GVN.cpp revision 88365bb4047a91d42af2aa42839b21e701ea1b03
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/ParameterAttributes.h" 25#include "llvm/Value.h" 26#include "llvm/ADT/BitVector.h" 27#include "llvm/ADT/DenseMap.h" 28#include "llvm/ADT/DepthFirstIterator.h" 29#include "llvm/ADT/SmallPtrSet.h" 30#include "llvm/ADT/SmallVector.h" 31#include "llvm/ADT/Statistic.h" 32#include "llvm/Analysis/Dominators.h" 33#include "llvm/Analysis/AliasAnalysis.h" 34#include "llvm/Analysis/MemoryDependenceAnalysis.h" 35#include "llvm/Support/CFG.h" 36#include "llvm/Support/Compiler.h" 37#include "llvm/Target/TargetData.h" 38using namespace llvm; 39 40//===----------------------------------------------------------------------===// 41// ValueTable Class 42//===----------------------------------------------------------------------===// 43 44/// This class holds the mapping between values and value numbers. It is used 45/// as an efficient mechanism to determine the expression-wise equivalence of 46/// two values. 47namespace { 48 struct VISIBILITY_HIDDEN Expression { 49 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, 50 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 51 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 52 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 53 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 54 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 55 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 56 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 57 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 58 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, EMPTY, 59 TOMBSTONE }; 60 61 ExpressionOpcode opcode; 62 const Type* type; 63 uint32_t firstVN; 64 uint32_t secondVN; 65 uint32_t thirdVN; 66 SmallVector<uint32_t, 4> varargs; 67 Value* function; 68 69 Expression() { } 70 Expression(ExpressionOpcode o) : opcode(o) { } 71 72 bool operator==(const Expression &other) const { 73 if (opcode != other.opcode) 74 return false; 75 else if (opcode == EMPTY || opcode == TOMBSTONE) 76 return true; 77 else if (type != other.type) 78 return false; 79 else if (function != other.function) 80 return false; 81 else if (firstVN != other.firstVN) 82 return false; 83 else if (secondVN != other.secondVN) 84 return false; 85 else if (thirdVN != other.thirdVN) 86 return false; 87 else { 88 if (varargs.size() != other.varargs.size()) 89 return false; 90 91 for (size_t i = 0; i < varargs.size(); ++i) 92 if (varargs[i] != other.varargs[i]) 93 return false; 94 95 return true; 96 } 97 } 98 99 bool operator!=(const Expression &other) const { 100 if (opcode != other.opcode) 101 return true; 102 else if (opcode == EMPTY || opcode == TOMBSTONE) 103 return false; 104 else if (type != other.type) 105 return true; 106 else if (function != other.function) 107 return true; 108 else if (firstVN != other.firstVN) 109 return true; 110 else if (secondVN != other.secondVN) 111 return true; 112 else if (thirdVN != other.thirdVN) 113 return true; 114 else { 115 if (varargs.size() != other.varargs.size()) 116 return true; 117 118 for (size_t i = 0; i < varargs.size(); ++i) 119 if (varargs[i] != other.varargs[i]) 120 return true; 121 122 return false; 123 } 124 } 125 }; 126 127 class VISIBILITY_HIDDEN ValueTable { 128 private: 129 DenseMap<Value*, uint32_t> valueNumbering; 130 DenseMap<Expression, uint32_t> expressionNumbering; 131 AliasAnalysis* AA; 132 133 uint32_t nextValueNumber; 134 135 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 136 Expression::ExpressionOpcode getOpcode(CmpInst* C); 137 Expression::ExpressionOpcode getOpcode(CastInst* C); 138 Expression create_expression(BinaryOperator* BO); 139 Expression create_expression(CmpInst* C); 140 Expression create_expression(ShuffleVectorInst* V); 141 Expression create_expression(ExtractElementInst* C); 142 Expression create_expression(InsertElementInst* V); 143 Expression create_expression(SelectInst* V); 144 Expression create_expression(CastInst* C); 145 Expression create_expression(GetElementPtrInst* G); 146 Expression create_expression(CallInst* C); 147 public: 148 ValueTable() : nextValueNumber(1) { } 149 uint32_t lookup_or_add(Value* V); 150 uint32_t lookup(Value* V) const; 151 void add(Value* V, uint32_t num); 152 void clear(); 153 void erase(Value* v); 154 unsigned size(); 155 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 156 uint32_t hash_operand(Value* v); 157 }; 158} 159 160namespace llvm { 161template <> struct DenseMapInfo<Expression> { 162 static inline Expression getEmptyKey() { 163 return Expression(Expression::EMPTY); 164 } 165 166 static inline Expression getTombstoneKey() { 167 return Expression(Expression::TOMBSTONE); 168 } 169 170 static unsigned getHashValue(const Expression e) { 171 unsigned hash = e.opcode; 172 173 hash = e.firstVN + hash * 37; 174 hash = e.secondVN + hash * 37; 175 hash = e.thirdVN + hash * 37; 176 177 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 178 (unsigned)((uintptr_t)e.type >> 9)) + 179 hash * 37; 180 181 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 182 E = e.varargs.end(); I != E; ++I) 183 hash = *I + hash * 37; 184 185 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 186 (unsigned)((uintptr_t)e.function >> 9)) + 187 hash * 37; 188 189 return hash; 190 } 191 static bool isEqual(const Expression &LHS, const Expression &RHS) { 192 return LHS == RHS; 193 } 194 static bool isPod() { return true; } 195}; 196} 197 198//===----------------------------------------------------------------------===// 199// ValueTable Internal Functions 200//===----------------------------------------------------------------------===// 201Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 202 switch(BO->getOpcode()) { 203 default: // THIS SHOULD NEVER HAPPEN 204 assert(0 && "Binary operator with unknown opcode?"); 205 case Instruction::Add: return Expression::ADD; 206 case Instruction::Sub: return Expression::SUB; 207 case Instruction::Mul: return Expression::MUL; 208 case Instruction::UDiv: return Expression::UDIV; 209 case Instruction::SDiv: return Expression::SDIV; 210 case Instruction::FDiv: return Expression::FDIV; 211 case Instruction::URem: return Expression::UREM; 212 case Instruction::SRem: return Expression::SREM; 213 case Instruction::FRem: return Expression::FREM; 214 case Instruction::Shl: return Expression::SHL; 215 case Instruction::LShr: return Expression::LSHR; 216 case Instruction::AShr: return Expression::ASHR; 217 case Instruction::And: return Expression::AND; 218 case Instruction::Or: return Expression::OR; 219 case Instruction::Xor: return Expression::XOR; 220 } 221} 222 223Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 224 if (isa<ICmpInst>(C)) { 225 switch (C->getPredicate()) { 226 default: // THIS SHOULD NEVER HAPPEN 227 assert(0 && "Comparison with unknown predicate?"); 228 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 229 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 230 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 231 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 232 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 233 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 234 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 235 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 236 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 237 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 238 } 239 } 240 assert(isa<FCmpInst>(C) && "Unknown compare"); 241 switch (C->getPredicate()) { 242 default: // THIS SHOULD NEVER HAPPEN 243 assert(0 && "Comparison with unknown predicate?"); 244 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 245 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 246 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 247 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 248 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 249 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 250 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 251 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 252 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 253 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 254 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 255 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 256 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 257 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 258 } 259} 260 261Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 262 switch(C->getOpcode()) { 263 default: // THIS SHOULD NEVER HAPPEN 264 assert(0 && "Cast operator with unknown opcode?"); 265 case Instruction::Trunc: return Expression::TRUNC; 266 case Instruction::ZExt: return Expression::ZEXT; 267 case Instruction::SExt: return Expression::SEXT; 268 case Instruction::FPToUI: return Expression::FPTOUI; 269 case Instruction::FPToSI: return Expression::FPTOSI; 270 case Instruction::UIToFP: return Expression::UITOFP; 271 case Instruction::SIToFP: return Expression::SITOFP; 272 case Instruction::FPTrunc: return Expression::FPTRUNC; 273 case Instruction::FPExt: return Expression::FPEXT; 274 case Instruction::PtrToInt: return Expression::PTRTOINT; 275 case Instruction::IntToPtr: return Expression::INTTOPTR; 276 case Instruction::BitCast: return Expression::BITCAST; 277 } 278} 279 280uint32_t ValueTable::hash_operand(Value* v) { 281 if (CallInst* CI = dyn_cast<CallInst>(v)) 282 if (!AA->doesNotAccessMemory(CI)) 283 return nextValueNumber++; 284 285 return lookup_or_add(v); 286} 287 288Expression ValueTable::create_expression(CallInst* C) { 289 Expression e; 290 291 e.type = C->getType(); 292 e.firstVN = 0; 293 e.secondVN = 0; 294 e.thirdVN = 0; 295 e.function = C->getCalledFunction(); 296 e.opcode = Expression::CALL; 297 298 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 299 I != E; ++I) 300 e.varargs.push_back(hash_operand(*I)); 301 302 return e; 303} 304 305Expression ValueTable::create_expression(BinaryOperator* BO) { 306 Expression e; 307 308 e.firstVN = hash_operand(BO->getOperand(0)); 309 e.secondVN = hash_operand(BO->getOperand(1)); 310 e.thirdVN = 0; 311 e.function = 0; 312 e.type = BO->getType(); 313 e.opcode = getOpcode(BO); 314 315 return e; 316} 317 318Expression ValueTable::create_expression(CmpInst* C) { 319 Expression e; 320 321 e.firstVN = hash_operand(C->getOperand(0)); 322 e.secondVN = hash_operand(C->getOperand(1)); 323 e.thirdVN = 0; 324 e.function = 0; 325 e.type = C->getType(); 326 e.opcode = getOpcode(C); 327 328 return e; 329} 330 331Expression ValueTable::create_expression(CastInst* C) { 332 Expression e; 333 334 e.firstVN = hash_operand(C->getOperand(0)); 335 e.secondVN = 0; 336 e.thirdVN = 0; 337 e.function = 0; 338 e.type = C->getType(); 339 e.opcode = getOpcode(C); 340 341 return e; 342} 343 344Expression ValueTable::create_expression(ShuffleVectorInst* S) { 345 Expression e; 346 347 e.firstVN = hash_operand(S->getOperand(0)); 348 e.secondVN = hash_operand(S->getOperand(1)); 349 e.thirdVN = hash_operand(S->getOperand(2)); 350 e.function = 0; 351 e.type = S->getType(); 352 e.opcode = Expression::SHUFFLE; 353 354 return e; 355} 356 357Expression ValueTable::create_expression(ExtractElementInst* E) { 358 Expression e; 359 360 e.firstVN = hash_operand(E->getOperand(0)); 361 e.secondVN = hash_operand(E->getOperand(1)); 362 e.thirdVN = 0; 363 e.function = 0; 364 e.type = E->getType(); 365 e.opcode = Expression::EXTRACT; 366 367 return e; 368} 369 370Expression ValueTable::create_expression(InsertElementInst* I) { 371 Expression e; 372 373 e.firstVN = hash_operand(I->getOperand(0)); 374 e.secondVN = hash_operand(I->getOperand(1)); 375 e.thirdVN = hash_operand(I->getOperand(2)); 376 e.function = 0; 377 e.type = I->getType(); 378 e.opcode = Expression::INSERT; 379 380 return e; 381} 382 383Expression ValueTable::create_expression(SelectInst* I) { 384 Expression e; 385 386 e.firstVN = hash_operand(I->getCondition()); 387 e.secondVN = hash_operand(I->getTrueValue()); 388 e.thirdVN = hash_operand(I->getFalseValue()); 389 e.function = 0; 390 e.type = I->getType(); 391 e.opcode = Expression::SELECT; 392 393 return e; 394} 395 396Expression ValueTable::create_expression(GetElementPtrInst* G) { 397 Expression e; 398 399 e.firstVN = hash_operand(G->getPointerOperand()); 400 e.secondVN = 0; 401 e.thirdVN = 0; 402 e.function = 0; 403 e.type = G->getType(); 404 e.opcode = Expression::GEP; 405 406 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 407 I != E; ++I) 408 e.varargs.push_back(hash_operand(*I)); 409 410 return e; 411} 412 413//===----------------------------------------------------------------------===// 414// ValueTable External Functions 415//===----------------------------------------------------------------------===// 416 417/// lookup_or_add - Returns the value number for the specified value, assigning 418/// it a new number if it did not have one before. 419uint32_t ValueTable::lookup_or_add(Value* V) { 420 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 421 if (VI != valueNumbering.end()) 422 return VI->second; 423 424 if (CallInst* C = dyn_cast<CallInst>(V)) { 425 if (AA->onlyReadsMemory(C)) { // includes doesNotAccessMemory 426 Expression e = create_expression(C); 427 428 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 429 if (EI != expressionNumbering.end()) { 430 valueNumbering.insert(std::make_pair(V, EI->second)); 431 return EI->second; 432 } else { 433 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 434 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 435 436 return nextValueNumber++; 437 } 438 } else { 439 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 440 return nextValueNumber++; 441 } 442 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 443 Expression e = create_expression(BO); 444 445 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 446 if (EI != expressionNumbering.end()) { 447 valueNumbering.insert(std::make_pair(V, EI->second)); 448 return EI->second; 449 } else { 450 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 451 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 452 453 return nextValueNumber++; 454 } 455 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 456 Expression e = create_expression(C); 457 458 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 459 if (EI != expressionNumbering.end()) { 460 valueNumbering.insert(std::make_pair(V, EI->second)); 461 return EI->second; 462 } else { 463 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 464 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 465 466 return nextValueNumber++; 467 } 468 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 469 Expression e = create_expression(U); 470 471 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 472 if (EI != expressionNumbering.end()) { 473 valueNumbering.insert(std::make_pair(V, EI->second)); 474 return EI->second; 475 } else { 476 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 477 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 478 479 return nextValueNumber++; 480 } 481 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 482 Expression e = create_expression(U); 483 484 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 485 if (EI != expressionNumbering.end()) { 486 valueNumbering.insert(std::make_pair(V, EI->second)); 487 return EI->second; 488 } else { 489 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 490 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 491 492 return nextValueNumber++; 493 } 494 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 495 Expression e = create_expression(U); 496 497 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 498 if (EI != expressionNumbering.end()) { 499 valueNumbering.insert(std::make_pair(V, EI->second)); 500 return EI->second; 501 } else { 502 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 503 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 504 505 return nextValueNumber++; 506 } 507 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 508 Expression e = create_expression(U); 509 510 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 511 if (EI != expressionNumbering.end()) { 512 valueNumbering.insert(std::make_pair(V, EI->second)); 513 return EI->second; 514 } else { 515 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 516 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 517 518 return nextValueNumber++; 519 } 520 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 521 Expression e = create_expression(U); 522 523 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 524 if (EI != expressionNumbering.end()) { 525 valueNumbering.insert(std::make_pair(V, EI->second)); 526 return EI->second; 527 } else { 528 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 529 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 530 531 return nextValueNumber++; 532 } 533 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 534 Expression e = create_expression(U); 535 536 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 537 if (EI != expressionNumbering.end()) { 538 valueNumbering.insert(std::make_pair(V, EI->second)); 539 return EI->second; 540 } else { 541 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 542 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 543 544 return nextValueNumber++; 545 } 546 } else { 547 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 548 return nextValueNumber++; 549 } 550} 551 552/// lookup - Returns the value number of the specified value. Fails if 553/// the value has not yet been numbered. 554uint32_t ValueTable::lookup(Value* V) const { 555 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 556 assert(VI != valueNumbering.end() && "Value not numbered?"); 557 return VI->second; 558} 559 560/// clear - Remove all entries from the ValueTable 561void ValueTable::clear() { 562 valueNumbering.clear(); 563 expressionNumbering.clear(); 564 nextValueNumber = 1; 565} 566 567/// erase - Remove a value from the value numbering 568void ValueTable::erase(Value* V) { 569 valueNumbering.erase(V); 570} 571 572//===----------------------------------------------------------------------===// 573// ValueNumberedSet Class 574//===----------------------------------------------------------------------===// 575namespace { 576class VISIBILITY_HIDDEN ValueNumberedSet { 577 private: 578 SmallPtrSet<Value*, 8> contents; 579 BitVector numbers; 580 public: 581 ValueNumberedSet() { numbers.resize(1); } 582 ValueNumberedSet(const ValueNumberedSet& other) { 583 numbers = other.numbers; 584 contents = other.contents; 585 } 586 587 typedef SmallPtrSet<Value*, 8>::iterator iterator; 588 589 iterator begin() { return contents.begin(); } 590 iterator end() { return contents.end(); } 591 592 bool insert(Value* v) { return contents.insert(v); } 593 void insert(iterator I, iterator E) { contents.insert(I, E); } 594 void erase(Value* v) { contents.erase(v); } 595 unsigned count(Value* v) { return contents.count(v); } 596 size_t size() { return contents.size(); } 597 598 void set(unsigned i) { 599 if (i >= numbers.size()) 600 numbers.resize(i+1); 601 602 numbers.set(i); 603 } 604 605 void operator=(const ValueNumberedSet& other) { 606 contents = other.contents; 607 numbers = other.numbers; 608 } 609 610 void reset(unsigned i) { 611 if (i < numbers.size()) 612 numbers.reset(i); 613 } 614 615 bool test(unsigned i) { 616 if (i >= numbers.size()) 617 return false; 618 619 return numbers.test(i); 620 } 621 622 void clear() { 623 contents.clear(); 624 numbers.clear(); 625 } 626}; 627} 628 629//===----------------------------------------------------------------------===// 630// GVN Pass 631//===----------------------------------------------------------------------===// 632 633namespace { 634 635 class VISIBILITY_HIDDEN GVN : public FunctionPass { 636 bool runOnFunction(Function &F); 637 public: 638 static char ID; // Pass identification, replacement for typeid 639 GVN() : FunctionPass((intptr_t)&ID) { } 640 641 private: 642 ValueTable VN; 643 644 DenseMap<BasicBlock*, ValueNumberedSet> availableOut; 645 646 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 647 PhiMapType phiMap; 648 649 650 // This transformation requires dominator postdominator info 651 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 652 AU.setPreservesCFG(); 653 AU.addRequired<DominatorTree>(); 654 AU.addRequired<MemoryDependenceAnalysis>(); 655 AU.addRequired<AliasAnalysis>(); 656 AU.addRequired<TargetData>(); 657 AU.addPreserved<AliasAnalysis>(); 658 AU.addPreserved<MemoryDependenceAnalysis>(); 659 AU.addPreserved<TargetData>(); 660 } 661 662 // Helper fuctions 663 // FIXME: eliminate or document these better 664 Value* find_leader(ValueNumberedSet& vals, uint32_t v) ; 665 void val_insert(ValueNumberedSet& s, Value* v); 666 bool processLoad(LoadInst* L, 667 DenseMap<Value*, LoadInst*>& lastLoad, 668 SmallVector<Instruction*, 4>& toErase); 669 bool processInstruction(Instruction* I, 670 ValueNumberedSet& currAvail, 671 DenseMap<Value*, LoadInst*>& lastSeenLoad, 672 SmallVector<Instruction*, 4>& toErase); 673 bool processNonLocalLoad(LoadInst* L, 674 SmallVector<Instruction*, 4>& toErase); 675 bool processMemCpy(MemCpyInst* M, MemCpyInst* MDep, 676 SmallVector<Instruction*, 4>& toErase); 677 bool performCallSlotOptzn(MemCpyInst* cpy, CallInst* C, 678 SmallVector<Instruction*, 4>& toErase); 679 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig, 680 DenseMap<BasicBlock*, Value*> &Phis, 681 bool top_level = false); 682 void dump(DenseMap<BasicBlock*, Value*>& d); 683 bool iterateOnFunction(Function &F); 684 Value* CollapsePhi(PHINode* p); 685 bool isSafeReplacement(PHINode* p, Instruction* inst); 686 }; 687 688 char GVN::ID = 0; 689} 690 691// createGVNPass - The public interface to this file... 692FunctionPass *llvm::createGVNPass() { return new GVN(); } 693 694static RegisterPass<GVN> X("gvn", 695 "Global Value Numbering"); 696 697STATISTIC(NumGVNInstr, "Number of instructions deleted"); 698STATISTIC(NumGVNLoad, "Number of loads deleted"); 699 700/// find_leader - Given a set and a value number, return the first 701/// element of the set with that value number, or 0 if no such element 702/// is present 703Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) { 704 if (!vals.test(v)) 705 return 0; 706 707 for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end(); 708 I != E; ++I) 709 if (v == VN.lookup(*I)) 710 return *I; 711 712 assert(0 && "No leader found, but present bit is set?"); 713 return 0; 714} 715 716/// val_insert - Insert a value into a set only if there is not a value 717/// with the same value number already in the set 718void GVN::val_insert(ValueNumberedSet& s, Value* v) { 719 uint32_t num = VN.lookup(v); 720 if (!s.test(num)) 721 s.insert(v); 722} 723 724void GVN::dump(DenseMap<BasicBlock*, Value*>& d) { 725 printf("{\n"); 726 for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(), 727 E = d.end(); I != E; ++I) { 728 if (I->second == MemoryDependenceAnalysis::None) 729 printf("None\n"); 730 else 731 I->second->dump(); 732 } 733 printf("}\n"); 734} 735 736Value* GVN::CollapsePhi(PHINode* p) { 737 DominatorTree &DT = getAnalysis<DominatorTree>(); 738 Value* constVal = p->hasConstantValue(); 739 740 if (!constVal) return 0; 741 742 Instruction* inst = dyn_cast<Instruction>(constVal); 743 if (!inst) 744 return constVal; 745 746 if (DT.dominates(inst, p)) 747 if (isSafeReplacement(p, inst)) 748 return inst; 749 return 0; 750} 751 752bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 753 if (!isa<PHINode>(inst)) 754 return true; 755 756 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 757 UI != E; ++UI) 758 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 759 if (use_phi->getParent() == inst->getParent()) 760 return false; 761 762 return true; 763} 764 765/// GetValueForBlock - Get the value to use within the specified basic block. 766/// available values are in Phis. 767Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig, 768 DenseMap<BasicBlock*, Value*> &Phis, 769 bool top_level) { 770 771 // If we have already computed this value, return the previously computed val. 772 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 773 if (V != Phis.end() && !top_level) return V->second; 774 775 BasicBlock* singlePred = BB->getSinglePredecessor(); 776 if (singlePred) { 777 Value *ret = GetValueForBlock(singlePred, orig, Phis); 778 Phis[BB] = ret; 779 return ret; 780 } 781 782 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 783 // now, then get values to fill in the incoming values for the PHI. 784 PHINode *PN = new PHINode(orig->getType(), orig->getName()+".rle", 785 BB->begin()); 786 PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB))); 787 788 if (Phis.count(BB) == 0) 789 Phis.insert(std::make_pair(BB, PN)); 790 791 // Fill in the incoming values for the block. 792 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 793 Value* val = GetValueForBlock(*PI, orig, Phis); 794 PN->addIncoming(val, *PI); 795 } 796 797 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 798 AA.copyValue(orig, PN); 799 800 // Attempt to collapse PHI nodes that are trivially redundant 801 Value* v = CollapsePhi(PN); 802 if (!v) { 803 // Cache our phi construction results 804 phiMap[orig->getPointerOperand()].insert(PN); 805 return PN; 806 } 807 808 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 809 810 MD.removeInstruction(PN); 811 PN->replaceAllUsesWith(v); 812 813 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 814 E = Phis.end(); I != E; ++I) 815 if (I->second == PN) 816 I->second = v; 817 818 PN->eraseFromParent(); 819 820 Phis[BB] = v; 821 return v; 822} 823 824/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 825/// non-local by performing PHI construction. 826bool GVN::processNonLocalLoad(LoadInst* L, 827 SmallVector<Instruction*, 4>& toErase) { 828 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 829 830 // Find the non-local dependencies of the load 831 DenseMap<BasicBlock*, Value*> deps; 832 MD.getNonLocalDependency(L, deps); 833 834 DenseMap<BasicBlock*, Value*> repl; 835 836 // Filter out useless results (non-locals, etc) 837 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end(); 838 I != E; ++I) { 839 if (I->second == MemoryDependenceAnalysis::None) 840 return false; 841 842 if (I->second == MemoryDependenceAnalysis::NonLocal) 843 continue; 844 845 if (StoreInst* S = dyn_cast<StoreInst>(I->second)) { 846 if (S->getPointerOperand() != L->getPointerOperand()) 847 return false; 848 repl[I->first] = S->getOperand(0); 849 } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) { 850 if (LD->getPointerOperand() != L->getPointerOperand()) 851 return false; 852 repl[I->first] = LD; 853 } else { 854 return false; 855 } 856 } 857 858 // Use cached PHI construction information from previous runs 859 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()]; 860 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 861 I != E; ++I) { 862 if ((*I)->getParent() == L->getParent()) { 863 MD.removeInstruction(L); 864 L->replaceAllUsesWith(*I); 865 toErase.push_back(L); 866 NumGVNLoad++; 867 return true; 868 } 869 870 repl.insert(std::make_pair((*I)->getParent(), *I)); 871 } 872 873 // Perform PHI construction 874 SmallPtrSet<BasicBlock*, 4> visited; 875 Value* v = GetValueForBlock(L->getParent(), L, repl, true); 876 877 MD.removeInstruction(L); 878 L->replaceAllUsesWith(v); 879 toErase.push_back(L); 880 NumGVNLoad++; 881 882 return true; 883} 884 885/// processLoad - Attempt to eliminate a load, first by eliminating it 886/// locally, and then attempting non-local elimination if that fails. 887bool GVN::processLoad(LoadInst* L, 888 DenseMap<Value*, LoadInst*>& lastLoad, 889 SmallVector<Instruction*, 4>& toErase) { 890 if (L->isVolatile()) { 891 lastLoad[L->getPointerOperand()] = L; 892 return false; 893 } 894 895 Value* pointer = L->getPointerOperand(); 896 LoadInst*& last = lastLoad[pointer]; 897 898 // ... to a pointer that has been loaded from before... 899 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 900 bool removedNonLocal = false; 901 Instruction* dep = MD.getDependency(L); 902 if (dep == MemoryDependenceAnalysis::NonLocal && 903 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) { 904 removedNonLocal = processNonLocalLoad(L, toErase); 905 906 if (!removedNonLocal) 907 last = L; 908 909 return removedNonLocal; 910 } 911 912 913 bool deletedLoad = false; 914 915 // Walk up the dependency chain until we either find 916 // a dependency we can use, or we can't walk any further 917 while (dep != MemoryDependenceAnalysis::None && 918 dep != MemoryDependenceAnalysis::NonLocal && 919 (isa<LoadInst>(dep) || isa<StoreInst>(dep))) { 920 // ... that depends on a store ... 921 if (StoreInst* S = dyn_cast<StoreInst>(dep)) { 922 if (S->getPointerOperand() == pointer) { 923 // Remove it! 924 MD.removeInstruction(L); 925 926 L->replaceAllUsesWith(S->getOperand(0)); 927 toErase.push_back(L); 928 deletedLoad = true; 929 NumGVNLoad++; 930 } 931 932 // Whether we removed it or not, we can't 933 // go any further 934 break; 935 } else if (!last) { 936 // If we don't depend on a store, and we haven't 937 // been loaded before, bail. 938 break; 939 } else if (dep == last) { 940 // Remove it! 941 MD.removeInstruction(L); 942 943 L->replaceAllUsesWith(last); 944 toErase.push_back(L); 945 deletedLoad = true; 946 NumGVNLoad++; 947 948 break; 949 } else { 950 dep = MD.getDependency(L, dep); 951 } 952 } 953 954 if (dep != MemoryDependenceAnalysis::None && 955 dep != MemoryDependenceAnalysis::NonLocal && 956 isa<AllocationInst>(dep)) { 957 // Check that this load is actually from the 958 // allocation we found 959 Value* v = L->getOperand(0); 960 while (true) { 961 if (BitCastInst *BC = dyn_cast<BitCastInst>(v)) 962 v = BC->getOperand(0); 963 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v)) 964 v = GEP->getOperand(0); 965 else 966 break; 967 } 968 if (v == dep) { 969 // If this load depends directly on an allocation, there isn't 970 // anything stored there; therefore, we can optimize this load 971 // to undef. 972 MD.removeInstruction(L); 973 974 L->replaceAllUsesWith(UndefValue::get(L->getType())); 975 toErase.push_back(L); 976 deletedLoad = true; 977 NumGVNLoad++; 978 } 979 } 980 981 if (!deletedLoad) 982 last = L; 983 984 return deletedLoad; 985} 986 987/// performCallSlotOptzn - takes a memcpy and a call that it depends on, 988/// and checks for the possibility of a call slot optimization by having 989/// the call write its result directly into the destination of the memcpy. 990bool GVN::performCallSlotOptzn(MemCpyInst* cpy, CallInst* C, 991 SmallVector<Instruction*, 4>& toErase) { 992 // The general transformation to keep in mind is 993 // 994 // call @func(..., src, ...) 995 // memcpy(dest, src, ...) 996 // 997 // -> 998 // 999 // memcpy(dest, src, ...) 1000 // call @func(..., dest, ...) 1001 // 1002 // Since moving the memcpy is technically awkward, we additionally check that 1003 // src only holds uninitialized values at the moment of the call, meaning that 1004 // the memcpy can be discarded rather than moved. 1005 1006 // Deliberately get the source and destination with bitcasts stripped away, 1007 // because we'll need to do type comparisons based on the underlying type. 1008 Value* cpyDest = cpy->getDest(); 1009 Value* cpySrc = cpy->getSource(); 1010 CallSite CS = CallSite::get(C); 1011 1012 // We need to be able to reason about the size of the memcpy, so we require 1013 // that it be a constant. 1014 ConstantInt* cpyLength = dyn_cast<ConstantInt>(cpy->getLength()); 1015 if (!cpyLength) 1016 return false; 1017 1018 // Require that src be an alloca. This simplifies the reasoning considerably. 1019 AllocaInst* srcAlloca = dyn_cast<AllocaInst>(cpySrc); 1020 if (!srcAlloca) 1021 return false; 1022 1023 // Check that all of src is copied to dest. 1024 TargetData& TD = getAnalysis<TargetData>(); 1025 1026 ConstantInt* srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize()); 1027 if (!srcArraySize) 1028 return false; 1029 1030 uint64_t srcSize = TD.getABITypeSize(srcAlloca->getAllocatedType()) * 1031 srcArraySize->getZExtValue(); 1032 1033 if (cpyLength->getZExtValue() < srcSize) 1034 return false; 1035 1036 // Check that accessing the first srcSize bytes of dest will not cause a 1037 // trap. Otherwise the transform is invalid since it might cause a trap 1038 // to occur earlier than it otherwise would. 1039 if (AllocaInst* A = dyn_cast<AllocaInst>(cpyDest)) { 1040 // The destination is an alloca. Check it is larger than srcSize. 1041 ConstantInt* destArraySize = dyn_cast<ConstantInt>(A->getArraySize()); 1042 if (!destArraySize) 1043 return false; 1044 1045 uint64_t destSize = TD.getABITypeSize(A->getAllocatedType()) * 1046 destArraySize->getZExtValue(); 1047 1048 if (destSize < srcSize) 1049 return false; 1050 } else if (Argument* A = dyn_cast<Argument>(cpyDest)) { 1051 // If the destination is an sret parameter then only accesses that are 1052 // outside of the returned struct type can trap. 1053 if (!A->hasStructRetAttr()) 1054 return false; 1055 1056 const Type* StructTy = cast<PointerType>(A->getType())->getElementType(); 1057 uint64_t destSize = TD.getABITypeSize(StructTy); 1058 1059 if (destSize < srcSize) 1060 return false; 1061 } else { 1062 return false; 1063 } 1064 1065 // Check that src is not accessed except via the call and the memcpy. This 1066 // guarantees that it holds only undefined values when passed in (so the final 1067 // memcpy can be dropped), that it is not read or written between the call and 1068 // the memcpy, and that writing beyond the end of it is undefined. 1069 1070 SmallVector<User*, 8> srcUseList(srcAlloca->use_begin(), 1071 srcAlloca->use_end()); 1072 while (!srcUseList.empty()) { 1073 User* UI = srcUseList.back(); 1074 srcUseList.pop_back(); 1075 1076 if (isa<GetElementPtrInst>(UI) || isa<BitCastInst>(UI)) { 1077 for (User::use_iterator I = UI->use_begin(), E = UI->use_end(); 1078 I != E; ++I) 1079 srcUseList.push_back(*I); 1080 } else if (UI != C && UI != cpy) { 1081 return false; 1082 } 1083 } 1084 1085 // Since we're changing the parameter to the callsite, we need to make sure 1086 // that what would be the new parameter dominates the callsite. 1087 DominatorTree& DT = getAnalysis<DominatorTree>(); 1088 if (Instruction* cpyDestInst = dyn_cast<Instruction>(cpyDest)) 1089 if (!DT.dominates(cpyDestInst, C)) 1090 return false; 1091 1092 // In addition to knowing that the call does not access src in some 1093 // unexpected manner, for example via a global, which we deduce from 1094 // the use analysis, we also need to know that it does not sneakily 1095 // access dest. We rely on AA to figure this out for us. 1096 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 1097 if (AA.getModRefInfo(C, cpy->getRawDest(), srcSize) != 1098 AliasAnalysis::NoModRef) 1099 return false; 1100 1101 // All the checks have passed, so do the transformation. 1102 for (unsigned i = 0; i < CS.arg_size(); ++i) 1103 if (CS.getArgument(i) == cpySrc) { 1104 if (cpySrc->getType() != cpyDest->getType()) 1105 cpyDest = CastInst::createPointerCast(cpyDest, cpySrc->getType(), 1106 cpyDest->getName(), C); 1107 CS.setArgument(i, cpyDest); 1108 } 1109 1110 // Drop any cached information about the call, because we may have changed 1111 // its dependence information by changing its parameter. 1112 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1113 MD.dropInstruction(C); 1114 1115 // Remove the memcpy 1116 MD.removeInstruction(cpy); 1117 toErase.push_back(cpy); 1118 1119 return true; 1120} 1121 1122/// processMemCpy - perform simplication of memcpy's. If we have memcpy A which 1123/// copies X to Y, and memcpy B which copies Y to Z, then we can rewrite B to be 1124/// a memcpy from X to Z (or potentially a memmove, depending on circumstances). 1125/// This allows later passes to remove the first memcpy altogether. 1126bool GVN::processMemCpy(MemCpyInst* M, MemCpyInst* MDep, 1127 SmallVector<Instruction*, 4>& toErase) { 1128 // We can only transforms memcpy's where the dest of one is the source of the 1129 // other 1130 if (M->getSource() != MDep->getDest()) 1131 return false; 1132 1133 // Second, the length of the memcpy's must be the same, or the preceeding one 1134 // must be larger than the following one. 1135 ConstantInt* C1 = dyn_cast<ConstantInt>(MDep->getLength()); 1136 ConstantInt* C2 = dyn_cast<ConstantInt>(M->getLength()); 1137 if (!C1 || !C2) 1138 return false; 1139 1140 uint64_t DepSize = C1->getValue().getZExtValue(); 1141 uint64_t CpySize = C2->getValue().getZExtValue(); 1142 1143 if (DepSize < CpySize) 1144 return false; 1145 1146 // Finally, we have to make sure that the dest of the second does not 1147 // alias the source of the first 1148 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 1149 if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) != 1150 AliasAnalysis::NoAlias) 1151 return false; 1152 else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) != 1153 AliasAnalysis::NoAlias) 1154 return false; 1155 else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize) 1156 != AliasAnalysis::NoAlias) 1157 return false; 1158 1159 // If all checks passed, then we can transform these memcpy's 1160 Function* MemCpyFun = Intrinsic::getDeclaration( 1161 M->getParent()->getParent()->getParent(), 1162 M->getIntrinsicID()); 1163 1164 std::vector<Value*> args; 1165 args.push_back(M->getRawDest()); 1166 args.push_back(MDep->getRawSource()); 1167 args.push_back(M->getLength()); 1168 args.push_back(M->getAlignment()); 1169 1170 CallInst* C = new CallInst(MemCpyFun, args.begin(), args.end(), "", M); 1171 1172 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1173 if (MD.getDependency(C) == MDep) { 1174 MD.dropInstruction(M); 1175 toErase.push_back(M); 1176 return true; 1177 } 1178 1179 MD.removeInstruction(C); 1180 toErase.push_back(C); 1181 return false; 1182} 1183 1184/// processInstruction - When calculating availability, handle an instruction 1185/// by inserting it into the appropriate sets 1186bool GVN::processInstruction(Instruction* I, 1187 ValueNumberedSet& currAvail, 1188 DenseMap<Value*, LoadInst*>& lastSeenLoad, 1189 SmallVector<Instruction*, 4>& toErase) { 1190 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1191 return processLoad(L, lastSeenLoad, toErase); 1192 } else if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) { 1193 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1194 1195 // The are two possible optimizations we can do for memcpy: 1196 // a) memcpy-memcpy xform which exposes redundance for DSE 1197 // b) call-memcpy xform for return slot optimization 1198 Instruction* dep = MD.getDependency(M); 1199 if (dep == MemoryDependenceAnalysis::None || 1200 dep == MemoryDependenceAnalysis::NonLocal) 1201 return false; 1202 if (MemCpyInst *MemCpy = dyn_cast<MemCpyInst>(dep)) 1203 return processMemCpy(M, MemCpy, toErase); 1204 if (CallInst* C = dyn_cast<CallInst>(dep)) 1205 return performCallSlotOptzn(M, C, toErase); 1206 return false; 1207 } 1208 1209 unsigned num = VN.lookup_or_add(I); 1210 1211 // Collapse PHI nodes 1212 if (PHINode* p = dyn_cast<PHINode>(I)) { 1213 Value* constVal = CollapsePhi(p); 1214 1215 if (constVal) { 1216 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1217 PI != PE; ++PI) 1218 if (PI->second.count(p)) 1219 PI->second.erase(p); 1220 1221 p->replaceAllUsesWith(constVal); 1222 toErase.push_back(p); 1223 } 1224 // Perform value-number based elimination 1225 } else if (currAvail.test(num)) { 1226 Value* repl = find_leader(currAvail, num); 1227 1228 if (CallInst* CI = dyn_cast<CallInst>(I)) { 1229 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 1230 if (!AA.doesNotAccessMemory(CI)) { 1231 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1232 if (cast<Instruction>(repl)->getParent() != CI->getParent() || 1233 MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) { 1234 // There must be an intervening may-alias store, so nothing from 1235 // this point on will be able to be replaced with the preceding call 1236 currAvail.erase(repl); 1237 currAvail.insert(I); 1238 1239 return false; 1240 } 1241 } 1242 } 1243 1244 // Remove it! 1245 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1246 MD.removeInstruction(I); 1247 1248 VN.erase(I); 1249 I->replaceAllUsesWith(repl); 1250 toErase.push_back(I); 1251 return true; 1252 } else if (!I->isTerminator()) { 1253 currAvail.set(num); 1254 currAvail.insert(I); 1255 } 1256 1257 return false; 1258} 1259 1260// GVN::runOnFunction - This is the main transformation entry point for a 1261// function. 1262// 1263bool GVN::runOnFunction(Function& F) { 1264 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1265 1266 bool changed = false; 1267 bool shouldContinue = true; 1268 1269 while (shouldContinue) { 1270 shouldContinue = iterateOnFunction(F); 1271 changed |= shouldContinue; 1272 } 1273 1274 return changed; 1275} 1276 1277 1278// GVN::iterateOnFunction - Executes one iteration of GVN 1279bool GVN::iterateOnFunction(Function &F) { 1280 // Clean out global sets from any previous functions 1281 VN.clear(); 1282 availableOut.clear(); 1283 phiMap.clear(); 1284 1285 bool changed_function = false; 1286 1287 DominatorTree &DT = getAnalysis<DominatorTree>(); 1288 1289 SmallVector<Instruction*, 4> toErase; 1290 1291 // Top-down walk of the dominator tree 1292 for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()), 1293 E = df_end(DT.getRootNode()); DI != E; ++DI) { 1294 1295 // Get the set to update for this block 1296 ValueNumberedSet& currAvail = availableOut[DI->getBlock()]; 1297 DenseMap<Value*, LoadInst*> lastSeenLoad; 1298 1299 BasicBlock* BB = DI->getBlock(); 1300 1301 // A block inherits AVAIL_OUT from its dominator 1302 if (DI->getIDom() != 0) 1303 currAvail = availableOut[DI->getIDom()->getBlock()]; 1304 1305 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1306 BI != BE; ) { 1307 changed_function |= processInstruction(BI, currAvail, 1308 lastSeenLoad, toErase); 1309 1310 NumGVNInstr += toErase.size(); 1311 1312 // Avoid iterator invalidation 1313 ++BI; 1314 1315 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1316 E = toErase.end(); I != E; ++I) 1317 (*I)->eraseFromParent(); 1318 1319 toErase.clear(); 1320 } 1321 } 1322 1323 return changed_function; 1324} 1325