instruction_simplifier.cc revision a83a54d7f2322060f08480f8aabac5eb07268912
1/* 2 * Copyright (C) 2014 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17#include "instruction_simplifier.h" 18 19#include "intrinsics.h" 20#include "mirror/class-inl.h" 21#include "scoped_thread_state_change.h" 22 23namespace art { 24 25class InstructionSimplifierVisitor : public HGraphDelegateVisitor { 26 public: 27 InstructionSimplifierVisitor(HGraph* graph, OptimizingCompilerStats* stats) 28 : HGraphDelegateVisitor(graph), 29 stats_(stats) {} 30 31 void Run(); 32 33 private: 34 void RecordSimplification() { 35 simplification_occurred_ = true; 36 simplifications_at_current_position_++; 37 if (stats_) { 38 stats_->RecordStat(kInstructionSimplifications); 39 } 40 } 41 42 bool TryMoveNegOnInputsAfterBinop(HBinaryOperation* binop); 43 void VisitShift(HBinaryOperation* shift); 44 45 void VisitSuspendCheck(HSuspendCheck* check) OVERRIDE; 46 void VisitEqual(HEqual* equal) OVERRIDE; 47 void VisitNotEqual(HNotEqual* equal) OVERRIDE; 48 void VisitBooleanNot(HBooleanNot* bool_not) OVERRIDE; 49 void VisitInstanceFieldSet(HInstanceFieldSet* equal) OVERRIDE; 50 void VisitStaticFieldSet(HStaticFieldSet* equal) OVERRIDE; 51 void VisitArraySet(HArraySet* equal) OVERRIDE; 52 void VisitTypeConversion(HTypeConversion* instruction) OVERRIDE; 53 void VisitNullCheck(HNullCheck* instruction) OVERRIDE; 54 void VisitArrayLength(HArrayLength* instruction) OVERRIDE; 55 void VisitCheckCast(HCheckCast* instruction) OVERRIDE; 56 void VisitAdd(HAdd* instruction) OVERRIDE; 57 void VisitAnd(HAnd* instruction) OVERRIDE; 58 void VisitCondition(HCondition* instruction) OVERRIDE; 59 void VisitGreaterThan(HGreaterThan* condition) OVERRIDE; 60 void VisitGreaterThanOrEqual(HGreaterThanOrEqual* condition) OVERRIDE; 61 void VisitLessThan(HLessThan* condition) OVERRIDE; 62 void VisitLessThanOrEqual(HLessThanOrEqual* condition) OVERRIDE; 63 void VisitDiv(HDiv* instruction) OVERRIDE; 64 void VisitMul(HMul* instruction) OVERRIDE; 65 void VisitNeg(HNeg* instruction) OVERRIDE; 66 void VisitNot(HNot* instruction) OVERRIDE; 67 void VisitOr(HOr* instruction) OVERRIDE; 68 void VisitShl(HShl* instruction) OVERRIDE; 69 void VisitShr(HShr* instruction) OVERRIDE; 70 void VisitSub(HSub* instruction) OVERRIDE; 71 void VisitUShr(HUShr* instruction) OVERRIDE; 72 void VisitXor(HXor* instruction) OVERRIDE; 73 void VisitInstanceOf(HInstanceOf* instruction) OVERRIDE; 74 void VisitFakeString(HFakeString* fake_string) OVERRIDE; 75 void VisitInvoke(HInvoke* invoke) OVERRIDE; 76 77 bool CanEnsureNotNullAt(HInstruction* instr, HInstruction* at) const; 78 79 OptimizingCompilerStats* stats_; 80 bool simplification_occurred_ = false; 81 int simplifications_at_current_position_ = 0; 82 // We ensure we do not loop infinitely. The value is a finger in the air guess 83 // that should allow enough simplification. 84 static constexpr int kMaxSamePositionSimplifications = 10; 85}; 86 87void InstructionSimplifier::Run() { 88 InstructionSimplifierVisitor visitor(graph_, stats_); 89 visitor.Run(); 90} 91 92void InstructionSimplifierVisitor::Run() { 93 // Iterate in reverse post order to open up more simplifications to users 94 // of instructions that got simplified. 95 for (HReversePostOrderIterator it(*GetGraph()); !it.Done();) { 96 // The simplification of an instruction to another instruction may yield 97 // possibilities for other simplifications. So although we perform a reverse 98 // post order visit, we sometimes need to revisit an instruction index. 99 simplification_occurred_ = false; 100 VisitBasicBlock(it.Current()); 101 if (simplification_occurred_ && 102 (simplifications_at_current_position_ < kMaxSamePositionSimplifications)) { 103 // New simplifications may be applicable to the instruction at the 104 // current index, so don't advance the iterator. 105 continue; 106 } 107 simplifications_at_current_position_ = 0; 108 it.Advance(); 109 } 110} 111 112namespace { 113 114bool AreAllBitsSet(HConstant* constant) { 115 return Int64FromConstant(constant) == -1; 116} 117 118} // namespace 119 120// Returns true if the code was simplified to use only one negation operation 121// after the binary operation instead of one on each of the inputs. 122bool InstructionSimplifierVisitor::TryMoveNegOnInputsAfterBinop(HBinaryOperation* binop) { 123 DCHECK(binop->IsAdd() || binop->IsSub()); 124 DCHECK(binop->GetLeft()->IsNeg() && binop->GetRight()->IsNeg()); 125 HNeg* left_neg = binop->GetLeft()->AsNeg(); 126 HNeg* right_neg = binop->GetRight()->AsNeg(); 127 if (!left_neg->HasOnlyOneNonEnvironmentUse() || 128 !right_neg->HasOnlyOneNonEnvironmentUse()) { 129 return false; 130 } 131 // Replace code looking like 132 // NEG tmp1, a 133 // NEG tmp2, b 134 // ADD dst, tmp1, tmp2 135 // with 136 // ADD tmp, a, b 137 // NEG dst, tmp 138 // Note that we cannot optimize `(-a) + (-b)` to `-(a + b)` for floating-point. 139 // When `a` is `-0.0` and `b` is `0.0`, the former expression yields `0.0`, 140 // while the later yields `-0.0`. 141 if (!Primitive::IsIntegralType(binop->GetType())) { 142 return false; 143 } 144 binop->ReplaceInput(left_neg->GetInput(), 0); 145 binop->ReplaceInput(right_neg->GetInput(), 1); 146 left_neg->GetBlock()->RemoveInstruction(left_neg); 147 right_neg->GetBlock()->RemoveInstruction(right_neg); 148 HNeg* neg = new (GetGraph()->GetArena()) HNeg(binop->GetType(), binop); 149 binop->GetBlock()->InsertInstructionBefore(neg, binop->GetNext()); 150 binop->ReplaceWithExceptInReplacementAtIndex(neg, 0); 151 RecordSimplification(); 152 return true; 153} 154 155void InstructionSimplifierVisitor::VisitShift(HBinaryOperation* instruction) { 156 DCHECK(instruction->IsShl() || instruction->IsShr() || instruction->IsUShr()); 157 HConstant* input_cst = instruction->GetConstantRight(); 158 HInstruction* input_other = instruction->GetLeastConstantLeft(); 159 160 if (input_cst != nullptr) { 161 if (input_cst->IsZero()) { 162 // Replace code looking like 163 // SHL dst, src, 0 164 // with 165 // src 166 instruction->ReplaceWith(input_other); 167 instruction->GetBlock()->RemoveInstruction(instruction); 168 } else if (instruction->IsShl() && input_cst->IsOne()) { 169 // Replace Shl looking like 170 // SHL dst, src, 1 171 // with 172 // ADD dst, src, src 173 HAdd *add = new(GetGraph()->GetArena()) HAdd(instruction->GetType(), 174 input_other, 175 input_other); 176 instruction->GetBlock()->ReplaceAndRemoveInstructionWith(instruction, add); 177 RecordSimplification(); 178 } 179 } 180} 181 182void InstructionSimplifierVisitor::VisitNullCheck(HNullCheck* null_check) { 183 HInstruction* obj = null_check->InputAt(0); 184 if (!obj->CanBeNull()) { 185 null_check->ReplaceWith(obj); 186 null_check->GetBlock()->RemoveInstruction(null_check); 187 if (stats_ != nullptr) { 188 stats_->RecordStat(MethodCompilationStat::kRemovedNullCheck); 189 } 190 } 191} 192 193bool InstructionSimplifierVisitor::CanEnsureNotNullAt(HInstruction* input, HInstruction* at) const { 194 if (!input->CanBeNull()) { 195 return true; 196 } 197 198 for (HUseIterator<HInstruction*> it(input->GetUses()); !it.Done(); it.Advance()) { 199 HInstruction* use = it.Current()->GetUser(); 200 if (use->IsNullCheck() && use->StrictlyDominates(at)) { 201 return true; 202 } 203 } 204 205 return false; 206} 207 208// Returns whether doing a type test between the class of `object` against `klass` has 209// a statically known outcome. The result of the test is stored in `outcome`. 210static bool TypeCheckHasKnownOutcome(HLoadClass* klass, HInstruction* object, bool* outcome) { 211 DCHECK(!object->IsNullConstant()) << "Null constants should be special cased"; 212 ReferenceTypeInfo obj_rti = object->GetReferenceTypeInfo(); 213 ScopedObjectAccess soa(Thread::Current()); 214 if (!obj_rti.IsValid()) { 215 // We run the simplifier before the reference type propagation so type info might not be 216 // available. 217 return false; 218 } 219 220 ReferenceTypeInfo class_rti = klass->GetLoadedClassRTI(); 221 DCHECK(class_rti.IsValid() && class_rti.IsExact()); 222 if (class_rti.IsSupertypeOf(obj_rti)) { 223 *outcome = true; 224 return true; 225 } else if (obj_rti.IsExact()) { 226 // The test failed at compile time so will also fail at runtime. 227 *outcome = false; 228 return true; 229 } else if (!class_rti.IsInterface() 230 && !obj_rti.IsInterface() 231 && !obj_rti.IsSupertypeOf(class_rti)) { 232 // Different type hierarchy. The test will fail. 233 *outcome = false; 234 return true; 235 } 236 return false; 237} 238 239void InstructionSimplifierVisitor::VisitCheckCast(HCheckCast* check_cast) { 240 HInstruction* object = check_cast->InputAt(0); 241 if (CanEnsureNotNullAt(object, check_cast)) { 242 check_cast->ClearMustDoNullCheck(); 243 } 244 245 if (object->IsNullConstant()) { 246 check_cast->GetBlock()->RemoveInstruction(check_cast); 247 if (stats_ != nullptr) { 248 stats_->RecordStat(MethodCompilationStat::kRemovedCheckedCast); 249 } 250 return; 251 } 252 253 bool outcome; 254 HLoadClass* load_class = check_cast->InputAt(1)->AsLoadClass(); 255 if (TypeCheckHasKnownOutcome(load_class, object, &outcome)) { 256 if (outcome) { 257 check_cast->GetBlock()->RemoveInstruction(check_cast); 258 if (stats_ != nullptr) { 259 stats_->RecordStat(MethodCompilationStat::kRemovedCheckedCast); 260 } 261 if (!load_class->HasUses()) { 262 // We cannot rely on DCE to remove the class because the `HLoadClass` thinks it can throw. 263 // However, here we know that it cannot because the checkcast was successfull, hence 264 // the class was already loaded. 265 load_class->GetBlock()->RemoveInstruction(load_class); 266 } 267 } else { 268 // Don't do anything for exceptional cases for now. Ideally we should remove 269 // all instructions and blocks this instruction dominates. 270 } 271 } 272} 273 274void InstructionSimplifierVisitor::VisitInstanceOf(HInstanceOf* instruction) { 275 HInstruction* object = instruction->InputAt(0); 276 bool can_be_null = true; 277 if (CanEnsureNotNullAt(object, instruction)) { 278 can_be_null = false; 279 instruction->ClearMustDoNullCheck(); 280 } 281 282 HGraph* graph = GetGraph(); 283 if (object->IsNullConstant()) { 284 instruction->ReplaceWith(graph->GetIntConstant(0)); 285 instruction->GetBlock()->RemoveInstruction(instruction); 286 RecordSimplification(); 287 return; 288 } 289 290 bool outcome; 291 HLoadClass* load_class = instruction->InputAt(1)->AsLoadClass(); 292 if (TypeCheckHasKnownOutcome(load_class, object, &outcome)) { 293 if (outcome && can_be_null) { 294 // Type test will succeed, we just need a null test. 295 HNotEqual* test = new (graph->GetArena()) HNotEqual(graph->GetNullConstant(), object); 296 instruction->GetBlock()->InsertInstructionBefore(test, instruction); 297 instruction->ReplaceWith(test); 298 } else { 299 // We've statically determined the result of the instanceof. 300 instruction->ReplaceWith(graph->GetIntConstant(outcome)); 301 } 302 RecordSimplification(); 303 instruction->GetBlock()->RemoveInstruction(instruction); 304 if (outcome && !load_class->HasUses()) { 305 // We cannot rely on DCE to remove the class because the `HLoadClass` thinks it can throw. 306 // However, here we know that it cannot because the instanceof check was successfull, hence 307 // the class was already loaded. 308 load_class->GetBlock()->RemoveInstruction(load_class); 309 } 310 } 311} 312 313void InstructionSimplifierVisitor::VisitInstanceFieldSet(HInstanceFieldSet* instruction) { 314 if ((instruction->GetValue()->GetType() == Primitive::kPrimNot) 315 && CanEnsureNotNullAt(instruction->GetValue(), instruction)) { 316 instruction->ClearValueCanBeNull(); 317 } 318} 319 320void InstructionSimplifierVisitor::VisitStaticFieldSet(HStaticFieldSet* instruction) { 321 if ((instruction->GetValue()->GetType() == Primitive::kPrimNot) 322 && CanEnsureNotNullAt(instruction->GetValue(), instruction)) { 323 instruction->ClearValueCanBeNull(); 324 } 325} 326 327void InstructionSimplifierVisitor::VisitSuspendCheck(HSuspendCheck* check) { 328 HBasicBlock* block = check->GetBlock(); 329 // Currently always keep the suspend check at entry. 330 if (block->IsEntryBlock()) return; 331 332 // Currently always keep suspend checks at loop entry. 333 if (block->IsLoopHeader() && block->GetFirstInstruction() == check) { 334 DCHECK(block->GetLoopInformation()->GetSuspendCheck() == check); 335 return; 336 } 337 338 // Remove the suspend check that was added at build time for the baseline 339 // compiler. 340 block->RemoveInstruction(check); 341} 342 343void InstructionSimplifierVisitor::VisitEqual(HEqual* equal) { 344 HInstruction* input_const = equal->GetConstantRight(); 345 if (input_const != nullptr) { 346 HInstruction* input_value = equal->GetLeastConstantLeft(); 347 if (input_value->GetType() == Primitive::kPrimBoolean && input_const->IsIntConstant()) { 348 HBasicBlock* block = equal->GetBlock(); 349 // We are comparing the boolean to a constant which is of type int and can 350 // be any constant. 351 if (input_const->AsIntConstant()->IsOne()) { 352 // Replace (bool_value == true) with bool_value 353 equal->ReplaceWith(input_value); 354 block->RemoveInstruction(equal); 355 RecordSimplification(); 356 } else if (input_const->AsIntConstant()->IsZero()) { 357 // Replace (bool_value == false) with !bool_value 358 block->ReplaceAndRemoveInstructionWith( 359 equal, new (block->GetGraph()->GetArena()) HBooleanNot(input_value)); 360 RecordSimplification(); 361 } else { 362 // Replace (bool_value == integer_not_zero_nor_one_constant) with false 363 equal->ReplaceWith(GetGraph()->GetIntConstant(0)); 364 block->RemoveInstruction(equal); 365 RecordSimplification(); 366 } 367 } else { 368 VisitCondition(equal); 369 } 370 } else { 371 VisitCondition(equal); 372 } 373} 374 375void InstructionSimplifierVisitor::VisitNotEqual(HNotEqual* not_equal) { 376 HInstruction* input_const = not_equal->GetConstantRight(); 377 if (input_const != nullptr) { 378 HInstruction* input_value = not_equal->GetLeastConstantLeft(); 379 if (input_value->GetType() == Primitive::kPrimBoolean && input_const->IsIntConstant()) { 380 HBasicBlock* block = not_equal->GetBlock(); 381 // We are comparing the boolean to a constant which is of type int and can 382 // be any constant. 383 if (input_const->AsIntConstant()->IsOne()) { 384 // Replace (bool_value != true) with !bool_value 385 block->ReplaceAndRemoveInstructionWith( 386 not_equal, new (block->GetGraph()->GetArena()) HBooleanNot(input_value)); 387 RecordSimplification(); 388 } else if (input_const->AsIntConstant()->IsZero()) { 389 // Replace (bool_value != false) with bool_value 390 not_equal->ReplaceWith(input_value); 391 block->RemoveInstruction(not_equal); 392 RecordSimplification(); 393 } else { 394 // Replace (bool_value != integer_not_zero_nor_one_constant) with true 395 not_equal->ReplaceWith(GetGraph()->GetIntConstant(1)); 396 block->RemoveInstruction(not_equal); 397 RecordSimplification(); 398 } 399 } else { 400 VisitCondition(not_equal); 401 } 402 } else { 403 VisitCondition(not_equal); 404 } 405} 406 407void InstructionSimplifierVisitor::VisitBooleanNot(HBooleanNot* bool_not) { 408 HInstruction* parent = bool_not->InputAt(0); 409 if (parent->IsBooleanNot()) { 410 HInstruction* value = parent->InputAt(0); 411 // Replace (!(!bool_value)) with bool_value 412 bool_not->ReplaceWith(value); 413 bool_not->GetBlock()->RemoveInstruction(bool_not); 414 // It is possible that `parent` is dead at this point but we leave 415 // its removal to DCE for simplicity. 416 RecordSimplification(); 417 } 418} 419 420void InstructionSimplifierVisitor::VisitArrayLength(HArrayLength* instruction) { 421 HInstruction* input = instruction->InputAt(0); 422 // If the array is a NewArray with constant size, replace the array length 423 // with the constant instruction. This helps the bounds check elimination phase. 424 if (input->IsNewArray()) { 425 input = input->InputAt(0); 426 if (input->IsIntConstant()) { 427 instruction->ReplaceWith(input); 428 } 429 } 430} 431 432void InstructionSimplifierVisitor::VisitArraySet(HArraySet* instruction) { 433 HInstruction* value = instruction->GetValue(); 434 if (value->GetType() != Primitive::kPrimNot) return; 435 436 if (CanEnsureNotNullAt(value, instruction)) { 437 instruction->ClearValueCanBeNull(); 438 } 439 440 if (value->IsArrayGet()) { 441 if (value->AsArrayGet()->GetArray() == instruction->GetArray()) { 442 // If the code is just swapping elements in the array, no need for a type check. 443 instruction->ClearNeedsTypeCheck(); 444 return; 445 } 446 } 447 448 if (value->IsNullConstant()) { 449 instruction->ClearNeedsTypeCheck(); 450 return; 451 } 452 453 ScopedObjectAccess soa(Thread::Current()); 454 ReferenceTypeInfo array_rti = instruction->GetArray()->GetReferenceTypeInfo(); 455 ReferenceTypeInfo value_rti = value->GetReferenceTypeInfo(); 456 if (!array_rti.IsValid()) { 457 return; 458 } 459 460 if (value_rti.IsValid() && array_rti.CanArrayHold(value_rti)) { 461 instruction->ClearNeedsTypeCheck(); 462 return; 463 } 464 465 if (array_rti.IsObjectArray()) { 466 if (array_rti.IsExact()) { 467 instruction->ClearNeedsTypeCheck(); 468 return; 469 } 470 instruction->SetStaticTypeOfArrayIsObjectArray(); 471 } 472} 473 474void InstructionSimplifierVisitor::VisitTypeConversion(HTypeConversion* instruction) { 475 if (instruction->GetResultType() == instruction->GetInputType()) { 476 // Remove the instruction if it's converting to the same type. 477 instruction->ReplaceWith(instruction->GetInput()); 478 instruction->GetBlock()->RemoveInstruction(instruction); 479 } 480} 481 482void InstructionSimplifierVisitor::VisitAdd(HAdd* instruction) { 483 HConstant* input_cst = instruction->GetConstantRight(); 484 HInstruction* input_other = instruction->GetLeastConstantLeft(); 485 if ((input_cst != nullptr) && input_cst->IsZero()) { 486 // Replace code looking like 487 // ADD dst, src, 0 488 // with 489 // src 490 // Note that we cannot optimize `x + 0.0` to `x` for floating-point. When 491 // `x` is `-0.0`, the former expression yields `0.0`, while the later 492 // yields `-0.0`. 493 if (Primitive::IsIntegralType(instruction->GetType())) { 494 instruction->ReplaceWith(input_other); 495 instruction->GetBlock()->RemoveInstruction(instruction); 496 return; 497 } 498 } 499 500 HInstruction* left = instruction->GetLeft(); 501 HInstruction* right = instruction->GetRight(); 502 bool left_is_neg = left->IsNeg(); 503 bool right_is_neg = right->IsNeg(); 504 505 if (left_is_neg && right_is_neg) { 506 if (TryMoveNegOnInputsAfterBinop(instruction)) { 507 return; 508 } 509 } 510 511 HNeg* neg = left_is_neg ? left->AsNeg() : right->AsNeg(); 512 if ((left_is_neg ^ right_is_neg) && neg->HasOnlyOneNonEnvironmentUse()) { 513 // Replace code looking like 514 // NEG tmp, b 515 // ADD dst, a, tmp 516 // with 517 // SUB dst, a, b 518 // We do not perform the optimization if the input negation has environment 519 // uses or multiple non-environment uses as it could lead to worse code. In 520 // particular, we do not want the live range of `b` to be extended if we are 521 // not sure the initial 'NEG' instruction can be removed. 522 HInstruction* other = left_is_neg ? right : left; 523 HSub* sub = new(GetGraph()->GetArena()) HSub(instruction->GetType(), other, neg->GetInput()); 524 instruction->GetBlock()->ReplaceAndRemoveInstructionWith(instruction, sub); 525 RecordSimplification(); 526 neg->GetBlock()->RemoveInstruction(neg); 527 } 528} 529 530void InstructionSimplifierVisitor::VisitAnd(HAnd* instruction) { 531 HConstant* input_cst = instruction->GetConstantRight(); 532 HInstruction* input_other = instruction->GetLeastConstantLeft(); 533 534 if (input_cst != nullptr) { 535 int64_t value = Int64FromConstant(input_cst); 536 if (value == -1) { 537 // Replace code looking like 538 // AND dst, src, 0xFFF...FF 539 // with 540 // src 541 instruction->ReplaceWith(input_other); 542 instruction->GetBlock()->RemoveInstruction(instruction); 543 RecordSimplification(); 544 return; 545 } 546 // Eliminate And from UShr+And if the And-mask contains all the bits that 547 // can be non-zero after UShr. Transform Shr+And to UShr if the And-mask 548 // precisely clears the shifted-in sign bits. 549 if ((input_other->IsUShr() || input_other->IsShr()) && input_other->InputAt(1)->IsConstant()) { 550 size_t reg_bits = (instruction->GetResultType() == Primitive::kPrimLong) ? 64 : 32; 551 size_t shift = Int64FromConstant(input_other->InputAt(1)->AsConstant()) & (reg_bits - 1); 552 size_t num_tail_bits_set = CTZ(value + 1); 553 if ((num_tail_bits_set >= reg_bits - shift) && input_other->IsUShr()) { 554 // This AND clears only bits known to be clear, for example "(x >>> 24) & 0xff". 555 instruction->ReplaceWith(input_other); 556 instruction->GetBlock()->RemoveInstruction(instruction); 557 RecordSimplification(); 558 return; 559 } else if ((num_tail_bits_set == reg_bits - shift) && IsPowerOfTwo(value + 1) && 560 input_other->HasOnlyOneNonEnvironmentUse()) { 561 DCHECK(input_other->IsShr()); // For UShr, we would have taken the branch above. 562 // Replace SHR+AND with USHR, for example "(x >> 24) & 0xff" -> "x >>> 24". 563 HUShr* ushr = new (GetGraph()->GetArena()) HUShr(instruction->GetType(), 564 input_other->InputAt(0), 565 input_other->InputAt(1), 566 input_other->GetDexPc()); 567 instruction->GetBlock()->ReplaceAndRemoveInstructionWith(instruction, ushr); 568 input_other->GetBlock()->RemoveInstruction(input_other); 569 RecordSimplification(); 570 return; 571 } 572 } 573 } 574 575 // We assume that GVN has run before, so we only perform a pointer comparison. 576 // If for some reason the values are equal but the pointers are different, we 577 // are still correct and only miss an optimization opportunity. 578 if (instruction->GetLeft() == instruction->GetRight()) { 579 // Replace code looking like 580 // AND dst, src, src 581 // with 582 // src 583 instruction->ReplaceWith(instruction->GetLeft()); 584 instruction->GetBlock()->RemoveInstruction(instruction); 585 } 586} 587 588void InstructionSimplifierVisitor::VisitGreaterThan(HGreaterThan* condition) { 589 VisitCondition(condition); 590} 591 592void InstructionSimplifierVisitor::VisitGreaterThanOrEqual(HGreaterThanOrEqual* condition) { 593 VisitCondition(condition); 594} 595 596void InstructionSimplifierVisitor::VisitLessThan(HLessThan* condition) { 597 VisitCondition(condition); 598} 599 600void InstructionSimplifierVisitor::VisitLessThanOrEqual(HLessThanOrEqual* condition) { 601 VisitCondition(condition); 602} 603 604void InstructionSimplifierVisitor::VisitCondition(HCondition* condition) { 605 // Try to fold an HCompare into this HCondition. 606 607 // This simplification is currently supported on x86, x86_64, ARM and ARM64. 608 // TODO: Implement it for MIPS64. 609 InstructionSet instruction_set = GetGraph()->GetInstructionSet(); 610 if (instruction_set == kMips64) { 611 return; 612 } 613 614 HInstruction* left = condition->GetLeft(); 615 HInstruction* right = condition->GetRight(); 616 // We can only replace an HCondition which compares a Compare to 0. 617 // Both 'dx' and 'jack' generate a compare to 0 when compiling a 618 // condition with a long, float or double comparison as input. 619 if (!left->IsCompare() || !right->IsConstant() || right->AsIntConstant()->GetValue() != 0) { 620 // Conversion is not possible. 621 return; 622 } 623 624 // Is the Compare only used for this purpose? 625 if (!left->GetUses().HasOnlyOneUse()) { 626 // Someone else also wants the result of the compare. 627 return; 628 } 629 630 if (!left->GetEnvUses().IsEmpty()) { 631 // There is a reference to the compare result in an environment. Do we really need it? 632 if (GetGraph()->IsDebuggable()) { 633 return; 634 } 635 636 // We have to ensure that there are no deopt points in the sequence. 637 if (left->HasAnyEnvironmentUseBefore(condition)) { 638 return; 639 } 640 } 641 642 // Clean up any environment uses from the HCompare, if any. 643 left->RemoveEnvironmentUsers(); 644 645 // We have decided to fold the HCompare into the HCondition. Transfer the information. 646 condition->SetBias(left->AsCompare()->GetBias()); 647 648 // Replace the operands of the HCondition. 649 condition->ReplaceInput(left->InputAt(0), 0); 650 condition->ReplaceInput(left->InputAt(1), 1); 651 652 // Remove the HCompare. 653 left->GetBlock()->RemoveInstruction(left); 654 655 RecordSimplification(); 656} 657 658void InstructionSimplifierVisitor::VisitDiv(HDiv* instruction) { 659 HConstant* input_cst = instruction->GetConstantRight(); 660 HInstruction* input_other = instruction->GetLeastConstantLeft(); 661 Primitive::Type type = instruction->GetType(); 662 663 if ((input_cst != nullptr) && input_cst->IsOne()) { 664 // Replace code looking like 665 // DIV dst, src, 1 666 // with 667 // src 668 instruction->ReplaceWith(input_other); 669 instruction->GetBlock()->RemoveInstruction(instruction); 670 return; 671 } 672 673 if ((input_cst != nullptr) && input_cst->IsMinusOne()) { 674 // Replace code looking like 675 // DIV dst, src, -1 676 // with 677 // NEG dst, src 678 instruction->GetBlock()->ReplaceAndRemoveInstructionWith( 679 instruction, new (GetGraph()->GetArena()) HNeg(type, input_other)); 680 RecordSimplification(); 681 return; 682 } 683 684 if ((input_cst != nullptr) && Primitive::IsFloatingPointType(type)) { 685 // Try replacing code looking like 686 // DIV dst, src, constant 687 // with 688 // MUL dst, src, 1 / constant 689 HConstant* reciprocal = nullptr; 690 if (type == Primitive::Primitive::kPrimDouble) { 691 double value = input_cst->AsDoubleConstant()->GetValue(); 692 if (CanDivideByReciprocalMultiplyDouble(bit_cast<int64_t, double>(value))) { 693 reciprocal = GetGraph()->GetDoubleConstant(1.0 / value); 694 } 695 } else { 696 DCHECK_EQ(type, Primitive::kPrimFloat); 697 float value = input_cst->AsFloatConstant()->GetValue(); 698 if (CanDivideByReciprocalMultiplyFloat(bit_cast<int32_t, float>(value))) { 699 reciprocal = GetGraph()->GetFloatConstant(1.0f / value); 700 } 701 } 702 703 if (reciprocal != nullptr) { 704 instruction->GetBlock()->ReplaceAndRemoveInstructionWith( 705 instruction, new (GetGraph()->GetArena()) HMul(type, input_other, reciprocal)); 706 RecordSimplification(); 707 return; 708 } 709 } 710} 711 712void InstructionSimplifierVisitor::VisitMul(HMul* instruction) { 713 HConstant* input_cst = instruction->GetConstantRight(); 714 HInstruction* input_other = instruction->GetLeastConstantLeft(); 715 Primitive::Type type = instruction->GetType(); 716 HBasicBlock* block = instruction->GetBlock(); 717 ArenaAllocator* allocator = GetGraph()->GetArena(); 718 719 if (input_cst == nullptr) { 720 return; 721 } 722 723 if (input_cst->IsOne()) { 724 // Replace code looking like 725 // MUL dst, src, 1 726 // with 727 // src 728 instruction->ReplaceWith(input_other); 729 instruction->GetBlock()->RemoveInstruction(instruction); 730 return; 731 } 732 733 if (input_cst->IsMinusOne() && 734 (Primitive::IsFloatingPointType(type) || Primitive::IsIntOrLongType(type))) { 735 // Replace code looking like 736 // MUL dst, src, -1 737 // with 738 // NEG dst, src 739 HNeg* neg = new (allocator) HNeg(type, input_other); 740 block->ReplaceAndRemoveInstructionWith(instruction, neg); 741 RecordSimplification(); 742 return; 743 } 744 745 if (Primitive::IsFloatingPointType(type) && 746 ((input_cst->IsFloatConstant() && input_cst->AsFloatConstant()->GetValue() == 2.0f) || 747 (input_cst->IsDoubleConstant() && input_cst->AsDoubleConstant()->GetValue() == 2.0))) { 748 // Replace code looking like 749 // FP_MUL dst, src, 2.0 750 // with 751 // FP_ADD dst, src, src 752 // The 'int' and 'long' cases are handled below. 753 block->ReplaceAndRemoveInstructionWith(instruction, 754 new (allocator) HAdd(type, input_other, input_other)); 755 RecordSimplification(); 756 return; 757 } 758 759 if (Primitive::IsIntOrLongType(type)) { 760 int64_t factor = Int64FromConstant(input_cst); 761 // Even though constant propagation also takes care of the zero case, other 762 // optimizations can lead to having a zero multiplication. 763 if (factor == 0) { 764 // Replace code looking like 765 // MUL dst, src, 0 766 // with 767 // 0 768 instruction->ReplaceWith(input_cst); 769 instruction->GetBlock()->RemoveInstruction(instruction); 770 } else if (IsPowerOfTwo(factor)) { 771 // Replace code looking like 772 // MUL dst, src, pow_of_2 773 // with 774 // SHL dst, src, log2(pow_of_2) 775 HIntConstant* shift = GetGraph()->GetIntConstant(WhichPowerOf2(factor)); 776 HShl* shl = new(allocator) HShl(type, input_other, shift); 777 block->ReplaceAndRemoveInstructionWith(instruction, shl); 778 RecordSimplification(); 779 } 780 } 781} 782 783void InstructionSimplifierVisitor::VisitNeg(HNeg* instruction) { 784 HInstruction* input = instruction->GetInput(); 785 if (input->IsNeg()) { 786 // Replace code looking like 787 // NEG tmp, src 788 // NEG dst, tmp 789 // with 790 // src 791 HNeg* previous_neg = input->AsNeg(); 792 instruction->ReplaceWith(previous_neg->GetInput()); 793 instruction->GetBlock()->RemoveInstruction(instruction); 794 // We perform the optimization even if the input negation has environment 795 // uses since it allows removing the current instruction. But we only delete 796 // the input negation only if it is does not have any uses left. 797 if (!previous_neg->HasUses()) { 798 previous_neg->GetBlock()->RemoveInstruction(previous_neg); 799 } 800 RecordSimplification(); 801 return; 802 } 803 804 if (input->IsSub() && input->HasOnlyOneNonEnvironmentUse() && 805 !Primitive::IsFloatingPointType(input->GetType())) { 806 // Replace code looking like 807 // SUB tmp, a, b 808 // NEG dst, tmp 809 // with 810 // SUB dst, b, a 811 // We do not perform the optimization if the input subtraction has 812 // environment uses or multiple non-environment uses as it could lead to 813 // worse code. In particular, we do not want the live ranges of `a` and `b` 814 // to be extended if we are not sure the initial 'SUB' instruction can be 815 // removed. 816 // We do not perform optimization for fp because we could lose the sign of zero. 817 HSub* sub = input->AsSub(); 818 HSub* new_sub = 819 new (GetGraph()->GetArena()) HSub(instruction->GetType(), sub->GetRight(), sub->GetLeft()); 820 instruction->GetBlock()->ReplaceAndRemoveInstructionWith(instruction, new_sub); 821 if (!sub->HasUses()) { 822 sub->GetBlock()->RemoveInstruction(sub); 823 } 824 RecordSimplification(); 825 } 826} 827 828void InstructionSimplifierVisitor::VisitNot(HNot* instruction) { 829 HInstruction* input = instruction->GetInput(); 830 if (input->IsNot()) { 831 // Replace code looking like 832 // NOT tmp, src 833 // NOT dst, tmp 834 // with 835 // src 836 // We perform the optimization even if the input negation has environment 837 // uses since it allows removing the current instruction. But we only delete 838 // the input negation only if it is does not have any uses left. 839 HNot* previous_not = input->AsNot(); 840 instruction->ReplaceWith(previous_not->GetInput()); 841 instruction->GetBlock()->RemoveInstruction(instruction); 842 if (!previous_not->HasUses()) { 843 previous_not->GetBlock()->RemoveInstruction(previous_not); 844 } 845 RecordSimplification(); 846 } 847} 848 849void InstructionSimplifierVisitor::VisitOr(HOr* instruction) { 850 HConstant* input_cst = instruction->GetConstantRight(); 851 HInstruction* input_other = instruction->GetLeastConstantLeft(); 852 853 if ((input_cst != nullptr) && input_cst->IsZero()) { 854 // Replace code looking like 855 // OR dst, src, 0 856 // with 857 // src 858 instruction->ReplaceWith(input_other); 859 instruction->GetBlock()->RemoveInstruction(instruction); 860 return; 861 } 862 863 // We assume that GVN has run before, so we only perform a pointer comparison. 864 // If for some reason the values are equal but the pointers are different, we 865 // are still correct and only miss an optimization opportunity. 866 if (instruction->GetLeft() == instruction->GetRight()) { 867 // Replace code looking like 868 // OR dst, src, src 869 // with 870 // src 871 instruction->ReplaceWith(instruction->GetLeft()); 872 instruction->GetBlock()->RemoveInstruction(instruction); 873 } 874} 875 876void InstructionSimplifierVisitor::VisitShl(HShl* instruction) { 877 VisitShift(instruction); 878} 879 880void InstructionSimplifierVisitor::VisitShr(HShr* instruction) { 881 VisitShift(instruction); 882} 883 884void InstructionSimplifierVisitor::VisitSub(HSub* instruction) { 885 HConstant* input_cst = instruction->GetConstantRight(); 886 HInstruction* input_other = instruction->GetLeastConstantLeft(); 887 888 Primitive::Type type = instruction->GetType(); 889 if (Primitive::IsFloatingPointType(type)) { 890 return; 891 } 892 893 if ((input_cst != nullptr) && input_cst->IsZero()) { 894 // Replace code looking like 895 // SUB dst, src, 0 896 // with 897 // src 898 // Note that we cannot optimize `x - 0.0` to `x` for floating-point. When 899 // `x` is `-0.0`, the former expression yields `0.0`, while the later 900 // yields `-0.0`. 901 instruction->ReplaceWith(input_other); 902 instruction->GetBlock()->RemoveInstruction(instruction); 903 return; 904 } 905 906 HBasicBlock* block = instruction->GetBlock(); 907 ArenaAllocator* allocator = GetGraph()->GetArena(); 908 909 HInstruction* left = instruction->GetLeft(); 910 HInstruction* right = instruction->GetRight(); 911 if (left->IsConstant()) { 912 if (Int64FromConstant(left->AsConstant()) == 0) { 913 // Replace code looking like 914 // SUB dst, 0, src 915 // with 916 // NEG dst, src 917 // Note that we cannot optimize `0.0 - x` to `-x` for floating-point. When 918 // `x` is `0.0`, the former expression yields `0.0`, while the later 919 // yields `-0.0`. 920 HNeg* neg = new (allocator) HNeg(type, right); 921 block->ReplaceAndRemoveInstructionWith(instruction, neg); 922 RecordSimplification(); 923 return; 924 } 925 } 926 927 if (left->IsNeg() && right->IsNeg()) { 928 if (TryMoveNegOnInputsAfterBinop(instruction)) { 929 return; 930 } 931 } 932 933 if (right->IsNeg() && right->HasOnlyOneNonEnvironmentUse()) { 934 // Replace code looking like 935 // NEG tmp, b 936 // SUB dst, a, tmp 937 // with 938 // ADD dst, a, b 939 HAdd* add = new(GetGraph()->GetArena()) HAdd(type, left, right->AsNeg()->GetInput()); 940 instruction->GetBlock()->ReplaceAndRemoveInstructionWith(instruction, add); 941 RecordSimplification(); 942 right->GetBlock()->RemoveInstruction(right); 943 return; 944 } 945 946 if (left->IsNeg() && left->HasOnlyOneNonEnvironmentUse()) { 947 // Replace code looking like 948 // NEG tmp, a 949 // SUB dst, tmp, b 950 // with 951 // ADD tmp, a, b 952 // NEG dst, tmp 953 // The second version is not intrinsically better, but enables more 954 // transformations. 955 HAdd* add = new(GetGraph()->GetArena()) HAdd(type, left->AsNeg()->GetInput(), right); 956 instruction->GetBlock()->InsertInstructionBefore(add, instruction); 957 HNeg* neg = new (GetGraph()->GetArena()) HNeg(instruction->GetType(), add); 958 instruction->GetBlock()->InsertInstructionBefore(neg, instruction); 959 instruction->ReplaceWith(neg); 960 instruction->GetBlock()->RemoveInstruction(instruction); 961 RecordSimplification(); 962 left->GetBlock()->RemoveInstruction(left); 963 } 964} 965 966void InstructionSimplifierVisitor::VisitUShr(HUShr* instruction) { 967 VisitShift(instruction); 968} 969 970void InstructionSimplifierVisitor::VisitXor(HXor* instruction) { 971 HConstant* input_cst = instruction->GetConstantRight(); 972 HInstruction* input_other = instruction->GetLeastConstantLeft(); 973 974 if ((input_cst != nullptr) && input_cst->IsZero()) { 975 // Replace code looking like 976 // XOR dst, src, 0 977 // with 978 // src 979 instruction->ReplaceWith(input_other); 980 instruction->GetBlock()->RemoveInstruction(instruction); 981 return; 982 } 983 984 if ((input_cst != nullptr) && AreAllBitsSet(input_cst)) { 985 // Replace code looking like 986 // XOR dst, src, 0xFFF...FF 987 // with 988 // NOT dst, src 989 HNot* bitwise_not = new (GetGraph()->GetArena()) HNot(instruction->GetType(), input_other); 990 instruction->GetBlock()->ReplaceAndRemoveInstructionWith(instruction, bitwise_not); 991 RecordSimplification(); 992 return; 993 } 994} 995 996void InstructionSimplifierVisitor::VisitFakeString(HFakeString* instruction) { 997 HInstruction* actual_string = nullptr; 998 999 // Find the string we need to replace this instruction with. The actual string is 1000 // the return value of a StringFactory call. 1001 for (HUseIterator<HInstruction*> it(instruction->GetUses()); !it.Done(); it.Advance()) { 1002 HInstruction* use = it.Current()->GetUser(); 1003 if (use->IsInvokeStaticOrDirect() 1004 && use->AsInvokeStaticOrDirect()->IsStringFactoryFor(instruction)) { 1005 use->AsInvokeStaticOrDirect()->RemoveFakeStringArgumentAsLastInput(); 1006 actual_string = use; 1007 break; 1008 } 1009 } 1010 1011 // Check that there is no other instruction that thinks it is the factory for that string. 1012 if (kIsDebugBuild) { 1013 CHECK(actual_string != nullptr); 1014 for (HUseIterator<HInstruction*> it(instruction->GetUses()); !it.Done(); it.Advance()) { 1015 HInstruction* use = it.Current()->GetUser(); 1016 if (use->IsInvokeStaticOrDirect()) { 1017 CHECK(!use->AsInvokeStaticOrDirect()->IsStringFactoryFor(instruction)); 1018 } 1019 } 1020 } 1021 1022 // We need to remove any environment uses of the fake string that are not dominated by 1023 // `actual_string` to null. 1024 for (HUseIterator<HEnvironment*> it(instruction->GetEnvUses()); !it.Done(); it.Advance()) { 1025 HEnvironment* environment = it.Current()->GetUser(); 1026 if (!actual_string->StrictlyDominates(environment->GetHolder())) { 1027 environment->RemoveAsUserOfInput(it.Current()->GetIndex()); 1028 environment->SetRawEnvAt(it.Current()->GetIndex(), nullptr); 1029 } 1030 } 1031 1032 // Only uses dominated by `actual_string` must remain. We can safely replace and remove 1033 // `instruction`. 1034 instruction->ReplaceWith(actual_string); 1035 instruction->GetBlock()->RemoveInstruction(instruction); 1036} 1037 1038void InstructionSimplifierVisitor::VisitInvoke(HInvoke* instruction) { 1039 if (instruction->GetIntrinsic() == Intrinsics::kStringEquals) { 1040 HInstruction* argument = instruction->InputAt(1); 1041 HInstruction* receiver = instruction->InputAt(0); 1042 if (receiver == argument) { 1043 // Because String.equals is an instance call, the receiver is 1044 // a null check if we don't know it's null. The argument however, will 1045 // be the actual object. So we cannot end up in a situation where both 1046 // are equal but could be null. 1047 DCHECK(CanEnsureNotNullAt(argument, instruction)); 1048 instruction->ReplaceWith(GetGraph()->GetIntConstant(1)); 1049 instruction->GetBlock()->RemoveInstruction(instruction); 1050 } else { 1051 StringEqualsOptimizations optimizations(instruction); 1052 if (CanEnsureNotNullAt(argument, instruction)) { 1053 optimizations.SetArgumentNotNull(); 1054 } 1055 ScopedObjectAccess soa(Thread::Current()); 1056 if (argument->GetReferenceTypeInfo().IsStringClass()) { 1057 optimizations.SetArgumentIsString(); 1058 } 1059 } 1060 } 1061} 1062 1063} // namespace art 1064