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      1 /*
      2  * Copyright (C) 2014 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 #include "side_effects_analysis.h"
     18 
     19 namespace art {
     20 
     21 void SideEffectsAnalysis::Run() {
     22   // Inlining might have created more blocks, so we need to increase the size
     23   // if needed.
     24   block_effects_.resize(graph_->GetBlocks().size());
     25   loop_effects_.resize(graph_->GetBlocks().size());
     26 
     27   // In DEBUG mode, ensure side effects are properly initialized to empty.
     28   if (kIsDebugBuild) {
     29     for (HBasicBlock* block : graph_->GetReversePostOrder()) {
     30       SideEffects effects = GetBlockEffects(block);
     31       DCHECK(effects.DoesNothing());
     32       if (block->IsLoopHeader()) {
     33         effects = GetLoopEffects(block);
     34         DCHECK(effects.DoesNothing());
     35       }
     36     }
     37   }
     38 
     39   // Do a post order visit to ensure we visit a loop header after its loop body.
     40   for (HBasicBlock* block : graph_->GetPostOrder()) {
     41     SideEffects effects = SideEffects::None();
     42     // Update `effects` with the side effects of all instructions in this block.
     43     for (HInstructionIterator inst_it(block->GetInstructions()); !inst_it.Done();
     44          inst_it.Advance()) {
     45       HInstruction* instruction = inst_it.Current();
     46       effects = effects.Union(instruction->GetSideEffects());
     47       // If all side effects are represented, scanning further will not add any
     48       // more information to side-effects of this block.
     49       if (effects.DoesAll()) {
     50         break;
     51       }
     52     }
     53 
     54     block_effects_[block->GetBlockId()] = effects;
     55 
     56     if (block->IsLoopHeader()) {
     57       // The side effects of the loop header are part of the loop.
     58       UpdateLoopEffects(block->GetLoopInformation(), effects);
     59       HBasicBlock* pre_header = block->GetLoopInformation()->GetPreHeader();
     60       if (pre_header->IsInLoop()) {
     61         // Update the side effects of the outer loop with the side effects of the inner loop.
     62         // Note that this works because we know all the blocks of the inner loop are visited
     63         // before the loop header of the outer loop.
     64         UpdateLoopEffects(pre_header->GetLoopInformation(), GetLoopEffects(block));
     65       }
     66     } else if (block->IsInLoop()) {
     67       // Update the side effects of the loop with the side effects of this block.
     68       UpdateLoopEffects(block->GetLoopInformation(), effects);
     69     }
     70   }
     71   has_run_ = true;
     72 }
     73 
     74 SideEffects SideEffectsAnalysis::GetLoopEffects(HBasicBlock* block) const {
     75   DCHECK(block->IsLoopHeader());
     76   return loop_effects_[block->GetBlockId()];
     77 }
     78 
     79 SideEffects SideEffectsAnalysis::GetBlockEffects(HBasicBlock* block) const {
     80   return block_effects_[block->GetBlockId()];
     81 }
     82 
     83 void SideEffectsAnalysis::UpdateLoopEffects(HLoopInformation* info, SideEffects effects) {
     84   uint32_t id = info->GetHeader()->GetBlockId();
     85   loop_effects_[id] = loop_effects_[id].Union(effects);
     86 }
     87 
     88 }  // namespace art
     89