instruction_simplifier.cc revision 0304e182adee81be32c744fd3c0d28add29974ff 
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 "instruction_simplifier.h"
18
19namespace art {
20
21class InstructionSimplifierVisitor : public HGraphVisitor {
22 public:
23  explicit InstructionSimplifierVisitor(HGraph* graph) : HGraphVisitor(graph) {}
24
25 private:
26  void VisitSuspendCheck(HSuspendCheck* check) OVERRIDE;
27  void VisitEqual(HEqual* equal) OVERRIDE;
28  void VisitArraySet(HArraySet* equal) OVERRIDE;
29  void VisitTypeConversion(HTypeConversion* instruction) OVERRIDE;
30  void VisitNullCheck(HNullCheck* instruction) OVERRIDE;
31  void VisitArrayLength(HArrayLength* instruction) OVERRIDE;
32};
33
34void InstructionSimplifier::Run() {
35  InstructionSimplifierVisitor visitor(graph_);
36  visitor.VisitInsertionOrder();
37}
38
39void InstructionSimplifierVisitor::VisitNullCheck(HNullCheck* null_check) {
40  HInstruction* obj = null_check->InputAt(0);
41  if (!obj->CanBeNull()) {
42    null_check->ReplaceWith(obj);
43    null_check->GetBlock()->RemoveInstruction(null_check);
44  }
45}
46
47void InstructionSimplifierVisitor::VisitSuspendCheck(HSuspendCheck* check) {
48  HBasicBlock* block = check->GetBlock();
49  // Currently always keep the suspend check at entry.
50  if (block->IsEntryBlock()) return;
51
52  // Currently always keep suspend checks at loop entry.
53  if (block->IsLoopHeader() && block->GetFirstInstruction() == check) {
54    DCHECK(block->GetLoopInformation()->GetSuspendCheck() == check);
55    return;
56  }
57
58  // Remove the suspend check that was added at build time for the baseline
59  // compiler.
60  block->RemoveInstruction(check);
61}
62
63void InstructionSimplifierVisitor::VisitEqual(HEqual* equal) {
64  HInstruction* input1 = equal->InputAt(0);
65  HInstruction* input2 = equal->InputAt(1);
66  if (input1->GetType() == Primitive::kPrimBoolean && input2->IsIntConstant()) {
67    if (input2->AsIntConstant()->GetValue() == 1) {
68      // Replace (bool_value == 1) with bool_value
69      equal->ReplaceWith(equal->InputAt(0));
70      equal->GetBlock()->RemoveInstruction(equal);
71    } else {
72      // We should replace (bool_value == 0) with !bool_value, but we unfortunately
73      // do not have such instruction.
74      DCHECK_EQ(input2->AsIntConstant()->GetValue(), 0);
75    }
76  }
77}
78
79void InstructionSimplifierVisitor::VisitArrayLength(HArrayLength* instruction) {
80  HInstruction* input = instruction->InputAt(0);
81  // If the array is a NewArray with constant size, replace the array length
82  // with the constant instruction. This helps the bounds check elimination phase.
83  if (input->IsNewArray()) {
84    input = input->InputAt(0);
85    if (input->IsIntConstant()) {
86      instruction->ReplaceWith(input);
87    }
88  }
89}
90
91void InstructionSimplifierVisitor::VisitArraySet(HArraySet* instruction) {
92  HInstruction* value = instruction->GetValue();
93  if (value->GetType() != Primitive::kPrimNot) return;
94
95  if (value->IsArrayGet()) {
96    if (value->AsArrayGet()->GetArray() == instruction->GetArray()) {
97      // If the code is just swapping elements in the array, no need for a type check.
98      instruction->ClearNeedsTypeCheck();
99    }
100  }
101}
102
103void InstructionSimplifierVisitor::VisitTypeConversion(HTypeConversion* instruction) {
104  if (instruction->GetResultType() == instruction->GetInputType()) {
105    // Remove the instruction if it's converting to the same type.
106    instruction->ReplaceWith(instruction->GetInput());
107    instruction->GetBlock()->RemoveInstruction(instruction);
108  }
109}
110
111}  // namespace art
112