GVN.cpp revision 978796eaad4f6cefc2069dc5183679ac7dd8f666
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 AliasAnalysis *getAliasAnalysis() const { return AA; } 170 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 171 void setDomTree(DominatorTree* D) { DT = D; } 172 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 173 }; 174} 175 176namespace llvm { 177template <> struct DenseMapInfo<Expression> { 178 static inline Expression getEmptyKey() { 179 return Expression(Expression::EMPTY); 180 } 181 182 static inline Expression getTombstoneKey() { 183 return Expression(Expression::TOMBSTONE); 184 } 185 186 static unsigned getHashValue(const Expression e) { 187 unsigned hash = e.opcode; 188 189 hash = e.firstVN + hash * 37; 190 hash = e.secondVN + hash * 37; 191 hash = e.thirdVN + hash * 37; 192 193 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 194 (unsigned)((uintptr_t)e.type >> 9)) + 195 hash * 37; 196 197 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 198 E = e.varargs.end(); I != E; ++I) 199 hash = *I + hash * 37; 200 201 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 202 (unsigned)((uintptr_t)e.function >> 9)) + 203 hash * 37; 204 205 return hash; 206 } 207 static bool isEqual(const Expression &LHS, const Expression &RHS) { 208 return LHS == RHS; 209 } 210 static bool isPod() { return true; } 211}; 212} 213 214//===----------------------------------------------------------------------===// 215// ValueTable Internal Functions 216//===----------------------------------------------------------------------===// 217Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 218 switch(BO->getOpcode()) { 219 default: // THIS SHOULD NEVER HAPPEN 220 assert(0 && "Binary operator with unknown opcode?"); 221 case Instruction::Add: return Expression::ADD; 222 case Instruction::Sub: return Expression::SUB; 223 case Instruction::Mul: return Expression::MUL; 224 case Instruction::UDiv: return Expression::UDIV; 225 case Instruction::SDiv: return Expression::SDIV; 226 case Instruction::FDiv: return Expression::FDIV; 227 case Instruction::URem: return Expression::UREM; 228 case Instruction::SRem: return Expression::SREM; 229 case Instruction::FRem: return Expression::FREM; 230 case Instruction::Shl: return Expression::SHL; 231 case Instruction::LShr: return Expression::LSHR; 232 case Instruction::AShr: return Expression::ASHR; 233 case Instruction::And: return Expression::AND; 234 case Instruction::Or: return Expression::OR; 235 case Instruction::Xor: return Expression::XOR; 236 } 237} 238 239Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 240 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) { 241 switch (C->getPredicate()) { 242 default: // THIS SHOULD NEVER HAPPEN 243 assert(0 && "Comparison with unknown predicate?"); 244 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 245 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 246 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 247 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 248 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 249 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 250 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 251 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 252 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 253 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 254 } 255 } 256 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare"); 257 switch (C->getPredicate()) { 258 default: // THIS SHOULD NEVER HAPPEN 259 assert(0 && "Comparison with unknown predicate?"); 260 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 261 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 262 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 263 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 264 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 265 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 266 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 267 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 268 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 269 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 270 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 271 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 272 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 273 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 274 } 275} 276 277Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 278 switch(C->getOpcode()) { 279 default: // THIS SHOULD NEVER HAPPEN 280 assert(0 && "Cast operator with unknown opcode?"); 281 case Instruction::Trunc: return Expression::TRUNC; 282 case Instruction::ZExt: return Expression::ZEXT; 283 case Instruction::SExt: return Expression::SEXT; 284 case Instruction::FPToUI: return Expression::FPTOUI; 285 case Instruction::FPToSI: return Expression::FPTOSI; 286 case Instruction::UIToFP: return Expression::UITOFP; 287 case Instruction::SIToFP: return Expression::SITOFP; 288 case Instruction::FPTrunc: return Expression::FPTRUNC; 289 case Instruction::FPExt: return Expression::FPEXT; 290 case Instruction::PtrToInt: return Expression::PTRTOINT; 291 case Instruction::IntToPtr: return Expression::INTTOPTR; 292 case Instruction::BitCast: return Expression::BITCAST; 293 } 294} 295 296Expression ValueTable::create_expression(CallInst* C) { 297 Expression e; 298 299 e.type = C->getType(); 300 e.firstVN = 0; 301 e.secondVN = 0; 302 e.thirdVN = 0; 303 e.function = C->getCalledFunction(); 304 e.opcode = Expression::CALL; 305 306 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 307 I != E; ++I) 308 e.varargs.push_back(lookup_or_add(*I)); 309 310 return e; 311} 312 313Expression ValueTable::create_expression(BinaryOperator* BO) { 314 Expression e; 315 316 e.firstVN = lookup_or_add(BO->getOperand(0)); 317 e.secondVN = lookup_or_add(BO->getOperand(1)); 318 e.thirdVN = 0; 319 e.function = 0; 320 e.type = BO->getType(); 321 e.opcode = getOpcode(BO); 322 323 return e; 324} 325 326Expression ValueTable::create_expression(CmpInst* C) { 327 Expression e; 328 329 e.firstVN = lookup_or_add(C->getOperand(0)); 330 e.secondVN = lookup_or_add(C->getOperand(1)); 331 e.thirdVN = 0; 332 e.function = 0; 333 e.type = C->getType(); 334 e.opcode = getOpcode(C); 335 336 return e; 337} 338 339Expression ValueTable::create_expression(CastInst* C) { 340 Expression e; 341 342 e.firstVN = lookup_or_add(C->getOperand(0)); 343 e.secondVN = 0; 344 e.thirdVN = 0; 345 e.function = 0; 346 e.type = C->getType(); 347 e.opcode = getOpcode(C); 348 349 return e; 350} 351 352Expression ValueTable::create_expression(ShuffleVectorInst* S) { 353 Expression e; 354 355 e.firstVN = lookup_or_add(S->getOperand(0)); 356 e.secondVN = lookup_or_add(S->getOperand(1)); 357 e.thirdVN = lookup_or_add(S->getOperand(2)); 358 e.function = 0; 359 e.type = S->getType(); 360 e.opcode = Expression::SHUFFLE; 361 362 return e; 363} 364 365Expression ValueTable::create_expression(ExtractElementInst* E) { 366 Expression e; 367 368 e.firstVN = lookup_or_add(E->getOperand(0)); 369 e.secondVN = lookup_or_add(E->getOperand(1)); 370 e.thirdVN = 0; 371 e.function = 0; 372 e.type = E->getType(); 373 e.opcode = Expression::EXTRACT; 374 375 return e; 376} 377 378Expression ValueTable::create_expression(InsertElementInst* I) { 379 Expression e; 380 381 e.firstVN = lookup_or_add(I->getOperand(0)); 382 e.secondVN = lookup_or_add(I->getOperand(1)); 383 e.thirdVN = lookup_or_add(I->getOperand(2)); 384 e.function = 0; 385 e.type = I->getType(); 386 e.opcode = Expression::INSERT; 387 388 return e; 389} 390 391Expression ValueTable::create_expression(SelectInst* I) { 392 Expression e; 393 394 e.firstVN = lookup_or_add(I->getCondition()); 395 e.secondVN = lookup_or_add(I->getTrueValue()); 396 e.thirdVN = lookup_or_add(I->getFalseValue()); 397 e.function = 0; 398 e.type = I->getType(); 399 e.opcode = Expression::SELECT; 400 401 return e; 402} 403 404Expression ValueTable::create_expression(GetElementPtrInst* G) { 405 Expression e; 406 407 e.firstVN = lookup_or_add(G->getPointerOperand()); 408 e.secondVN = 0; 409 e.thirdVN = 0; 410 e.function = 0; 411 e.type = G->getType(); 412 e.opcode = Expression::GEP; 413 414 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 415 I != E; ++I) 416 e.varargs.push_back(lookup_or_add(*I)); 417 418 return e; 419} 420 421//===----------------------------------------------------------------------===// 422// ValueTable External Functions 423//===----------------------------------------------------------------------===// 424 425/// add - Insert a value into the table with a specified value number. 426void ValueTable::add(Value* V, uint32_t num) { 427 valueNumbering.insert(std::make_pair(V, num)); 428} 429 430/// lookup_or_add - Returns the value number for the specified value, assigning 431/// it a new number if it did not have one before. 432uint32_t ValueTable::lookup_or_add(Value* V) { 433 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 434 if (VI != valueNumbering.end()) 435 return VI->second; 436 437 if (CallInst* C = dyn_cast<CallInst>(V)) { 438 if (AA->doesNotAccessMemory(C)) { 439 Expression e = create_expression(C); 440 441 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 442 if (EI != expressionNumbering.end()) { 443 valueNumbering.insert(std::make_pair(V, EI->second)); 444 return EI->second; 445 } else { 446 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 447 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 448 449 return nextValueNumber++; 450 } 451 } else if (AA->onlyReadsMemory(C)) { 452 Expression e = create_expression(C); 453 454 if (expressionNumbering.find(e) == expressionNumbering.end()) { 455 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 456 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 457 return nextValueNumber++; 458 } 459 460 MemDepResult local_dep = MD->getDependency(C); 461 462 if (local_dep.isNone()) { 463 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 464 return nextValueNumber++; 465 } 466 467 if (Instruction *LocalDepInst = local_dep.getInst()) { 468 if (!isa<CallInst>(LocalDepInst)) { 469 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 470 return nextValueNumber++; 471 } 472 473 CallInst* local_cdep = cast<CallInst>(LocalDepInst); 474 475 if (local_cdep->getCalledFunction() != C->getCalledFunction() || 476 local_cdep->getNumOperands() != C->getNumOperands()) { 477 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 478 return nextValueNumber++; 479 } 480 481 if (!C->getCalledFunction()) { 482 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 483 return nextValueNumber++; 484 } 485 486 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 487 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 488 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 489 if (c_vn != cd_vn) { 490 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 491 return nextValueNumber++; 492 } 493 } 494 495 uint32_t v = lookup_or_add(local_cdep); 496 valueNumbering.insert(std::make_pair(V, v)); 497 return v; 498 } 499 500 501 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 502 MD->getNonLocalDependency(C); 503 CallInst* cdep = 0; 504 505 // Check to see if we have a single dominating call instruction that is 506 // identical to C. 507 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 508 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i]; 509 // Ignore non-local dependencies. 510 if (I->second.isNonLocal()) 511 continue; 512 513 // We don't handle non-depedencies. If we already have a call, reject 514 // instruction dependencies. 515 if (I->second.isNone() || cdep != 0) { 516 cdep = 0; 517 break; 518 } 519 520 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst()); 521 // FIXME: All duplicated with non-local case. 522 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){ 523 cdep = NonLocalDepCall; 524 continue; 525 } 526 527 cdep = 0; 528 break; 529 } 530 531 if (!cdep) { 532 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 533 return nextValueNumber++; 534 } 535 536 if (cdep->getCalledFunction() != C->getCalledFunction() || 537 cdep->getNumOperands() != C->getNumOperands()) { 538 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 539 return nextValueNumber++; 540 } 541 if (!C->getCalledFunction()) { 542 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 543 return nextValueNumber++; 544 } 545 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 546 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 547 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 548 if (c_vn != cd_vn) { 549 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 550 return nextValueNumber++; 551 } 552 } 553 554 uint32_t v = lookup_or_add(cdep); 555 valueNumbering.insert(std::make_pair(V, v)); 556 return v; 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 MemoryDependenceAnalysis *MD; 715 DominatorTree *DT; 716 717 ValueTable VN; 718 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 719 720 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 721 PhiMapType phiMap; 722 723 724 // This transformation requires dominator postdominator info 725 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 726 AU.addRequired<DominatorTree>(); 727 AU.addRequired<MemoryDependenceAnalysis>(); 728 AU.addRequired<AliasAnalysis>(); 729 730 AU.addPreserved<DominatorTree>(); 731 AU.addPreserved<AliasAnalysis>(); 732 } 733 734 // Helper fuctions 735 // FIXME: eliminate or document these better 736 bool processLoad(LoadInst* L, 737 DenseMap<Value*, LoadInst*> &lastLoad, 738 SmallVectorImpl<Instruction*> &toErase); 739 bool processInstruction(Instruction* I, 740 DenseMap<Value*, LoadInst*>& lastSeenLoad, 741 SmallVectorImpl<Instruction*> &toErase); 742 bool processNonLocalLoad(LoadInst* L, 743 SmallVectorImpl<Instruction*> &toErase); 744 bool processBlock(DomTreeNode* DTN); 745 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig, 746 DenseMap<BasicBlock*, Value*> &Phis, 747 bool top_level = false); 748 void dump(DenseMap<uint32_t, Value*>& d); 749 bool iterateOnFunction(Function &F); 750 Value* CollapsePhi(PHINode* p); 751 bool isSafeReplacement(PHINode* p, Instruction* inst); 752 bool performPRE(Function& F); 753 Value* lookupNumber(BasicBlock* BB, uint32_t num); 754 bool mergeBlockIntoPredecessor(BasicBlock* BB); 755 void cleanupGlobalSets(); 756 }; 757 758 char GVN::ID = 0; 759} 760 761// createGVNPass - The public interface to this file... 762FunctionPass *llvm::createGVNPass() { return new GVN(); } 763 764static RegisterPass<GVN> X("gvn", 765 "Global Value Numbering"); 766 767void GVN::dump(DenseMap<uint32_t, Value*>& d) { 768 printf("{\n"); 769 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 770 E = d.end(); I != E; ++I) { 771 printf("%d\n", I->first); 772 I->second->dump(); 773 } 774 printf("}\n"); 775} 776 777Value* GVN::CollapsePhi(PHINode* p) { 778 Value* constVal = p->hasConstantValue(); 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 (!DT->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 VN.getAliasAnalysis()->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 PN->replaceAllUsesWith(v); 852 853 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 854 E = Phis.end(); I != E; ++I) 855 if (I->second == PN) 856 I->second = v; 857 858 DEBUG(cerr << "GVN removed: " << *PN); 859 MD->removeInstruction(PN); 860 PN->eraseFromParent(); 861 862 Phis[BB] = v; 863 return v; 864} 865 866/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 867/// non-local by performing PHI construction. 868bool GVN::processNonLocalLoad(LoadInst* L, 869 SmallVectorImpl<Instruction*> &toErase) { 870 // Find the non-local dependencies of the load 871 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 872 MD->getNonLocalDependency(L); 873 DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << deps.size() << *L); 874#if 0 875 DEBUG(for (unsigned i = 0, e = deps.size(); i != e; ++i) { 876 cerr << " " << deps[i].first->getName(); 877 if (Instruction *I = deps[i].second.getInst()) 878 cerr << *I; 879 else 880 cerr << "\n"; 881 }); 882#endif 883 884 // If we had to process more than one hundred blocks to find the 885 // dependencies, this load isn't worth worrying about. Optimizing 886 // it will be too expensive. 887 if (deps.size() > 100) 888 return false; 889 890 BasicBlock *EntryBlock = &L->getParent()->getParent()->getEntryBlock(); 891 892 DenseMap<BasicBlock*, Value*> repl; 893 894 // Filter out useless results (non-locals, etc) 895 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 896 BasicBlock *DepBB = deps[i].first; 897 MemDepResult DepInfo = deps[i].second; 898 899 if (DepInfo.isNonLocal()) { 900 // If this is a non-local dependency in the entry block, then we depend on 901 // the value live-in at the start of the function. We could insert a load 902 // in the entry block to get this, but for now we'll just bail out. 903 // 904 // FIXME: Consider emitting a load in the entry block to catch this case! 905 // Tricky part is to sink so that it doesn't execute in places where it 906 // isn't needed. 907 if (DepBB == EntryBlock) 908 return false; 909 continue; 910 } 911 912 if (DepInfo.isNone()) { 913 repl[DepBB] = UndefValue::get(L->getType()); 914 continue; 915 } 916 917 if (StoreInst* S = dyn_cast<StoreInst>(DepInfo.getInst())) { 918 // Reject loads and stores that are to the same address but are of 919 // different types. 920 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because 921 // of bitfield access, it would be interesting to optimize for it at some 922 // point. 923 if (S->getOperand(0)->getType() != L->getType()) 924 return false; 925 926 if (S->getPointerOperand() != L->getPointerOperand() && 927 VN.getAliasAnalysis()->alias(S->getPointerOperand(), 1, 928 L->getPointerOperand(), 1) 929 != AliasAnalysis::MustAlias) 930 return false; 931 repl[DepBB] = S->getOperand(0); 932 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInfo.getInst())) { 933 if (LD->getType() != L->getType()) 934 return false; 935 936 if (LD->getPointerOperand() != L->getPointerOperand() && 937 VN.getAliasAnalysis()->alias(LD->getPointerOperand(), 1, 938 L->getPointerOperand(), 1) 939 != AliasAnalysis::MustAlias) 940 return false; 941 repl[DepBB] = LD; 942 } else { 943 return false; 944 } 945 } 946 947 // Use cached PHI construction information from previous runs 948 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()]; 949 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 950 I != E; ++I) { 951 if ((*I)->getParent() == L->getParent()) { 952 L->replaceAllUsesWith(*I); 953 toErase.push_back(L); 954 NumGVNLoad++; 955 return true; 956 } 957 958 repl.insert(std::make_pair((*I)->getParent(), *I)); 959 } 960 961 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *L); 962 963 // Perform PHI construction 964 SmallPtrSet<BasicBlock*, 4> visited; 965 Value* v = GetValueForBlock(L->getParent(), L, repl, true); 966 L->replaceAllUsesWith(v); 967 toErase.push_back(L); 968 NumGVNLoad++; 969 return true; 970} 971 972/// processLoad - Attempt to eliminate a load, first by eliminating it 973/// locally, and then attempting non-local elimination if that fails. 974bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad, 975 SmallVectorImpl<Instruction*> &toErase) { 976 if (L->isVolatile()) { 977 lastLoad[L->getPointerOperand()] = L; 978 return false; 979 } 980 981 Value* pointer = L->getPointerOperand(); 982 LoadInst*& last = lastLoad[pointer]; 983 984 // ... to a pointer that has been loaded from before... 985 bool removedNonLocal = false; 986 MemDepResult dep = MD->getDependency(L); 987 if (dep.isNonLocal() && 988 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) { 989 removedNonLocal = processNonLocalLoad(L, toErase); 990 991 if (!removedNonLocal) 992 last = L; 993 994 return removedNonLocal; 995 } 996 997 998 bool deletedLoad = false; 999 1000 // Walk up the dependency chain until we either find 1001 // a dependency we can use, or we can't walk any further 1002 while (Instruction *DepInst = dep.getInst()) { 1003 // ... that depends on a store ... 1004 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) { 1005 if (S->getPointerOperand() == pointer) { 1006 // Remove it! 1007 L->replaceAllUsesWith(S->getOperand(0)); 1008 toErase.push_back(L); 1009 deletedLoad = true; 1010 NumGVNLoad++; 1011 } 1012 1013 // Whether we removed it or not, we can't 1014 // go any further 1015 break; 1016 } else if (!isa<LoadInst>(DepInst)) { 1017 // Only want to handle loads below. 1018 break; 1019 } else if (!last) { 1020 // If we don't depend on a store, and we haven't 1021 // been loaded before, bail. 1022 break; 1023 } else if (DepInst == last) { 1024 // Remove it! 1025 L->replaceAllUsesWith(last); 1026 toErase.push_back(L); 1027 deletedLoad = true; 1028 NumGVNLoad++; 1029 break; 1030 } else { 1031 dep = MD->getDependencyFrom(L, DepInst, DepInst->getParent()); 1032 } 1033 } 1034 1035 // If this load really doesn't depend on anything, then we must be loading an 1036 // undef value. This can happen when loading for a fresh allocation with no 1037 // intervening stores, for example. 1038 if (dep.isNone()) { 1039 // If this load depends directly on an allocation, there isn't 1040 // anything stored there; therefore, we can optimize this load 1041 // to undef. 1042 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1043 toErase.push_back(L); 1044 deletedLoad = true; 1045 NumGVNLoad++; 1046 } 1047 1048 if (!deletedLoad) 1049 last = L; 1050 1051 return deletedLoad; 1052} 1053 1054Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) { 1055 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1056 if (I == localAvail.end()) 1057 return 0; 1058 1059 ValueNumberScope* locals = I->second; 1060 1061 while (locals) { 1062 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num); 1063 if (I != locals->table.end()) 1064 return I->second; 1065 else 1066 locals = locals->parent; 1067 } 1068 1069 return 0; 1070} 1071 1072/// processInstruction - When calculating availability, handle an instruction 1073/// by inserting it into the appropriate sets 1074bool GVN::processInstruction(Instruction *I, 1075 DenseMap<Value*, LoadInst*> &lastSeenLoad, 1076 SmallVectorImpl<Instruction*> &toErase) { 1077 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1078 bool changed = processLoad(L, lastSeenLoad, toErase); 1079 1080 if (!changed) { 1081 unsigned num = VN.lookup_or_add(L); 1082 localAvail[I->getParent()]->table.insert(std::make_pair(num, L)); 1083 } 1084 1085 return changed; 1086 } 1087 1088 uint32_t nextNum = VN.getNextUnusedValueNumber(); 1089 unsigned num = VN.lookup_or_add(I); 1090 1091 // Allocations are always uniquely numbered, so we can save time and memory 1092 // by fast failing them. 1093 if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1094 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1095 return false; 1096 } 1097 1098 // Collapse PHI nodes 1099 if (PHINode* p = dyn_cast<PHINode>(I)) { 1100 Value* constVal = CollapsePhi(p); 1101 1102 if (constVal) { 1103 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1104 PI != PE; ++PI) 1105 if (PI->second.count(p)) 1106 PI->second.erase(p); 1107 1108 p->replaceAllUsesWith(constVal); 1109 toErase.push_back(p); 1110 } else { 1111 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1112 } 1113 1114 // If the number we were assigned was a brand new VN, then we don't 1115 // need to do a lookup to see if the number already exists 1116 // somewhere in the domtree: it can't! 1117 } else if (num == nextNum) { 1118 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1119 1120 // Perform value-number based elimination 1121 } else if (Value* repl = lookupNumber(I->getParent(), num)) { 1122 // Remove it! 1123 VN.erase(I); 1124 I->replaceAllUsesWith(repl); 1125 toErase.push_back(I); 1126 return true; 1127 } else { 1128 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1129 } 1130 1131 return false; 1132} 1133 1134// GVN::runOnFunction - This is the main transformation entry point for a 1135// function. 1136// 1137bool GVN::runOnFunction(Function& F) { 1138 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1139 DT = &getAnalysis<DominatorTree>(); 1140 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1141 VN.setMemDep(MD); 1142 VN.setDomTree(DT); 1143 1144 bool changed = false; 1145 bool shouldContinue = true; 1146 1147 // Merge unconditional branches, allowing PRE to catch more 1148 // optimization opportunities. 1149 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1150 BasicBlock* BB = FI; 1151 ++FI; 1152 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1153 if (removedBlock) NumGVNBlocks++; 1154 1155 changed |= removedBlock; 1156 } 1157 1158 while (shouldContinue) { 1159 shouldContinue = iterateOnFunction(F); 1160 changed |= shouldContinue; 1161 } 1162 1163 if (EnablePRE) { 1164 bool PREChanged = true; 1165 while (PREChanged) { 1166 PREChanged = performPRE(F); 1167 changed |= PREChanged; 1168 } 1169 } 1170 1171 cleanupGlobalSets(); 1172 1173 return changed; 1174} 1175 1176 1177bool GVN::processBlock(DomTreeNode* DTN) { 1178 BasicBlock* BB = DTN->getBlock(); 1179 SmallVector<Instruction*, 8> toErase; 1180 DenseMap<Value*, LoadInst*> lastSeenLoad; 1181 bool changed_function = false; 1182 1183 if (DTN->getIDom()) 1184 localAvail[BB] = 1185 new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]); 1186 else 1187 localAvail[BB] = new ValueNumberScope(0); 1188 1189 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1190 BI != BE;) { 1191 changed_function |= processInstruction(BI, lastSeenLoad, toErase); 1192 if (toErase.empty()) { 1193 ++BI; 1194 continue; 1195 } 1196 1197 // If we need some instructions deleted, do it now. 1198 NumGVNInstr += toErase.size(); 1199 1200 // Avoid iterator invalidation. 1201 bool AtStart = BI == BB->begin(); 1202 if (!AtStart) 1203 --BI; 1204 1205 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1206 E = toErase.end(); I != E; ++I) { 1207 DEBUG(cerr << "GVN removed: " << **I); 1208 MD->removeInstruction(*I); 1209 (*I)->eraseFromParent(); 1210 } 1211 1212 if (AtStart) 1213 BI = BB->begin(); 1214 else 1215 ++BI; 1216 1217 toErase.clear(); 1218 } 1219 1220 return changed_function; 1221} 1222 1223/// performPRE - Perform a purely local form of PRE that looks for diamond 1224/// control flow patterns and attempts to perform simple PRE at the join point. 1225bool GVN::performPRE(Function& F) { 1226 bool changed = false; 1227 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1228 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1229 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1230 BasicBlock* CurrentBlock = *DI; 1231 1232 // Nothing to PRE in the entry block. 1233 if (CurrentBlock == &F.getEntryBlock()) continue; 1234 1235 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1236 BE = CurrentBlock->end(); BI != BE; ) { 1237 if (isa<AllocationInst>(BI) || isa<TerminatorInst>(BI) || 1238 isa<PHINode>(BI) || BI->mayReadFromMemory() || 1239 BI->mayWriteToMemory()) { 1240 BI++; 1241 continue; 1242 } 1243 1244 uint32_t valno = VN.lookup(BI); 1245 1246 // Look for the predecessors for PRE opportunities. We're 1247 // only trying to solve the basic diamond case, where 1248 // a value is computed in the successor and one predecessor, 1249 // but not the other. We also explicitly disallow cases 1250 // where the successor is its own predecessor, because they're 1251 // more complicated to get right. 1252 unsigned numWith = 0; 1253 unsigned numWithout = 0; 1254 BasicBlock* PREPred = 0; 1255 DenseMap<BasicBlock*, Value*> predMap; 1256 for (pred_iterator PI = pred_begin(CurrentBlock), 1257 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1258 // We're not interested in PRE where the block is its 1259 // own predecessor, on in blocks with predecessors 1260 // that are not reachable. 1261 if (*PI == CurrentBlock) { 1262 numWithout = 2; 1263 break; 1264 } else if (!localAvail.count(*PI)) { 1265 numWithout = 2; 1266 break; 1267 } 1268 1269 DenseMap<uint32_t, Value*>::iterator predV = 1270 localAvail[*PI]->table.find(valno); 1271 if (predV == localAvail[*PI]->table.end()) { 1272 PREPred = *PI; 1273 numWithout++; 1274 } else if (predV->second == BI) { 1275 numWithout = 2; 1276 } else { 1277 predMap[*PI] = predV->second; 1278 numWith++; 1279 } 1280 } 1281 1282 // Don't do PRE when it might increase code size, i.e. when 1283 // we would need to insert instructions in more than one pred. 1284 if (numWithout != 1 || numWith == 0) { 1285 BI++; 1286 continue; 1287 } 1288 1289 // We can't do PRE safely on a critical edge, so instead we schedule 1290 // the edge to be split and perform the PRE the next time we iterate 1291 // on the function. 1292 unsigned succNum = 0; 1293 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1294 i != e; ++i) 1295 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 1296 succNum = i; 1297 break; 1298 } 1299 1300 if (isCriticalEdge(PREPred->getTerminator(), succNum)) { 1301 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum)); 1302 changed = true; 1303 BI++; 1304 continue; 1305 } 1306 1307 // Instantiate the expression the in predecessor that lacked it. 1308 // Because we are going top-down through the block, all value numbers 1309 // will be available in the predecessor by the time we need them. Any 1310 // that weren't original present will have been instantiated earlier 1311 // in this loop. 1312 Instruction* PREInstr = BI->clone(); 1313 bool success = true; 1314 for (unsigned i = 0; i < BI->getNumOperands(); ++i) { 1315 Value* op = BI->getOperand(i); 1316 if (isa<Argument>(op) || isa<Constant>(op) || isa<GlobalValue>(op)) 1317 PREInstr->setOperand(i, op); 1318 else { 1319 Value* V = lookupNumber(PREPred, VN.lookup(op)); 1320 if (!V) { 1321 success = false; 1322 break; 1323 } else 1324 PREInstr->setOperand(i, V); 1325 } 1326 } 1327 1328 // Fail out if we encounter an operand that is not available in 1329 // the PRE predecessor. This is typically because of loads which 1330 // are not value numbered precisely. 1331 if (!success) { 1332 delete PREInstr; 1333 BI++; 1334 continue; 1335 } 1336 1337 PREInstr->insertBefore(PREPred->getTerminator()); 1338 PREInstr->setName(BI->getName() + ".pre"); 1339 predMap[PREPred] = PREInstr; 1340 VN.add(PREInstr, valno); 1341 NumGVNPRE++; 1342 1343 // Update the availability map to include the new instruction. 1344 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr)); 1345 1346 // Create a PHI to make the value available in this block. 1347 PHINode* Phi = PHINode::Create(BI->getType(), 1348 BI->getName() + ".pre-phi", 1349 CurrentBlock->begin()); 1350 for (pred_iterator PI = pred_begin(CurrentBlock), 1351 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1352 Phi->addIncoming(predMap[*PI], *PI); 1353 1354 VN.add(Phi, valno); 1355 localAvail[CurrentBlock]->table[valno] = Phi; 1356 1357 BI->replaceAllUsesWith(Phi); 1358 VN.erase(BI); 1359 1360 Instruction* erase = BI; 1361 BI++; 1362 DEBUG(cerr << "GVN removed: " << *erase); 1363 MD->removeInstruction(erase); 1364 erase->eraseFromParent(); 1365 changed = true; 1366 } 1367 } 1368 1369 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 1370 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 1371 SplitCriticalEdge(I->first, I->second, this); 1372 1373 return changed || toSplit.size(); 1374} 1375 1376// iterateOnFunction - Executes one iteration of GVN 1377bool GVN::iterateOnFunction(Function &F) { 1378 cleanupGlobalSets(); 1379 1380 // Top-down walk of the dominator tree 1381 bool changed = false; 1382 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 1383 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 1384 changed |= processBlock(*DI); 1385 1386 return changed; 1387} 1388 1389void GVN::cleanupGlobalSets() { 1390 VN.clear(); 1391 phiMap.clear(); 1392 1393 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1394 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 1395 delete I->second; 1396 localAvail.clear(); 1397} 1398