GVN.cpp revision f2aa160b357c98d8c37b69ea9775aa3e097d1319
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"); 44 45static cl::opt<bool> EnablePRE("enable-pre", 46 cl::init(false), cl::Hidden); 47 48//===----------------------------------------------------------------------===// 49// ValueTable Class 50//===----------------------------------------------------------------------===// 51 52/// This class holds the mapping between values and value numbers. It is used 53/// as an efficient mechanism to determine the expression-wise equivalence of 54/// two values. 55namespace { 56 struct VISIBILITY_HIDDEN Expression { 57 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, 58 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 59 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 60 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 61 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 62 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 63 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 64 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 65 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 66 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 67 EMPTY, TOMBSTONE }; 68 69 ExpressionOpcode opcode; 70 const Type* type; 71 uint32_t firstVN; 72 uint32_t secondVN; 73 uint32_t thirdVN; 74 SmallVector<uint32_t, 4> varargs; 75 Value* function; 76 77 Expression() { } 78 Expression(ExpressionOpcode o) : opcode(o) { } 79 80 bool operator==(const Expression &other) const { 81 if (opcode != other.opcode) 82 return false; 83 else if (opcode == EMPTY || opcode == TOMBSTONE) 84 return true; 85 else if (type != other.type) 86 return false; 87 else if (function != other.function) 88 return false; 89 else if (firstVN != other.firstVN) 90 return false; 91 else if (secondVN != other.secondVN) 92 return false; 93 else if (thirdVN != other.thirdVN) 94 return false; 95 else { 96 if (varargs.size() != other.varargs.size()) 97 return false; 98 99 for (size_t i = 0; i < varargs.size(); ++i) 100 if (varargs[i] != other.varargs[i]) 101 return false; 102 103 return true; 104 } 105 } 106 107 bool operator!=(const Expression &other) const { 108 if (opcode != other.opcode) 109 return true; 110 else if (opcode == EMPTY || opcode == TOMBSTONE) 111 return false; 112 else if (type != other.type) 113 return true; 114 else if (function != other.function) 115 return true; 116 else if (firstVN != other.firstVN) 117 return true; 118 else if (secondVN != other.secondVN) 119 return true; 120 else if (thirdVN != other.thirdVN) 121 return true; 122 else { 123 if (varargs.size() != other.varargs.size()) 124 return true; 125 126 for (size_t i = 0; i < varargs.size(); ++i) 127 if (varargs[i] != other.varargs[i]) 128 return true; 129 130 return false; 131 } 132 } 133 }; 134 135 class VISIBILITY_HIDDEN ValueTable { 136 private: 137 DenseMap<Value*, uint32_t> valueNumbering; 138 DenseMap<Expression, uint32_t> expressionNumbering; 139 AliasAnalysis* AA; 140 MemoryDependenceAnalysis* MD; 141 DominatorTree* DT; 142 143 uint32_t nextValueNumber; 144 145 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 146 Expression::ExpressionOpcode getOpcode(CmpInst* C); 147 Expression::ExpressionOpcode getOpcode(CastInst* C); 148 Expression create_expression(BinaryOperator* BO); 149 Expression create_expression(CmpInst* C); 150 Expression create_expression(ShuffleVectorInst* V); 151 Expression create_expression(ExtractElementInst* C); 152 Expression create_expression(InsertElementInst* V); 153 Expression create_expression(SelectInst* V); 154 Expression create_expression(CastInst* C); 155 Expression create_expression(GetElementPtrInst* G); 156 Expression create_expression(CallInst* C); 157 Expression create_expression(Constant* C); 158 public: 159 ValueTable() : nextValueNumber(1) { } 160 uint32_t lookup_or_add(Value* V); 161 uint32_t lookup(Value* V) const; 162 void add(Value* V, uint32_t num); 163 void clear(); 164 void erase(Value* v); 165 unsigned size(); 166 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 167 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 168 void setDomTree(DominatorTree* D) { DT = D; } 169 }; 170} 171 172namespace llvm { 173template <> struct DenseMapInfo<Expression> { 174 static inline Expression getEmptyKey() { 175 return Expression(Expression::EMPTY); 176 } 177 178 static inline Expression getTombstoneKey() { 179 return Expression(Expression::TOMBSTONE); 180 } 181 182 static unsigned getHashValue(const Expression e) { 183 unsigned hash = e.opcode; 184 185 hash = e.firstVN + hash * 37; 186 hash = e.secondVN + hash * 37; 187 hash = e.thirdVN + hash * 37; 188 189 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 190 (unsigned)((uintptr_t)e.type >> 9)) + 191 hash * 37; 192 193 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 194 E = e.varargs.end(); I != E; ++I) 195 hash = *I + hash * 37; 196 197 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 198 (unsigned)((uintptr_t)e.function >> 9)) + 199 hash * 37; 200 201 return hash; 202 } 203 static bool isEqual(const Expression &LHS, const Expression &RHS) { 204 return LHS == RHS; 205 } 206 static bool isPod() { return true; } 207}; 208} 209 210//===----------------------------------------------------------------------===// 211// ValueTable Internal Functions 212//===----------------------------------------------------------------------===// 213Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 214 switch(BO->getOpcode()) { 215 default: // THIS SHOULD NEVER HAPPEN 216 assert(0 && "Binary operator with unknown opcode?"); 217 case Instruction::Add: return Expression::ADD; 218 case Instruction::Sub: return Expression::SUB; 219 case Instruction::Mul: return Expression::MUL; 220 case Instruction::UDiv: return Expression::UDIV; 221 case Instruction::SDiv: return Expression::SDIV; 222 case Instruction::FDiv: return Expression::FDIV; 223 case Instruction::URem: return Expression::UREM; 224 case Instruction::SRem: return Expression::SREM; 225 case Instruction::FRem: return Expression::FREM; 226 case Instruction::Shl: return Expression::SHL; 227 case Instruction::LShr: return Expression::LSHR; 228 case Instruction::AShr: return Expression::ASHR; 229 case Instruction::And: return Expression::AND; 230 case Instruction::Or: return Expression::OR; 231 case Instruction::Xor: return Expression::XOR; 232 } 233} 234 235Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 236 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) { 237 switch (C->getPredicate()) { 238 default: // THIS SHOULD NEVER HAPPEN 239 assert(0 && "Comparison with unknown predicate?"); 240 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 241 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 242 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 243 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 244 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 245 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 246 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 247 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 248 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 249 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 250 } 251 } 252 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare"); 253 switch (C->getPredicate()) { 254 default: // THIS SHOULD NEVER HAPPEN 255 assert(0 && "Comparison with unknown predicate?"); 256 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 257 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 258 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 259 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 260 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 261 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 262 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 263 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 264 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 265 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 266 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 267 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 268 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 269 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 270 } 271} 272 273Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 274 switch(C->getOpcode()) { 275 default: // THIS SHOULD NEVER HAPPEN 276 assert(0 && "Cast operator with unknown opcode?"); 277 case Instruction::Trunc: return Expression::TRUNC; 278 case Instruction::ZExt: return Expression::ZEXT; 279 case Instruction::SExt: return Expression::SEXT; 280 case Instruction::FPToUI: return Expression::FPTOUI; 281 case Instruction::FPToSI: return Expression::FPTOSI; 282 case Instruction::UIToFP: return Expression::UITOFP; 283 case Instruction::SIToFP: return Expression::SITOFP; 284 case Instruction::FPTrunc: return Expression::FPTRUNC; 285 case Instruction::FPExt: return Expression::FPEXT; 286 case Instruction::PtrToInt: return Expression::PTRTOINT; 287 case Instruction::IntToPtr: return Expression::INTTOPTR; 288 case Instruction::BitCast: return Expression::BITCAST; 289 } 290} 291 292Expression ValueTable::create_expression(CallInst* C) { 293 Expression e; 294 295 e.type = C->getType(); 296 e.firstVN = 0; 297 e.secondVN = 0; 298 e.thirdVN = 0; 299 e.function = C->getCalledFunction(); 300 e.opcode = Expression::CALL; 301 302 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 303 I != E; ++I) 304 e.varargs.push_back(lookup_or_add(*I)); 305 306 return e; 307} 308 309Expression ValueTable::create_expression(BinaryOperator* BO) { 310 Expression e; 311 312 e.firstVN = lookup_or_add(BO->getOperand(0)); 313 e.secondVN = lookup_or_add(BO->getOperand(1)); 314 e.thirdVN = 0; 315 e.function = 0; 316 e.type = BO->getType(); 317 e.opcode = getOpcode(BO); 318 319 return e; 320} 321 322Expression ValueTable::create_expression(CmpInst* C) { 323 Expression e; 324 325 e.firstVN = lookup_or_add(C->getOperand(0)); 326 e.secondVN = lookup_or_add(C->getOperand(1)); 327 e.thirdVN = 0; 328 e.function = 0; 329 e.type = C->getType(); 330 e.opcode = getOpcode(C); 331 332 return e; 333} 334 335Expression ValueTable::create_expression(CastInst* C) { 336 Expression e; 337 338 e.firstVN = lookup_or_add(C->getOperand(0)); 339 e.secondVN = 0; 340 e.thirdVN = 0; 341 e.function = 0; 342 e.type = C->getType(); 343 e.opcode = getOpcode(C); 344 345 return e; 346} 347 348Expression ValueTable::create_expression(ShuffleVectorInst* S) { 349 Expression e; 350 351 e.firstVN = lookup_or_add(S->getOperand(0)); 352 e.secondVN = lookup_or_add(S->getOperand(1)); 353 e.thirdVN = lookup_or_add(S->getOperand(2)); 354 e.function = 0; 355 e.type = S->getType(); 356 e.opcode = Expression::SHUFFLE; 357 358 return e; 359} 360 361Expression ValueTable::create_expression(ExtractElementInst* E) { 362 Expression e; 363 364 e.firstVN = lookup_or_add(E->getOperand(0)); 365 e.secondVN = lookup_or_add(E->getOperand(1)); 366 e.thirdVN = 0; 367 e.function = 0; 368 e.type = E->getType(); 369 e.opcode = Expression::EXTRACT; 370 371 return e; 372} 373 374Expression ValueTable::create_expression(InsertElementInst* I) { 375 Expression e; 376 377 e.firstVN = lookup_or_add(I->getOperand(0)); 378 e.secondVN = lookup_or_add(I->getOperand(1)); 379 e.thirdVN = lookup_or_add(I->getOperand(2)); 380 e.function = 0; 381 e.type = I->getType(); 382 e.opcode = Expression::INSERT; 383 384 return e; 385} 386 387Expression ValueTable::create_expression(SelectInst* I) { 388 Expression e; 389 390 e.firstVN = lookup_or_add(I->getCondition()); 391 e.secondVN = lookup_or_add(I->getTrueValue()); 392 e.thirdVN = lookup_or_add(I->getFalseValue()); 393 e.function = 0; 394 e.type = I->getType(); 395 e.opcode = Expression::SELECT; 396 397 return e; 398} 399 400Expression ValueTable::create_expression(GetElementPtrInst* G) { 401 Expression e; 402 403 e.firstVN = lookup_or_add(G->getPointerOperand()); 404 e.secondVN = 0; 405 e.thirdVN = 0; 406 e.function = 0; 407 e.type = G->getType(); 408 e.opcode = Expression::GEP; 409 410 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 411 I != E; ++I) 412 e.varargs.push_back(lookup_or_add(*I)); 413 414 return e; 415} 416 417//===----------------------------------------------------------------------===// 418// ValueTable External Functions 419//===----------------------------------------------------------------------===// 420 421/// add - Insert a value into the table with a specified value number. 422void ValueTable::add(Value* V, uint32_t num) { 423 valueNumbering.insert(std::make_pair(V, num)); 424} 425 426/// lookup_or_add - Returns the value number for the specified value, assigning 427/// it a new number if it did not have one before. 428uint32_t ValueTable::lookup_or_add(Value* V) { 429 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 430 if (VI != valueNumbering.end()) 431 return VI->second; 432 433 if (CallInst* C = dyn_cast<CallInst>(V)) { 434 if (AA->doesNotAccessMemory(C)) { 435 Expression e = create_expression(C); 436 437 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 438 if (EI != expressionNumbering.end()) { 439 valueNumbering.insert(std::make_pair(V, EI->second)); 440 return EI->second; 441 } else { 442 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 443 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 444 445 return nextValueNumber++; 446 } 447 } else if (AA->onlyReadsMemory(C)) { 448 Expression e = create_expression(C); 449 450 if (expressionNumbering.find(e) == expressionNumbering.end()) { 451 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 452 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 453 return nextValueNumber++; 454 } 455 456 Instruction* local_dep = MD->getDependency(C); 457 458 if (local_dep == MemoryDependenceAnalysis::None) { 459 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 460 return nextValueNumber++; 461 } else if (local_dep != MemoryDependenceAnalysis::NonLocal) { 462 if (!isa<CallInst>(local_dep)) { 463 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 464 return nextValueNumber++; 465 } 466 467 CallInst* local_cdep = cast<CallInst>(local_dep); 468 469 if (local_cdep->getCalledFunction() != C->getCalledFunction() || 470 local_cdep->getNumOperands() != C->getNumOperands()) { 471 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 472 return nextValueNumber++; 473 } else if (!C->getCalledFunction()) { 474 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 475 return nextValueNumber++; 476 } else { 477 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 478 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 479 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 480 if (c_vn != cd_vn) { 481 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 482 return nextValueNumber++; 483 } 484 } 485 486 uint32_t v = lookup_or_add(local_cdep); 487 valueNumbering.insert(std::make_pair(V, v)); 488 return v; 489 } 490 } 491 492 493 DenseMap<BasicBlock*, Value*> deps; 494 MD->getNonLocalDependency(C, deps); 495 CallInst* cdep = 0; 496 497 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), 498 E = deps.end(); I != E; ++I) { 499 if (I->second == MemoryDependenceAnalysis::None) { 500 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 501 502 return nextValueNumber++; 503 } else if (I->second != MemoryDependenceAnalysis::NonLocal) { 504 if (DT->properlyDominates(I->first, C->getParent())) { 505 if (CallInst* CD = dyn_cast<CallInst>(I->second)) 506 cdep = CD; 507 else { 508 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 509 return nextValueNumber++; 510 } 511 } else { 512 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 513 return nextValueNumber++; 514 } 515 } 516 } 517 518 if (!cdep) { 519 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 520 return nextValueNumber++; 521 } 522 523 if (cdep->getCalledFunction() != C->getCalledFunction() || 524 cdep->getNumOperands() != C->getNumOperands()) { 525 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 526 return nextValueNumber++; 527 } else if (!C->getCalledFunction()) { 528 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 529 return nextValueNumber++; 530 } else { 531 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 532 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 533 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 534 if (c_vn != cd_vn) { 535 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 536 return nextValueNumber++; 537 } 538 } 539 540 uint32_t v = lookup_or_add(cdep); 541 valueNumbering.insert(std::make_pair(V, v)); 542 return v; 543 } 544 545 } else { 546 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 547 return nextValueNumber++; 548 } 549 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 550 Expression e = create_expression(BO); 551 552 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 553 if (EI != expressionNumbering.end()) { 554 valueNumbering.insert(std::make_pair(V, EI->second)); 555 return EI->second; 556 } else { 557 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 558 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 559 560 return nextValueNumber++; 561 } 562 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 563 Expression e = create_expression(C); 564 565 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 566 if (EI != expressionNumbering.end()) { 567 valueNumbering.insert(std::make_pair(V, EI->second)); 568 return EI->second; 569 } else { 570 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 571 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 572 573 return nextValueNumber++; 574 } 575 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 576 Expression e = create_expression(U); 577 578 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 579 if (EI != expressionNumbering.end()) { 580 valueNumbering.insert(std::make_pair(V, EI->second)); 581 return EI->second; 582 } else { 583 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 584 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 585 586 return nextValueNumber++; 587 } 588 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 589 Expression e = create_expression(U); 590 591 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 592 if (EI != expressionNumbering.end()) { 593 valueNumbering.insert(std::make_pair(V, EI->second)); 594 return EI->second; 595 } else { 596 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 597 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 598 599 return nextValueNumber++; 600 } 601 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 602 Expression e = create_expression(U); 603 604 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 605 if (EI != expressionNumbering.end()) { 606 valueNumbering.insert(std::make_pair(V, EI->second)); 607 return EI->second; 608 } else { 609 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 610 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 611 612 return nextValueNumber++; 613 } 614 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 615 Expression e = create_expression(U); 616 617 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 618 if (EI != expressionNumbering.end()) { 619 valueNumbering.insert(std::make_pair(V, EI->second)); 620 return EI->second; 621 } else { 622 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 623 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 624 625 return nextValueNumber++; 626 } 627 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 628 Expression e = create_expression(U); 629 630 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 631 if (EI != expressionNumbering.end()) { 632 valueNumbering.insert(std::make_pair(V, EI->second)); 633 return EI->second; 634 } else { 635 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 636 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 637 638 return nextValueNumber++; 639 } 640 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 641 Expression e = create_expression(U); 642 643 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 644 if (EI != expressionNumbering.end()) { 645 valueNumbering.insert(std::make_pair(V, EI->second)); 646 return EI->second; 647 } else { 648 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 649 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 650 651 return nextValueNumber++; 652 } 653 } else { 654 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 655 return nextValueNumber++; 656 } 657} 658 659/// lookup - Returns the value number of the specified value. Fails if 660/// the value has not yet been numbered. 661uint32_t ValueTable::lookup(Value* V) const { 662 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 663 assert(VI != valueNumbering.end() && "Value not numbered?"); 664 return VI->second; 665} 666 667/// clear - Remove all entries from the ValueTable 668void ValueTable::clear() { 669 valueNumbering.clear(); 670 expressionNumbering.clear(); 671 nextValueNumber = 1; 672} 673 674/// erase - Remove a value from the value numbering 675void ValueTable::erase(Value* V) { 676 valueNumbering.erase(V); 677} 678 679//===----------------------------------------------------------------------===// 680// GVN Pass 681//===----------------------------------------------------------------------===// 682 683namespace llvm { 684 template<> struct DenseMapInfo<uint32_t> { 685 static inline uint32_t getEmptyKey() { return ~0; } 686 static inline uint32_t getTombstoneKey() { return ~0 - 1; } 687 static unsigned getHashValue(const uint32_t& Val) { return Val * 37; } 688 static bool isPod() { return true; } 689 static bool isEqual(const uint32_t& LHS, const uint32_t& RHS) { 690 return LHS == RHS; 691 } 692 }; 693} 694 695namespace { 696 struct VISIBILITY_HIDDEN ValueNumberScope { 697 ValueNumberScope* parent; 698 DenseMap<uint32_t, Value*> table; 699 700 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 701 }; 702} 703 704namespace { 705 706 class VISIBILITY_HIDDEN GVN : public FunctionPass { 707 bool runOnFunction(Function &F); 708 public: 709 static char ID; // Pass identification, replacement for typeid 710 GVN() : FunctionPass((intptr_t)&ID) { } 711 712 private: 713 ValueTable VN; 714 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 715 716 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 717 PhiMapType phiMap; 718 719 720 // This transformation requires dominator postdominator info 721 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 722 AU.addRequired<DominatorTree>(); 723 AU.addRequired<MemoryDependenceAnalysis>(); 724 AU.addRequired<AliasAnalysis>(); 725 726 AU.addPreserved<DominatorTree>(); 727 AU.addPreserved<AliasAnalysis>(); 728 AU.addPreserved<MemoryDependenceAnalysis>(); 729 } 730 731 // Helper fuctions 732 // FIXME: eliminate or document these better 733 bool processLoad(LoadInst* L, 734 DenseMap<Value*, LoadInst*> &lastLoad, 735 SmallVectorImpl<Instruction*> &toErase); 736 bool processInstruction(Instruction* I, 737 DenseMap<Value*, LoadInst*>& lastSeenLoad, 738 SmallVectorImpl<Instruction*> &toErase); 739 bool processNonLocalLoad(LoadInst* L, 740 SmallVectorImpl<Instruction*> &toErase); 741 bool processBlock(DomTreeNode* DTN); 742 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig, 743 DenseMap<BasicBlock*, Value*> &Phis, 744 bool top_level = false); 745 void dump(DenseMap<uint32_t, Value*>& d); 746 bool iterateOnFunction(Function &F); 747 Value* CollapsePhi(PHINode* p); 748 bool isSafeReplacement(PHINode* p, Instruction* inst); 749 bool performPRE(Function& F); 750 Value* lookupNumber(BasicBlock* BB, uint32_t num); 751 }; 752 753 char GVN::ID = 0; 754} 755 756// createGVNPass - The public interface to this file... 757FunctionPass *llvm::createGVNPass() { return new GVN(); } 758 759static RegisterPass<GVN> X("gvn", 760 "Global Value Numbering"); 761 762void GVN::dump(DenseMap<uint32_t, Value*>& d) { 763 printf("{\n"); 764 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 765 E = d.end(); I != E; ++I) { 766 printf("%d\n", I->first); 767 I->second->dump(); 768 } 769 printf("}\n"); 770} 771 772Value* GVN::CollapsePhi(PHINode* p) { 773 DominatorTree &DT = getAnalysis<DominatorTree>(); 774 Value* constVal = p->hasConstantValue(); 775 776 if (!constVal) return 0; 777 778 Instruction* inst = dyn_cast<Instruction>(constVal); 779 if (!inst) 780 return constVal; 781 782 if (DT.dominates(inst, p)) 783 if (isSafeReplacement(p, inst)) 784 return inst; 785 return 0; 786} 787 788bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 789 if (!isa<PHINode>(inst)) 790 return true; 791 792 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 793 UI != E; ++UI) 794 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 795 if (use_phi->getParent() == inst->getParent()) 796 return false; 797 798 return true; 799} 800 801/// GetValueForBlock - Get the value to use within the specified basic block. 802/// available values are in Phis. 803Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig, 804 DenseMap<BasicBlock*, Value*> &Phis, 805 bool top_level) { 806 807 // If we have already computed this value, return the previously computed val. 808 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 809 if (V != Phis.end() && !top_level) return V->second; 810 811 if (!getAnalysis<DominatorTree>().isReachableFromEntry(BB)) { 812 Phis[BB] = UndefValue::get(orig->getType()); 813 return UndefValue::get(orig->getType()); 814 } 815 816 BasicBlock* singlePred = BB->getSinglePredecessor(); 817 if (singlePred) { 818 Value *ret = GetValueForBlock(singlePred, orig, Phis); 819 Phis[BB] = ret; 820 return ret; 821 } 822 823 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 824 // now, then get values to fill in the incoming values for the PHI. 825 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", 826 BB->begin()); 827 PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB))); 828 829 if (Phis.count(BB) == 0) 830 Phis.insert(std::make_pair(BB, PN)); 831 832 // Fill in the incoming values for the block. 833 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 834 Value* val = GetValueForBlock(*PI, orig, Phis); 835 PN->addIncoming(val, *PI); 836 } 837 838 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 839 AA.copyValue(orig, PN); 840 841 // Attempt to collapse PHI nodes that are trivially redundant 842 Value* v = CollapsePhi(PN); 843 if (!v) { 844 // Cache our phi construction results 845 phiMap[orig->getPointerOperand()].insert(PN); 846 return PN; 847 } 848 849 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 850 851 MD.removeInstruction(PN); 852 PN->replaceAllUsesWith(v); 853 854 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 855 E = Phis.end(); I != E; ++I) 856 if (I->second == PN) 857 I->second = v; 858 859 PN->eraseFromParent(); 860 861 Phis[BB] = v; 862 return v; 863} 864 865/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 866/// non-local by performing PHI construction. 867bool GVN::processNonLocalLoad(LoadInst* L, 868 SmallVectorImpl<Instruction*> &toErase) { 869 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 870 871 // Find the non-local dependencies of the load 872 DenseMap<BasicBlock*, Value*> deps; 873 MD.getNonLocalDependency(L, deps); 874 875 DenseMap<BasicBlock*, Value*> repl; 876 877 // Filter out useless results (non-locals, etc) 878 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end(); 879 I != E; ++I) { 880 if (I->second == MemoryDependenceAnalysis::None) 881 return false; 882 883 if (I->second == MemoryDependenceAnalysis::NonLocal) 884 continue; 885 886 if (StoreInst* S = dyn_cast<StoreInst>(I->second)) { 887 if (S->getPointerOperand() != L->getPointerOperand()) 888 return false; 889 repl[I->first] = S->getOperand(0); 890 } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) { 891 if (LD->getPointerOperand() != L->getPointerOperand()) 892 return false; 893 repl[I->first] = LD; 894 } else { 895 return false; 896 } 897 } 898 899 // Use cached PHI construction information from previous runs 900 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()]; 901 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 902 I != E; ++I) { 903 if ((*I)->getParent() == L->getParent()) { 904 MD.removeInstruction(L); 905 L->replaceAllUsesWith(*I); 906 toErase.push_back(L); 907 NumGVNLoad++; 908 return true; 909 } 910 911 repl.insert(std::make_pair((*I)->getParent(), *I)); 912 } 913 914 // Perform PHI construction 915 SmallPtrSet<BasicBlock*, 4> visited; 916 Value* v = GetValueForBlock(L->getParent(), L, repl, true); 917 918 MD.removeInstruction(L); 919 L->replaceAllUsesWith(v); 920 toErase.push_back(L); 921 NumGVNLoad++; 922 923 return true; 924} 925 926/// processLoad - Attempt to eliminate a load, first by eliminating it 927/// locally, and then attempting non-local elimination if that fails. 928bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad, 929 SmallVectorImpl<Instruction*> &toErase) { 930 if (L->isVolatile()) { 931 lastLoad[L->getPointerOperand()] = L; 932 return false; 933 } 934 935 Value* pointer = L->getPointerOperand(); 936 LoadInst*& last = lastLoad[pointer]; 937 938 // ... to a pointer that has been loaded from before... 939 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 940 bool removedNonLocal = false; 941 Instruction* dep = MD.getDependency(L); 942 if (dep == MemoryDependenceAnalysis::NonLocal && 943 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) { 944 removedNonLocal = processNonLocalLoad(L, toErase); 945 946 if (!removedNonLocal) 947 last = L; 948 949 return removedNonLocal; 950 } 951 952 953 bool deletedLoad = false; 954 955 // Walk up the dependency chain until we either find 956 // a dependency we can use, or we can't walk any further 957 while (dep != MemoryDependenceAnalysis::None && 958 dep != MemoryDependenceAnalysis::NonLocal && 959 (isa<LoadInst>(dep) || isa<StoreInst>(dep))) { 960 // ... that depends on a store ... 961 if (StoreInst* S = dyn_cast<StoreInst>(dep)) { 962 if (S->getPointerOperand() == pointer) { 963 // Remove it! 964 MD.removeInstruction(L); 965 966 L->replaceAllUsesWith(S->getOperand(0)); 967 toErase.push_back(L); 968 deletedLoad = true; 969 NumGVNLoad++; 970 } 971 972 // Whether we removed it or not, we can't 973 // go any further 974 break; 975 } else if (!last) { 976 // If we don't depend on a store, and we haven't 977 // been loaded before, bail. 978 break; 979 } else if (dep == last) { 980 // Remove it! 981 MD.removeInstruction(L); 982 983 L->replaceAllUsesWith(last); 984 toErase.push_back(L); 985 deletedLoad = true; 986 NumGVNLoad++; 987 988 break; 989 } else { 990 dep = MD.getDependency(L, dep); 991 } 992 } 993 994 if (dep != MemoryDependenceAnalysis::None && 995 dep != MemoryDependenceAnalysis::NonLocal && 996 isa<AllocationInst>(dep)) { 997 // Check that this load is actually from the 998 // allocation we found 999 Value* v = L->getOperand(0); 1000 while (true) { 1001 if (BitCastInst *BC = dyn_cast<BitCastInst>(v)) 1002 v = BC->getOperand(0); 1003 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v)) 1004 v = GEP->getOperand(0); 1005 else 1006 break; 1007 } 1008 if (v == dep) { 1009 // If this load depends directly on an allocation, there isn't 1010 // anything stored there; therefore, we can optimize this load 1011 // to undef. 1012 MD.removeInstruction(L); 1013 1014 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1015 toErase.push_back(L); 1016 deletedLoad = true; 1017 NumGVNLoad++; 1018 } 1019 } 1020 1021 if (!deletedLoad) 1022 last = L; 1023 1024 return deletedLoad; 1025} 1026 1027Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) { 1028 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1029 if (I == localAvail.end()) 1030 return 0; 1031 1032 ValueNumberScope* locals = I->second; 1033 1034 while (locals) { 1035 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num); 1036 if (I != locals->table.end()) 1037 return I->second; 1038 else 1039 locals = locals->parent; 1040 } 1041 1042 return 0; 1043} 1044 1045/// processInstruction - When calculating availability, handle an instruction 1046/// by inserting it into the appropriate sets 1047bool GVN::processInstruction(Instruction *I, 1048 DenseMap<Value*, LoadInst*> &lastSeenLoad, 1049 SmallVectorImpl<Instruction*> &toErase) { 1050 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1051 bool changed = processLoad(L, lastSeenLoad, toErase); 1052 1053 if (!changed) { 1054 unsigned num = VN.lookup_or_add(L); 1055 localAvail[I->getParent()]->table.insert(std::make_pair(num, L)); 1056 } 1057 1058 return changed; 1059 } 1060 1061 unsigned num = VN.lookup_or_add(I); 1062 1063 // Allocations are always uniquely numbered, so we can save time and memory 1064 // by fast failing them. 1065 if (isa<AllocationInst>(I)) { 1066 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1067 return false; 1068 } 1069 1070 // Collapse PHI nodes 1071 if (PHINode* p = dyn_cast<PHINode>(I)) { 1072 Value* constVal = CollapsePhi(p); 1073 1074 if (constVal) { 1075 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1076 PI != PE; ++PI) 1077 if (PI->second.count(p)) 1078 PI->second.erase(p); 1079 1080 p->replaceAllUsesWith(constVal); 1081 toErase.push_back(p); 1082 } else { 1083 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1084 } 1085 // Perform value-number based elimination 1086 } else if (Value* repl = lookupNumber(I->getParent(), num)) { 1087 // Remove it! 1088 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1089 MD.removeInstruction(I); 1090 1091 VN.erase(I); 1092 I->replaceAllUsesWith(repl); 1093 toErase.push_back(I); 1094 return true; 1095 } else if (!I->isTerminator()) { 1096 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1097 } 1098 1099 return false; 1100} 1101 1102// GVN::runOnFunction - This is the main transformation entry point for a 1103// function. 1104// 1105bool GVN::runOnFunction(Function& F) { 1106 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1107 VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>()); 1108 VN.setDomTree(&getAnalysis<DominatorTree>()); 1109 1110 bool changed = false; 1111 bool shouldContinue = true; 1112 1113 while (shouldContinue) { 1114 shouldContinue = iterateOnFunction(F); 1115 changed |= shouldContinue; 1116 } 1117 1118 return changed; 1119} 1120 1121 1122bool GVN::processBlock(DomTreeNode* DTN) { 1123 BasicBlock* BB = DTN->getBlock(); 1124 1125 SmallVector<Instruction*, 8> toErase; 1126 DenseMap<Value*, LoadInst*> lastSeenLoad; 1127 bool changed_function = false; 1128 1129 if (DTN->getIDom()) 1130 localAvail[BB] = 1131 new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]); 1132 else 1133 localAvail[BB] = new ValueNumberScope(0); 1134 1135 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1136 BI != BE;) { 1137 changed_function |= processInstruction(BI, lastSeenLoad, toErase); 1138 if (toErase.empty()) { 1139 ++BI; 1140 continue; 1141 } 1142 1143 // If we need some instructions deleted, do it now. 1144 NumGVNInstr += toErase.size(); 1145 1146 // Avoid iterator invalidation. 1147 bool AtStart = BI == BB->begin(); 1148 if (!AtStart) 1149 --BI; 1150 1151 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1152 E = toErase.end(); I != E; ++I) 1153 (*I)->eraseFromParent(); 1154 1155 if (AtStart) 1156 BI = BB->begin(); 1157 else 1158 ++BI; 1159 1160 toErase.clear(); 1161 } 1162 1163 return changed_function; 1164} 1165 1166/// performPRE - Perform a purely local form of PRE that looks for diamond 1167/// control flow patterns and attempts to perform simple PRE at the join point. 1168bool GVN::performPRE(Function& F) { 1169 bool changed = false; 1170 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1171 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1172 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1173 BasicBlock* CurrentBlock = *DI; 1174 1175 // Nothing to PRE in the entry block. 1176 if (CurrentBlock == &F.getEntryBlock()) continue; 1177 1178 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1179 BE = CurrentBlock->end(); BI != BE; ) { 1180 if (isa<AllocationInst>(BI) || isa<TerminatorInst>(BI) || 1181 isa<PHINode>(BI) || BI->mayReadFromMemory() || 1182 BI->mayWriteToMemory()) { 1183 BI++; 1184 continue; 1185 } 1186 1187 uint32_t valno = VN.lookup(BI); 1188 1189 // Look for the predecessors for PRE opportunities. We're 1190 // only trying to solve the basic diamond case, where 1191 // a value is computed in the successor and one predecessor, 1192 // but not the other. We also explicitly disallow cases 1193 // where the successor is its own predecessor, because they're 1194 // more complicated to get right. 1195 unsigned numWith = 0; 1196 unsigned numWithout = 0; 1197 BasicBlock* PREPred = 0; 1198 DenseMap<BasicBlock*, Value*> predMap; 1199 for (pred_iterator PI = pred_begin(CurrentBlock), 1200 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1201 // We're not interested in PRE where the block is its 1202 // own predecessor, on in blocks with predecessors 1203 // that are not reachable. 1204 if (*PI == CurrentBlock) { 1205 numWithout = 2; 1206 break; 1207 } else if (!localAvail.count(*PI)) { 1208 numWithout = 2; 1209 break; 1210 } 1211 1212 DenseMap<uint32_t, Value*>::iterator predV = 1213 localAvail[*PI]->table.find(valno); 1214 if (predV == localAvail[*PI]->table.end()) { 1215 PREPred = *PI; 1216 numWithout++; 1217 } else if (predV->second == BI) { 1218 numWithout = 2; 1219 } else { 1220 predMap[*PI] = predV->second; 1221 numWith++; 1222 } 1223 } 1224 1225 // Don't do PRE when it might increase code size, i.e. when 1226 // we would need to insert instructions in more than one pred. 1227 if (numWithout != 1 || numWith == 0) { 1228 BI++; 1229 continue; 1230 } 1231 1232 // We can't do PRE safely on a critical edge, so instead we schedule 1233 // the edge to be split and perform the PRE the next time we iterate 1234 // on the function. 1235 unsigned succNum = 0; 1236 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1237 i != e; ++i) 1238 if (PREPred->getTerminator()->getSuccessor(i) == PREPred) { 1239 succNum = i; 1240 break; 1241 } 1242 1243 if (isCriticalEdge(PREPred->getTerminator(), succNum)) { 1244 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum)); 1245 changed = true; 1246 BI++; 1247 continue; 1248 } 1249 1250 // Instantiate the expression the in predecessor that lacked it. 1251 // Because we are going top-down through the block, all value numbers 1252 // will be available in the predecessor by the time we need them. Any 1253 // that weren't original present will have been instantiated earlier 1254 // in this loop. 1255 Instruction* PREInstr = BI->clone(); 1256 bool success = true; 1257 for (unsigned i = 0; i < BI->getNumOperands(); ++i) { 1258 Value* op = BI->getOperand(i); 1259 if (isa<Argument>(op) || isa<Constant>(op) || isa<GlobalValue>(op)) 1260 PREInstr->setOperand(i, op); 1261 else if (!lookupNumber(PREPred, VN.lookup(op))) { 1262 success = false; 1263 break; 1264 } else 1265 PREInstr->setOperand(i, lookupNumber(PREPred, VN.lookup(op))); 1266 } 1267 1268 // Fail out if we encounter an operand that is not available in 1269 // the PRE predecessor. This is typically because of loads which 1270 // are not value numbered precisely. 1271 if (!success) { 1272 delete PREInstr; 1273 BI++; 1274 continue; 1275 } 1276 1277 PREInstr->insertBefore(PREPred->getTerminator()); 1278 PREInstr->setName(BI->getName() + ".pre"); 1279 predMap[PREPred] = PREInstr; 1280 VN.add(PREInstr, valno); 1281 NumGVNPRE++; 1282 1283 // Update the availability map to include the new instruction. 1284 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr)); 1285 1286 // Create a PHI to make the value available in this block. 1287 PHINode* Phi = PHINode::Create(BI->getType(), 1288 BI->getName() + ".pre-phi", 1289 CurrentBlock->begin()); 1290 for (pred_iterator PI = pred_begin(CurrentBlock), 1291 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1292 Phi->addIncoming(predMap[*PI], *PI); 1293 1294 VN.add(Phi, valno); 1295 localAvail[CurrentBlock]->table[valno] = Phi; 1296 1297 BI->replaceAllUsesWith(Phi); 1298 VN.erase(BI); 1299 1300 Instruction* erase = BI; 1301 BI++; 1302 erase->eraseFromParent(); 1303 1304 changed = true; 1305 } 1306 } 1307 1308 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 1309 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 1310 SplitCriticalEdge(I->first, I->second, this); 1311 1312 return changed; 1313} 1314 1315// GVN::iterateOnFunction - Executes one iteration of GVN 1316bool GVN::iterateOnFunction(Function &F) { 1317 // Clean out global sets from any previous functions 1318 VN.clear(); 1319 phiMap.clear(); 1320 1321 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1322 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 1323 delete I->second; 1324 localAvail.clear(); 1325 1326 DominatorTree &DT = getAnalysis<DominatorTree>(); 1327 1328 // Top-down walk of the dominator tree 1329 bool changed = false; 1330 for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()), 1331 DE = df_end(DT.getRootNode()); DI != DE; ++DI) 1332 changed |= processBlock(*DI); 1333 1334 if (EnablePRE) 1335 changed |= performPRE(F); 1336 1337 return changed; 1338} 1339