mirror of
https://github.com/KhronosGroup/SPIRV-Tools
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0a07cd1c9a
If the fuzzer's fact manager knows that ids A and B are synonymous, it can replace a use of A with a use of B, so long as various conditions hold (e.g. the definition of B must dominate the use of A, and it is not legal to replace a use of an OpConstant in a struct's access chain with a synonym that is not an OpConstant). This change adds a fuzzer pass to sprinke such synonym replacements through the module.
96 lines
4.3 KiB
C++
96 lines
4.3 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_add_dead_breaks.h"
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#include "source/fuzz/transformation_add_dead_break.h"
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#include "source/opt/ir_context.h"
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namespace spvtools {
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namespace fuzz {
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FuzzerPassAddDeadBreaks::FuzzerPassAddDeadBreaks(
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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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FuzzerPassAddDeadBreaks::~FuzzerPassAddDeadBreaks() = default;
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void FuzzerPassAddDeadBreaks::Apply() {
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// We first collect up lots of possibly-applicable transformations.
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std::vector<TransformationAddDeadBreak> candidate_transformations;
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// We consider each function separately.
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for (auto& function : *GetIRContext()->module()) {
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// For a given function, we find all the merge blocks in that function.
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std::vector<uint32_t> merge_block_ids;
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for (auto& block : function) {
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auto maybe_merge_id = block.MergeBlockIdIfAny();
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if (maybe_merge_id) {
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merge_block_ids.push_back(maybe_merge_id);
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}
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}
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// We rather aggressively consider the possibility of adding a break from
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// every block in the function to every merge block. Many of these will be
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// inapplicable as they would be illegal. That's OK - we later discard the
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// ones that turn out to be no good.
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for (auto& block : function) {
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for (auto merge_block_id : merge_block_ids) {
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// TODO(https://github.com/KhronosGroup/SPIRV-Tools/issues/2856): right
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// now we completely ignore OpPhi instructions at merge blocks. This
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// will lead to interesting opportunities being missed.
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auto candidate_transformation = TransformationAddDeadBreak(
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block.id(), merge_block_id, GetFuzzerContext()->ChooseEven(), {});
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if (candidate_transformation.IsApplicable(GetIRContext(),
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*GetFactManager())) {
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// Only consider a transformation as a candidate if it is applicable.
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candidate_transformations.push_back(
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std::move(candidate_transformation));
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}
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}
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}
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}
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// Go through the candidate transformations that were accumulated,
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// probabilistically deciding whether to consider each one further and
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// applying the still-applicable ones that are considered further.
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//
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// We iterate through the candidate transformations in a random order by
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// repeatedly removing a random candidate transformation from the sequence
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// until no candidate transformations remain. This is done because
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// transformations can potentially disable one another, so that iterating
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// through them in order would lead to a higher probability of
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// transformations appearing early in the sequence being applied compared
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// with later transformations.
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while (!candidate_transformations.empty()) {
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// Choose a random index into the sequence of remaining candidate
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// transformations.
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auto index = GetFuzzerContext()->RandomIndex(candidate_transformations);
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// Remove the transformation at the chosen index from the sequence.
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auto transformation = std::move(candidate_transformations[index]);
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candidate_transformations.erase(candidate_transformations.begin() + index);
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// Probabilistically decide whether to try to apply it vs. ignore it, in the
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// case that it is applicable.
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if (transformation.IsApplicable(GetIRContext(), *GetFactManager()) &&
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GetFuzzerContext()->ChoosePercentage(
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GetFuzzerContext()->GetChanceOfAddingDeadBreak())) {
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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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