Home | History | Annotate | Download | only in optimizing 
      1 /*
      2  * Copyright (C) 2016 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 /*
     18  * This optimization recognizes the common diamond selection pattern and
     19  * replaces it with an instance of the HSelect instruction.
     20  *
     21  * Recognized patterns:
     22  *
     23  *          If [ Condition ]
     24  *            /          \
     25  *      false branch  true branch
     26  *            \          /
     27  *     Phi [FalseValue, TrueValue]
     28  *
     29  * and
     30  *
     31  *             If [ Condition ]
     32  *               /          \
     33  *     false branch        true branch
     34  *     return FalseValue   return TrueValue
     35  *
     36  * The pattern will be simplified if `true_branch` and `false_branch` each
     37  * contain at most one instruction without any side effects.
     38  *
     39  * Blocks are merged into one and Select replaces the If and the Phi.
     40  *
     41  * For the first pattern it simplifies to:
     42  *
     43  *              true branch
     44  *              false branch
     45  *              Select [FalseValue, TrueValue, Condition]
     46  *
     47  * For the second pattern it simplifies to:
     48  *
     49  *              true branch
     50  *              false branch
     51  *              return Select [FalseValue, TrueValue, Condition]
     52  *
     53  * Note: In order to recognize no side-effect blocks, this optimization must be
     54  * run after the instruction simplifier has removed redundant suspend checks.
     55  */
     56 
     57 #ifndef ART_COMPILER_OPTIMIZING_SELECT_GENERATOR_H_
     58 #define ART_COMPILER_OPTIMIZING_SELECT_GENERATOR_H_
     59 
     60 #include "optimization.h"
     61 
     62 namespace art {
     63 
     64 class HSelectGenerator : public HOptimization {
     65  public:
     66   HSelectGenerator(HGraph* graph,
     67                    VariableSizedHandleScope* handles,
     68                    OptimizingCompilerStats* stats,
     69                    const char* name = kSelectGeneratorPassName);
     70 
     71   void Run() OVERRIDE;
     72 
     73   static constexpr const char* kSelectGeneratorPassName = "select_generator";
     74 
     75  private:
     76   VariableSizedHandleScope* handle_scope_;
     77   DISALLOW_COPY_AND_ASSIGN(HSelectGenerator);
     78 };
     79 
     80 }  // namespace art
     81 
     82 #endif  // ART_COMPILER_OPTIMIZING_SELECT_GENERATOR_H_
     83