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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_permute_blocks.h"
#include "source/fuzz/transformation_move_block_down.h"
namespace spvtools {
namespace fuzz {
FuzzerPassPermuteBlocks::FuzzerPassPermuteBlocks(
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 FuzzerPassPermuteBlocks::Apply() {
// For now we do something very simple: we randomly decide whether to move a
// block, and for each block that we do move, we push it down as far as we
// legally can.
// TODO(https://github.com/KhronosGroup/SPIRV-Tools/issues/2635): it would be
// nice to randomly sample from the set of legal block permutations and then
// encode the chosen permutation via a series of move-block-down
// transformations. This should be possible but will require some thought.
for (auto& function : *GetIRContext()->module()) {
std::vector<uint32_t> block_ids;
// Collect all block ids for the function before messing with block
// ordering.
for (auto& block : function) {
block_ids.push_back(block.id());
}
// Now consider each block id. We consider block ids in reverse, because
// e.g. in code generated from the following:
//
// if (...) {
// A
// B
// } else {
// C
// }
//
// block A cannot be moved down, but B has freedom to move and that movement
// would provide more freedom for A to move.
for (auto id = block_ids.rbegin(); id != block_ids.rend(); ++id) {
// Randomly decide whether to ignore the block id.
if (!GetFuzzerContext()->ChoosePercentage(
GetFuzzerContext()->GetChanceOfMovingBlockDown())) {
continue;
}
// Keep pushing the block down, until pushing down fails.
// The loop is guaranteed to terminate because a block cannot be pushed
// down indefinitely.
while (true) {
TransformationMoveBlockDown transformation(*id);
if (!MaybeApplyTransformation(transformation)) {
break;
}
}
}
}
}
} // namespace fuzz
} // namespace spvtools
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