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| 1 // Copyright 2015 the V8 project authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. |
| 4 |
| 5 #include "src/compiler/dead-code-elimination.h" |
| 6 |
| 7 #include "src/compiler/common-operator.h" |
| 8 #include "src/compiler/graph.h" |
| 9 #include "src/compiler/node-properties.h" |
| 10 #include "src/compiler/operator-properties.h" |
| 11 |
| 12 namespace v8 { |
| 13 namespace internal { |
| 14 namespace compiler { |
| 15 |
| 16 DeadCodeElimination::DeadCodeElimination(Editor* editor, Graph* graph, |
| 17 CommonOperatorBuilder* common) |
| 18 : AdvancedReducer(editor), |
| 19 graph_(graph), |
| 20 common_(common), |
| 21 dead_(graph->NewNode(common->Dead())) {} |
| 22 |
| 23 |
| 24 Reduction DeadCodeElimination::Reduce(Node* node) { |
| 25 switch (node->opcode()) { |
| 26 case IrOpcode::kEnd: |
| 27 return ReduceEnd(node); |
| 28 case IrOpcode::kLoop: |
| 29 case IrOpcode::kMerge: |
| 30 return ReduceLoopOrMerge(node); |
| 31 default: |
| 32 return ReduceNode(node); |
| 33 } |
| 34 UNREACHABLE(); |
| 35 return NoChange(); |
| 36 } |
| 37 |
| 38 |
| 39 Reduction DeadCodeElimination::ReduceEnd(Node* node) { |
| 40 DCHECK_EQ(IrOpcode::kEnd, node->opcode()); |
| 41 int const input_count = node->InputCount(); |
| 42 DCHECK_LE(1, input_count); |
| 43 int live_input_count = 0; |
| 44 for (int i = 0; i < input_count; ++i) { |
| 45 Node* const input = node->InputAt(i); |
| 46 // Skip dead inputs. |
| 47 if (input->opcode() == IrOpcode::kDead) continue; |
| 48 // Compact live inputs. |
| 49 if (i != live_input_count) node->ReplaceInput(live_input_count, input); |
| 50 ++live_input_count; |
| 51 } |
| 52 if (live_input_count == 0) { |
| 53 return Replace(dead()); |
| 54 } else if (live_input_count < input_count) { |
| 55 node->set_op(common()->End(live_input_count)); |
| 56 node->TrimInputCount(live_input_count); |
| 57 return Changed(node); |
| 58 } |
| 59 DCHECK_EQ(input_count, live_input_count); |
| 60 return NoChange(); |
| 61 } |
| 62 |
| 63 |
| 64 Reduction DeadCodeElimination::ReduceLoopOrMerge(Node* node) { |
| 65 DCHECK(IrOpcode::IsMergeOpcode(node->opcode())); |
| 66 int const input_count = node->InputCount(); |
| 67 DCHECK_LE(1, input_count); |
| 68 // Count the number of live inputs to {node} and compact them on the fly, also |
| 69 // compacting the inputs of the associated {Phi} and {EffectPhi} uses at the |
| 70 // same time. We consider {Loop}s dead even if only the first control input |
| 71 // is dead. |
| 72 int live_input_count = 0; |
| 73 if (node->opcode() != IrOpcode::kLoop || |
| 74 node->InputAt(0)->opcode() != IrOpcode::kDead) { |
| 75 for (int i = 0; i < input_count; ++i) { |
| 76 Node* const input = node->InputAt(i); |
| 77 // Skip dead inputs. |
| 78 if (input->opcode() == IrOpcode::kDead) continue; |
| 79 // Compact live inputs. |
| 80 if (live_input_count != i) { |
| 81 node->ReplaceInput(live_input_count, input); |
| 82 for (Node* const use : node->uses()) { |
| 83 if (NodeProperties::IsPhi(use)) { |
| 84 DCHECK_EQ(input_count + 1, use->InputCount()); |
| 85 use->ReplaceInput(live_input_count, use->InputAt(i)); |
| 86 } |
| 87 } |
| 88 } |
| 89 ++live_input_count; |
| 90 } |
| 91 } |
| 92 if (live_input_count == 0) { |
| 93 return Replace(dead()); |
| 94 } else if (live_input_count == 1) { |
| 95 // Due to compaction above, the live input is at offset 0. |
| 96 for (Node* const use : node->uses()) { |
| 97 if (NodeProperties::IsPhi(use)) { |
| 98 Replace(use, use->InputAt(0)); |
| 99 } else if (use->opcode() == IrOpcode::kTerminate) { |
| 100 DCHECK_EQ(IrOpcode::kLoop, node->opcode()); |
| 101 Replace(use, dead()); |
| 102 } |
| 103 } |
| 104 return Replace(node->InputAt(0)); |
| 105 } |
| 106 DCHECK_LE(2, live_input_count); |
| 107 DCHECK_LE(live_input_count, input_count); |
| 108 // Trim input count for the {Merge} or {Loop} node. |
| 109 if (live_input_count < input_count) { |
| 110 // Trim input counts for all phi uses and revisit them. |
| 111 for (Node* const use : node->uses()) { |
| 112 if (NodeProperties::IsPhi(use)) { |
| 113 use->ReplaceInput(live_input_count, node); |
| 114 TrimMergeOrPhi(use, live_input_count); |
| 115 Revisit(use); |
| 116 } |
| 117 } |
| 118 TrimMergeOrPhi(node, live_input_count); |
| 119 return Changed(node); |
| 120 } |
| 121 return NoChange(); |
| 122 } |
| 123 |
| 124 |
| 125 Reduction DeadCodeElimination::ReduceNode(Node* node) { |
| 126 // If {node} has exactly one control input and this is {Dead}, |
| 127 // replace {node} with {Dead}. |
| 128 int const control_input_count = node->op()->ControlInputCount(); |
| 129 if (control_input_count == 0) return NoChange(); |
| 130 DCHECK_EQ(1, control_input_count); |
| 131 Node* control = NodeProperties::GetControlInput(node); |
| 132 if (control->opcode() == IrOpcode::kDead) return Replace(control); |
| 133 return NoChange(); |
| 134 } |
| 135 |
| 136 |
| 137 void DeadCodeElimination::TrimMergeOrPhi(Node* node, int size) { |
| 138 const Operator* const op = common()->ResizeMergeOrPhi(node->op(), size); |
| 139 node->TrimInputCount(OperatorProperties::GetTotalInputCount(op)); |
| 140 node->set_op(op); |
| 141 } |
| 142 |
| 143 } // namespace compiler |
| 144 } // namespace internal |
| 145 } // namespace v8 |
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