GVN.cpp revision 241f65321efc6ad84ed875cd9494df8ca1cff309
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//===----------------------------------------------------------------------===// 14 15#define DEBUG_TYPE "gvn" 16#include "llvm/Transforms/Scalar.h" 17#include "llvm/BasicBlock.h" 18#include "llvm/Constants.h" 19#include "llvm/DerivedTypes.h" 20#include "llvm/Function.h" 21#include "llvm/IntrinsicInst.h" 22#include "llvm/Instructions.h" 23#include "llvm/ParameterAttributes.h" 24#include "llvm/Value.h" 25#include "llvm/ADT/DenseMap.h" 26#include "llvm/ADT/DepthFirstIterator.h" 27#include "llvm/ADT/SmallPtrSet.h" 28#include "llvm/ADT/SmallVector.h" 29#include "llvm/ADT/SparseBitVector.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/Support/GetElementPtrTypeIterator.h" 39#include "llvm/Target/TargetData.h" 40#include <list> 41using namespace llvm; 42 43STATISTIC(NumGVNInstr, "Number of instructions deleted"); 44STATISTIC(NumGVNLoad, "Number of loads deleted"); 45 46//===----------------------------------------------------------------------===// 47// ValueTable Class 48//===----------------------------------------------------------------------===// 49 50/// This class holds the mapping between values and value numbers. It is used 51/// as an efficient mechanism to determine the expression-wise equivalence of 52/// two values. 53namespace { 54 struct VISIBILITY_HIDDEN Expression { 55 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, 56 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 57 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 58 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 59 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 60 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 61 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 62 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 63 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 64 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, EMPTY, 65 TOMBSTONE }; 66 67 ExpressionOpcode opcode; 68 const Type* type; 69 uint32_t firstVN; 70 uint32_t secondVN; 71 uint32_t thirdVN; 72 SmallVector<uint32_t, 4> varargs; 73 Value* function; 74 75 Expression() { } 76 Expression(ExpressionOpcode o) : opcode(o) { } 77 78 bool operator==(const Expression &other) const { 79 if (opcode != other.opcode) 80 return false; 81 else if (opcode == EMPTY || opcode == TOMBSTONE) 82 return true; 83 else if (type != other.type) 84 return false; 85 else if (function != other.function) 86 return false; 87 else if (firstVN != other.firstVN) 88 return false; 89 else if (secondVN != other.secondVN) 90 return false; 91 else if (thirdVN != other.thirdVN) 92 return false; 93 else { 94 if (varargs.size() != other.varargs.size()) 95 return false; 96 97 for (size_t i = 0; i < varargs.size(); ++i) 98 if (varargs[i] != other.varargs[i]) 99 return false; 100 101 return true; 102 } 103 } 104 105 bool operator!=(const Expression &other) const { 106 if (opcode != other.opcode) 107 return true; 108 else if (opcode == EMPTY || opcode == TOMBSTONE) 109 return false; 110 else if (type != other.type) 111 return true; 112 else if (function != other.function) 113 return true; 114 else if (firstVN != other.firstVN) 115 return true; 116 else if (secondVN != other.secondVN) 117 return true; 118 else if (thirdVN != other.thirdVN) 119 return true; 120 else { 121 if (varargs.size() != other.varargs.size()) 122 return true; 123 124 for (size_t i = 0; i < varargs.size(); ++i) 125 if (varargs[i] != other.varargs[i]) 126 return true; 127 128 return false; 129 } 130 } 131 }; 132 133 class VISIBILITY_HIDDEN ValueTable { 134 private: 135 DenseMap<Value*, uint32_t> valueNumbering; 136 DenseMap<Expression, uint32_t> expressionNumbering; 137 AliasAnalysis* AA; 138 MemoryDependenceAnalysis* MD; 139 140 uint32_t nextValueNumber; 141 142 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 143 Expression::ExpressionOpcode getOpcode(CmpInst* C); 144 Expression::ExpressionOpcode getOpcode(CastInst* C); 145 Expression create_expression(BinaryOperator* BO); 146 Expression create_expression(CmpInst* C); 147 Expression create_expression(ShuffleVectorInst* V); 148 Expression create_expression(ExtractElementInst* C); 149 Expression create_expression(InsertElementInst* V); 150 Expression create_expression(SelectInst* V); 151 Expression create_expression(CastInst* C); 152 Expression create_expression(GetElementPtrInst* G); 153 Expression create_expression(CallInst* C); 154 public: 155 ValueTable() : nextValueNumber(1) { } 156 uint32_t lookup_or_add(Value* V); 157 uint32_t lookup(Value* V) const; 158 void add(Value* V, uint32_t num); 159 void clear(); 160 void erase(Value* v); 161 unsigned size(); 162 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 163 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 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)) { 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) && "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/// lookup_or_add - Returns the value number for the specified value, assigning 417/// it a new number if it did not have one before. 418uint32_t ValueTable::lookup_or_add(Value* V) { 419 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 420 if (VI != valueNumbering.end()) 421 return VI->second; 422 423 if (CallInst* C = dyn_cast<CallInst>(V)) { 424 if (AA->doesNotAccessMemory(C)) { 425 Expression e = create_expression(C); 426 427 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 428 if (EI != expressionNumbering.end()) { 429 valueNumbering.insert(std::make_pair(V, EI->second)); 430 return EI->second; 431 } else { 432 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 433 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 434 435 return nextValueNumber++; 436 } 437 } else if (AA->onlyReadsMemory(C)) { 438 Expression e = create_expression(C); 439 440 Instruction* dep = MD->getDependency(C); 441 442 if (dep == MemoryDependenceAnalysis::NonLocal || 443 !isa<CallInst>(dep)) { 444 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 445 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 446 447 return nextValueNumber++; 448 } 449 450 CallInst* cdep = cast<CallInst>(dep); 451 Expression d_exp = create_expression(cdep); 452 453 if (e != d_exp) { 454 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 455 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 456 457 return nextValueNumber++; 458 } else { 459 uint32_t v = expressionNumbering[d_exp]; 460 valueNumbering.insert(std::make_pair(V, v)); 461 return v; 462 } 463 464 } else { 465 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 466 return nextValueNumber++; 467 } 468 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 469 Expression e = create_expression(BO); 470 471 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 472 if (EI != expressionNumbering.end()) { 473 valueNumbering.insert(std::make_pair(V, EI->second)); 474 return EI->second; 475 } else { 476 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 477 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 478 479 return nextValueNumber++; 480 } 481 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 482 Expression e = create_expression(C); 483 484 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 485 if (EI != expressionNumbering.end()) { 486 valueNumbering.insert(std::make_pair(V, EI->second)); 487 return EI->second; 488 } else { 489 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 490 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 491 492 return nextValueNumber++; 493 } 494 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 495 Expression e = create_expression(U); 496 497 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 498 if (EI != expressionNumbering.end()) { 499 valueNumbering.insert(std::make_pair(V, EI->second)); 500 return EI->second; 501 } else { 502 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 503 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 504 505 return nextValueNumber++; 506 } 507 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 508 Expression e = create_expression(U); 509 510 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 511 if (EI != expressionNumbering.end()) { 512 valueNumbering.insert(std::make_pair(V, EI->second)); 513 return EI->second; 514 } else { 515 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 516 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 517 518 return nextValueNumber++; 519 } 520 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 521 Expression e = create_expression(U); 522 523 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 524 if (EI != expressionNumbering.end()) { 525 valueNumbering.insert(std::make_pair(V, EI->second)); 526 return EI->second; 527 } else { 528 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 529 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 530 531 return nextValueNumber++; 532 } 533 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 534 Expression e = create_expression(U); 535 536 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 537 if (EI != expressionNumbering.end()) { 538 valueNumbering.insert(std::make_pair(V, EI->second)); 539 return EI->second; 540 } else { 541 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 542 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 543 544 return nextValueNumber++; 545 } 546 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 547 Expression e = create_expression(U); 548 549 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 550 if (EI != expressionNumbering.end()) { 551 valueNumbering.insert(std::make_pair(V, EI->second)); 552 return EI->second; 553 } else { 554 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 555 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 556 557 return nextValueNumber++; 558 } 559 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 560 Expression e = create_expression(U); 561 562 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 563 if (EI != expressionNumbering.end()) { 564 valueNumbering.insert(std::make_pair(V, EI->second)); 565 return EI->second; 566 } else { 567 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 568 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 569 570 return nextValueNumber++; 571 } 572 } else { 573 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 574 return nextValueNumber++; 575 } 576} 577 578/// lookup - Returns the value number of the specified value. Fails if 579/// the value has not yet been numbered. 580uint32_t ValueTable::lookup(Value* V) const { 581 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 582 assert(VI != valueNumbering.end() && "Value not numbered?"); 583 return VI->second; 584} 585 586/// clear - Remove all entries from the ValueTable 587void ValueTable::clear() { 588 valueNumbering.clear(); 589 expressionNumbering.clear(); 590 nextValueNumber = 1; 591} 592 593/// erase - Remove a value from the value numbering 594void ValueTable::erase(Value* V) { 595 valueNumbering.erase(V); 596} 597 598//===----------------------------------------------------------------------===// 599// ValueNumberedSet Class 600//===----------------------------------------------------------------------===// 601namespace { 602class VISIBILITY_HIDDEN ValueNumberedSet { 603 private: 604 SmallPtrSet<Value*, 8> contents; 605 SparseBitVector<64> numbers; 606 public: 607 ValueNumberedSet() { } 608 ValueNumberedSet(const ValueNumberedSet& other) { 609 numbers = other.numbers; 610 contents = other.contents; 611 } 612 613 typedef SmallPtrSet<Value*, 8>::iterator iterator; 614 615 iterator begin() { return contents.begin(); } 616 iterator end() { return contents.end(); } 617 618 bool insert(Value* v) { return contents.insert(v); } 619 void insert(iterator I, iterator E) { contents.insert(I, E); } 620 void erase(Value* v) { contents.erase(v); } 621 unsigned count(Value* v) { return contents.count(v); } 622 size_t size() { return contents.size(); } 623 624 void set(unsigned i) { 625 numbers.set(i); 626 } 627 628 void operator=(const ValueNumberedSet& other) { 629 contents = other.contents; 630 numbers = other.numbers; 631 } 632 633 void reset(unsigned i) { 634 numbers.reset(i); 635 } 636 637 bool test(unsigned i) { 638 return numbers.test(i); 639 } 640}; 641} 642 643//===----------------------------------------------------------------------===// 644// GVN Pass 645//===----------------------------------------------------------------------===// 646 647namespace { 648 649 class VISIBILITY_HIDDEN GVN : public FunctionPass { 650 bool runOnFunction(Function &F); 651 public: 652 static char ID; // Pass identification, replacement for typeid 653 GVN() : FunctionPass((intptr_t)&ID) { } 654 655 private: 656 ValueTable VN; 657 658 DenseMap<BasicBlock*, ValueNumberedSet> availableOut; 659 660 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 661 PhiMapType phiMap; 662 663 664 // This transformation requires dominator postdominator info 665 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 666 AU.setPreservesCFG(); 667 AU.addRequired<DominatorTree>(); 668 AU.addRequired<MemoryDependenceAnalysis>(); 669 AU.addRequired<AliasAnalysis>(); 670 AU.addRequired<TargetData>(); 671 AU.addPreserved<AliasAnalysis>(); 672 AU.addPreserved<MemoryDependenceAnalysis>(); 673 AU.addPreserved<TargetData>(); 674 } 675 676 // Helper fuctions 677 // FIXME: eliminate or document these better 678 Value* find_leader(ValueNumberedSet& vals, uint32_t v) ; 679 void val_insert(ValueNumberedSet& s, Value* v); 680 bool processLoad(LoadInst* L, 681 DenseMap<Value*, LoadInst*> &lastLoad, 682 SmallVectorImpl<Instruction*> &toErase); 683 bool processInstruction(Instruction* I, 684 ValueNumberedSet& currAvail, 685 DenseMap<Value*, LoadInst*>& lastSeenLoad, 686 SmallVectorImpl<Instruction*> &toErase); 687 bool processNonLocalLoad(LoadInst* L, 688 SmallVectorImpl<Instruction*> &toErase); 689 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig, 690 DenseMap<BasicBlock*, Value*> &Phis, 691 bool top_level = false); 692 void dump(DenseMap<BasicBlock*, Value*>& d); 693 bool iterateOnFunction(Function &F); 694 Value* CollapsePhi(PHINode* p); 695 bool isSafeReplacement(PHINode* p, Instruction* inst); 696 }; 697 698 char GVN::ID = 0; 699} 700 701// createGVNPass - The public interface to this file... 702FunctionPass *llvm::createGVNPass() { return new GVN(); } 703 704static RegisterPass<GVN> X("gvn", 705 "Global Value Numbering"); 706 707/// find_leader - Given a set and a value number, return the first 708/// element of the set with that value number, or 0 if no such element 709/// is present 710Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) { 711 if (!vals.test(v)) 712 return 0; 713 714 for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end(); 715 I != E; ++I) 716 if (v == VN.lookup(*I)) 717 return *I; 718 719 assert(0 && "No leader found, but present bit is set?"); 720 return 0; 721} 722 723/// val_insert - Insert a value into a set only if there is not a value 724/// with the same value number already in the set 725void GVN::val_insert(ValueNumberedSet& s, Value* v) { 726 uint32_t num = VN.lookup(v); 727 if (!s.test(num)) 728 s.insert(v); 729} 730 731void GVN::dump(DenseMap<BasicBlock*, Value*>& d) { 732 printf("{\n"); 733 for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(), 734 E = d.end(); I != E; ++I) { 735 if (I->second == MemoryDependenceAnalysis::None) 736 printf("None\n"); 737 else 738 I->second->dump(); 739 } 740 printf("}\n"); 741} 742 743Value* GVN::CollapsePhi(PHINode* p) { 744 DominatorTree &DT = getAnalysis<DominatorTree>(); 745 Value* constVal = p->hasConstantValue(); 746 747 if (!constVal) return 0; 748 749 Instruction* inst = dyn_cast<Instruction>(constVal); 750 if (!inst) 751 return constVal; 752 753 if (DT.dominates(inst, p)) 754 if (isSafeReplacement(p, inst)) 755 return inst; 756 return 0; 757} 758 759bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 760 if (!isa<PHINode>(inst)) 761 return true; 762 763 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 764 UI != E; ++UI) 765 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 766 if (use_phi->getParent() == inst->getParent()) 767 return false; 768 769 return true; 770} 771 772/// GetValueForBlock - Get the value to use within the specified basic block. 773/// available values are in Phis. 774Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig, 775 DenseMap<BasicBlock*, Value*> &Phis, 776 bool top_level) { 777 778 // If we have already computed this value, return the previously computed val. 779 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 780 if (V != Phis.end() && !top_level) return V->second; 781 782 BasicBlock* singlePred = BB->getSinglePredecessor(); 783 if (singlePred) { 784 Value *ret = GetValueForBlock(singlePred, orig, Phis); 785 Phis[BB] = ret; 786 return ret; 787 } 788 789 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 790 // now, then get values to fill in the incoming values for the PHI. 791 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", 792 BB->begin()); 793 PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB))); 794 795 if (Phis.count(BB) == 0) 796 Phis.insert(std::make_pair(BB, PN)); 797 798 // Fill in the incoming values for the block. 799 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 800 Value* val = GetValueForBlock(*PI, orig, Phis); 801 PN->addIncoming(val, *PI); 802 } 803 804 AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); 805 AA.copyValue(orig, PN); 806 807 // Attempt to collapse PHI nodes that are trivially redundant 808 Value* v = CollapsePhi(PN); 809 if (!v) { 810 // Cache our phi construction results 811 phiMap[orig->getPointerOperand()].insert(PN); 812 return PN; 813 } 814 815 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 816 817 MD.removeInstruction(PN); 818 PN->replaceAllUsesWith(v); 819 820 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 821 E = Phis.end(); I != E; ++I) 822 if (I->second == PN) 823 I->second = v; 824 825 PN->eraseFromParent(); 826 827 Phis[BB] = v; 828 return v; 829} 830 831/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 832/// non-local by performing PHI construction. 833bool GVN::processNonLocalLoad(LoadInst* L, 834 SmallVectorImpl<Instruction*> &toErase) { 835 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 836 837 // Find the non-local dependencies of the load 838 DenseMap<BasicBlock*, Value*> deps; 839 MD.getNonLocalDependency(L, deps); 840 841 DenseMap<BasicBlock*, Value*> repl; 842 843 // Filter out useless results (non-locals, etc) 844 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end(); 845 I != E; ++I) { 846 if (I->second == MemoryDependenceAnalysis::None) 847 return false; 848 849 if (I->second == MemoryDependenceAnalysis::NonLocal) 850 continue; 851 852 if (StoreInst* S = dyn_cast<StoreInst>(I->second)) { 853 if (S->getPointerOperand() != L->getPointerOperand()) 854 return false; 855 repl[I->first] = S->getOperand(0); 856 } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) { 857 if (LD->getPointerOperand() != L->getPointerOperand()) 858 return false; 859 repl[I->first] = LD; 860 } else { 861 return false; 862 } 863 } 864 865 // Use cached PHI construction information from previous runs 866 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()]; 867 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 868 I != E; ++I) { 869 if ((*I)->getParent() == L->getParent()) { 870 MD.removeInstruction(L); 871 L->replaceAllUsesWith(*I); 872 toErase.push_back(L); 873 NumGVNLoad++; 874 return true; 875 } 876 877 repl.insert(std::make_pair((*I)->getParent(), *I)); 878 } 879 880 // Perform PHI construction 881 SmallPtrSet<BasicBlock*, 4> visited; 882 Value* v = GetValueForBlock(L->getParent(), L, repl, true); 883 884 MD.removeInstruction(L); 885 L->replaceAllUsesWith(v); 886 toErase.push_back(L); 887 NumGVNLoad++; 888 889 return true; 890} 891 892/// processLoad - Attempt to eliminate a load, first by eliminating it 893/// locally, and then attempting non-local elimination if that fails. 894bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad, 895 SmallVectorImpl<Instruction*> &toErase) { 896 if (L->isVolatile()) { 897 lastLoad[L->getPointerOperand()] = L; 898 return false; 899 } 900 901 Value* pointer = L->getPointerOperand(); 902 LoadInst*& last = lastLoad[pointer]; 903 904 // ... to a pointer that has been loaded from before... 905 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 906 bool removedNonLocal = false; 907 Instruction* dep = MD.getDependency(L); 908 if (dep == MemoryDependenceAnalysis::NonLocal && 909 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) { 910 removedNonLocal = processNonLocalLoad(L, toErase); 911 912 if (!removedNonLocal) 913 last = L; 914 915 return removedNonLocal; 916 } 917 918 919 bool deletedLoad = false; 920 921 // Walk up the dependency chain until we either find 922 // a dependency we can use, or we can't walk any further 923 while (dep != MemoryDependenceAnalysis::None && 924 dep != MemoryDependenceAnalysis::NonLocal && 925 (isa<LoadInst>(dep) || isa<StoreInst>(dep))) { 926 // ... that depends on a store ... 927 if (StoreInst* S = dyn_cast<StoreInst>(dep)) { 928 if (S->getPointerOperand() == pointer) { 929 // Remove it! 930 MD.removeInstruction(L); 931 932 L->replaceAllUsesWith(S->getOperand(0)); 933 toErase.push_back(L); 934 deletedLoad = true; 935 NumGVNLoad++; 936 } 937 938 // Whether we removed it or not, we can't 939 // go any further 940 break; 941 } else if (!last) { 942 // If we don't depend on a store, and we haven't 943 // been loaded before, bail. 944 break; 945 } else if (dep == last) { 946 // Remove it! 947 MD.removeInstruction(L); 948 949 L->replaceAllUsesWith(last); 950 toErase.push_back(L); 951 deletedLoad = true; 952 NumGVNLoad++; 953 954 break; 955 } else { 956 dep = MD.getDependency(L, dep); 957 } 958 } 959 960 if (dep != MemoryDependenceAnalysis::None && 961 dep != MemoryDependenceAnalysis::NonLocal && 962 isa<AllocationInst>(dep)) { 963 // Check that this load is actually from the 964 // allocation we found 965 Value* v = L->getOperand(0); 966 while (true) { 967 if (BitCastInst *BC = dyn_cast<BitCastInst>(v)) 968 v = BC->getOperand(0); 969 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v)) 970 v = GEP->getOperand(0); 971 else 972 break; 973 } 974 if (v == dep) { 975 // If this load depends directly on an allocation, there isn't 976 // anything stored there; therefore, we can optimize this load 977 // to undef. 978 MD.removeInstruction(L); 979 980 L->replaceAllUsesWith(UndefValue::get(L->getType())); 981 toErase.push_back(L); 982 deletedLoad = true; 983 NumGVNLoad++; 984 } 985 } 986 987 if (!deletedLoad) 988 last = L; 989 990 return deletedLoad; 991} 992 993/// processInstruction - When calculating availability, handle an instruction 994/// by inserting it into the appropriate sets 995bool GVN::processInstruction(Instruction *I, ValueNumberedSet &currAvail, 996 DenseMap<Value*, LoadInst*> &lastSeenLoad, 997 SmallVectorImpl<Instruction*> &toErase) { 998 if (LoadInst* L = dyn_cast<LoadInst>(I)) 999 return processLoad(L, lastSeenLoad, toErase); 1000 1001 // Allocations are always uniquely numbered, so we can save time and memory 1002 // by fast failing them. 1003 if (isa<AllocationInst>(I)) 1004 return false; 1005 1006 unsigned num = VN.lookup_or_add(I); 1007 1008 // Collapse PHI nodes 1009 if (PHINode* p = dyn_cast<PHINode>(I)) { 1010 Value* constVal = CollapsePhi(p); 1011 1012 if (constVal) { 1013 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1014 PI != PE; ++PI) 1015 if (PI->second.count(p)) 1016 PI->second.erase(p); 1017 1018 p->replaceAllUsesWith(constVal); 1019 toErase.push_back(p); 1020 } 1021 // Perform value-number based elimination 1022 } else if (currAvail.test(num)) { 1023 Value* repl = find_leader(currAvail, num); 1024 1025 // Remove it! 1026 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); 1027 MD.removeInstruction(I); 1028 1029 VN.erase(I); 1030 I->replaceAllUsesWith(repl); 1031 toErase.push_back(I); 1032 return true; 1033 } else if (!I->isTerminator()) { 1034 currAvail.set(num); 1035 currAvail.insert(I); 1036 } 1037 1038 return false; 1039} 1040 1041// GVN::runOnFunction - This is the main transformation entry point for a 1042// function. 1043// 1044bool GVN::runOnFunction(Function& F) { 1045 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1046 VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>()); 1047 1048 bool changed = false; 1049 bool shouldContinue = true; 1050 1051 while (shouldContinue) { 1052 shouldContinue = iterateOnFunction(F); 1053 changed |= shouldContinue; 1054 } 1055 1056 return changed; 1057} 1058 1059 1060// GVN::iterateOnFunction - Executes one iteration of GVN 1061bool GVN::iterateOnFunction(Function &F) { 1062 // Clean out global sets from any previous functions 1063 VN.clear(); 1064 availableOut.clear(); 1065 phiMap.clear(); 1066 1067 bool changed_function = false; 1068 1069 DominatorTree &DT = getAnalysis<DominatorTree>(); 1070 1071 SmallVector<Instruction*, 8> toErase; 1072 DenseMap<Value*, LoadInst*> lastSeenLoad; 1073 DenseMap<DomTreeNode*, size_t> numChildrenVisited; 1074 1075 // Top-down walk of the dominator tree 1076 for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()), 1077 E = df_end(DT.getRootNode()); DI != E; ++DI) { 1078 1079 // Get the set to update for this block 1080 ValueNumberedSet& currAvail = availableOut[DI->getBlock()]; 1081 lastSeenLoad.clear(); 1082 1083 BasicBlock* BB = DI->getBlock(); 1084 1085 // A block inherits AVAIL_OUT from its dominator 1086 if (DI->getIDom() != 0) { 1087 currAvail = availableOut[DI->getIDom()->getBlock()]; 1088 1089 numChildrenVisited[DI->getIDom()]++; 1090 1091 if (numChildrenVisited[DI->getIDom()] == DI->getIDom()->getNumChildren()) { 1092 availableOut.erase(DI->getIDom()->getBlock()); 1093 numChildrenVisited.erase(DI->getIDom()); 1094 } 1095 } 1096 1097 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1098 BI != BE;) { 1099 changed_function |= processInstruction(BI, currAvail, 1100 lastSeenLoad, toErase); 1101 if (toErase.empty()) { 1102 ++BI; 1103 continue; 1104 } 1105 1106 // If we need some instructions deleted, do it now. 1107 NumGVNInstr += toErase.size(); 1108 1109 // Avoid iterator invalidation. 1110 bool AtStart = BI == BB->begin(); 1111 if (!AtStart) 1112 --BI; 1113 1114 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1115 E = toErase.end(); I != E; ++I) 1116 (*I)->eraseFromParent(); 1117 1118 if (AtStart) 1119 BI = BB->begin(); 1120 else 1121 ++BI; 1122 1123 toErase.clear(); 1124 } 1125 } 1126 1127 return changed_function; 1128} 1129