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