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// Copyright (c) 2021 Alastair F. Donaldson
//
// 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/reduce/structured_construct_to_block_reduction_opportunity.h"
namespace spvtools {
namespace reduce {
bool StructuredConstructToBlockReductionOpportunity::PreconditionHolds() {
return context_->get_def_use_mgr()->GetDef(construct_header_) != nullptr;
}
void StructuredConstructToBlockReductionOpportunity::Apply() {
auto header_block = context_->cfg()->block(construct_header_);
auto merge_block = context_->cfg()->block(header_block->MergeBlockId());
auto* enclosing_function = header_block->GetParent();
// A region of blocks is defined in terms of dominators and post-dominators,
// so we compute these for the enclosing function.
auto* dominators = context_->GetDominatorAnalysis(enclosing_function);
auto* postdominators = context_->GetPostDominatorAnalysis(enclosing_function);
// For each block in the function, determine whether it is inside the region.
// If it is, delete it.
for (auto block_it = enclosing_function->begin();
block_it != enclosing_function->end();) {
if (header_block != &*block_it && merge_block != &*block_it &&
dominators->Dominates(header_block, &*block_it) &&
postdominators->Dominates(merge_block, &*block_it)) {
block_it = block_it.Erase();
} else {
++block_it;
}
}
// Having removed some blocks from the module it is necessary to invalidate
// analyses, since the remaining patch-up work depends on various analyses
// which will otherwise reference blocks that have been deleted.
context_->InvalidateAnalysesExceptFor(opt::IRContext::kAnalysisNone);
// We demote the header of the region to a regular block by deleting its merge
// instruction.
context_->KillInst(header_block->GetMergeInst());
// The terminator for the header block is changed to be an unconditional
// branch to the merge block.
header_block->terminator()->SetOpcode(spv::Op::OpBranch);
header_block->terminator()->SetInOperands(
{{SPV_OPERAND_TYPE_ID, {merge_block->id()}}});
// This is an intrusive change, so we invalidate all analyses.
context_->InvalidateAnalysesExceptFor(opt::IRContext::kAnalysisNone);
}
} // namespace reduce
} // namespace spvtools
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