Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 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->TrimInputCount(live_input_count); |
| 56 | NodeProperties::ChangeOp(node, common()->End(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 | NodeProperties::ChangeOp(node, op); |
| 141 | } |
| 142 | |
| 143 | } // namespace compiler |
| 144 | } // namespace internal |
| 145 | } // namespace v8 |