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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 #include "x86_memory_gen.h"
     18 #include "code_generator.h"
     19 #include "driver/compiler_options.h"
     20 
     21 namespace art {
     22 namespace x86 {
     23 
     24 /**
     25  * Replace instructions with memory operand forms.
     26  */
     27 class MemoryOperandVisitor : public HGraphVisitor {
     28  public:
     29   MemoryOperandVisitor(HGraph* graph, bool do_implicit_null_checks)
     30       : HGraphVisitor(graph),
     31         do_implicit_null_checks_(do_implicit_null_checks) {}
     32 
     33  private:
     34   void VisitBoundsCheck(HBoundsCheck* check) OVERRIDE {
     35     // Replace the length by the array itself, so that we can do compares to memory.
     36     HArrayLength* array_len = check->InputAt(1)->AsArrayLength();
     37 
     38     // We only want to replace an ArrayLength.
     39     if (array_len == nullptr) {
     40       return;
     41     }
     42 
     43     HInstruction* array = array_len->InputAt(0);
     44     DCHECK_EQ(array->GetType(), DataType::Type::kReference);
     45 
     46     // Don't apply this optimization when the array is nullptr.
     47     if (array->IsConstant() || (array->IsNullCheck() && array->InputAt(0)->IsConstant())) {
     48       return;
     49     }
     50 
     51     // Is there a null check that could be an implicit check?
     52     if (array->IsNullCheck() && do_implicit_null_checks_) {
     53       // The ArrayLen may generate the implicit null check.  Can the
     54       // bounds check do so as well?
     55       if (array_len->GetNextDisregardingMoves() != check) {
     56         // No, it won't.  Leave as is.
     57         return;
     58       }
     59     }
     60 
     61     // Can we suppress the ArrayLength and generate at BoundCheck?
     62     if (array_len->HasOnlyOneNonEnvironmentUse()) {
     63       array_len->MarkEmittedAtUseSite();
     64       // We need the ArrayLength just before the BoundsCheck.
     65       array_len->MoveBefore(check);
     66     }
     67   }
     68 
     69   bool do_implicit_null_checks_;
     70 };
     71 
     72 X86MemoryOperandGeneration::X86MemoryOperandGeneration(HGraph* graph,
     73                                                        CodeGenerator* codegen,
     74                                                        OptimizingCompilerStats* stats)
     75     : HOptimization(graph, kX86MemoryOperandGenerationPassName, stats),
     76       do_implicit_null_checks_(codegen->GetCompilerOptions().GetImplicitNullChecks()) {
     77 }
     78 
     79 void X86MemoryOperandGeneration::Run() {
     80   MemoryOperandVisitor visitor(graph_, do_implicit_null_checks_);
     81   visitor.VisitInsertionOrder();
     82 }
     83 
     84 }  // namespace x86
     85 }  // namespace art
     86