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// Copyright (c) 2019 Google LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include "source/fuzz/fuzzer_pass_split_blocks.h"
#include <utility>
#include <vector>
#include "source/fuzz/transformation_split_block.h"
namespace spvtools {
namespace fuzz {
opt::IRContext* ir_context, FactManager* fact_manager,
FuzzerContext* fuzzer_context,
protobufs::TransformationSequence* transformations)
: FuzzerPass(ir_context, fact_manager, fuzzer_context, transformations) {}
FuzzerPassSplitBlocks::~FuzzerPassSplitBlocks() = default;
void FuzzerPassSplitBlocks::Apply() {
// Gather up pointers to all the blocks in the module. We are then able to
// iterate over these pointers and split the blocks to which they point;
// we cannot safely split blocks while we iterate through the module.
std::vector<opt::BasicBlock*> blocks;
for (auto& function : *GetIRContext()->module()) {
for (auto& block : function) {
// Now go through all the block pointers that were gathered.
for (auto& block : blocks) {
// Probabilistically decide whether to try to split this block.
if (!GetFuzzerContext()->ChoosePercentage(
GetFuzzerContext()->GetChanceOfSplittingBlock())) {
// We are not going to try to split this block.
// We are going to try to split this block. We now need to choose where
// to split it. We do this by finding a base instruction that has a
// result id, and an offset from that base instruction. We would like
// offsets to be as small as possible and ideally 0 - we only need offsets
// because not all instructions can be identified by a result id (e.g.
// OpStore instructions cannot).
std::vector<std::pair<uint32_t, uint32_t>> base_offset_pairs;
// The initial base instruction is the block label.
uint32_t base = block->id();
uint32_t offset = 0;
// Consider every instruction in the block. The label is excluded: it is
// only necessary to consider it as a base in case the first instruction
// in the block does not have a result id.
for (auto& inst : *block) {
if (inst.HasResultId()) {
// In the case that the instruction has a result id, we use the
// instruction as its own base, with zero offset.
base = inst.result_id();
offset = 0;
} else {
// The instruction does not have a result id, so we need to identify
// it via the latest instruction that did have a result id (base), and
// an incremented offset.
base_offset_pairs.emplace_back(base, offset);
// Having identified all the places we might be able to split the block,
// we choose one of them.
auto base_offset =
auto transformation =
TransformationSplitBlock(base_offset.first, base_offset.second,
// If the position we have chosen turns out to be a valid place to split
// the block, we apply the split. Otherwise the block just doesn't get
// split.
if (transformation.IsApplicable(GetIRContext(), *GetFactManager())) {
transformation.Apply(GetIRContext(), GetFactManager());
*GetTransformations()->add_transformation() = transformation.ToMessage();
} // namespace fuzz
} // namespace spvtools