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