GVN.cpp revision 246dbbb8befcb04abb5451d73b5d94f7d21f22c6
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/PostOrderIterator.h" 29#include "llvm/ADT/SmallPtrSet.h" 30#include "llvm/ADT/SmallVector.h" 31#include "llvm/ADT/Statistic.h" 32#include "llvm/Analysis/Dominators.h" 33#include "llvm/Analysis/AliasAnalysis.h" 34#include "llvm/Analysis/MemoryDependenceAnalysis.h" 35#include "llvm/Support/CFG.h" 36#include "llvm/Support/CommandLine.h" 37#include "llvm/Support/Compiler.h" 38#include "llvm/Support/Debug.h" 39#include "llvm/Transforms/Utils/BasicBlockUtils.h" 40#include <cstdio> 41using namespace llvm; 42 43STATISTIC(NumGVNInstr, "Number of instructions deleted"); 44STATISTIC(NumGVNLoad, "Number of loads deleted"); 45STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 46STATISTIC(NumGVNBlocks, "Number of blocks merged"); 47STATISTIC(NumPRELoad, "Number of loads PRE'd"); 48 49static cl::opt<bool> EnablePRE("enable-pre", 50 cl::init(true), cl::Hidden); 51cl::opt<bool> EnableLoadPRE("enable-load-pre"/*, cl::init(true)*/); 52 53//===----------------------------------------------------------------------===// 54// ValueTable Class 55//===----------------------------------------------------------------------===// 56 57/// This class holds the mapping between values and value numbers. It is used 58/// as an efficient mechanism to determine the expression-wise equivalence of 59/// two values. 60namespace { 61 struct VISIBILITY_HIDDEN Expression { 62 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, 63 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 64 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 65 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 66 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 67 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 68 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 69 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 70 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 71 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 72 EMPTY, TOMBSTONE }; 73 74 ExpressionOpcode opcode; 75 const Type* type; 76 uint32_t firstVN; 77 uint32_t secondVN; 78 uint32_t thirdVN; 79 SmallVector<uint32_t, 4> varargs; 80 Value* function; 81 82 Expression() { } 83 Expression(ExpressionOpcode o) : opcode(o) { } 84 85 bool operator==(const Expression &other) const { 86 if (opcode != other.opcode) 87 return false; 88 else if (opcode == EMPTY || opcode == TOMBSTONE) 89 return true; 90 else if (type != other.type) 91 return false; 92 else if (function != other.function) 93 return false; 94 else if (firstVN != other.firstVN) 95 return false; 96 else if (secondVN != other.secondVN) 97 return false; 98 else if (thirdVN != other.thirdVN) 99 return false; 100 else { 101 if (varargs.size() != other.varargs.size()) 102 return false; 103 104 for (size_t i = 0; i < varargs.size(); ++i) 105 if (varargs[i] != other.varargs[i]) 106 return false; 107 108 return true; 109 } 110 } 111 112 bool operator!=(const Expression &other) const { 113 if (opcode != other.opcode) 114 return true; 115 else if (opcode == EMPTY || opcode == TOMBSTONE) 116 return false; 117 else if (type != other.type) 118 return true; 119 else if (function != other.function) 120 return true; 121 else if (firstVN != other.firstVN) 122 return true; 123 else if (secondVN != other.secondVN) 124 return true; 125 else if (thirdVN != other.thirdVN) 126 return true; 127 else { 128 if (varargs.size() != other.varargs.size()) 129 return true; 130 131 for (size_t i = 0; i < varargs.size(); ++i) 132 if (varargs[i] != other.varargs[i]) 133 return true; 134 135 return false; 136 } 137 } 138 }; 139 140 class VISIBILITY_HIDDEN ValueTable { 141 private: 142 DenseMap<Value*, uint32_t> valueNumbering; 143 DenseMap<Expression, uint32_t> expressionNumbering; 144 AliasAnalysis* AA; 145 MemoryDependenceAnalysis* MD; 146 DominatorTree* DT; 147 148 uint32_t nextValueNumber; 149 150 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 151 Expression::ExpressionOpcode getOpcode(CmpInst* C); 152 Expression::ExpressionOpcode getOpcode(CastInst* C); 153 Expression create_expression(BinaryOperator* BO); 154 Expression create_expression(CmpInst* C); 155 Expression create_expression(ShuffleVectorInst* V); 156 Expression create_expression(ExtractElementInst* C); 157 Expression create_expression(InsertElementInst* V); 158 Expression create_expression(SelectInst* V); 159 Expression create_expression(CastInst* C); 160 Expression create_expression(GetElementPtrInst* G); 161 Expression create_expression(CallInst* C); 162 Expression create_expression(Constant* C); 163 public: 164 ValueTable() : nextValueNumber(1) { } 165 uint32_t lookup_or_add(Value* V); 166 uint32_t lookup(Value* V) const; 167 void add(Value* V, uint32_t num); 168 void clear(); 169 void erase(Value* v); 170 unsigned size(); 171 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 172 AliasAnalysis *getAliasAnalysis() const { return AA; } 173 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 174 void setDomTree(DominatorTree* D) { DT = D; } 175 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 176 void verifyRemoved(const Value *) const; 177 }; 178} 179 180namespace llvm { 181template <> struct DenseMapInfo<Expression> { 182 static inline Expression getEmptyKey() { 183 return Expression(Expression::EMPTY); 184 } 185 186 static inline Expression getTombstoneKey() { 187 return Expression(Expression::TOMBSTONE); 188 } 189 190 static unsigned getHashValue(const Expression e) { 191 unsigned hash = e.opcode; 192 193 hash = e.firstVN + hash * 37; 194 hash = e.secondVN + hash * 37; 195 hash = e.thirdVN + hash * 37; 196 197 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 198 (unsigned)((uintptr_t)e.type >> 9)) + 199 hash * 37; 200 201 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 202 E = e.varargs.end(); I != E; ++I) 203 hash = *I + hash * 37; 204 205 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 206 (unsigned)((uintptr_t)e.function >> 9)) + 207 hash * 37; 208 209 return hash; 210 } 211 static bool isEqual(const Expression &LHS, const Expression &RHS) { 212 return LHS == RHS; 213 } 214 static bool isPod() { return true; } 215}; 216} 217 218//===----------------------------------------------------------------------===// 219// ValueTable Internal Functions 220//===----------------------------------------------------------------------===// 221Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 222 switch(BO->getOpcode()) { 223 default: // THIS SHOULD NEVER HAPPEN 224 assert(0 && "Binary operator with unknown opcode?"); 225 case Instruction::Add: return Expression::ADD; 226 case Instruction::Sub: return Expression::SUB; 227 case Instruction::Mul: return Expression::MUL; 228 case Instruction::UDiv: return Expression::UDIV; 229 case Instruction::SDiv: return Expression::SDIV; 230 case Instruction::FDiv: return Expression::FDIV; 231 case Instruction::URem: return Expression::UREM; 232 case Instruction::SRem: return Expression::SREM; 233 case Instruction::FRem: return Expression::FREM; 234 case Instruction::Shl: return Expression::SHL; 235 case Instruction::LShr: return Expression::LSHR; 236 case Instruction::AShr: return Expression::ASHR; 237 case Instruction::And: return Expression::AND; 238 case Instruction::Or: return Expression::OR; 239 case Instruction::Xor: return Expression::XOR; 240 } 241} 242 243Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 244 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) { 245 switch (C->getPredicate()) { 246 default: // THIS SHOULD NEVER HAPPEN 247 assert(0 && "Comparison with unknown predicate?"); 248 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 249 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 250 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 251 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 252 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 253 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 254 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 255 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 256 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 257 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 258 } 259 } 260 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare"); 261 switch (C->getPredicate()) { 262 default: // THIS SHOULD NEVER HAPPEN 263 assert(0 && "Comparison with unknown predicate?"); 264 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 265 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 266 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 267 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 268 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 269 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 270 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 271 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 272 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 273 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 274 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 275 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 276 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 277 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 278 } 279} 280 281Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 282 switch(C->getOpcode()) { 283 default: // THIS SHOULD NEVER HAPPEN 284 assert(0 && "Cast operator with unknown opcode?"); 285 case Instruction::Trunc: return Expression::TRUNC; 286 case Instruction::ZExt: return Expression::ZEXT; 287 case Instruction::SExt: return Expression::SEXT; 288 case Instruction::FPToUI: return Expression::FPTOUI; 289 case Instruction::FPToSI: return Expression::FPTOSI; 290 case Instruction::UIToFP: return Expression::UITOFP; 291 case Instruction::SIToFP: return Expression::SITOFP; 292 case Instruction::FPTrunc: return Expression::FPTRUNC; 293 case Instruction::FPExt: return Expression::FPEXT; 294 case Instruction::PtrToInt: return Expression::PTRTOINT; 295 case Instruction::IntToPtr: return Expression::INTTOPTR; 296 case Instruction::BitCast: return Expression::BITCAST; 297 } 298} 299 300Expression ValueTable::create_expression(CallInst* C) { 301 Expression e; 302 303 e.type = C->getType(); 304 e.firstVN = 0; 305 e.secondVN = 0; 306 e.thirdVN = 0; 307 e.function = C->getCalledFunction(); 308 e.opcode = Expression::CALL; 309 310 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 311 I != E; ++I) 312 e.varargs.push_back(lookup_or_add(*I)); 313 314 return e; 315} 316 317Expression ValueTable::create_expression(BinaryOperator* BO) { 318 Expression e; 319 320 e.firstVN = lookup_or_add(BO->getOperand(0)); 321 e.secondVN = lookup_or_add(BO->getOperand(1)); 322 e.thirdVN = 0; 323 e.function = 0; 324 e.type = BO->getType(); 325 e.opcode = getOpcode(BO); 326 327 return e; 328} 329 330Expression ValueTable::create_expression(CmpInst* C) { 331 Expression e; 332 333 e.firstVN = lookup_or_add(C->getOperand(0)); 334 e.secondVN = lookup_or_add(C->getOperand(1)); 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(CastInst* C) { 344 Expression e; 345 346 e.firstVN = lookup_or_add(C->getOperand(0)); 347 e.secondVN = 0; 348 e.thirdVN = 0; 349 e.function = 0; 350 e.type = C->getType(); 351 e.opcode = getOpcode(C); 352 353 return e; 354} 355 356Expression ValueTable::create_expression(ShuffleVectorInst* S) { 357 Expression e; 358 359 e.firstVN = lookup_or_add(S->getOperand(0)); 360 e.secondVN = lookup_or_add(S->getOperand(1)); 361 e.thirdVN = lookup_or_add(S->getOperand(2)); 362 e.function = 0; 363 e.type = S->getType(); 364 e.opcode = Expression::SHUFFLE; 365 366 return e; 367} 368 369Expression ValueTable::create_expression(ExtractElementInst* E) { 370 Expression e; 371 372 e.firstVN = lookup_or_add(E->getOperand(0)); 373 e.secondVN = lookup_or_add(E->getOperand(1)); 374 e.thirdVN = 0; 375 e.function = 0; 376 e.type = E->getType(); 377 e.opcode = Expression::EXTRACT; 378 379 return e; 380} 381 382Expression ValueTable::create_expression(InsertElementInst* I) { 383 Expression e; 384 385 e.firstVN = lookup_or_add(I->getOperand(0)); 386 e.secondVN = lookup_or_add(I->getOperand(1)); 387 e.thirdVN = lookup_or_add(I->getOperand(2)); 388 e.function = 0; 389 e.type = I->getType(); 390 e.opcode = Expression::INSERT; 391 392 return e; 393} 394 395Expression ValueTable::create_expression(SelectInst* I) { 396 Expression e; 397 398 e.firstVN = lookup_or_add(I->getCondition()); 399 e.secondVN = lookup_or_add(I->getTrueValue()); 400 e.thirdVN = lookup_or_add(I->getFalseValue()); 401 e.function = 0; 402 e.type = I->getType(); 403 e.opcode = Expression::SELECT; 404 405 return e; 406} 407 408Expression ValueTable::create_expression(GetElementPtrInst* G) { 409 Expression e; 410 411 e.firstVN = lookup_or_add(G->getPointerOperand()); 412 e.secondVN = 0; 413 e.thirdVN = 0; 414 e.function = 0; 415 e.type = G->getType(); 416 e.opcode = Expression::GEP; 417 418 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 419 I != E; ++I) 420 e.varargs.push_back(lookup_or_add(*I)); 421 422 return e; 423} 424 425//===----------------------------------------------------------------------===// 426// ValueTable External Functions 427//===----------------------------------------------------------------------===// 428 429/// add - Insert a value into the table with a specified value number. 430void ValueTable::add(Value* V, uint32_t num) { 431 valueNumbering.insert(std::make_pair(V, num)); 432} 433 434/// lookup_or_add - Returns the value number for the specified value, assigning 435/// it a new number if it did not have one before. 436uint32_t ValueTable::lookup_or_add(Value* V) { 437 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 438 if (VI != valueNumbering.end()) 439 return VI->second; 440 441 if (CallInst* C = dyn_cast<CallInst>(V)) { 442 if (AA->doesNotAccessMemory(C)) { 443 Expression e = create_expression(C); 444 445 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 446 if (EI != expressionNumbering.end()) { 447 valueNumbering.insert(std::make_pair(V, EI->second)); 448 return EI->second; 449 } else { 450 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 451 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 452 453 return nextValueNumber++; 454 } 455 } else if (AA->onlyReadsMemory(C)) { 456 Expression e = create_expression(C); 457 458 if (expressionNumbering.find(e) == expressionNumbering.end()) { 459 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 460 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 461 return nextValueNumber++; 462 } 463 464 MemDepResult local_dep = MD->getDependency(C); 465 466 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 467 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 468 return nextValueNumber++; 469 } 470 471 if (local_dep.isDef()) { 472 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 473 474 if (local_cdep->getNumOperands() != C->getNumOperands()) { 475 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 476 return nextValueNumber++; 477 } 478 479 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 480 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 481 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 482 if (c_vn != cd_vn) { 483 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 484 return nextValueNumber++; 485 } 486 } 487 488 uint32_t v = lookup_or_add(local_cdep); 489 valueNumbering.insert(std::make_pair(V, v)); 490 return v; 491 } 492 493 // Non-local case. 494 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 495 MD->getNonLocalCallDependency(CallSite(C)); 496 // FIXME: call/call dependencies for readonly calls should return def, not 497 // clobber! Move the checking logic to MemDep! 498 CallInst* cdep = 0; 499 500 // Check to see if we have a single dominating call instruction that is 501 // identical to C. 502 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 503 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i]; 504 // Ignore non-local dependencies. 505 if (I->second.isNonLocal()) 506 continue; 507 508 // We don't handle non-depedencies. If we already have a call, reject 509 // instruction dependencies. 510 if (I->second.isClobber() || cdep != 0) { 511 cdep = 0; 512 break; 513 } 514 515 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst()); 516 // FIXME: All duplicated with non-local case. 517 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){ 518 cdep = NonLocalDepCall; 519 continue; 520 } 521 522 cdep = 0; 523 break; 524 } 525 526 if (!cdep) { 527 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 528 return nextValueNumber++; 529 } 530 531 if (cdep->getNumOperands() != C->getNumOperands()) { 532 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 533 return nextValueNumber++; 534 } 535 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 536 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 537 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 538 if (c_vn != cd_vn) { 539 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 540 return nextValueNumber++; 541 } 542 } 543 544 uint32_t v = lookup_or_add(cdep); 545 valueNumbering.insert(std::make_pair(V, v)); 546 return v; 547 548 } else { 549 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 550 return nextValueNumber++; 551 } 552 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 553 Expression e = create_expression(BO); 554 555 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 556 if (EI != expressionNumbering.end()) { 557 valueNumbering.insert(std::make_pair(V, EI->second)); 558 return EI->second; 559 } else { 560 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 561 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 562 563 return nextValueNumber++; 564 } 565 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 566 Expression e = create_expression(C); 567 568 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 569 if (EI != expressionNumbering.end()) { 570 valueNumbering.insert(std::make_pair(V, EI->second)); 571 return EI->second; 572 } else { 573 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 574 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 575 576 return nextValueNumber++; 577 } 578 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 579 Expression e = create_expression(U); 580 581 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 582 if (EI != expressionNumbering.end()) { 583 valueNumbering.insert(std::make_pair(V, EI->second)); 584 return EI->second; 585 } else { 586 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 587 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 588 589 return nextValueNumber++; 590 } 591 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 592 Expression e = create_expression(U); 593 594 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 595 if (EI != expressionNumbering.end()) { 596 valueNumbering.insert(std::make_pair(V, EI->second)); 597 return EI->second; 598 } else { 599 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 600 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 601 602 return nextValueNumber++; 603 } 604 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 605 Expression e = create_expression(U); 606 607 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 608 if (EI != expressionNumbering.end()) { 609 valueNumbering.insert(std::make_pair(V, EI->second)); 610 return EI->second; 611 } else { 612 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 613 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 614 615 return nextValueNumber++; 616 } 617 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 618 Expression e = create_expression(U); 619 620 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 621 if (EI != expressionNumbering.end()) { 622 valueNumbering.insert(std::make_pair(V, EI->second)); 623 return EI->second; 624 } else { 625 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 626 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 627 628 return nextValueNumber++; 629 } 630 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 631 Expression e = create_expression(U); 632 633 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 634 if (EI != expressionNumbering.end()) { 635 valueNumbering.insert(std::make_pair(V, EI->second)); 636 return EI->second; 637 } else { 638 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 639 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 640 641 return nextValueNumber++; 642 } 643 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 644 Expression e = create_expression(U); 645 646 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 647 if (EI != expressionNumbering.end()) { 648 valueNumbering.insert(std::make_pair(V, EI->second)); 649 return EI->second; 650 } else { 651 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 652 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 653 654 return nextValueNumber++; 655 } 656 } else { 657 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 658 return nextValueNumber++; 659 } 660} 661 662/// lookup - Returns the value number of the specified value. Fails if 663/// the value has not yet been numbered. 664uint32_t ValueTable::lookup(Value* V) const { 665 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 666 assert(VI != valueNumbering.end() && "Value not numbered?"); 667 return VI->second; 668} 669 670/// clear - Remove all entries from the ValueTable 671void ValueTable::clear() { 672 valueNumbering.clear(); 673 expressionNumbering.clear(); 674 nextValueNumber = 1; 675} 676 677/// erase - Remove a value from the value numbering 678void ValueTable::erase(Value* V) { 679 valueNumbering.erase(V); 680} 681 682/// verifyRemoved - Verify that the value is removed from all internal data 683/// structures. 684void ValueTable::verifyRemoved(const Value *V) const { 685 for (DenseMap<Value*, uint32_t>::iterator 686 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 687 assert(I->first != V && "Inst still occurs in value numbering map!"); 688 } 689} 690 691//===----------------------------------------------------------------------===// 692// GVN Pass 693//===----------------------------------------------------------------------===// 694 695namespace { 696 struct VISIBILITY_HIDDEN ValueNumberScope { 697 ValueNumberScope* parent; 698 DenseMap<uint32_t, Value*> table; 699 700 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 701 }; 702} 703 704namespace { 705 706 class VISIBILITY_HIDDEN GVN : public FunctionPass { 707 bool runOnFunction(Function &F); 708 public: 709 static char ID; // Pass identification, replacement for typeid 710 GVN() : FunctionPass(&ID) { } 711 712 private: 713 MemoryDependenceAnalysis *MD; 714 DominatorTree *DT; 715 716 ValueTable VN; 717 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 718 719 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 720 PhiMapType phiMap; 721 722 723 // This transformation requires dominator postdominator info 724 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 725 AU.addRequired<DominatorTree>(); 726 AU.addRequired<MemoryDependenceAnalysis>(); 727 AU.addRequired<AliasAnalysis>(); 728 729 AU.addPreserved<DominatorTree>(); 730 AU.addPreserved<AliasAnalysis>(); 731 } 732 733 // Helper fuctions 734 // FIXME: eliminate or document these better 735 bool processLoad(LoadInst* L, 736 SmallVectorImpl<Instruction*> &toErase); 737 bool processInstruction(Instruction* I, 738 SmallVectorImpl<Instruction*> &toErase); 739 bool processNonLocalLoad(LoadInst* L, 740 SmallVectorImpl<Instruction*> &toErase); 741 bool processBlock(BasicBlock* BB); 742 Value *GetValueForBlock(BasicBlock *BB, Instruction* 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 Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno); 753 void cleanupGlobalSets(); 754 void verifyRemoved(const Instruction *I) const; 755 }; 756 757 char GVN::ID = 0; 758} 759 760// createGVNPass - The public interface to this file... 761FunctionPass *llvm::createGVNPass() { return new GVN(); } 762 763static RegisterPass<GVN> X("gvn", 764 "Global Value Numbering"); 765 766void GVN::dump(DenseMap<uint32_t, Value*>& d) { 767 printf("{\n"); 768 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 769 E = d.end(); I != E; ++I) { 770 printf("%d\n", I->first); 771 I->second->dump(); 772 } 773 printf("}\n"); 774} 775 776Value* GVN::CollapsePhi(PHINode* p) { 777 Value* constVal = p->hasConstantValue(); 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, Instruction* 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 (!DT->isReachableFromEntry(BB)) 816 return Phis[BB] = UndefValue::get(orig->getType()); 817 818 if (BasicBlock *Pred = BB->getSinglePredecessor()) { 819 Value *ret = GetValueForBlock(Pred, orig, Phis); 820 Phis[BB] = ret; 821 return ret; 822 } 823 824 // Get the number of predecessors of this block so we can reserve space later. 825 // If there is already a PHI in it, use the #preds from it, otherwise count. 826 // Getting it from the PHI is constant time. 827 unsigned NumPreds; 828 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin())) 829 NumPreds = ExistingPN->getNumIncomingValues(); 830 else 831 NumPreds = std::distance(pred_begin(BB), pred_end(BB)); 832 833 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 834 // now, then get values to fill in the incoming values for the PHI. 835 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", 836 BB->begin()); 837 PN->reserveOperandSpace(NumPreds); 838 839 Phis.insert(std::make_pair(BB, PN)); 840 841 // Fill in the incoming values for the block. 842 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 843 Value* val = GetValueForBlock(*PI, orig, Phis); 844 PN->addIncoming(val, *PI); 845 } 846 847 VN.getAliasAnalysis()->copyValue(orig, PN); 848 849 // Attempt to collapse PHI nodes that are trivially redundant 850 Value* v = CollapsePhi(PN); 851 if (!v) { 852 // Cache our phi construction results 853 if (LoadInst* L = dyn_cast<LoadInst>(orig)) 854 phiMap[L->getPointerOperand()].insert(PN); 855 else 856 phiMap[orig].insert(PN); 857 858 return PN; 859 } 860 861 PN->replaceAllUsesWith(v); 862 if (isa<PointerType>(v->getType())) 863 MD->invalidateCachedPointerInfo(v); 864 865 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 866 E = Phis.end(); I != E; ++I) 867 if (I->second == PN) 868 I->second = v; 869 870 DEBUG(cerr << "GVN removed: " << *PN); 871 MD->removeInstruction(PN); 872 PN->eraseFromParent(); 873 DEBUG(verifyRemoved(PN)); 874 875 Phis[BB] = v; 876 return v; 877} 878 879/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 880/// we're analyzing is fully available in the specified block. As we go, keep 881/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 882/// map is actually a tri-state map with the following values: 883/// 0) we know the block *is not* fully available. 884/// 1) we know the block *is* fully available. 885/// 2) we do not know whether the block is fully available or not, but we are 886/// currently speculating that it will be. 887/// 3) we are speculating for this block and have used that to speculate for 888/// other blocks. 889static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 890 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 891 // Optimistically assume that the block is fully available and check to see 892 // if we already know about this block in one lookup. 893 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 894 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 895 896 // If the entry already existed for this block, return the precomputed value. 897 if (!IV.second) { 898 // If this is a speculative "available" value, mark it as being used for 899 // speculation of other blocks. 900 if (IV.first->second == 2) 901 IV.first->second = 3; 902 return IV.first->second != 0; 903 } 904 905 // Otherwise, see if it is fully available in all predecessors. 906 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 907 908 // If this block has no predecessors, it isn't live-in here. 909 if (PI == PE) 910 goto SpeculationFailure; 911 912 for (; PI != PE; ++PI) 913 // If the value isn't fully available in one of our predecessors, then it 914 // isn't fully available in this block either. Undo our previous 915 // optimistic assumption and bail out. 916 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 917 goto SpeculationFailure; 918 919 return true; 920 921// SpeculationFailure - If we get here, we found out that this is not, after 922// all, a fully-available block. We have a problem if we speculated on this and 923// used the speculation to mark other blocks as available. 924SpeculationFailure: 925 char &BBVal = FullyAvailableBlocks[BB]; 926 927 // If we didn't speculate on this, just return with it set to false. 928 if (BBVal == 2) { 929 BBVal = 0; 930 return false; 931 } 932 933 // If we did speculate on this value, we could have blocks set to 1 that are 934 // incorrect. Walk the (transitive) successors of this block and mark them as 935 // 0 if set to one. 936 SmallVector<BasicBlock*, 32> BBWorklist; 937 BBWorklist.push_back(BB); 938 939 while (!BBWorklist.empty()) { 940 BasicBlock *Entry = BBWorklist.pop_back_val(); 941 // Note that this sets blocks to 0 (unavailable) if they happen to not 942 // already be in FullyAvailableBlocks. This is safe. 943 char &EntryVal = FullyAvailableBlocks[Entry]; 944 if (EntryVal == 0) continue; // Already unavailable. 945 946 // Mark as unavailable. 947 EntryVal = 0; 948 949 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 950 BBWorklist.push_back(*I); 951 } 952 953 return false; 954} 955 956/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 957/// non-local by performing PHI construction. 958bool GVN::processNonLocalLoad(LoadInst *LI, 959 SmallVectorImpl<Instruction*> &toErase) { 960 // Find the non-local dependencies of the load. 961 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; 962 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 963 Deps); 964 //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI); 965 966 // If we had to process more than one hundred blocks to find the 967 // dependencies, this load isn't worth worrying about. Optimizing 968 // it will be too expensive. 969 if (Deps.size() > 100) 970 return false; 971 972 // If we had a phi translation failure, we'll have a single entry which is a 973 // clobber in the current block. Reject this early. 974 if (Deps.size() == 1 && Deps[0].second.isClobber()) 975 return false; 976 977 // Filter out useless results (non-locals, etc). Keep track of the blocks 978 // where we have a value available in repl, also keep track of whether we see 979 // dependencies that produce an unknown value for the load (such as a call 980 // that could potentially clobber the load). 981 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock; 982 SmallVector<BasicBlock*, 16> UnavailableBlocks; 983 984 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 985 BasicBlock *DepBB = Deps[i].first; 986 MemDepResult DepInfo = Deps[i].second; 987 988 if (DepInfo.isClobber()) { 989 UnavailableBlocks.push_back(DepBB); 990 continue; 991 } 992 993 Instruction *DepInst = DepInfo.getInst(); 994 995 // Loading the allocation -> undef. 996 if (isa<AllocationInst>(DepInst)) { 997 ValuesPerBlock.push_back(std::make_pair(DepBB, 998 UndefValue::get(LI->getType()))); 999 continue; 1000 } 1001 1002 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) { 1003 // Reject loads and stores that are to the same address but are of 1004 // different types. 1005 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because 1006 // of bitfield access, it would be interesting to optimize for it at some 1007 // point. 1008 if (S->getOperand(0)->getType() != LI->getType()) { 1009 UnavailableBlocks.push_back(DepBB); 1010 continue; 1011 } 1012 1013 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0))); 1014 1015 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) { 1016 if (LD->getType() != LI->getType()) { 1017 UnavailableBlocks.push_back(DepBB); 1018 continue; 1019 } 1020 ValuesPerBlock.push_back(std::make_pair(DepBB, LD)); 1021 } else { 1022 UnavailableBlocks.push_back(DepBB); 1023 continue; 1024 } 1025 } 1026 1027 // If we have no predecessors that produce a known value for this load, exit 1028 // early. 1029 if (ValuesPerBlock.empty()) return false; 1030 1031 // If all of the instructions we depend on produce a known value for this 1032 // load, then it is fully redundant and we can use PHI insertion to compute 1033 // its value. Insert PHIs and remove the fully redundant value now. 1034 if (UnavailableBlocks.empty()) { 1035 // Use cached PHI construction information from previous runs 1036 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1037 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated? 1038 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1039 I != E; ++I) { 1040 if ((*I)->getParent() == LI->getParent()) { 1041 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI); 1042 LI->replaceAllUsesWith(*I); 1043 if (isa<PointerType>((*I)->getType())) 1044 MD->invalidateCachedPointerInfo(*I); 1045 toErase.push_back(LI); 1046 NumGVNLoad++; 1047 return true; 1048 } 1049 1050 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I)); 1051 } 1052 1053 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI); 1054 1055 DenseMap<BasicBlock*, Value*> BlockReplValues; 1056 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end()); 1057 // Perform PHI construction. 1058 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1059 LI->replaceAllUsesWith(v); 1060 1061 if (!isa<GlobalValue>(v)) 1062 v->takeName(LI); 1063 if (isa<PointerType>(v->getType())) 1064 MD->invalidateCachedPointerInfo(v); 1065 toErase.push_back(LI); 1066 NumGVNLoad++; 1067 return true; 1068 } 1069 1070 if (!EnablePRE || !EnableLoadPRE) 1071 return false; 1072 1073 // Okay, we have *some* definitions of the value. This means that the value 1074 // is available in some of our (transitive) predecessors. Lets think about 1075 // doing PRE of this load. This will involve inserting a new load into the 1076 // predecessor when it's not available. We could do this in general, but 1077 // prefer to not increase code size. As such, we only do this when we know 1078 // that we only have to insert *one* load (which means we're basically moving 1079 // the load, not inserting a new one). 1080 1081 // Everything we do here is based on local predecessors of LI's block. If it 1082 // only has one predecessor, bail now. 1083 BasicBlock *LoadBB = LI->getParent(); 1084 if (LoadBB->getSinglePredecessor()) 1085 return false; 1086 1087 // If we have a repl set with LI itself in it, this means we have a loop where 1088 // at least one of the values is LI. Since this means that we won't be able 1089 // to eliminate LI even if we insert uses in the other predecessors, we will 1090 // end up increasing code size. Reject this by scanning for LI. 1091 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1092 if (ValuesPerBlock[i].second == LI) 1093 return false; 1094 1095 // Okay, we have some hope :). Check to see if the loaded value is fully 1096 // available in all but one predecessor. 1097 // FIXME: If we could restructure the CFG, we could make a common pred with 1098 // all the preds that don't have an available LI and insert a new load into 1099 // that one block. 1100 BasicBlock *UnavailablePred = 0; 1101 1102 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1103 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1104 FullyAvailableBlocks[ValuesPerBlock[i].first] = true; 1105 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1106 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1107 1108 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1109 PI != E; ++PI) { 1110 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 1111 continue; 1112 1113 // If this load is not available in multiple predecessors, reject it. 1114 if (UnavailablePred && UnavailablePred != *PI) 1115 return false; 1116 UnavailablePred = *PI; 1117 } 1118 1119 assert(UnavailablePred != 0 && 1120 "Fully available value should be eliminated above!"); 1121 1122 // If the loaded pointer is PHI node defined in this block, do PHI translation 1123 // to get its value in the predecessor. 1124 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred); 1125 1126 // Make sure the value is live in the predecessor. If it was defined by a 1127 // non-PHI instruction in this block, we don't know how to recompute it above. 1128 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr)) 1129 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) { 1130 DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: " 1131 << *LPInst << *LI << "\n"); 1132 return false; 1133 } 1134 1135 // We don't currently handle critical edges :( 1136 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) { 1137 DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '" 1138 << UnavailablePred->getName() << "': " << *LI); 1139 return false; 1140 } 1141 1142 // Okay, we can eliminate this load by inserting a reload in the predecessor 1143 // and using PHI construction to get the value in the other predecessors, do 1144 // it. 1145 DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI); 1146 1147 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1148 LI->getAlignment(), 1149 UnavailablePred->getTerminator()); 1150 1151 DenseMap<BasicBlock*, Value*> BlockReplValues; 1152 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end()); 1153 BlockReplValues[UnavailablePred] = NewLoad; 1154 1155 // Perform PHI construction. 1156 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1157 LI->replaceAllUsesWith(v); 1158 if (!isa<GlobalValue>(v)) 1159 v->takeName(LI); 1160 if (isa<PointerType>(v->getType())) 1161 MD->invalidateCachedPointerInfo(v); 1162 toErase.push_back(LI); 1163 NumPRELoad++; 1164 return true; 1165} 1166 1167/// processLoad - Attempt to eliminate a load, first by eliminating it 1168/// locally, and then attempting non-local elimination if that fails. 1169bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1170 if (L->isVolatile()) 1171 return false; 1172 1173 Value* pointer = L->getPointerOperand(); 1174 1175 // ... to a pointer that has been loaded from before... 1176 MemDepResult dep = MD->getDependency(L); 1177 1178 // If the value isn't available, don't do anything! 1179 if (dep.isClobber()) 1180 return false; 1181 1182 // If it is defined in another block, try harder. 1183 if (dep.isNonLocal()) 1184 return processNonLocalLoad(L, toErase); 1185 1186 Instruction *DepInst = dep.getInst(); 1187 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1188 // Only forward substitute stores to loads of the same type. 1189 // FIXME: Could do better! 1190 if (DepSI->getPointerOperand()->getType() != pointer->getType()) 1191 return false; 1192 1193 // Remove it! 1194 L->replaceAllUsesWith(DepSI->getOperand(0)); 1195 if (isa<PointerType>(DepSI->getOperand(0)->getType())) 1196 MD->invalidateCachedPointerInfo(DepSI->getOperand(0)); 1197 toErase.push_back(L); 1198 NumGVNLoad++; 1199 return true; 1200 } 1201 1202 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1203 // Only forward substitute stores to loads of the same type. 1204 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian. 1205 if (DepLI->getType() != L->getType()) 1206 return false; 1207 1208 // Remove it! 1209 L->replaceAllUsesWith(DepLI); 1210 if (isa<PointerType>(DepLI->getType())) 1211 MD->invalidateCachedPointerInfo(DepLI); 1212 toErase.push_back(L); 1213 NumGVNLoad++; 1214 return true; 1215 } 1216 1217 // If this load really doesn't depend on anything, then we must be loading an 1218 // undef value. This can happen when loading for a fresh allocation with no 1219 // intervening stores, for example. 1220 if (isa<AllocationInst>(DepInst)) { 1221 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1222 toErase.push_back(L); 1223 NumGVNLoad++; 1224 return true; 1225 } 1226 1227 return false; 1228} 1229 1230Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) { 1231 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1232 if (I == localAvail.end()) 1233 return 0; 1234 1235 ValueNumberScope* locals = I->second; 1236 1237 while (locals) { 1238 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num); 1239 if (I != locals->table.end()) 1240 return I->second; 1241 else 1242 locals = locals->parent; 1243 } 1244 1245 return 0; 1246} 1247 1248/// AttemptRedundancyElimination - If the "fast path" of redundancy elimination 1249/// by inheritance from the dominator fails, see if we can perform phi 1250/// construction to eliminate the redundancy. 1251Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) { 1252 BasicBlock* BaseBlock = orig->getParent(); 1253 1254 SmallPtrSet<BasicBlock*, 4> Visited; 1255 SmallVector<BasicBlock*, 8> Stack; 1256 Stack.push_back(BaseBlock); 1257 1258 DenseMap<BasicBlock*, Value*> Results; 1259 1260 // Walk backwards through our predecessors, looking for instances of the 1261 // value number we're looking for. Instances are recorded in the Results 1262 // map, which is then used to perform phi construction. 1263 while (!Stack.empty()) { 1264 BasicBlock* Current = Stack.back(); 1265 Stack.pop_back(); 1266 1267 // If we've walked all the way to a proper dominator, then give up. Cases 1268 // where the instance is in the dominator will have been caught by the fast 1269 // path, and any cases that require phi construction further than this are 1270 // probably not worth it anyways. Note that this is a SIGNIFICANT compile 1271 // time improvement. 1272 if (DT->properlyDominates(Current, orig->getParent())) return 0; 1273 1274 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA = 1275 localAvail.find(Current); 1276 if (LA == localAvail.end()) return 0; 1277 DenseMap<unsigned, Value*>::iterator V = LA->second->table.find(valno); 1278 1279 if (V != LA->second->table.end()) { 1280 // Found an instance, record it. 1281 Results.insert(std::make_pair(Current, V->second)); 1282 continue; 1283 } 1284 1285 // If we reach the beginning of the function, then give up. 1286 if (pred_begin(Current) == pred_end(Current)) 1287 return 0; 1288 1289 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current); 1290 PI != PE; ++PI) 1291 if (Visited.insert(*PI)) 1292 Stack.push_back(*PI); 1293 } 1294 1295 // If we didn't find instances, give up. Otherwise, perform phi construction. 1296 if (Results.size() == 0) 1297 return 0; 1298 else 1299 return GetValueForBlock(BaseBlock, orig, Results, true); 1300} 1301 1302/// processInstruction - When calculating availability, handle an instruction 1303/// by inserting it into the appropriate sets 1304bool GVN::processInstruction(Instruction *I, 1305 SmallVectorImpl<Instruction*> &toErase) { 1306 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1307 bool changed = processLoad(L, toErase); 1308 1309 if (!changed) { 1310 unsigned num = VN.lookup_or_add(L); 1311 localAvail[I->getParent()]->table.insert(std::make_pair(num, L)); 1312 } 1313 1314 return changed; 1315 } 1316 1317 uint32_t nextNum = VN.getNextUnusedValueNumber(); 1318 unsigned num = VN.lookup_or_add(I); 1319 1320 // Allocations are always uniquely numbered, so we can save time and memory 1321 // by fast failing them. 1322 if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1323 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1324 return false; 1325 } 1326 1327 // Collapse PHI nodes 1328 if (PHINode* p = dyn_cast<PHINode>(I)) { 1329 Value* constVal = CollapsePhi(p); 1330 1331 if (constVal) { 1332 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1333 PI != PE; ++PI) 1334 PI->second.erase(p); 1335 1336 p->replaceAllUsesWith(constVal); 1337 if (isa<PointerType>(constVal->getType())) 1338 MD->invalidateCachedPointerInfo(constVal); 1339 toErase.push_back(p); 1340 } else { 1341 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1342 } 1343 1344 // If the number we were assigned was a brand new VN, then we don't 1345 // need to do a lookup to see if the number already exists 1346 // somewhere in the domtree: it can't! 1347 } else if (num == nextNum) { 1348 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1349 1350 // Perform fast-path value-number based elimination of values inherited from 1351 // dominators. 1352 } else if (Value* repl = lookupNumber(I->getParent(), num)) { 1353 // Remove it! 1354 VN.erase(I); 1355 I->replaceAllUsesWith(repl); 1356 if (isa<PointerType>(repl->getType())) 1357 MD->invalidateCachedPointerInfo(repl); 1358 toErase.push_back(I); 1359 return true; 1360 1361#if 0 1362 // Perform slow-pathvalue-number based elimination with phi construction. 1363 } else if (Value* repl = AttemptRedundancyElimination(I, num)) { 1364 // Remove it! 1365 VN.erase(I); 1366 I->replaceAllUsesWith(repl); 1367 if (isa<PointerType>(repl->getType())) 1368 MD->invalidateCachedPointerInfo(repl); 1369 toErase.push_back(I); 1370 return true; 1371#endif 1372 } else { 1373 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1374 } 1375 1376 return false; 1377} 1378 1379// GVN::runOnFunction - This is the main transformation entry point for a 1380// function. 1381// 1382bool GVN::runOnFunction(Function& F) { 1383 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1384 DT = &getAnalysis<DominatorTree>(); 1385 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1386 VN.setMemDep(MD); 1387 VN.setDomTree(DT); 1388 1389 bool changed = false; 1390 bool shouldContinue = true; 1391 1392 // Merge unconditional branches, allowing PRE to catch more 1393 // optimization opportunities. 1394 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1395 BasicBlock* BB = FI; 1396 ++FI; 1397 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1398 if (removedBlock) NumGVNBlocks++; 1399 1400 changed |= removedBlock; 1401 } 1402 1403 unsigned Iteration = 0; 1404 1405 while (shouldContinue) { 1406 DEBUG(cerr << "GVN iteration: " << Iteration << "\n"); 1407 shouldContinue = iterateOnFunction(F); 1408 changed |= shouldContinue; 1409 ++Iteration; 1410 } 1411 1412 if (EnablePRE) { 1413 bool PREChanged = true; 1414 while (PREChanged) { 1415 PREChanged = performPRE(F); 1416 changed |= PREChanged; 1417 } 1418 } 1419 // FIXME: Should perform GVN again after PRE does something. PRE can move 1420 // computations into blocks where they become fully redundant. Note that 1421 // we can't do this until PRE's critical edge splitting updates memdep. 1422 // Actually, when this happens, we should just fully integrate PRE into GVN. 1423 1424 cleanupGlobalSets(); 1425 1426 return changed; 1427} 1428 1429 1430bool GVN::processBlock(BasicBlock* BB) { 1431 DomTreeNode* DTN = DT->getNode(BB); 1432 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1433 // incrementing BI before processing an instruction). 1434 SmallVector<Instruction*, 8> toErase; 1435 bool changed_function = false; 1436 1437 if (DTN->getIDom()) 1438 localAvail[BB] = 1439 new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]); 1440 else 1441 localAvail[BB] = new ValueNumberScope(0); 1442 1443 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1444 BI != BE;) { 1445 changed_function |= processInstruction(BI, toErase); 1446 if (toErase.empty()) { 1447 ++BI; 1448 continue; 1449 } 1450 1451 // If we need some instructions deleted, do it now. 1452 NumGVNInstr += toErase.size(); 1453 1454 // Avoid iterator invalidation. 1455 bool AtStart = BI == BB->begin(); 1456 if (!AtStart) 1457 --BI; 1458 1459 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1460 E = toErase.end(); I != E; ++I) { 1461 DEBUG(cerr << "GVN removed: " << **I); 1462 MD->removeInstruction(*I); 1463 (*I)->eraseFromParent(); 1464 } 1465 toErase.clear(); 1466 1467 if (AtStart) 1468 BI = BB->begin(); 1469 else 1470 ++BI; 1471 } 1472 1473 return changed_function; 1474} 1475 1476/// performPRE - Perform a purely local form of PRE that looks for diamond 1477/// control flow patterns and attempts to perform simple PRE at the join point. 1478bool GVN::performPRE(Function& F) { 1479 bool Changed = false; 1480 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1481 DenseMap<BasicBlock*, Value*> predMap; 1482 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1483 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1484 BasicBlock* CurrentBlock = *DI; 1485 1486 // Nothing to PRE in the entry block. 1487 if (CurrentBlock == &F.getEntryBlock()) continue; 1488 1489 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1490 BE = CurrentBlock->end(); BI != BE; ) { 1491 Instruction *CurInst = BI++; 1492 1493 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) || 1494 isa<PHINode>(CurInst) || CurInst->mayReadFromMemory() || 1495 CurInst->mayWriteToMemory()) 1496 continue; 1497 1498 uint32_t valno = VN.lookup(CurInst); 1499 1500 // Look for the predecessors for PRE opportunities. We're 1501 // only trying to solve the basic diamond case, where 1502 // a value is computed in the successor and one predecessor, 1503 // but not the other. We also explicitly disallow cases 1504 // where the successor is its own predecessor, because they're 1505 // more complicated to get right. 1506 unsigned numWith = 0; 1507 unsigned numWithout = 0; 1508 BasicBlock* PREPred = 0; 1509 predMap.clear(); 1510 1511 for (pred_iterator PI = pred_begin(CurrentBlock), 1512 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1513 // We're not interested in PRE where the block is its 1514 // own predecessor, on in blocks with predecessors 1515 // that are not reachable. 1516 if (*PI == CurrentBlock) { 1517 numWithout = 2; 1518 break; 1519 } else if (!localAvail.count(*PI)) { 1520 numWithout = 2; 1521 break; 1522 } 1523 1524 DenseMap<uint32_t, Value*>::iterator predV = 1525 localAvail[*PI]->table.find(valno); 1526 if (predV == localAvail[*PI]->table.end()) { 1527 PREPred = *PI; 1528 numWithout++; 1529 } else if (predV->second == CurInst) { 1530 numWithout = 2; 1531 } else { 1532 predMap[*PI] = predV->second; 1533 numWith++; 1534 } 1535 } 1536 1537 // Don't do PRE when it might increase code size, i.e. when 1538 // we would need to insert instructions in more than one pred. 1539 if (numWithout != 1 || numWith == 0) 1540 continue; 1541 1542 // We can't do PRE safely on a critical edge, so instead we schedule 1543 // the edge to be split and perform the PRE the next time we iterate 1544 // on the function. 1545 unsigned succNum = 0; 1546 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1547 i != e; ++i) 1548 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 1549 succNum = i; 1550 break; 1551 } 1552 1553 if (isCriticalEdge(PREPred->getTerminator(), succNum)) { 1554 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum)); 1555 continue; 1556 } 1557 1558 // Instantiate the expression the in predecessor that lacked it. 1559 // Because we are going top-down through the block, all value numbers 1560 // will be available in the predecessor by the time we need them. Any 1561 // that weren't original present will have been instantiated earlier 1562 // in this loop. 1563 Instruction* PREInstr = CurInst->clone(); 1564 bool success = true; 1565 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 1566 Value *Op = PREInstr->getOperand(i); 1567 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 1568 continue; 1569 1570 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 1571 PREInstr->setOperand(i, V); 1572 } else { 1573 success = false; 1574 break; 1575 } 1576 } 1577 1578 // Fail out if we encounter an operand that is not available in 1579 // the PRE predecessor. This is typically because of loads which 1580 // are not value numbered precisely. 1581 if (!success) { 1582 delete PREInstr; 1583 continue; 1584 } 1585 1586 PREInstr->insertBefore(PREPred->getTerminator()); 1587 PREInstr->setName(CurInst->getName() + ".pre"); 1588 predMap[PREPred] = PREInstr; 1589 VN.add(PREInstr, valno); 1590 NumGVNPRE++; 1591 1592 // Update the availability map to include the new instruction. 1593 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr)); 1594 1595 // Create a PHI to make the value available in this block. 1596 PHINode* Phi = PHINode::Create(CurInst->getType(), 1597 CurInst->getName() + ".pre-phi", 1598 CurrentBlock->begin()); 1599 for (pred_iterator PI = pred_begin(CurrentBlock), 1600 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1601 Phi->addIncoming(predMap[*PI], *PI); 1602 1603 VN.add(Phi, valno); 1604 localAvail[CurrentBlock]->table[valno] = Phi; 1605 1606 CurInst->replaceAllUsesWith(Phi); 1607 if (isa<PointerType>(Phi->getType())) 1608 MD->invalidateCachedPointerInfo(Phi); 1609 VN.erase(CurInst); 1610 1611 DEBUG(cerr << "GVN PRE removed: " << *CurInst); 1612 MD->removeInstruction(CurInst); 1613 CurInst->eraseFromParent(); 1614 Changed = true; 1615 } 1616 } 1617 1618 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 1619 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 1620 SplitCriticalEdge(I->first, I->second, this); 1621 1622 return Changed || toSplit.size(); 1623} 1624 1625// iterateOnFunction - Executes one iteration of GVN 1626bool GVN::iterateOnFunction(Function &F) { 1627 cleanupGlobalSets(); 1628 1629 // Top-down walk of the dominator tree 1630 bool changed = false; 1631#if 0 1632 // Needed for value numbering with phi construction to work. 1633 ReversePostOrderTraversal<Function*> RPOT(&F); 1634 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 1635 RE = RPOT.end(); RI != RE; ++RI) 1636 changed |= processBlock(*RI); 1637#else 1638 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 1639 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 1640 changed |= processBlock(DI->getBlock()); 1641#endif 1642 1643 return changed; 1644} 1645 1646void GVN::cleanupGlobalSets() { 1647 VN.clear(); 1648 phiMap.clear(); 1649 1650 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1651 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 1652 delete I->second; 1653 localAvail.clear(); 1654} 1655 1656/// verifyRemoved - Verify that the specified instruction does not occur in our 1657/// internal data structures. 1658void GVN::verifyRemoved(const Instruction *I) const { 1659 VN.verifyRemoved(I); 1660} 1661