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/*
* Copyright (C) 2016 The Android Open Source Project
*
* 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.
*/
/*
* This optimization recognizes the common diamond selection pattern and
* replaces it with an instance of the HSelect instruction.
*
* Recognized patterns:
*
* If [ Condition ]
* / \
* false branch true branch
* \ /
* Phi [FalseValue, TrueValue]
*
* and
*
* If [ Condition ]
* / \
* false branch true branch
* return FalseValue return TrueValue
*
* The pattern will be simplified if `true_branch` and `false_branch` each
* contain at most one instruction without any side effects.
*
* Blocks are merged into one and Select replaces the If and the Phi.
*
* For the first pattern it simplifies to:
*
* true branch
* false branch
* Select [FalseValue, TrueValue, Condition]
*
* For the second pattern it simplifies to:
*
* true branch
* false branch
* return Select [FalseValue, TrueValue, Condition]
*
* Note: In order to recognize no side-effect blocks, this optimization must be
* run after the instruction simplifier has removed redundant suspend checks.
*/
#ifndef ART_COMPILER_OPTIMIZING_SELECT_GENERATOR_H_
#define ART_COMPILER_OPTIMIZING_SELECT_GENERATOR_H_
#include "base/macros.h"
#include "base/scoped_arena_containers.h"
#include "optimization.h"
#include "optimizing/nodes.h"
namespace art HIDDEN {
class HSelectGenerator : public HOptimization {
public:
HSelectGenerator(HGraph* graph,
OptimizingCompilerStats* stats,
const char* name = kSelectGeneratorPassName);
bool Run() override;
static constexpr const char* kSelectGeneratorPassName = "select_generator";
private:
bool TryGenerateSelectSimpleDiamondPattern(HBasicBlock* block,
ScopedArenaSafeMap<HInstruction*, HSelect*>* cache);
// When generating code for nested ternary operators (e.g. `return (x > 100) ? 100 : ((x < -100) ?
// -100 : x);`), a dexer can generate a double diamond pattern but it is not a clear cut one due
// to the merging of the blocks. `TryFixupDoubleDiamondPattern` recognizes that pattern and fixes
// up the graph to have a clean double diamond that `TryGenerateSelectSimpleDiamondPattern` can
// use to generate selects.
//
// In ASCII, it turns:
//
// 1 (outer if)
// / \
// 2 3 (inner if)
// | / \
// | 4 5
// \/ |
// 6 |
// \ |
// 7
// |
// 8
// into:
// 1 (outer if)
// / \
// 2 3 (inner if)
// | / \
// | 4 5
// \/ /
// 6
// |
// 8
//
// In short, block 7 disappears and we merge 6 and 7. Now we have a diamond with {3,4,5,6}, and
// when that gets resolved we get another one with the outer if.
HBasicBlock* TryFixupDoubleDiamondPattern(HBasicBlock* block);
DISALLOW_COPY_AND_ASSIGN(HSelectGenerator);
};
} // namespace art
#endif // ART_COMPILER_OPTIMIZING_SELECT_GENERATOR_H_
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