GVN.cpp revision b33f7cc7e6ef84127b35c729b65d43a8edd20366
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 llvm { 686 template<> struct DenseMapInfo<uint32_t> { 687 static inline uint32_t getEmptyKey() { return ~0; } 688 static inline uint32_t getTombstoneKey() { return ~0 - 1; } 689 static unsigned getHashValue(const uint32_t& Val) { return Val * 37; } 690 static bool isPod() { return true; } 691 static bool isEqual(const uint32_t& LHS, const uint32_t& RHS) { 692 return LHS == RHS; 693 } 694 }; 695} 696 697namespace { 698 struct VISIBILITY_HIDDEN ValueNumberScope { 699 ValueNumberScope* parent; 700 DenseMap<uint32_t, Value*> table; 701 702 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 703 }; 704} 705 706namespace { 707 708 class VISIBILITY_HIDDEN GVN : public FunctionPass { 709 bool runOnFunction(Function &F); 710 public: 711 static char ID; // Pass identification, replacement for typeid 712 GVN() : FunctionPass((intptr_t)&ID) { } 713 714 private: 715 ValueTable VN; 716 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 717 718 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 719 PhiMapType phiMap; 720 721 722 // This transformation requires dominator postdominator info 723 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 724 AU.addRequired<DominatorTree>(); 725 AU.addRequired<MemoryDependenceAnalysis>(); 726 AU.addRequired<AliasAnalysis>(); 727 728 AU.addPreserved<DominatorTree>(); 729 AU.addPreserved<AliasAnalysis>(); 730 AU.addPreserved<MemoryDependenceAnalysis>(); 731 } 732 733 // Helper fuctions 734 // FIXME: eliminate or document these better 735 bool processLoad(LoadInst* L, 736 DenseMap<Value*, LoadInst*> &lastLoad, 737 SmallVectorImpl<Instruction*> &toErase); 738 bool processInstruction(Instruction* I, 739 DenseMap<Value*, LoadInst*>& lastSeenLoad, 740 SmallVectorImpl<Instruction*> &toErase); 741 bool processNonLocalLoad(LoadInst* L, 742 SmallVectorImpl<Instruction*> &toErase); 743 bool processBlock(DomTreeNode* DTN); 744 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig, 745 DenseMap<BasicBlock*, Value*> &Phis, 746 bool top_level = false); 747 void dump(DenseMap<uint32_t, Value*>& d); 748 bool iterateOnFunction(Function &F); 749 Value* CollapsePhi(PHINode* p); 750 bool isSafeReplacement(PHINode* p, Instruction* inst); 751 bool performPRE(Function& F); 752 Value* lookupNumber(BasicBlock* BB, uint32_t num); 753 bool mergeBlockIntoPredecessor(BasicBlock* BB); 754 }; 755 756 char GVN::ID = 0; 757} 758 759// createGVNPass - The public interface to this file... 760FunctionPass *llvm::createGVNPass() { return new GVN(); } 761 762static RegisterPass<GVN> X("gvn", 763 "Global Value Numbering"); 764 765void GVN::dump(DenseMap<uint32_t, Value*>& d) { 766 printf("{\n"); 767 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 768 E = d.end(); I != E; ++I) { 769 printf("%d\n", I->first); 770 I->second->dump(); 771 } 772 printf("}\n"); 773} 774 775Value* GVN::CollapsePhi(PHINode* p) { 776 DominatorTree &DT = getAnalysis<DominatorTree>(); 777 Value* constVal = p->hasConstantValue(); 778 779 if (!constVal) return 0; 780 781 Instruction* inst = dyn_cast<Instruction>(constVal); 782 if (!inst) 783 return constVal; 784 785 if (DT.dominates(inst, p)) 786 if (isSafeReplacement(p, inst)) 787 return inst; 788 return 0; 789} 790 791bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 792 if (!isa<PHINode>(inst)) 793 return true; 794 795 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 796 UI != E; ++UI) 797 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 798 if (use_phi->getParent() == inst->getParent()) 799 return false; 800 801 return true; 802} 803 804/// GetValueForBlock - Get the value to use within the specified basic block. 805/// available values are in Phis. 806Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig, 807 DenseMap<BasicBlock*, Value*> &Phis, 808 bool top_level) { 809 810 // If we have already computed this value, return the previously computed val. 811 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 812 if (V != Phis.end() && !top_level) return V->second; 813 814 // If the block is unreachable, just return undef, since this path 815 // can't actually occur at runtime. 816 if (!getAnalysis<DominatorTree>().isReachableFromEntry(BB)) 817 return Phis[BB] = UndefValue::get(orig->getType()); 818 819 BasicBlock* singlePred = BB->getSinglePredecessor(); 820 if (singlePred) { 821 Value *ret = GetValueForBlock(singlePred, orig, Phis); 822 Phis[BB] = ret; 823 return ret; 824 } 825 826 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 827 // now, then get values to fill in the incoming values for the PHI. 828 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", 829 BB->begin()); 830 PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB))); 831 832 if (Phis.count(BB) == 0) 833 Phis.insert(std::make_pair(BB, PN)); 834 835 // Fill in the incoming values for the block. 836 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 837 Value* val = GetValueForBlock(*PI, orig, Phis); 838 PN->addIncoming(val, *PI); 839 } 840 841 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 842 AA.copyValue(orig, PN); 843 844 // Attempt to collapse PHI nodes that are trivially redundant 845 Value* v = CollapsePhi(PN); 846 if (!v) { 847 // Cache our phi construction results 848 phiMap[orig->getPointerOperand()].insert(PN); 849 return PN; 850 } 851 852 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 853 854 MD.removeInstruction(PN); 855 PN->replaceAllUsesWith(v); 856 857 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 858 E = Phis.end(); I != E; ++I) 859 if (I->second == PN) 860 I->second = v; 861 862 PN->eraseFromParent(); 863 864 Phis[BB] = v; 865 return v; 866} 867 868/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 869/// non-local by performing PHI construction. 870bool GVN::processNonLocalLoad(LoadInst* L, 871 SmallVectorImpl<Instruction*> &toErase) { 872 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 873 874 // Find the non-local dependencies of the load 875 DenseMap<BasicBlock*, Value*> deps; 876 MD.getNonLocalDependency(L, deps); 877 878 DenseMap<BasicBlock*, Value*> repl; 879 880 // Filter out useless results (non-locals, etc) 881 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end(); 882 I != E; ++I) { 883 if (I->second == MemoryDependenceAnalysis::None) 884 return false; 885 886 if (I->second == MemoryDependenceAnalysis::NonLocal) 887 continue; 888 889 if (StoreInst* S = dyn_cast<StoreInst>(I->second)) { 890 if (S->getPointerOperand() != L->getPointerOperand()) 891 return false; 892 repl[I->first] = S->getOperand(0); 893 } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) { 894 if (LD->getPointerOperand() != L->getPointerOperand()) 895 return false; 896 repl[I->first] = LD; 897 } else { 898 return false; 899 } 900 } 901 902 // Use cached PHI construction information from previous runs 903 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()]; 904 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 905 I != E; ++I) { 906 if ((*I)->getParent() == L->getParent()) { 907 MD.removeInstruction(L); 908 L->replaceAllUsesWith(*I); 909 toErase.push_back(L); 910 NumGVNLoad++; 911 return true; 912 } 913 914 repl.insert(std::make_pair((*I)->getParent(), *I)); 915 } 916 917 // Perform PHI construction 918 SmallPtrSet<BasicBlock*, 4> visited; 919 Value* v = GetValueForBlock(L->getParent(), L, repl, true); 920 921 MD.removeInstruction(L); 922 L->replaceAllUsesWith(v); 923 toErase.push_back(L); 924 NumGVNLoad++; 925 926 return true; 927} 928 929/// processLoad - Attempt to eliminate a load, first by eliminating it 930/// locally, and then attempting non-local elimination if that fails. 931bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad, 932 SmallVectorImpl<Instruction*> &toErase) { 933 if (L->isVolatile()) { 934 lastLoad[L->getPointerOperand()] = L; 935 return false; 936 } 937 938 Value* pointer = L->getPointerOperand(); 939 LoadInst*& last = lastLoad[pointer]; 940 941 // ... to a pointer that has been loaded from before... 942 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 943 bool removedNonLocal = false; 944 Instruction* dep = MD.getDependency(L); 945 if (dep == MemoryDependenceAnalysis::NonLocal && 946 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) { 947 removedNonLocal = processNonLocalLoad(L, toErase); 948 949 if (!removedNonLocal) 950 last = L; 951 952 return removedNonLocal; 953 } 954 955 956 bool deletedLoad = false; 957 958 // Walk up the dependency chain until we either find 959 // a dependency we can use, or we can't walk any further 960 while (dep != MemoryDependenceAnalysis::None && 961 dep != MemoryDependenceAnalysis::NonLocal && 962 (isa<LoadInst>(dep) || isa<StoreInst>(dep))) { 963 // ... that depends on a store ... 964 if (StoreInst* S = dyn_cast<StoreInst>(dep)) { 965 if (S->getPointerOperand() == pointer) { 966 // Remove it! 967 MD.removeInstruction(L); 968 969 L->replaceAllUsesWith(S->getOperand(0)); 970 toErase.push_back(L); 971 deletedLoad = true; 972 NumGVNLoad++; 973 } 974 975 // Whether we removed it or not, we can't 976 // go any further 977 break; 978 } else if (!last) { 979 // If we don't depend on a store, and we haven't 980 // been loaded before, bail. 981 break; 982 } else if (dep == last) { 983 // Remove it! 984 MD.removeInstruction(L); 985 986 L->replaceAllUsesWith(last); 987 toErase.push_back(L); 988 deletedLoad = true; 989 NumGVNLoad++; 990 991 break; 992 } else { 993 dep = MD.getDependency(L, dep); 994 } 995 } 996 997 if (dep != MemoryDependenceAnalysis::None && 998 dep != MemoryDependenceAnalysis::NonLocal && 999 isa<AllocationInst>(dep)) { 1000 // Check that this load is actually from the 1001 // allocation we found 1002 Value* v = L->getOperand(0); 1003 while (true) { 1004 if (BitCastInst *BC = dyn_cast<BitCastInst>(v)) 1005 v = BC->getOperand(0); 1006 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v)) 1007 v = GEP->getOperand(0); 1008 else 1009 break; 1010 } 1011 if (v == dep) { 1012 // If this load depends directly on an allocation, there isn't 1013 // anything stored there; therefore, we can optimize this load 1014 // to undef. 1015 MD.removeInstruction(L); 1016 1017 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1018 toErase.push_back(L); 1019 deletedLoad = true; 1020 NumGVNLoad++; 1021 } 1022 } 1023 1024 if (!deletedLoad) 1025 last = L; 1026 1027 return deletedLoad; 1028} 1029 1030Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) { 1031 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1032 if (I == localAvail.end()) 1033 return 0; 1034 1035 ValueNumberScope* locals = I->second; 1036 1037 while (locals) { 1038 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num); 1039 if (I != locals->table.end()) 1040 return I->second; 1041 else 1042 locals = locals->parent; 1043 } 1044 1045 return 0; 1046} 1047 1048/// processInstruction - When calculating availability, handle an instruction 1049/// by inserting it into the appropriate sets 1050bool GVN::processInstruction(Instruction *I, 1051 DenseMap<Value*, LoadInst*> &lastSeenLoad, 1052 SmallVectorImpl<Instruction*> &toErase) { 1053 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1054 bool changed = processLoad(L, lastSeenLoad, toErase); 1055 1056 if (!changed) { 1057 unsigned num = VN.lookup_or_add(L); 1058 localAvail[I->getParent()]->table.insert(std::make_pair(num, L)); 1059 } 1060 1061 return changed; 1062 } 1063 1064 uint32_t nextNum = VN.getNextUnusedValueNumber(); 1065 unsigned num = VN.lookup_or_add(I); 1066 1067 // Allocations are always uniquely numbered, so we can save time and memory 1068 // by fast failing them. 1069 if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1070 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1071 return false; 1072 } 1073 1074 // Collapse PHI nodes 1075 if (PHINode* p = dyn_cast<PHINode>(I)) { 1076 Value* constVal = CollapsePhi(p); 1077 1078 if (constVal) { 1079 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1080 PI != PE; ++PI) 1081 if (PI->second.count(p)) 1082 PI->second.erase(p); 1083 1084 p->replaceAllUsesWith(constVal); 1085 toErase.push_back(p); 1086 } else { 1087 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1088 } 1089 1090 // If the number we were assigned was a brand new VN, then we don't 1091 // need to do a lookup to see if the number already exists 1092 // somewhere in the domtree: it can't! 1093 } else if (num == nextNum) { 1094 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1095 1096 // Perform value-number based elimination 1097 } else if (Value* repl = lookupNumber(I->getParent(), num)) { 1098 // Remove it! 1099 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1100 MD.removeInstruction(I); 1101 1102 VN.erase(I); 1103 I->replaceAllUsesWith(repl); 1104 toErase.push_back(I); 1105 return true; 1106 } else { 1107 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1108 } 1109 1110 return false; 1111} 1112 1113// GVN::runOnFunction - This is the main transformation entry point for a 1114// function. 1115// 1116bool GVN::runOnFunction(Function& F) { 1117 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1118 VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>()); 1119 VN.setDomTree(&getAnalysis<DominatorTree>()); 1120 1121 bool changed = false; 1122 bool shouldContinue = true; 1123 1124 while (shouldContinue) { 1125 shouldContinue = iterateOnFunction(F); 1126 changed |= shouldContinue; 1127 } 1128 1129 return changed; 1130} 1131 1132 1133bool GVN::processBlock(DomTreeNode* DTN) { 1134 BasicBlock* BB = DTN->getBlock(); 1135 1136 SmallVector<Instruction*, 8> toErase; 1137 DenseMap<Value*, LoadInst*> lastSeenLoad; 1138 bool changed_function = false; 1139 1140 if (DTN->getIDom()) 1141 localAvail[BB] = 1142 new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]); 1143 else 1144 localAvail[BB] = new ValueNumberScope(0); 1145 1146 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1147 BI != BE;) { 1148 changed_function |= processInstruction(BI, lastSeenLoad, toErase); 1149 if (toErase.empty()) { 1150 ++BI; 1151 continue; 1152 } 1153 1154 // If we need some instructions deleted, do it now. 1155 NumGVNInstr += toErase.size(); 1156 1157 // Avoid iterator invalidation. 1158 bool AtStart = BI == BB->begin(); 1159 if (!AtStart) 1160 --BI; 1161 1162 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1163 E = toErase.end(); I != E; ++I) 1164 (*I)->eraseFromParent(); 1165 1166 if (AtStart) 1167 BI = BB->begin(); 1168 else 1169 ++BI; 1170 1171 toErase.clear(); 1172 } 1173 1174 return changed_function; 1175} 1176 1177/// performPRE - Perform a purely local form of PRE that looks for diamond 1178/// control flow patterns and attempts to perform simple PRE at the join point. 1179bool GVN::performPRE(Function& F) { 1180 bool changed = false; 1181 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1182 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1183 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1184 BasicBlock* CurrentBlock = *DI; 1185 1186 // Nothing to PRE in the entry block. 1187 if (CurrentBlock == &F.getEntryBlock()) continue; 1188 1189 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1190 BE = CurrentBlock->end(); BI != BE; ) { 1191 if (isa<AllocationInst>(BI) || isa<TerminatorInst>(BI) || 1192 isa<PHINode>(BI) || BI->mayReadFromMemory() || 1193 BI->mayWriteToMemory()) { 1194 BI++; 1195 continue; 1196 } 1197 1198 uint32_t valno = VN.lookup(BI); 1199 1200 // Look for the predecessors for PRE opportunities. We're 1201 // only trying to solve the basic diamond case, where 1202 // a value is computed in the successor and one predecessor, 1203 // but not the other. We also explicitly disallow cases 1204 // where the successor is its own predecessor, because they're 1205 // more complicated to get right. 1206 unsigned numWith = 0; 1207 unsigned numWithout = 0; 1208 BasicBlock* PREPred = 0; 1209 DenseMap<BasicBlock*, Value*> predMap; 1210 for (pred_iterator PI = pred_begin(CurrentBlock), 1211 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1212 // We're not interested in PRE where the block is its 1213 // own predecessor, on in blocks with predecessors 1214 // that are not reachable. 1215 if (*PI == CurrentBlock) { 1216 numWithout = 2; 1217 break; 1218 } else if (!localAvail.count(*PI)) { 1219 numWithout = 2; 1220 break; 1221 } 1222 1223 DenseMap<uint32_t, Value*>::iterator predV = 1224 localAvail[*PI]->table.find(valno); 1225 if (predV == localAvail[*PI]->table.end()) { 1226 PREPred = *PI; 1227 numWithout++; 1228 } else if (predV->second == BI) { 1229 numWithout = 2; 1230 } else { 1231 predMap[*PI] = predV->second; 1232 numWith++; 1233 } 1234 } 1235 1236 // Don't do PRE when it might increase code size, i.e. when 1237 // we would need to insert instructions in more than one pred. 1238 if (numWithout != 1 || numWith == 0) { 1239 BI++; 1240 continue; 1241 } 1242 1243 // We can't do PRE safely on a critical edge, so instead we schedule 1244 // the edge to be split and perform the PRE the next time we iterate 1245 // on the function. 1246 unsigned succNum = 0; 1247 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1248 i != e; ++i) 1249 if (PREPred->getTerminator()->getSuccessor(i) == PREPred) { 1250 succNum = i; 1251 break; 1252 } 1253 1254 if (isCriticalEdge(PREPred->getTerminator(), succNum)) { 1255 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum)); 1256 changed = true; 1257 BI++; 1258 continue; 1259 } 1260 1261 // Instantiate the expression the in predecessor that lacked it. 1262 // Because we are going top-down through the block, all value numbers 1263 // will be available in the predecessor by the time we need them. Any 1264 // that weren't original present will have been instantiated earlier 1265 // in this loop. 1266 Instruction* PREInstr = BI->clone(); 1267 bool success = true; 1268 for (unsigned i = 0; i < BI->getNumOperands(); ++i) { 1269 Value* op = BI->getOperand(i); 1270 if (isa<Argument>(op) || isa<Constant>(op) || isa<GlobalValue>(op)) 1271 PREInstr->setOperand(i, op); 1272 else { 1273 Value* V = lookupNumber(PREPred, VN.lookup(op)); 1274 if (!V) { 1275 success = false; 1276 break; 1277 } else 1278 PREInstr->setOperand(i, V); 1279 } 1280 } 1281 1282 // Fail out if we encounter an operand that is not available in 1283 // the PRE predecessor. This is typically because of loads which 1284 // are not value numbered precisely. 1285 if (!success) { 1286 delete PREInstr; 1287 BI++; 1288 continue; 1289 } 1290 1291 PREInstr->insertBefore(PREPred->getTerminator()); 1292 PREInstr->setName(BI->getName() + ".pre"); 1293 predMap[PREPred] = PREInstr; 1294 VN.add(PREInstr, valno); 1295 NumGVNPRE++; 1296 1297 // Update the availability map to include the new instruction. 1298 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr)); 1299 1300 // Create a PHI to make the value available in this block. 1301 PHINode* Phi = PHINode::Create(BI->getType(), 1302 BI->getName() + ".pre-phi", 1303 CurrentBlock->begin()); 1304 for (pred_iterator PI = pred_begin(CurrentBlock), 1305 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1306 Phi->addIncoming(predMap[*PI], *PI); 1307 1308 VN.add(Phi, valno); 1309 localAvail[CurrentBlock]->table[valno] = Phi; 1310 1311 BI->replaceAllUsesWith(Phi); 1312 VN.erase(BI); 1313 1314 Instruction* erase = BI; 1315 BI++; 1316 erase->eraseFromParent(); 1317 1318 changed = true; 1319 } 1320 } 1321 1322 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 1323 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 1324 SplitCriticalEdge(I->first, I->second, this); 1325 1326 return changed; 1327} 1328 1329// mergeBlockIntoPredecessor - If this block is the only successor 1330// of its predecessor, and the edge is non-critical, 1331// fold it into that predecessor. 1332bool GVN::mergeBlockIntoPredecessor(BasicBlock* BB) { 1333 // Can't merge the entry block. 1334 if (pred_begin(BB) == pred_end(BB)) return false; 1335 // Can't merge if there are multiple preds. 1336 if (++pred_begin(BB) != pred_end(BB)) return false; 1337 1338 BasicBlock* PredBB = *pred_begin(BB); 1339 1340 // Can't merge if the edge is critical. 1341 if (PredBB->getTerminator()->getNumSuccessors() != 1) return false; 1342 1343 // Begin by getting rid of unneeded PHIs. 1344 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 1345 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 1346 BB->getInstList().pop_front(); // Delete the phi node... 1347 } 1348 1349 // Delete the unconditional branch from the predecessor... 1350 PredBB->getInstList().pop_back(); 1351 1352 // Move all definitions in the successor to the predecessor... 1353 PredBB->getInstList().splice(PredBB->end(), BB->getInstList()); 1354 1355 // Make all PHI nodes that referred to BB now refer to Pred as their 1356 // source... 1357 BB->replaceAllUsesWith(PredBB); 1358 1359 // Finally, erase the old block and update dominator info. 1360 DominatorTree& DT = getAnalysis<DominatorTree>(); 1361 DomTreeNode* DTN = DT[BB]; 1362 DomTreeNode* PredDTN = DT[PredBB]; 1363 1364 if (DTN) { 1365 SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end()); 1366 for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(), 1367 DE = Children.end(); DI != DE; ++DI) 1368 DT.changeImmediateDominator(*DI, PredDTN); 1369 1370 DT.eraseNode(BB); 1371 } 1372 1373 BB->eraseFromParent(); 1374 1375 NumGVNBlocks++; 1376 return true; 1377} 1378 1379// iterateOnFunction - Executes one iteration of GVN 1380bool GVN::iterateOnFunction(Function &F) { 1381 // Clean out global sets from any previous functions 1382 VN.clear(); 1383 phiMap.clear(); 1384 1385 // Merge unconditional branches, allowing PRE to catch more 1386 // optimization opportunities. 1387 bool mergedBlocks = false; 1388 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1389 BasicBlock* BB = FI; 1390 ++FI; 1391 mergedBlocks |= mergeBlockIntoPredecessor(BB); 1392 } 1393 1394 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1395 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 1396 delete I->second; 1397 localAvail.clear(); 1398 1399 DominatorTree &DT = getAnalysis<DominatorTree>(); 1400 1401 // Top-down walk of the dominator tree 1402 bool changed = false; 1403 for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()), 1404 DE = df_end(DT.getRootNode()); DI != DE; ++DI) 1405 changed |= processBlock(*DI); 1406 1407 if (EnablePRE) 1408 changed |= performPRE(F); 1409 1410 return changed || mergedBlocks; 1411} 1412