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// Copyright (c) 2018 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.
#ifndef SOURCE_REDUCE_STRUCTURED_LOOP_TO_SELECTION_REDUCTION_OPPORTUNITY_H_
#define SOURCE_REDUCE_STRUCTURED_LOOP_TO_SELECTION_REDUCTION_OPPORTUNITY_H_
#include "source/opt/def_use_manager.h"
#include "source/opt/dominator_analysis.h"
#include "source/opt/function.h"
#include "source/reduce/reduction_opportunity.h"
namespace spvtools {
namespace reduce {
// An opportunity to replace a structured loop with a selection.
class StructuredLoopToSelectionReductionOpportunity
: public ReductionOpportunity {
public:
// Constructs an opportunity from a loop header block and the function that
// encloses it.
explicit StructuredLoopToSelectionReductionOpportunity(
opt::IRContext* context, opt::BasicBlock* loop_construct_header)
: context_(context), loop_construct_header_(loop_construct_header) {}
// Returns true if the loop header is reachable. A structured loop might
// become unreachable as a result of turning another structured loop into
// a selection.
bool PreconditionHolds() override;
protected:
void Apply() override;
private:
// Parameter |original_target_id| is the id of the loop's merge block or
// continue target. This method considers each edge of the form
// b->original_target_id and transforms it into an edge of the form b->c,
// where c is the merge block of the structured control flow construct that
// most tightly contains b.
void RedirectToClosestMergeBlock(uint32_t original_target_id);
// |source_id|, |original_target_id| and |new_target_id| are required to all
// be distinct, with a CFG edge existing from |source_id| to
// |original_target_id|, and |original_target_id| being either the merge block
// or continue target for the loop being operated on.
// The method removes this edge and adds an edge from
// |source_id| to |new_target_id|. It takes care of fixing up any OpPhi
// instructions associated with |original_target_id| and |new_target_id|.
void RedirectEdge(uint32_t source_id, uint32_t original_target_id,
uint32_t new_target_id);
// Adds components to |to_block|'s phi instructions to account for a new
// incoming edge from |from_id|.
void AdaptPhiInstructionsForAddedEdge(uint32_t from_id,
opt::BasicBlock* to_block);
// Turns the OpLoopMerge for the loop into OpSelectionMerge, and adapts the
// following branch instruction accordingly.
void ChangeLoopToSelection();
// Fixes any scenarios where, due to CFG changes, ids have uses not dominated
// by their definitions, by changing such uses to uses of OpUndef or of
// placeholder variables.
void FixNonDominatedIdUses();
// Returns true if and only if at least one of the following holds:
// 1) |def| dominates |use|
// 2) |def| is an OpVariable
// 3) |use| is part of an OpPhi, with associated incoming block b, and |def|
// dominates b.
bool DefinitionSufficientlyDominatesUse(opt::Instruction* def,
opt::Instruction* use,
uint32_t use_index,
opt::BasicBlock& def_block);
opt::IRContext* context_;
opt::BasicBlock* loop_construct_header_;
};
} // namespace reduce
} // namespace spvtools
#endif // SOURCE_REDUCE_STRUCTURED_LOOP_TO_SELECTION_REDUCTION_OPPORTUNITY_H_
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