GVN.cpp revision 5d0392c6b370758750b397e254a6c6f028479969
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// Note that this pass does the value numbering itself, it does not use the 14// ValueNumbering analysis passes. 15// 16//===----------------------------------------------------------------------===// 17 18#define DEBUG_TYPE "gvn" 19#include "llvm/Transforms/Scalar.h" 20#include "llvm/BasicBlock.h" 21#include "llvm/Constants.h" 22#include "llvm/DerivedTypes.h" 23#include "llvm/Function.h" 24#include "llvm/Instructions.h" 25#include "llvm/Value.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/CommandLine.h" 36#include "llvm/Support/Compiler.h" 37#include "llvm/Support/Debug.h" 38#include "llvm/Transforms/Utils/BasicBlockUtils.h" 39using namespace llvm; 40 41STATISTIC(NumGVNInstr, "Number of instructions deleted"); 42STATISTIC(NumGVNLoad, "Number of loads deleted"); 43STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 44STATISTIC(NumGVNBlocks, "Number of blocks merged"); 45 46static cl::opt<bool> EnablePRE("enable-pre", 47 cl::init(true), cl::Hidden); 48 49//===----------------------------------------------------------------------===// 50// ValueTable Class 51//===----------------------------------------------------------------------===// 52 53/// This class holds the mapping between values and value numbers. It is used 54/// as an efficient mechanism to determine the expression-wise equivalence of 55/// two values. 56namespace { 57 struct VISIBILITY_HIDDEN Expression { 58 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, 59 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 60 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 61 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 62 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 63 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 64 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 65 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 66 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 67 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 68 EMPTY, TOMBSTONE }; 69 70 ExpressionOpcode opcode; 71 const Type* type; 72 uint32_t firstVN; 73 uint32_t secondVN; 74 uint32_t thirdVN; 75 SmallVector<uint32_t, 4> varargs; 76 Value* function; 77 78 Expression() { } 79 Expression(ExpressionOpcode o) : opcode(o) { } 80 81 bool operator==(const Expression &other) const { 82 if (opcode != other.opcode) 83 return false; 84 else if (opcode == EMPTY || opcode == TOMBSTONE) 85 return true; 86 else if (type != other.type) 87 return false; 88 else if (function != other.function) 89 return false; 90 else if (firstVN != other.firstVN) 91 return false; 92 else if (secondVN != other.secondVN) 93 return false; 94 else if (thirdVN != other.thirdVN) 95 return false; 96 else { 97 if (varargs.size() != other.varargs.size()) 98 return false; 99 100 for (size_t i = 0; i < varargs.size(); ++i) 101 if (varargs[i] != other.varargs[i]) 102 return false; 103 104 return true; 105 } 106 } 107 108 bool operator!=(const Expression &other) const { 109 if (opcode != other.opcode) 110 return true; 111 else if (opcode == EMPTY || opcode == TOMBSTONE) 112 return false; 113 else if (type != other.type) 114 return true; 115 else if (function != other.function) 116 return true; 117 else if (firstVN != other.firstVN) 118 return true; 119 else if (secondVN != other.secondVN) 120 return true; 121 else if (thirdVN != other.thirdVN) 122 return true; 123 else { 124 if (varargs.size() != other.varargs.size()) 125 return true; 126 127 for (size_t i = 0; i < varargs.size(); ++i) 128 if (varargs[i] != other.varargs[i]) 129 return true; 130 131 return false; 132 } 133 } 134 }; 135 136 class VISIBILITY_HIDDEN ValueTable { 137 private: 138 DenseMap<Value*, uint32_t> valueNumbering; 139 DenseMap<Expression, uint32_t> expressionNumbering; 140 AliasAnalysis* AA; 141 MemoryDependenceAnalysis* MD; 142 DominatorTree* DT; 143 144 uint32_t nextValueNumber; 145 146 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 147 Expression::ExpressionOpcode getOpcode(CmpInst* C); 148 Expression::ExpressionOpcode getOpcode(CastInst* C); 149 Expression create_expression(BinaryOperator* BO); 150 Expression create_expression(CmpInst* C); 151 Expression create_expression(ShuffleVectorInst* V); 152 Expression create_expression(ExtractElementInst* C); 153 Expression create_expression(InsertElementInst* V); 154 Expression create_expression(SelectInst* V); 155 Expression create_expression(CastInst* C); 156 Expression create_expression(GetElementPtrInst* G); 157 Expression create_expression(CallInst* C); 158 Expression create_expression(Constant* C); 159 public: 160 ValueTable() : nextValueNumber(1) { } 161 uint32_t lookup_or_add(Value* V); 162 uint32_t lookup(Value* V) const; 163 void add(Value* V, uint32_t num); 164 void clear(); 165 void erase(Value* v); 166 unsigned size(); 167 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 168 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 169 void setDomTree(DominatorTree* D) { DT = D; } 170 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 171 }; 172} 173 174namespace llvm { 175template <> struct DenseMapInfo<Expression> { 176 static inline Expression getEmptyKey() { 177 return Expression(Expression::EMPTY); 178 } 179 180 static inline Expression getTombstoneKey() { 181 return Expression(Expression::TOMBSTONE); 182 } 183 184 static unsigned getHashValue(const Expression e) { 185 unsigned hash = e.opcode; 186 187 hash = e.firstVN + hash * 37; 188 hash = e.secondVN + hash * 37; 189 hash = e.thirdVN + hash * 37; 190 191 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 192 (unsigned)((uintptr_t)e.type >> 9)) + 193 hash * 37; 194 195 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 196 E = e.varargs.end(); I != E; ++I) 197 hash = *I + hash * 37; 198 199 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 200 (unsigned)((uintptr_t)e.function >> 9)) + 201 hash * 37; 202 203 return hash; 204 } 205 static bool isEqual(const Expression &LHS, const Expression &RHS) { 206 return LHS == RHS; 207 } 208 static bool isPod() { return true; } 209}; 210} 211 212//===----------------------------------------------------------------------===// 213// ValueTable Internal Functions 214//===----------------------------------------------------------------------===// 215Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 216 switch(BO->getOpcode()) { 217 default: // THIS SHOULD NEVER HAPPEN 218 assert(0 && "Binary operator with unknown opcode?"); 219 case Instruction::Add: return Expression::ADD; 220 case Instruction::Sub: return Expression::SUB; 221 case Instruction::Mul: return Expression::MUL; 222 case Instruction::UDiv: return Expression::UDIV; 223 case Instruction::SDiv: return Expression::SDIV; 224 case Instruction::FDiv: return Expression::FDIV; 225 case Instruction::URem: return Expression::UREM; 226 case Instruction::SRem: return Expression::SREM; 227 case Instruction::FRem: return Expression::FREM; 228 case Instruction::Shl: return Expression::SHL; 229 case Instruction::LShr: return Expression::LSHR; 230 case Instruction::AShr: return Expression::ASHR; 231 case Instruction::And: return Expression::AND; 232 case Instruction::Or: return Expression::OR; 233 case Instruction::Xor: return Expression::XOR; 234 } 235} 236 237Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 238 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) { 239 switch (C->getPredicate()) { 240 default: // THIS SHOULD NEVER HAPPEN 241 assert(0 && "Comparison with unknown predicate?"); 242 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 243 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 244 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 245 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 246 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 247 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 248 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 249 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 250 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 251 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 252 } 253 } 254 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare"); 255 switch (C->getPredicate()) { 256 default: // THIS SHOULD NEVER HAPPEN 257 assert(0 && "Comparison with unknown predicate?"); 258 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 259 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 260 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 261 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 262 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 263 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 264 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 265 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 266 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 267 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 268 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 269 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 270 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 271 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 272 } 273} 274 275Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 276 switch(C->getOpcode()) { 277 default: // THIS SHOULD NEVER HAPPEN 278 assert(0 && "Cast operator with unknown opcode?"); 279 case Instruction::Trunc: return Expression::TRUNC; 280 case Instruction::ZExt: return Expression::ZEXT; 281 case Instruction::SExt: return Expression::SEXT; 282 case Instruction::FPToUI: return Expression::FPTOUI; 283 case Instruction::FPToSI: return Expression::FPTOSI; 284 case Instruction::UIToFP: return Expression::UITOFP; 285 case Instruction::SIToFP: return Expression::SITOFP; 286 case Instruction::FPTrunc: return Expression::FPTRUNC; 287 case Instruction::FPExt: return Expression::FPEXT; 288 case Instruction::PtrToInt: return Expression::PTRTOINT; 289 case Instruction::IntToPtr: return Expression::INTTOPTR; 290 case Instruction::BitCast: return Expression::BITCAST; 291 } 292} 293 294Expression ValueTable::create_expression(CallInst* C) { 295 Expression e; 296 297 e.type = C->getType(); 298 e.firstVN = 0; 299 e.secondVN = 0; 300 e.thirdVN = 0; 301 e.function = C->getCalledFunction(); 302 e.opcode = Expression::CALL; 303 304 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 305 I != E; ++I) 306 e.varargs.push_back(lookup_or_add(*I)); 307 308 return e; 309} 310 311Expression ValueTable::create_expression(BinaryOperator* BO) { 312 Expression e; 313 314 e.firstVN = lookup_or_add(BO->getOperand(0)); 315 e.secondVN = lookup_or_add(BO->getOperand(1)); 316 e.thirdVN = 0; 317 e.function = 0; 318 e.type = BO->getType(); 319 e.opcode = getOpcode(BO); 320 321 return e; 322} 323 324Expression ValueTable::create_expression(CmpInst* C) { 325 Expression e; 326 327 e.firstVN = lookup_or_add(C->getOperand(0)); 328 e.secondVN = lookup_or_add(C->getOperand(1)); 329 e.thirdVN = 0; 330 e.function = 0; 331 e.type = C->getType(); 332 e.opcode = getOpcode(C); 333 334 return e; 335} 336 337Expression ValueTable::create_expression(CastInst* C) { 338 Expression e; 339 340 e.firstVN = lookup_or_add(C->getOperand(0)); 341 e.secondVN = 0; 342 e.thirdVN = 0; 343 e.function = 0; 344 e.type = C->getType(); 345 e.opcode = getOpcode(C); 346 347 return e; 348} 349 350Expression ValueTable::create_expression(ShuffleVectorInst* S) { 351 Expression e; 352 353 e.firstVN = lookup_or_add(S->getOperand(0)); 354 e.secondVN = lookup_or_add(S->getOperand(1)); 355 e.thirdVN = lookup_or_add(S->getOperand(2)); 356 e.function = 0; 357 e.type = S->getType(); 358 e.opcode = Expression::SHUFFLE; 359 360 return e; 361} 362 363Expression ValueTable::create_expression(ExtractElementInst* E) { 364 Expression e; 365 366 e.firstVN = lookup_or_add(E->getOperand(0)); 367 e.secondVN = lookup_or_add(E->getOperand(1)); 368 e.thirdVN = 0; 369 e.function = 0; 370 e.type = E->getType(); 371 e.opcode = Expression::EXTRACT; 372 373 return e; 374} 375 376Expression ValueTable::create_expression(InsertElementInst* I) { 377 Expression e; 378 379 e.firstVN = lookup_or_add(I->getOperand(0)); 380 e.secondVN = lookup_or_add(I->getOperand(1)); 381 e.thirdVN = lookup_or_add(I->getOperand(2)); 382 e.function = 0; 383 e.type = I->getType(); 384 e.opcode = Expression::INSERT; 385 386 return e; 387} 388 389Expression ValueTable::create_expression(SelectInst* I) { 390 Expression e; 391 392 e.firstVN = lookup_or_add(I->getCondition()); 393 e.secondVN = lookup_or_add(I->getTrueValue()); 394 e.thirdVN = lookup_or_add(I->getFalseValue()); 395 e.function = 0; 396 e.type = I->getType(); 397 e.opcode = Expression::SELECT; 398 399 return e; 400} 401 402Expression ValueTable::create_expression(GetElementPtrInst* G) { 403 Expression e; 404 405 e.firstVN = lookup_or_add(G->getPointerOperand()); 406 e.secondVN = 0; 407 e.thirdVN = 0; 408 e.function = 0; 409 e.type = G->getType(); 410 e.opcode = Expression::GEP; 411 412 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 413 I != E; ++I) 414 e.varargs.push_back(lookup_or_add(*I)); 415 416 return e; 417} 418 419//===----------------------------------------------------------------------===// 420// ValueTable External Functions 421//===----------------------------------------------------------------------===// 422 423/// add - Insert a value into the table with a specified value number. 424void ValueTable::add(Value* V, uint32_t num) { 425 valueNumbering.insert(std::make_pair(V, num)); 426} 427 428/// lookup_or_add - Returns the value number for the specified value, assigning 429/// it a new number if it did not have one before. 430uint32_t ValueTable::lookup_or_add(Value* V) { 431 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 432 if (VI != valueNumbering.end()) 433 return VI->second; 434 435 if (CallInst* C = dyn_cast<CallInst>(V)) { 436 if (AA->doesNotAccessMemory(C)) { 437 Expression e = create_expression(C); 438 439 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 440 if (EI != expressionNumbering.end()) { 441 valueNumbering.insert(std::make_pair(V, EI->second)); 442 return EI->second; 443 } else { 444 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 445 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 446 447 return nextValueNumber++; 448 } 449 } else if (AA->onlyReadsMemory(C)) { 450 Expression e = create_expression(C); 451 452 if (expressionNumbering.find(e) == expressionNumbering.end()) { 453 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 454 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 455 return nextValueNumber++; 456 } 457 458 Instruction* local_dep = MD->getDependency(C); 459 460 if (local_dep == MemoryDependenceAnalysis::None) { 461 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 462 return nextValueNumber++; 463 } else if (local_dep != MemoryDependenceAnalysis::NonLocal) { 464 if (!isa<CallInst>(local_dep)) { 465 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 466 return nextValueNumber++; 467 } 468 469 CallInst* local_cdep = cast<CallInst>(local_dep); 470 471 if (local_cdep->getCalledFunction() != C->getCalledFunction() || 472 local_cdep->getNumOperands() != C->getNumOperands()) { 473 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 474 return nextValueNumber++; 475 } else if (!C->getCalledFunction()) { 476 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 477 return nextValueNumber++; 478 } else { 479 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 480 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 481 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 482 if (c_vn != cd_vn) { 483 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 484 return nextValueNumber++; 485 } 486 } 487 488 uint32_t v = lookup_or_add(local_cdep); 489 valueNumbering.insert(std::make_pair(V, v)); 490 return v; 491 } 492 } 493 494 495 DenseMap<BasicBlock*, Value*> deps; 496 MD->getNonLocalDependency(C, deps); 497 CallInst* cdep = 0; 498 499 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), 500 E = deps.end(); I != E; ++I) { 501 if (I->second == MemoryDependenceAnalysis::None) { 502 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 503 504 return nextValueNumber++; 505 } else if (I->second != MemoryDependenceAnalysis::NonLocal) { 506 if (DT->properlyDominates(I->first, C->getParent())) { 507 if (CallInst* CD = dyn_cast<CallInst>(I->second)) 508 cdep = CD; 509 else { 510 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 511 return nextValueNumber++; 512 } 513 } else { 514 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 515 return nextValueNumber++; 516 } 517 } 518 } 519 520 if (!cdep) { 521 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 522 return nextValueNumber++; 523 } 524 525 if (cdep->getCalledFunction() != C->getCalledFunction() || 526 cdep->getNumOperands() != C->getNumOperands()) { 527 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 528 return nextValueNumber++; 529 } else if (!C->getCalledFunction()) { 530 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 531 return nextValueNumber++; 532 } else { 533 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 534 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 535 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 536 if (c_vn != cd_vn) { 537 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 538 return nextValueNumber++; 539 } 540 } 541 542 uint32_t v = lookup_or_add(cdep); 543 valueNumbering.insert(std::make_pair(V, v)); 544 return v; 545 } 546 547 } else { 548 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 549 return nextValueNumber++; 550 } 551 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 552 Expression e = create_expression(BO); 553 554 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 555 if (EI != expressionNumbering.end()) { 556 valueNumbering.insert(std::make_pair(V, EI->second)); 557 return EI->second; 558 } else { 559 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 560 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 561 562 return nextValueNumber++; 563 } 564 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 565 Expression e = create_expression(C); 566 567 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 568 if (EI != expressionNumbering.end()) { 569 valueNumbering.insert(std::make_pair(V, EI->second)); 570 return EI->second; 571 } else { 572 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 573 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 574 575 return nextValueNumber++; 576 } 577 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 578 Expression e = create_expression(U); 579 580 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 581 if (EI != expressionNumbering.end()) { 582 valueNumbering.insert(std::make_pair(V, EI->second)); 583 return EI->second; 584 } else { 585 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 586 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 587 588 return nextValueNumber++; 589 } 590 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 591 Expression e = create_expression(U); 592 593 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 594 if (EI != expressionNumbering.end()) { 595 valueNumbering.insert(std::make_pair(V, EI->second)); 596 return EI->second; 597 } else { 598 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 599 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 600 601 return nextValueNumber++; 602 } 603 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 604 Expression e = create_expression(U); 605 606 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 607 if (EI != expressionNumbering.end()) { 608 valueNumbering.insert(std::make_pair(V, EI->second)); 609 return EI->second; 610 } else { 611 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 612 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 613 614 return nextValueNumber++; 615 } 616 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 617 Expression e = create_expression(U); 618 619 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 620 if (EI != expressionNumbering.end()) { 621 valueNumbering.insert(std::make_pair(V, EI->second)); 622 return EI->second; 623 } else { 624 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 625 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 626 627 return nextValueNumber++; 628 } 629 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 630 Expression e = create_expression(U); 631 632 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 633 if (EI != expressionNumbering.end()) { 634 valueNumbering.insert(std::make_pair(V, EI->second)); 635 return EI->second; 636 } else { 637 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 638 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 639 640 return nextValueNumber++; 641 } 642 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 643 Expression e = create_expression(U); 644 645 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 646 if (EI != expressionNumbering.end()) { 647 valueNumbering.insert(std::make_pair(V, EI->second)); 648 return EI->second; 649 } else { 650 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 651 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 652 653 return nextValueNumber++; 654 } 655 } else { 656 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 657 return nextValueNumber++; 658 } 659} 660 661/// lookup - Returns the value number of the specified value. Fails if 662/// the value has not yet been numbered. 663uint32_t ValueTable::lookup(Value* V) const { 664 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 665 assert(VI != valueNumbering.end() && "Value not numbered?"); 666 return VI->second; 667} 668 669/// clear - Remove all entries from the ValueTable 670void ValueTable::clear() { 671 valueNumbering.clear(); 672 expressionNumbering.clear(); 673 nextValueNumber = 1; 674} 675 676/// erase - Remove a value from the value numbering 677void ValueTable::erase(Value* V) { 678 valueNumbering.erase(V); 679} 680 681//===----------------------------------------------------------------------===// 682// GVN Pass 683//===----------------------------------------------------------------------===// 684 685namespace { 686 struct VISIBILITY_HIDDEN ValueNumberScope { 687 ValueNumberScope* parent; 688 DenseMap<uint32_t, Value*> table; 689 690 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 691 }; 692} 693 694namespace { 695 696 class VISIBILITY_HIDDEN GVN : public FunctionPass { 697 bool runOnFunction(Function &F); 698 public: 699 static char ID; // Pass identification, replacement for typeid 700 GVN() : FunctionPass(&ID) { } 701 702 private: 703 ValueTable VN; 704 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 705 706 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 707 PhiMapType phiMap; 708 709 710 // This transformation requires dominator postdominator info 711 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 712 AU.addRequired<DominatorTree>(); 713 AU.addRequired<MemoryDependenceAnalysis>(); 714 AU.addRequired<AliasAnalysis>(); 715 716 AU.addPreserved<DominatorTree>(); 717 AU.addPreserved<AliasAnalysis>(); 718 } 719 720 // Helper fuctions 721 // FIXME: eliminate or document these better 722 bool processLoad(LoadInst* L, 723 DenseMap<Value*, LoadInst*> &lastLoad, 724 SmallVectorImpl<Instruction*> &toErase); 725 bool processInstruction(Instruction* I, 726 DenseMap<Value*, LoadInst*>& lastSeenLoad, 727 SmallVectorImpl<Instruction*> &toErase); 728 bool processNonLocalLoad(LoadInst* L, 729 SmallVectorImpl<Instruction*> &toErase); 730 bool processBlock(DomTreeNode* DTN); 731 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig, 732 DenseMap<BasicBlock*, Value*> &Phis, 733 bool top_level = false); 734 void dump(DenseMap<uint32_t, Value*>& d); 735 bool iterateOnFunction(Function &F); 736 Value* CollapsePhi(PHINode* p); 737 bool isSafeReplacement(PHINode* p, Instruction* inst); 738 bool performPRE(Function& F); 739 Value* lookupNumber(BasicBlock* BB, uint32_t num); 740 bool mergeBlockIntoPredecessor(BasicBlock* BB); 741 }; 742 743 char GVN::ID = 0; 744} 745 746// createGVNPass - The public interface to this file... 747FunctionPass *llvm::createGVNPass() { return new GVN(); } 748 749static RegisterPass<GVN> X("gvn", 750 "Global Value Numbering"); 751 752void GVN::dump(DenseMap<uint32_t, Value*>& d) { 753 printf("{\n"); 754 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 755 E = d.end(); I != E; ++I) { 756 printf("%d\n", I->first); 757 I->second->dump(); 758 } 759 printf("}\n"); 760} 761 762Value* GVN::CollapsePhi(PHINode* p) { 763 DominatorTree &DT = getAnalysis<DominatorTree>(); 764 Value* constVal = p->hasConstantValue(); 765 766 if (!constVal) return 0; 767 768 Instruction* inst = dyn_cast<Instruction>(constVal); 769 if (!inst) 770 return constVal; 771 772 if (DT.dominates(inst, p)) 773 if (isSafeReplacement(p, inst)) 774 return inst; 775 return 0; 776} 777 778bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 779 if (!isa<PHINode>(inst)) 780 return true; 781 782 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 783 UI != E; ++UI) 784 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 785 if (use_phi->getParent() == inst->getParent()) 786 return false; 787 788 return true; 789} 790 791/// GetValueForBlock - Get the value to use within the specified basic block. 792/// available values are in Phis. 793Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig, 794 DenseMap<BasicBlock*, Value*> &Phis, 795 bool top_level) { 796 797 // If we have already computed this value, return the previously computed val. 798 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 799 if (V != Phis.end() && !top_level) return V->second; 800 801 // If the block is unreachable, just return undef, since this path 802 // can't actually occur at runtime. 803 if (!getAnalysis<DominatorTree>().isReachableFromEntry(BB)) 804 return Phis[BB] = UndefValue::get(orig->getType()); 805 806 BasicBlock* singlePred = BB->getSinglePredecessor(); 807 if (singlePred) { 808 Value *ret = GetValueForBlock(singlePred, orig, Phis); 809 Phis[BB] = ret; 810 return ret; 811 } 812 813 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 814 // now, then get values to fill in the incoming values for the PHI. 815 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", 816 BB->begin()); 817 PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB))); 818 819 if (Phis.count(BB) == 0) 820 Phis.insert(std::make_pair(BB, PN)); 821 822 // Fill in the incoming values for the block. 823 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 824 Value* val = GetValueForBlock(*PI, orig, Phis); 825 PN->addIncoming(val, *PI); 826 } 827 828 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 829 AA.copyValue(orig, PN); 830 831 // Attempt to collapse PHI nodes that are trivially redundant 832 Value* v = CollapsePhi(PN); 833 if (!v) { 834 // Cache our phi construction results 835 phiMap[orig->getPointerOperand()].insert(PN); 836 return PN; 837 } 838 839 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 840 841 MD.removeInstruction(PN); 842 PN->replaceAllUsesWith(v); 843 844 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 845 E = Phis.end(); I != E; ++I) 846 if (I->second == PN) 847 I->second = v; 848 849 PN->eraseFromParent(); 850 851 Phis[BB] = v; 852 return v; 853} 854 855/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 856/// non-local by performing PHI construction. 857bool GVN::processNonLocalLoad(LoadInst* L, 858 SmallVectorImpl<Instruction*> &toErase) { 859 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 860 861 // Find the non-local dependencies of the load 862 DenseMap<BasicBlock*, Value*> deps; 863 MD.getNonLocalDependency(L, deps); 864 865 // If we had to process more than one hundred blocks to find the 866 // dependencies, this load isn't worth worrying about. Optimizing 867 // it will be too expensive. 868 if (deps.size() > 100) 869 return false; 870 871 DenseMap<BasicBlock*, Value*> repl; 872 873 // Filter out useless results (non-locals, etc) 874 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end(); 875 I != E; ++I) { 876 if (I->second == MemoryDependenceAnalysis::None) 877 return false; 878 879 if (I->second == MemoryDependenceAnalysis::NonLocal) 880 continue; 881 882 if (StoreInst* S = dyn_cast<StoreInst>(I->second)) { 883 if (S->getPointerOperand() != L->getPointerOperand()) 884 return false; 885 repl[I->first] = S->getOperand(0); 886 } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) { 887 if (LD->getPointerOperand() != L->getPointerOperand()) 888 return false; 889 repl[I->first] = LD; 890 } else { 891 return false; 892 } 893 } 894 895 // Use cached PHI construction information from previous runs 896 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()]; 897 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 898 I != E; ++I) { 899 if ((*I)->getParent() == L->getParent()) { 900 MD.removeInstruction(L); 901 L->replaceAllUsesWith(*I); 902 toErase.push_back(L); 903 NumGVNLoad++; 904 return true; 905 } 906 907 repl.insert(std::make_pair((*I)->getParent(), *I)); 908 } 909 910 // Perform PHI construction 911 SmallPtrSet<BasicBlock*, 4> visited; 912 Value* v = GetValueForBlock(L->getParent(), L, repl, true); 913 914 MD.removeInstruction(L); 915 L->replaceAllUsesWith(v); 916 toErase.push_back(L); 917 NumGVNLoad++; 918 919 return true; 920} 921 922/// processLoad - Attempt to eliminate a load, first by eliminating it 923/// locally, and then attempting non-local elimination if that fails. 924bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad, 925 SmallVectorImpl<Instruction*> &toErase) { 926 if (L->isVolatile()) { 927 lastLoad[L->getPointerOperand()] = L; 928 return false; 929 } 930 931 Value* pointer = L->getPointerOperand(); 932 LoadInst*& last = lastLoad[pointer]; 933 934 // ... to a pointer that has been loaded from before... 935 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 936 bool removedNonLocal = false; 937 Instruction* dep = MD.getDependency(L); 938 if (dep == MemoryDependenceAnalysis::NonLocal && 939 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) { 940 removedNonLocal = processNonLocalLoad(L, toErase); 941 942 if (!removedNonLocal) 943 last = L; 944 945 return removedNonLocal; 946 } 947 948 949 bool deletedLoad = false; 950 951 // Walk up the dependency chain until we either find 952 // a dependency we can use, or we can't walk any further 953 while (dep != MemoryDependenceAnalysis::None && 954 dep != MemoryDependenceAnalysis::NonLocal && 955 (isa<LoadInst>(dep) || isa<StoreInst>(dep))) { 956 // ... that depends on a store ... 957 if (StoreInst* S = dyn_cast<StoreInst>(dep)) { 958 if (S->getPointerOperand() == pointer) { 959 // Remove it! 960 MD.removeInstruction(L); 961 962 L->replaceAllUsesWith(S->getOperand(0)); 963 toErase.push_back(L); 964 deletedLoad = true; 965 NumGVNLoad++; 966 } 967 968 // Whether we removed it or not, we can't 969 // go any further 970 break; 971 } else if (!last) { 972 // If we don't depend on a store, and we haven't 973 // been loaded before, bail. 974 break; 975 } else if (dep == last) { 976 // Remove it! 977 MD.removeInstruction(L); 978 979 L->replaceAllUsesWith(last); 980 toErase.push_back(L); 981 deletedLoad = true; 982 NumGVNLoad++; 983 984 break; 985 } else { 986 dep = MD.getDependency(L, dep); 987 } 988 } 989 990 if (dep != MemoryDependenceAnalysis::None && 991 dep != MemoryDependenceAnalysis::NonLocal && 992 isa<AllocationInst>(dep)) { 993 // Check that this load is actually from the 994 // allocation we found 995 if (L->getOperand(0)->getUnderlyingObject() == dep) { 996 // If this load depends directly on an allocation, there isn't 997 // anything stored there; therefore, we can optimize this load 998 // to undef. 999 MD.removeInstruction(L); 1000 1001 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1002 toErase.push_back(L); 1003 deletedLoad = true; 1004 NumGVNLoad++; 1005 } 1006 } 1007 1008 if (!deletedLoad) 1009 last = L; 1010 1011 return deletedLoad; 1012} 1013 1014Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) { 1015 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1016 if (I == localAvail.end()) 1017 return 0; 1018 1019 ValueNumberScope* locals = I->second; 1020 1021 while (locals) { 1022 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num); 1023 if (I != locals->table.end()) 1024 return I->second; 1025 else 1026 locals = locals->parent; 1027 } 1028 1029 return 0; 1030} 1031 1032/// processInstruction - When calculating availability, handle an instruction 1033/// by inserting it into the appropriate sets 1034bool GVN::processInstruction(Instruction *I, 1035 DenseMap<Value*, LoadInst*> &lastSeenLoad, 1036 SmallVectorImpl<Instruction*> &toErase) { 1037 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1038 bool changed = processLoad(L, lastSeenLoad, toErase); 1039 1040 if (!changed) { 1041 unsigned num = VN.lookup_or_add(L); 1042 localAvail[I->getParent()]->table.insert(std::make_pair(num, L)); 1043 } 1044 1045 return changed; 1046 } 1047 1048 uint32_t nextNum = VN.getNextUnusedValueNumber(); 1049 unsigned num = VN.lookup_or_add(I); 1050 1051 // Allocations are always uniquely numbered, so we can save time and memory 1052 // by fast failing them. 1053 if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1054 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1055 return false; 1056 } 1057 1058 // Collapse PHI nodes 1059 if (PHINode* p = dyn_cast<PHINode>(I)) { 1060 Value* constVal = CollapsePhi(p); 1061 1062 if (constVal) { 1063 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1064 PI != PE; ++PI) 1065 if (PI->second.count(p)) 1066 PI->second.erase(p); 1067 1068 p->replaceAllUsesWith(constVal); 1069 toErase.push_back(p); 1070 } else { 1071 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1072 } 1073 1074 // If the number we were assigned was a brand new VN, then we don't 1075 // need to do a lookup to see if the number already exists 1076 // somewhere in the domtree: it can't! 1077 } else if (num == nextNum) { 1078 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1079 1080 // Perform value-number based elimination 1081 } else if (Value* repl = lookupNumber(I->getParent(), num)) { 1082 // Remove it! 1083 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1084 MD.removeInstruction(I); 1085 1086 VN.erase(I); 1087 I->replaceAllUsesWith(repl); 1088 toErase.push_back(I); 1089 return true; 1090 } else { 1091 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1092 } 1093 1094 return false; 1095} 1096 1097// GVN::runOnFunction - This is the main transformation entry point for a 1098// function. 1099// 1100bool GVN::runOnFunction(Function& F) { 1101 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1102 VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>()); 1103 VN.setDomTree(&getAnalysis<DominatorTree>()); 1104 1105 bool changed = false; 1106 bool shouldContinue = true; 1107 1108 // Merge unconditional branches, allowing PRE to catch more 1109 // optimization opportunities. 1110 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1111 BasicBlock* BB = FI; 1112 ++FI; 1113 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1114 if (removedBlock) NumGVNBlocks++; 1115 1116 changed |= removedBlock; 1117 } 1118 1119 while (shouldContinue) { 1120 shouldContinue = iterateOnFunction(F); 1121 changed |= shouldContinue; 1122 } 1123 1124 if (EnablePRE) { 1125 bool PREChanged = true; 1126 while (PREChanged) { 1127 PREChanged = performPRE(F); 1128 changed |= PREChanged; 1129 } 1130 } 1131 1132 return changed; 1133} 1134 1135 1136bool GVN::processBlock(DomTreeNode* DTN) { 1137 BasicBlock* BB = DTN->getBlock(); 1138 1139 SmallVector<Instruction*, 8> toErase; 1140 DenseMap<Value*, LoadInst*> lastSeenLoad; 1141 bool changed_function = false; 1142 1143 if (DTN->getIDom()) 1144 localAvail[BB] = 1145 new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]); 1146 else 1147 localAvail[BB] = new ValueNumberScope(0); 1148 1149 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1150 BI != BE;) { 1151 changed_function |= processInstruction(BI, lastSeenLoad, toErase); 1152 if (toErase.empty()) { 1153 ++BI; 1154 continue; 1155 } 1156 1157 // If we need some instructions deleted, do it now. 1158 NumGVNInstr += toErase.size(); 1159 1160 // Avoid iterator invalidation. 1161 bool AtStart = BI == BB->begin(); 1162 if (!AtStart) 1163 --BI; 1164 1165 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1166 E = toErase.end(); I != E; ++I) 1167 (*I)->eraseFromParent(); 1168 1169 if (AtStart) 1170 BI = BB->begin(); 1171 else 1172 ++BI; 1173 1174 toErase.clear(); 1175 } 1176 1177 return changed_function; 1178} 1179 1180/// performPRE - Perform a purely local form of PRE that looks for diamond 1181/// control flow patterns and attempts to perform simple PRE at the join point. 1182bool GVN::performPRE(Function& F) { 1183 bool changed = false; 1184 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1185 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1186 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1187 BasicBlock* CurrentBlock = *DI; 1188 1189 // Nothing to PRE in the entry block. 1190 if (CurrentBlock == &F.getEntryBlock()) continue; 1191 1192 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1193 BE = CurrentBlock->end(); BI != BE; ) { 1194 if (isa<AllocationInst>(BI) || isa<TerminatorInst>(BI) || 1195 isa<PHINode>(BI) || BI->mayReadFromMemory() || 1196 BI->mayWriteToMemory()) { 1197 BI++; 1198 continue; 1199 } 1200 1201 uint32_t valno = VN.lookup(BI); 1202 1203 // Look for the predecessors for PRE opportunities. We're 1204 // only trying to solve the basic diamond case, where 1205 // a value is computed in the successor and one predecessor, 1206 // but not the other. We also explicitly disallow cases 1207 // where the successor is its own predecessor, because they're 1208 // more complicated to get right. 1209 unsigned numWith = 0; 1210 unsigned numWithout = 0; 1211 BasicBlock* PREPred = 0; 1212 DenseMap<BasicBlock*, Value*> predMap; 1213 for (pred_iterator PI = pred_begin(CurrentBlock), 1214 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1215 // We're not interested in PRE where the block is its 1216 // own predecessor, on in blocks with predecessors 1217 // that are not reachable. 1218 if (*PI == CurrentBlock) { 1219 numWithout = 2; 1220 break; 1221 } else if (!localAvail.count(*PI)) { 1222 numWithout = 2; 1223 break; 1224 } 1225 1226 DenseMap<uint32_t, Value*>::iterator predV = 1227 localAvail[*PI]->table.find(valno); 1228 if (predV == localAvail[*PI]->table.end()) { 1229 PREPred = *PI; 1230 numWithout++; 1231 } else if (predV->second == BI) { 1232 numWithout = 2; 1233 } else { 1234 predMap[*PI] = predV->second; 1235 numWith++; 1236 } 1237 } 1238 1239 // Don't do PRE when it might increase code size, i.e. when 1240 // we would need to insert instructions in more than one pred. 1241 if (numWithout != 1 || numWith == 0) { 1242 BI++; 1243 continue; 1244 } 1245 1246 // We can't do PRE safely on a critical edge, so instead we schedule 1247 // the edge to be split and perform the PRE the next time we iterate 1248 // on the function. 1249 unsigned succNum = 0; 1250 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1251 i != e; ++i) 1252 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 1253 succNum = i; 1254 break; 1255 } 1256 1257 if (isCriticalEdge(PREPred->getTerminator(), succNum)) { 1258 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum)); 1259 changed = true; 1260 BI++; 1261 continue; 1262 } 1263 1264 // Instantiate the expression the in predecessor that lacked it. 1265 // Because we are going top-down through the block, all value numbers 1266 // will be available in the predecessor by the time we need them. Any 1267 // that weren't original present will have been instantiated earlier 1268 // in this loop. 1269 Instruction* PREInstr = BI->clone(); 1270 bool success = true; 1271 for (unsigned i = 0; i < BI->getNumOperands(); ++i) { 1272 Value* op = BI->getOperand(i); 1273 if (isa<Argument>(op) || isa<Constant>(op) || isa<GlobalValue>(op)) 1274 PREInstr->setOperand(i, op); 1275 else { 1276 Value* V = lookupNumber(PREPred, VN.lookup(op)); 1277 if (!V) { 1278 success = false; 1279 break; 1280 } else 1281 PREInstr->setOperand(i, V); 1282 } 1283 } 1284 1285 // Fail out if we encounter an operand that is not available in 1286 // the PRE predecessor. This is typically because of loads which 1287 // are not value numbered precisely. 1288 if (!success) { 1289 delete PREInstr; 1290 BI++; 1291 continue; 1292 } 1293 1294 PREInstr->insertBefore(PREPred->getTerminator()); 1295 PREInstr->setName(BI->getName() + ".pre"); 1296 predMap[PREPred] = PREInstr; 1297 VN.add(PREInstr, valno); 1298 NumGVNPRE++; 1299 1300 // Update the availability map to include the new instruction. 1301 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr)); 1302 1303 // Create a PHI to make the value available in this block. 1304 PHINode* Phi = PHINode::Create(BI->getType(), 1305 BI->getName() + ".pre-phi", 1306 CurrentBlock->begin()); 1307 for (pred_iterator PI = pred_begin(CurrentBlock), 1308 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1309 Phi->addIncoming(predMap[*PI], *PI); 1310 1311 VN.add(Phi, valno); 1312 localAvail[CurrentBlock]->table[valno] = Phi; 1313 1314 BI->replaceAllUsesWith(Phi); 1315 VN.erase(BI); 1316 1317 Instruction* erase = BI; 1318 BI++; 1319 erase->eraseFromParent(); 1320 1321 changed = true; 1322 } 1323 } 1324 1325 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 1326 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 1327 SplitCriticalEdge(I->first, I->second, this); 1328 1329 return changed || toSplit.size(); 1330} 1331 1332// iterateOnFunction - Executes one iteration of GVN 1333bool GVN::iterateOnFunction(Function &F) { 1334 // Clean out global sets from any previous functions 1335 VN.clear(); 1336 phiMap.clear(); 1337 1338 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1339 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 1340 delete I->second; 1341 localAvail.clear(); 1342 1343 DominatorTree &DT = getAnalysis<DominatorTree>(); 1344 1345 // Top-down walk of the dominator tree 1346 bool changed = false; 1347 for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()), 1348 DE = df_end(DT.getRootNode()); DI != DE; ++DI) 1349 changed |= processBlock(*DI); 1350 1351 return changed; 1352} 1353