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/control-flow-optimizer.h" |
| 6 | |
| 7 | #include "src/compiler/common-operator.h" |
| 8 | #include "src/compiler/graph.h" |
| 9 | #include "src/compiler/node-matchers.h" |
| 10 | #include "src/compiler/node-properties.h" |
| 11 | |
| 12 | namespace v8 { |
| 13 | namespace internal { |
| 14 | namespace compiler { |
| 15 | |
| 16 | ControlFlowOptimizer::ControlFlowOptimizer(Graph* graph, |
| 17 | CommonOperatorBuilder* common, |
| 18 | MachineOperatorBuilder* machine, |
| 19 | Zone* zone) |
| 20 | : graph_(graph), |
| 21 | common_(common), |
| 22 | machine_(machine), |
| 23 | queue_(zone), |
| 24 | queued_(graph, 2), |
| 25 | zone_(zone) {} |
| 26 | |
| 27 | |
| 28 | void ControlFlowOptimizer::Optimize() { |
| 29 | Enqueue(graph()->start()); |
| 30 | while (!queue_.empty()) { |
| 31 | Node* node = queue_.front(); |
| 32 | queue_.pop(); |
| 33 | if (node->IsDead()) continue; |
| 34 | switch (node->opcode()) { |
| 35 | case IrOpcode::kBranch: |
| 36 | VisitBranch(node); |
| 37 | break; |
| 38 | default: |
| 39 | VisitNode(node); |
| 40 | break; |
| 41 | } |
| 42 | } |
| 43 | } |
| 44 | |
| 45 | |
| 46 | void ControlFlowOptimizer::Enqueue(Node* node) { |
| 47 | DCHECK_NOT_NULL(node); |
| 48 | if (node->IsDead() || queued_.Get(node)) return; |
| 49 | queued_.Set(node, true); |
| 50 | queue_.push(node); |
| 51 | } |
| 52 | |
| 53 | |
| 54 | void ControlFlowOptimizer::VisitNode(Node* node) { |
| 55 | for (Edge edge : node->use_edges()) { |
| 56 | if (NodeProperties::IsControlEdge(edge)) { |
| 57 | Enqueue(edge.from()); |
| 58 | } |
| 59 | } |
| 60 | } |
| 61 | |
| 62 | |
| 63 | void ControlFlowOptimizer::VisitBranch(Node* node) { |
| 64 | DCHECK_EQ(IrOpcode::kBranch, node->opcode()); |
| 65 | if (TryBuildSwitch(node)) return; |
| 66 | if (TryCloneBranch(node)) return; |
| 67 | VisitNode(node); |
| 68 | } |
| 69 | |
| 70 | |
| 71 | bool ControlFlowOptimizer::TryCloneBranch(Node* node) { |
| 72 | DCHECK_EQ(IrOpcode::kBranch, node->opcode()); |
| 73 | |
| 74 | // This optimization is a special case of (super)block cloning. It takes an |
| 75 | // input graph as shown below and clones the Branch node for every predecessor |
| 76 | // to the Merge, essentially removing the Merge completely. This avoids |
| 77 | // materializing the bit for the Phi and may offer potential for further |
| 78 | // branch folding optimizations (i.e. because one or more inputs to the Phi is |
| 79 | // a constant). Note that there may be more Phi nodes hanging off the Merge, |
| 80 | // but we can only a certain subset of them currently (actually only Phi and |
| 81 | // EffectPhi nodes whose uses have either the IfTrue or IfFalse as control |
| 82 | // input). |
| 83 | |
| 84 | // Control1 ... ControlN |
| 85 | // ^ ^ |
| 86 | // | | Cond1 ... CondN |
| 87 | // +----+ +----+ ^ ^ |
| 88 | // | | | | |
| 89 | // | | +----+ | |
| 90 | // Merge<--+ | +------------+ |
| 91 | // ^ \|/ |
| 92 | // | Phi |
| 93 | // | | |
| 94 | // Branch----+ |
| 95 | // ^ |
| 96 | // | |
| 97 | // +-----+-----+ |
| 98 | // | | |
| 99 | // IfTrue IfFalse |
| 100 | // ^ ^ |
| 101 | // | | |
| 102 | |
| 103 | // The resulting graph (modulo the Phi and EffectPhi nodes) looks like this: |
| 104 | |
| 105 | // Control1 Cond1 ... ControlN CondN |
| 106 | // ^ ^ ^ ^ |
| 107 | // \ / \ / |
| 108 | // Branch ... Branch |
| 109 | // ^ ^ |
| 110 | // | | |
| 111 | // +---+---+ +---+----+ |
| 112 | // | | | | |
| 113 | // IfTrue IfFalse ... IfTrue IfFalse |
| 114 | // ^ ^ ^ ^ |
| 115 | // | | | | |
| 116 | // +--+ +-------------+ | |
| 117 | // | | +--------------+ +--+ |
| 118 | // | | | | |
| 119 | // Merge Merge |
| 120 | // ^ ^ |
| 121 | // | | |
| 122 | |
| 123 | Node* branch = node; |
| 124 | Node* cond = NodeProperties::GetValueInput(branch, 0); |
| 125 | if (!cond->OwnedBy(branch) || cond->opcode() != IrOpcode::kPhi) return false; |
| 126 | Node* merge = NodeProperties::GetControlInput(branch); |
| 127 | if (merge->opcode() != IrOpcode::kMerge || |
| 128 | NodeProperties::GetControlInput(cond) != merge) { |
| 129 | return false; |
| 130 | } |
| 131 | // Grab the IfTrue/IfFalse projections of the Branch. |
| 132 | BranchMatcher matcher(branch); |
| 133 | // Check/collect other Phi/EffectPhi nodes hanging off the Merge. |
| 134 | NodeVector phis(zone()); |
| 135 | for (Node* const use : merge->uses()) { |
| 136 | if (use == branch || use == cond) continue; |
| 137 | // We cannot currently deal with non-Phi/EffectPhi nodes hanging off the |
| 138 | // Merge. Ideally, we would just clone the nodes (and everything that |
| 139 | // depends on it to some distant join point), but that requires knowledge |
| 140 | // about dominance/post-dominance. |
| 141 | if (!NodeProperties::IsPhi(use)) return false; |
| 142 | for (Edge edge : use->use_edges()) { |
| 143 | // Right now we can only handle Phi/EffectPhi nodes whose uses are |
| 144 | // directly control-dependend on either the IfTrue or the IfFalse |
| 145 | // successor, because we know exactly how to update those uses. |
| 146 | // TODO(turbofan): Generalize this to all Phi/EffectPhi nodes using |
| 147 | // dominance/post-dominance on the sea of nodes. |
| 148 | if (edge.from()->op()->ControlInputCount() != 1) return false; |
| 149 | Node* control = NodeProperties::GetControlInput(edge.from()); |
| 150 | if (NodeProperties::IsPhi(edge.from())) { |
| 151 | control = NodeProperties::GetControlInput(control, edge.index()); |
| 152 | } |
| 153 | if (control != matcher.IfTrue() && control != matcher.IfFalse()) |
| 154 | return false; |
| 155 | } |
| 156 | phis.push_back(use); |
| 157 | } |
| 158 | BranchHint const hint = BranchHintOf(branch->op()); |
| 159 | int const input_count = merge->op()->ControlInputCount(); |
| 160 | DCHECK_LE(1, input_count); |
| 161 | Node** const inputs = zone()->NewArray<Node*>(2 * input_count); |
| 162 | Node** const merge_true_inputs = &inputs[0]; |
| 163 | Node** const merge_false_inputs = &inputs[input_count]; |
| 164 | for (int index = 0; index < input_count; ++index) { |
| 165 | Node* cond1 = NodeProperties::GetValueInput(cond, index); |
| 166 | Node* control1 = NodeProperties::GetControlInput(merge, index); |
| 167 | Node* branch1 = graph()->NewNode(common()->Branch(hint), cond1, control1); |
| 168 | merge_true_inputs[index] = graph()->NewNode(common()->IfTrue(), branch1); |
| 169 | merge_false_inputs[index] = graph()->NewNode(common()->IfFalse(), branch1); |
| 170 | Enqueue(branch1); |
| 171 | } |
| 172 | Node* const merge_true = graph()->NewNode(common()->Merge(input_count), |
| 173 | input_count, merge_true_inputs); |
| 174 | Node* const merge_false = graph()->NewNode(common()->Merge(input_count), |
| 175 | input_count, merge_false_inputs); |
| 176 | for (Node* const phi : phis) { |
| 177 | for (int index = 0; index < input_count; ++index) { |
| 178 | inputs[index] = phi->InputAt(index); |
| 179 | } |
| 180 | inputs[input_count] = merge_true; |
| 181 | Node* phi_true = graph()->NewNode(phi->op(), input_count + 1, inputs); |
| 182 | inputs[input_count] = merge_false; |
| 183 | Node* phi_false = graph()->NewNode(phi->op(), input_count + 1, inputs); |
| 184 | for (Edge edge : phi->use_edges()) { |
| 185 | Node* control = NodeProperties::GetControlInput(edge.from()); |
| 186 | if (NodeProperties::IsPhi(edge.from())) { |
| 187 | control = NodeProperties::GetControlInput(control, edge.index()); |
| 188 | } |
| 189 | DCHECK(control == matcher.IfTrue() || control == matcher.IfFalse()); |
| 190 | edge.UpdateTo((control == matcher.IfTrue()) ? phi_true : phi_false); |
| 191 | } |
| 192 | phi->Kill(); |
| 193 | } |
| 194 | // Fix up IfTrue and IfFalse and kill all dead nodes. |
| 195 | matcher.IfFalse()->ReplaceUses(merge_false); |
| 196 | matcher.IfTrue()->ReplaceUses(merge_true); |
| 197 | matcher.IfFalse()->Kill(); |
| 198 | matcher.IfTrue()->Kill(); |
| 199 | branch->Kill(); |
| 200 | cond->Kill(); |
| 201 | merge->Kill(); |
| 202 | return true; |
| 203 | } |
| 204 | |
| 205 | |
| 206 | bool ControlFlowOptimizer::TryBuildSwitch(Node* node) { |
| 207 | DCHECK_EQ(IrOpcode::kBranch, node->opcode()); |
| 208 | |
| 209 | Node* branch = node; |
| 210 | if (BranchHintOf(branch->op()) != BranchHint::kNone) return false; |
| 211 | Node* cond = NodeProperties::GetValueInput(branch, 0); |
| 212 | if (cond->opcode() != IrOpcode::kWord32Equal) return false; |
| 213 | Int32BinopMatcher m(cond); |
| 214 | Node* index = m.left().node(); |
| 215 | if (!m.right().HasValue()) return false; |
| 216 | int32_t value = m.right().Value(); |
| 217 | ZoneSet<int32_t> values(zone()); |
| 218 | values.insert(value); |
| 219 | |
| 220 | Node* if_false; |
| 221 | Node* if_true; |
| 222 | while (true) { |
| 223 | BranchMatcher matcher(branch); |
| 224 | DCHECK(matcher.Matched()); |
| 225 | |
| 226 | if_true = matcher.IfTrue(); |
| 227 | if_false = matcher.IfFalse(); |
| 228 | |
| 229 | auto it = if_false->uses().begin(); |
| 230 | if (it == if_false->uses().end()) break; |
| 231 | Node* branch1 = *it++; |
| 232 | if (branch1->opcode() != IrOpcode::kBranch) break; |
| 233 | if (BranchHintOf(branch1->op()) != BranchHint::kNone) break; |
| 234 | if (it != if_false->uses().end()) break; |
| 235 | Node* cond1 = branch1->InputAt(0); |
| 236 | if (cond1->opcode() != IrOpcode::kWord32Equal) break; |
| 237 | Int32BinopMatcher m1(cond1); |
| 238 | if (m1.left().node() != index) break; |
| 239 | if (!m1.right().HasValue()) break; |
| 240 | int32_t value1 = m1.right().Value(); |
| 241 | if (values.find(value1) != values.end()) break; |
| 242 | DCHECK_NE(value, value1); |
| 243 | |
| 244 | if (branch != node) { |
| 245 | branch->NullAllInputs(); |
| 246 | if_true->ReplaceInput(0, node); |
| 247 | } |
| 248 | NodeProperties::ChangeOp(if_true, common()->IfValue(value)); |
| 249 | if_false->NullAllInputs(); |
| 250 | Enqueue(if_true); |
| 251 | |
| 252 | branch = branch1; |
| 253 | value = value1; |
| 254 | values.insert(value); |
| 255 | } |
| 256 | |
| 257 | DCHECK_EQ(IrOpcode::kBranch, node->opcode()); |
| 258 | DCHECK_EQ(IrOpcode::kBranch, branch->opcode()); |
| 259 | if (branch == node) { |
| 260 | DCHECK_EQ(1u, values.size()); |
| 261 | return false; |
| 262 | } |
| 263 | DCHECK_LT(1u, values.size()); |
| 264 | node->ReplaceInput(0, index); |
| 265 | NodeProperties::ChangeOp(node, common()->Switch(values.size() + 1)); |
| 266 | if_true->ReplaceInput(0, node); |
| 267 | NodeProperties::ChangeOp(if_true, common()->IfValue(value)); |
| 268 | Enqueue(if_true); |
| 269 | if_false->ReplaceInput(0, node); |
| 270 | NodeProperties::ChangeOp(if_false, common()->IfDefault()); |
| 271 | Enqueue(if_false); |
| 272 | branch->NullAllInputs(); |
| 273 | return true; |
| 274 | } |
| 275 | |
| 276 | } // namespace compiler |
| 277 | } // namespace internal |
| 278 | } // namespace v8 |