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_split_blocks.h"
16
17 #include <vector>
18
19 #include "source/fuzz/instruction_descriptor.h"
20 #include "source/fuzz/transformation_split_block.h"
21
22 namespace spvtools {
23 namespace fuzz {
24
FuzzerPassSplitBlocks(opt::IRContext * ir_context,FactManager * fact_manager,FuzzerContext * fuzzer_context,protobufs::TransformationSequence * transformations)25 FuzzerPassSplitBlocks::FuzzerPassSplitBlocks(
26 opt::IRContext* ir_context, FactManager* fact_manager,
27 FuzzerContext* fuzzer_context,
28 protobufs::TransformationSequence* transformations)
29 : FuzzerPass(ir_context, fact_manager, fuzzer_context, transformations) {}
30
31 FuzzerPassSplitBlocks::~FuzzerPassSplitBlocks() = default;
32
Apply()33 void FuzzerPassSplitBlocks::Apply() {
34 // Gather up pointers to all the blocks in the module. We are then able to
35 // iterate over these pointers and split the blocks to which they point;
36 // we cannot safely split blocks while we iterate through the module.
37 std::vector<opt::BasicBlock*> blocks;
38 for (auto& function : *GetIRContext()->module()) {
39 for (auto& block : function) {
40 blocks.push_back(&block);
41 }
42 }
43
44 // Now go through all the block pointers that were gathered.
45 for (auto& block : blocks) {
46 // Probabilistically decide whether to try to split this block.
47 if (!GetFuzzerContext()->ChoosePercentage(
48 GetFuzzerContext()->GetChanceOfSplittingBlock())) {
49 // We are not going to try to split this block.
50 continue;
51 }
52
53 // TODO(https://github.com/KhronosGroup/SPIRV-Tools/issues/2964): consider
54 // taking a simpler approach to identifying the instruction before which
55 // to split a block.
56
57 // We are going to try to split this block. We now need to choose where
58 // to split it. We describe the instruction before which we would like to
59 // split a block via an InstructionDescriptor, details of which are
60 // commented in the protobufs definition file.
61 std::vector<protobufs::InstructionDescriptor> instruction_descriptors;
62
63 // The initial base instruction is the block label.
64 uint32_t base = block->id();
65
66 // Counts the number of times we have seen each opcode since we reset the
67 // base instruction.
68 std::map<SpvOp, uint32_t> skip_count;
69
70 // Consider every instruction in the block. The label is excluded: it is
71 // only necessary to consider it as a base in case the first instruction
72 // in the block does not have a result id.
73 for (auto& inst : *block) {
74 if (inst.HasResultId()) {
75 // In the case that the instruction has a result id, we use the
76 // instruction as its own base, and clear the skip counts we have
77 // collected.
78 base = inst.result_id();
79 skip_count.clear();
80 }
81 const SpvOp opcode = inst.opcode();
82 instruction_descriptors.emplace_back(MakeInstructionDescriptor(
83 base, opcode, skip_count.count(opcode) ? skip_count.at(opcode) : 0));
84 if (!inst.HasResultId()) {
85 skip_count[opcode] =
86 skip_count.count(opcode) ? skip_count.at(opcode) + 1 : 1;
87 }
88 }
89 // Having identified all the places we might be able to split the block,
90 // we choose one of them.
91 auto transformation = TransformationSplitBlock(
92 instruction_descriptors[GetFuzzerContext()->RandomIndex(
93 instruction_descriptors)],
94 GetFuzzerContext()->GetFreshId());
95 // If the position we have chosen turns out to be a valid place to split
96 // the block, we apply the split. Otherwise the block just doesn't get
97 // split.
98 if (transformation.IsApplicable(GetIRContext(), *GetFactManager())) {
99 transformation.Apply(GetIRContext(), GetFactManager());
100 *GetTransformations()->add_transformation() = transformation.ToMessage();
101 }
102 }
103 }
104
105 } // namespace fuzz
106 } // namespace spvtools
107