100 lines
4.0 KiB
C++
100 lines
4.0 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()->GetRandomGenerator()->RandomPercentage() >
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GetFuzzerContext()->GetChanceOfSplittingBlock()) {
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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 = base_offset_pairs
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[GetFuzzerContext()->GetRandomGenerator()->RandomUint32(
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static_cast<uint32_t>(base_offset_pairs.size()))];
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auto message = transformation::MakeTransformationSplitBlock(
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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(message, GetIRContext(),
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*GetFactManager())) {
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transformation::Apply(message, GetIRContext(), GetFactManager());
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*GetTransformations()->add_transformation()->mutable_split_block() =
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message;
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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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