GVN.cpp revision ae3a0be92e33bc716722aa600983fc1535acb122
145afe016bed87b9c6946184709058b39ede3f77ajwong@chromium.org//===- GVN.cpp - Eliminate redundant values and loads ---------------------===// 245afe016bed87b9c6946184709058b39ede3f77ajwong@chromium.org// 345afe016bed87b9c6946184709058b39ede3f77ajwong@chromium.org// The LLVM Compiler Infrastructure 445afe016bed87b9c6946184709058b39ede3f77ajwong@chromium.org// 545afe016bed87b9c6946184709058b39ede3f77ajwong@chromium.org// This file is distributed under the University of Illinois Open Source 645afe016bed87b9c6946184709058b39ede3f77ajwong@chromium.org// 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/IntrinsicInst.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, FADD, SUB, FSUB, MUL, FMUL, 63 UDIV, SDIV, FDIV, UREM, SREM, 64 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 65 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 66 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 67 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 68 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 69 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 70 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 71 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 72 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 73 EMPTY, TOMBSTONE }; 74 75 ExpressionOpcode opcode; 76 const Type* type; 77 uint32_t firstVN; 78 uint32_t secondVN; 79 uint32_t thirdVN; 80 SmallVector<uint32_t, 4> varargs; 81 Value* function; 82 83 Expression() { } 84 Expression(ExpressionOpcode o) : opcode(o) { } 85 86 bool operator==(const Expression &other) const { 87 if (opcode != other.opcode) 88 return false; 89 else if (opcode == EMPTY || opcode == TOMBSTONE) 90 return true; 91 else if (type != other.type) 92 return false; 93 else if (function != other.function) 94 return false; 95 else if (firstVN != other.firstVN) 96 return false; 97 else if (secondVN != other.secondVN) 98 return false; 99 else if (thirdVN != other.thirdVN) 100 return false; 101 else { 102 if (varargs.size() != other.varargs.size()) 103 return false; 104 105 for (size_t i = 0; i < varargs.size(); ++i) 106 if (varargs[i] != other.varargs[i]) 107 return false; 108 109 return true; 110 } 111 } 112 113 bool operator!=(const Expression &other) const { 114 return !(*this == other); 115 } 116 }; 117 118 class VISIBILITY_HIDDEN ValueTable { 119 private: 120 DenseMap<Value*, uint32_t> valueNumbering; 121 DenseMap<Expression, uint32_t> expressionNumbering; 122 AliasAnalysis* AA; 123 MemoryDependenceAnalysis* MD; 124 DominatorTree* DT; 125 126 uint32_t nextValueNumber; 127 128 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 129 Expression::ExpressionOpcode getOpcode(CmpInst* C); 130 Expression::ExpressionOpcode getOpcode(CastInst* C); 131 Expression create_expression(BinaryOperator* BO); 132 Expression create_expression(CmpInst* C); 133 Expression create_expression(ShuffleVectorInst* V); 134 Expression create_expression(ExtractElementInst* C); 135 Expression create_expression(InsertElementInst* V); 136 Expression create_expression(SelectInst* V); 137 Expression create_expression(CastInst* C); 138 Expression create_expression(GetElementPtrInst* G); 139 Expression create_expression(CallInst* C); 140 Expression create_expression(Constant* C); 141 public: 142 ValueTable() : nextValueNumber(1) { } 143 uint32_t lookup_or_add(Value* V); 144 uint32_t lookup(Value* V) const; 145 void add(Value* V, uint32_t num); 146 void clear(); 147 void erase(Value* v); 148 unsigned size(); 149 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 150 AliasAnalysis *getAliasAnalysis() const { return AA; } 151 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 152 void setDomTree(DominatorTree* D) { DT = D; } 153 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 154 void verifyRemoved(const Value *) const; 155 }; 156} 157 158namespace llvm { 159template <> struct DenseMapInfo<Expression> { 160 static inline Expression getEmptyKey() { 161 return Expression(Expression::EMPTY); 162 } 163 164 static inline Expression getTombstoneKey() { 165 return Expression(Expression::TOMBSTONE); 166 } 167 168 static unsigned getHashValue(const Expression e) { 169 unsigned hash = e.opcode; 170 171 hash = e.firstVN + hash * 37; 172 hash = e.secondVN + hash * 37; 173 hash = e.thirdVN + hash * 37; 174 175 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 176 (unsigned)((uintptr_t)e.type >> 9)) + 177 hash * 37; 178 179 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 180 E = e.varargs.end(); I != E; ++I) 181 hash = *I + hash * 37; 182 183 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 184 (unsigned)((uintptr_t)e.function >> 9)) + 185 hash * 37; 186 187 return hash; 188 } 189 static bool isEqual(const Expression &LHS, const Expression &RHS) { 190 return LHS == RHS; 191 } 192 static bool isPod() { return true; } 193}; 194} 195 196//===----------------------------------------------------------------------===// 197// ValueTable Internal Functions 198//===----------------------------------------------------------------------===// 199Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 200 switch(BO->getOpcode()) { 201 default: // THIS SHOULD NEVER HAPPEN 202 assert(0 && "Binary operator with unknown opcode?"); 203 case Instruction::Add: return Expression::ADD; 204 case Instruction::FAdd: return Expression::FADD; 205 case Instruction::Sub: return Expression::SUB; 206 case Instruction::FSub: return Expression::FSUB; 207 case Instruction::Mul: return Expression::MUL; 208 case Instruction::FMul: return Expression::FMUL; 209 case Instruction::UDiv: return Expression::UDIV; 210 case Instruction::SDiv: return Expression::SDIV; 211 case Instruction::FDiv: return Expression::FDIV; 212 case Instruction::URem: return Expression::UREM; 213 case Instruction::SRem: return Expression::SREM; 214 case Instruction::FRem: return Expression::FREM; 215 case Instruction::Shl: return Expression::SHL; 216 case Instruction::LShr: return Expression::LSHR; 217 case Instruction::AShr: return Expression::ASHR; 218 case Instruction::And: return Expression::AND; 219 case Instruction::Or: return Expression::OR; 220 case Instruction::Xor: return Expression::XOR; 221 } 222} 223 224Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 225 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) { 226 switch (C->getPredicate()) { 227 default: // THIS SHOULD NEVER HAPPEN 228 assert(0 && "Comparison with unknown predicate?"); 229 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 230 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 231 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 232 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 233 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 234 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 235 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 236 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 237 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 238 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 239 } 240 } 241 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare"); 242 switch (C->getPredicate()) { 243 default: // THIS SHOULD NEVER HAPPEN 244 assert(0 && "Comparison with unknown predicate?"); 245 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 246 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 247 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 248 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 249 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 250 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 251 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 252 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 253 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 254 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 255 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 256 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 257 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 258 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 259 } 260} 261 262Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 263 switch(C->getOpcode()) { 264 default: // THIS SHOULD NEVER HAPPEN 265 assert(0 && "Cast operator with unknown opcode?"); 266 case Instruction::Trunc: return Expression::TRUNC; 267 case Instruction::ZExt: return Expression::ZEXT; 268 case Instruction::SExt: return Expression::SEXT; 269 case Instruction::FPToUI: return Expression::FPTOUI; 270 case Instruction::FPToSI: return Expression::FPTOSI; 271 case Instruction::UIToFP: return Expression::UITOFP; 272 case Instruction::SIToFP: return Expression::SITOFP; 273 case Instruction::FPTrunc: return Expression::FPTRUNC; 274 case Instruction::FPExt: return Expression::FPEXT; 275 case Instruction::PtrToInt: return Expression::PTRTOINT; 276 case Instruction::IntToPtr: return Expression::INTTOPTR; 277 case Instruction::BitCast: return Expression::BITCAST; 278 } 279} 280 281Expression ValueTable::create_expression(CallInst* C) { 282 Expression e; 283 284 e.type = C->getType(); 285 e.firstVN = 0; 286 e.secondVN = 0; 287 e.thirdVN = 0; 288 e.function = C->getCalledFunction(); 289 e.opcode = Expression::CALL; 290 291 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 292 I != E; ++I) 293 e.varargs.push_back(lookup_or_add(*I)); 294 295 return e; 296} 297 298Expression ValueTable::create_expression(BinaryOperator* BO) { 299 Expression e; 300 301 e.firstVN = lookup_or_add(BO->getOperand(0)); 302 e.secondVN = lookup_or_add(BO->getOperand(1)); 303 e.thirdVN = 0; 304 e.function = 0; 305 e.type = BO->getType(); 306 e.opcode = getOpcode(BO); 307 308 return e; 309} 310 311Expression ValueTable::create_expression(CmpInst* C) { 312 Expression e; 313 314 e.firstVN = lookup_or_add(C->getOperand(0)); 315 e.secondVN = lookup_or_add(C->getOperand(1)); 316 e.thirdVN = 0; 317 e.function = 0; 318 e.type = C->getType(); 319 e.opcode = getOpcode(C); 320 321 return e; 322} 323 324Expression ValueTable::create_expression(CastInst* C) { 325 Expression e; 326 327 e.firstVN = lookup_or_add(C->getOperand(0)); 328 e.secondVN = 0; 329 e.thirdVN = 0; 330 e.function = 0; 331 e.type = C->getType(); 332 e.opcode = getOpcode(C); 333 334 return e; 335} 336 337Expression ValueTable::create_expression(ShuffleVectorInst* S) { 338 Expression e; 339 340 e.firstVN = lookup_or_add(S->getOperand(0)); 341 e.secondVN = lookup_or_add(S->getOperand(1)); 342 e.thirdVN = lookup_or_add(S->getOperand(2)); 343 e.function = 0; 344 e.type = S->getType(); 345 e.opcode = Expression::SHUFFLE; 346 347 return e; 348} 349 350Expression ValueTable::create_expression(ExtractElementInst* E) { 351 Expression e; 352 353 e.firstVN = lookup_or_add(E->getOperand(0)); 354 e.secondVN = lookup_or_add(E->getOperand(1)); 355 e.thirdVN = 0; 356 e.function = 0; 357 e.type = E->getType(); 358 e.opcode = Expression::EXTRACT; 359 360 return e; 361} 362 363Expression ValueTable::create_expression(InsertElementInst* I) { 364 Expression e; 365 366 e.firstVN = lookup_or_add(I->getOperand(0)); 367 e.secondVN = lookup_or_add(I->getOperand(1)); 368 e.thirdVN = lookup_or_add(I->getOperand(2)); 369 e.function = 0; 370 e.type = I->getType(); 371 e.opcode = Expression::INSERT; 372 373 return e; 374} 375 376Expression ValueTable::create_expression(SelectInst* I) { 377 Expression e; 378 379 e.firstVN = lookup_or_add(I->getCondition()); 380 e.secondVN = lookup_or_add(I->getTrueValue()); 381 e.thirdVN = lookup_or_add(I->getFalseValue()); 382 e.function = 0; 383 e.type = I->getType(); 384 e.opcode = Expression::SELECT; 385 386 return e; 387} 388 389Expression ValueTable::create_expression(GetElementPtrInst* G) { 390 Expression e; 391 392 e.firstVN = lookup_or_add(G->getPointerOperand()); 393 e.secondVN = 0; 394 e.thirdVN = 0; 395 e.function = 0; 396 e.type = G->getType(); 397 e.opcode = Expression::GEP; 398 399 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 400 I != E; ++I) 401 e.varargs.push_back(lookup_or_add(*I)); 402 403 return e; 404} 405 406//===----------------------------------------------------------------------===// 407// ValueTable External Functions 408//===----------------------------------------------------------------------===// 409 410/// add - Insert a value into the table with a specified value number. 411void ValueTable::add(Value* V, uint32_t num) { 412 valueNumbering.insert(std::make_pair(V, num)); 413} 414 415/// lookup_or_add - Returns the value number for the specified value, assigning 416/// it a new number if it did not have one before. 417uint32_t ValueTable::lookup_or_add(Value* V) { 418 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 419 if (VI != valueNumbering.end()) 420 return VI->second; 421 422 if (CallInst* C = dyn_cast<CallInst>(V)) { 423 if (AA->doesNotAccessMemory(C)) { 424 Expression e = create_expression(C); 425 426 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 427 if (EI != expressionNumbering.end()) { 428 valueNumbering.insert(std::make_pair(V, EI->second)); 429 return EI->second; 430 } else { 431 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 432 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 433 434 return nextValueNumber++; 435 } 436 } else if (AA->onlyReadsMemory(C)) { 437 Expression e = create_expression(C); 438 439 if (expressionNumbering.find(e) == expressionNumbering.end()) { 440 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 441 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 442 return nextValueNumber++; 443 } 444 445 MemDepResult local_dep = MD->getDependency(C); 446 447 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 448 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 449 return nextValueNumber++; 450 } 451 452 if (local_dep.isDef()) { 453 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 454 455 if (local_cdep->getNumOperands() != C->getNumOperands()) { 456 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 457 return nextValueNumber++; 458 } 459 460 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 461 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 462 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 463 if (c_vn != cd_vn) { 464 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 465 return nextValueNumber++; 466 } 467 } 468 469 uint32_t v = lookup_or_add(local_cdep); 470 valueNumbering.insert(std::make_pair(V, v)); 471 return v; 472 } 473 474 // Non-local case. 475 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 476 MD->getNonLocalCallDependency(CallSite(C)); 477 // FIXME: call/call dependencies for readonly calls should return def, not 478 // clobber! Move the checking logic to MemDep! 479 CallInst* cdep = 0; 480 481 // Check to see if we have a single dominating call instruction that is 482 // identical to C. 483 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 484 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i]; 485 // Ignore non-local dependencies. 486 if (I->second.isNonLocal()) 487 continue; 488 489 // We don't handle non-depedencies. If we already have a call, reject 490 // instruction dependencies. 491 if (I->second.isClobber() || cdep != 0) { 492 cdep = 0; 493 break; 494 } 495 496 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst()); 497 // FIXME: All duplicated with non-local case. 498 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){ 499 cdep = NonLocalDepCall; 500 continue; 501 } 502 503 cdep = 0; 504 break; 505 } 506 507 if (!cdep) { 508 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 509 return nextValueNumber++; 510 } 511 512 if (cdep->getNumOperands() != C->getNumOperands()) { 513 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 514 return nextValueNumber++; 515 } 516 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 517 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 518 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 519 if (c_vn != cd_vn) { 520 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 521 return nextValueNumber++; 522 } 523 } 524 525 uint32_t v = lookup_or_add(cdep); 526 valueNumbering.insert(std::make_pair(V, v)); 527 return v; 528 529 } else { 530 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 531 return nextValueNumber++; 532 } 533 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 534 Expression e = create_expression(BO); 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 (CmpInst* C = dyn_cast<CmpInst>(V)) { 547 Expression e = create_expression(C); 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 (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(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 if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 573 Expression e = create_expression(U); 574 575 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 576 if (EI != expressionNumbering.end()) { 577 valueNumbering.insert(std::make_pair(V, EI->second)); 578 return EI->second; 579 } else { 580 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 581 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 582 583 return nextValueNumber++; 584 } 585 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 586 Expression e = create_expression(U); 587 588 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 589 if (EI != expressionNumbering.end()) { 590 valueNumbering.insert(std::make_pair(V, EI->second)); 591 return EI->second; 592 } else { 593 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 594 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 595 596 return nextValueNumber++; 597 } 598 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 599 Expression e = create_expression(U); 600 601 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 602 if (EI != expressionNumbering.end()) { 603 valueNumbering.insert(std::make_pair(V, EI->second)); 604 return EI->second; 605 } else { 606 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 607 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 608 609 return nextValueNumber++; 610 } 611 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 612 Expression e = create_expression(U); 613 614 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 615 if (EI != expressionNumbering.end()) { 616 valueNumbering.insert(std::make_pair(V, EI->second)); 617 return EI->second; 618 } else { 619 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 620 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 621 622 return nextValueNumber++; 623 } 624 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 625 Expression e = create_expression(U); 626 627 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 628 if (EI != expressionNumbering.end()) { 629 valueNumbering.insert(std::make_pair(V, EI->second)); 630 return EI->second; 631 } else { 632 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 633 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 634 635 return nextValueNumber++; 636 } 637 } else { 638 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 639 return nextValueNumber++; 640 } 641} 642 643/// lookup - Returns the value number of the specified value. Fails if 644/// the value has not yet been numbered. 645uint32_t ValueTable::lookup(Value* V) const { 646 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 647 assert(VI != valueNumbering.end() && "Value not numbered?"); 648 return VI->second; 649} 650 651/// clear - Remove all entries from the ValueTable 652void ValueTable::clear() { 653 valueNumbering.clear(); 654 expressionNumbering.clear(); 655 nextValueNumber = 1; 656} 657 658/// erase - Remove a value from the value numbering 659void ValueTable::erase(Value* V) { 660 valueNumbering.erase(V); 661} 662 663/// verifyRemoved - Verify that the value is removed from all internal data 664/// structures. 665void ValueTable::verifyRemoved(const Value *V) const { 666 for (DenseMap<Value*, uint32_t>::iterator 667 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 668 assert(I->first != V && "Inst still occurs in value numbering map!"); 669 } 670} 671 672//===----------------------------------------------------------------------===// 673// GVN Pass 674//===----------------------------------------------------------------------===// 675 676namespace { 677 struct VISIBILITY_HIDDEN ValueNumberScope { 678 ValueNumberScope* parent; 679 DenseMap<uint32_t, Value*> table; 680 681 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 682 }; 683} 684 685namespace { 686 687 class VISIBILITY_HIDDEN GVN : public FunctionPass { 688 bool runOnFunction(Function &F); 689 public: 690 static char ID; // Pass identification, replacement for typeid 691 GVN() : FunctionPass(&ID) { } 692 693 private: 694 MemoryDependenceAnalysis *MD; 695 DominatorTree *DT; 696 697 ValueTable VN; 698 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 699 700 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 701 PhiMapType phiMap; 702 703 704 // This transformation requires dominator postdominator info 705 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 706 AU.addRequired<DominatorTree>(); 707 AU.addRequired<MemoryDependenceAnalysis>(); 708 AU.addRequired<AliasAnalysis>(); 709 710 AU.addPreserved<DominatorTree>(); 711 AU.addPreserved<AliasAnalysis>(); 712 } 713 714 // Helper fuctions 715 // FIXME: eliminate or document these better 716 bool processLoad(LoadInst* L, 717 SmallVectorImpl<Instruction*> &toErase); 718 bool processInstruction(Instruction* I, 719 SmallVectorImpl<Instruction*> &toErase); 720 bool processNonLocalLoad(LoadInst* L, 721 SmallVectorImpl<Instruction*> &toErase); 722 bool processBlock(BasicBlock* BB); 723 Value *GetValueForBlock(BasicBlock *BB, Instruction* orig, 724 DenseMap<BasicBlock*, Value*> &Phis, 725 bool top_level = false); 726 void dump(DenseMap<uint32_t, Value*>& d); 727 bool iterateOnFunction(Function &F); 728 Value* CollapsePhi(PHINode* p); 729 bool isSafeReplacement(PHINode* p, Instruction* inst); 730 bool performPRE(Function& F); 731 Value* lookupNumber(BasicBlock* BB, uint32_t num); 732 bool mergeBlockIntoPredecessor(BasicBlock* BB); 733 Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno); 734 void cleanupGlobalSets(); 735 void verifyRemoved(const Instruction *I) const; 736 }; 737 738 char GVN::ID = 0; 739} 740 741// createGVNPass - The public interface to this file... 742FunctionPass *llvm::createGVNPass() { return new GVN(); } 743 744static RegisterPass<GVN> X("gvn", 745 "Global Value Numbering"); 746 747void GVN::dump(DenseMap<uint32_t, Value*>& d) { 748 printf("{\n"); 749 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 750 E = d.end(); I != E; ++I) { 751 printf("%d\n", I->first); 752 I->second->dump(); 753 } 754 printf("}\n"); 755} 756 757Value* GVN::CollapsePhi(PHINode* p) { 758 Value* constVal = p->hasConstantValue(); 759 if (!constVal) return 0; 760 761 Instruction* inst = dyn_cast<Instruction>(constVal); 762 if (!inst) 763 return constVal; 764 765 if (DT->dominates(inst, p)) 766 if (isSafeReplacement(p, inst)) 767 return inst; 768 return 0; 769} 770 771bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 772 if (!isa<PHINode>(inst)) 773 return true; 774 775 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 776 UI != E; ++UI) 777 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 778 if (use_phi->getParent() == inst->getParent()) 779 return false; 780 781 return true; 782} 783 784/// GetValueForBlock - Get the value to use within the specified basic block. 785/// available values are in Phis. 786Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig, 787 DenseMap<BasicBlock*, Value*> &Phis, 788 bool top_level) { 789 790 // If we have already computed this value, return the previously computed val. 791 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 792 if (V != Phis.end() && !top_level) return V->second; 793 794 // If the block is unreachable, just return undef, since this path 795 // can't actually occur at runtime. 796 if (!DT->isReachableFromEntry(BB)) 797 return Phis[BB] = UndefValue::get(orig->getType()); 798 799 if (BasicBlock *Pred = BB->getSinglePredecessor()) { 800 Value *ret = GetValueForBlock(Pred, orig, Phis); 801 Phis[BB] = ret; 802 return ret; 803 } 804 805 // Get the number of predecessors of this block so we can reserve space later. 806 // If there is already a PHI in it, use the #preds from it, otherwise count. 807 // Getting it from the PHI is constant time. 808 unsigned NumPreds; 809 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin())) 810 NumPreds = ExistingPN->getNumIncomingValues(); 811 else 812 NumPreds = std::distance(pred_begin(BB), pred_end(BB)); 813 814 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 815 // now, then get values to fill in the incoming values for the PHI. 816 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", 817 BB->begin()); 818 PN->reserveOperandSpace(NumPreds); 819 820 Phis.insert(std::make_pair(BB, PN)); 821 822 // Fill in the incoming values for the block. 823 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 824 Value* val = GetValueForBlock(*PI, orig, Phis); 825 PN->addIncoming(val, *PI); 826 } 827 828 VN.getAliasAnalysis()->copyValue(orig, PN); 829 830 // Attempt to collapse PHI nodes that are trivially redundant 831 Value* v = CollapsePhi(PN); 832 if (!v) { 833 // Cache our phi construction results 834 if (LoadInst* L = dyn_cast<LoadInst>(orig)) 835 phiMap[L->getPointerOperand()].insert(PN); 836 else 837 phiMap[orig].insert(PN); 838 839 return PN; 840 } 841 842 PN->replaceAllUsesWith(v); 843 if (isa<PointerType>(v->getType())) 844 MD->invalidateCachedPointerInfo(v); 845 846 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 847 E = Phis.end(); I != E; ++I) 848 if (I->second == PN) 849 I->second = v; 850 851 DEBUG(cerr << "GVN removed: " << *PN); 852 MD->removeInstruction(PN); 853 PN->eraseFromParent(); 854 DEBUG(verifyRemoved(PN)); 855 856 Phis[BB] = v; 857 return v; 858} 859 860/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 861/// we're analyzing is fully available in the specified block. As we go, keep 862/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 863/// map is actually a tri-state map with the following values: 864/// 0) we know the block *is not* fully available. 865/// 1) we know the block *is* fully available. 866/// 2) we do not know whether the block is fully available or not, but we are 867/// currently speculating that it will be. 868/// 3) we are speculating for this block and have used that to speculate for 869/// other blocks. 870static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 871 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 872 // Optimistically assume that the block is fully available and check to see 873 // if we already know about this block in one lookup. 874 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 875 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 876 877 // If the entry already existed for this block, return the precomputed value. 878 if (!IV.second) { 879 // If this is a speculative "available" value, mark it as being used for 880 // speculation of other blocks. 881 if (IV.first->second == 2) 882 IV.first->second = 3; 883 return IV.first->second != 0; 884 } 885 886 // Otherwise, see if it is fully available in all predecessors. 887 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 888 889 // If this block has no predecessors, it isn't live-in here. 890 if (PI == PE) 891 goto SpeculationFailure; 892 893 for (; PI != PE; ++PI) 894 // If the value isn't fully available in one of our predecessors, then it 895 // isn't fully available in this block either. Undo our previous 896 // optimistic assumption and bail out. 897 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 898 goto SpeculationFailure; 899 900 return true; 901 902// SpeculationFailure - If we get here, we found out that this is not, after 903// all, a fully-available block. We have a problem if we speculated on this and 904// used the speculation to mark other blocks as available. 905SpeculationFailure: 906 char &BBVal = FullyAvailableBlocks[BB]; 907 908 // If we didn't speculate on this, just return with it set to false. 909 if (BBVal == 2) { 910 BBVal = 0; 911 return false; 912 } 913 914 // If we did speculate on this value, we could have blocks set to 1 that are 915 // incorrect. Walk the (transitive) successors of this block and mark them as 916 // 0 if set to one. 917 SmallVector<BasicBlock*, 32> BBWorklist; 918 BBWorklist.push_back(BB); 919 920 while (!BBWorklist.empty()) { 921 BasicBlock *Entry = BBWorklist.pop_back_val(); 922 // Note that this sets blocks to 0 (unavailable) if they happen to not 923 // already be in FullyAvailableBlocks. This is safe. 924 char &EntryVal = FullyAvailableBlocks[Entry]; 925 if (EntryVal == 0) continue; // Already unavailable. 926 927 // Mark as unavailable. 928 EntryVal = 0; 929 930 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 931 BBWorklist.push_back(*I); 932 } 933 934 return false; 935} 936 937/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 938/// non-local by performing PHI construction. 939bool GVN::processNonLocalLoad(LoadInst *LI, 940 SmallVectorImpl<Instruction*> &toErase) { 941 // Find the non-local dependencies of the load. 942 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; 943 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 944 Deps); 945 //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI); 946 947 // If we had to process more than one hundred blocks to find the 948 // dependencies, this load isn't worth worrying about. Optimizing 949 // it will be too expensive. 950 if (Deps.size() > 100) 951 return false; 952 953 // If we had a phi translation failure, we'll have a single entry which is a 954 // clobber in the current block. Reject this early. 955 if (Deps.size() == 1 && Deps[0].second.isClobber()) 956 return false; 957 958 // Filter out useless results (non-locals, etc). Keep track of the blocks 959 // where we have a value available in repl, also keep track of whether we see 960 // dependencies that produce an unknown value for the load (such as a call 961 // that could potentially clobber the load). 962 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock; 963 SmallVector<BasicBlock*, 16> UnavailableBlocks; 964 965 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 966 BasicBlock *DepBB = Deps[i].first; 967 MemDepResult DepInfo = Deps[i].second; 968 969 if (DepInfo.isClobber()) { 970 UnavailableBlocks.push_back(DepBB); 971 continue; 972 } 973 974 Instruction *DepInst = DepInfo.getInst(); 975 976 // Loading the allocation -> undef. 977 if (isa<AllocationInst>(DepInst)) { 978 ValuesPerBlock.push_back(std::make_pair(DepBB, 979 UndefValue::get(LI->getType()))); 980 continue; 981 } 982 983 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) { 984 // Reject loads and stores that are to the same address but are of 985 // different types. 986 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because 987 // of bitfield access, it would be interesting to optimize for it at some 988 // point. 989 if (S->getOperand(0)->getType() != LI->getType()) { 990 UnavailableBlocks.push_back(DepBB); 991 continue; 992 } 993 994 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0))); 995 996 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) { 997 if (LD->getType() != LI->getType()) { 998 UnavailableBlocks.push_back(DepBB); 999 continue; 1000 } 1001 ValuesPerBlock.push_back(std::make_pair(DepBB, LD)); 1002 } else { 1003 UnavailableBlocks.push_back(DepBB); 1004 continue; 1005 } 1006 } 1007 1008 // If we have no predecessors that produce a known value for this load, exit 1009 // early. 1010 if (ValuesPerBlock.empty()) return false; 1011 1012 // If all of the instructions we depend on produce a known value for this 1013 // load, then it is fully redundant and we can use PHI insertion to compute 1014 // its value. Insert PHIs and remove the fully redundant value now. 1015 if (UnavailableBlocks.empty()) { 1016 // Use cached PHI construction information from previous runs 1017 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1018 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated? 1019 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1020 I != E; ++I) { 1021 if ((*I)->getParent() == LI->getParent()) { 1022 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI); 1023 LI->replaceAllUsesWith(*I); 1024 if (isa<PointerType>((*I)->getType())) 1025 MD->invalidateCachedPointerInfo(*I); 1026 toErase.push_back(LI); 1027 NumGVNLoad++; 1028 return true; 1029 } 1030 1031 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I)); 1032 } 1033 1034 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI); 1035 1036 DenseMap<BasicBlock*, Value*> BlockReplValues; 1037 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end()); 1038 // Perform PHI construction. 1039 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1040 LI->replaceAllUsesWith(v); 1041 1042 if (isa<PHINode>(v)) 1043 v->takeName(LI); 1044 if (isa<PointerType>(v->getType())) 1045 MD->invalidateCachedPointerInfo(v); 1046 toErase.push_back(LI); 1047 NumGVNLoad++; 1048 return true; 1049 } 1050 1051 if (!EnablePRE || !EnableLoadPRE) 1052 return false; 1053 1054 // Okay, we have *some* definitions of the value. This means that the value 1055 // is available in some of our (transitive) predecessors. Lets think about 1056 // doing PRE of this load. This will involve inserting a new load into the 1057 // predecessor when it's not available. We could do this in general, but 1058 // prefer to not increase code size. As such, we only do this when we know 1059 // that we only have to insert *one* load (which means we're basically moving 1060 // the load, not inserting a new one). 1061 1062 SmallPtrSet<BasicBlock *, 4> Blockers; 1063 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1064 Blockers.insert(UnavailableBlocks[i]); 1065 1066 // Lets find first basic block with more than one predecessor. Walk backwards 1067 // through predecessors if needed. 1068 BasicBlock *LoadBB = LI->getParent(); 1069 BasicBlock *TmpBB = LoadBB; 1070 1071 bool isSinglePred = false; 1072 while (TmpBB->getSinglePredecessor()) { 1073 isSinglePred = true; 1074 TmpBB = TmpBB->getSinglePredecessor(); 1075 if (!TmpBB) // If haven't found any, bail now. 1076 return false; 1077 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1078 return false; 1079 if (Blockers.count(TmpBB)) 1080 return false; 1081 } 1082 1083 assert(TmpBB); 1084 LoadBB = TmpBB; 1085 1086 // If we have a repl set with LI itself in it, this means we have a loop where 1087 // at least one of the values is LI. Since this means that we won't be able 1088 // to eliminate LI even if we insert uses in the other predecessors, we will 1089 // end up increasing code size. Reject this by scanning for LI. 1090 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1091 if (ValuesPerBlock[i].second == LI) 1092 return false; 1093 1094 if (isSinglePred) { 1095 bool isHot = false; 1096 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1097 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].second)) 1098 // "Hot" Instruction is in some loop (because it dominates its dep. 1099 // instruction). 1100 if (DT->dominates(LI, I)) { 1101 isHot = true; 1102 break; 1103 } 1104 1105 // We are interested only in "hot" instructions. We don't want to do any 1106 // mis-optimizations here. 1107 if (!isHot) 1108 return false; 1109 } 1110 1111 // Okay, we have some hope :). Check to see if the loaded value is fully 1112 // available in all but one predecessor. 1113 // FIXME: If we could restructure the CFG, we could make a common pred with 1114 // all the preds that don't have an available LI and insert a new load into 1115 // that one block. 1116 BasicBlock *UnavailablePred = 0; 1117 1118 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1119 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1120 FullyAvailableBlocks[ValuesPerBlock[i].first] = true; 1121 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1122 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1123 1124 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1125 PI != E; ++PI) { 1126 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 1127 continue; 1128 1129 // If this load is not available in multiple predecessors, reject it. 1130 if (UnavailablePred && UnavailablePred != *PI) 1131 return false; 1132 UnavailablePred = *PI; 1133 } 1134 1135 assert(UnavailablePred != 0 && 1136 "Fully available value should be eliminated above!"); 1137 1138 // If the loaded pointer is PHI node defined in this block, do PHI translation 1139 // to get its value in the predecessor. 1140 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred); 1141 1142 // Make sure the value is live in the predecessor. If it was defined by a 1143 // non-PHI instruction in this block, we don't know how to recompute it above. 1144 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr)) 1145 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) { 1146 DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: " 1147 << *LPInst << *LI << "\n"); 1148 return false; 1149 } 1150 1151 // We don't currently handle critical edges :( 1152 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) { 1153 DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '" 1154 << UnavailablePred->getName() << "': " << *LI); 1155 return false; 1156 } 1157 1158 // Okay, we can eliminate this load by inserting a reload in the predecessor 1159 // and using PHI construction to get the value in the other predecessors, do 1160 // it. 1161 DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI); 1162 1163 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1164 LI->getAlignment(), 1165 UnavailablePred->getTerminator()); 1166 1167 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1168 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1169 I != E; ++I) 1170 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I)); 1171 1172 DenseMap<BasicBlock*, Value*> BlockReplValues; 1173 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end()); 1174 BlockReplValues[UnavailablePred] = NewLoad; 1175 1176 // Perform PHI construction. 1177 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1178 LI->replaceAllUsesWith(v); 1179 if (isa<PHINode>(v)) 1180 v->takeName(LI); 1181 if (isa<PointerType>(v->getType())) 1182 MD->invalidateCachedPointerInfo(v); 1183 toErase.push_back(LI); 1184 NumPRELoad++; 1185 return true; 1186} 1187 1188/// processLoad - Attempt to eliminate a load, first by eliminating it 1189/// locally, and then attempting non-local elimination if that fails. 1190bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1191 if (L->isVolatile()) 1192 return false; 1193 1194 Value* pointer = L->getPointerOperand(); 1195 1196 // ... to a pointer that has been loaded from before... 1197 MemDepResult dep = MD->getDependency(L); 1198 1199 // If the value isn't available, don't do anything! 1200 if (dep.isClobber()) { 1201 DEBUG( 1202 // fast print dep, using operator<< on instruction would be too slow 1203 DOUT << "GVN: load "; 1204 WriteAsOperand(*DOUT.stream(), L); 1205 Instruction *I = dep.getInst(); 1206 DOUT << " is clobbered by " << *I; 1207 ); 1208 return false; 1209 } 1210 1211 // If it is defined in another block, try harder. 1212 if (dep.isNonLocal()) 1213 return processNonLocalLoad(L, toErase); 1214 1215 Instruction *DepInst = dep.getInst(); 1216 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1217 // Only forward substitute stores to loads of the same type. 1218 // FIXME: Could do better! 1219 if (DepSI->getPointerOperand()->getType() != pointer->getType()) 1220 return false; 1221 1222 // Remove it! 1223 L->replaceAllUsesWith(DepSI->getOperand(0)); 1224 if (isa<PointerType>(DepSI->getOperand(0)->getType())) 1225 MD->invalidateCachedPointerInfo(DepSI->getOperand(0)); 1226 toErase.push_back(L); 1227 NumGVNLoad++; 1228 return true; 1229 } 1230 1231 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1232 // Only forward substitute stores to loads of the same type. 1233 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian. 1234 if (DepLI->getType() != L->getType()) 1235 return false; 1236 1237 // Remove it! 1238 L->replaceAllUsesWith(DepLI); 1239 if (isa<PointerType>(DepLI->getType())) 1240 MD->invalidateCachedPointerInfo(DepLI); 1241 toErase.push_back(L); 1242 NumGVNLoad++; 1243 return true; 1244 } 1245 1246 // If this load really doesn't depend on anything, then we must be loading an 1247 // undef value. This can happen when loading for a fresh allocation with no 1248 // intervening stores, for example. 1249 if (isa<AllocationInst>(DepInst)) { 1250 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1251 toErase.push_back(L); 1252 NumGVNLoad++; 1253 return true; 1254 } 1255 1256 return false; 1257} 1258 1259Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) { 1260 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1261 if (I == localAvail.end()) 1262 return 0; 1263 1264 ValueNumberScope* locals = I->second; 1265 1266 while (locals) { 1267 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num); 1268 if (I != locals->table.end()) 1269 return I->second; 1270 else 1271 locals = locals->parent; 1272 } 1273 1274 return 0; 1275} 1276 1277/// AttemptRedundancyElimination - If the "fast path" of redundancy elimination 1278/// by inheritance from the dominator fails, see if we can perform phi 1279/// construction to eliminate the redundancy. 1280Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) { 1281 BasicBlock* BaseBlock = orig->getParent(); 1282 1283 SmallPtrSet<BasicBlock*, 4> Visited; 1284 SmallVector<BasicBlock*, 8> Stack; 1285 Stack.push_back(BaseBlock); 1286 1287 DenseMap<BasicBlock*, Value*> Results; 1288 1289 // Walk backwards through our predecessors, looking for instances of the 1290 // value number we're looking for. Instances are recorded in the Results 1291 // map, which is then used to perform phi construction. 1292 while (!Stack.empty()) { 1293 BasicBlock* Current = Stack.back(); 1294 Stack.pop_back(); 1295 1296 // If we've walked all the way to a proper dominator, then give up. Cases 1297 // where the instance is in the dominator will have been caught by the fast 1298 // path, and any cases that require phi construction further than this are 1299 // probably not worth it anyways. Note that this is a SIGNIFICANT compile 1300 // time improvement. 1301 if (DT->properlyDominates(Current, orig->getParent())) return 0; 1302 1303 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA = 1304 localAvail.find(Current); 1305 if (LA == localAvail.end()) return 0; 1306 DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno); 1307 1308 if (V != LA->second->table.end()) { 1309 // Found an instance, record it. 1310 Results.insert(std::make_pair(Current, V->second)); 1311 continue; 1312 } 1313 1314 // If we reach the beginning of the function, then give up. 1315 if (pred_begin(Current) == pred_end(Current)) 1316 return 0; 1317 1318 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current); 1319 PI != PE; ++PI) 1320 if (Visited.insert(*PI)) 1321 Stack.push_back(*PI); 1322 } 1323 1324 // If we didn't find instances, give up. Otherwise, perform phi construction. 1325 if (Results.size() == 0) 1326 return 0; 1327 else 1328 return GetValueForBlock(BaseBlock, orig, Results, true); 1329} 1330 1331/// processInstruction - When calculating availability, handle an instruction 1332/// by inserting it into the appropriate sets 1333bool GVN::processInstruction(Instruction *I, 1334 SmallVectorImpl<Instruction*> &toErase) { 1335 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1336 bool changed = processLoad(L, toErase); 1337 1338 if (!changed) { 1339 unsigned num = VN.lookup_or_add(L); 1340 localAvail[I->getParent()]->table.insert(std::make_pair(num, L)); 1341 } 1342 1343 return changed; 1344 } 1345 1346 uint32_t nextNum = VN.getNextUnusedValueNumber(); 1347 unsigned num = VN.lookup_or_add(I); 1348 1349 if (BranchInst* BI = dyn_cast<BranchInst>(I)) { 1350 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1351 1352 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1353 return false; 1354 1355 Value* branchCond = BI->getCondition(); 1356 uint32_t condVN = VN.lookup_or_add(branchCond); 1357 1358 BasicBlock* trueSucc = BI->getSuccessor(0); 1359 BasicBlock* falseSucc = BI->getSuccessor(1); 1360 1361 if (trueSucc->getSinglePredecessor()) 1362 localAvail[trueSucc]->table[condVN] = ConstantInt::getTrue(); 1363 if (falseSucc->getSinglePredecessor()) 1364 localAvail[falseSucc]->table[condVN] = ConstantInt::getFalse(); 1365 1366 return false; 1367 1368 // Allocations are always uniquely numbered, so we can save time and memory 1369 // by fast failing them. 1370 } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1371 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1372 return false; 1373 } 1374 1375 // Collapse PHI nodes 1376 if (PHINode* p = dyn_cast<PHINode>(I)) { 1377 Value* constVal = CollapsePhi(p); 1378 1379 if (constVal) { 1380 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1381 PI != PE; ++PI) 1382 PI->second.erase(p); 1383 1384 p->replaceAllUsesWith(constVal); 1385 if (isa<PointerType>(constVal->getType())) 1386 MD->invalidateCachedPointerInfo(constVal); 1387 VN.erase(p); 1388 1389 toErase.push_back(p); 1390 } else { 1391 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1392 } 1393 1394 // If the number we were assigned was a brand new VN, then we don't 1395 // need to do a lookup to see if the number already exists 1396 // somewhere in the domtree: it can't! 1397 } else if (num == nextNum) { 1398 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1399 1400 // Perform fast-path value-number based elimination of values inherited from 1401 // dominators. 1402 } else if (Value* repl = lookupNumber(I->getParent(), num)) { 1403 // Remove it! 1404 VN.erase(I); 1405 I->replaceAllUsesWith(repl); 1406 if (isa<PointerType>(repl->getType())) 1407 MD->invalidateCachedPointerInfo(repl); 1408 toErase.push_back(I); 1409 return true; 1410 1411#if 0 1412 // Perform slow-pathvalue-number based elimination with phi construction. 1413 } else if (Value* repl = AttemptRedundancyElimination(I, num)) { 1414 // Remove it! 1415 VN.erase(I); 1416 I->replaceAllUsesWith(repl); 1417 if (isa<PointerType>(repl->getType())) 1418 MD->invalidateCachedPointerInfo(repl); 1419 toErase.push_back(I); 1420 return true; 1421#endif 1422 } else { 1423 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1424 } 1425 1426 return false; 1427} 1428 1429/// runOnFunction - This is the main transformation entry point for a function. 1430bool GVN::runOnFunction(Function& F) { 1431 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1432 DT = &getAnalysis<DominatorTree>(); 1433 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1434 VN.setMemDep(MD); 1435 VN.setDomTree(DT); 1436 1437 bool changed = false; 1438 bool shouldContinue = true; 1439 1440 // Merge unconditional branches, allowing PRE to catch more 1441 // optimization opportunities. 1442 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1443 BasicBlock* BB = FI; 1444 ++FI; 1445 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1446 if (removedBlock) NumGVNBlocks++; 1447 1448 changed |= removedBlock; 1449 } 1450 1451 unsigned Iteration = 0; 1452 1453 while (shouldContinue) { 1454 DEBUG(cerr << "GVN iteration: " << Iteration << "\n"); 1455 shouldContinue = iterateOnFunction(F); 1456 changed |= shouldContinue; 1457 ++Iteration; 1458 } 1459 1460 if (EnablePRE) { 1461 bool PREChanged = true; 1462 while (PREChanged) { 1463 PREChanged = performPRE(F); 1464 changed |= PREChanged; 1465 } 1466 } 1467 // FIXME: Should perform GVN again after PRE does something. PRE can move 1468 // computations into blocks where they become fully redundant. Note that 1469 // we can't do this until PRE's critical edge splitting updates memdep. 1470 // Actually, when this happens, we should just fully integrate PRE into GVN. 1471 1472 cleanupGlobalSets(); 1473 1474 return changed; 1475} 1476 1477 1478bool GVN::processBlock(BasicBlock* BB) { 1479 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1480 // incrementing BI before processing an instruction). 1481 SmallVector<Instruction*, 8> toErase; 1482 bool changed_function = false; 1483 1484 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1485 BI != BE;) { 1486 changed_function |= processInstruction(BI, toErase); 1487 if (toErase.empty()) { 1488 ++BI; 1489 continue; 1490 } 1491 1492 // If we need some instructions deleted, do it now. 1493 NumGVNInstr += toErase.size(); 1494 1495 // Avoid iterator invalidation. 1496 bool AtStart = BI == BB->begin(); 1497 if (!AtStart) 1498 --BI; 1499 1500 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1501 E = toErase.end(); I != E; ++I) { 1502 DEBUG(cerr << "GVN removed: " << **I); 1503 MD->removeInstruction(*I); 1504 (*I)->eraseFromParent(); 1505 DEBUG(verifyRemoved(*I)); 1506 } 1507 toErase.clear(); 1508 1509 if (AtStart) 1510 BI = BB->begin(); 1511 else 1512 ++BI; 1513 } 1514 1515 return changed_function; 1516} 1517 1518/// performPRE - Perform a purely local form of PRE that looks for diamond 1519/// control flow patterns and attempts to perform simple PRE at the join point. 1520bool GVN::performPRE(Function& F) { 1521 bool Changed = false; 1522 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1523 DenseMap<BasicBlock*, Value*> predMap; 1524 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1525 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1526 BasicBlock* CurrentBlock = *DI; 1527 1528 // Nothing to PRE in the entry block. 1529 if (CurrentBlock == &F.getEntryBlock()) continue; 1530 1531 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1532 BE = CurrentBlock->end(); BI != BE; ) { 1533 Instruction *CurInst = BI++; 1534 1535 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) || 1536 isa<PHINode>(CurInst) || (CurInst->getType() == Type::VoidTy) || 1537 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 1538 isa<DbgInfoIntrinsic>(CurInst)) 1539 continue; 1540 1541 uint32_t valno = VN.lookup(CurInst); 1542 1543 // Look for the predecessors for PRE opportunities. We're 1544 // only trying to solve the basic diamond case, where 1545 // a value is computed in the successor and one predecessor, 1546 // but not the other. We also explicitly disallow cases 1547 // where the successor is its own predecessor, because they're 1548 // more complicated to get right. 1549 unsigned numWith = 0; 1550 unsigned numWithout = 0; 1551 BasicBlock* PREPred = 0; 1552 predMap.clear(); 1553 1554 for (pred_iterator PI = pred_begin(CurrentBlock), 1555 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1556 // We're not interested in PRE where the block is its 1557 // own predecessor, on in blocks with predecessors 1558 // that are not reachable. 1559 if (*PI == CurrentBlock) { 1560 numWithout = 2; 1561 break; 1562 } else if (!localAvail.count(*PI)) { 1563 numWithout = 2; 1564 break; 1565 } 1566 1567 DenseMap<uint32_t, Value*>::iterator predV = 1568 localAvail[*PI]->table.find(valno); 1569 if (predV == localAvail[*PI]->table.end()) { 1570 PREPred = *PI; 1571 numWithout++; 1572 } else if (predV->second == CurInst) { 1573 numWithout = 2; 1574 } else { 1575 predMap[*PI] = predV->second; 1576 numWith++; 1577 } 1578 } 1579 1580 // Don't do PRE when it might increase code size, i.e. when 1581 // we would need to insert instructions in more than one pred. 1582 if (numWithout != 1 || numWith == 0) 1583 continue; 1584 1585 // We can't do PRE safely on a critical edge, so instead we schedule 1586 // the edge to be split and perform the PRE the next time we iterate 1587 // on the function. 1588 unsigned succNum = 0; 1589 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1590 i != e; ++i) 1591 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 1592 succNum = i; 1593 break; 1594 } 1595 1596 if (isCriticalEdge(PREPred->getTerminator(), succNum)) { 1597 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum)); 1598 continue; 1599 } 1600 1601 // Instantiate the expression the in predecessor that lacked it. 1602 // Because we are going top-down through the block, all value numbers 1603 // will be available in the predecessor by the time we need them. Any 1604 // that weren't original present will have been instantiated earlier 1605 // in this loop. 1606 Instruction* PREInstr = CurInst->clone(); 1607 bool success = true; 1608 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 1609 Value *Op = PREInstr->getOperand(i); 1610 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 1611 continue; 1612 1613 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 1614 PREInstr->setOperand(i, V); 1615 } else { 1616 success = false; 1617 break; 1618 } 1619 } 1620 1621 // Fail out if we encounter an operand that is not available in 1622 // the PRE predecessor. This is typically because of loads which 1623 // are not value numbered precisely. 1624 if (!success) { 1625 delete PREInstr; 1626 DEBUG(verifyRemoved(PREInstr)); 1627 continue; 1628 } 1629 1630 PREInstr->insertBefore(PREPred->getTerminator()); 1631 PREInstr->setName(CurInst->getName() + ".pre"); 1632 predMap[PREPred] = PREInstr; 1633 VN.add(PREInstr, valno); 1634 NumGVNPRE++; 1635 1636 // Update the availability map to include the new instruction. 1637 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr)); 1638 1639 // Create a PHI to make the value available in this block. 1640 PHINode* Phi = PHINode::Create(CurInst->getType(), 1641 CurInst->getName() + ".pre-phi", 1642 CurrentBlock->begin()); 1643 for (pred_iterator PI = pred_begin(CurrentBlock), 1644 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1645 Phi->addIncoming(predMap[*PI], *PI); 1646 1647 VN.add(Phi, valno); 1648 localAvail[CurrentBlock]->table[valno] = Phi; 1649 1650 CurInst->replaceAllUsesWith(Phi); 1651 if (isa<PointerType>(Phi->getType())) 1652 MD->invalidateCachedPointerInfo(Phi); 1653 VN.erase(CurInst); 1654 1655 DEBUG(cerr << "GVN PRE removed: " << *CurInst); 1656 MD->removeInstruction(CurInst); 1657 CurInst->eraseFromParent(); 1658 DEBUG(verifyRemoved(CurInst)); 1659 Changed = true; 1660 } 1661 } 1662 1663 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 1664 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 1665 SplitCriticalEdge(I->first, I->second, this); 1666 1667 return Changed || toSplit.size(); 1668} 1669 1670/// iterateOnFunction - Executes one iteration of GVN 1671bool GVN::iterateOnFunction(Function &F) { 1672 cleanupGlobalSets(); 1673 1674 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 1675 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 1676 if (DI->getIDom()) 1677 localAvail[DI->getBlock()] = 1678 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 1679 else 1680 localAvail[DI->getBlock()] = new ValueNumberScope(0); 1681 } 1682 1683 // Top-down walk of the dominator tree 1684 bool changed = false; 1685#if 0 1686 // Needed for value numbering with phi construction to work. 1687 ReversePostOrderTraversal<Function*> RPOT(&F); 1688 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 1689 RE = RPOT.end(); RI != RE; ++RI) 1690 changed |= processBlock(*RI); 1691#else 1692 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 1693 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 1694 changed |= processBlock(DI->getBlock()); 1695#endif 1696 1697 return changed; 1698} 1699 1700void GVN::cleanupGlobalSets() { 1701 VN.clear(); 1702 phiMap.clear(); 1703 1704 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1705 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 1706 delete I->second; 1707 localAvail.clear(); 1708} 1709 1710/// verifyRemoved - Verify that the specified instruction does not occur in our 1711/// internal data structures. 1712void GVN::verifyRemoved(const Instruction *Inst) const { 1713 VN.verifyRemoved(Inst); 1714 1715 // Walk through the PHI map to make sure the instruction isn't hiding in there 1716 // somewhere. 1717 for (PhiMapType::iterator 1718 I = phiMap.begin(), E = phiMap.end(); I != E; ++I) { 1719 assert(I->first != Inst && "Inst is still a key in PHI map!"); 1720 1721 for (SmallPtrSet<Instruction*, 4>::iterator 1722 II = I->second.begin(), IE = I->second.end(); II != IE; ++II) { 1723 assert(*II != Inst && "Inst is still a value in PHI map!"); 1724 } 1725 } 1726 1727 // Walk through the value number scope to make sure the instruction isn't 1728 // ferreted away in it. 1729 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1730 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { 1731 const ValueNumberScope *VNS = I->second; 1732 1733 while (VNS) { 1734 for (DenseMap<uint32_t, Value*>::iterator 1735 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { 1736 assert(II->second != Inst && "Inst still in value numbering scope!"); 1737 } 1738 1739 VNS = VNS->parent; 1740 } 1741 } 1742} 1743