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efde682369
Fixes #2695. Allowing unreachable blocks to be moved can lead to an unreachable block A getting placed after an unreachable successor B, which is a problem if B uses ids that A generates.
110 lines
4.2 KiB
C++
110 lines
4.2 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/transformation_move_block_down.h"
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#include "source/opt/basic_block.h"
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namespace spvtools {
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namespace fuzz {
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TransformationMoveBlockDown::TransformationMoveBlockDown(
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const spvtools::fuzz::protobufs::TransformationMoveBlockDown& message)
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: message_(message) {}
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TransformationMoveBlockDown::TransformationMoveBlockDown(uint32_t id) {
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message_.set_block_id(id);
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}
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bool TransformationMoveBlockDown::IsApplicable(
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opt::IRContext* context, const FactManager& /*unused*/) const {
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// Go through every block in every function, looking for a block whose id
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// matches that of the block we want to consider moving down.
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for (auto& function : *context->module()) {
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for (auto block_it = function.begin(); block_it != function.end();
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++block_it) {
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if (block_it->id() == message_.block_id()) {
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// We have found a match.
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if (block_it == function.begin()) {
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// The block is the first one appearing in the function. We are not
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// allowed to move this block down.
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return false;
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}
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// Record the block we would like to consider moving down.
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opt::BasicBlock* block_matching_id = &*block_it;
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if (!context->GetDominatorAnalysis(&function)->IsReachable(
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block_matching_id)) {
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// The block is not reachable. We are not allowed to move it down.
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return false;
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}
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// Now see whether there is some block following that block in program
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// order.
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++block_it;
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if (block_it == function.end()) {
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// There is no such block; i.e., the block we are considering moving
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// is the last one in the function. The transformation thus does not
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// apply.
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return false;
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}
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opt::BasicBlock* next_block_in_program_order = &*block_it;
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// We can move the block of interest down if and only if it does not
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// dominate the block that comes next.
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return !context->GetDominatorAnalysis(&function)->Dominates(
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block_matching_id, next_block_in_program_order);
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}
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}
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}
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// We did not find a matching block, so the transformation is not applicable:
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// there is no relevant block to move.
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return false;
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}
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void TransformationMoveBlockDown::Apply(opt::IRContext* context,
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FactManager* /*unused*/) const {
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// Go through every block in every function, looking for a block whose id
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// matches that of the block we want to move down.
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for (auto& function : *context->module()) {
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for (auto block_it = function.begin(); block_it != function.end();
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++block_it) {
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if (block_it->id() == message_.block_id()) {
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++block_it;
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assert(block_it != function.end() &&
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"To be able to move a block down, it needs to have a "
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"program-order successor.");
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function.MoveBasicBlockToAfter(message_.block_id(), &*block_it);
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// It is prudent to invalidate analyses after changing block ordering in
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// case any of them depend on it, but the ones that definitely do not
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// depend on ordering can be preserved. These include the following,
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// which can likely be extended.
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context->InvalidateAnalysesExceptFor(
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opt::IRContext::Analysis::kAnalysisDefUse |
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opt::IRContext::Analysis::kAnalysisDominatorAnalysis);
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return;
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}
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}
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}
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assert(false && "No block was found to move down.");
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}
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protobufs::Transformation TransformationMoveBlockDown::ToMessage() const {
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protobufs::Transformation result;
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*result.mutable_move_block_down() = message_;
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return result;
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}
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} // namespace fuzz
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} // namespace spvtools
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