GVN.cpp revision 3cd8eb314a5f41b93a0f1d627fe905caf5651b3c
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/Compiler.h" 36#include "llvm/Support/Debug.h" 37using namespace llvm; 38 39STATISTIC(NumGVNInstr, "Number of instructions deleted"); 40STATISTIC(NumGVNLoad, "Number of loads deleted"); 41STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 42 43//===----------------------------------------------------------------------===// 44// ValueTable Class 45//===----------------------------------------------------------------------===// 46 47/// This class holds the mapping between values and value numbers. It is used 48/// as an efficient mechanism to determine the expression-wise equivalence of 49/// two values. 50namespace { 51 struct VISIBILITY_HIDDEN Expression { 52 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, 53 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 54 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 55 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 56 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 57 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 58 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 59 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 60 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 61 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 62 EMPTY, TOMBSTONE }; 63 64 ExpressionOpcode opcode; 65 const Type* type; 66 uint32_t firstVN; 67 uint32_t secondVN; 68 uint32_t thirdVN; 69 SmallVector<uint32_t, 4> varargs; 70 Value* function; 71 72 Expression() { } 73 Expression(ExpressionOpcode o) : opcode(o) { } 74 75 bool operator==(const Expression &other) const { 76 if (opcode != other.opcode) 77 return false; 78 else if (opcode == EMPTY || opcode == TOMBSTONE) 79 return true; 80 else if (type != other.type) 81 return false; 82 else if (function != other.function) 83 return false; 84 else if (firstVN != other.firstVN) 85 return false; 86 else if (secondVN != other.secondVN) 87 return false; 88 else if (thirdVN != other.thirdVN) 89 return false; 90 else { 91 if (varargs.size() != other.varargs.size()) 92 return false; 93 94 for (size_t i = 0; i < varargs.size(); ++i) 95 if (varargs[i] != other.varargs[i]) 96 return false; 97 98 return true; 99 } 100 } 101 102 bool operator!=(const Expression &other) const { 103 if (opcode != other.opcode) 104 return true; 105 else if (opcode == EMPTY || opcode == TOMBSTONE) 106 return false; 107 else if (type != other.type) 108 return true; 109 else if (function != other.function) 110 return true; 111 else if (firstVN != other.firstVN) 112 return true; 113 else if (secondVN != other.secondVN) 114 return true; 115 else if (thirdVN != other.thirdVN) 116 return true; 117 else { 118 if (varargs.size() != other.varargs.size()) 119 return true; 120 121 for (size_t i = 0; i < varargs.size(); ++i) 122 if (varargs[i] != other.varargs[i]) 123 return true; 124 125 return false; 126 } 127 } 128 }; 129 130 class VISIBILITY_HIDDEN ValueTable { 131 private: 132 DenseMap<Value*, uint32_t> valueNumbering; 133 DenseMap<Expression, uint32_t> expressionNumbering; 134 AliasAnalysis* AA; 135 MemoryDependenceAnalysis* MD; 136 DominatorTree* DT; 137 138 uint32_t nextValueNumber; 139 140 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 141 Expression::ExpressionOpcode getOpcode(CmpInst* C); 142 Expression::ExpressionOpcode getOpcode(CastInst* C); 143 Expression create_expression(BinaryOperator* BO); 144 Expression create_expression(CmpInst* C); 145 Expression create_expression(ShuffleVectorInst* V); 146 Expression create_expression(ExtractElementInst* C); 147 Expression create_expression(InsertElementInst* V); 148 Expression create_expression(SelectInst* V); 149 Expression create_expression(CastInst* C); 150 Expression create_expression(GetElementPtrInst* G); 151 Expression create_expression(CallInst* C); 152 Expression create_expression(Constant* C); 153 public: 154 ValueTable() : nextValueNumber(1) { } 155 uint32_t lookup_or_add(Value* V); 156 uint32_t lookup(Value* V) const; 157 void add(Value* V, uint32_t num); 158 void clear(); 159 void erase(Value* v); 160 unsigned size(); 161 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 162 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 163 void setDomTree(DominatorTree* D) { DT = D; } 164 }; 165} 166 167namespace llvm { 168template <> struct DenseMapInfo<Expression> { 169 static inline Expression getEmptyKey() { 170 return Expression(Expression::EMPTY); 171 } 172 173 static inline Expression getTombstoneKey() { 174 return Expression(Expression::TOMBSTONE); 175 } 176 177 static unsigned getHashValue(const Expression e) { 178 unsigned hash = e.opcode; 179 180 hash = e.firstVN + hash * 37; 181 hash = e.secondVN + hash * 37; 182 hash = e.thirdVN + hash * 37; 183 184 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 185 (unsigned)((uintptr_t)e.type >> 9)) + 186 hash * 37; 187 188 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 189 E = e.varargs.end(); I != E; ++I) 190 hash = *I + hash * 37; 191 192 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 193 (unsigned)((uintptr_t)e.function >> 9)) + 194 hash * 37; 195 196 return hash; 197 } 198 static bool isEqual(const Expression &LHS, const Expression &RHS) { 199 return LHS == RHS; 200 } 201 static bool isPod() { return true; } 202}; 203} 204 205//===----------------------------------------------------------------------===// 206// ValueTable Internal Functions 207//===----------------------------------------------------------------------===// 208Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 209 switch(BO->getOpcode()) { 210 default: // THIS SHOULD NEVER HAPPEN 211 assert(0 && "Binary operator with unknown opcode?"); 212 case Instruction::Add: return Expression::ADD; 213 case Instruction::Sub: return Expression::SUB; 214 case Instruction::Mul: return Expression::MUL; 215 case Instruction::UDiv: return Expression::UDIV; 216 case Instruction::SDiv: return Expression::SDIV; 217 case Instruction::FDiv: return Expression::FDIV; 218 case Instruction::URem: return Expression::UREM; 219 case Instruction::SRem: return Expression::SREM; 220 case Instruction::FRem: return Expression::FREM; 221 case Instruction::Shl: return Expression::SHL; 222 case Instruction::LShr: return Expression::LSHR; 223 case Instruction::AShr: return Expression::ASHR; 224 case Instruction::And: return Expression::AND; 225 case Instruction::Or: return Expression::OR; 226 case Instruction::Xor: return Expression::XOR; 227 } 228} 229 230Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 231 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) { 232 switch (C->getPredicate()) { 233 default: // THIS SHOULD NEVER HAPPEN 234 assert(0 && "Comparison with unknown predicate?"); 235 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 236 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 237 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 238 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 239 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 240 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 241 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 242 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 243 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 244 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 245 } 246 } 247 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare"); 248 switch (C->getPredicate()) { 249 default: // THIS SHOULD NEVER HAPPEN 250 assert(0 && "Comparison with unknown predicate?"); 251 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 252 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 253 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 254 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 255 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 256 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 257 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 258 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 259 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 260 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 261 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 262 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 263 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 264 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 265 } 266} 267 268Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 269 switch(C->getOpcode()) { 270 default: // THIS SHOULD NEVER HAPPEN 271 assert(0 && "Cast operator with unknown opcode?"); 272 case Instruction::Trunc: return Expression::TRUNC; 273 case Instruction::ZExt: return Expression::ZEXT; 274 case Instruction::SExt: return Expression::SEXT; 275 case Instruction::FPToUI: return Expression::FPTOUI; 276 case Instruction::FPToSI: return Expression::FPTOSI; 277 case Instruction::UIToFP: return Expression::UITOFP; 278 case Instruction::SIToFP: return Expression::SITOFP; 279 case Instruction::FPTrunc: return Expression::FPTRUNC; 280 case Instruction::FPExt: return Expression::FPEXT; 281 case Instruction::PtrToInt: return Expression::PTRTOINT; 282 case Instruction::IntToPtr: return Expression::INTTOPTR; 283 case Instruction::BitCast: return Expression::BITCAST; 284 } 285} 286 287Expression ValueTable::create_expression(CallInst* C) { 288 Expression e; 289 290 e.type = C->getType(); 291 e.firstVN = 0; 292 e.secondVN = 0; 293 e.thirdVN = 0; 294 e.function = C->getCalledFunction(); 295 e.opcode = Expression::CALL; 296 297 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 298 I != E; ++I) 299 e.varargs.push_back(lookup_or_add(*I)); 300 301 return e; 302} 303 304Expression ValueTable::create_expression(BinaryOperator* BO) { 305 Expression e; 306 307 e.firstVN = lookup_or_add(BO->getOperand(0)); 308 e.secondVN = lookup_or_add(BO->getOperand(1)); 309 e.thirdVN = 0; 310 e.function = 0; 311 e.type = BO->getType(); 312 e.opcode = getOpcode(BO); 313 314 return e; 315} 316 317Expression ValueTable::create_expression(CmpInst* C) { 318 Expression e; 319 320 e.firstVN = lookup_or_add(C->getOperand(0)); 321 e.secondVN = lookup_or_add(C->getOperand(1)); 322 e.thirdVN = 0; 323 e.function = 0; 324 e.type = C->getType(); 325 e.opcode = getOpcode(C); 326 327 return e; 328} 329 330Expression ValueTable::create_expression(CastInst* C) { 331 Expression e; 332 333 e.firstVN = lookup_or_add(C->getOperand(0)); 334 e.secondVN = 0; 335 e.thirdVN = 0; 336 e.function = 0; 337 e.type = C->getType(); 338 e.opcode = getOpcode(C); 339 340 return e; 341} 342 343Expression ValueTable::create_expression(ShuffleVectorInst* S) { 344 Expression e; 345 346 e.firstVN = lookup_or_add(S->getOperand(0)); 347 e.secondVN = lookup_or_add(S->getOperand(1)); 348 e.thirdVN = lookup_or_add(S->getOperand(2)); 349 e.function = 0; 350 e.type = S->getType(); 351 e.opcode = Expression::SHUFFLE; 352 353 return e; 354} 355 356Expression ValueTable::create_expression(ExtractElementInst* E) { 357 Expression e; 358 359 e.firstVN = lookup_or_add(E->getOperand(0)); 360 e.secondVN = lookup_or_add(E->getOperand(1)); 361 e.thirdVN = 0; 362 e.function = 0; 363 e.type = E->getType(); 364 e.opcode = Expression::EXTRACT; 365 366 return e; 367} 368 369Expression ValueTable::create_expression(InsertElementInst* I) { 370 Expression e; 371 372 e.firstVN = lookup_or_add(I->getOperand(0)); 373 e.secondVN = lookup_or_add(I->getOperand(1)); 374 e.thirdVN = lookup_or_add(I->getOperand(2)); 375 e.function = 0; 376 e.type = I->getType(); 377 e.opcode = Expression::INSERT; 378 379 return e; 380} 381 382Expression ValueTable::create_expression(SelectInst* I) { 383 Expression e; 384 385 e.firstVN = lookup_or_add(I->getCondition()); 386 e.secondVN = lookup_or_add(I->getTrueValue()); 387 e.thirdVN = lookup_or_add(I->getFalseValue()); 388 e.function = 0; 389 e.type = I->getType(); 390 e.opcode = Expression::SELECT; 391 392 return e; 393} 394 395Expression ValueTable::create_expression(GetElementPtrInst* G) { 396 Expression e; 397 398 e.firstVN = lookup_or_add(G->getPointerOperand()); 399 e.secondVN = 0; 400 e.thirdVN = 0; 401 e.function = 0; 402 e.type = G->getType(); 403 e.opcode = Expression::GEP; 404 405 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 406 I != E; ++I) 407 e.varargs.push_back(lookup_or_add(*I)); 408 409 return e; 410} 411 412//===----------------------------------------------------------------------===// 413// ValueTable External Functions 414//===----------------------------------------------------------------------===// 415 416/// add - Insert a value into the table with a specified value number. 417void ValueTable::add(Value* V, uint32_t num) { 418 valueNumbering.insert(std::make_pair(V, num)); 419} 420 421/// lookup_or_add - Returns the value number for the specified value, assigning 422/// it a new number if it did not have one before. 423uint32_t ValueTable::lookup_or_add(Value* V) { 424 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 425 if (VI != valueNumbering.end()) 426 return VI->second; 427 428 if (CallInst* C = dyn_cast<CallInst>(V)) { 429 if (AA->doesNotAccessMemory(C)) { 430 Expression e = create_expression(C); 431 432 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 433 if (EI != expressionNumbering.end()) { 434 valueNumbering.insert(std::make_pair(V, EI->second)); 435 return EI->second; 436 } else { 437 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 438 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 439 440 return nextValueNumber++; 441 } 442 } else if (AA->onlyReadsMemory(C)) { 443 Expression e = create_expression(C); 444 445 if (expressionNumbering.find(e) == expressionNumbering.end()) { 446 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 447 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 448 return nextValueNumber++; 449 } 450 451 Instruction* local_dep = MD->getDependency(C); 452 453 if (local_dep == MemoryDependenceAnalysis::None) { 454 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 455 return nextValueNumber++; 456 } else if (local_dep != MemoryDependenceAnalysis::NonLocal) { 457 if (!isa<CallInst>(local_dep)) { 458 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 459 return nextValueNumber++; 460 } 461 462 CallInst* local_cdep = cast<CallInst>(local_dep); 463 464 if (local_cdep->getCalledFunction() != C->getCalledFunction() || 465 local_cdep->getNumOperands() != C->getNumOperands()) { 466 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 467 return nextValueNumber++; 468 } else if (!C->getCalledFunction()) { 469 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 470 return nextValueNumber++; 471 } else { 472 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 473 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 474 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 475 if (c_vn != cd_vn) { 476 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 477 return nextValueNumber++; 478 } 479 } 480 481 uint32_t v = lookup_or_add(local_cdep); 482 valueNumbering.insert(std::make_pair(V, v)); 483 return v; 484 } 485 } 486 487 488 DenseMap<BasicBlock*, Value*> deps; 489 MD->getNonLocalDependency(C, deps); 490 CallInst* cdep = 0; 491 492 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), 493 E = deps.end(); I != E; ++I) { 494 if (I->second == MemoryDependenceAnalysis::None) { 495 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 496 497 return nextValueNumber++; 498 } else if (I->second != MemoryDependenceAnalysis::NonLocal) { 499 if (DT->properlyDominates(I->first, C->getParent())) { 500 if (CallInst* CD = dyn_cast<CallInst>(I->second)) 501 cdep = CD; 502 else { 503 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 504 return nextValueNumber++; 505 } 506 } else { 507 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 508 return nextValueNumber++; 509 } 510 } 511 } 512 513 if (!cdep) { 514 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 515 return nextValueNumber++; 516 } 517 518 if (cdep->getCalledFunction() != C->getCalledFunction() || 519 cdep->getNumOperands() != C->getNumOperands()) { 520 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 521 return nextValueNumber++; 522 } else if (!C->getCalledFunction()) { 523 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 524 return nextValueNumber++; 525 } else { 526 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 527 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 528 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 529 if (c_vn != cd_vn) { 530 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 531 return nextValueNumber++; 532 } 533 } 534 535 uint32_t v = lookup_or_add(cdep); 536 valueNumbering.insert(std::make_pair(V, v)); 537 return v; 538 } 539 540 } else { 541 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 542 return nextValueNumber++; 543 } 544 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 545 Expression e = create_expression(BO); 546 547 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 548 if (EI != expressionNumbering.end()) { 549 valueNumbering.insert(std::make_pair(V, EI->second)); 550 return EI->second; 551 } else { 552 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 553 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 554 555 return nextValueNumber++; 556 } 557 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 558 Expression e = create_expression(C); 559 560 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 561 if (EI != expressionNumbering.end()) { 562 valueNumbering.insert(std::make_pair(V, EI->second)); 563 return EI->second; 564 } else { 565 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 566 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 567 568 return nextValueNumber++; 569 } 570 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 571 Expression e = create_expression(U); 572 573 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 574 if (EI != expressionNumbering.end()) { 575 valueNumbering.insert(std::make_pair(V, EI->second)); 576 return EI->second; 577 } else { 578 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 579 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 580 581 return nextValueNumber++; 582 } 583 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 584 Expression e = create_expression(U); 585 586 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 587 if (EI != expressionNumbering.end()) { 588 valueNumbering.insert(std::make_pair(V, EI->second)); 589 return EI->second; 590 } else { 591 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 592 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 593 594 return nextValueNumber++; 595 } 596 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 597 Expression e = create_expression(U); 598 599 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 600 if (EI != expressionNumbering.end()) { 601 valueNumbering.insert(std::make_pair(V, EI->second)); 602 return EI->second; 603 } else { 604 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 605 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 606 607 return nextValueNumber++; 608 } 609 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 610 Expression e = create_expression(U); 611 612 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 613 if (EI != expressionNumbering.end()) { 614 valueNumbering.insert(std::make_pair(V, EI->second)); 615 return EI->second; 616 } else { 617 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 618 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 619 620 return nextValueNumber++; 621 } 622 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 623 Expression e = create_expression(U); 624 625 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 626 if (EI != expressionNumbering.end()) { 627 valueNumbering.insert(std::make_pair(V, EI->second)); 628 return EI->second; 629 } else { 630 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 631 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 632 633 return nextValueNumber++; 634 } 635 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 636 Expression e = create_expression(U); 637 638 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 639 if (EI != expressionNumbering.end()) { 640 valueNumbering.insert(std::make_pair(V, EI->second)); 641 return EI->second; 642 } else { 643 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 644 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 645 646 return nextValueNumber++; 647 } 648 } else { 649 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 650 return nextValueNumber++; 651 } 652} 653 654/// lookup - Returns the value number of the specified value. Fails if 655/// the value has not yet been numbered. 656uint32_t ValueTable::lookup(Value* V) const { 657 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 658 assert(VI != valueNumbering.end() && "Value not numbered?"); 659 return VI->second; 660} 661 662/// clear - Remove all entries from the ValueTable 663void ValueTable::clear() { 664 valueNumbering.clear(); 665 expressionNumbering.clear(); 666 nextValueNumber = 1; 667} 668 669/// erase - Remove a value from the value numbering 670void ValueTable::erase(Value* V) { 671 valueNumbering.erase(V); 672} 673 674//===----------------------------------------------------------------------===// 675// GVN Pass 676//===----------------------------------------------------------------------===// 677 678namespace llvm { 679 template<> struct DenseMapInfo<uint32_t> { 680 static inline uint32_t getEmptyKey() { return ~0; } 681 static inline uint32_t getTombstoneKey() { return ~0 - 1; } 682 static unsigned getHashValue(const uint32_t& Val) { return Val * 37; } 683 static bool isPod() { return true; } 684 static bool isEqual(const uint32_t& LHS, const uint32_t& RHS) { 685 return LHS == RHS; 686 } 687 }; 688} 689 690namespace { 691 692 class VISIBILITY_HIDDEN GVN : public FunctionPass { 693 bool runOnFunction(Function &F); 694 public: 695 static char ID; // Pass identification, replacement for typeid 696 GVN() : FunctionPass((intptr_t)&ID) { } 697 698 private: 699 ValueTable VN; 700 DenseMap<BasicBlock*, DenseMap<uint32_t, Value*> > localAvail; 701 702 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 703 PhiMapType phiMap; 704 705 706 // This transformation requires dominator postdominator info 707 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 708 AU.setPreservesCFG(); 709 AU.addRequired<DominatorTree>(); 710 AU.addRequired<MemoryDependenceAnalysis>(); 711 AU.addRequired<AliasAnalysis>(); 712 AU.addPreserved<AliasAnalysis>(); 713 AU.addPreserved<MemoryDependenceAnalysis>(); 714 } 715 716 // Helper fuctions 717 // FIXME: eliminate or document these better 718 bool processLoad(LoadInst* L, 719 DenseMap<Value*, LoadInst*> &lastLoad, 720 SmallVectorImpl<Instruction*> &toErase); 721 bool processInstruction(Instruction* I, 722 DenseMap<Value*, LoadInst*>& lastSeenLoad, 723 SmallVectorImpl<Instruction*> &toErase); 724 bool processNonLocalLoad(LoadInst* L, 725 SmallVectorImpl<Instruction*> &toErase); 726 bool processBlock(DomTreeNode* DTN); 727 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig, 728 DenseMap<BasicBlock*, Value*> &Phis, 729 bool top_level = false); 730 void dump(DenseMap<uint32_t, Value*>& d); 731 bool iterateOnFunction(Function &F); 732 Value* CollapsePhi(PHINode* p); 733 bool isSafeReplacement(PHINode* p, Instruction* inst); 734 bool performPRE(Function& F); 735 }; 736 737 char GVN::ID = 0; 738} 739 740// createGVNPass - The public interface to this file... 741FunctionPass *llvm::createGVNPass() { return new GVN(); } 742 743static RegisterPass<GVN> X("gvn", 744 "Global Value Numbering"); 745 746void GVN::dump(DenseMap<uint32_t, Value*>& d) { 747 printf("{\n"); 748 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 749 E = d.end(); I != E; ++I) { 750 printf("%d\n", I->first); 751 I->second->dump(); 752 } 753 printf("}\n"); 754} 755 756Value* GVN::CollapsePhi(PHINode* p) { 757 DominatorTree &DT = getAnalysis<DominatorTree>(); 758 Value* constVal = p->hasConstantValue(); 759 760 if (!constVal) return 0; 761 762 Instruction* inst = dyn_cast<Instruction>(constVal); 763 if (!inst) 764 return constVal; 765 766 if (DT.dominates(inst, p)) 767 if (isSafeReplacement(p, inst)) 768 return inst; 769 return 0; 770} 771 772bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 773 if (!isa<PHINode>(inst)) 774 return true; 775 776 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 777 UI != E; ++UI) 778 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 779 if (use_phi->getParent() == inst->getParent()) 780 return false; 781 782 return true; 783} 784 785/// GetValueForBlock - Get the value to use within the specified basic block. 786/// available values are in Phis. 787Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig, 788 DenseMap<BasicBlock*, Value*> &Phis, 789 bool top_level) { 790 791 // If we have already computed this value, return the previously computed val. 792 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 793 if (V != Phis.end() && !top_level) return V->second; 794 795 BasicBlock* singlePred = BB->getSinglePredecessor(); 796 if (singlePred) { 797 Value *ret = GetValueForBlock(singlePred, orig, Phis); 798 Phis[BB] = ret; 799 return ret; 800 } 801 802 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 803 // now, then get values to fill in the incoming values for the PHI. 804 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", 805 BB->begin()); 806 PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB))); 807 808 if (Phis.count(BB) == 0) 809 Phis.insert(std::make_pair(BB, PN)); 810 811 // Fill in the incoming values for the block. 812 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 813 Value* val = GetValueForBlock(*PI, orig, Phis); 814 PN->addIncoming(val, *PI); 815 } 816 817 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 818 AA.copyValue(orig, PN); 819 820 // Attempt to collapse PHI nodes that are trivially redundant 821 Value* v = CollapsePhi(PN); 822 if (!v) { 823 // Cache our phi construction results 824 phiMap[orig->getPointerOperand()].insert(PN); 825 return PN; 826 } 827 828 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 829 830 MD.removeInstruction(PN); 831 PN->replaceAllUsesWith(v); 832 833 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 834 E = Phis.end(); I != E; ++I) 835 if (I->second == PN) 836 I->second = v; 837 838 PN->eraseFromParent(); 839 840 Phis[BB] = v; 841 return v; 842} 843 844/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 845/// non-local by performing PHI construction. 846bool GVN::processNonLocalLoad(LoadInst* L, 847 SmallVectorImpl<Instruction*> &toErase) { 848 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 849 850 // Find the non-local dependencies of the load 851 DenseMap<BasicBlock*, Value*> deps; 852 MD.getNonLocalDependency(L, deps); 853 854 DenseMap<BasicBlock*, Value*> repl; 855 856 // Filter out useless results (non-locals, etc) 857 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end(); 858 I != E; ++I) { 859 if (I->second == MemoryDependenceAnalysis::None) 860 return false; 861 862 if (I->second == MemoryDependenceAnalysis::NonLocal) 863 continue; 864 865 if (StoreInst* S = dyn_cast<StoreInst>(I->second)) { 866 if (S->getPointerOperand() != L->getPointerOperand()) 867 return false; 868 repl[I->first] = S->getOperand(0); 869 } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) { 870 if (LD->getPointerOperand() != L->getPointerOperand()) 871 return false; 872 repl[I->first] = LD; 873 } else { 874 return false; 875 } 876 } 877 878 // Use cached PHI construction information from previous runs 879 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()]; 880 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 881 I != E; ++I) { 882 if ((*I)->getParent() == L->getParent()) { 883 MD.removeInstruction(L); 884 L->replaceAllUsesWith(*I); 885 toErase.push_back(L); 886 NumGVNLoad++; 887 return true; 888 } 889 890 repl.insert(std::make_pair((*I)->getParent(), *I)); 891 } 892 893 // Perform PHI construction 894 SmallPtrSet<BasicBlock*, 4> visited; 895 Value* v = GetValueForBlock(L->getParent(), L, repl, true); 896 897 MD.removeInstruction(L); 898 L->replaceAllUsesWith(v); 899 toErase.push_back(L); 900 NumGVNLoad++; 901 902 return true; 903} 904 905/// processLoad - Attempt to eliminate a load, first by eliminating it 906/// locally, and then attempting non-local elimination if that fails. 907bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad, 908 SmallVectorImpl<Instruction*> &toErase) { 909 if (L->isVolatile()) { 910 lastLoad[L->getPointerOperand()] = L; 911 return false; 912 } 913 914 Value* pointer = L->getPointerOperand(); 915 LoadInst*& last = lastLoad[pointer]; 916 917 // ... to a pointer that has been loaded from before... 918 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 919 bool removedNonLocal = false; 920 Instruction* dep = MD.getDependency(L); 921 if (dep == MemoryDependenceAnalysis::NonLocal && 922 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) { 923 removedNonLocal = processNonLocalLoad(L, toErase); 924 925 if (!removedNonLocal) 926 last = L; 927 928 return removedNonLocal; 929 } 930 931 932 bool deletedLoad = false; 933 934 // Walk up the dependency chain until we either find 935 // a dependency we can use, or we can't walk any further 936 while (dep != MemoryDependenceAnalysis::None && 937 dep != MemoryDependenceAnalysis::NonLocal && 938 (isa<LoadInst>(dep) || isa<StoreInst>(dep))) { 939 // ... that depends on a store ... 940 if (StoreInst* S = dyn_cast<StoreInst>(dep)) { 941 if (S->getPointerOperand() == pointer) { 942 // Remove it! 943 MD.removeInstruction(L); 944 945 L->replaceAllUsesWith(S->getOperand(0)); 946 toErase.push_back(L); 947 deletedLoad = true; 948 NumGVNLoad++; 949 } 950 951 // Whether we removed it or not, we can't 952 // go any further 953 break; 954 } else if (!last) { 955 // If we don't depend on a store, and we haven't 956 // been loaded before, bail. 957 break; 958 } else if (dep == last) { 959 // Remove it! 960 MD.removeInstruction(L); 961 962 L->replaceAllUsesWith(last); 963 toErase.push_back(L); 964 deletedLoad = true; 965 NumGVNLoad++; 966 967 break; 968 } else { 969 dep = MD.getDependency(L, dep); 970 } 971 } 972 973 if (dep != MemoryDependenceAnalysis::None && 974 dep != MemoryDependenceAnalysis::NonLocal && 975 isa<AllocationInst>(dep)) { 976 // Check that this load is actually from the 977 // allocation we found 978 Value* v = L->getOperand(0); 979 while (true) { 980 if (BitCastInst *BC = dyn_cast<BitCastInst>(v)) 981 v = BC->getOperand(0); 982 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v)) 983 v = GEP->getOperand(0); 984 else 985 break; 986 } 987 if (v == dep) { 988 // If this load depends directly on an allocation, there isn't 989 // anything stored there; therefore, we can optimize this load 990 // to undef. 991 MD.removeInstruction(L); 992 993 L->replaceAllUsesWith(UndefValue::get(L->getType())); 994 toErase.push_back(L); 995 deletedLoad = true; 996 NumGVNLoad++; 997 } 998 } 999 1000 if (!deletedLoad) 1001 last = L; 1002 1003 return deletedLoad; 1004} 1005 1006/// processInstruction - When calculating availability, handle an instruction 1007/// by inserting it into the appropriate sets 1008bool GVN::processInstruction(Instruction *I, 1009 DenseMap<Value*, LoadInst*> &lastSeenLoad, 1010 SmallVectorImpl<Instruction*> &toErase) { 1011 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1012 bool changed = processLoad(L, lastSeenLoad, toErase); 1013 1014 if (!changed) { 1015 unsigned num = VN.lookup_or_add(L); 1016 localAvail[I->getParent()].insert(std::make_pair(num, L)); 1017 } 1018 1019 return changed; 1020 } 1021 1022 unsigned num = VN.lookup_or_add(I); 1023 1024 // Allocations are always uniquely numbered, so we can save time and memory 1025 // by fast failing them. 1026 if (isa<AllocationInst>(I)) { 1027 localAvail[I->getParent()].insert(std::make_pair(num, I)); 1028 return false; 1029 } 1030 1031 // Collapse PHI nodes 1032 if (PHINode* p = dyn_cast<PHINode>(I)) { 1033 Value* constVal = CollapsePhi(p); 1034 1035 if (constVal) { 1036 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1037 PI != PE; ++PI) 1038 if (PI->second.count(p)) 1039 PI->second.erase(p); 1040 1041 p->replaceAllUsesWith(constVal); 1042 toErase.push_back(p); 1043 } else { 1044 localAvail[I->getParent()].insert(std::make_pair(num, I)); 1045 } 1046 // Perform value-number based elimination 1047 } else if (localAvail[I->getParent()].count(num)) { 1048 Value* repl = localAvail[I->getParent()][num]; 1049 1050 // Remove it! 1051 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1052 MD.removeInstruction(I); 1053 1054 VN.erase(I); 1055 I->replaceAllUsesWith(repl); 1056 toErase.push_back(I); 1057 return true; 1058 } else if (!I->isTerminator()) { 1059 localAvail[I->getParent()].insert(std::make_pair(num, I)); 1060 } 1061 1062 return false; 1063} 1064 1065// GVN::runOnFunction - This is the main transformation entry point for a 1066// function. 1067// 1068bool GVN::runOnFunction(Function& F) { 1069 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1070 VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>()); 1071 VN.setDomTree(&getAnalysis<DominatorTree>()); 1072 1073 bool changed = false; 1074 bool shouldContinue = true; 1075 1076 while (shouldContinue) { 1077 shouldContinue = iterateOnFunction(F); 1078 changed |= shouldContinue; 1079 } 1080 1081 return changed; 1082} 1083 1084 1085bool GVN::processBlock(DomTreeNode* DTN) { 1086 BasicBlock* BB = DTN->getBlock(); 1087 1088 SmallVector<Instruction*, 8> toErase; 1089 DenseMap<Value*, LoadInst*> lastSeenLoad; 1090 bool changed_function = false; 1091 1092 if (DTN->getIDom()) 1093 localAvail.insert(std::make_pair(BB, 1094 localAvail[DTN->getIDom()->getBlock()])); 1095 1096 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1097 BI != BE;) { 1098 changed_function |= processInstruction(BI, lastSeenLoad, toErase); 1099 if (toErase.empty()) { 1100 ++BI; 1101 continue; 1102 } 1103 1104 // If we need some instructions deleted, do it now. 1105 NumGVNInstr += toErase.size(); 1106 1107 // Avoid iterator invalidation. 1108 bool AtStart = BI == BB->begin(); 1109 if (!AtStart) 1110 --BI; 1111 1112 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1113 E = toErase.end(); I != E; ++I) 1114 (*I)->eraseFromParent(); 1115 1116 if (AtStart) 1117 BI = BB->begin(); 1118 else 1119 ++BI; 1120 1121 toErase.clear(); 1122 } 1123 1124 return changed_function; 1125} 1126 1127/// performPRE - Perform a purely local form of PRE that looks for diamond 1128/// control flow patterns and attempts to perform simple PRE at the join point. 1129bool GVN::performPRE(Function& F) { 1130 bool changed = false; 1131 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1132 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1133 BasicBlock* CurrentBlock = *DI; 1134 1135 // Nothing to PRE in the entry block. 1136 if (CurrentBlock == &F.getEntryBlock()) continue; 1137 1138 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1139 BE = CurrentBlock->end(); BI != BE; ) { 1140 if (isa<AllocaInst>(BI) || isa<TerminatorInst>(BI) || 1141 isa<LoadInst>(BI) || isa<StoreInst>(BI) || 1142 isa<CallInst>(BI) || isa<PHINode>(BI)) { 1143 BI++; 1144 continue; 1145 } 1146 1147 uint32_t valno = VN.lookup(BI); 1148 1149 // Look for the predecessors for PRE opportunities. We're 1150 // only trying to solve the basic diamond case, where 1151 // a value is computed in the successor and one predecessor, 1152 // but not the other. We also explicitly disallow cases 1153 // where the successor is its own predecessor, because they're 1154 // more complicated to get right. 1155 unsigned numWith = 0; 1156 unsigned numWithout = 0; 1157 BasicBlock* PREPred = 0; 1158 for (pred_iterator PI = pred_begin(CurrentBlock), 1159 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1160 // We're not interested in PRE where the block is its 1161 // own predecessor. 1162 if (*PI == CurrentBlock) 1163 numWithout = 2; 1164 1165 if (!localAvail[*PI].count(valno)) { 1166 PREPred = *PI; 1167 numWithout++; 1168 } else if (localAvail[*PI][valno] == BI) { 1169 numWithout = 2; 1170 } else { 1171 numWith++; 1172 } 1173 } 1174 1175 // Don't do PRE when it might increase code size, i.e. when 1176 // we would need to insert instructions in more than one pred. 1177 if (numWithout != 1 || numWith == 0) { 1178 BI++; 1179 continue; 1180 } 1181 1182 // Instantiate the expression the in predecessor that lacked it. 1183 // Because we are going top-down through the block, all value numbers 1184 // will be available in the predecessor by the time we need them. Any 1185 // that weren't original present will have been instantiated earlier 1186 // in this loop. 1187 Instruction* PREInstr = BI->clone(); 1188 bool success = true; 1189 for (unsigned i = 0; i < BI->getNumOperands(); ++i) { 1190 Value* op = BI->getOperand(i); 1191 if (isa<Argument>(op) || isa<Constant>(op) || isa<GlobalValue>(op)) 1192 PREInstr->setOperand(i, op); 1193 else if (!localAvail[PREPred].count(VN.lookup(op))) { 1194 success = false; 1195 break; 1196 } else 1197 PREInstr->setOperand(i, localAvail[PREPred][VN.lookup(op)]); 1198 } 1199 1200 // Fail out if we encounter an operand that is not available in 1201 // the PRE predecessor. This is typically because of loads which 1202 // are not value numbered precisely. 1203 if (!success) { 1204 delete PREInstr; 1205 BI++; 1206 continue; 1207 } 1208 1209 PREInstr->insertBefore(PREPred->getTerminator()); 1210 PREInstr->setName(BI->getName() + ".pre"); 1211 VN.add(PREInstr, valno); 1212 NumGVNPRE++; 1213 1214 // Update the availability map to include the new instruction. 1215 localAvail[PREPred].insert(std::make_pair(valno, PREInstr)); 1216 1217 // Create a PHI to make the value available in this block. 1218 PHINode* Phi = PHINode::Create(BI->getType(), 1219 BI->getName() + ".pre-phi", 1220 CurrentBlock->begin()); 1221 for (pred_iterator PI = pred_begin(CurrentBlock), 1222 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1223 Phi->addIncoming(localAvail[*PI][valno], *PI); 1224 1225 VN.add(Phi, valno); 1226 1227 // The newly created PHI completely replaces the old instruction, 1228 // so we need to update the maps to reflect this. 1229 for (DenseMap<BasicBlock*, DenseMap<uint32_t, Value*> >::iterator 1230 UI = localAvail.begin(), UE = localAvail.end(); UI != UE; ++UI) 1231 for (DenseMap<uint32_t, Value*>::iterator UUI = UI->second.begin(), 1232 UUE = UI->second.end(); UUI != UUE; ++UUI) 1233 if (UUI->second == BI) 1234 UUI->second = Phi; 1235 1236 BI->replaceAllUsesWith(Phi); 1237 1238 Instruction* erase = BI; 1239 BI++; 1240 erase->eraseFromParent(); 1241 1242 changed = true; 1243 } 1244 } 1245 1246 return changed; 1247} 1248 1249// GVN::iterateOnFunction - Executes one iteration of GVN 1250bool GVN::iterateOnFunction(Function &F) { 1251 // Clean out global sets from any previous functions 1252 VN.clear(); 1253 localAvail.clear(); 1254 phiMap.clear(); 1255 1256 DominatorTree &DT = getAnalysis<DominatorTree>(); 1257 1258 // Top-down walk of the dominator tree 1259 bool changed = false; 1260 for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()), 1261 DE = df_end(DT.getRootNode()); DI != DE; ++DI) 1262 changed |= processBlock(*DI); 1263 1264 changed |= performPRE(F); 1265 return changed; 1266} 1267