GVN.cpp revision 237a8287454389a5b940e18c1efb2201fc443208
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" 39#include <cstdio> 40using namespace llvm; 41 42STATISTIC(NumGVNInstr, "Number of instructions deleted"); 43STATISTIC(NumGVNLoad, "Number of loads deleted"); 44STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 45STATISTIC(NumGVNBlocks, "Number of blocks merged"); 46 47static cl::opt<bool> EnablePRE("enable-pre", 48 cl::init(true), cl::Hidden); 49 50//===----------------------------------------------------------------------===// 51// ValueTable Class 52//===----------------------------------------------------------------------===// 53 54/// This class holds the mapping between values and value numbers. It is used 55/// as an efficient mechanism to determine the expression-wise equivalence of 56/// two values. 57namespace { 58 struct VISIBILITY_HIDDEN Expression { 59 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, 60 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 61 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 62 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 63 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 64 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 65 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 66 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 67 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 68 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 69 EMPTY, TOMBSTONE }; 70 71 ExpressionOpcode opcode; 72 const Type* type; 73 uint32_t firstVN; 74 uint32_t secondVN; 75 uint32_t thirdVN; 76 SmallVector<uint32_t, 4> varargs; 77 Value* function; 78 79 Expression() { } 80 Expression(ExpressionOpcode o) : opcode(o) { } 81 82 bool operator==(const Expression &other) const { 83 if (opcode != other.opcode) 84 return false; 85 else if (opcode == EMPTY || opcode == TOMBSTONE) 86 return true; 87 else if (type != other.type) 88 return false; 89 else if (function != other.function) 90 return false; 91 else if (firstVN != other.firstVN) 92 return false; 93 else if (secondVN != other.secondVN) 94 return false; 95 else if (thirdVN != other.thirdVN) 96 return false; 97 else { 98 if (varargs.size() != other.varargs.size()) 99 return false; 100 101 for (size_t i = 0; i < varargs.size(); ++i) 102 if (varargs[i] != other.varargs[i]) 103 return false; 104 105 return true; 106 } 107 } 108 109 bool operator!=(const Expression &other) const { 110 if (opcode != other.opcode) 111 return true; 112 else if (opcode == EMPTY || opcode == TOMBSTONE) 113 return false; 114 else if (type != other.type) 115 return true; 116 else if (function != other.function) 117 return true; 118 else if (firstVN != other.firstVN) 119 return true; 120 else if (secondVN != other.secondVN) 121 return true; 122 else if (thirdVN != other.thirdVN) 123 return true; 124 else { 125 if (varargs.size() != other.varargs.size()) 126 return true; 127 128 for (size_t i = 0; i < varargs.size(); ++i) 129 if (varargs[i] != other.varargs[i]) 130 return true; 131 132 return false; 133 } 134 } 135 }; 136 137 class VISIBILITY_HIDDEN ValueTable { 138 private: 139 DenseMap<Value*, uint32_t> valueNumbering; 140 DenseMap<Expression, uint32_t> expressionNumbering; 141 AliasAnalysis* AA; 142 MemoryDependenceAnalysis* MD; 143 DominatorTree* DT; 144 145 uint32_t nextValueNumber; 146 147 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 148 Expression::ExpressionOpcode getOpcode(CmpInst* C); 149 Expression::ExpressionOpcode getOpcode(CastInst* C); 150 Expression create_expression(BinaryOperator* BO); 151 Expression create_expression(CmpInst* C); 152 Expression create_expression(ShuffleVectorInst* V); 153 Expression create_expression(ExtractElementInst* C); 154 Expression create_expression(InsertElementInst* V); 155 Expression create_expression(SelectInst* V); 156 Expression create_expression(CastInst* C); 157 Expression create_expression(GetElementPtrInst* G); 158 Expression create_expression(CallInst* C); 159 Expression create_expression(Constant* C); 160 public: 161 ValueTable() : nextValueNumber(1) { } 162 uint32_t lookup_or_add(Value* V); 163 uint32_t lookup(Value* V) const; 164 void add(Value* V, uint32_t num); 165 void clear(); 166 void erase(Value* v); 167 unsigned size(); 168 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 169 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 170 void setDomTree(DominatorTree* D) { DT = D; } 171 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 172 }; 173} 174 175namespace llvm { 176template <> struct DenseMapInfo<Expression> { 177 static inline Expression getEmptyKey() { 178 return Expression(Expression::EMPTY); 179 } 180 181 static inline Expression getTombstoneKey() { 182 return Expression(Expression::TOMBSTONE); 183 } 184 185 static unsigned getHashValue(const Expression e) { 186 unsigned hash = e.opcode; 187 188 hash = e.firstVN + hash * 37; 189 hash = e.secondVN + hash * 37; 190 hash = e.thirdVN + hash * 37; 191 192 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 193 (unsigned)((uintptr_t)e.type >> 9)) + 194 hash * 37; 195 196 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 197 E = e.varargs.end(); I != E; ++I) 198 hash = *I + hash * 37; 199 200 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 201 (unsigned)((uintptr_t)e.function >> 9)) + 202 hash * 37; 203 204 return hash; 205 } 206 static bool isEqual(const Expression &LHS, const Expression &RHS) { 207 return LHS == RHS; 208 } 209 static bool isPod() { return true; } 210}; 211} 212 213//===----------------------------------------------------------------------===// 214// ValueTable Internal Functions 215//===----------------------------------------------------------------------===// 216Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 217 switch(BO->getOpcode()) { 218 default: // THIS SHOULD NEVER HAPPEN 219 assert(0 && "Binary operator with unknown opcode?"); 220 case Instruction::Add: return Expression::ADD; 221 case Instruction::Sub: return Expression::SUB; 222 case Instruction::Mul: return Expression::MUL; 223 case Instruction::UDiv: return Expression::UDIV; 224 case Instruction::SDiv: return Expression::SDIV; 225 case Instruction::FDiv: return Expression::FDIV; 226 case Instruction::URem: return Expression::UREM; 227 case Instruction::SRem: return Expression::SREM; 228 case Instruction::FRem: return Expression::FREM; 229 case Instruction::Shl: return Expression::SHL; 230 case Instruction::LShr: return Expression::LSHR; 231 case Instruction::AShr: return Expression::ASHR; 232 case Instruction::And: return Expression::AND; 233 case Instruction::Or: return Expression::OR; 234 case Instruction::Xor: return Expression::XOR; 235 } 236} 237 238Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 239 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) { 240 switch (C->getPredicate()) { 241 default: // THIS SHOULD NEVER HAPPEN 242 assert(0 && "Comparison with unknown predicate?"); 243 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 244 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 245 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 246 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 247 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 248 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 249 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 250 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 251 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 252 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 253 } 254 } 255 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare"); 256 switch (C->getPredicate()) { 257 default: // THIS SHOULD NEVER HAPPEN 258 assert(0 && "Comparison with unknown predicate?"); 259 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 260 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 261 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 262 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 263 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 264 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 265 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 266 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 267 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 268 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 269 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 270 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 271 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 272 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 273 } 274} 275 276Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 277 switch(C->getOpcode()) { 278 default: // THIS SHOULD NEVER HAPPEN 279 assert(0 && "Cast operator with unknown opcode?"); 280 case Instruction::Trunc: return Expression::TRUNC; 281 case Instruction::ZExt: return Expression::ZEXT; 282 case Instruction::SExt: return Expression::SEXT; 283 case Instruction::FPToUI: return Expression::FPTOUI; 284 case Instruction::FPToSI: return Expression::FPTOSI; 285 case Instruction::UIToFP: return Expression::UITOFP; 286 case Instruction::SIToFP: return Expression::SITOFP; 287 case Instruction::FPTrunc: return Expression::FPTRUNC; 288 case Instruction::FPExt: return Expression::FPEXT; 289 case Instruction::PtrToInt: return Expression::PTRTOINT; 290 case Instruction::IntToPtr: return Expression::INTTOPTR; 291 case Instruction::BitCast: return Expression::BITCAST; 292 } 293} 294 295Expression ValueTable::create_expression(CallInst* C) { 296 Expression e; 297 298 e.type = C->getType(); 299 e.firstVN = 0; 300 e.secondVN = 0; 301 e.thirdVN = 0; 302 e.function = C->getCalledFunction(); 303 e.opcode = Expression::CALL; 304 305 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 306 I != E; ++I) 307 e.varargs.push_back(lookup_or_add(*I)); 308 309 return e; 310} 311 312Expression ValueTable::create_expression(BinaryOperator* BO) { 313 Expression e; 314 315 e.firstVN = lookup_or_add(BO->getOperand(0)); 316 e.secondVN = lookup_or_add(BO->getOperand(1)); 317 e.thirdVN = 0; 318 e.function = 0; 319 e.type = BO->getType(); 320 e.opcode = getOpcode(BO); 321 322 return e; 323} 324 325Expression ValueTable::create_expression(CmpInst* C) { 326 Expression e; 327 328 e.firstVN = lookup_or_add(C->getOperand(0)); 329 e.secondVN = lookup_or_add(C->getOperand(1)); 330 e.thirdVN = 0; 331 e.function = 0; 332 e.type = C->getType(); 333 e.opcode = getOpcode(C); 334 335 return e; 336} 337 338Expression ValueTable::create_expression(CastInst* C) { 339 Expression e; 340 341 e.firstVN = lookup_or_add(C->getOperand(0)); 342 e.secondVN = 0; 343 e.thirdVN = 0; 344 e.function = 0; 345 e.type = C->getType(); 346 e.opcode = getOpcode(C); 347 348 return e; 349} 350 351Expression ValueTable::create_expression(ShuffleVectorInst* S) { 352 Expression e; 353 354 e.firstVN = lookup_or_add(S->getOperand(0)); 355 e.secondVN = lookup_or_add(S->getOperand(1)); 356 e.thirdVN = lookup_or_add(S->getOperand(2)); 357 e.function = 0; 358 e.type = S->getType(); 359 e.opcode = Expression::SHUFFLE; 360 361 return e; 362} 363 364Expression ValueTable::create_expression(ExtractElementInst* E) { 365 Expression e; 366 367 e.firstVN = lookup_or_add(E->getOperand(0)); 368 e.secondVN = lookup_or_add(E->getOperand(1)); 369 e.thirdVN = 0; 370 e.function = 0; 371 e.type = E->getType(); 372 e.opcode = Expression::EXTRACT; 373 374 return e; 375} 376 377Expression ValueTable::create_expression(InsertElementInst* I) { 378 Expression e; 379 380 e.firstVN = lookup_or_add(I->getOperand(0)); 381 e.secondVN = lookup_or_add(I->getOperand(1)); 382 e.thirdVN = lookup_or_add(I->getOperand(2)); 383 e.function = 0; 384 e.type = I->getType(); 385 e.opcode = Expression::INSERT; 386 387 return e; 388} 389 390Expression ValueTable::create_expression(SelectInst* I) { 391 Expression e; 392 393 e.firstVN = lookup_or_add(I->getCondition()); 394 e.secondVN = lookup_or_add(I->getTrueValue()); 395 e.thirdVN = lookup_or_add(I->getFalseValue()); 396 e.function = 0; 397 e.type = I->getType(); 398 e.opcode = Expression::SELECT; 399 400 return e; 401} 402 403Expression ValueTable::create_expression(GetElementPtrInst* G) { 404 Expression e; 405 406 e.firstVN = lookup_or_add(G->getPointerOperand()); 407 e.secondVN = 0; 408 e.thirdVN = 0; 409 e.function = 0; 410 e.type = G->getType(); 411 e.opcode = Expression::GEP; 412 413 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 414 I != E; ++I) 415 e.varargs.push_back(lookup_or_add(*I)); 416 417 return e; 418} 419 420//===----------------------------------------------------------------------===// 421// ValueTable External Functions 422//===----------------------------------------------------------------------===// 423 424/// add - Insert a value into the table with a specified value number. 425void ValueTable::add(Value* V, uint32_t num) { 426 valueNumbering.insert(std::make_pair(V, num)); 427} 428 429/// lookup_or_add - Returns the value number for the specified value, assigning 430/// it a new number if it did not have one before. 431uint32_t ValueTable::lookup_or_add(Value* V) { 432 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 433 if (VI != valueNumbering.end()) 434 return VI->second; 435 436 if (CallInst* C = dyn_cast<CallInst>(V)) { 437 if (AA->doesNotAccessMemory(C)) { 438 Expression e = create_expression(C); 439 440 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 441 if (EI != expressionNumbering.end()) { 442 valueNumbering.insert(std::make_pair(V, EI->second)); 443 return EI->second; 444 } else { 445 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 446 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 447 448 return nextValueNumber++; 449 } 450 } else if (AA->onlyReadsMemory(C)) { 451 Expression e = create_expression(C); 452 453 if (expressionNumbering.find(e) == expressionNumbering.end()) { 454 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 455 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 456 return nextValueNumber++; 457 } 458 459 MemDepResult local_dep = MD->getDependency(C); 460 461 if (local_dep.isNone()) { 462 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 463 return nextValueNumber++; 464 } else if (Instruction *LocalDepInst = local_dep.getInst()) { 465 // FIXME: INDENT PROPERLY! 466 if (!isa<CallInst>(LocalDepInst)) { 467 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 468 return nextValueNumber++; 469 } 470 471 CallInst* local_cdep = cast<CallInst>(LocalDepInst); 472 473 // FIXME: INDENT PROPERLY. 474 if (local_cdep->getCalledFunction() != C->getCalledFunction() || 475 local_cdep->getNumOperands() != C->getNumOperands()) { 476 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 477 return nextValueNumber++; 478 } else if (!C->getCalledFunction()) { 479 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 480 return nextValueNumber++; 481 } else { 482 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 483 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 484 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 485 if (c_vn != cd_vn) { 486 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 487 return nextValueNumber++; 488 } 489 } 490 491 uint32_t v = lookup_or_add(local_cdep); 492 valueNumbering.insert(std::make_pair(V, v)); 493 return v; 494 } 495 } 496 497 498 SmallVector<std::pair<BasicBlock*, MemDepResult>, 32> deps; 499 MD->getNonLocalDependency(C, deps); 500 CallInst* cdep = 0; 501 502 for (SmallVector<std::pair<BasicBlock*, MemDepResult>, 32> 503 ::iterator I = deps.begin(), E = deps.end(); I != E; ++I) { 504 if (I->second.isNone()) { 505 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 506 507 return nextValueNumber++; 508 } else if (Instruction *NonLocalDepInst = I->second.getInst()) { 509 // FIXME: INDENT PROPERLY 510 // FIXME: All duplicated with non-local case. 511 if (cdep == 0 && DT->properlyDominates(I->first, C->getParent())) { 512 if (CallInst* CD = dyn_cast<CallInst>(NonLocalDepInst)) 513 cdep = CD; 514 else { 515 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 516 return nextValueNumber++; 517 } 518 } else { 519 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 520 return nextValueNumber++; 521 } 522 } 523 } 524 525 if (!cdep) { 526 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 527 return nextValueNumber++; 528 } 529 530 // FIXME: THIS ISN'T SAFE: CONSIDER: 531 // X = strlen(str) 532 // if (C) 533 // str[0] = 1; 534 // Y = strlen(str) 535 // This doesn't guarantee all-paths availability! 536 if (cdep->getCalledFunction() != C->getCalledFunction() || 537 cdep->getNumOperands() != C->getNumOperands()) { 538 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 539 return nextValueNumber++; 540 } else if (!C->getCalledFunction()) { 541 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 542 return nextValueNumber++; 543 } else { 544 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 545 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 546 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 547 if (c_vn != cd_vn) { 548 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 549 return nextValueNumber++; 550 } 551 } 552 553 uint32_t v = lookup_or_add(cdep); 554 valueNumbering.insert(std::make_pair(V, v)); 555 return v; 556 } 557 558 } else { 559 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 560 return nextValueNumber++; 561 } 562 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 563 Expression e = create_expression(BO); 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 (CmpInst* C = dyn_cast<CmpInst>(V)) { 576 Expression e = create_expression(C); 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 (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(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 (ExtractElementInst* U = dyn_cast<ExtractElementInst>(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 (InsertElementInst* U = dyn_cast<InsertElementInst>(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 (SelectInst* U = dyn_cast<SelectInst>(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 (CastInst* U = dyn_cast<CastInst>(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 if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 654 Expression e = create_expression(U); 655 656 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 657 if (EI != expressionNumbering.end()) { 658 valueNumbering.insert(std::make_pair(V, EI->second)); 659 return EI->second; 660 } else { 661 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 662 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 663 664 return nextValueNumber++; 665 } 666 } else { 667 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 668 return nextValueNumber++; 669 } 670} 671 672/// lookup - Returns the value number of the specified value. Fails if 673/// the value has not yet been numbered. 674uint32_t ValueTable::lookup(Value* V) const { 675 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 676 assert(VI != valueNumbering.end() && "Value not numbered?"); 677 return VI->second; 678} 679 680/// clear - Remove all entries from the ValueTable 681void ValueTable::clear() { 682 valueNumbering.clear(); 683 expressionNumbering.clear(); 684 nextValueNumber = 1; 685} 686 687/// erase - Remove a value from the value numbering 688void ValueTable::erase(Value* V) { 689 valueNumbering.erase(V); 690} 691 692//===----------------------------------------------------------------------===// 693// GVN Pass 694//===----------------------------------------------------------------------===// 695 696namespace { 697 struct VISIBILITY_HIDDEN ValueNumberScope { 698 ValueNumberScope* parent; 699 DenseMap<uint32_t, Value*> table; 700 701 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 702 }; 703} 704 705namespace { 706 707 class VISIBILITY_HIDDEN GVN : public FunctionPass { 708 bool runOnFunction(Function &F); 709 public: 710 static char ID; // Pass identification, replacement for typeid 711 GVN() : FunctionPass(&ID) { } 712 713 private: 714 ValueTable VN; 715 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 716 717 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 718 PhiMapType phiMap; 719 720 721 // This transformation requires dominator postdominator info 722 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 723 AU.addRequired<DominatorTree>(); 724 AU.addRequired<MemoryDependenceAnalysis>(); 725 AU.addRequired<AliasAnalysis>(); 726 727 AU.addPreserved<DominatorTree>(); 728 AU.addPreserved<AliasAnalysis>(); 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 bool mergeBlockIntoPredecessor(BasicBlock* BB); 752 void cleanupGlobalSets(); 753 }; 754 755 char GVN::ID = 0; 756} 757 758// createGVNPass - The public interface to this file... 759FunctionPass *llvm::createGVNPass() { return new GVN(); } 760 761static RegisterPass<GVN> X("gvn", 762 "Global Value Numbering"); 763 764void GVN::dump(DenseMap<uint32_t, Value*>& d) { 765 printf("{\n"); 766 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 767 E = d.end(); I != E; ++I) { 768 printf("%d\n", I->first); 769 I->second->dump(); 770 } 771 printf("}\n"); 772} 773 774Value* GVN::CollapsePhi(PHINode* p) { 775 DominatorTree &DT = getAnalysis<DominatorTree>(); 776 Value* constVal = p->hasConstantValue(); 777 778 if (!constVal) return 0; 779 780 Instruction* inst = dyn_cast<Instruction>(constVal); 781 if (!inst) 782 return constVal; 783 784 if (DT.dominates(inst, p)) 785 if (isSafeReplacement(p, inst)) 786 return inst; 787 return 0; 788} 789 790bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 791 if (!isa<PHINode>(inst)) 792 return true; 793 794 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 795 UI != E; ++UI) 796 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 797 if (use_phi->getParent() == inst->getParent()) 798 return false; 799 800 return true; 801} 802 803/// GetValueForBlock - Get the value to use within the specified basic block. 804/// available values are in Phis. 805Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig, 806 DenseMap<BasicBlock*, Value*> &Phis, 807 bool top_level) { 808 809 // If we have already computed this value, return the previously computed val. 810 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 811 if (V != Phis.end() && !top_level) return V->second; 812 813 // If the block is unreachable, just return undef, since this path 814 // can't actually occur at runtime. 815 if (!getAnalysis<DominatorTree>().isReachableFromEntry(BB)) 816 return Phis[BB] = UndefValue::get(orig->getType()); 817 818 BasicBlock* singlePred = BB->getSinglePredecessor(); 819 if (singlePred) { 820 Value *ret = GetValueForBlock(singlePred, orig, Phis); 821 Phis[BB] = ret; 822 return ret; 823 } 824 825 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 826 // now, then get values to fill in the incoming values for the PHI. 827 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", 828 BB->begin()); 829 PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB))); 830 831 if (Phis.count(BB) == 0) 832 Phis.insert(std::make_pair(BB, PN)); 833 834 // Fill in the incoming values for the block. 835 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 836 Value* val = GetValueForBlock(*PI, orig, Phis); 837 PN->addIncoming(val, *PI); 838 } 839 840 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 841 AA.copyValue(orig, PN); 842 843 // Attempt to collapse PHI nodes that are trivially redundant 844 Value* v = CollapsePhi(PN); 845 if (!v) { 846 // Cache our phi construction results 847 phiMap[orig->getPointerOperand()].insert(PN); 848 return PN; 849 } 850 851 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 852 853 MD.removeInstruction(PN); 854 PN->replaceAllUsesWith(v); 855 856 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 857 E = Phis.end(); I != E; ++I) 858 if (I->second == PN) 859 I->second = v; 860 861 PN->eraseFromParent(); 862 863 Phis[BB] = v; 864 return v; 865} 866 867/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 868/// non-local by performing PHI construction. 869bool GVN::processNonLocalLoad(LoadInst* L, 870 SmallVectorImpl<Instruction*> &toErase) { 871 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 872 873 // Find the non-local dependencies of the load 874 SmallVector<std::pair<BasicBlock*, MemDepResult>, 32> deps; 875 MD.getNonLocalDependency(L, deps); 876 877 // If we had to process more than one hundred blocks to find the 878 // dependencies, this load isn't worth worrying about. Optimizing 879 // it will be too expensive. 880 if (deps.size() > 100) 881 return false; 882 883 BasicBlock *EntryBlock = &L->getParent()->getParent()->getEntryBlock(); 884 885 DenseMap<BasicBlock*, Value*> repl; 886 887 // Filter out useless results (non-locals, etc) 888 for (SmallVector<std::pair<BasicBlock*, MemDepResult>, 32>::iterator 889 I = deps.begin(), E = deps.end(); I != E; ++I) { 890 if (I->second.isNone()) { 891 repl[I->first] = UndefValue::get(L->getType()); 892 continue; 893 } 894 895 if (I->second.isNonLocal()) { 896 // If this is a non-local dependency in the entry block, then we depend on 897 // the value live-in at the start of the function. We could insert a load 898 // in the entry block to get this, but for now we'll just bail out. 899 // FIXME: Consider emitting a load in the entry block to catch this case! 900 if (I->first == EntryBlock) 901 return false; 902 continue; 903 } 904 905 if (StoreInst* S = dyn_cast<StoreInst>(I->second.getInst())) { 906 if (S->getPointerOperand() != L->getPointerOperand()) 907 return false; 908 repl[I->first] = S->getOperand(0); 909 } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second.getInst())) { 910 if (LD->getPointerOperand() != L->getPointerOperand()) 911 return false; 912 repl[I->first] = LD; 913 } else { 914 return false; 915 } 916 } 917 918 // Use cached PHI construction information from previous runs 919 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()]; 920 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 921 I != E; ++I) { 922 if ((*I)->getParent() == L->getParent()) { 923 MD.removeInstruction(L); 924 L->replaceAllUsesWith(*I); 925 toErase.push_back(L); 926 NumGVNLoad++; 927 return true; 928 } 929 930 repl.insert(std::make_pair((*I)->getParent(), *I)); 931 } 932 933 // Perform PHI construction 934 SmallPtrSet<BasicBlock*, 4> visited; 935 Value* v = GetValueForBlock(L->getParent(), L, repl, true); 936 937 MD.removeInstruction(L); 938 L->replaceAllUsesWith(v); 939 toErase.push_back(L); 940 NumGVNLoad++; 941 942 return true; 943} 944 945/// processLoad - Attempt to eliminate a load, first by eliminating it 946/// locally, and then attempting non-local elimination if that fails. 947bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad, 948 SmallVectorImpl<Instruction*> &toErase) { 949 if (L->isVolatile()) { 950 lastLoad[L->getPointerOperand()] = L; 951 return false; 952 } 953 954 Value* pointer = L->getPointerOperand(); 955 LoadInst*& last = lastLoad[pointer]; 956 957 // ... to a pointer that has been loaded from before... 958 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 959 bool removedNonLocal = false; 960 MemDepResult dep = MD.getDependency(L); 961 if (dep.isNonLocal() && 962 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) { 963 removedNonLocal = processNonLocalLoad(L, toErase); 964 965 if (!removedNonLocal) 966 last = L; 967 968 return removedNonLocal; 969 } 970 971 972 bool deletedLoad = false; 973 974 // Walk up the dependency chain until we either find 975 // a dependency we can use, or we can't walk any further 976 while (Instruction *DepInst = dep.getInst()) { 977 // ... that depends on a store ... 978 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) { 979 if (S->getPointerOperand() == pointer) { 980 // Remove it! 981 MD.removeInstruction(L); 982 983 L->replaceAllUsesWith(S->getOperand(0)); 984 toErase.push_back(L); 985 deletedLoad = true; 986 NumGVNLoad++; 987 } 988 989 // Whether we removed it or not, we can't 990 // go any further 991 break; 992 } else if (!isa<LoadInst>(DepInst)) { 993 // Only want to handle loads below. 994 break; 995 } else if (!last) { 996 // If we don't depend on a store, and we haven't 997 // been loaded before, bail. 998 break; 999 } else if (DepInst == last) { 1000 // Remove it! 1001 MD.removeInstruction(L); 1002 1003 L->replaceAllUsesWith(last); 1004 toErase.push_back(L); 1005 deletedLoad = true; 1006 NumGVNLoad++; 1007 break; 1008 } else { 1009 dep = MD.getDependencyFrom(L, DepInst, DepInst->getParent()); 1010 } 1011 } 1012 1013 // If this load really doesn't depend on anything, then we must be loading an 1014 // undef value. This can happen when loading for a fresh allocation with no 1015 // intervening stores, for example. 1016 if (dep.isNone()) { 1017 // If this load depends directly on an allocation, there isn't 1018 // anything stored there; therefore, we can optimize this load 1019 // to undef. 1020 MD.removeInstruction(L); 1021 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1022 toErase.push_back(L); 1023 deletedLoad = true; 1024 NumGVNLoad++; 1025 } 1026 1027 if (!deletedLoad) 1028 last = L; 1029 1030 return deletedLoad; 1031} 1032 1033Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) { 1034 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1035 if (I == localAvail.end()) 1036 return 0; 1037 1038 ValueNumberScope* locals = I->second; 1039 1040 while (locals) { 1041 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num); 1042 if (I != locals->table.end()) 1043 return I->second; 1044 else 1045 locals = locals->parent; 1046 } 1047 1048 return 0; 1049} 1050 1051/// processInstruction - When calculating availability, handle an instruction 1052/// by inserting it into the appropriate sets 1053bool GVN::processInstruction(Instruction *I, 1054 DenseMap<Value*, LoadInst*> &lastSeenLoad, 1055 SmallVectorImpl<Instruction*> &toErase) { 1056 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1057 bool changed = processLoad(L, lastSeenLoad, toErase); 1058 1059 if (!changed) { 1060 unsigned num = VN.lookup_or_add(L); 1061 localAvail[I->getParent()]->table.insert(std::make_pair(num, L)); 1062 } 1063 1064 return changed; 1065 } 1066 1067 uint32_t nextNum = VN.getNextUnusedValueNumber(); 1068 unsigned num = VN.lookup_or_add(I); 1069 1070 // Allocations are always uniquely numbered, so we can save time and memory 1071 // by fast failing them. 1072 if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1073 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1074 return false; 1075 } 1076 1077 // Collapse PHI nodes 1078 if (PHINode* p = dyn_cast<PHINode>(I)) { 1079 Value* constVal = CollapsePhi(p); 1080 1081 if (constVal) { 1082 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1083 PI != PE; ++PI) 1084 if (PI->second.count(p)) 1085 PI->second.erase(p); 1086 1087 p->replaceAllUsesWith(constVal); 1088 toErase.push_back(p); 1089 } else { 1090 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1091 } 1092 1093 // If the number we were assigned was a brand new VN, then we don't 1094 // need to do a lookup to see if the number already exists 1095 // somewhere in the domtree: it can't! 1096 } else if (num == nextNum) { 1097 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1098 1099 // Perform value-number based elimination 1100 } else if (Value* repl = lookupNumber(I->getParent(), num)) { 1101 // Remove it! 1102 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1103 MD.removeInstruction(I); 1104 1105 VN.erase(I); 1106 I->replaceAllUsesWith(repl); 1107 toErase.push_back(I); 1108 return true; 1109 } else { 1110 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1111 } 1112 1113 return false; 1114} 1115 1116// GVN::runOnFunction - This is the main transformation entry point for a 1117// function. 1118// 1119bool GVN::runOnFunction(Function& F) { 1120 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1121 VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>()); 1122 VN.setDomTree(&getAnalysis<DominatorTree>()); 1123 1124 bool changed = false; 1125 bool shouldContinue = true; 1126 1127 // Merge unconditional branches, allowing PRE to catch more 1128 // optimization opportunities. 1129 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1130 BasicBlock* BB = FI; 1131 ++FI; 1132 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1133 if (removedBlock) NumGVNBlocks++; 1134 1135 changed |= removedBlock; 1136 } 1137 1138 while (shouldContinue) { 1139 shouldContinue = iterateOnFunction(F); 1140 changed |= shouldContinue; 1141 } 1142 1143 if (EnablePRE) { 1144 bool PREChanged = true; 1145 while (PREChanged) { 1146 PREChanged = performPRE(F); 1147 changed |= PREChanged; 1148 } 1149 } 1150 1151 cleanupGlobalSets(); 1152 1153 return changed; 1154} 1155 1156 1157bool GVN::processBlock(DomTreeNode* DTN) { 1158 BasicBlock* BB = DTN->getBlock(); 1159 1160 SmallVector<Instruction*, 8> toErase; 1161 DenseMap<Value*, LoadInst*> lastSeenLoad; 1162 bool changed_function = false; 1163 1164 if (DTN->getIDom()) 1165 localAvail[BB] = 1166 new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]); 1167 else 1168 localAvail[BB] = new ValueNumberScope(0); 1169 1170 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1171 BI != BE;) { 1172 changed_function |= processInstruction(BI, lastSeenLoad, toErase); 1173 if (toErase.empty()) { 1174 ++BI; 1175 continue; 1176 } 1177 1178 // If we need some instructions deleted, do it now. 1179 NumGVNInstr += toErase.size(); 1180 1181 // Avoid iterator invalidation. 1182 bool AtStart = BI == BB->begin(); 1183 if (!AtStart) 1184 --BI; 1185 1186 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1187 E = toErase.end(); I != E; ++I) 1188 (*I)->eraseFromParent(); 1189 1190 if (AtStart) 1191 BI = BB->begin(); 1192 else 1193 ++BI; 1194 1195 toErase.clear(); 1196 } 1197 1198 return changed_function; 1199} 1200 1201/// performPRE - Perform a purely local form of PRE that looks for diamond 1202/// control flow patterns and attempts to perform simple PRE at the join point. 1203bool GVN::performPRE(Function& F) { 1204 bool changed = false; 1205 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1206 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1207 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1208 BasicBlock* CurrentBlock = *DI; 1209 1210 // Nothing to PRE in the entry block. 1211 if (CurrentBlock == &F.getEntryBlock()) continue; 1212 1213 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1214 BE = CurrentBlock->end(); BI != BE; ) { 1215 if (isa<AllocationInst>(BI) || isa<TerminatorInst>(BI) || 1216 isa<PHINode>(BI) || BI->mayReadFromMemory() || 1217 BI->mayWriteToMemory()) { 1218 BI++; 1219 continue; 1220 } 1221 1222 uint32_t valno = VN.lookup(BI); 1223 1224 // Look for the predecessors for PRE opportunities. We're 1225 // only trying to solve the basic diamond case, where 1226 // a value is computed in the successor and one predecessor, 1227 // but not the other. We also explicitly disallow cases 1228 // where the successor is its own predecessor, because they're 1229 // more complicated to get right. 1230 unsigned numWith = 0; 1231 unsigned numWithout = 0; 1232 BasicBlock* PREPred = 0; 1233 DenseMap<BasicBlock*, Value*> predMap; 1234 for (pred_iterator PI = pred_begin(CurrentBlock), 1235 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1236 // We're not interested in PRE where the block is its 1237 // own predecessor, on in blocks with predecessors 1238 // that are not reachable. 1239 if (*PI == CurrentBlock) { 1240 numWithout = 2; 1241 break; 1242 } else if (!localAvail.count(*PI)) { 1243 numWithout = 2; 1244 break; 1245 } 1246 1247 DenseMap<uint32_t, Value*>::iterator predV = 1248 localAvail[*PI]->table.find(valno); 1249 if (predV == localAvail[*PI]->table.end()) { 1250 PREPred = *PI; 1251 numWithout++; 1252 } else if (predV->second == BI) { 1253 numWithout = 2; 1254 } else { 1255 predMap[*PI] = predV->second; 1256 numWith++; 1257 } 1258 } 1259 1260 // Don't do PRE when it might increase code size, i.e. when 1261 // we would need to insert instructions in more than one pred. 1262 if (numWithout != 1 || numWith == 0) { 1263 BI++; 1264 continue; 1265 } 1266 1267 // We can't do PRE safely on a critical edge, so instead we schedule 1268 // the edge to be split and perform the PRE the next time we iterate 1269 // on the function. 1270 unsigned succNum = 0; 1271 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1272 i != e; ++i) 1273 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 1274 succNum = i; 1275 break; 1276 } 1277 1278 if (isCriticalEdge(PREPred->getTerminator(), succNum)) { 1279 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum)); 1280 changed = true; 1281 BI++; 1282 continue; 1283 } 1284 1285 // Instantiate the expression the in predecessor that lacked it. 1286 // Because we are going top-down through the block, all value numbers 1287 // will be available in the predecessor by the time we need them. Any 1288 // that weren't original present will have been instantiated earlier 1289 // in this loop. 1290 Instruction* PREInstr = BI->clone(); 1291 bool success = true; 1292 for (unsigned i = 0; i < BI->getNumOperands(); ++i) { 1293 Value* op = BI->getOperand(i); 1294 if (isa<Argument>(op) || isa<Constant>(op) || isa<GlobalValue>(op)) 1295 PREInstr->setOperand(i, op); 1296 else { 1297 Value* V = lookupNumber(PREPred, VN.lookup(op)); 1298 if (!V) { 1299 success = false; 1300 break; 1301 } else 1302 PREInstr->setOperand(i, V); 1303 } 1304 } 1305 1306 // Fail out if we encounter an operand that is not available in 1307 // the PRE predecessor. This is typically because of loads which 1308 // are not value numbered precisely. 1309 if (!success) { 1310 delete PREInstr; 1311 BI++; 1312 continue; 1313 } 1314 1315 PREInstr->insertBefore(PREPred->getTerminator()); 1316 PREInstr->setName(BI->getName() + ".pre"); 1317 predMap[PREPred] = PREInstr; 1318 VN.add(PREInstr, valno); 1319 NumGVNPRE++; 1320 1321 // Update the availability map to include the new instruction. 1322 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr)); 1323 1324 // Create a PHI to make the value available in this block. 1325 PHINode* Phi = PHINode::Create(BI->getType(), 1326 BI->getName() + ".pre-phi", 1327 CurrentBlock->begin()); 1328 for (pred_iterator PI = pred_begin(CurrentBlock), 1329 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1330 Phi->addIncoming(predMap[*PI], *PI); 1331 1332 VN.add(Phi, valno); 1333 localAvail[CurrentBlock]->table[valno] = Phi; 1334 1335 BI->replaceAllUsesWith(Phi); 1336 VN.erase(BI); 1337 1338 Instruction* erase = BI; 1339 BI++; 1340 erase->eraseFromParent(); 1341 1342 changed = true; 1343 } 1344 } 1345 1346 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 1347 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 1348 SplitCriticalEdge(I->first, I->second, this); 1349 1350 return changed || toSplit.size(); 1351} 1352 1353// iterateOnFunction - Executes one iteration of GVN 1354bool GVN::iterateOnFunction(Function &F) { 1355 DominatorTree &DT = getAnalysis<DominatorTree>(); 1356 1357 cleanupGlobalSets(); 1358 1359 // Top-down walk of the dominator tree 1360 bool changed = false; 1361 for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()), 1362 DE = df_end(DT.getRootNode()); DI != DE; ++DI) 1363 changed |= processBlock(*DI); 1364 1365 return changed; 1366} 1367 1368void GVN::cleanupGlobalSets() { 1369 VN.clear(); 1370 phiMap.clear(); 1371 1372 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1373 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 1374 delete I->second; 1375 localAvail.clear(); 1376} 1377