mirror of
https://github.com/KhronosGroup/SPIRV-Tools
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e2e95172df
Before this change there was quite a lot of duplication in the code being used to choose random percentages, and some of it was incorrect so that a percentage chance of (100-N)% instead of N% was being used. Also there was a lot of duplicate code to choose a random index into a vector. This change eliminates that duplication (fixing up the percentage problem), and gets rid of direct access to the random number generator being used for fuzzing, so that all randomization requests must go through the FuzzerContext class, discouraging future ad-hoc uses of the random number generator.
98 lines
3.9 KiB
C++
98 lines
3.9 KiB
C++
// Copyright (c) 2019 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "source/fuzz/fuzzer_pass_split_blocks.h"
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#include <utility>
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#include <vector>
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#include "source/fuzz/transformation_split_block.h"
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namespace spvtools {
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namespace fuzz {
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FuzzerPassSplitBlocks::FuzzerPassSplitBlocks(
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opt::IRContext* ir_context, FactManager* fact_manager,
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FuzzerContext* fuzzer_context,
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protobufs::TransformationSequence* transformations)
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: FuzzerPass(ir_context, fact_manager, fuzzer_context, transformations) {}
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FuzzerPassSplitBlocks::~FuzzerPassSplitBlocks() = default;
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void FuzzerPassSplitBlocks::Apply() {
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// Gather up pointers to all the blocks in the module. We are then able to
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// iterate over these pointers and split the blocks to which they point;
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// we cannot safely split blocks while we iterate through the module.
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std::vector<opt::BasicBlock*> blocks;
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for (auto& function : *GetIRContext()->module()) {
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for (auto& block : function) {
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blocks.push_back(&block);
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}
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}
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// Now go through all the block pointers that were gathered.
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for (auto& block : blocks) {
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// Probabilistically decide whether to try to split this block.
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if (!GetFuzzerContext()->ChoosePercentage(
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GetFuzzerContext()->GetChanceOfSplittingBlock())) {
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// We are not going to try to split this block.
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continue;
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}
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// We are going to try to split this block. We now need to choose where
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// to split it. We do this by finding a base instruction that has a
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// result id, and an offset from that base instruction. We would like
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// offsets to be as small as possible and ideally 0 - we only need offsets
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// because not all instructions can be identified by a result id (e.g.
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// OpStore instructions cannot).
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std::vector<std::pair<uint32_t, uint32_t>> base_offset_pairs;
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// The initial base instruction is the block label.
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uint32_t base = block->id();
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uint32_t offset = 0;
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// Consider every instruction in the block. The label is excluded: it is
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// only necessary to consider it as a base in case the first instruction
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// in the block does not have a result id.
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for (auto& inst : *block) {
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if (inst.HasResultId()) {
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// In the case that the instruction has a result id, we use the
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// instruction as its own base, with zero offset.
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base = inst.result_id();
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offset = 0;
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} else {
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// The instruction does not have a result id, so we need to identify
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// it via the latest instruction that did have a result id (base), and
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// an incremented offset.
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offset++;
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}
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base_offset_pairs.emplace_back(base, offset);
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}
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// Having identified all the places we might be able to split the block,
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// we choose one of them.
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auto base_offset =
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base_offset_pairs[GetFuzzerContext()->RandomIndex(base_offset_pairs)];
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auto transformation =
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TransformationSplitBlock(base_offset.first, base_offset.second,
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GetFuzzerContext()->GetFreshId());
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// If the position we have chosen turns out to be a valid place to split
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// the block, we apply the split. Otherwise the block just doesn't get
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// split.
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if (transformation.IsApplicable(GetIRContext(), *GetFactManager())) {
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transformation.Apply(GetIRContext(), GetFactManager());
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*GetTransformations()->add_transformation() = transformation.ToMessage();
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}
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}
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}
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} // namespace fuzz
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} // namespace spvtools
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