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      1 /*
      2  * Copyright (C) 2015 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 #ifndef ART_COMPILER_OPTIMIZING_COMMON_DOMINATOR_H_
     18 #define ART_COMPILER_OPTIMIZING_COMMON_DOMINATOR_H_
     19 
     20 #include "nodes.h"
     21 
     22 namespace art {
     23 
     24 // Helper class for finding common dominators of two or more blocks in a graph.
     25 // The domination information of a graph must not be modified while there is
     26 // a CommonDominator object as it's internal state could become invalid.
     27 class CommonDominator {
     28  public:
     29   // Convenience function to find the common dominator of 2 blocks.
     30   static HBasicBlock* ForPair(HBasicBlock* block1, HBasicBlock* block2) {
     31     CommonDominator finder(block1);
     32     finder.Update(block2);
     33     return finder.Get();
     34   }
     35 
     36   // Create a finder starting with a given block.
     37   explicit CommonDominator(HBasicBlock* block)
     38       : dominator_(block), chain_length_(ChainLength(block)) {
     39     DCHECK(block != nullptr);
     40   }
     41 
     42   // Update the common dominator with another block.
     43   void Update(HBasicBlock* block) {
     44     DCHECK(block != nullptr);
     45     HBasicBlock* block2 = dominator_;
     46     DCHECK(block2 != nullptr);
     47     if (block == block2) {
     48       return;
     49     }
     50     size_t chain_length = ChainLength(block);
     51     size_t chain_length2 = chain_length_;
     52     // Equalize the chain lengths
     53     for ( ; chain_length > chain_length2; --chain_length) {
     54       block = block->GetDominator();
     55       DCHECK(block != nullptr);
     56     }
     57     for ( ; chain_length2 > chain_length; --chain_length2) {
     58       block2 = block2->GetDominator();
     59       DCHECK(block2 != nullptr);
     60     }
     61     // Now run up the chain until we hit the common dominator.
     62     while (block != block2) {
     63       --chain_length;
     64       block = block->GetDominator();
     65       DCHECK(block != nullptr);
     66       block2 = block2->GetDominator();
     67       DCHECK(block2 != nullptr);
     68     }
     69     dominator_ = block;
     70     chain_length_ = chain_length;
     71   }
     72 
     73   HBasicBlock* Get() const {
     74     return dominator_;
     75   }
     76 
     77  private:
     78   static size_t ChainLength(HBasicBlock* block) {
     79     size_t result = 0;
     80     while (block != nullptr) {
     81       ++result;
     82       block = block->GetDominator();
     83     }
     84     return result;
     85   }
     86 
     87   HBasicBlock* dominator_;
     88   size_t chain_length_;
     89 };
     90 
     91 }  // namespace art
     92 
     93 #endif  // ART_COMPILER_OPTIMIZING_COMMON_DOMINATOR_H_
     94