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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
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "source/fuzz/fuzzer_pass_split_blocks.h"
#include <vector>
#include "source/fuzz/instruction_descriptor.h"
#include "source/fuzz/transformation_split_block.h"
namespace spvtools {
namespace fuzz {
FuzzerPassSplitBlocks::FuzzerPassSplitBlocks(
opt::IRContext* ir_context, TransformationContext* transformation_context,
FuzzerContext* fuzzer_context,
protobufs::TransformationSequence* transformations,
bool ignore_inapplicable_transformations)
: FuzzerPass(ir_context, transformation_context, fuzzer_context,
transformations, ignore_inapplicable_transformations) {}
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) {
blocks.push_back(&block);
}
}
// 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.
continue;
}
// TODO(https://github.com/KhronosGroup/SPIRV-Tools/issues/2964): consider
// taking a simpler approach to identifying the instruction before which
// to split a block.
// We are going to try to split this block. We now need to choose where
// to split it. We describe the instruction before which we would like to
// split a block via an InstructionDescriptor, details of which are
// commented in the protobufs definition file.
std::vector<protobufs::InstructionDescriptor> instruction_descriptors;
// The initial base instruction is the block label.
uint32_t base = block->id();
// Counts the number of times we have seen each opcode since we reset the
// base instruction.
std::map<SpvOp, uint32_t> skip_count;
// 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, and clear the skip counts we have
// collected.
base = inst.result_id();
skip_count.clear();
}
const SpvOp opcode = inst.opcode();
instruction_descriptors.emplace_back(MakeInstructionDescriptor(
base, opcode, skip_count.count(opcode) ? skip_count.at(opcode) : 0));
if (!inst.HasResultId()) {
skip_count[opcode] =
skip_count.count(opcode) ? skip_count.at(opcode) + 1 : 1;
}
}
// Having identified all the places we might be able to split the block,
// we choose one of them.
auto transformation = TransformationSplitBlock(
instruction_descriptors[GetFuzzerContext()->RandomIndex(
instruction_descriptors)],
GetFuzzerContext()->GetFreshId());
// 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.
MaybeApplyTransformation(transformation);
}
}
} // namespace fuzz
} // namespace spvtools
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