danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 1 | // Copyright 2013 the V8 project authors. All rights reserved. |
| 2 | // Redistribution and use in source and binary forms, with or without |
| 3 | // modification, are permitted provided that the following conditions are |
| 4 | // met: |
| 5 | // |
| 6 | // * Redistributions of source code must retain the above copyright |
| 7 | // notice, this list of conditions and the following disclaimer. |
| 8 | // * Redistributions in binary form must reproduce the above |
| 9 | // copyright notice, this list of conditions and the following |
| 10 | // disclaimer in the documentation and/or other materials provided |
| 11 | // with the distribution. |
| 12 | // * Neither the name of Google Inc. nor the names of its |
| 13 | // contributors may be used to endorse or promote products derived |
| 14 | // from this software without specific prior written permission. |
| 15 | // |
| 16 | // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 17 | // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 18 | // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| 19 | // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| 20 | // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| 21 | // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| 22 | // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 23 | // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 24 | // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 25 | // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| 26 | // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| 27 | |
| 28 | #include "hydrogen-bce.h" |
| 29 | |
| 30 | namespace v8 { |
| 31 | namespace internal { |
| 32 | |
| 33 | // We try to "factor up" HBoundsCheck instructions towards the root of the |
| 34 | // dominator tree. |
| 35 | // For now we handle checks where the index is like "exp + int32value". |
| 36 | // If in the dominator tree we check "exp + v1" and later (dominated) |
| 37 | // "exp + v2", if v2 <= v1 we can safely remove the second check, and if |
| 38 | // v2 > v1 we can use v2 in the 1st check and again remove the second. |
| 39 | // To do so we keep a dictionary of all checks where the key if the pair |
| 40 | // "exp, length". |
| 41 | // The class BoundsCheckKey represents this key. |
| 42 | class BoundsCheckKey : public ZoneObject { |
| 43 | public: |
| 44 | HValue* IndexBase() const { return index_base_; } |
| 45 | HValue* Length() const { return length_; } |
| 46 | |
| 47 | uint32_t Hash() { |
| 48 | return static_cast<uint32_t>(index_base_->Hashcode() ^ length_->Hashcode()); |
| 49 | } |
| 50 | |
| 51 | static BoundsCheckKey* Create(Zone* zone, |
| 52 | HBoundsCheck* check, |
| 53 | int32_t* offset) { |
| 54 | if (!check->index()->representation().IsSmiOrInteger32()) return NULL; |
| 55 | |
| 56 | HValue* index_base = NULL; |
| 57 | HConstant* constant = NULL; |
| 58 | bool is_sub = false; |
| 59 | |
| 60 | if (check->index()->IsAdd()) { |
| 61 | HAdd* index = HAdd::cast(check->index()); |
| 62 | if (index->left()->IsConstant()) { |
| 63 | constant = HConstant::cast(index->left()); |
| 64 | index_base = index->right(); |
| 65 | } else if (index->right()->IsConstant()) { |
| 66 | constant = HConstant::cast(index->right()); |
| 67 | index_base = index->left(); |
| 68 | } |
| 69 | } else if (check->index()->IsSub()) { |
| 70 | HSub* index = HSub::cast(check->index()); |
| 71 | is_sub = true; |
| 72 | if (index->left()->IsConstant()) { |
| 73 | constant = HConstant::cast(index->left()); |
| 74 | index_base = index->right(); |
| 75 | } else if (index->right()->IsConstant()) { |
| 76 | constant = HConstant::cast(index->right()); |
| 77 | index_base = index->left(); |
| 78 | } |
| 79 | } |
| 80 | |
| 81 | if (constant != NULL && constant->HasInteger32Value()) { |
| 82 | *offset = is_sub ? - constant->Integer32Value() |
| 83 | : constant->Integer32Value(); |
| 84 | } else { |
| 85 | *offset = 0; |
| 86 | index_base = check->index(); |
| 87 | } |
| 88 | |
| 89 | return new(zone) BoundsCheckKey(index_base, check->length()); |
| 90 | } |
| 91 | |
| 92 | private: |
| 93 | BoundsCheckKey(HValue* index_base, HValue* length) |
| 94 | : index_base_(index_base), |
| 95 | length_(length) { } |
| 96 | |
| 97 | HValue* index_base_; |
| 98 | HValue* length_; |
| 99 | |
| 100 | DISALLOW_COPY_AND_ASSIGN(BoundsCheckKey); |
| 101 | }; |
| 102 | |
| 103 | |
| 104 | // Data about each HBoundsCheck that can be eliminated or moved. |
| 105 | // It is the "value" in the dictionary indexed by "base-index, length" |
| 106 | // (the key is BoundsCheckKey). |
| 107 | // We scan the code with a dominator tree traversal. |
| 108 | // Traversing the dominator tree we keep a stack (implemented as a singly |
| 109 | // linked list) of "data" for each basic block that contains a relevant check |
| 110 | // with the same key (the dictionary holds the head of the list). |
| 111 | // We also keep all the "data" created for a given basic block in a list, and |
| 112 | // use it to "clean up" the dictionary when backtracking in the dominator tree |
| 113 | // traversal. |
| 114 | // Doing this each dictionary entry always directly points to the check that |
| 115 | // is dominating the code being examined now. |
| 116 | // We also track the current "offset" of the index expression and use it to |
| 117 | // decide if any check is already "covered" (so it can be removed) or not. |
| 118 | class BoundsCheckBbData: public ZoneObject { |
| 119 | public: |
| 120 | BoundsCheckKey* Key() const { return key_; } |
| 121 | int32_t LowerOffset() const { return lower_offset_; } |
| 122 | int32_t UpperOffset() const { return upper_offset_; } |
| 123 | HBasicBlock* BasicBlock() const { return basic_block_; } |
| 124 | HBoundsCheck* LowerCheck() const { return lower_check_; } |
| 125 | HBoundsCheck* UpperCheck() const { return upper_check_; } |
| 126 | BoundsCheckBbData* NextInBasicBlock() const { return next_in_bb_; } |
| 127 | BoundsCheckBbData* FatherInDominatorTree() const { return father_in_dt_; } |
| 128 | |
| 129 | bool OffsetIsCovered(int32_t offset) const { |
| 130 | return offset >= LowerOffset() && offset <= UpperOffset(); |
| 131 | } |
| 132 | |
| 133 | bool HasSingleCheck() { return lower_check_ == upper_check_; } |
| 134 | |
| 135 | // The goal of this method is to modify either upper_offset_ or |
| 136 | // lower_offset_ so that also new_offset is covered (the covered |
| 137 | // range grows). |
| 138 | // |
| 139 | // The precondition is that new_check follows UpperCheck() and |
| 140 | // LowerCheck() in the same basic block, and that new_offset is not |
| 141 | // covered (otherwise we could simply remove new_check). |
| 142 | // |
| 143 | // If HasSingleCheck() is true then new_check is added as "second check" |
| 144 | // (either upper or lower; note that HasSingleCheck() becomes false). |
| 145 | // Otherwise one of the current checks is modified so that it also covers |
| 146 | // new_offset, and new_check is removed. |
| 147 | // |
| 148 | // If the check cannot be modified because the context is unknown it |
| 149 | // returns false, otherwise it returns true. |
| 150 | bool CoverCheck(HBoundsCheck* new_check, |
| 151 | int32_t new_offset) { |
| 152 | ASSERT(new_check->index()->representation().IsSmiOrInteger32()); |
| 153 | bool keep_new_check = false; |
| 154 | |
| 155 | if (new_offset > upper_offset_) { |
| 156 | upper_offset_ = new_offset; |
| 157 | if (HasSingleCheck()) { |
| 158 | keep_new_check = true; |
| 159 | upper_check_ = new_check; |
| 160 | } else { |
| 161 | bool result = BuildOffsetAdd(upper_check_, |
| 162 | &added_upper_index_, |
| 163 | &added_upper_offset_, |
| 164 | Key()->IndexBase(), |
| 165 | new_check->index()->representation(), |
| 166 | new_offset); |
| 167 | if (!result) return false; |
| 168 | upper_check_->ReplaceAllUsesWith(upper_check_->index()); |
| 169 | upper_check_->SetOperandAt(0, added_upper_index_); |
| 170 | } |
| 171 | } else if (new_offset < lower_offset_) { |
| 172 | lower_offset_ = new_offset; |
| 173 | if (HasSingleCheck()) { |
| 174 | keep_new_check = true; |
| 175 | lower_check_ = new_check; |
| 176 | } else { |
| 177 | bool result = BuildOffsetAdd(lower_check_, |
| 178 | &added_lower_index_, |
| 179 | &added_lower_offset_, |
| 180 | Key()->IndexBase(), |
| 181 | new_check->index()->representation(), |
| 182 | new_offset); |
| 183 | if (!result) return false; |
| 184 | lower_check_->ReplaceAllUsesWith(lower_check_->index()); |
| 185 | lower_check_->SetOperandAt(0, added_lower_index_); |
| 186 | } |
| 187 | } else { |
| 188 | ASSERT(false); |
| 189 | } |
| 190 | |
| 191 | if (!keep_new_check) { |
jkummerow@chromium.org | fb732b1 | 2013-07-26 10:27:09 +0000 | [diff] [blame] | 192 | new_check->block()->graph()->isolate()->counters()-> |
| 193 | bounds_checks_eliminated()->Increment(); |
danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 194 | new_check->DeleteAndReplaceWith(new_check->ActualValue()); |
| 195 | } |
| 196 | |
| 197 | return true; |
| 198 | } |
| 199 | |
| 200 | void RemoveZeroOperations() { |
| 201 | RemoveZeroAdd(&added_lower_index_, &added_lower_offset_); |
| 202 | RemoveZeroAdd(&added_upper_index_, &added_upper_offset_); |
| 203 | } |
| 204 | |
| 205 | BoundsCheckBbData(BoundsCheckKey* key, |
| 206 | int32_t lower_offset, |
| 207 | int32_t upper_offset, |
| 208 | HBasicBlock* bb, |
| 209 | HBoundsCheck* lower_check, |
| 210 | HBoundsCheck* upper_check, |
| 211 | BoundsCheckBbData* next_in_bb, |
| 212 | BoundsCheckBbData* father_in_dt) |
| 213 | : key_(key), |
| 214 | lower_offset_(lower_offset), |
| 215 | upper_offset_(upper_offset), |
| 216 | basic_block_(bb), |
| 217 | lower_check_(lower_check), |
| 218 | upper_check_(upper_check), |
| 219 | added_lower_index_(NULL), |
| 220 | added_lower_offset_(NULL), |
| 221 | added_upper_index_(NULL), |
| 222 | added_upper_offset_(NULL), |
| 223 | next_in_bb_(next_in_bb), |
| 224 | father_in_dt_(father_in_dt) { } |
| 225 | |
| 226 | private: |
| 227 | BoundsCheckKey* key_; |
| 228 | int32_t lower_offset_; |
| 229 | int32_t upper_offset_; |
| 230 | HBasicBlock* basic_block_; |
| 231 | HBoundsCheck* lower_check_; |
| 232 | HBoundsCheck* upper_check_; |
| 233 | HInstruction* added_lower_index_; |
| 234 | HConstant* added_lower_offset_; |
| 235 | HInstruction* added_upper_index_; |
| 236 | HConstant* added_upper_offset_; |
| 237 | BoundsCheckBbData* next_in_bb_; |
| 238 | BoundsCheckBbData* father_in_dt_; |
| 239 | |
| 240 | // Given an existing add instruction and a bounds check it tries to |
| 241 | // find the current context (either of the add or of the check index). |
| 242 | HValue* IndexContext(HInstruction* add, HBoundsCheck* check) { |
| 243 | if (add != NULL && add->IsAdd()) { |
| 244 | return HAdd::cast(add)->context(); |
| 245 | } |
| 246 | if (check->index()->IsBinaryOperation()) { |
| 247 | return HBinaryOperation::cast(check->index())->context(); |
| 248 | } |
| 249 | return NULL; |
| 250 | } |
| 251 | |
| 252 | // This function returns false if it cannot build the add because the |
| 253 | // current context cannot be determined. |
| 254 | bool BuildOffsetAdd(HBoundsCheck* check, |
| 255 | HInstruction** add, |
| 256 | HConstant** constant, |
| 257 | HValue* original_value, |
| 258 | Representation representation, |
| 259 | int32_t new_offset) { |
| 260 | HValue* index_context = IndexContext(*add, check); |
| 261 | if (index_context == NULL) return false; |
| 262 | |
danno@chromium.org | d3c4210 | 2013-08-01 16:58:23 +0000 | [diff] [blame] | 263 | Zone* zone = BasicBlock()->zone(); |
| 264 | HConstant* new_constant = HConstant::New(zone, index_context, |
| 265 | new_offset, representation); |
danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 266 | if (*add == NULL) { |
| 267 | new_constant->InsertBefore(check); |
danno@chromium.org | d3c4210 | 2013-08-01 16:58:23 +0000 | [diff] [blame] | 268 | (*add) = HAdd::New(zone, index_context, original_value, new_constant); |
danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 269 | (*add)->AssumeRepresentation(representation); |
| 270 | (*add)->InsertBefore(check); |
| 271 | } else { |
| 272 | new_constant->InsertBefore(*add); |
| 273 | (*constant)->DeleteAndReplaceWith(new_constant); |
| 274 | } |
| 275 | *constant = new_constant; |
| 276 | return true; |
| 277 | } |
| 278 | |
| 279 | void RemoveZeroAdd(HInstruction** add, HConstant** constant) { |
| 280 | if (*add != NULL && (*add)->IsAdd() && (*constant)->Integer32Value() == 0) { |
| 281 | (*add)->DeleteAndReplaceWith(HAdd::cast(*add)->left()); |
| 282 | (*constant)->DeleteAndReplaceWith(NULL); |
| 283 | } |
| 284 | } |
| 285 | |
| 286 | DISALLOW_COPY_AND_ASSIGN(BoundsCheckBbData); |
| 287 | }; |
| 288 | |
| 289 | |
| 290 | static bool BoundsCheckKeyMatch(void* key1, void* key2) { |
| 291 | BoundsCheckKey* k1 = static_cast<BoundsCheckKey*>(key1); |
| 292 | BoundsCheckKey* k2 = static_cast<BoundsCheckKey*>(key2); |
| 293 | return k1->IndexBase() == k2->IndexBase() && k1->Length() == k2->Length(); |
| 294 | } |
| 295 | |
| 296 | |
| 297 | BoundsCheckTable::BoundsCheckTable(Zone* zone) |
| 298 | : ZoneHashMap(BoundsCheckKeyMatch, ZoneHashMap::kDefaultHashMapCapacity, |
| 299 | ZoneAllocationPolicy(zone)) { } |
| 300 | |
| 301 | |
| 302 | BoundsCheckBbData** BoundsCheckTable::LookupOrInsert(BoundsCheckKey* key, |
| 303 | Zone* zone) { |
| 304 | return reinterpret_cast<BoundsCheckBbData**>( |
| 305 | &(Lookup(key, key->Hash(), true, ZoneAllocationPolicy(zone))->value)); |
| 306 | } |
| 307 | |
| 308 | |
| 309 | void BoundsCheckTable::Insert(BoundsCheckKey* key, |
| 310 | BoundsCheckBbData* data, |
| 311 | Zone* zone) { |
| 312 | Lookup(key, key->Hash(), true, ZoneAllocationPolicy(zone))->value = data; |
| 313 | } |
| 314 | |
| 315 | |
| 316 | void BoundsCheckTable::Delete(BoundsCheckKey* key) { |
| 317 | Remove(key, key->Hash()); |
| 318 | } |
| 319 | |
| 320 | |
machenbach@chromium.org | 528ce02 | 2013-09-23 14:09:36 +0000 | [diff] [blame] | 321 | class HBoundsCheckEliminationState { |
| 322 | public: |
| 323 | HBasicBlock* block_; |
| 324 | BoundsCheckBbData* bb_data_list_; |
| 325 | int index_; |
| 326 | }; |
| 327 | |
| 328 | |
danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 329 | // Eliminates checks in bb and recursively in the dominated blocks. |
| 330 | // Also replace the results of check instructions with the original value, if |
| 331 | // the result is used. This is safe now, since we don't do code motion after |
| 332 | // this point. It enables better register allocation since the value produced |
| 333 | // by check instructions is really a copy of the original value. |
| 334 | void HBoundsCheckEliminationPhase::EliminateRedundantBoundsChecks( |
machenbach@chromium.org | 528ce02 | 2013-09-23 14:09:36 +0000 | [diff] [blame] | 335 | HBasicBlock* entry) { |
| 336 | // Allocate the stack. |
| 337 | HBoundsCheckEliminationState* stack = |
| 338 | zone()->NewArray<HBoundsCheckEliminationState>(graph()->blocks()->length()); |
| 339 | |
| 340 | // Explicitly push the entry block. |
| 341 | stack[0].block_ = entry; |
| 342 | stack[0].bb_data_list_ = PreProcessBlock(entry); |
| 343 | stack[0].index_ = 0; |
| 344 | int stack_depth = 1; |
| 345 | |
| 346 | // Implement depth-first traversal with a stack. |
| 347 | while (stack_depth > 0) { |
| 348 | int current = stack_depth - 1; |
| 349 | HBoundsCheckEliminationState* state = &stack[current]; |
| 350 | const ZoneList<HBasicBlock*>* children = state->block_->dominated_blocks(); |
| 351 | |
| 352 | if (state->index_ < children->length()) { |
| 353 | // Recursively visit children blocks. |
| 354 | HBasicBlock* child = children->at(state->index_++); |
| 355 | int next = stack_depth++; |
| 356 | stack[next].block_ = child; |
| 357 | stack[next].bb_data_list_ = PreProcessBlock(child); |
| 358 | stack[next].index_ = 0; |
| 359 | } else { |
| 360 | // Finished with all children; post process the block. |
| 361 | PostProcessBlock(state->block_, state->bb_data_list_); |
| 362 | stack_depth--; |
| 363 | } |
| 364 | } |
| 365 | } |
| 366 | |
| 367 | |
| 368 | BoundsCheckBbData* HBoundsCheckEliminationPhase::PreProcessBlock( |
danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 369 | HBasicBlock* bb) { |
| 370 | BoundsCheckBbData* bb_data_list = NULL; |
| 371 | |
| 372 | for (HInstructionIterator it(bb); !it.Done(); it.Advance()) { |
| 373 | HInstruction* i = it.Current(); |
| 374 | if (!i->IsBoundsCheck()) continue; |
| 375 | |
| 376 | HBoundsCheck* check = HBoundsCheck::cast(i); |
| 377 | int32_t offset; |
| 378 | BoundsCheckKey* key = |
| 379 | BoundsCheckKey::Create(zone(), check, &offset); |
| 380 | if (key == NULL) continue; |
| 381 | BoundsCheckBbData** data_p = table_.LookupOrInsert(key, zone()); |
| 382 | BoundsCheckBbData* data = *data_p; |
| 383 | if (data == NULL) { |
| 384 | bb_data_list = new(zone()) BoundsCheckBbData(key, |
| 385 | offset, |
| 386 | offset, |
| 387 | bb, |
| 388 | check, |
| 389 | check, |
| 390 | bb_data_list, |
| 391 | NULL); |
| 392 | *data_p = bb_data_list; |
| 393 | } else if (data->OffsetIsCovered(offset)) { |
jkummerow@chromium.org | fb732b1 | 2013-07-26 10:27:09 +0000 | [diff] [blame] | 394 | bb->graph()->isolate()->counters()-> |
| 395 | bounds_checks_eliminated()->Increment(); |
danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 396 | check->DeleteAndReplaceWith(check->ActualValue()); |
| 397 | } else if (data->BasicBlock() != bb || |
| 398 | !data->CoverCheck(check, offset)) { |
| 399 | // If the check is in the current BB we try to modify it by calling |
| 400 | // "CoverCheck", but if also that fails we record the current offsets |
| 401 | // in a new data instance because from now on they are covered. |
| 402 | int32_t new_lower_offset = offset < data->LowerOffset() |
| 403 | ? offset |
| 404 | : data->LowerOffset(); |
| 405 | int32_t new_upper_offset = offset > data->UpperOffset() |
| 406 | ? offset |
| 407 | : data->UpperOffset(); |
| 408 | bb_data_list = new(zone()) BoundsCheckBbData(key, |
| 409 | new_lower_offset, |
| 410 | new_upper_offset, |
| 411 | bb, |
| 412 | data->LowerCheck(), |
| 413 | data->UpperCheck(), |
| 414 | bb_data_list, |
| 415 | data); |
| 416 | table_.Insert(key, bb_data_list, zone()); |
| 417 | } |
| 418 | } |
| 419 | |
machenbach@chromium.org | 528ce02 | 2013-09-23 14:09:36 +0000 | [diff] [blame] | 420 | return bb_data_list; |
| 421 | } |
danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 422 | |
machenbach@chromium.org | 528ce02 | 2013-09-23 14:09:36 +0000 | [diff] [blame] | 423 | |
| 424 | void HBoundsCheckEliminationPhase::PostProcessBlock( |
| 425 | HBasicBlock* block, BoundsCheckBbData* data) { |
| 426 | while (data != NULL) { |
danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 427 | data->RemoveZeroOperations(); |
| 428 | if (data->FatherInDominatorTree()) { |
| 429 | table_.Insert(data->Key(), data->FatherInDominatorTree(), zone()); |
| 430 | } else { |
| 431 | table_.Delete(data->Key()); |
| 432 | } |
machenbach@chromium.org | 528ce02 | 2013-09-23 14:09:36 +0000 | [diff] [blame] | 433 | data = data->NextInBasicBlock(); |
danno@chromium.org | bee5199 | 2013-07-10 14:57:15 +0000 | [diff] [blame] | 434 | } |
| 435 | } |
| 436 | |
| 437 | } } // namespace v8::internal |