; i < std::min(kMaxTransformationsInOnePass,
76 candidate_transformations.size());
77 i++) {
78 MaybeApplyTransformation(candidate_transformations[i]);
79 }
80 }
81
82 } // namespace fuzz
83 } // namespace spvtools
84