GVN.cpp revision 24473120a253a05f3601cd3373403b47e6d03d41
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/GlobalVariable.h" 21#include "llvm/IntrinsicInst.h" 22#include "llvm/LLVMContext.h" 23#include "llvm/Analysis/AliasAnalysis.h" 24#include "llvm/Analysis/ConstantFolding.h" 25#include "llvm/Analysis/Dominators.h" 26#include "llvm/Analysis/InstructionSimplify.h" 27#include "llvm/Analysis/Loads.h" 28#include "llvm/Analysis/MemoryBuiltins.h" 29#include "llvm/Analysis/MemoryDependenceAnalysis.h" 30#include "llvm/Analysis/PHITransAddr.h" 31#include "llvm/Analysis/ValueTracking.h" 32#include "llvm/Assembly/Writer.h" 33#include "llvm/Target/TargetData.h" 34#include "llvm/Target/TargetLibraryInfo.h" 35#include "llvm/Transforms/Utils/BasicBlockUtils.h" 36#include "llvm/Transforms/Utils/SSAUpdater.h" 37#include "llvm/ADT/DenseMap.h" 38#include "llvm/ADT/DepthFirstIterator.h" 39#include "llvm/ADT/SmallPtrSet.h" 40#include "llvm/ADT/Statistic.h" 41#include "llvm/Support/Allocator.h" 42#include "llvm/Support/CommandLine.h" 43#include "llvm/Support/Debug.h" 44#include "llvm/Support/IRBuilder.h" 45#include "llvm/Support/PatternMatch.h" 46using namespace llvm; 47using namespace PatternMatch; 48 49STATISTIC(NumGVNInstr, "Number of instructions deleted"); 50STATISTIC(NumGVNLoad, "Number of loads deleted"); 51STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 52STATISTIC(NumGVNBlocks, "Number of blocks merged"); 53STATISTIC(NumGVNSimpl, "Number of instructions simplified"); 54STATISTIC(NumGVNEqProp, "Number of equalities propagated"); 55STATISTIC(NumPRELoad, "Number of loads PRE'd"); 56 57static cl::opt<bool> EnablePRE("enable-pre", 58 cl::init(true), cl::Hidden); 59static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 60 61//===----------------------------------------------------------------------===// 62// ValueTable Class 63//===----------------------------------------------------------------------===// 64 65/// This class holds the mapping between values and value numbers. It is used 66/// as an efficient mechanism to determine the expression-wise equivalence of 67/// two values. 68namespace { 69 struct Expression { 70 uint32_t opcode; 71 Type *type; 72 SmallVector<uint32_t, 4> varargs; 73 74 Expression(uint32_t o = ~2U) : opcode(o) { } 75 76 bool operator==(const Expression &other) const { 77 if (opcode != other.opcode) 78 return false; 79 if (opcode == ~0U || opcode == ~1U) 80 return true; 81 if (type != other.type) 82 return false; 83 if (varargs != other.varargs) 84 return false; 85 return true; 86 } 87 }; 88 89 class ValueTable { 90 DenseMap<Value*, uint32_t> valueNumbering; 91 DenseMap<Expression, uint32_t> expressionNumbering; 92 AliasAnalysis *AA; 93 MemoryDependenceAnalysis *MD; 94 DominatorTree *DT; 95 96 uint32_t nextValueNumber; 97 98 Expression create_expression(Instruction* I); 99 Expression create_extractvalue_expression(ExtractValueInst* EI); 100 uint32_t lookup_or_add_call(CallInst* C); 101 public: 102 ValueTable() : nextValueNumber(1) { } 103 uint32_t lookup_or_add(Value *V); 104 uint32_t lookup(Value *V) const; 105 void add(Value *V, uint32_t num); 106 void clear(); 107 void erase(Value *v); 108 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 109 AliasAnalysis *getAliasAnalysis() const { return AA; } 110 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 111 void setDomTree(DominatorTree* D) { DT = D; } 112 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 113 void verifyRemoved(const Value *) const; 114 }; 115} 116 117namespace llvm { 118template <> struct DenseMapInfo<Expression> { 119 static inline Expression getEmptyKey() { 120 return ~0U; 121 } 122 123 static inline Expression getTombstoneKey() { 124 return ~1U; 125 } 126 127 static unsigned getHashValue(const Expression e) { 128 unsigned hash = e.opcode; 129 130 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 131 (unsigned)((uintptr_t)e.type >> 9)); 132 133 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 134 E = e.varargs.end(); I != E; ++I) 135 hash = *I + hash * 37; 136 137 return hash; 138 } 139 static bool isEqual(const Expression &LHS, const Expression &RHS) { 140 return LHS == RHS; 141 } 142}; 143 144} 145 146//===----------------------------------------------------------------------===// 147// ValueTable Internal Functions 148//===----------------------------------------------------------------------===// 149 150Expression ValueTable::create_expression(Instruction *I) { 151 Expression e; 152 e.type = I->getType(); 153 e.opcode = I->getOpcode(); 154 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); 155 OI != OE; ++OI) 156 e.varargs.push_back(lookup_or_add(*OI)); 157 158 if (CmpInst *C = dyn_cast<CmpInst>(I)) { 159 e.opcode = (C->getOpcode() << 8) | C->getPredicate(); 160 } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) { 161 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 162 II != IE; ++II) 163 e.varargs.push_back(*II); 164 } 165 166 return e; 167} 168 169Expression ValueTable::create_extractvalue_expression(ExtractValueInst *EI) { 170 assert(EI != 0 && "Not an ExtractValueInst?"); 171 Expression e; 172 e.type = EI->getType(); 173 e.opcode = 0; 174 175 IntrinsicInst *I = dyn_cast<IntrinsicInst>(EI->getAggregateOperand()); 176 if (I != 0 && EI->getNumIndices() == 1 && *EI->idx_begin() == 0 ) { 177 // EI might be an extract from one of our recognised intrinsics. If it 178 // is we'll synthesize a semantically equivalent expression instead on 179 // an extract value expression. 180 switch (I->getIntrinsicID()) { 181 case Intrinsic::sadd_with_overflow: 182 case Intrinsic::uadd_with_overflow: 183 e.opcode = Instruction::Add; 184 break; 185 case Intrinsic::ssub_with_overflow: 186 case Intrinsic::usub_with_overflow: 187 e.opcode = Instruction::Sub; 188 break; 189 case Intrinsic::smul_with_overflow: 190 case Intrinsic::umul_with_overflow: 191 e.opcode = Instruction::Mul; 192 break; 193 default: 194 break; 195 } 196 197 if (e.opcode != 0) { 198 // Intrinsic recognized. Grab its args to finish building the expression. 199 assert(I->getNumArgOperands() == 2 && 200 "Expect two args for recognised intrinsics."); 201 e.varargs.push_back(lookup_or_add(I->getArgOperand(0))); 202 e.varargs.push_back(lookup_or_add(I->getArgOperand(1))); 203 return e; 204 } 205 } 206 207 // Not a recognised intrinsic. Fall back to producing an extract value 208 // expression. 209 e.opcode = EI->getOpcode(); 210 for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end(); 211 OI != OE; ++OI) 212 e.varargs.push_back(lookup_or_add(*OI)); 213 214 for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end(); 215 II != IE; ++II) 216 e.varargs.push_back(*II); 217 218 return e; 219} 220 221//===----------------------------------------------------------------------===// 222// ValueTable External Functions 223//===----------------------------------------------------------------------===// 224 225/// add - Insert a value into the table with a specified value number. 226void ValueTable::add(Value *V, uint32_t num) { 227 valueNumbering.insert(std::make_pair(V, num)); 228} 229 230uint32_t ValueTable::lookup_or_add_call(CallInst* C) { 231 if (AA->doesNotAccessMemory(C)) { 232 Expression exp = create_expression(C); 233 uint32_t& e = expressionNumbering[exp]; 234 if (!e) e = nextValueNumber++; 235 valueNumbering[C] = e; 236 return e; 237 } else if (AA->onlyReadsMemory(C)) { 238 Expression exp = create_expression(C); 239 uint32_t& e = expressionNumbering[exp]; 240 if (!e) { 241 e = nextValueNumber++; 242 valueNumbering[C] = e; 243 return e; 244 } 245 if (!MD) { 246 e = nextValueNumber++; 247 valueNumbering[C] = e; 248 return e; 249 } 250 251 MemDepResult local_dep = MD->getDependency(C); 252 253 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 254 valueNumbering[C] = nextValueNumber; 255 return nextValueNumber++; 256 } 257 258 if (local_dep.isDef()) { 259 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 260 261 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) { 262 valueNumbering[C] = nextValueNumber; 263 return nextValueNumber++; 264 } 265 266 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 267 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 268 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i)); 269 if (c_vn != cd_vn) { 270 valueNumbering[C] = nextValueNumber; 271 return nextValueNumber++; 272 } 273 } 274 275 uint32_t v = lookup_or_add(local_cdep); 276 valueNumbering[C] = v; 277 return v; 278 } 279 280 // Non-local case. 281 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 282 MD->getNonLocalCallDependency(CallSite(C)); 283 // FIXME: Move the checking logic to MemDep! 284 CallInst* cdep = 0; 285 286 // Check to see if we have a single dominating call instruction that is 287 // identical to C. 288 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 289 const NonLocalDepEntry *I = &deps[i]; 290 if (I->getResult().isNonLocal()) 291 continue; 292 293 // We don't handle non-definitions. If we already have a call, reject 294 // instruction dependencies. 295 if (!I->getResult().isDef() || cdep != 0) { 296 cdep = 0; 297 break; 298 } 299 300 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); 301 // FIXME: All duplicated with non-local case. 302 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ 303 cdep = NonLocalDepCall; 304 continue; 305 } 306 307 cdep = 0; 308 break; 309 } 310 311 if (!cdep) { 312 valueNumbering[C] = nextValueNumber; 313 return nextValueNumber++; 314 } 315 316 if (cdep->getNumArgOperands() != C->getNumArgOperands()) { 317 valueNumbering[C] = nextValueNumber; 318 return nextValueNumber++; 319 } 320 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 321 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 322 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i)); 323 if (c_vn != cd_vn) { 324 valueNumbering[C] = nextValueNumber; 325 return nextValueNumber++; 326 } 327 } 328 329 uint32_t v = lookup_or_add(cdep); 330 valueNumbering[C] = v; 331 return v; 332 333 } else { 334 valueNumbering[C] = nextValueNumber; 335 return nextValueNumber++; 336 } 337} 338 339/// lookup_or_add - Returns the value number for the specified value, assigning 340/// it a new number if it did not have one before. 341uint32_t ValueTable::lookup_or_add(Value *V) { 342 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 343 if (VI != valueNumbering.end()) 344 return VI->second; 345 346 if (!isa<Instruction>(V)) { 347 valueNumbering[V] = nextValueNumber; 348 return nextValueNumber++; 349 } 350 351 Instruction* I = cast<Instruction>(V); 352 Expression exp; 353 switch (I->getOpcode()) { 354 case Instruction::Call: 355 return lookup_or_add_call(cast<CallInst>(I)); 356 case Instruction::Add: 357 case Instruction::FAdd: 358 case Instruction::Sub: 359 case Instruction::FSub: 360 case Instruction::Mul: 361 case Instruction::FMul: 362 case Instruction::UDiv: 363 case Instruction::SDiv: 364 case Instruction::FDiv: 365 case Instruction::URem: 366 case Instruction::SRem: 367 case Instruction::FRem: 368 case Instruction::Shl: 369 case Instruction::LShr: 370 case Instruction::AShr: 371 case Instruction::And: 372 case Instruction::Or : 373 case Instruction::Xor: 374 case Instruction::ICmp: 375 case Instruction::FCmp: 376 case Instruction::Trunc: 377 case Instruction::ZExt: 378 case Instruction::SExt: 379 case Instruction::FPToUI: 380 case Instruction::FPToSI: 381 case Instruction::UIToFP: 382 case Instruction::SIToFP: 383 case Instruction::FPTrunc: 384 case Instruction::FPExt: 385 case Instruction::PtrToInt: 386 case Instruction::IntToPtr: 387 case Instruction::BitCast: 388 case Instruction::Select: 389 case Instruction::ExtractElement: 390 case Instruction::InsertElement: 391 case Instruction::ShuffleVector: 392 case Instruction::InsertValue: 393 case Instruction::GetElementPtr: 394 exp = create_expression(I); 395 break; 396 case Instruction::ExtractValue: 397 exp = create_extractvalue_expression(cast<ExtractValueInst>(I)); 398 break; 399 default: 400 valueNumbering[V] = nextValueNumber; 401 return nextValueNumber++; 402 } 403 404 uint32_t& e = expressionNumbering[exp]; 405 if (!e) e = nextValueNumber++; 406 valueNumbering[V] = e; 407 return e; 408} 409 410/// lookup - Returns the value number of the specified value. Fails if 411/// the value has not yet been numbered. 412uint32_t ValueTable::lookup(Value *V) const { 413 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); 414 assert(VI != valueNumbering.end() && "Value not numbered?"); 415 return VI->second; 416} 417 418/// clear - Remove all entries from the ValueTable. 419void ValueTable::clear() { 420 valueNumbering.clear(); 421 expressionNumbering.clear(); 422 nextValueNumber = 1; 423} 424 425/// erase - Remove a value from the value numbering. 426void ValueTable::erase(Value *V) { 427 valueNumbering.erase(V); 428} 429 430/// verifyRemoved - Verify that the value is removed from all internal data 431/// structures. 432void ValueTable::verifyRemoved(const Value *V) const { 433 for (DenseMap<Value*, uint32_t>::const_iterator 434 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 435 assert(I->first != V && "Inst still occurs in value numbering map!"); 436 } 437} 438 439//===----------------------------------------------------------------------===// 440// GVN Pass 441//===----------------------------------------------------------------------===// 442 443namespace { 444 445 class GVN : public FunctionPass { 446 bool NoLoads; 447 MemoryDependenceAnalysis *MD; 448 DominatorTree *DT; 449 const TargetData *TD; 450 const TargetLibraryInfo *TLI; 451 452 ValueTable VN; 453 454 /// LeaderTable - A mapping from value numbers to lists of Value*'s that 455 /// have that value number. Use findLeader to query it. 456 struct LeaderTableEntry { 457 Value *Val; 458 BasicBlock *BB; 459 LeaderTableEntry *Next; 460 }; 461 DenseMap<uint32_t, LeaderTableEntry> LeaderTable; 462 BumpPtrAllocator TableAllocator; 463 464 SmallVector<Instruction*, 8> InstrsToErase; 465 public: 466 static char ID; // Pass identification, replacement for typeid 467 explicit GVN(bool noloads = false) 468 : FunctionPass(ID), NoLoads(noloads), MD(0) { 469 initializeGVNPass(*PassRegistry::getPassRegistry()); 470 } 471 472 bool runOnFunction(Function &F); 473 474 /// markInstructionForDeletion - This removes the specified instruction from 475 /// our various maps and marks it for deletion. 476 void markInstructionForDeletion(Instruction *I) { 477 VN.erase(I); 478 InstrsToErase.push_back(I); 479 } 480 481 const TargetData *getTargetData() const { return TD; } 482 DominatorTree &getDominatorTree() const { return *DT; } 483 AliasAnalysis *getAliasAnalysis() const { return VN.getAliasAnalysis(); } 484 MemoryDependenceAnalysis &getMemDep() const { return *MD; } 485 private: 486 /// addToLeaderTable - Push a new Value to the LeaderTable onto the list for 487 /// its value number. 488 void addToLeaderTable(uint32_t N, Value *V, BasicBlock *BB) { 489 LeaderTableEntry &Curr = LeaderTable[N]; 490 if (!Curr.Val) { 491 Curr.Val = V; 492 Curr.BB = BB; 493 return; 494 } 495 496 LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>(); 497 Node->Val = V; 498 Node->BB = BB; 499 Node->Next = Curr.Next; 500 Curr.Next = Node; 501 } 502 503 /// removeFromLeaderTable - Scan the list of values corresponding to a given 504 /// value number, and remove the given value if encountered. 505 void removeFromLeaderTable(uint32_t N, Value *V, BasicBlock *BB) { 506 LeaderTableEntry* Prev = 0; 507 LeaderTableEntry* Curr = &LeaderTable[N]; 508 509 while (Curr->Val != V || Curr->BB != BB) { 510 Prev = Curr; 511 Curr = Curr->Next; 512 } 513 514 if (Prev) { 515 Prev->Next = Curr->Next; 516 } else { 517 if (!Curr->Next) { 518 Curr->Val = 0; 519 Curr->BB = 0; 520 } else { 521 LeaderTableEntry* Next = Curr->Next; 522 Curr->Val = Next->Val; 523 Curr->BB = Next->BB; 524 Curr->Next = Next->Next; 525 } 526 } 527 } 528 529 // List of critical edges to be split between iterations. 530 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 531 532 // This transformation requires dominator postdominator info 533 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 534 AU.addRequired<DominatorTree>(); 535 AU.addRequired<TargetLibraryInfo>(); 536 if (!NoLoads) 537 AU.addRequired<MemoryDependenceAnalysis>(); 538 AU.addRequired<AliasAnalysis>(); 539 540 AU.addPreserved<DominatorTree>(); 541 AU.addPreserved<AliasAnalysis>(); 542 } 543 544 545 // Helper fuctions 546 // FIXME: eliminate or document these better 547 bool processLoad(LoadInst *L); 548 bool processInstruction(Instruction *I); 549 bool processNonLocalLoad(LoadInst *L); 550 bool processBlock(BasicBlock *BB); 551 void dump(DenseMap<uint32_t, Value*> &d); 552 bool iterateOnFunction(Function &F); 553 bool performPRE(Function &F); 554 Value *findLeader(BasicBlock *BB, uint32_t num); 555 void cleanupGlobalSets(); 556 void verifyRemoved(const Instruction *I) const; 557 bool splitCriticalEdges(); 558 unsigned replaceAllDominatedUsesWith(Value *From, Value *To, 559 BasicBlock *Root); 560 bool propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root); 561 }; 562 563 char GVN::ID = 0; 564} 565 566// createGVNPass - The public interface to this file... 567FunctionPass *llvm::createGVNPass(bool NoLoads) { 568 return new GVN(NoLoads); 569} 570 571INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false) 572INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) 573INITIALIZE_PASS_DEPENDENCY(DominatorTree) 574INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 575INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 576INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false) 577 578void GVN::dump(DenseMap<uint32_t, Value*>& d) { 579 errs() << "{\n"; 580 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 581 E = d.end(); I != E; ++I) { 582 errs() << I->first << "\n"; 583 I->second->dump(); 584 } 585 errs() << "}\n"; 586} 587 588/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 589/// we're analyzing is fully available in the specified block. As we go, keep 590/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 591/// map is actually a tri-state map with the following values: 592/// 0) we know the block *is not* fully available. 593/// 1) we know the block *is* fully available. 594/// 2) we do not know whether the block is fully available or not, but we are 595/// currently speculating that it will be. 596/// 3) we are speculating for this block and have used that to speculate for 597/// other blocks. 598static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 599 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 600 // Optimistically assume that the block is fully available and check to see 601 // if we already know about this block in one lookup. 602 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 603 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 604 605 // If the entry already existed for this block, return the precomputed value. 606 if (!IV.second) { 607 // If this is a speculative "available" value, mark it as being used for 608 // speculation of other blocks. 609 if (IV.first->second == 2) 610 IV.first->second = 3; 611 return IV.first->second != 0; 612 } 613 614 // Otherwise, see if it is fully available in all predecessors. 615 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 616 617 // If this block has no predecessors, it isn't live-in here. 618 if (PI == PE) 619 goto SpeculationFailure; 620 621 for (; PI != PE; ++PI) 622 // If the value isn't fully available in one of our predecessors, then it 623 // isn't fully available in this block either. Undo our previous 624 // optimistic assumption and bail out. 625 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 626 goto SpeculationFailure; 627 628 return true; 629 630// SpeculationFailure - If we get here, we found out that this is not, after 631// all, a fully-available block. We have a problem if we speculated on this and 632// used the speculation to mark other blocks as available. 633SpeculationFailure: 634 char &BBVal = FullyAvailableBlocks[BB]; 635 636 // If we didn't speculate on this, just return with it set to false. 637 if (BBVal == 2) { 638 BBVal = 0; 639 return false; 640 } 641 642 // If we did speculate on this value, we could have blocks set to 1 that are 643 // incorrect. Walk the (transitive) successors of this block and mark them as 644 // 0 if set to one. 645 SmallVector<BasicBlock*, 32> BBWorklist; 646 BBWorklist.push_back(BB); 647 648 do { 649 BasicBlock *Entry = BBWorklist.pop_back_val(); 650 // Note that this sets blocks to 0 (unavailable) if they happen to not 651 // already be in FullyAvailableBlocks. This is safe. 652 char &EntryVal = FullyAvailableBlocks[Entry]; 653 if (EntryVal == 0) continue; // Already unavailable. 654 655 // Mark as unavailable. 656 EntryVal = 0; 657 658 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 659 BBWorklist.push_back(*I); 660 } while (!BBWorklist.empty()); 661 662 return false; 663} 664 665 666/// CanCoerceMustAliasedValueToLoad - Return true if 667/// CoerceAvailableValueToLoadType will succeed. 668static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 669 Type *LoadTy, 670 const TargetData &TD) { 671 // If the loaded or stored value is an first class array or struct, don't try 672 // to transform them. We need to be able to bitcast to integer. 673 if (LoadTy->isStructTy() || LoadTy->isArrayTy() || 674 StoredVal->getType()->isStructTy() || 675 StoredVal->getType()->isArrayTy()) 676 return false; 677 678 // The store has to be at least as big as the load. 679 if (TD.getTypeSizeInBits(StoredVal->getType()) < 680 TD.getTypeSizeInBits(LoadTy)) 681 return false; 682 683 return true; 684} 685 686 687/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 688/// then a load from a must-aliased pointer of a different type, try to coerce 689/// the stored value. LoadedTy is the type of the load we want to replace and 690/// InsertPt is the place to insert new instructions. 691/// 692/// If we can't do it, return null. 693static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 694 Type *LoadedTy, 695 Instruction *InsertPt, 696 const TargetData &TD) { 697 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 698 return 0; 699 700 // If this is already the right type, just return it. 701 Type *StoredValTy = StoredVal->getType(); 702 703 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); 704 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 705 706 // If the store and reload are the same size, we can always reuse it. 707 if (StoreSize == LoadSize) { 708 // Pointer to Pointer -> use bitcast. 709 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) 710 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 711 712 // Convert source pointers to integers, which can be bitcast. 713 if (StoredValTy->isPointerTy()) { 714 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 715 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 716 } 717 718 Type *TypeToCastTo = LoadedTy; 719 if (TypeToCastTo->isPointerTy()) 720 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 721 722 if (StoredValTy != TypeToCastTo) 723 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 724 725 // Cast to pointer if the load needs a pointer type. 726 if (LoadedTy->isPointerTy()) 727 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 728 729 return StoredVal; 730 } 731 732 // If the loaded value is smaller than the available value, then we can 733 // extract out a piece from it. If the available value is too small, then we 734 // can't do anything. 735 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 736 737 // Convert source pointers to integers, which can be manipulated. 738 if (StoredValTy->isPointerTy()) { 739 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 740 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 741 } 742 743 // Convert vectors and fp to integer, which can be manipulated. 744 if (!StoredValTy->isIntegerTy()) { 745 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 746 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 747 } 748 749 // If this is a big-endian system, we need to shift the value down to the low 750 // bits so that a truncate will work. 751 if (TD.isBigEndian()) { 752 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 753 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 754 } 755 756 // Truncate the integer to the right size now. 757 Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 758 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 759 760 if (LoadedTy == NewIntTy) 761 return StoredVal; 762 763 // If the result is a pointer, inttoptr. 764 if (LoadedTy->isPointerTy()) 765 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 766 767 // Otherwise, bitcast. 768 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 769} 770 771/// AnalyzeLoadFromClobberingWrite - This function is called when we have a 772/// memdep query of a load that ends up being a clobbering memory write (store, 773/// memset, memcpy, memmove). This means that the write *may* provide bits used 774/// by the load but we can't be sure because the pointers don't mustalias. 775/// 776/// Check this case to see if there is anything more we can do before we give 777/// up. This returns -1 if we have to give up, or a byte number in the stored 778/// value of the piece that feeds the load. 779static int AnalyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr, 780 Value *WritePtr, 781 uint64_t WriteSizeInBits, 782 const TargetData &TD) { 783 // If the loaded or stored value is a first class array or struct, don't try 784 // to transform them. We need to be able to bitcast to integer. 785 if (LoadTy->isStructTy() || LoadTy->isArrayTy()) 786 return -1; 787 788 int64_t StoreOffset = 0, LoadOffset = 0; 789 Value *StoreBase = GetPointerBaseWithConstantOffset(WritePtr, StoreOffset,TD); 790 Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, TD); 791 if (StoreBase != LoadBase) 792 return -1; 793 794 // If the load and store are to the exact same address, they should have been 795 // a must alias. AA must have gotten confused. 796 // FIXME: Study to see if/when this happens. One case is forwarding a memset 797 // to a load from the base of the memset. 798#if 0 799 if (LoadOffset == StoreOffset) { 800 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 801 << "Base = " << *StoreBase << "\n" 802 << "Store Ptr = " << *WritePtr << "\n" 803 << "Store Offs = " << StoreOffset << "\n" 804 << "Load Ptr = " << *LoadPtr << "\n"; 805 abort(); 806 } 807#endif 808 809 // If the load and store don't overlap at all, the store doesn't provide 810 // anything to the load. In this case, they really don't alias at all, AA 811 // must have gotten confused. 812 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy); 813 814 if ((WriteSizeInBits & 7) | (LoadSize & 7)) 815 return -1; 816 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. 817 LoadSize >>= 3; 818 819 820 bool isAAFailure = false; 821 if (StoreOffset < LoadOffset) 822 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 823 else 824 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 825 826 if (isAAFailure) { 827#if 0 828 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" 829 << "Base = " << *StoreBase << "\n" 830 << "Store Ptr = " << *WritePtr << "\n" 831 << "Store Offs = " << StoreOffset << "\n" 832 << "Load Ptr = " << *LoadPtr << "\n"; 833 abort(); 834#endif 835 return -1; 836 } 837 838 // If the Load isn't completely contained within the stored bits, we don't 839 // have all the bits to feed it. We could do something crazy in the future 840 // (issue a smaller load then merge the bits in) but this seems unlikely to be 841 // valuable. 842 if (StoreOffset > LoadOffset || 843 StoreOffset+StoreSize < LoadOffset+LoadSize) 844 return -1; 845 846 // Okay, we can do this transformation. Return the number of bytes into the 847 // store that the load is. 848 return LoadOffset-StoreOffset; 849} 850 851/// AnalyzeLoadFromClobberingStore - This function is called when we have a 852/// memdep query of a load that ends up being a clobbering store. 853static int AnalyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr, 854 StoreInst *DepSI, 855 const TargetData &TD) { 856 // Cannot handle reading from store of first-class aggregate yet. 857 if (DepSI->getValueOperand()->getType()->isStructTy() || 858 DepSI->getValueOperand()->getType()->isArrayTy()) 859 return -1; 860 861 Value *StorePtr = DepSI->getPointerOperand(); 862 uint64_t StoreSize =TD.getTypeSizeInBits(DepSI->getValueOperand()->getType()); 863 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 864 StorePtr, StoreSize, TD); 865} 866 867/// AnalyzeLoadFromClobberingLoad - This function is called when we have a 868/// memdep query of a load that ends up being clobbered by another load. See if 869/// the other load can feed into the second load. 870static int AnalyzeLoadFromClobberingLoad(Type *LoadTy, Value *LoadPtr, 871 LoadInst *DepLI, const TargetData &TD){ 872 // Cannot handle reading from store of first-class aggregate yet. 873 if (DepLI->getType()->isStructTy() || DepLI->getType()->isArrayTy()) 874 return -1; 875 876 Value *DepPtr = DepLI->getPointerOperand(); 877 uint64_t DepSize = TD.getTypeSizeInBits(DepLI->getType()); 878 int R = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, DepSize, TD); 879 if (R != -1) return R; 880 881 // If we have a load/load clobber an DepLI can be widened to cover this load, 882 // then we should widen it! 883 int64_t LoadOffs = 0; 884 const Value *LoadBase = 885 GetPointerBaseWithConstantOffset(LoadPtr, LoadOffs, TD); 886 unsigned LoadSize = TD.getTypeStoreSize(LoadTy); 887 888 unsigned Size = MemoryDependenceAnalysis:: 889 getLoadLoadClobberFullWidthSize(LoadBase, LoadOffs, LoadSize, DepLI, TD); 890 if (Size == 0) return -1; 891 892 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, Size*8, TD); 893} 894 895 896 897static int AnalyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr, 898 MemIntrinsic *MI, 899 const TargetData &TD) { 900 // If the mem operation is a non-constant size, we can't handle it. 901 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); 902 if (SizeCst == 0) return -1; 903 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; 904 905 // If this is memset, we just need to see if the offset is valid in the size 906 // of the memset.. 907 if (MI->getIntrinsicID() == Intrinsic::memset) 908 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), 909 MemSizeInBits, TD); 910 911 // If we have a memcpy/memmove, the only case we can handle is if this is a 912 // copy from constant memory. In that case, we can read directly from the 913 // constant memory. 914 MemTransferInst *MTI = cast<MemTransferInst>(MI); 915 916 Constant *Src = dyn_cast<Constant>(MTI->getSource()); 917 if (Src == 0) return -1; 918 919 GlobalVariable *GV = dyn_cast<GlobalVariable>(GetUnderlyingObject(Src, &TD)); 920 if (GV == 0 || !GV->isConstant()) return -1; 921 922 // See if the access is within the bounds of the transfer. 923 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 924 MI->getDest(), MemSizeInBits, TD); 925 if (Offset == -1) 926 return Offset; 927 928 // Otherwise, see if we can constant fold a load from the constant with the 929 // offset applied as appropriate. 930 Src = ConstantExpr::getBitCast(Src, 931 llvm::Type::getInt8PtrTy(Src->getContext())); 932 Constant *OffsetCst = 933 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 934 Src = ConstantExpr::getGetElementPtr(Src, OffsetCst); 935 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 936 if (ConstantFoldLoadFromConstPtr(Src, &TD)) 937 return Offset; 938 return -1; 939} 940 941 942/// GetStoreValueForLoad - This function is called when we have a 943/// memdep query of a load that ends up being a clobbering store. This means 944/// that the store provides bits used by the load but we the pointers don't 945/// mustalias. Check this case to see if there is anything more we can do 946/// before we give up. 947static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 948 Type *LoadTy, 949 Instruction *InsertPt, const TargetData &TD){ 950 LLVMContext &Ctx = SrcVal->getType()->getContext(); 951 952 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8; 953 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8; 954 955 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 956 957 // Compute which bits of the stored value are being used by the load. Convert 958 // to an integer type to start with. 959 if (SrcVal->getType()->isPointerTy()) 960 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx)); 961 if (!SrcVal->getType()->isIntegerTy()) 962 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8)); 963 964 // Shift the bits to the least significant depending on endianness. 965 unsigned ShiftAmt; 966 if (TD.isLittleEndian()) 967 ShiftAmt = Offset*8; 968 else 969 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 970 971 if (ShiftAmt) 972 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt); 973 974 if (LoadSize != StoreSize) 975 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8)); 976 977 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 978} 979 980/// GetLoadValueForLoad - This function is called when we have a 981/// memdep query of a load that ends up being a clobbering load. This means 982/// that the load *may* provide bits used by the load but we can't be sure 983/// because the pointers don't mustalias. Check this case to see if there is 984/// anything more we can do before we give up. 985static Value *GetLoadValueForLoad(LoadInst *SrcVal, unsigned Offset, 986 Type *LoadTy, Instruction *InsertPt, 987 GVN &gvn) { 988 const TargetData &TD = *gvn.getTargetData(); 989 // If Offset+LoadTy exceeds the size of SrcVal, then we must be wanting to 990 // widen SrcVal out to a larger load. 991 unsigned SrcValSize = TD.getTypeStoreSize(SrcVal->getType()); 992 unsigned LoadSize = TD.getTypeStoreSize(LoadTy); 993 if (Offset+LoadSize > SrcValSize) { 994 assert(SrcVal->isSimple() && "Cannot widen volatile/atomic load!"); 995 assert(SrcVal->getType()->isIntegerTy() && "Can't widen non-integer load"); 996 // If we have a load/load clobber an DepLI can be widened to cover this 997 // load, then we should widen it to the next power of 2 size big enough! 998 unsigned NewLoadSize = Offset+LoadSize; 999 if (!isPowerOf2_32(NewLoadSize)) 1000 NewLoadSize = NextPowerOf2(NewLoadSize); 1001 1002 Value *PtrVal = SrcVal->getPointerOperand(); 1003 1004 // Insert the new load after the old load. This ensures that subsequent 1005 // memdep queries will find the new load. We can't easily remove the old 1006 // load completely because it is already in the value numbering table. 1007 IRBuilder<> Builder(SrcVal->getParent(), ++BasicBlock::iterator(SrcVal)); 1008 Type *DestPTy = 1009 IntegerType::get(LoadTy->getContext(), NewLoadSize*8); 1010 DestPTy = PointerType::get(DestPTy, 1011 cast<PointerType>(PtrVal->getType())->getAddressSpace()); 1012 Builder.SetCurrentDebugLocation(SrcVal->getDebugLoc()); 1013 PtrVal = Builder.CreateBitCast(PtrVal, DestPTy); 1014 LoadInst *NewLoad = Builder.CreateLoad(PtrVal); 1015 NewLoad->takeName(SrcVal); 1016 NewLoad->setAlignment(SrcVal->getAlignment()); 1017 1018 DEBUG(dbgs() << "GVN WIDENED LOAD: " << *SrcVal << "\n"); 1019 DEBUG(dbgs() << "TO: " << *NewLoad << "\n"); 1020 1021 // Replace uses of the original load with the wider load. On a big endian 1022 // system, we need to shift down to get the relevant bits. 1023 Value *RV = NewLoad; 1024 if (TD.isBigEndian()) 1025 RV = Builder.CreateLShr(RV, 1026 NewLoadSize*8-SrcVal->getType()->getPrimitiveSizeInBits()); 1027 RV = Builder.CreateTrunc(RV, SrcVal->getType()); 1028 SrcVal->replaceAllUsesWith(RV); 1029 1030 // We would like to use gvn.markInstructionForDeletion here, but we can't 1031 // because the load is already memoized into the leader map table that GVN 1032 // tracks. It is potentially possible to remove the load from the table, 1033 // but then there all of the operations based on it would need to be 1034 // rehashed. Just leave the dead load around. 1035 gvn.getMemDep().removeInstruction(SrcVal); 1036 SrcVal = NewLoad; 1037 } 1038 1039 return GetStoreValueForLoad(SrcVal, Offset, LoadTy, InsertPt, TD); 1040} 1041 1042 1043/// GetMemInstValueForLoad - This function is called when we have a 1044/// memdep query of a load that ends up being a clobbering mem intrinsic. 1045static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, 1046 Type *LoadTy, Instruction *InsertPt, 1047 const TargetData &TD){ 1048 LLVMContext &Ctx = LoadTy->getContext(); 1049 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1050 1051 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1052 1053 // We know that this method is only called when the mem transfer fully 1054 // provides the bits for the load. 1055 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { 1056 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and 1057 // independently of what the offset is. 1058 Value *Val = MSI->getValue(); 1059 if (LoadSize != 1) 1060 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); 1061 1062 Value *OneElt = Val; 1063 1064 // Splat the value out to the right number of bits. 1065 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { 1066 // If we can double the number of bytes set, do it. 1067 if (NumBytesSet*2 <= LoadSize) { 1068 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); 1069 Val = Builder.CreateOr(Val, ShVal); 1070 NumBytesSet <<= 1; 1071 continue; 1072 } 1073 1074 // Otherwise insert one byte at a time. 1075 Value *ShVal = Builder.CreateShl(Val, 1*8); 1076 Val = Builder.CreateOr(OneElt, ShVal); 1077 ++NumBytesSet; 1078 } 1079 1080 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD); 1081 } 1082 1083 // Otherwise, this is a memcpy/memmove from a constant global. 1084 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); 1085 Constant *Src = cast<Constant>(MTI->getSource()); 1086 1087 // Otherwise, see if we can constant fold a load from the constant with the 1088 // offset applied as appropriate. 1089 Src = ConstantExpr::getBitCast(Src, 1090 llvm::Type::getInt8PtrTy(Src->getContext())); 1091 Constant *OffsetCst = 1092 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1093 Src = ConstantExpr::getGetElementPtr(Src, OffsetCst); 1094 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1095 return ConstantFoldLoadFromConstPtr(Src, &TD); 1096} 1097 1098namespace { 1099 1100struct AvailableValueInBlock { 1101 /// BB - The basic block in question. 1102 BasicBlock *BB; 1103 enum ValType { 1104 SimpleVal, // A simple offsetted value that is accessed. 1105 LoadVal, // A value produced by a load. 1106 MemIntrin // A memory intrinsic which is loaded from. 1107 }; 1108 1109 /// V - The value that is live out of the block. 1110 PointerIntPair<Value *, 2, ValType> Val; 1111 1112 /// Offset - The byte offset in Val that is interesting for the load query. 1113 unsigned Offset; 1114 1115 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1116 unsigned Offset = 0) { 1117 AvailableValueInBlock Res; 1118 Res.BB = BB; 1119 Res.Val.setPointer(V); 1120 Res.Val.setInt(SimpleVal); 1121 Res.Offset = Offset; 1122 return Res; 1123 } 1124 1125 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, 1126 unsigned Offset = 0) { 1127 AvailableValueInBlock Res; 1128 Res.BB = BB; 1129 Res.Val.setPointer(MI); 1130 Res.Val.setInt(MemIntrin); 1131 Res.Offset = Offset; 1132 return Res; 1133 } 1134 1135 static AvailableValueInBlock getLoad(BasicBlock *BB, LoadInst *LI, 1136 unsigned Offset = 0) { 1137 AvailableValueInBlock Res; 1138 Res.BB = BB; 1139 Res.Val.setPointer(LI); 1140 Res.Val.setInt(LoadVal); 1141 Res.Offset = Offset; 1142 return Res; 1143 } 1144 1145 bool isSimpleValue() const { return Val.getInt() == SimpleVal; } 1146 bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; } 1147 bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; } 1148 1149 Value *getSimpleValue() const { 1150 assert(isSimpleValue() && "Wrong accessor"); 1151 return Val.getPointer(); 1152 } 1153 1154 LoadInst *getCoercedLoadValue() const { 1155 assert(isCoercedLoadValue() && "Wrong accessor"); 1156 return cast<LoadInst>(Val.getPointer()); 1157 } 1158 1159 MemIntrinsic *getMemIntrinValue() const { 1160 assert(isMemIntrinValue() && "Wrong accessor"); 1161 return cast<MemIntrinsic>(Val.getPointer()); 1162 } 1163 1164 /// MaterializeAdjustedValue - Emit code into this block to adjust the value 1165 /// defined here to the specified type. This handles various coercion cases. 1166 Value *MaterializeAdjustedValue(Type *LoadTy, GVN &gvn) const { 1167 Value *Res; 1168 if (isSimpleValue()) { 1169 Res = getSimpleValue(); 1170 if (Res->getType() != LoadTy) { 1171 const TargetData *TD = gvn.getTargetData(); 1172 assert(TD && "Need target data to handle type mismatch case"); 1173 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), 1174 *TD); 1175 1176 DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " 1177 << *getSimpleValue() << '\n' 1178 << *Res << '\n' << "\n\n\n"); 1179 } 1180 } else if (isCoercedLoadValue()) { 1181 LoadInst *Load = getCoercedLoadValue(); 1182 if (Load->getType() == LoadTy && Offset == 0) { 1183 Res = Load; 1184 } else { 1185 Res = GetLoadValueForLoad(Load, Offset, LoadTy, BB->getTerminator(), 1186 gvn); 1187 1188 DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset << " " 1189 << *getCoercedLoadValue() << '\n' 1190 << *Res << '\n' << "\n\n\n"); 1191 } 1192 } else { 1193 const TargetData *TD = gvn.getTargetData(); 1194 assert(TD && "Need target data to handle type mismatch case"); 1195 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, 1196 LoadTy, BB->getTerminator(), *TD); 1197 DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset 1198 << " " << *getMemIntrinValue() << '\n' 1199 << *Res << '\n' << "\n\n\n"); 1200 } 1201 return Res; 1202 } 1203}; 1204 1205} // end anonymous namespace 1206 1207/// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, 1208/// construct SSA form, allowing us to eliminate LI. This returns the value 1209/// that should be used at LI's definition site. 1210static Value *ConstructSSAForLoadSet(LoadInst *LI, 1211 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1212 GVN &gvn) { 1213 // Check for the fully redundant, dominating load case. In this case, we can 1214 // just use the dominating value directly. 1215 if (ValuesPerBlock.size() == 1 && 1216 gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB, 1217 LI->getParent())) 1218 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), gvn); 1219 1220 // Otherwise, we have to construct SSA form. 1221 SmallVector<PHINode*, 8> NewPHIs; 1222 SSAUpdater SSAUpdate(&NewPHIs); 1223 SSAUpdate.Initialize(LI->getType(), LI->getName()); 1224 1225 Type *LoadTy = LI->getType(); 1226 1227 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1228 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1229 BasicBlock *BB = AV.BB; 1230 1231 if (SSAUpdate.HasValueForBlock(BB)) 1232 continue; 1233 1234 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, gvn)); 1235 } 1236 1237 // Perform PHI construction. 1238 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1239 1240 // If new PHI nodes were created, notify alias analysis. 1241 if (V->getType()->isPointerTy()) { 1242 AliasAnalysis *AA = gvn.getAliasAnalysis(); 1243 1244 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 1245 AA->copyValue(LI, NewPHIs[i]); 1246 1247 // Now that we've copied information to the new PHIs, scan through 1248 // them again and inform alias analysis that we've added potentially 1249 // escaping uses to any values that are operands to these PHIs. 1250 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) { 1251 PHINode *P = NewPHIs[i]; 1252 for (unsigned ii = 0, ee = P->getNumIncomingValues(); ii != ee; ++ii) { 1253 unsigned jj = PHINode::getOperandNumForIncomingValue(ii); 1254 AA->addEscapingUse(P->getOperandUse(jj)); 1255 } 1256 } 1257 } 1258 1259 return V; 1260} 1261 1262static bool isLifetimeStart(const Instruction *Inst) { 1263 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) 1264 return II->getIntrinsicID() == Intrinsic::lifetime_start; 1265 return false; 1266} 1267 1268/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1269/// non-local by performing PHI construction. 1270bool GVN::processNonLocalLoad(LoadInst *LI) { 1271 // Find the non-local dependencies of the load. 1272 SmallVector<NonLocalDepResult, 64> Deps; 1273 AliasAnalysis::Location Loc = VN.getAliasAnalysis()->getLocation(LI); 1274 MD->getNonLocalPointerDependency(Loc, true, LI->getParent(), Deps); 1275 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: " 1276 // << Deps.size() << *LI << '\n'); 1277 1278 // If we had to process more than one hundred blocks to find the 1279 // dependencies, this load isn't worth worrying about. Optimizing 1280 // it will be too expensive. 1281 unsigned NumDeps = Deps.size(); 1282 if (NumDeps > 100) 1283 return false; 1284 1285 // If we had a phi translation failure, we'll have a single entry which is a 1286 // clobber in the current block. Reject this early. 1287 if (NumDeps == 1 && 1288 !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) { 1289 DEBUG( 1290 dbgs() << "GVN: non-local load "; 1291 WriteAsOperand(dbgs(), LI); 1292 dbgs() << " has unknown dependencies\n"; 1293 ); 1294 return false; 1295 } 1296 1297 // Filter out useless results (non-locals, etc). Keep track of the blocks 1298 // where we have a value available in repl, also keep track of whether we see 1299 // dependencies that produce an unknown value for the load (such as a call 1300 // that could potentially clobber the load). 1301 SmallVector<AvailableValueInBlock, 64> ValuesPerBlock; 1302 SmallVector<BasicBlock*, 64> UnavailableBlocks; 1303 1304 for (unsigned i = 0, e = NumDeps; i != e; ++i) { 1305 BasicBlock *DepBB = Deps[i].getBB(); 1306 MemDepResult DepInfo = Deps[i].getResult(); 1307 1308 if (!DepInfo.isDef() && !DepInfo.isClobber()) { 1309 UnavailableBlocks.push_back(DepBB); 1310 continue; 1311 } 1312 1313 if (DepInfo.isClobber()) { 1314 // The address being loaded in this non-local block may not be the same as 1315 // the pointer operand of the load if PHI translation occurs. Make sure 1316 // to consider the right address. 1317 Value *Address = Deps[i].getAddress(); 1318 1319 // If the dependence is to a store that writes to a superset of the bits 1320 // read by the load, we can extract the bits we need for the load from the 1321 // stored value. 1322 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1323 if (TD && Address) { 1324 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address, 1325 DepSI, *TD); 1326 if (Offset != -1) { 1327 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1328 DepSI->getValueOperand(), 1329 Offset)); 1330 continue; 1331 } 1332 } 1333 } 1334 1335 // Check to see if we have something like this: 1336 // load i32* P 1337 // load i8* (P+1) 1338 // if we have this, replace the later with an extraction from the former. 1339 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) { 1340 // If this is a clobber and L is the first instruction in its block, then 1341 // we have the first instruction in the entry block. 1342 if (DepLI != LI && Address && TD) { 1343 int Offset = AnalyzeLoadFromClobberingLoad(LI->getType(), 1344 LI->getPointerOperand(), 1345 DepLI, *TD); 1346 1347 if (Offset != -1) { 1348 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB,DepLI, 1349 Offset)); 1350 continue; 1351 } 1352 } 1353 } 1354 1355 // If the clobbering value is a memset/memcpy/memmove, see if we can 1356 // forward a value on from it. 1357 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { 1358 if (TD && Address) { 1359 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address, 1360 DepMI, *TD); 1361 if (Offset != -1) { 1362 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, 1363 Offset)); 1364 continue; 1365 } 1366 } 1367 } 1368 1369 UnavailableBlocks.push_back(DepBB); 1370 continue; 1371 } 1372 1373 // DepInfo.isDef() here 1374 1375 Instruction *DepInst = DepInfo.getInst(); 1376 1377 // Loading the allocation -> undef. 1378 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) || 1379 // Loading immediately after lifetime begin -> undef. 1380 isLifetimeStart(DepInst)) { 1381 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1382 UndefValue::get(LI->getType()))); 1383 continue; 1384 } 1385 1386 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1387 // Reject loads and stores that are to the same address but are of 1388 // different types if we have to. 1389 if (S->getValueOperand()->getType() != LI->getType()) { 1390 // If the stored value is larger or equal to the loaded value, we can 1391 // reuse it. 1392 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(), 1393 LI->getType(), *TD)) { 1394 UnavailableBlocks.push_back(DepBB); 1395 continue; 1396 } 1397 } 1398 1399 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1400 S->getValueOperand())); 1401 continue; 1402 } 1403 1404 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1405 // If the types mismatch and we can't handle it, reject reuse of the load. 1406 if (LD->getType() != LI->getType()) { 1407 // If the stored value is larger or equal to the loaded value, we can 1408 // reuse it. 1409 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1410 UnavailableBlocks.push_back(DepBB); 1411 continue; 1412 } 1413 } 1414 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB, LD)); 1415 continue; 1416 } 1417 1418 UnavailableBlocks.push_back(DepBB); 1419 continue; 1420 } 1421 1422 // If we have no predecessors that produce a known value for this load, exit 1423 // early. 1424 if (ValuesPerBlock.empty()) return false; 1425 1426 // If all of the instructions we depend on produce a known value for this 1427 // load, then it is fully redundant and we can use PHI insertion to compute 1428 // its value. Insert PHIs and remove the fully redundant value now. 1429 if (UnavailableBlocks.empty()) { 1430 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1431 1432 // Perform PHI construction. 1433 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); 1434 LI->replaceAllUsesWith(V); 1435 1436 if (isa<PHINode>(V)) 1437 V->takeName(LI); 1438 if (V->getType()->isPointerTy()) 1439 MD->invalidateCachedPointerInfo(V); 1440 markInstructionForDeletion(LI); 1441 ++NumGVNLoad; 1442 return true; 1443 } 1444 1445 if (!EnablePRE || !EnableLoadPRE) 1446 return false; 1447 1448 // Okay, we have *some* definitions of the value. This means that the value 1449 // is available in some of our (transitive) predecessors. Lets think about 1450 // doing PRE of this load. This will involve inserting a new load into the 1451 // predecessor when it's not available. We could do this in general, but 1452 // prefer to not increase code size. As such, we only do this when we know 1453 // that we only have to insert *one* load (which means we're basically moving 1454 // the load, not inserting a new one). 1455 1456 SmallPtrSet<BasicBlock *, 4> Blockers; 1457 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1458 Blockers.insert(UnavailableBlocks[i]); 1459 1460 // Let's find the first basic block with more than one predecessor. Walk 1461 // backwards through predecessors if needed. 1462 BasicBlock *LoadBB = LI->getParent(); 1463 BasicBlock *TmpBB = LoadBB; 1464 1465 bool isSinglePred = false; 1466 bool allSingleSucc = true; 1467 while (TmpBB->getSinglePredecessor()) { 1468 isSinglePred = true; 1469 TmpBB = TmpBB->getSinglePredecessor(); 1470 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1471 return false; 1472 if (Blockers.count(TmpBB)) 1473 return false; 1474 1475 // If any of these blocks has more than one successor (i.e. if the edge we 1476 // just traversed was critical), then there are other paths through this 1477 // block along which the load may not be anticipated. Hoisting the load 1478 // above this block would be adding the load to execution paths along 1479 // which it was not previously executed. 1480 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1481 return false; 1482 } 1483 1484 assert(TmpBB); 1485 LoadBB = TmpBB; 1486 1487 // FIXME: It is extremely unclear what this loop is doing, other than 1488 // artificially restricting loadpre. 1489 if (isSinglePred) { 1490 bool isHot = false; 1491 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1492 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1493 if (AV.isSimpleValue()) 1494 // "Hot" Instruction is in some loop (because it dominates its dep. 1495 // instruction). 1496 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue())) 1497 if (DT->dominates(LI, I)) { 1498 isHot = true; 1499 break; 1500 } 1501 } 1502 1503 // We are interested only in "hot" instructions. We don't want to do any 1504 // mis-optimizations here. 1505 if (!isHot) 1506 return false; 1507 } 1508 1509 // Check to see how many predecessors have the loaded value fully 1510 // available. 1511 DenseMap<BasicBlock*, Value*> PredLoads; 1512 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1513 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1514 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1515 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1516 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1517 1518 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit; 1519 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1520 PI != E; ++PI) { 1521 BasicBlock *Pred = *PI; 1522 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) { 1523 continue; 1524 } 1525 PredLoads[Pred] = 0; 1526 1527 if (Pred->getTerminator()->getNumSuccessors() != 1) { 1528 if (isa<IndirectBrInst>(Pred->getTerminator())) { 1529 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" 1530 << Pred->getName() << "': " << *LI << '\n'); 1531 return false; 1532 } 1533 1534 if (LoadBB->isLandingPad()) { 1535 DEBUG(dbgs() 1536 << "COULD NOT PRE LOAD BECAUSE OF LANDING PAD CRITICAL EDGE '" 1537 << Pred->getName() << "': " << *LI << '\n'); 1538 return false; 1539 } 1540 1541 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB); 1542 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum)); 1543 } 1544 } 1545 1546 if (!NeedToSplit.empty()) { 1547 toSplit.append(NeedToSplit.begin(), NeedToSplit.end()); 1548 return false; 1549 } 1550 1551 // Decide whether PRE is profitable for this load. 1552 unsigned NumUnavailablePreds = PredLoads.size(); 1553 assert(NumUnavailablePreds != 0 && 1554 "Fully available value should be eliminated above!"); 1555 1556 // If this load is unavailable in multiple predecessors, reject it. 1557 // FIXME: If we could restructure the CFG, we could make a common pred with 1558 // all the preds that don't have an available LI and insert a new load into 1559 // that one block. 1560 if (NumUnavailablePreds != 1) 1561 return false; 1562 1563 // Check if the load can safely be moved to all the unavailable predecessors. 1564 bool CanDoPRE = true; 1565 SmallVector<Instruction*, 8> NewInsts; 1566 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1567 E = PredLoads.end(); I != E; ++I) { 1568 BasicBlock *UnavailablePred = I->first; 1569 1570 // Do PHI translation to get its value in the predecessor if necessary. The 1571 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. 1572 1573 // If all preds have a single successor, then we know it is safe to insert 1574 // the load on the pred (?!?), so we can insert code to materialize the 1575 // pointer if it is not available. 1576 PHITransAddr Address(LI->getPointerOperand(), TD); 1577 Value *LoadPtr = 0; 1578 if (allSingleSucc) { 1579 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, 1580 *DT, NewInsts); 1581 } else { 1582 Address.PHITranslateValue(LoadBB, UnavailablePred, DT); 1583 LoadPtr = Address.getAddr(); 1584 } 1585 1586 // If we couldn't find or insert a computation of this phi translated value, 1587 // we fail PRE. 1588 if (LoadPtr == 0) { 1589 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " 1590 << *LI->getPointerOperand() << "\n"); 1591 CanDoPRE = false; 1592 break; 1593 } 1594 1595 // Make sure it is valid to move this load here. We have to watch out for: 1596 // @1 = getelementptr (i8* p, ... 1597 // test p and branch if == 0 1598 // load @1 1599 // It is valid to have the getelementptr before the test, even if p can 1600 // be 0, as getelementptr only does address arithmetic. 1601 // If we are not pushing the value through any multiple-successor blocks 1602 // we do not have this case. Otherwise, check that the load is safe to 1603 // put anywhere; this can be improved, but should be conservatively safe. 1604 if (!allSingleSucc && 1605 // FIXME: REEVALUTE THIS. 1606 !isSafeToLoadUnconditionally(LoadPtr, 1607 UnavailablePred->getTerminator(), 1608 LI->getAlignment(), TD)) { 1609 CanDoPRE = false; 1610 break; 1611 } 1612 1613 I->second = LoadPtr; 1614 } 1615 1616 if (!CanDoPRE) { 1617 while (!NewInsts.empty()) { 1618 Instruction *I = NewInsts.pop_back_val(); 1619 if (MD) MD->removeInstruction(I); 1620 I->eraseFromParent(); 1621 } 1622 return false; 1623 } 1624 1625 // Okay, we can eliminate this load by inserting a reload in the predecessor 1626 // and using PHI construction to get the value in the other predecessors, do 1627 // it. 1628 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1629 DEBUG(if (!NewInsts.empty()) 1630 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " 1631 << *NewInsts.back() << '\n'); 1632 1633 // Assign value numbers to the new instructions. 1634 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) { 1635 // FIXME: We really _ought_ to insert these value numbers into their 1636 // parent's availability map. However, in doing so, we risk getting into 1637 // ordering issues. If a block hasn't been processed yet, we would be 1638 // marking a value as AVAIL-IN, which isn't what we intend. 1639 VN.lookup_or_add(NewInsts[i]); 1640 } 1641 1642 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1643 E = PredLoads.end(); I != E; ++I) { 1644 BasicBlock *UnavailablePred = I->first; 1645 Value *LoadPtr = I->second; 1646 1647 Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1648 LI->getAlignment(), 1649 UnavailablePred->getTerminator()); 1650 1651 // Transfer the old load's TBAA tag to the new load. 1652 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) 1653 NewLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1654 1655 // Transfer DebugLoc. 1656 NewLoad->setDebugLoc(LI->getDebugLoc()); 1657 1658 // Add the newly created load. 1659 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, 1660 NewLoad)); 1661 MD->invalidateCachedPointerInfo(LoadPtr); 1662 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); 1663 } 1664 1665 // Perform PHI construction. 1666 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); 1667 LI->replaceAllUsesWith(V); 1668 if (isa<PHINode>(V)) 1669 V->takeName(LI); 1670 if (V->getType()->isPointerTy()) 1671 MD->invalidateCachedPointerInfo(V); 1672 markInstructionForDeletion(LI); 1673 ++NumPRELoad; 1674 return true; 1675} 1676 1677/// processLoad - Attempt to eliminate a load, first by eliminating it 1678/// locally, and then attempting non-local elimination if that fails. 1679bool GVN::processLoad(LoadInst *L) { 1680 if (!MD) 1681 return false; 1682 1683 if (!L->isSimple()) 1684 return false; 1685 1686 if (L->use_empty()) { 1687 markInstructionForDeletion(L); 1688 return true; 1689 } 1690 1691 // ... to a pointer that has been loaded from before... 1692 MemDepResult Dep = MD->getDependency(L); 1693 1694 // If we have a clobber and target data is around, see if this is a clobber 1695 // that we can fix up through code synthesis. 1696 if (Dep.isClobber() && TD) { 1697 // Check to see if we have something like this: 1698 // store i32 123, i32* %P 1699 // %A = bitcast i32* %P to i8* 1700 // %B = gep i8* %A, i32 1 1701 // %C = load i8* %B 1702 // 1703 // We could do that by recognizing if the clobber instructions are obviously 1704 // a common base + constant offset, and if the previous store (or memset) 1705 // completely covers this load. This sort of thing can happen in bitfield 1706 // access code. 1707 Value *AvailVal = 0; 1708 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) { 1709 int Offset = AnalyzeLoadFromClobberingStore(L->getType(), 1710 L->getPointerOperand(), 1711 DepSI, *TD); 1712 if (Offset != -1) 1713 AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset, 1714 L->getType(), L, *TD); 1715 } 1716 1717 // Check to see if we have something like this: 1718 // load i32* P 1719 // load i8* (P+1) 1720 // if we have this, replace the later with an extraction from the former. 1721 if (LoadInst *DepLI = dyn_cast<LoadInst>(Dep.getInst())) { 1722 // If this is a clobber and L is the first instruction in its block, then 1723 // we have the first instruction in the entry block. 1724 if (DepLI == L) 1725 return false; 1726 1727 int Offset = AnalyzeLoadFromClobberingLoad(L->getType(), 1728 L->getPointerOperand(), 1729 DepLI, *TD); 1730 if (Offset != -1) 1731 AvailVal = GetLoadValueForLoad(DepLI, Offset, L->getType(), L, *this); 1732 } 1733 1734 // If the clobbering value is a memset/memcpy/memmove, see if we can forward 1735 // a value on from it. 1736 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { 1737 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(), 1738 L->getPointerOperand(), 1739 DepMI, *TD); 1740 if (Offset != -1) 1741 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L, *TD); 1742 } 1743 1744 if (AvailVal) { 1745 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' 1746 << *AvailVal << '\n' << *L << "\n\n\n"); 1747 1748 // Replace the load! 1749 L->replaceAllUsesWith(AvailVal); 1750 if (AvailVal->getType()->isPointerTy()) 1751 MD->invalidateCachedPointerInfo(AvailVal); 1752 markInstructionForDeletion(L); 1753 ++NumGVNLoad; 1754 return true; 1755 } 1756 } 1757 1758 // If the value isn't available, don't do anything! 1759 if (Dep.isClobber()) { 1760 DEBUG( 1761 // fast print dep, using operator<< on instruction is too slow. 1762 dbgs() << "GVN: load "; 1763 WriteAsOperand(dbgs(), L); 1764 Instruction *I = Dep.getInst(); 1765 dbgs() << " is clobbered by " << *I << '\n'; 1766 ); 1767 return false; 1768 } 1769 1770 // If it is defined in another block, try harder. 1771 if (Dep.isNonLocal()) 1772 return processNonLocalLoad(L); 1773 1774 if (!Dep.isDef()) { 1775 DEBUG( 1776 // fast print dep, using operator<< on instruction is too slow. 1777 dbgs() << "GVN: load "; 1778 WriteAsOperand(dbgs(), L); 1779 dbgs() << " has unknown dependence\n"; 1780 ); 1781 return false; 1782 } 1783 1784 Instruction *DepInst = Dep.getInst(); 1785 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1786 Value *StoredVal = DepSI->getValueOperand(); 1787 1788 // The store and load are to a must-aliased pointer, but they may not 1789 // actually have the same type. See if we know how to reuse the stored 1790 // value (depending on its type). 1791 if (StoredVal->getType() != L->getType()) { 1792 if (TD) { 1793 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1794 L, *TD); 1795 if (StoredVal == 0) 1796 return false; 1797 1798 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1799 << '\n' << *L << "\n\n\n"); 1800 } 1801 else 1802 return false; 1803 } 1804 1805 // Remove it! 1806 L->replaceAllUsesWith(StoredVal); 1807 if (StoredVal->getType()->isPointerTy()) 1808 MD->invalidateCachedPointerInfo(StoredVal); 1809 markInstructionForDeletion(L); 1810 ++NumGVNLoad; 1811 return true; 1812 } 1813 1814 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1815 Value *AvailableVal = DepLI; 1816 1817 // The loads are of a must-aliased pointer, but they may not actually have 1818 // the same type. See if we know how to reuse the previously loaded value 1819 // (depending on its type). 1820 if (DepLI->getType() != L->getType()) { 1821 if (TD) { 1822 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), 1823 L, *TD); 1824 if (AvailableVal == 0) 1825 return false; 1826 1827 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1828 << "\n" << *L << "\n\n\n"); 1829 } 1830 else 1831 return false; 1832 } 1833 1834 // Remove it! 1835 L->replaceAllUsesWith(AvailableVal); 1836 if (DepLI->getType()->isPointerTy()) 1837 MD->invalidateCachedPointerInfo(DepLI); 1838 markInstructionForDeletion(L); 1839 ++NumGVNLoad; 1840 return true; 1841 } 1842 1843 // If this load really doesn't depend on anything, then we must be loading an 1844 // undef value. This can happen when loading for a fresh allocation with no 1845 // intervening stores, for example. 1846 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) { 1847 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1848 markInstructionForDeletion(L); 1849 ++NumGVNLoad; 1850 return true; 1851 } 1852 1853 // If this load occurs either right after a lifetime begin, 1854 // then the loaded value is undefined. 1855 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(DepInst)) { 1856 if (II->getIntrinsicID() == Intrinsic::lifetime_start) { 1857 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1858 markInstructionForDeletion(L); 1859 ++NumGVNLoad; 1860 return true; 1861 } 1862 } 1863 1864 return false; 1865} 1866 1867// findLeader - In order to find a leader for a given value number at a 1868// specific basic block, we first obtain the list of all Values for that number, 1869// and then scan the list to find one whose block dominates the block in 1870// question. This is fast because dominator tree queries consist of only 1871// a few comparisons of DFS numbers. 1872Value *GVN::findLeader(BasicBlock *BB, uint32_t num) { 1873 LeaderTableEntry Vals = LeaderTable[num]; 1874 if (!Vals.Val) return 0; 1875 1876 Value *Val = 0; 1877 if (DT->dominates(Vals.BB, BB)) { 1878 Val = Vals.Val; 1879 if (isa<Constant>(Val)) return Val; 1880 } 1881 1882 LeaderTableEntry* Next = Vals.Next; 1883 while (Next) { 1884 if (DT->dominates(Next->BB, BB)) { 1885 if (isa<Constant>(Next->Val)) return Next->Val; 1886 if (!Val) Val = Next->Val; 1887 } 1888 1889 Next = Next->Next; 1890 } 1891 1892 return Val; 1893} 1894 1895/// replaceAllDominatedUsesWith - Replace all uses of 'From' with 'To' if the 1896/// use is dominated by the given basic block. Returns the number of uses that 1897/// were replaced. 1898unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To, 1899 BasicBlock *Root) { 1900 unsigned Count = 0; 1901 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end(); 1902 UI != UE; ) { 1903 Instruction *User = cast<Instruction>(*UI); 1904 unsigned OpNum = UI.getOperandNo(); 1905 ++UI; 1906 1907 if (DT->dominates(Root, User->getParent())) { 1908 User->setOperand(OpNum, To); 1909 ++Count; 1910 } 1911 } 1912 return Count; 1913} 1914 1915/// propagateEquality - The given values are known to be equal in every block 1916/// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with 1917/// 'RHS' everywhere in the scope. Returns whether a change was made. 1918bool GVN::propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root) { 1919 if (LHS == RHS) return false; 1920 assert(LHS->getType() == RHS->getType() && "Equal but types differ!"); 1921 1922 // Don't try to propagate equalities between constants. 1923 if (isa<Constant>(LHS) && isa<Constant>(RHS)) 1924 return false; 1925 1926 // Make sure that any constants are on the right-hand side. In general the 1927 // best results are obtained by placing the longest lived value on the RHS. 1928 if (isa<Constant>(LHS)) 1929 std::swap(LHS, RHS); 1930 1931 // If neither term is constant then bail out. This is not for correctness, 1932 // it's just that the non-constant case is much less useful: it occurs just 1933 // as often as the constant case but handling it hardly ever results in an 1934 // improvement. 1935 if (!isa<Constant>(RHS)) 1936 return false; 1937 1938 // If value numbering later deduces that an instruction in the scope is equal 1939 // to 'LHS' then ensure it will be turned into 'RHS'. 1940 addToLeaderTable(VN.lookup_or_add(LHS), RHS, Root); 1941 1942 // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As 1943 // LHS always has at least one use that is not dominated by Root, this will 1944 // never do anything if LHS has only one use. 1945 bool Changed = false; 1946 if (!LHS->hasOneUse()) { 1947 unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root); 1948 Changed |= NumReplacements > 0; 1949 NumGVNEqProp += NumReplacements; 1950 } 1951 1952 // Now try to deduce additional equalities from this one. For example, if the 1953 // known equality was "(A != B)" == "false" then it follows that A and B are 1954 // equal in the scope. Only boolean equalities with an explicit true or false 1955 // RHS are currently supported. 1956 if (!RHS->getType()->isIntegerTy(1)) 1957 // Not a boolean equality - bail out. 1958 return Changed; 1959 ConstantInt *CI = dyn_cast<ConstantInt>(RHS); 1960 if (!CI) 1961 // RHS neither 'true' nor 'false' - bail out. 1962 return Changed; 1963 // Whether RHS equals 'true'. Otherwise it equals 'false'. 1964 bool isKnownTrue = CI->isAllOnesValue(); 1965 bool isKnownFalse = !isKnownTrue; 1966 1967 // If "A && B" is known true then both A and B are known true. If "A || B" 1968 // is known false then both A and B are known false. 1969 Value *A, *B; 1970 if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) || 1971 (isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) { 1972 Changed |= propagateEquality(A, RHS, Root); 1973 Changed |= propagateEquality(B, RHS, Root); 1974 return Changed; 1975 } 1976 1977 // If we are propagating an equality like "(A == B)" == "true" then also 1978 // propagate the equality A == B. 1979 if (ICmpInst *Cmp = dyn_cast<ICmpInst>(LHS)) { 1980 // Only equality comparisons are supported. 1981 if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) || 1982 (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE)) { 1983 Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1); 1984 Changed |= propagateEquality(Op0, Op1, Root); 1985 } 1986 return Changed; 1987 } 1988 1989 return Changed; 1990} 1991 1992/// isOnlyReachableViaThisEdge - There is an edge from 'Src' to 'Dst'. Return 1993/// true if every path from the entry block to 'Dst' passes via this edge. In 1994/// particular 'Dst' must not be reachable via another edge from 'Src'. 1995static bool isOnlyReachableViaThisEdge(BasicBlock *Src, BasicBlock *Dst, 1996 DominatorTree *DT) { 1997 // First off, there must not be more than one edge from Src to Dst, there 1998 // should be exactly one. So keep track of the number of times Src occurs 1999 // as a predecessor of Dst and fail if it's more than once. Secondly, any 2000 // other predecessors of Dst should be dominated by Dst (see logic below). 2001 bool SawEdgeFromSrc = false; 2002 for (pred_iterator PI = pred_begin(Dst), PE = pred_end(Dst); PI != PE; ++PI) { 2003 BasicBlock *Pred = *PI; 2004 if (Pred == Src) { 2005 // An edge from Src to Dst. 2006 if (SawEdgeFromSrc) 2007 // There are multiple edges from Src to Dst - fail. 2008 return false; 2009 SawEdgeFromSrc = true; 2010 continue; 2011 } 2012 // If the predecessor is not dominated by Dst, then it must be possible to 2013 // reach it either without passing through Src (and thus not via the edge) 2014 // or by passing through Src but taking a different edge out of Src. Either 2015 // way it is possible to reach Dst without passing via the edge, so fail. 2016 if (!DT->dominates(Dst, *PI)) 2017 return false; 2018 } 2019 assert(SawEdgeFromSrc && "No edge between these basic blocks!"); 2020 2021 // Every path from the entry block to Dst must at some point pass to Dst from 2022 // a predecessor that is not dominated by Dst. This predecessor can only be 2023 // Src, since all others are dominated by Dst. As there is only one edge from 2024 // Src to Dst, the path passes by this edge. 2025 return true; 2026} 2027 2028/// processInstruction - When calculating availability, handle an instruction 2029/// by inserting it into the appropriate sets 2030bool GVN::processInstruction(Instruction *I) { 2031 // Ignore dbg info intrinsics. 2032 if (isa<DbgInfoIntrinsic>(I)) 2033 return false; 2034 2035 // If the instruction can be easily simplified then do so now in preference 2036 // to value numbering it. Value numbering often exposes redundancies, for 2037 // example if it determines that %y is equal to %x then the instruction 2038 // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. 2039 if (Value *V = SimplifyInstruction(I, TD, TLI, DT)) { 2040 I->replaceAllUsesWith(V); 2041 if (MD && V->getType()->isPointerTy()) 2042 MD->invalidateCachedPointerInfo(V); 2043 markInstructionForDeletion(I); 2044 ++NumGVNSimpl; 2045 return true; 2046 } 2047 2048 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 2049 if (processLoad(LI)) 2050 return true; 2051 2052 unsigned Num = VN.lookup_or_add(LI); 2053 addToLeaderTable(Num, LI, LI->getParent()); 2054 return false; 2055 } 2056 2057 // For conditional branches, we can perform simple conditional propagation on 2058 // the condition value itself. 2059 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 2060 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 2061 return false; 2062 2063 Value *BranchCond = BI->getCondition(); 2064 2065 BasicBlock *TrueSucc = BI->getSuccessor(0); 2066 BasicBlock *FalseSucc = BI->getSuccessor(1); 2067 BasicBlock *Parent = BI->getParent(); 2068 bool Changed = false; 2069 2070 if (isOnlyReachableViaThisEdge(Parent, TrueSucc, DT)) 2071 Changed |= propagateEquality(BranchCond, 2072 ConstantInt::getTrue(TrueSucc->getContext()), 2073 TrueSucc); 2074 2075 if (isOnlyReachableViaThisEdge(Parent, FalseSucc, DT)) 2076 Changed |= propagateEquality(BranchCond, 2077 ConstantInt::getFalse(FalseSucc->getContext()), 2078 FalseSucc); 2079 2080 return Changed; 2081 } 2082 2083 // For switches, propagate the case values into the case destinations. 2084 if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { 2085 Value *SwitchCond = SI->getCondition(); 2086 BasicBlock *Parent = SI->getParent(); 2087 bool Changed = false; 2088 for (unsigned i = 0, e = SI->getNumCases(); i != e; ++i) { 2089 BasicBlock *Dst = SI->getCaseSuccessor(i); 2090 if (isOnlyReachableViaThisEdge(Parent, Dst, DT)) 2091 Changed |= propagateEquality(SwitchCond, SI->getCaseValue(i), Dst); 2092 } 2093 return Changed; 2094 } 2095 2096 // Instructions with void type don't return a value, so there's 2097 // no point in trying to find redudancies in them. 2098 if (I->getType()->isVoidTy()) return false; 2099 2100 uint32_t NextNum = VN.getNextUnusedValueNumber(); 2101 unsigned Num = VN.lookup_or_add(I); 2102 2103 // Allocations are always uniquely numbered, so we can save time and memory 2104 // by fast failing them. 2105 if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) { 2106 addToLeaderTable(Num, I, I->getParent()); 2107 return false; 2108 } 2109 2110 // If the number we were assigned was a brand new VN, then we don't 2111 // need to do a lookup to see if the number already exists 2112 // somewhere in the domtree: it can't! 2113 if (Num == NextNum) { 2114 addToLeaderTable(Num, I, I->getParent()); 2115 return false; 2116 } 2117 2118 // Perform fast-path value-number based elimination of values inherited from 2119 // dominators. 2120 Value *repl = findLeader(I->getParent(), Num); 2121 if (repl == 0) { 2122 // Failure, just remember this instance for future use. 2123 addToLeaderTable(Num, I, I->getParent()); 2124 return false; 2125 } 2126 2127 // Remove it! 2128 I->replaceAllUsesWith(repl); 2129 if (MD && repl->getType()->isPointerTy()) 2130 MD->invalidateCachedPointerInfo(repl); 2131 markInstructionForDeletion(I); 2132 return true; 2133} 2134 2135/// runOnFunction - This is the main transformation entry point for a function. 2136bool GVN::runOnFunction(Function& F) { 2137 if (!NoLoads) 2138 MD = &getAnalysis<MemoryDependenceAnalysis>(); 2139 DT = &getAnalysis<DominatorTree>(); 2140 TD = getAnalysisIfAvailable<TargetData>(); 2141 TLI = &getAnalysis<TargetLibraryInfo>(); 2142 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 2143 VN.setMemDep(MD); 2144 VN.setDomTree(DT); 2145 2146 bool Changed = false; 2147 bool ShouldContinue = true; 2148 2149 // Merge unconditional branches, allowing PRE to catch more 2150 // optimization opportunities. 2151 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 2152 BasicBlock *BB = FI++; 2153 2154 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 2155 if (removedBlock) ++NumGVNBlocks; 2156 2157 Changed |= removedBlock; 2158 } 2159 2160 unsigned Iteration = 0; 2161 while (ShouldContinue) { 2162 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); 2163 ShouldContinue = iterateOnFunction(F); 2164 if (splitCriticalEdges()) 2165 ShouldContinue = true; 2166 Changed |= ShouldContinue; 2167 ++Iteration; 2168 } 2169 2170 if (EnablePRE) { 2171 bool PREChanged = true; 2172 while (PREChanged) { 2173 PREChanged = performPRE(F); 2174 Changed |= PREChanged; 2175 } 2176 } 2177 // FIXME: Should perform GVN again after PRE does something. PRE can move 2178 // computations into blocks where they become fully redundant. Note that 2179 // we can't do this until PRE's critical edge splitting updates memdep. 2180 // Actually, when this happens, we should just fully integrate PRE into GVN. 2181 2182 cleanupGlobalSets(); 2183 2184 return Changed; 2185} 2186 2187 2188bool GVN::processBlock(BasicBlock *BB) { 2189 // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function 2190 // (and incrementing BI before processing an instruction). 2191 assert(InstrsToErase.empty() && 2192 "We expect InstrsToErase to be empty across iterations"); 2193 bool ChangedFunction = false; 2194 2195 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 2196 BI != BE;) { 2197 ChangedFunction |= processInstruction(BI); 2198 if (InstrsToErase.empty()) { 2199 ++BI; 2200 continue; 2201 } 2202 2203 // If we need some instructions deleted, do it now. 2204 NumGVNInstr += InstrsToErase.size(); 2205 2206 // Avoid iterator invalidation. 2207 bool AtStart = BI == BB->begin(); 2208 if (!AtStart) 2209 --BI; 2210 2211 for (SmallVector<Instruction*, 4>::iterator I = InstrsToErase.begin(), 2212 E = InstrsToErase.end(); I != E; ++I) { 2213 DEBUG(dbgs() << "GVN removed: " << **I << '\n'); 2214 if (MD) MD->removeInstruction(*I); 2215 (*I)->eraseFromParent(); 2216 DEBUG(verifyRemoved(*I)); 2217 } 2218 InstrsToErase.clear(); 2219 2220 if (AtStart) 2221 BI = BB->begin(); 2222 else 2223 ++BI; 2224 } 2225 2226 return ChangedFunction; 2227} 2228 2229/// performPRE - Perform a purely local form of PRE that looks for diamond 2230/// control flow patterns and attempts to perform simple PRE at the join point. 2231bool GVN::performPRE(Function &F) { 2232 bool Changed = false; 2233 DenseMap<BasicBlock*, Value*> predMap; 2234 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 2235 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 2236 BasicBlock *CurrentBlock = *DI; 2237 2238 // Nothing to PRE in the entry block. 2239 if (CurrentBlock == &F.getEntryBlock()) continue; 2240 2241 // Don't perform PRE on a landing pad. 2242 if (CurrentBlock->isLandingPad()) continue; 2243 2244 for (BasicBlock::iterator BI = CurrentBlock->begin(), 2245 BE = CurrentBlock->end(); BI != BE; ) { 2246 Instruction *CurInst = BI++; 2247 2248 if (isa<AllocaInst>(CurInst) || 2249 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 2250 CurInst->getType()->isVoidTy() || 2251 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 2252 isa<DbgInfoIntrinsic>(CurInst)) 2253 continue; 2254 2255 // We don't currently value number ANY inline asm calls. 2256 if (CallInst *CallI = dyn_cast<CallInst>(CurInst)) 2257 if (CallI->isInlineAsm()) 2258 continue; 2259 2260 uint32_t ValNo = VN.lookup(CurInst); 2261 2262 // Look for the predecessors for PRE opportunities. We're 2263 // only trying to solve the basic diamond case, where 2264 // a value is computed in the successor and one predecessor, 2265 // but not the other. We also explicitly disallow cases 2266 // where the successor is its own predecessor, because they're 2267 // more complicated to get right. 2268 unsigned NumWith = 0; 2269 unsigned NumWithout = 0; 2270 BasicBlock *PREPred = 0; 2271 predMap.clear(); 2272 2273 for (pred_iterator PI = pred_begin(CurrentBlock), 2274 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2275 BasicBlock *P = *PI; 2276 // We're not interested in PRE where the block is its 2277 // own predecessor, or in blocks with predecessors 2278 // that are not reachable. 2279 if (P == CurrentBlock) { 2280 NumWithout = 2; 2281 break; 2282 } else if (!DT->dominates(&F.getEntryBlock(), P)) { 2283 NumWithout = 2; 2284 break; 2285 } 2286 2287 Value* predV = findLeader(P, ValNo); 2288 if (predV == 0) { 2289 PREPred = P; 2290 ++NumWithout; 2291 } else if (predV == CurInst) { 2292 NumWithout = 2; 2293 } else { 2294 predMap[P] = predV; 2295 ++NumWith; 2296 } 2297 } 2298 2299 // Don't do PRE when it might increase code size, i.e. when 2300 // we would need to insert instructions in more than one pred. 2301 if (NumWithout != 1 || NumWith == 0) 2302 continue; 2303 2304 // Don't do PRE across indirect branch. 2305 if (isa<IndirectBrInst>(PREPred->getTerminator())) 2306 continue; 2307 2308 // We can't do PRE safely on a critical edge, so instead we schedule 2309 // the edge to be split and perform the PRE the next time we iterate 2310 // on the function. 2311 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); 2312 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2313 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2314 continue; 2315 } 2316 2317 // Instantiate the expression in the predecessor that lacked it. 2318 // Because we are going top-down through the block, all value numbers 2319 // will be available in the predecessor by the time we need them. Any 2320 // that weren't originally present will have been instantiated earlier 2321 // in this loop. 2322 Instruction *PREInstr = CurInst->clone(); 2323 bool success = true; 2324 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2325 Value *Op = PREInstr->getOperand(i); 2326 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2327 continue; 2328 2329 if (Value *V = findLeader(PREPred, VN.lookup(Op))) { 2330 PREInstr->setOperand(i, V); 2331 } else { 2332 success = false; 2333 break; 2334 } 2335 } 2336 2337 // Fail out if we encounter an operand that is not available in 2338 // the PRE predecessor. This is typically because of loads which 2339 // are not value numbered precisely. 2340 if (!success) { 2341 delete PREInstr; 2342 DEBUG(verifyRemoved(PREInstr)); 2343 continue; 2344 } 2345 2346 PREInstr->insertBefore(PREPred->getTerminator()); 2347 PREInstr->setName(CurInst->getName() + ".pre"); 2348 PREInstr->setDebugLoc(CurInst->getDebugLoc()); 2349 predMap[PREPred] = PREInstr; 2350 VN.add(PREInstr, ValNo); 2351 ++NumGVNPRE; 2352 2353 // Update the availability map to include the new instruction. 2354 addToLeaderTable(ValNo, PREInstr, PREPred); 2355 2356 // Create a PHI to make the value available in this block. 2357 pred_iterator PB = pred_begin(CurrentBlock), PE = pred_end(CurrentBlock); 2358 PHINode* Phi = PHINode::Create(CurInst->getType(), std::distance(PB, PE), 2359 CurInst->getName() + ".pre-phi", 2360 CurrentBlock->begin()); 2361 for (pred_iterator PI = PB; PI != PE; ++PI) { 2362 BasicBlock *P = *PI; 2363 Phi->addIncoming(predMap[P], P); 2364 } 2365 2366 VN.add(Phi, ValNo); 2367 addToLeaderTable(ValNo, Phi, CurrentBlock); 2368 Phi->setDebugLoc(CurInst->getDebugLoc()); 2369 CurInst->replaceAllUsesWith(Phi); 2370 if (Phi->getType()->isPointerTy()) { 2371 // Because we have added a PHI-use of the pointer value, it has now 2372 // "escaped" from alias analysis' perspective. We need to inform 2373 // AA of this. 2374 for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee; 2375 ++ii) { 2376 unsigned jj = PHINode::getOperandNumForIncomingValue(ii); 2377 VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(jj)); 2378 } 2379 2380 if (MD) 2381 MD->invalidateCachedPointerInfo(Phi); 2382 } 2383 VN.erase(CurInst); 2384 removeFromLeaderTable(ValNo, CurInst, CurrentBlock); 2385 2386 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); 2387 if (MD) MD->removeInstruction(CurInst); 2388 CurInst->eraseFromParent(); 2389 DEBUG(verifyRemoved(CurInst)); 2390 Changed = true; 2391 } 2392 } 2393 2394 if (splitCriticalEdges()) 2395 Changed = true; 2396 2397 return Changed; 2398} 2399 2400/// splitCriticalEdges - Split critical edges found during the previous 2401/// iteration that may enable further optimization. 2402bool GVN::splitCriticalEdges() { 2403 if (toSplit.empty()) 2404 return false; 2405 do { 2406 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); 2407 SplitCriticalEdge(Edge.first, Edge.second, this); 2408 } while (!toSplit.empty()); 2409 if (MD) MD->invalidateCachedPredecessors(); 2410 return true; 2411} 2412 2413/// iterateOnFunction - Executes one iteration of GVN 2414bool GVN::iterateOnFunction(Function &F) { 2415 cleanupGlobalSets(); 2416 2417 // Top-down walk of the dominator tree 2418 bool Changed = false; 2419#if 0 2420 // Needed for value numbering with phi construction to work. 2421 ReversePostOrderTraversal<Function*> RPOT(&F); 2422 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2423 RE = RPOT.end(); RI != RE; ++RI) 2424 Changed |= processBlock(*RI); 2425#else 2426 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2427 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2428 Changed |= processBlock(DI->getBlock()); 2429#endif 2430 2431 return Changed; 2432} 2433 2434void GVN::cleanupGlobalSets() { 2435 VN.clear(); 2436 LeaderTable.clear(); 2437 TableAllocator.Reset(); 2438} 2439 2440/// verifyRemoved - Verify that the specified instruction does not occur in our 2441/// internal data structures. 2442void GVN::verifyRemoved(const Instruction *Inst) const { 2443 VN.verifyRemoved(Inst); 2444 2445 // Walk through the value number scope to make sure the instruction isn't 2446 // ferreted away in it. 2447 for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator 2448 I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) { 2449 const LeaderTableEntry *Node = &I->second; 2450 assert(Node->Val != Inst && "Inst still in value numbering scope!"); 2451 2452 while (Node->Next) { 2453 Node = Node->Next; 2454 assert(Node->Val != Inst && "Inst still in value numbering scope!"); 2455 } 2456 } 2457} 2458