GVN.cpp revision 95f0ba2703b2a49fb6f2373703fb42915774ee94
1//===- GVN.cpp - Eliminate redundant values and loads ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass performs global value numbering to eliminate fully redundant 11// instructions. It also performs simple dead load elimination. 12// 13//===----------------------------------------------------------------------===// 14 15#define DEBUG_TYPE "gvn" 16 17#include "llvm/Transforms/Scalar.h" 18#include "llvm/BasicBlock.h" 19#include "llvm/Constants.h" 20#include "llvm/DerivedTypes.h" 21#include "llvm/Function.h" 22#include "llvm/IntrinsicInst.h" 23#include "llvm/Instructions.h" 24#include "llvm/Value.h" 25#include "llvm/ADT/BitVector.h" 26#include "llvm/ADT/DenseMap.h" 27#include "llvm/ADT/DepthFirstIterator.h" 28#include "llvm/ADT/SmallPtrSet.h" 29#include "llvm/ADT/SmallVector.h" 30#include "llvm/ADT/Statistic.h" 31#include "llvm/Analysis/Dominators.h" 32#include "llvm/Analysis/AliasAnalysis.h" 33#include "llvm/Analysis/MemoryDependenceAnalysis.h" 34#include "llvm/Support/CFG.h" 35#include "llvm/Support/Compiler.h" 36using namespace llvm; 37 38//===----------------------------------------------------------------------===// 39// ValueTable Class 40//===----------------------------------------------------------------------===// 41 42/// This class holds the mapping between values and value numbers. It is used 43/// as an efficient mechanism to determine the expression-wise equivalence of 44/// two values. 45namespace { 46 struct VISIBILITY_HIDDEN Expression { 47 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, 48 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 49 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 50 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 51 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 52 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 53 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 54 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 55 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 56 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, EMPTY, 57 TOMBSTONE }; 58 59 ExpressionOpcode opcode; 60 const Type* type; 61 uint32_t firstVN; 62 uint32_t secondVN; 63 uint32_t thirdVN; 64 SmallVector<uint32_t, 4> varargs; 65 Value* function; 66 67 Expression() { } 68 Expression(ExpressionOpcode o) : opcode(o) { } 69 70 bool operator==(const Expression &other) const { 71 if (opcode != other.opcode) 72 return false; 73 else if (opcode == EMPTY || opcode == TOMBSTONE) 74 return true; 75 else if (type != other.type) 76 return false; 77 else if (function != other.function) 78 return false; 79 else if (firstVN != other.firstVN) 80 return false; 81 else if (secondVN != other.secondVN) 82 return false; 83 else if (thirdVN != other.thirdVN) 84 return false; 85 else { 86 if (varargs.size() != other.varargs.size()) 87 return false; 88 89 for (size_t i = 0; i < varargs.size(); ++i) 90 if (varargs[i] != other.varargs[i]) 91 return false; 92 93 return true; 94 } 95 } 96 97 bool operator!=(const Expression &other) const { 98 if (opcode != other.opcode) 99 return true; 100 else if (opcode == EMPTY || opcode == TOMBSTONE) 101 return false; 102 else if (type != other.type) 103 return true; 104 else if (function != other.function) 105 return true; 106 else if (firstVN != other.firstVN) 107 return true; 108 else if (secondVN != other.secondVN) 109 return true; 110 else if (thirdVN != other.thirdVN) 111 return true; 112 else { 113 if (varargs.size() != other.varargs.size()) 114 return true; 115 116 for (size_t i = 0; i < varargs.size(); ++i) 117 if (varargs[i] != other.varargs[i]) 118 return true; 119 120 return false; 121 } 122 } 123 }; 124 125 class VISIBILITY_HIDDEN ValueTable { 126 private: 127 DenseMap<Value*, uint32_t> valueNumbering; 128 DenseMap<Expression, uint32_t> expressionNumbering; 129 AliasAnalysis* AA; 130 131 uint32_t nextValueNumber; 132 133 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 134 Expression::ExpressionOpcode getOpcode(CmpInst* C); 135 Expression::ExpressionOpcode getOpcode(CastInst* C); 136 Expression create_expression(BinaryOperator* BO); 137 Expression create_expression(CmpInst* C); 138 Expression create_expression(ShuffleVectorInst* V); 139 Expression create_expression(ExtractElementInst* C); 140 Expression create_expression(InsertElementInst* V); 141 Expression create_expression(SelectInst* V); 142 Expression create_expression(CastInst* C); 143 Expression create_expression(GetElementPtrInst* G); 144 Expression create_expression(CallInst* C); 145 public: 146 ValueTable() : nextValueNumber(1) { } 147 uint32_t lookup_or_add(Value* V); 148 uint32_t lookup(Value* V) const; 149 void add(Value* V, uint32_t num); 150 void clear(); 151 void erase(Value* v); 152 unsigned size(); 153 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 154 uint32_t hash_operand(Value* v); 155 }; 156} 157 158namespace llvm { 159template <> struct DenseMapInfo<Expression> { 160 static inline Expression getEmptyKey() { 161 return Expression(Expression::EMPTY); 162 } 163 164 static inline Expression getTombstoneKey() { 165 return Expression(Expression::TOMBSTONE); 166 } 167 168 static unsigned getHashValue(const Expression e) { 169 unsigned hash = e.opcode; 170 171 hash = e.firstVN + hash * 37; 172 hash = e.secondVN + hash * 37; 173 hash = e.thirdVN + hash * 37; 174 175 hash = (unsigned)((uintptr_t)e.type >> 4) ^ 176 (unsigned)((uintptr_t)e.type >> 9) + 177 hash * 37; 178 179 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 180 E = e.varargs.end(); I != E; ++I) 181 hash = *I + hash * 37; 182 183 hash = (unsigned)((uintptr_t)e.function >> 4) ^ 184 (unsigned)((uintptr_t)e.function >> 9) + 185 hash * 37; 186 187 return hash; 188 } 189 static bool isEqual(const Expression &LHS, const Expression &RHS) { 190 return LHS == RHS; 191 } 192 static bool isPod() { return true; } 193}; 194} 195 196//===----------------------------------------------------------------------===// 197// ValueTable Internal Functions 198//===----------------------------------------------------------------------===// 199Expression::ExpressionOpcode 200 ValueTable::getOpcode(BinaryOperator* BO) { 201 switch(BO->getOpcode()) { 202 case Instruction::Add: 203 return Expression::ADD; 204 case Instruction::Sub: 205 return Expression::SUB; 206 case Instruction::Mul: 207 return Expression::MUL; 208 case Instruction::UDiv: 209 return Expression::UDIV; 210 case Instruction::SDiv: 211 return Expression::SDIV; 212 case Instruction::FDiv: 213 return Expression::FDIV; 214 case Instruction::URem: 215 return Expression::UREM; 216 case Instruction::SRem: 217 return Expression::SREM; 218 case Instruction::FRem: 219 return Expression::FREM; 220 case Instruction::Shl: 221 return Expression::SHL; 222 case Instruction::LShr: 223 return Expression::LSHR; 224 case Instruction::AShr: 225 return Expression::ASHR; 226 case Instruction::And: 227 return Expression::AND; 228 case Instruction::Or: 229 return Expression::OR; 230 case Instruction::Xor: 231 return Expression::XOR; 232 233 // THIS SHOULD NEVER HAPPEN 234 default: 235 assert(0 && "Binary operator with unknown opcode?"); 236 return Expression::ADD; 237 } 238} 239 240Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 241 if (C->getOpcode() == Instruction::ICmp) { 242 switch (C->getPredicate()) { 243 case ICmpInst::ICMP_EQ: 244 return Expression::ICMPEQ; 245 case ICmpInst::ICMP_NE: 246 return Expression::ICMPNE; 247 case ICmpInst::ICMP_UGT: 248 return Expression::ICMPUGT; 249 case ICmpInst::ICMP_UGE: 250 return Expression::ICMPUGE; 251 case ICmpInst::ICMP_ULT: 252 return Expression::ICMPULT; 253 case ICmpInst::ICMP_ULE: 254 return Expression::ICMPULE; 255 case ICmpInst::ICMP_SGT: 256 return Expression::ICMPSGT; 257 case ICmpInst::ICMP_SGE: 258 return Expression::ICMPSGE; 259 case ICmpInst::ICMP_SLT: 260 return Expression::ICMPSLT; 261 case ICmpInst::ICMP_SLE: 262 return Expression::ICMPSLE; 263 264 // THIS SHOULD NEVER HAPPEN 265 default: 266 assert(0 && "Comparison with unknown predicate?"); 267 return Expression::ICMPEQ; 268 } 269 } else { 270 switch (C->getPredicate()) { 271 case FCmpInst::FCMP_OEQ: 272 return Expression::FCMPOEQ; 273 case FCmpInst::FCMP_OGT: 274 return Expression::FCMPOGT; 275 case FCmpInst::FCMP_OGE: 276 return Expression::FCMPOGE; 277 case FCmpInst::FCMP_OLT: 278 return Expression::FCMPOLT; 279 case FCmpInst::FCMP_OLE: 280 return Expression::FCMPOLE; 281 case FCmpInst::FCMP_ONE: 282 return Expression::FCMPONE; 283 case FCmpInst::FCMP_ORD: 284 return Expression::FCMPORD; 285 case FCmpInst::FCMP_UNO: 286 return Expression::FCMPUNO; 287 case FCmpInst::FCMP_UEQ: 288 return Expression::FCMPUEQ; 289 case FCmpInst::FCMP_UGT: 290 return Expression::FCMPUGT; 291 case FCmpInst::FCMP_UGE: 292 return Expression::FCMPUGE; 293 case FCmpInst::FCMP_ULT: 294 return Expression::FCMPULT; 295 case FCmpInst::FCMP_ULE: 296 return Expression::FCMPULE; 297 case FCmpInst::FCMP_UNE: 298 return Expression::FCMPUNE; 299 300 // THIS SHOULD NEVER HAPPEN 301 default: 302 assert(0 && "Comparison with unknown predicate?"); 303 return Expression::FCMPOEQ; 304 } 305 } 306} 307 308Expression::ExpressionOpcode 309 ValueTable::getOpcode(CastInst* C) { 310 switch(C->getOpcode()) { 311 case Instruction::Trunc: 312 return Expression::TRUNC; 313 case Instruction::ZExt: 314 return Expression::ZEXT; 315 case Instruction::SExt: 316 return Expression::SEXT; 317 case Instruction::FPToUI: 318 return Expression::FPTOUI; 319 case Instruction::FPToSI: 320 return Expression::FPTOSI; 321 case Instruction::UIToFP: 322 return Expression::UITOFP; 323 case Instruction::SIToFP: 324 return Expression::SITOFP; 325 case Instruction::FPTrunc: 326 return Expression::FPTRUNC; 327 case Instruction::FPExt: 328 return Expression::FPEXT; 329 case Instruction::PtrToInt: 330 return Expression::PTRTOINT; 331 case Instruction::IntToPtr: 332 return Expression::INTTOPTR; 333 case Instruction::BitCast: 334 return Expression::BITCAST; 335 336 // THIS SHOULD NEVER HAPPEN 337 default: 338 assert(0 && "Cast operator with unknown opcode?"); 339 return Expression::BITCAST; 340 } 341} 342 343uint32_t ValueTable::hash_operand(Value* v) { 344 if (CallInst* CI = dyn_cast<CallInst>(v)) 345 if (!AA->doesNotAccessMemory(CI)) 346 return nextValueNumber++; 347 348 return lookup_or_add(v); 349} 350 351Expression ValueTable::create_expression(CallInst* C) { 352 Expression e; 353 354 e.type = C->getType(); 355 e.firstVN = 0; 356 e.secondVN = 0; 357 e.thirdVN = 0; 358 e.function = C->getCalledFunction(); 359 e.opcode = Expression::CALL; 360 361 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 362 I != E; ++I) 363 e.varargs.push_back(hash_operand(*I)); 364 365 return e; 366} 367 368Expression ValueTable::create_expression(BinaryOperator* BO) { 369 Expression e; 370 371 e.firstVN = hash_operand(BO->getOperand(0)); 372 e.secondVN = hash_operand(BO->getOperand(1)); 373 e.thirdVN = 0; 374 e.function = 0; 375 e.type = BO->getType(); 376 e.opcode = getOpcode(BO); 377 378 return e; 379} 380 381Expression ValueTable::create_expression(CmpInst* C) { 382 Expression e; 383 384 e.firstVN = hash_operand(C->getOperand(0)); 385 e.secondVN = hash_operand(C->getOperand(1)); 386 e.thirdVN = 0; 387 e.function = 0; 388 e.type = C->getType(); 389 e.opcode = getOpcode(C); 390 391 return e; 392} 393 394Expression ValueTable::create_expression(CastInst* C) { 395 Expression e; 396 397 e.firstVN = hash_operand(C->getOperand(0)); 398 e.secondVN = 0; 399 e.thirdVN = 0; 400 e.function = 0; 401 e.type = C->getType(); 402 e.opcode = getOpcode(C); 403 404 return e; 405} 406 407Expression ValueTable::create_expression(ShuffleVectorInst* S) { 408 Expression e; 409 410 e.firstVN = hash_operand(S->getOperand(0)); 411 e.secondVN = hash_operand(S->getOperand(1)); 412 e.thirdVN = hash_operand(S->getOperand(2)); 413 e.function = 0; 414 e.type = S->getType(); 415 e.opcode = Expression::SHUFFLE; 416 417 return e; 418} 419 420Expression ValueTable::create_expression(ExtractElementInst* E) { 421 Expression e; 422 423 e.firstVN = hash_operand(E->getOperand(0)); 424 e.secondVN = hash_operand(E->getOperand(1)); 425 e.thirdVN = 0; 426 e.function = 0; 427 e.type = E->getType(); 428 e.opcode = Expression::EXTRACT; 429 430 return e; 431} 432 433Expression ValueTable::create_expression(InsertElementInst* I) { 434 Expression e; 435 436 e.firstVN = hash_operand(I->getOperand(0)); 437 e.secondVN = hash_operand(I->getOperand(1)); 438 e.thirdVN = hash_operand(I->getOperand(2)); 439 e.function = 0; 440 e.type = I->getType(); 441 e.opcode = Expression::INSERT; 442 443 return e; 444} 445 446Expression ValueTable::create_expression(SelectInst* I) { 447 Expression e; 448 449 e.firstVN = hash_operand(I->getCondition()); 450 e.secondVN = hash_operand(I->getTrueValue()); 451 e.thirdVN = hash_operand(I->getFalseValue()); 452 e.function = 0; 453 e.type = I->getType(); 454 e.opcode = Expression::SELECT; 455 456 return e; 457} 458 459Expression ValueTable::create_expression(GetElementPtrInst* G) { 460 Expression e; 461 462 e.firstVN = hash_operand(G->getPointerOperand()); 463 e.secondVN = 0; 464 e.thirdVN = 0; 465 e.function = 0; 466 e.type = G->getType(); 467 e.opcode = Expression::GEP; 468 469 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 470 I != E; ++I) 471 e.varargs.push_back(hash_operand(*I)); 472 473 return e; 474} 475 476//===----------------------------------------------------------------------===// 477// ValueTable External Functions 478//===----------------------------------------------------------------------===// 479 480/// lookup_or_add - Returns the value number for the specified value, assigning 481/// it a new number if it did not have one before. 482uint32_t ValueTable::lookup_or_add(Value* V) { 483 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 484 if (VI != valueNumbering.end()) 485 return VI->second; 486 487 if (CallInst* C = dyn_cast<CallInst>(V)) { 488 if (AA->onlyReadsMemory(C)) { // includes doesNotAccessMemory 489 Expression e = create_expression(C); 490 491 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 492 if (EI != expressionNumbering.end()) { 493 valueNumbering.insert(std::make_pair(V, EI->second)); 494 return EI->second; 495 } else { 496 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 497 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 498 499 return nextValueNumber++; 500 } 501 } else { 502 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 503 return nextValueNumber++; 504 } 505 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 506 Expression e = create_expression(BO); 507 508 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 509 if (EI != expressionNumbering.end()) { 510 valueNumbering.insert(std::make_pair(V, EI->second)); 511 return EI->second; 512 } else { 513 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 514 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 515 516 return nextValueNumber++; 517 } 518 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 519 Expression e = create_expression(C); 520 521 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 522 if (EI != expressionNumbering.end()) { 523 valueNumbering.insert(std::make_pair(V, EI->second)); 524 return EI->second; 525 } else { 526 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 527 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 528 529 return nextValueNumber++; 530 } 531 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 532 Expression e = create_expression(U); 533 534 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 535 if (EI != expressionNumbering.end()) { 536 valueNumbering.insert(std::make_pair(V, EI->second)); 537 return EI->second; 538 } else { 539 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 540 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 541 542 return nextValueNumber++; 543 } 544 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 545 Expression e = create_expression(U); 546 547 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 548 if (EI != expressionNumbering.end()) { 549 valueNumbering.insert(std::make_pair(V, EI->second)); 550 return EI->second; 551 } else { 552 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 553 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 554 555 return nextValueNumber++; 556 } 557 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 558 Expression e = create_expression(U); 559 560 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 561 if (EI != expressionNumbering.end()) { 562 valueNumbering.insert(std::make_pair(V, EI->second)); 563 return EI->second; 564 } else { 565 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 566 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 567 568 return nextValueNumber++; 569 } 570 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 571 Expression e = create_expression(U); 572 573 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 574 if (EI != expressionNumbering.end()) { 575 valueNumbering.insert(std::make_pair(V, EI->second)); 576 return EI->second; 577 } else { 578 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 579 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 580 581 return nextValueNumber++; 582 } 583 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 584 Expression e = create_expression(U); 585 586 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 587 if (EI != expressionNumbering.end()) { 588 valueNumbering.insert(std::make_pair(V, EI->second)); 589 return EI->second; 590 } else { 591 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 592 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 593 594 return nextValueNumber++; 595 } 596 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 597 Expression e = create_expression(U); 598 599 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 600 if (EI != expressionNumbering.end()) { 601 valueNumbering.insert(std::make_pair(V, EI->second)); 602 return EI->second; 603 } else { 604 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 605 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 606 607 return nextValueNumber++; 608 } 609 } else { 610 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 611 return nextValueNumber++; 612 } 613} 614 615/// lookup - Returns the value number of the specified value. Fails if 616/// the value has not yet been numbered. 617uint32_t ValueTable::lookup(Value* V) const { 618 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 619 if (VI != valueNumbering.end()) 620 return VI->second; 621 else 622 assert(0 && "Value not numbered?"); 623 624 return 0; 625} 626 627/// clear - Remove all entries from the ValueTable 628void ValueTable::clear() { 629 valueNumbering.clear(); 630 expressionNumbering.clear(); 631 nextValueNumber = 1; 632} 633 634/// erase - Remove a value from the value numbering 635void ValueTable::erase(Value* V) { 636 valueNumbering.erase(V); 637} 638 639//===----------------------------------------------------------------------===// 640// ValueNumberedSet Class 641//===----------------------------------------------------------------------===// 642namespace { 643class ValueNumberedSet { 644 private: 645 SmallPtrSet<Value*, 8> contents; 646 BitVector numbers; 647 public: 648 ValueNumberedSet() { numbers.resize(1); } 649 ValueNumberedSet(const ValueNumberedSet& other) { 650 numbers = other.numbers; 651 contents = other.contents; 652 } 653 654 typedef SmallPtrSet<Value*, 8>::iterator iterator; 655 656 iterator begin() { return contents.begin(); } 657 iterator end() { return contents.end(); } 658 659 bool insert(Value* v) { return contents.insert(v); } 660 void insert(iterator I, iterator E) { contents.insert(I, E); } 661 void erase(Value* v) { contents.erase(v); } 662 unsigned count(Value* v) { return contents.count(v); } 663 size_t size() { return contents.size(); } 664 665 void set(unsigned i) { 666 if (i >= numbers.size()) 667 numbers.resize(i+1); 668 669 numbers.set(i); 670 } 671 672 void operator=(const ValueNumberedSet& other) { 673 contents = other.contents; 674 numbers = other.numbers; 675 } 676 677 void reset(unsigned i) { 678 if (i < numbers.size()) 679 numbers.reset(i); 680 } 681 682 bool test(unsigned i) { 683 if (i >= numbers.size()) 684 return false; 685 686 return numbers.test(i); 687 } 688 689 void clear() { 690 contents.clear(); 691 numbers.clear(); 692 } 693}; 694} 695 696//===----------------------------------------------------------------------===// 697// GVN Pass 698//===----------------------------------------------------------------------===// 699 700namespace { 701 702 class VISIBILITY_HIDDEN GVN : public FunctionPass { 703 bool runOnFunction(Function &F); 704 public: 705 static char ID; // Pass identification, replacement for typeid 706 GVN() : FunctionPass((intptr_t)&ID) { } 707 708 private: 709 ValueTable VN; 710 711 DenseMap<BasicBlock*, ValueNumberedSet> availableOut; 712 713 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 714 PhiMapType phiMap; 715 716 717 // This transformation requires dominator postdominator info 718 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 719 AU.setPreservesCFG(); 720 AU.addRequired<DominatorTree>(); 721 AU.addRequired<MemoryDependenceAnalysis>(); 722 AU.addRequired<AliasAnalysis>(); 723 AU.addPreserved<AliasAnalysis>(); 724 AU.addPreserved<MemoryDependenceAnalysis>(); 725 } 726 727 // Helper fuctions 728 // FIXME: eliminate or document these better 729 Value* find_leader(ValueNumberedSet& vals, uint32_t v) ; 730 void val_insert(ValueNumberedSet& s, Value* v); 731 bool processLoad(LoadInst* L, 732 DenseMap<Value*, LoadInst*>& lastLoad, 733 SmallVector<Instruction*, 4>& toErase); 734 bool processInstruction(Instruction* I, 735 ValueNumberedSet& currAvail, 736 DenseMap<Value*, LoadInst*>& lastSeenLoad, 737 SmallVector<Instruction*, 4>& toErase); 738 bool processNonLocalLoad(LoadInst* L, 739 SmallVector<Instruction*, 4>& toErase); 740 bool processMemCpy(MemCpyInst* M, SmallVector<Instruction*, 4>& toErase); 741 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig, 742 DenseMap<BasicBlock*, Value*> &Phis, 743 bool top_level = false); 744 void dump(DenseMap<BasicBlock*, Value*>& d); 745 bool iterateOnFunction(Function &F); 746 Value* CollapsePhi(PHINode* p); 747 bool isSafeReplacement(PHINode* p, Instruction* inst); 748 }; 749 750 char GVN::ID = 0; 751 752} 753 754// createGVNPass - The public interface to this file... 755FunctionPass *llvm::createGVNPass() { return new GVN(); } 756 757static RegisterPass<GVN> X("gvn", 758 "Global Value Numbering"); 759 760STATISTIC(NumGVNInstr, "Number of instructions deleted"); 761STATISTIC(NumGVNLoad, "Number of loads deleted"); 762 763/// find_leader - Given a set and a value number, return the first 764/// element of the set with that value number, or 0 if no such element 765/// is present 766Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) { 767 if (!vals.test(v)) 768 return 0; 769 770 for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end(); 771 I != E; ++I) 772 if (v == VN.lookup(*I)) 773 return *I; 774 775 assert(0 && "No leader found, but present bit is set?"); 776 return 0; 777} 778 779/// val_insert - Insert a value into a set only if there is not a value 780/// with the same value number already in the set 781void GVN::val_insert(ValueNumberedSet& s, Value* v) { 782 uint32_t num = VN.lookup(v); 783 if (!s.test(num)) 784 s.insert(v); 785} 786 787void GVN::dump(DenseMap<BasicBlock*, Value*>& d) { 788 printf("{\n"); 789 for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(), 790 E = d.end(); I != E; ++I) { 791 if (I->second == MemoryDependenceAnalysis::None) 792 printf("None\n"); 793 else 794 I->second->dump(); 795 } 796 printf("}\n"); 797} 798 799Value* GVN::CollapsePhi(PHINode* p) { 800 DominatorTree &DT = getAnalysis<DominatorTree>(); 801 Value* constVal = p->hasConstantValue(); 802 803 if (constVal) { 804 if (Instruction* inst = dyn_cast<Instruction>(constVal)) { 805 if (DT.dominates(inst, p)) 806 if (isSafeReplacement(p, inst)) 807 return inst; 808 } else { 809 return constVal; 810 } 811 } 812 813 return 0; 814} 815 816bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 817 if (!isa<PHINode>(inst)) 818 return true; 819 820 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 821 UI != E; ++UI) 822 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 823 if (use_phi->getParent() == inst->getParent()) 824 return false; 825 826 return true; 827} 828 829/// GetValueForBlock - Get the value to use within the specified basic block. 830/// available values are in Phis. 831Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig, 832 DenseMap<BasicBlock*, Value*> &Phis, 833 bool top_level) { 834 835 // If we have already computed this value, return the previously computed val. 836 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 837 if (V != Phis.end() && !top_level) return V->second; 838 839 BasicBlock* singlePred = BB->getSinglePredecessor(); 840 if (singlePred) { 841 Value *ret = GetValueForBlock(singlePred, orig, Phis); 842 Phis[BB] = ret; 843 return ret; 844 } 845 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 846 // now, then get values to fill in the incoming values for the PHI. 847 PHINode *PN = new PHINode(orig->getType(), orig->getName()+".rle", 848 BB->begin()); 849 PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB))); 850 851 if (Phis.count(BB) == 0) 852 Phis.insert(std::make_pair(BB, PN)); 853 854 // Fill in the incoming values for the block. 855 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 856 Value* val = GetValueForBlock(*PI, orig, Phis); 857 858 PN->addIncoming(val, *PI); 859 } 860 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 861 AA.copyValue(orig, PN); 862 863 // Attempt to collapse PHI nodes that are trivially redundant 864 Value* v = CollapsePhi(PN); 865 if (v) { 866 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 867 868 MD.removeInstruction(PN); 869 PN->replaceAllUsesWith(v); 870 871 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 872 E = Phis.end(); I != E; ++I) 873 if (I->second == PN) 874 I->second = v; 875 876 PN->eraseFromParent(); 877 878 Phis[BB] = v; 879 880 return v; 881 } 882 883 // Cache our phi construction results 884 phiMap[orig->getPointerOperand()].insert(PN); 885 return PN; 886} 887 888/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 889/// non-local by performing PHI construction. 890bool GVN::processNonLocalLoad(LoadInst* L, 891 SmallVector<Instruction*, 4>& toErase) { 892 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 893 894 // Find the non-local dependencies of the load 895 DenseMap<BasicBlock*, Value*> deps; 896 MD.getNonLocalDependency(L, deps); 897 898 DenseMap<BasicBlock*, Value*> repl; 899 900 // Filter out useless results (non-locals, etc) 901 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end(); 902 I != E; ++I) 903 if (I->second == MemoryDependenceAnalysis::None) { 904 return false; 905 } else if (I->second == MemoryDependenceAnalysis::NonLocal) { 906 continue; 907 } else if (StoreInst* S = dyn_cast<StoreInst>(I->second)) { 908 if (S->getPointerOperand() == L->getPointerOperand()) 909 repl[I->first] = S->getOperand(0); 910 else 911 return false; 912 } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) { 913 if (LD->getPointerOperand() == L->getPointerOperand()) 914 repl[I->first] = LD; 915 else 916 return false; 917 } else { 918 return false; 919 } 920 921 // Use cached PHI construction information from previous runs 922 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()]; 923 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 924 I != E; ++I) { 925 if ((*I)->getParent() == L->getParent()) { 926 MD.removeInstruction(L); 927 L->replaceAllUsesWith(*I); 928 toErase.push_back(L); 929 NumGVNLoad++; 930 931 return true; 932 } else { 933 repl.insert(std::make_pair((*I)->getParent(), *I)); 934 } 935 } 936 937 // Perform PHI construction 938 SmallPtrSet<BasicBlock*, 4> visited; 939 Value* v = GetValueForBlock(L->getParent(), L, repl, true); 940 941 MD.removeInstruction(L); 942 L->replaceAllUsesWith(v); 943 toErase.push_back(L); 944 NumGVNLoad++; 945 946 return true; 947} 948 949/// processLoad - Attempt to eliminate a load, first by eliminating it 950/// locally, and then attempting non-local elimination if that fails. 951bool GVN::processLoad(LoadInst* L, 952 DenseMap<Value*, LoadInst*>& lastLoad, 953 SmallVector<Instruction*, 4>& toErase) { 954 if (L->isVolatile()) { 955 lastLoad[L->getPointerOperand()] = L; 956 return false; 957 } 958 959 Value* pointer = L->getPointerOperand(); 960 LoadInst*& last = lastLoad[pointer]; 961 962 // ... to a pointer that has been loaded from before... 963 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 964 bool removedNonLocal = false; 965 Instruction* dep = MD.getDependency(L); 966 if (dep == MemoryDependenceAnalysis::NonLocal && 967 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) { 968 removedNonLocal = processNonLocalLoad(L, toErase); 969 970 if (!removedNonLocal) 971 last = L; 972 973 return removedNonLocal; 974 } 975 976 977 bool deletedLoad = false; 978 979 // Walk up the dependency chain until we either find 980 // a dependency we can use, or we can't walk any further 981 while (dep != MemoryDependenceAnalysis::None && 982 dep != MemoryDependenceAnalysis::NonLocal && 983 (isa<LoadInst>(dep) || isa<StoreInst>(dep))) { 984 // ... that depends on a store ... 985 if (StoreInst* S = dyn_cast<StoreInst>(dep)) { 986 if (S->getPointerOperand() == pointer) { 987 // Remove it! 988 MD.removeInstruction(L); 989 990 L->replaceAllUsesWith(S->getOperand(0)); 991 toErase.push_back(L); 992 deletedLoad = true; 993 NumGVNLoad++; 994 } 995 996 // Whether we removed it or not, we can't 997 // go any further 998 break; 999 } else if (!last) { 1000 // If we don't depend on a store, and we haven't 1001 // been loaded before, bail. 1002 break; 1003 } else if (dep == last) { 1004 // Remove it! 1005 MD.removeInstruction(L); 1006 1007 L->replaceAllUsesWith(last); 1008 toErase.push_back(L); 1009 deletedLoad = true; 1010 NumGVNLoad++; 1011 1012 break; 1013 } else { 1014 dep = MD.getDependency(L, dep); 1015 } 1016 } 1017 1018 if (dep != MemoryDependenceAnalysis::None && 1019 dep != MemoryDependenceAnalysis::NonLocal && 1020 isa<AllocationInst>(dep)) { 1021 // Check that this load is actually from the 1022 // allocation we found 1023 Value* v = L->getOperand(0); 1024 while (true) { 1025 if (BitCastInst *BC = dyn_cast<BitCastInst>(v)) 1026 v = BC->getOperand(0); 1027 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v)) 1028 v = GEP->getOperand(0); 1029 else 1030 break; 1031 } 1032 if (v == dep) { 1033 // If this load depends directly on an allocation, there isn't 1034 // anything stored there; therefore, we can optimize this load 1035 // to undef. 1036 MD.removeInstruction(L); 1037 1038 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1039 toErase.push_back(L); 1040 deletedLoad = true; 1041 NumGVNLoad++; 1042 } 1043 } 1044 1045 if (!deletedLoad) 1046 last = L; 1047 1048 return deletedLoad; 1049} 1050 1051/// processMemCpy - perform simplication of memcpy's. If we have memcpy A which 1052/// copies X to Y, and memcpy B which copies Y to Z, then we can rewrite B to be 1053/// a memcpy from X to Z (or potentially a memmove, depending on circumstances). 1054/// This allows later passes to remove the first memcpy altogether. 1055bool GVN::processMemCpy(MemCpyInst* M, 1056 SmallVector<Instruction*, 4>& toErase) { 1057 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1058 1059 // First, we have to check that the dependency is another memcpy 1060 Instruction* dep = MD.getDependency(M); 1061 if (dep == MemoryDependenceAnalysis::None || 1062 dep == MemoryDependenceAnalysis::NonLocal || 1063 !isa<MemCpyInst>(dep)) 1064 return false; 1065 1066 // We can only transforms memcpy's where the dest of one is the source of the 1067 // other 1068 MemCpyInst* MDep = cast<MemCpyInst>(dep); 1069 if (M->getSource() != MDep->getDest()) 1070 return false; 1071 1072 // Second, the length of the memcpy's must be the same, or the preceeding one 1073 // must be larger than the following one. 1074 ConstantInt* C1 = dyn_cast<ConstantInt>(MDep->getLength()); 1075 ConstantInt* C2 = dyn_cast<ConstantInt>(M->getLength()); 1076 if (!C1 || !C2) 1077 return false; 1078 1079 uint64_t CpySize = C1->getValue().getZExtValue(); 1080 uint64_t DepSize = C2->getValue().getZExtValue(); 1081 1082 if (DepSize < CpySize) 1083 return false; 1084 1085 // Finally, we have to make sure that the dest of the second does not 1086 // alias the source of the first 1087 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 1088 if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) != 1089 AliasAnalysis::NoAlias) 1090 return false; 1091 else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) != 1092 AliasAnalysis::NoAlias) 1093 return false; 1094 else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize) 1095 != AliasAnalysis::NoAlias) 1096 return false; 1097 1098 // If all checks passed, then we can transform these memcpy's 1099 bool is32bit = M->getIntrinsicID() == Intrinsic::memcpy_i32; 1100 Function* MemMoveFun = Intrinsic::getDeclaration( 1101 M->getParent()->getParent()->getParent(), 1102 is32bit ? Intrinsic::memcpy_i32 : 1103 Intrinsic::memcpy_i64); 1104 1105 std::vector<Value*> args; 1106 args.push_back(M->getRawDest()); 1107 args.push_back(MDep->getRawSource()); 1108 args.push_back(M->getLength()); 1109 args.push_back(M->getAlignment()); 1110 1111 CallInst* C = new CallInst(MemMoveFun, args.begin(), args.end(), "", M); 1112 1113 if (MD.getDependency(C) == MDep) { 1114 MD.dropInstruction(M); 1115 toErase.push_back(M); 1116 return true; 1117 } else { 1118 MD.removeInstruction(C); 1119 toErase.push_back(C); 1120 return false; 1121 } 1122} 1123 1124/// processInstruction - When calculating availability, handle an instruction 1125/// by inserting it into the appropriate sets 1126bool GVN::processInstruction(Instruction* I, 1127 ValueNumberedSet& currAvail, 1128 DenseMap<Value*, LoadInst*>& lastSeenLoad, 1129 SmallVector<Instruction*, 4>& toErase) { 1130 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1131 return processLoad(L, lastSeenLoad, toErase); 1132 } else if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) { 1133 return processMemCpy(M, toErase); 1134 } 1135 1136 unsigned num = VN.lookup_or_add(I); 1137 1138 // Collapse PHI nodes 1139 if (PHINode* p = dyn_cast<PHINode>(I)) { 1140 Value* constVal = CollapsePhi(p); 1141 1142 if (constVal) { 1143 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1144 PI != PE; ++PI) 1145 if (PI->second.count(p)) 1146 PI->second.erase(p); 1147 1148 p->replaceAllUsesWith(constVal); 1149 toErase.push_back(p); 1150 } 1151 // Perform value-number based elimination 1152 } else if (currAvail.test(num)) { 1153 Value* repl = find_leader(currAvail, num); 1154 1155 if (CallInst* CI = dyn_cast<CallInst>(I)) { 1156 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 1157 if (!AA.doesNotAccessMemory(CI)) { 1158 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1159 if (cast<Instruction>(repl)->getParent() != CI->getParent() || 1160 MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) { 1161 // There must be an intervening may-alias store, so nothing from 1162 // this point on will be able to be replaced with the preceding call 1163 currAvail.erase(repl); 1164 currAvail.insert(I); 1165 1166 return false; 1167 } 1168 } 1169 } 1170 1171 // Remove it! 1172 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1173 MD.removeInstruction(I); 1174 1175 VN.erase(I); 1176 I->replaceAllUsesWith(repl); 1177 toErase.push_back(I); 1178 return true; 1179 } else if (!I->isTerminator()) { 1180 currAvail.set(num); 1181 currAvail.insert(I); 1182 } 1183 1184 return false; 1185} 1186 1187// GVN::runOnFunction - This is the main transformation entry point for a 1188// function. 1189// 1190bool GVN::runOnFunction(Function& F) { 1191 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1192 1193 bool changed = false; 1194 bool shouldContinue = true; 1195 1196 while (shouldContinue) { 1197 shouldContinue = iterateOnFunction(F); 1198 changed |= shouldContinue; 1199 } 1200 1201 return changed; 1202} 1203 1204 1205// GVN::iterateOnFunction - Executes one iteration of GVN 1206bool GVN::iterateOnFunction(Function &F) { 1207 // Clean out global sets from any previous functions 1208 VN.clear(); 1209 availableOut.clear(); 1210 phiMap.clear(); 1211 1212 bool changed_function = false; 1213 1214 DominatorTree &DT = getAnalysis<DominatorTree>(); 1215 1216 SmallVector<Instruction*, 4> toErase; 1217 1218 // Top-down walk of the dominator tree 1219 for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()), 1220 E = df_end(DT.getRootNode()); DI != E; ++DI) { 1221 1222 // Get the set to update for this block 1223 ValueNumberedSet& currAvail = availableOut[DI->getBlock()]; 1224 DenseMap<Value*, LoadInst*> lastSeenLoad; 1225 1226 BasicBlock* BB = DI->getBlock(); 1227 1228 // A block inherits AVAIL_OUT from its dominator 1229 if (DI->getIDom() != 0) 1230 currAvail = availableOut[DI->getIDom()->getBlock()]; 1231 1232 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1233 BI != BE; ) { 1234 changed_function |= processInstruction(BI, currAvail, 1235 lastSeenLoad, toErase); 1236 1237 NumGVNInstr += toErase.size(); 1238 1239 // Avoid iterator invalidation 1240 ++BI; 1241 1242 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1243 E = toErase.end(); I != E; ++I) { 1244 (*I)->eraseFromParent(); 1245 } 1246 1247 toErase.clear(); 1248 } 1249 } 1250 1251 return changed_function; 1252} 1253