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Issue 141653009: Check elimination improvement: propagation of state through phis is supported, CheckMap narrowing i… (Closed) Base URL: https://v8.googlecode.com/svn/branches/bleeding_edge
Patch Set: Created 6 years, 11 months ago
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1 // Copyright 2013 the V8 project authors. All rights reserved. 1 // Copyright 2013 the V8 project authors. All rights reserved.
2 // Redistribution and use in source and binary forms, with or without 2 // Redistribution and use in source and binary forms, with or without
3 // modification, are permitted provided that the following conditions are 3 // modification, are permitted provided that the following conditions are
4 // met: 4 // met:
5 // 5 //
6 // * Redistributions of source code must retain the above copyright 6 // * Redistributions of source code must retain the above copyright
7 // notice, this list of conditions and the following disclaimer. 7 // notice, this list of conditions and the following disclaimer.
8 // * Redistributions in binary form must reproduce the above 8 // * Redistributions in binary form must reproduce the above
9 // copyright notice, this list of conditions and the following 9 // copyright notice, this list of conditions and the following
10 // disclaimer in the documentation and/or other materials provided 10 // disclaimer in the documentation and/or other materials provided
(...skipping 99 matching lines...) Expand 10 before | Expand all | Expand 10 after
110 } 110 }
111 // Improvements possible: 111 // Improvements possible:
112 // - eliminate redundant HCheckSmi, HCheckInstanceType instructions 112 // - eliminate redundant HCheckSmi, HCheckInstanceType instructions
113 // - track which values have been HCheckHeapObject'd 113 // - track which values have been HCheckHeapObject'd
114 } 114 }
115 115
116 return this; 116 return this;
117 } 117 }
118 118
119 // Global analysis: Copy state to successor block. 119 // Global analysis: Copy state to successor block.
120 HCheckTable* Copy(HBasicBlock* succ, Zone* zone) { 120 HCheckTable* Copy(HBasicBlock* succ, HBasicBlock* from_block, Zone* zone) {
121 HCheckTable* copy = new(phase_->zone()) HCheckTable(phase_); 121 HCheckTable* copy = new(phase_->zone()) HCheckTable(phase_);
122 for (int i = 0; i < size_; i++) { 122 for (int i = 0; i < size_; i++) {
123 HCheckTableEntry* old_entry = &entries_[i]; 123 HCheckTableEntry* old_entry = &entries_[i];
124 HCheckTableEntry* new_entry = &copy->entries_[i]; 124 HCheckTableEntry* new_entry = &copy->entries_[i];
125 // TODO(titzer): keep the check if this block dominates the successor? 125 // TODO(titzer): keep the check if this block dominates the successor?
126 new_entry->object_ = old_entry->object_; 126 new_entry->object_ = old_entry->object_;
127 new_entry->check_ = NULL; 127 new_entry->check_ = NULL;
128 new_entry->maps_ = old_entry->maps_->Copy(phase_->zone()); 128 new_entry->maps_ = old_entry->maps_->Copy(phase_->zone());
129 } 129 }
130 copy->cursor_ = cursor_; 130 copy->cursor_ = cursor_;
131 copy->size_ = size_; 131 copy->size_ = size_;
132 132
133 copy->InheritPhiOperands(succ, this, from_block, COPY, zone);
134
133 // Branch-sensitive analysis for certain comparisons may add more facts 135 // Branch-sensitive analysis for certain comparisons may add more facts
134 // to the state for the successor on the true branch. 136 // to the state for the successor on the true branch.
137 bool learned = false;
135 HControlInstruction* end = succ->predecessors()->at(0)->end(); 138 HControlInstruction* end = succ->predecessors()->at(0)->end();
136 if (succ->predecessors()->length() == 1 && end->SuccessorAt(0) == succ) { 139 if (succ->predecessors()->length() == 1 && end->SuccessorAt(0) == succ) {
137 if (end->IsCompareMap()) { 140 if (end->IsCompareMap()) {
138 // Learn on the true branch of if(CompareMap(x)). 141 // Learn on the true branch of if(CompareMap(x)).
139 HCompareMap* cmp = HCompareMap::cast(end); 142 HCompareMap* cmp = HCompareMap::cast(end);
140 HValue* object = cmp->value()->ActualValue(); 143 HValue* object = cmp->value()->ActualValue();
141 HCheckTableEntry* entry = copy->Find(object); 144 HCheckTableEntry* entry = copy->Find(object);
142 if (entry == NULL) { 145 if (entry == NULL) {
143 copy->Insert(object, cmp->map()); 146 copy->Insert(object, cmp->map());
144 } else { 147 } else {
145 MapSet list = new(phase_->zone()) UniqueSet<Map>(); 148 MapSet list = new(phase_->zone()) UniqueSet<Map>();
146 list->Add(cmp->map(), phase_->zone()); 149 list->Add(cmp->map(), phase_->zone());
147 entry->maps_ = list; 150 entry->maps_ = list;
148 } 151 }
152 learned = true;
149 } else if (end->IsCompareObjectEqAndBranch()) { 153 } else if (end->IsCompareObjectEqAndBranch()) {
150 // Learn on the true branch of if(CmpObjectEq(x, y)). 154 // Learn on the true branch of if(CmpObjectEq(x, y)).
151 HCompareObjectEqAndBranch* cmp = 155 HCompareObjectEqAndBranch* cmp =
152 HCompareObjectEqAndBranch::cast(end); 156 HCompareObjectEqAndBranch::cast(end);
153 HValue* left = cmp->left()->ActualValue(); 157 HValue* left = cmp->left()->ActualValue();
154 HValue* right = cmp->right()->ActualValue(); 158 HValue* right = cmp->right()->ActualValue();
155 HCheckTableEntry* le = copy->Find(left); 159 HCheckTableEntry* le = copy->Find(left);
156 HCheckTableEntry* re = copy->Find(right); 160 HCheckTableEntry* re = copy->Find(right);
157 if (le == NULL) { 161 if (le == NULL) {
158 if (re != NULL) { 162 if (re != NULL) {
159 copy->Insert(left, NULL, re->maps_->Copy(zone)); 163 copy->Insert(left, NULL, re->maps_->Copy(zone));
160 } 164 }
161 } else if (re == NULL) { 165 } else if (re == NULL) {
162 copy->Insert(right, NULL, le->maps_->Copy(zone)); 166 copy->Insert(right, NULL, le->maps_->Copy(zone));
163 } else { 167 } else {
164 MapSet intersect = le->maps_->Intersect(re->maps_, zone); 168 MapSet intersect = le->maps_->Intersect(re->maps_, zone);
165 le->maps_ = intersect; 169 le->maps_ = intersect;
166 re->maps_ = intersect->Copy(zone); 170 re->maps_ = intersect->Copy(zone);
167 } 171 }
172 learned = true;
168 } 173 }
169 // Learning on false branches requires storing negative facts. 174 // Learning on false branches requires storing negative facts.
170 } 175 }
171 176
177 if (FLAG_trace_check_elimination) {
178 PrintF("B%d checkmaps-table %s from B%d:\n",
179 succ->block_id(),
180 learned ? "learned" : "copied",
181 from_block->block_id());
182 copy->Print();
183 }
184
172 return copy; 185 return copy;
173 } 186 }
174 187
175 // Global analysis: Merge this state with the other incoming state. 188 // Global analysis: Merge this state with the other incoming state.
176 HCheckTable* Merge(HBasicBlock* succ, HCheckTable* that, Zone* zone) { 189 void Merge(HBasicBlock* succ, HCheckTable* that,
177 if (that->size_ == 0) { 190 HBasicBlock* that_block, Zone* zone) {
178 // If the other state is empty, simply reset. 191 if (that_block->IsReachable()) {
179 size_ = 0; 192 if (that->size_ == 0) {
180 cursor_ = 0; 193 // If the other state is empty, simply reset.
181 return this; 194 size_ = 0;
182 } 195 cursor_ = 0;
183 bool compact = false;
184 for (int i = 0; i < size_; i++) {
185 HCheckTableEntry* this_entry = &entries_[i];
186 HCheckTableEntry* that_entry = that->Find(this_entry->object_);
187 if (that_entry == NULL) {
188 this_entry->object_ = NULL;
189 compact = true;
190 } else { 196 } else {
191 this_entry->maps_ = this_entry->maps_->Union( 197 InheritPhiOperands(succ, that, that_block, MERGE, zone);
192 that_entry->maps_, phase_->zone()); 198
193 if (this_entry->check_ != that_entry->check_) this_entry->check_ = NULL; 199 bool compact = false;
194 ASSERT(this_entry->maps_->size() > 0); 200 for (int i = 0; i < size_; i++) {
201 HCheckTableEntry* this_entry = &entries_[i];
202 HCheckTableEntry* that_entry = that->Find(this_entry->object_);
203 // Keep those phis in the table that dominate succ block.
204 if (that_entry == NULL) {
205 if (!this_entry->object_->IsPhi() ||
206 !this_entry->object_->block()->EqualToOrDominates(succ)) {
207 this_entry->object_ = NULL;
208 compact = true;
209 }
210 } else {
211 this_entry->maps_ =
212 this_entry->maps_->Union(that_entry->maps_, phase_->zone());
213 if (this_entry->check_ != that_entry->check_) {
214 this_entry->check_ = NULL;
215 }
216 ASSERT(this_entry->maps_->size() > 0);
217 }
218 }
219 if (compact) Compact();
195 } 220 }
196 } 221 }
197 if (compact) Compact(); 222
198 return this; 223 if (FLAG_trace_check_elimination) {
224 PrintF("B%d checkmaps-table merged with B%d table:\n",
225 succ->block_id(), that_block->block_id());
226 Print();
227 }
228 }
229
230 enum InheritPhiOperandsMode { COPY, MERGE };
231 void InheritPhiOperands(HBasicBlock* succ, HCheckTable* that,
232 HBasicBlock* that_block, InheritPhiOperandsMode mode,
233 Zone* zone) {
234 if (succ->predecessors()->length() == 1) return;
235
236 int pred_index = succ->PredecessorIndexOf(that_block);
237
238 for (int i = 0; i < that->size_; i++) {
239 HCheckTableEntry* that_entry = &that->entries_[i];
240 if (that_entry->object_ != NULL) {
241 HPhi* phi = NULL;
242 for (int phi_index = 0;
243 phi_index < succ->phis()->length();
244 ++phi_index) {
245 HPhi* tmp_phi = succ->phis()->at(phi_index);
246 if (tmp_phi->OperandAt(pred_index) == that_entry->object_) {
247 phi = tmp_phi;
248 break;
249 }
250 }
251
252 if (phi != NULL) {
253 // Found a |phi| with operand equal to |that_entry->object_|.
254 HCheckTableEntry* phi_entry = (mode == MERGE) ? Find(phi) : NULL;
255 if (phi_entry == NULL) {
256 // Create an entry for a phi in the table.
257 Insert(phi, NULL, that_entry->maps_);
258 } else {
259 phi_entry->maps_ =
260 phi_entry->maps_->Union(that_entry->maps_, phase_->zone());
261 }
262 }
263 }
264 }
199 } 265 }
200 266
201 void ReduceCheckMaps(HCheckMaps* instr) { 267 void ReduceCheckMaps(HCheckMaps* instr) {
202 HValue* object = instr->value()->ActualValue(); 268 HValue* object = instr->value()->ActualValue();
203 HCheckTableEntry* entry = Find(object); 269 HCheckTableEntry* entry = Find(object);
204 if (entry != NULL) { 270 if (entry != NULL) {
205 // entry found; 271 // entry found;
206 MapSet a = entry->maps_; 272 MapSet a = entry->maps_;
207 MapSet i = instr->map_set().Copy(phase_->zone()); 273 MapSet i = instr->map_set().Copy(phase_->zone());
208 if (a->IsSubset(i)) { 274 if (a->IsSubset(i)) {
209 // The first check is more strict; the second is redundant. 275 // The first check is more strict; the second is redundant.
210 if (entry->check_ != NULL) { 276 if (entry->check_ != NULL) {
277 TRACE(("Replacing redundant CheckMaps #%d at B%d with #%d\n",
278 instr->id(), instr->block()->block_id(), entry->check_->id()));
211 instr->DeleteAndReplaceWith(entry->check_); 279 instr->DeleteAndReplaceWith(entry->check_);
212 INC_STAT(redundant_); 280 INC_STAT(redundant_);
213 } else { 281 } else {
214 instr->DeleteAndReplaceWith(instr->value()); 282 TRACE(("Marking redundant CheckMaps #%d at B%d as dead\n",
283 instr->id(), instr->block()->block_id()));
284 // Mark check as dead but leave it in the graph as a checkpoint for
285 // subsequent checks.
286 instr->SetFlag(HValue::kIsDead);
287 entry->check_ = instr;
215 INC_STAT(removed_); 288 INC_STAT(removed_);
216 } 289 }
217 return; 290 return;
218 } 291 }
219 i = i->Intersect(a, phase_->zone()); 292 MapSet narrowed_maps = i->Intersect(a, phase_->zone());
titzer 2014/01/23 18:40:55 Would prefer the name "intersection" instead of na
Igor Sheludko 2014/01/29 12:27:13 Done.
220 if (i->size() == 0) { 293 if (narrowed_maps->size() == 0) {
221 // Intersection is empty; probably megamorphic, which is likely to 294 // Intersection is empty; probably megamorphic, which is likely to
222 // deopt anyway, so just leave things as they are. 295 // deopt anyway, so just leave things as they are.
223 INC_STAT(empty_); 296 INC_STAT(empty_);
224 } else { 297 } else {
225 // TODO(titzer): replace the first check with a more strict check 298 // Narrow set of maps in the second check and replace the first
299 // check with a more strict one.
300 entry->maps_ = narrowed_maps;
301 if (narrowed_maps->size() != i->size()) {
302 // Narrow set of maps in the second check maps instruction.
303 HGraph* graph = instr->block()->graph();
304 HCheckMaps* new_check_maps =
305 HCheckMaps::New(graph->zone(), NULL, instr->value(),
306 narrowed_maps, instr->typecheck());
307 new_check_maps->InsertBefore(instr);
308 TRACE(("CheckMaps #%d for #%d narrowed to #%d:\n",
309 instr->id(), instr->value()->id(), new_check_maps->id()));
310 instr->DeleteAndReplaceWith(new_check_maps);
titzer 2014/01/23 18:40:55 I think you want to replace both entry->check_ (if
Igor Sheludko 2014/01/29 12:27:13 Done.
311 entry->check_ = new_check_maps;
312 } else {
313 TRACE(("CheckMaps #%d for #%d narrowed:\n",
314 instr->id(), instr->value()->id()));
titzer 2014/01/23 18:40:55 In this case, you haven't actually changed anythin
Igor Sheludko 2014/01/29 12:27:13 Done.
315 entry->check_ = instr;
316 }
317 if (FLAG_trace_check_elimination) {
318 Print();
319 }
226 INC_STAT(narrowed_); 320 INC_STAT(narrowed_);
227 } 321 }
228 } else { 322 } else {
229 // No entry; insert a new one. 323 // No entry; insert a new one.
230 Insert(object, instr, instr->map_set().Copy(phase_->zone())); 324 Insert(object, instr, instr->map_set().Copy(phase_->zone()));
231 } 325 }
232 } 326 }
233 327
234 void ReduceCheckValue(HCheckValue* instr) { 328 void ReduceCheckValue(HCheckValue* instr) {
235 // Canonicalize HCheckValues; they might have their values load-eliminated. 329 // Canonicalize HCheckValues; they might have their values load-eliminated.
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552 PRINT_STAT(removed_cho); 646 PRINT_STAT(removed_cho);
553 PRINT_STAT(narrowed); 647 PRINT_STAT(narrowed);
554 PRINT_STAT(loads); 648 PRINT_STAT(loads);
555 PRINT_STAT(empty); 649 PRINT_STAT(empty);
556 PRINT_STAT(compares_true); 650 PRINT_STAT(compares_true);
557 PRINT_STAT(compares_false); 651 PRINT_STAT(compares_false);
558 PRINT_STAT(transitions); 652 PRINT_STAT(transitions);
559 } 653 }
560 654
561 } } // namespace v8::internal 655 } } // namespace v8::internal
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