GVN.cpp revision 9750acc079409e52f6563636a112a9de50749b30
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/Transforms/Utils/BasicBlockUtils.h" 35#include "llvm/Transforms/Utils/SSAUpdater.h" 36#include "llvm/ADT/DenseMap.h" 37#include "llvm/ADT/DepthFirstIterator.h" 38#include "llvm/ADT/SmallPtrSet.h" 39#include "llvm/ADT/Statistic.h" 40#include "llvm/Support/Allocator.h" 41#include "llvm/Support/CommandLine.h" 42#include "llvm/Support/Debug.h" 43#include "llvm/Support/IRBuilder.h" 44using namespace llvm; 45 46STATISTIC(NumGVNInstr, "Number of instructions deleted"); 47STATISTIC(NumGVNLoad, "Number of loads deleted"); 48STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 49STATISTIC(NumGVNBlocks, "Number of blocks merged"); 50STATISTIC(NumPRELoad, "Number of loads PRE'd"); 51 52static cl::opt<bool> EnablePRE("enable-pre", 53 cl::init(true), cl::Hidden); 54static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 55 56//===----------------------------------------------------------------------===// 57// ValueTable Class 58//===----------------------------------------------------------------------===// 59 60/// This class holds the mapping between values and value numbers. It is used 61/// as an efficient mechanism to determine the expression-wise equivalence of 62/// two values. 63namespace { 64 struct Expression { 65 uint32_t opcode; 66 const Type* type; 67 SmallVector<uint32_t, 4> varargs; 68 69 Expression() { } 70 Expression(uint32_t o) : opcode(o) { } 71 72 bool operator==(const Expression &other) const { 73 if (opcode != other.opcode) 74 return false; 75 else if (opcode == ~0U || opcode == ~1U) 76 return true; 77 else if (type != other.type) 78 return false; 79 else if (varargs != other.varargs) 80 return false; 81 return true; 82 } 83 }; 84 85 class ValueTable { 86 private: 87 DenseMap<Value*, uint32_t> valueNumbering; 88 DenseMap<Expression, uint32_t> expressionNumbering; 89 AliasAnalysis* AA; 90 MemoryDependenceAnalysis* MD; 91 DominatorTree* DT; 92 93 uint32_t nextValueNumber; 94 95 Expression create_expression(Instruction* I); 96 uint32_t lookup_or_add_call(CallInst* C); 97 public: 98 ValueTable() : nextValueNumber(1) { } 99 uint32_t lookup_or_add(Value *V); 100 uint32_t lookup(Value *V) const; 101 void add(Value *V, uint32_t num); 102 void clear(); 103 void erase(Value *v); 104 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 105 AliasAnalysis *getAliasAnalysis() const { return AA; } 106 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 107 void setDomTree(DominatorTree* D) { DT = D; } 108 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 109 void verifyRemoved(const Value *) const; 110 }; 111} 112 113namespace llvm { 114template <> struct DenseMapInfo<Expression> { 115 static inline Expression getEmptyKey() { 116 return ~0U; 117 } 118 119 static inline Expression getTombstoneKey() { 120 return ~1U; 121 } 122 123 static unsigned getHashValue(const Expression e) { 124 unsigned hash = e.opcode; 125 126 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 127 (unsigned)((uintptr_t)e.type >> 9)); 128 129 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 130 E = e.varargs.end(); I != E; ++I) 131 hash = *I + hash * 37; 132 133 return hash; 134 } 135 static bool isEqual(const Expression &LHS, const Expression &RHS) { 136 return LHS == RHS; 137 } 138}; 139 140} 141 142//===----------------------------------------------------------------------===// 143// ValueTable Internal Functions 144//===----------------------------------------------------------------------===// 145 146 147Expression ValueTable::create_expression(Instruction *I) { 148 Expression e; 149 e.type = I->getType(); 150 e.opcode = I->getOpcode(); 151 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); 152 OI != OE; ++OI) 153 e.varargs.push_back(lookup_or_add(*OI)); 154 155 if (CmpInst *C = dyn_cast<CmpInst>(I)) 156 e.opcode = (C->getOpcode() << 8) | C->getPredicate(); 157 else if (ExtractValueInst *E = dyn_cast<ExtractValueInst>(I)) { 158 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 159 II != IE; ++II) 160 e.varargs.push_back(*II); 161 } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) { 162 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 163 II != IE; ++II) 164 e.varargs.push_back(*II); 165 } 166 167 return e; 168} 169 170//===----------------------------------------------------------------------===// 171// ValueTable External Functions 172//===----------------------------------------------------------------------===// 173 174/// add - Insert a value into the table with a specified value number. 175void ValueTable::add(Value *V, uint32_t num) { 176 valueNumbering.insert(std::make_pair(V, num)); 177} 178 179uint32_t ValueTable::lookup_or_add_call(CallInst* C) { 180 if (AA->doesNotAccessMemory(C)) { 181 Expression exp = create_expression(C); 182 uint32_t& e = expressionNumbering[exp]; 183 if (!e) e = nextValueNumber++; 184 valueNumbering[C] = e; 185 return e; 186 } else if (AA->onlyReadsMemory(C)) { 187 Expression exp = create_expression(C); 188 uint32_t& e = expressionNumbering[exp]; 189 if (!e) { 190 e = nextValueNumber++; 191 valueNumbering[C] = e; 192 return e; 193 } 194 if (!MD) { 195 e = nextValueNumber++; 196 valueNumbering[C] = e; 197 return e; 198 } 199 200 MemDepResult local_dep = MD->getDependency(C); 201 202 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 203 valueNumbering[C] = nextValueNumber; 204 return nextValueNumber++; 205 } 206 207 if (local_dep.isDef()) { 208 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 209 210 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) { 211 valueNumbering[C] = nextValueNumber; 212 return nextValueNumber++; 213 } 214 215 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 216 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 217 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i)); 218 if (c_vn != cd_vn) { 219 valueNumbering[C] = nextValueNumber; 220 return nextValueNumber++; 221 } 222 } 223 224 uint32_t v = lookup_or_add(local_cdep); 225 valueNumbering[C] = v; 226 return v; 227 } 228 229 // Non-local case. 230 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 231 MD->getNonLocalCallDependency(CallSite(C)); 232 // FIXME: call/call dependencies for readonly calls should return def, not 233 // clobber! Move the checking logic to MemDep! 234 CallInst* cdep = 0; 235 236 // Check to see if we have a single dominating call instruction that is 237 // identical to C. 238 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 239 const NonLocalDepEntry *I = &deps[i]; 240 // Ignore non-local dependencies. 241 if (I->getResult().isNonLocal()) 242 continue; 243 244 // We don't handle non-depedencies. If we already have a call, reject 245 // instruction dependencies. 246 if (I->getResult().isClobber() || cdep != 0) { 247 cdep = 0; 248 break; 249 } 250 251 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); 252 // FIXME: All duplicated with non-local case. 253 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ 254 cdep = NonLocalDepCall; 255 continue; 256 } 257 258 cdep = 0; 259 break; 260 } 261 262 if (!cdep) { 263 valueNumbering[C] = nextValueNumber; 264 return nextValueNumber++; 265 } 266 267 if (cdep->getNumArgOperands() != C->getNumArgOperands()) { 268 valueNumbering[C] = nextValueNumber; 269 return nextValueNumber++; 270 } 271 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 272 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 273 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i)); 274 if (c_vn != cd_vn) { 275 valueNumbering[C] = nextValueNumber; 276 return nextValueNumber++; 277 } 278 } 279 280 uint32_t v = lookup_or_add(cdep); 281 valueNumbering[C] = v; 282 return v; 283 284 } else { 285 valueNumbering[C] = nextValueNumber; 286 return nextValueNumber++; 287 } 288} 289 290/// lookup_or_add - Returns the value number for the specified value, assigning 291/// it a new number if it did not have one before. 292uint32_t ValueTable::lookup_or_add(Value *V) { 293 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 294 if (VI != valueNumbering.end()) 295 return VI->second; 296 297 if (!isa<Instruction>(V)) { 298 valueNumbering[V] = nextValueNumber; 299 return nextValueNumber++; 300 } 301 302 Instruction* I = cast<Instruction>(V); 303 Expression exp; 304 switch (I->getOpcode()) { 305 case Instruction::Call: 306 return lookup_or_add_call(cast<CallInst>(I)); 307 case Instruction::Add: 308 case Instruction::FAdd: 309 case Instruction::Sub: 310 case Instruction::FSub: 311 case Instruction::Mul: 312 case Instruction::FMul: 313 case Instruction::UDiv: 314 case Instruction::SDiv: 315 case Instruction::FDiv: 316 case Instruction::URem: 317 case Instruction::SRem: 318 case Instruction::FRem: 319 case Instruction::Shl: 320 case Instruction::LShr: 321 case Instruction::AShr: 322 case Instruction::And: 323 case Instruction::Or : 324 case Instruction::Xor: 325 case Instruction::ICmp: 326 case Instruction::FCmp: 327 case Instruction::Trunc: 328 case Instruction::ZExt: 329 case Instruction::SExt: 330 case Instruction::FPToUI: 331 case Instruction::FPToSI: 332 case Instruction::UIToFP: 333 case Instruction::SIToFP: 334 case Instruction::FPTrunc: 335 case Instruction::FPExt: 336 case Instruction::PtrToInt: 337 case Instruction::IntToPtr: 338 case Instruction::BitCast: 339 case Instruction::Select: 340 case Instruction::ExtractElement: 341 case Instruction::InsertElement: 342 case Instruction::ShuffleVector: 343 case Instruction::ExtractValue: 344 case Instruction::InsertValue: 345 case Instruction::GetElementPtr: 346 exp = create_expression(I); 347 break; 348 default: 349 valueNumbering[V] = nextValueNumber; 350 return nextValueNumber++; 351 } 352 353 uint32_t& e = expressionNumbering[exp]; 354 if (!e) e = nextValueNumber++; 355 valueNumbering[V] = e; 356 return e; 357} 358 359/// lookup - Returns the value number of the specified value. Fails if 360/// the value has not yet been numbered. 361uint32_t ValueTable::lookup(Value *V) const { 362 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); 363 assert(VI != valueNumbering.end() && "Value not numbered?"); 364 return VI->second; 365} 366 367/// clear - Remove all entries from the ValueTable 368void ValueTable::clear() { 369 valueNumbering.clear(); 370 expressionNumbering.clear(); 371 nextValueNumber = 1; 372} 373 374/// erase - Remove a value from the value numbering 375void ValueTable::erase(Value *V) { 376 valueNumbering.erase(V); 377} 378 379/// verifyRemoved - Verify that the value is removed from all internal data 380/// structures. 381void ValueTable::verifyRemoved(const Value *V) const { 382 for (DenseMap<Value*, uint32_t>::const_iterator 383 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 384 assert(I->first != V && "Inst still occurs in value numbering map!"); 385 } 386} 387 388//===----------------------------------------------------------------------===// 389// GVN Pass 390//===----------------------------------------------------------------------===// 391 392namespace { 393 394 class GVN : public FunctionPass { 395 bool runOnFunction(Function &F); 396 public: 397 static char ID; // Pass identification, replacement for typeid 398 explicit GVN(bool noloads = false) 399 : FunctionPass(ID), NoLoads(noloads), MD(0) { 400 initializeGVNPass(*PassRegistry::getPassRegistry()); 401 } 402 403 private: 404 bool NoLoads; 405 MemoryDependenceAnalysis *MD; 406 DominatorTree *DT; 407 const TargetData* TD; 408 409 ValueTable VN; 410 411 /// LeaderTable - A mapping from value numbers to lists of Value*'s that 412 /// have that value number. Use findLeader to query it. 413 struct LeaderTableEntry { 414 Value *Val; 415 BasicBlock *BB; 416 LeaderTableEntry *Next; 417 }; 418 DenseMap<uint32_t, LeaderTableEntry> LeaderTable; 419 BumpPtrAllocator TableAllocator; 420 421 /// addToLeaderTable - Push a new Value to the LeaderTable onto the list for 422 /// its value number. 423 void addToLeaderTable(uint32_t N, Value *V, BasicBlock *BB) { 424 LeaderTableEntry& Curr = LeaderTable[N]; 425 if (!Curr.Val) { 426 Curr.Val = V; 427 Curr.BB = BB; 428 return; 429 } 430 431 LeaderTableEntry* Node = TableAllocator.Allocate<LeaderTableEntry>(); 432 Node->Val = V; 433 Node->BB = BB; 434 Node->Next = Curr.Next; 435 Curr.Next = Node; 436 } 437 438 /// removeFromLeaderTable - Scan the list of values corresponding to a given 439 /// value number, and remove the given value if encountered. 440 void removeFromLeaderTable(uint32_t N, Value *V, BasicBlock *BB) { 441 LeaderTableEntry* Prev = 0; 442 LeaderTableEntry* Curr = &LeaderTable[N]; 443 444 while (Curr->Val != V || Curr->BB != BB) { 445 Prev = Curr; 446 Curr = Curr->Next; 447 } 448 449 if (Prev) { 450 Prev->Next = Curr->Next; 451 } else { 452 if (!Curr->Next) { 453 Curr->Val = 0; 454 Curr->BB = 0; 455 } else { 456 LeaderTableEntry* Next = Curr->Next; 457 Curr->Val = Next->Val; 458 Curr->BB = Next->BB; 459 Curr->Next = Next->Next; 460 } 461 } 462 } 463 464 // List of critical edges to be split between iterations. 465 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 466 467 // This transformation requires dominator postdominator info 468 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 469 AU.addRequired<DominatorTree>(); 470 if (!NoLoads) 471 AU.addRequired<MemoryDependenceAnalysis>(); 472 AU.addRequired<AliasAnalysis>(); 473 474 AU.addPreserved<DominatorTree>(); 475 AU.addPreserved<AliasAnalysis>(); 476 } 477 478 // Helper fuctions 479 // FIXME: eliminate or document these better 480 bool processLoad(LoadInst* L, 481 SmallVectorImpl<Instruction*> &toErase); 482 bool processInstruction(Instruction *I, 483 SmallVectorImpl<Instruction*> &toErase); 484 bool processNonLocalLoad(LoadInst* L, 485 SmallVectorImpl<Instruction*> &toErase); 486 bool processBlock(BasicBlock *BB); 487 void dump(DenseMap<uint32_t, Value*>& d); 488 bool iterateOnFunction(Function &F); 489 bool performPRE(Function& F); 490 Value *findLeader(BasicBlock *BB, uint32_t num); 491 void cleanupGlobalSets(); 492 void verifyRemoved(const Instruction *I) const; 493 bool splitCriticalEdges(); 494 }; 495 496 char GVN::ID = 0; 497} 498 499// createGVNPass - The public interface to this file... 500FunctionPass *llvm::createGVNPass(bool NoLoads) { 501 return new GVN(NoLoads); 502} 503 504INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false) 505INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) 506INITIALIZE_PASS_DEPENDENCY(DominatorTree) 507INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 508INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false) 509 510void GVN::dump(DenseMap<uint32_t, Value*>& d) { 511 errs() << "{\n"; 512 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 513 E = d.end(); I != E; ++I) { 514 errs() << I->first << "\n"; 515 I->second->dump(); 516 } 517 errs() << "}\n"; 518} 519 520/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 521/// we're analyzing is fully available in the specified block. As we go, keep 522/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 523/// map is actually a tri-state map with the following values: 524/// 0) we know the block *is not* fully available. 525/// 1) we know the block *is* fully available. 526/// 2) we do not know whether the block is fully available or not, but we are 527/// currently speculating that it will be. 528/// 3) we are speculating for this block and have used that to speculate for 529/// other blocks. 530static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 531 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 532 // Optimistically assume that the block is fully available and check to see 533 // if we already know about this block in one lookup. 534 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 535 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 536 537 // If the entry already existed for this block, return the precomputed value. 538 if (!IV.second) { 539 // If this is a speculative "available" value, mark it as being used for 540 // speculation of other blocks. 541 if (IV.first->second == 2) 542 IV.first->second = 3; 543 return IV.first->second != 0; 544 } 545 546 // Otherwise, see if it is fully available in all predecessors. 547 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 548 549 // If this block has no predecessors, it isn't live-in here. 550 if (PI == PE) 551 goto SpeculationFailure; 552 553 for (; PI != PE; ++PI) 554 // If the value isn't fully available in one of our predecessors, then it 555 // isn't fully available in this block either. Undo our previous 556 // optimistic assumption and bail out. 557 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 558 goto SpeculationFailure; 559 560 return true; 561 562// SpeculationFailure - If we get here, we found out that this is not, after 563// all, a fully-available block. We have a problem if we speculated on this and 564// used the speculation to mark other blocks as available. 565SpeculationFailure: 566 char &BBVal = FullyAvailableBlocks[BB]; 567 568 // If we didn't speculate on this, just return with it set to false. 569 if (BBVal == 2) { 570 BBVal = 0; 571 return false; 572 } 573 574 // If we did speculate on this value, we could have blocks set to 1 that are 575 // incorrect. Walk the (transitive) successors of this block and mark them as 576 // 0 if set to one. 577 SmallVector<BasicBlock*, 32> BBWorklist; 578 BBWorklist.push_back(BB); 579 580 do { 581 BasicBlock *Entry = BBWorklist.pop_back_val(); 582 // Note that this sets blocks to 0 (unavailable) if they happen to not 583 // already be in FullyAvailableBlocks. This is safe. 584 char &EntryVal = FullyAvailableBlocks[Entry]; 585 if (EntryVal == 0) continue; // Already unavailable. 586 587 // Mark as unavailable. 588 EntryVal = 0; 589 590 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 591 BBWorklist.push_back(*I); 592 } while (!BBWorklist.empty()); 593 594 return false; 595} 596 597 598/// CanCoerceMustAliasedValueToLoad - Return true if 599/// CoerceAvailableValueToLoadType will succeed. 600static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 601 const Type *LoadTy, 602 const TargetData &TD) { 603 // If the loaded or stored value is an first class array or struct, don't try 604 // to transform them. We need to be able to bitcast to integer. 605 if (LoadTy->isStructTy() || LoadTy->isArrayTy() || 606 StoredVal->getType()->isStructTy() || 607 StoredVal->getType()->isArrayTy()) 608 return false; 609 610 // The store has to be at least as big as the load. 611 if (TD.getTypeSizeInBits(StoredVal->getType()) < 612 TD.getTypeSizeInBits(LoadTy)) 613 return false; 614 615 return true; 616} 617 618 619/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 620/// then a load from a must-aliased pointer of a different type, try to coerce 621/// the stored value. LoadedTy is the type of the load we want to replace and 622/// InsertPt is the place to insert new instructions. 623/// 624/// If we can't do it, return null. 625static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 626 const Type *LoadedTy, 627 Instruction *InsertPt, 628 const TargetData &TD) { 629 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 630 return 0; 631 632 const Type *StoredValTy = StoredVal->getType(); 633 634 uint64_t StoreSize = TD.getTypeStoreSizeInBits(StoredValTy); 635 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 636 637 // If the store and reload are the same size, we can always reuse it. 638 if (StoreSize == LoadSize) { 639 // Pointer to Pointer -> use bitcast. 640 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) 641 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 642 643 // Convert source pointers to integers, which can be bitcast. 644 if (StoredValTy->isPointerTy()) { 645 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 646 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 647 } 648 649 const Type *TypeToCastTo = LoadedTy; 650 if (TypeToCastTo->isPointerTy()) 651 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 652 653 if (StoredValTy != TypeToCastTo) 654 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 655 656 // Cast to pointer if the load needs a pointer type. 657 if (LoadedTy->isPointerTy()) 658 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 659 660 return StoredVal; 661 } 662 663 // If the loaded value is smaller than the available value, then we can 664 // extract out a piece from it. If the available value is too small, then we 665 // can't do anything. 666 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 667 668 // Convert source pointers to integers, which can be manipulated. 669 if (StoredValTy->isPointerTy()) { 670 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 671 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 672 } 673 674 // Convert vectors and fp to integer, which can be manipulated. 675 if (!StoredValTy->isIntegerTy()) { 676 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 677 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 678 } 679 680 // If this is a big-endian system, we need to shift the value down to the low 681 // bits so that a truncate will work. 682 if (TD.isBigEndian()) { 683 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 684 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 685 } 686 687 // Truncate the integer to the right size now. 688 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 689 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 690 691 if (LoadedTy == NewIntTy) 692 return StoredVal; 693 694 // If the result is a pointer, inttoptr. 695 if (LoadedTy->isPointerTy()) 696 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 697 698 // Otherwise, bitcast. 699 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 700} 701 702/// AnalyzeLoadFromClobberingWrite - This function is called when we have a 703/// memdep query of a load that ends up being a clobbering memory write (store, 704/// memset, memcpy, memmove). This means that the write *may* provide bits used 705/// by the load but we can't be sure because the pointers don't mustalias. 706/// 707/// Check this case to see if there is anything more we can do before we give 708/// up. This returns -1 if we have to give up, or a byte number in the stored 709/// value of the piece that feeds the load. 710static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr, 711 Value *WritePtr, 712 uint64_t WriteSizeInBits, 713 const TargetData &TD) { 714 // If the loaded or stored value is an first class array or struct, don't try 715 // to transform them. We need to be able to bitcast to integer. 716 if (LoadTy->isStructTy() || LoadTy->isArrayTy()) 717 return -1; 718 719 int64_t StoreOffset = 0, LoadOffset = 0; 720 Value *StoreBase = GetPointerBaseWithConstantOffset(WritePtr, StoreOffset,TD); 721 Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, TD); 722 if (StoreBase != LoadBase) 723 return -1; 724 725 // If the load and store are to the exact same address, they should have been 726 // a must alias. AA must have gotten confused. 727 // FIXME: Study to see if/when this happens. One case is forwarding a memset 728 // to a load from the base of the memset. 729#if 0 730 if (LoadOffset == StoreOffset) { 731 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 732 << "Base = " << *StoreBase << "\n" 733 << "Store Ptr = " << *WritePtr << "\n" 734 << "Store Offs = " << StoreOffset << "\n" 735 << "Load Ptr = " << *LoadPtr << "\n"; 736 abort(); 737 } 738#endif 739 740 // If the load and store don't overlap at all, the store doesn't provide 741 // anything to the load. In this case, they really don't alias at all, AA 742 // must have gotten confused. 743 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy); 744 745 if ((WriteSizeInBits & 7) | (LoadSize & 7)) 746 return -1; 747 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. 748 LoadSize >>= 3; 749 750 751 bool isAAFailure = false; 752 if (StoreOffset < LoadOffset) 753 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 754 else 755 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 756 757 if (isAAFailure) { 758#if 0 759 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" 760 << "Base = " << *StoreBase << "\n" 761 << "Store Ptr = " << *WritePtr << "\n" 762 << "Store Offs = " << StoreOffset << "\n" 763 << "Load Ptr = " << *LoadPtr << "\n"; 764 abort(); 765#endif 766 return -1; 767 } 768 769 // If the Load isn't completely contained within the stored bits, we don't 770 // have all the bits to feed it. We could do something crazy in the future 771 // (issue a smaller load then merge the bits in) but this seems unlikely to be 772 // valuable. 773 if (StoreOffset > LoadOffset || 774 StoreOffset+StoreSize < LoadOffset+LoadSize) 775 return -1; 776 777 // Okay, we can do this transformation. Return the number of bytes into the 778 // store that the load is. 779 return LoadOffset-StoreOffset; 780} 781 782/// AnalyzeLoadFromClobberingStore - This function is called when we have a 783/// memdep query of a load that ends up being a clobbering store. 784static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr, 785 StoreInst *DepSI, 786 const TargetData &TD) { 787 // Cannot handle reading from store of first-class aggregate yet. 788 if (DepSI->getValueOperand()->getType()->isStructTy() || 789 DepSI->getValueOperand()->getType()->isArrayTy()) 790 return -1; 791 792 Value *StorePtr = DepSI->getPointerOperand(); 793 uint64_t StoreSize =TD.getTypeSizeInBits(DepSI->getValueOperand()->getType()); 794 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 795 StorePtr, StoreSize, TD); 796} 797 798/// AnalyzeLoadFromClobberingLoad - This function is called when we have a 799/// memdep query of a load that ends up being clobbered by another load. See if 800/// the other load can feed into the second load. 801static int AnalyzeLoadFromClobberingLoad(const Type *LoadTy, Value *LoadPtr, 802 LoadInst *DepLI, const TargetData &TD){ 803 // Cannot handle reading from store of first-class aggregate yet. 804 if (DepLI->getType()->isStructTy() || DepLI->getType()->isArrayTy()) 805 return -1; 806 807 Value *DepPtr = DepLI->getPointerOperand(); 808 uint64_t DepSize = TD.getTypeSizeInBits(DepLI->getType()); 809 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, DepSize, TD); 810} 811 812 813 814static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr, 815 MemIntrinsic *MI, 816 const TargetData &TD) { 817 // If the mem operation is a non-constant size, we can't handle it. 818 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); 819 if (SizeCst == 0) return -1; 820 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; 821 822 // If this is memset, we just need to see if the offset is valid in the size 823 // of the memset.. 824 if (MI->getIntrinsicID() == Intrinsic::memset) 825 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), 826 MemSizeInBits, TD); 827 828 // If we have a memcpy/memmove, the only case we can handle is if this is a 829 // copy from constant memory. In that case, we can read directly from the 830 // constant memory. 831 MemTransferInst *MTI = cast<MemTransferInst>(MI); 832 833 Constant *Src = dyn_cast<Constant>(MTI->getSource()); 834 if (Src == 0) return -1; 835 836 GlobalVariable *GV = dyn_cast<GlobalVariable>(GetUnderlyingObject(Src, &TD)); 837 if (GV == 0 || !GV->isConstant()) return -1; 838 839 // See if the access is within the bounds of the transfer. 840 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 841 MI->getDest(), MemSizeInBits, TD); 842 if (Offset == -1) 843 return Offset; 844 845 // Otherwise, see if we can constant fold a load from the constant with the 846 // offset applied as appropriate. 847 Src = ConstantExpr::getBitCast(Src, 848 llvm::Type::getInt8PtrTy(Src->getContext())); 849 Constant *OffsetCst = 850 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 851 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 852 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 853 if (ConstantFoldLoadFromConstPtr(Src, &TD)) 854 return Offset; 855 return -1; 856} 857 858 859/// GetStoreValueForLoad - This function is called when we have a 860/// memdep query of a load that ends up being a clobbering store. This means 861/// that the store *may* provide bits used by the load but we can't be sure 862/// because the pointers don't mustalias. Check this case to see if there is 863/// anything more we can do before we give up. 864static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 865 const Type *LoadTy, 866 Instruction *InsertPt, const TargetData &TD){ 867 LLVMContext &Ctx = SrcVal->getType()->getContext(); 868 869 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8; 870 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8; 871 872 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 873 874 // Compute which bits of the stored value are being used by the load. Convert 875 // to an integer type to start with. 876 if (SrcVal->getType()->isPointerTy()) 877 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp"); 878 if (!SrcVal->getType()->isIntegerTy()) 879 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8), 880 "tmp"); 881 882 // Shift the bits to the least significant depending on endianness. 883 unsigned ShiftAmt; 884 if (TD.isLittleEndian()) 885 ShiftAmt = Offset*8; 886 else 887 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 888 889 if (ShiftAmt) 890 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp"); 891 892 if (LoadSize != StoreSize) 893 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8), 894 "tmp"); 895 896 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 897} 898 899/// GetMemInstValueForLoad - This function is called when we have a 900/// memdep query of a load that ends up being a clobbering mem intrinsic. 901static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, 902 const Type *LoadTy, Instruction *InsertPt, 903 const TargetData &TD){ 904 LLVMContext &Ctx = LoadTy->getContext(); 905 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 906 907 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 908 909 // We know that this method is only called when the mem transfer fully 910 // provides the bits for the load. 911 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { 912 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and 913 // independently of what the offset is. 914 Value *Val = MSI->getValue(); 915 if (LoadSize != 1) 916 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); 917 918 Value *OneElt = Val; 919 920 // Splat the value out to the right number of bits. 921 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { 922 // If we can double the number of bytes set, do it. 923 if (NumBytesSet*2 <= LoadSize) { 924 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); 925 Val = Builder.CreateOr(Val, ShVal); 926 NumBytesSet <<= 1; 927 continue; 928 } 929 930 // Otherwise insert one byte at a time. 931 Value *ShVal = Builder.CreateShl(Val, 1*8); 932 Val = Builder.CreateOr(OneElt, ShVal); 933 ++NumBytesSet; 934 } 935 936 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD); 937 } 938 939 // Otherwise, this is a memcpy/memmove from a constant global. 940 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); 941 Constant *Src = cast<Constant>(MTI->getSource()); 942 943 // Otherwise, see if we can constant fold a load from the constant with the 944 // offset applied as appropriate. 945 Src = ConstantExpr::getBitCast(Src, 946 llvm::Type::getInt8PtrTy(Src->getContext())); 947 Constant *OffsetCst = 948 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 949 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 950 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 951 return ConstantFoldLoadFromConstPtr(Src, &TD); 952} 953 954namespace { 955 956struct AvailableValueInBlock { 957 /// BB - The basic block in question. 958 BasicBlock *BB; 959 enum ValType { 960 SimpleVal, // A simple offsetted value that is accessed. 961 MemIntrin // A memory intrinsic which is loaded from. 962 }; 963 964 /// V - The value that is live out of the block. 965 PointerIntPair<Value *, 1, ValType> Val; 966 967 /// Offset - The byte offset in Val that is interesting for the load query. 968 unsigned Offset; 969 970 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 971 unsigned Offset = 0) { 972 AvailableValueInBlock Res; 973 Res.BB = BB; 974 Res.Val.setPointer(V); 975 Res.Val.setInt(SimpleVal); 976 Res.Offset = Offset; 977 return Res; 978 } 979 980 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, 981 unsigned Offset = 0) { 982 AvailableValueInBlock Res; 983 Res.BB = BB; 984 Res.Val.setPointer(MI); 985 Res.Val.setInt(MemIntrin); 986 Res.Offset = Offset; 987 return Res; 988 } 989 990 bool isSimpleValue() const { return Val.getInt() == SimpleVal; } 991 Value *getSimpleValue() const { 992 assert(isSimpleValue() && "Wrong accessor"); 993 return Val.getPointer(); 994 } 995 996 MemIntrinsic *getMemIntrinValue() const { 997 assert(!isSimpleValue() && "Wrong accessor"); 998 return cast<MemIntrinsic>(Val.getPointer()); 999 } 1000 1001 /// MaterializeAdjustedValue - Emit code into this block to adjust the value 1002 /// defined here to the specified type. This handles various coercion cases. 1003 Value *MaterializeAdjustedValue(const Type *LoadTy, 1004 const TargetData *TD) const { 1005 Value *Res; 1006 if (isSimpleValue()) { 1007 Res = getSimpleValue(); 1008 if (Res->getType() != LoadTy) { 1009 assert(TD && "Need target data to handle type mismatch case"); 1010 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), 1011 *TD); 1012 1013 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " 1014 << *getSimpleValue() << '\n' 1015 << *Res << '\n' << "\n\n\n"); 1016 } 1017 } else { 1018 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, 1019 LoadTy, BB->getTerminator(), *TD); 1020 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset 1021 << " " << *getMemIntrinValue() << '\n' 1022 << *Res << '\n' << "\n\n\n"); 1023 } 1024 return Res; 1025 } 1026}; 1027 1028} 1029 1030/// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, 1031/// construct SSA form, allowing us to eliminate LI. This returns the value 1032/// that should be used at LI's definition site. 1033static Value *ConstructSSAForLoadSet(LoadInst *LI, 1034 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1035 const TargetData *TD, 1036 const DominatorTree &DT, 1037 AliasAnalysis *AA) { 1038 // Check for the fully redundant, dominating load case. In this case, we can 1039 // just use the dominating value directly. 1040 if (ValuesPerBlock.size() == 1 && 1041 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent())) 1042 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD); 1043 1044 // Otherwise, we have to construct SSA form. 1045 SmallVector<PHINode*, 8> NewPHIs; 1046 SSAUpdater SSAUpdate(&NewPHIs); 1047 SSAUpdate.Initialize(LI->getType(), LI->getName()); 1048 1049 const Type *LoadTy = LI->getType(); 1050 1051 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1052 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1053 BasicBlock *BB = AV.BB; 1054 1055 if (SSAUpdate.HasValueForBlock(BB)) 1056 continue; 1057 1058 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD)); 1059 } 1060 1061 // Perform PHI construction. 1062 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1063 1064 // If new PHI nodes were created, notify alias analysis. 1065 if (V->getType()->isPointerTy()) 1066 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 1067 AA->copyValue(LI, NewPHIs[i]); 1068 1069 // Now that we've copied information to the new PHIs, scan through 1070 // them again and inform alias analysis that we've added potentially 1071 // escaping uses to any values that are operands to these PHIs. 1072 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) { 1073 PHINode *P = NewPHIs[i]; 1074 for (unsigned ii = 0, ee = P->getNumIncomingValues(); ii != ee; ++ii) 1075 AA->addEscapingUse(P->getOperandUse(2*ii)); 1076 } 1077 1078 return V; 1079} 1080 1081static bool isLifetimeStart(const Instruction *Inst) { 1082 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) 1083 return II->getIntrinsicID() == Intrinsic::lifetime_start; 1084 return false; 1085} 1086 1087/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1088/// non-local by performing PHI construction. 1089bool GVN::processNonLocalLoad(LoadInst *LI, 1090 SmallVectorImpl<Instruction*> &toErase) { 1091 // Find the non-local dependencies of the load. 1092 SmallVector<NonLocalDepResult, 64> Deps; 1093 AliasAnalysis::Location Loc = VN.getAliasAnalysis()->getLocation(LI); 1094 MD->getNonLocalPointerDependency(Loc, true, LI->getParent(), Deps); 1095 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: " 1096 // << Deps.size() << *LI << '\n'); 1097 1098 // If we had to process more than one hundred blocks to find the 1099 // dependencies, this load isn't worth worrying about. Optimizing 1100 // it will be too expensive. 1101 if (Deps.size() > 100) 1102 return false; 1103 1104 // If we had a phi translation failure, we'll have a single entry which is a 1105 // clobber in the current block. Reject this early. 1106 if (Deps.size() == 1 && Deps[0].getResult().isClobber() && 1107 Deps[0].getResult().getInst()->getParent() == LI->getParent()) { 1108 DEBUG( 1109 dbgs() << "GVN: non-local load "; 1110 WriteAsOperand(dbgs(), LI); 1111 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n'; 1112 ); 1113 return false; 1114 } 1115 1116 // Filter out useless results (non-locals, etc). Keep track of the blocks 1117 // where we have a value available in repl, also keep track of whether we see 1118 // dependencies that produce an unknown value for the load (such as a call 1119 // that could potentially clobber the load). 1120 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1121 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1122 1123 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1124 BasicBlock *DepBB = Deps[i].getBB(); 1125 MemDepResult DepInfo = Deps[i].getResult(); 1126 1127 if (DepInfo.isClobber()) { 1128 // The address being loaded in this non-local block may not be the same as 1129 // the pointer operand of the load if PHI translation occurs. Make sure 1130 // to consider the right address. 1131 Value *Address = Deps[i].getAddress(); 1132 1133 // If the dependence is to a store that writes to a superset of the bits 1134 // read by the load, we can extract the bits we need for the load from the 1135 // stored value. 1136 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1137 if (TD && Address) { 1138 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address, 1139 DepSI, *TD); 1140 if (Offset != -1) { 1141 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1142 DepSI->getValueOperand(), 1143 Offset)); 1144 continue; 1145 } 1146 } 1147 } 1148 1149 // Check to see if we have something like this: 1150 // load i32* P 1151 // load i8* (P+1) 1152 // if we have this, replace the later with an extraction from the former. 1153 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) { 1154 // If this is a clobber and L is the first instruction in its block, then 1155 // we have the first instruction in the entry block. 1156 if (DepLI != LI && Address && TD) { 1157 int Offset = AnalyzeLoadFromClobberingLoad(LI->getType(), 1158 LI->getPointerOperand(), 1159 DepLI, *TD); 1160 1161 if (Offset != -1) { 1162 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, DepLI, 1163 Offset)); 1164 continue; 1165 } 1166 } 1167 } 1168 1169 // If the clobbering value is a memset/memcpy/memmove, see if we can 1170 // forward a value on from it. 1171 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { 1172 if (TD && Address) { 1173 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address, 1174 DepMI, *TD); 1175 if (Offset != -1) { 1176 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, 1177 Offset)); 1178 continue; 1179 } 1180 } 1181 } 1182 1183 UnavailableBlocks.push_back(DepBB); 1184 continue; 1185 } 1186 1187 Instruction *DepInst = DepInfo.getInst(); 1188 1189 // Loading the allocation -> undef. 1190 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) || 1191 // Loading immediately after lifetime begin -> undef. 1192 isLifetimeStart(DepInst)) { 1193 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1194 UndefValue::get(LI->getType()))); 1195 continue; 1196 } 1197 1198 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1199 // Reject loads and stores that are to the same address but are of 1200 // different types if we have to. 1201 if (S->getValueOperand()->getType() != LI->getType()) { 1202 // If the stored value is larger or equal to the loaded value, we can 1203 // reuse it. 1204 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(), 1205 LI->getType(), *TD)) { 1206 UnavailableBlocks.push_back(DepBB); 1207 continue; 1208 } 1209 } 1210 1211 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1212 S->getValueOperand())); 1213 continue; 1214 } 1215 1216 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1217 // If the types mismatch and we can't handle it, reject reuse of the load. 1218 if (LD->getType() != LI->getType()) { 1219 // If the stored value is larger or equal to the loaded value, we can 1220 // reuse it. 1221 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1222 UnavailableBlocks.push_back(DepBB); 1223 continue; 1224 } 1225 } 1226 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1227 continue; 1228 } 1229 1230 UnavailableBlocks.push_back(DepBB); 1231 continue; 1232 } 1233 1234 // If we have no predecessors that produce a known value for this load, exit 1235 // early. 1236 if (ValuesPerBlock.empty()) return false; 1237 1238 // If all of the instructions we depend on produce a known value for this 1239 // load, then it is fully redundant and we can use PHI insertion to compute 1240 // its value. Insert PHIs and remove the fully redundant value now. 1241 if (UnavailableBlocks.empty()) { 1242 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1243 1244 // Perform PHI construction. 1245 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1246 VN.getAliasAnalysis()); 1247 LI->replaceAllUsesWith(V); 1248 1249 if (isa<PHINode>(V)) 1250 V->takeName(LI); 1251 if (V->getType()->isPointerTy()) 1252 MD->invalidateCachedPointerInfo(V); 1253 VN.erase(LI); 1254 toErase.push_back(LI); 1255 ++NumGVNLoad; 1256 return true; 1257 } 1258 1259 if (!EnablePRE || !EnableLoadPRE) 1260 return false; 1261 1262 // Okay, we have *some* definitions of the value. This means that the value 1263 // is available in some of our (transitive) predecessors. Lets think about 1264 // doing PRE of this load. This will involve inserting a new load into the 1265 // predecessor when it's not available. We could do this in general, but 1266 // prefer to not increase code size. As such, we only do this when we know 1267 // that we only have to insert *one* load (which means we're basically moving 1268 // the load, not inserting a new one). 1269 1270 SmallPtrSet<BasicBlock *, 4> Blockers; 1271 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1272 Blockers.insert(UnavailableBlocks[i]); 1273 1274 // Lets find first basic block with more than one predecessor. Walk backwards 1275 // through predecessors if needed. 1276 BasicBlock *LoadBB = LI->getParent(); 1277 BasicBlock *TmpBB = LoadBB; 1278 1279 bool isSinglePred = false; 1280 bool allSingleSucc = true; 1281 while (TmpBB->getSinglePredecessor()) { 1282 isSinglePred = true; 1283 TmpBB = TmpBB->getSinglePredecessor(); 1284 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1285 return false; 1286 if (Blockers.count(TmpBB)) 1287 return false; 1288 1289 // If any of these blocks has more than one successor (i.e. if the edge we 1290 // just traversed was critical), then there are other paths through this 1291 // block along which the load may not be anticipated. Hoisting the load 1292 // above this block would be adding the load to execution paths along 1293 // which it was not previously executed. 1294 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1295 return false; 1296 } 1297 1298 assert(TmpBB); 1299 LoadBB = TmpBB; 1300 1301 // FIXME: It is extremely unclear what this loop is doing, other than 1302 // artificially restricting loadpre. 1303 if (isSinglePred) { 1304 bool isHot = false; 1305 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1306 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1307 if (AV.isSimpleValue()) 1308 // "Hot" Instruction is in some loop (because it dominates its dep. 1309 // instruction). 1310 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue())) 1311 if (DT->dominates(LI, I)) { 1312 isHot = true; 1313 break; 1314 } 1315 } 1316 1317 // We are interested only in "hot" instructions. We don't want to do any 1318 // mis-optimizations here. 1319 if (!isHot) 1320 return false; 1321 } 1322 1323 // Check to see how many predecessors have the loaded value fully 1324 // available. 1325 DenseMap<BasicBlock*, Value*> PredLoads; 1326 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1327 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1328 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1329 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1330 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1331 1332 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit; 1333 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1334 PI != E; ++PI) { 1335 BasicBlock *Pred = *PI; 1336 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) { 1337 continue; 1338 } 1339 PredLoads[Pred] = 0; 1340 1341 if (Pred->getTerminator()->getNumSuccessors() != 1) { 1342 if (isa<IndirectBrInst>(Pred->getTerminator())) { 1343 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" 1344 << Pred->getName() << "': " << *LI << '\n'); 1345 return false; 1346 } 1347 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB); 1348 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum)); 1349 } 1350 } 1351 if (!NeedToSplit.empty()) { 1352 toSplit.append(NeedToSplit.begin(), NeedToSplit.end()); 1353 return false; 1354 } 1355 1356 // Decide whether PRE is profitable for this load. 1357 unsigned NumUnavailablePreds = PredLoads.size(); 1358 assert(NumUnavailablePreds != 0 && 1359 "Fully available value should be eliminated above!"); 1360 1361 // If this load is unavailable in multiple predecessors, reject it. 1362 // FIXME: If we could restructure the CFG, we could make a common pred with 1363 // all the preds that don't have an available LI and insert a new load into 1364 // that one block. 1365 if (NumUnavailablePreds != 1) 1366 return false; 1367 1368 // Check if the load can safely be moved to all the unavailable predecessors. 1369 bool CanDoPRE = true; 1370 SmallVector<Instruction*, 8> NewInsts; 1371 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1372 E = PredLoads.end(); I != E; ++I) { 1373 BasicBlock *UnavailablePred = I->first; 1374 1375 // Do PHI translation to get its value in the predecessor if necessary. The 1376 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. 1377 1378 // If all preds have a single successor, then we know it is safe to insert 1379 // the load on the pred (?!?), so we can insert code to materialize the 1380 // pointer if it is not available. 1381 PHITransAddr Address(LI->getPointerOperand(), TD); 1382 Value *LoadPtr = 0; 1383 if (allSingleSucc) { 1384 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, 1385 *DT, NewInsts); 1386 } else { 1387 Address.PHITranslateValue(LoadBB, UnavailablePred, DT); 1388 LoadPtr = Address.getAddr(); 1389 } 1390 1391 // If we couldn't find or insert a computation of this phi translated value, 1392 // we fail PRE. 1393 if (LoadPtr == 0) { 1394 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " 1395 << *LI->getPointerOperand() << "\n"); 1396 CanDoPRE = false; 1397 break; 1398 } 1399 1400 // Make sure it is valid to move this load here. We have to watch out for: 1401 // @1 = getelementptr (i8* p, ... 1402 // test p and branch if == 0 1403 // load @1 1404 // It is valid to have the getelementptr before the test, even if p can 1405 // be 0, as getelementptr only does address arithmetic. 1406 // If we are not pushing the value through any multiple-successor blocks 1407 // we do not have this case. Otherwise, check that the load is safe to 1408 // put anywhere; this can be improved, but should be conservatively safe. 1409 if (!allSingleSucc && 1410 // FIXME: REEVALUTE THIS. 1411 !isSafeToLoadUnconditionally(LoadPtr, 1412 UnavailablePred->getTerminator(), 1413 LI->getAlignment(), TD)) { 1414 CanDoPRE = false; 1415 break; 1416 } 1417 1418 I->second = LoadPtr; 1419 } 1420 1421 if (!CanDoPRE) { 1422 while (!NewInsts.empty()) { 1423 Instruction *I = NewInsts.pop_back_val(); 1424 if (MD) MD->removeInstruction(I); 1425 I->eraseFromParent(); 1426 } 1427 return false; 1428 } 1429 1430 // Okay, we can eliminate this load by inserting a reload in the predecessor 1431 // and using PHI construction to get the value in the other predecessors, do 1432 // it. 1433 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1434 DEBUG(if (!NewInsts.empty()) 1435 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " 1436 << *NewInsts.back() << '\n'); 1437 1438 // Assign value numbers to the new instructions. 1439 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) { 1440 // FIXME: We really _ought_ to insert these value numbers into their 1441 // parent's availability map. However, in doing so, we risk getting into 1442 // ordering issues. If a block hasn't been processed yet, we would be 1443 // marking a value as AVAIL-IN, which isn't what we intend. 1444 VN.lookup_or_add(NewInsts[i]); 1445 } 1446 1447 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1448 E = PredLoads.end(); I != E; ++I) { 1449 BasicBlock *UnavailablePred = I->first; 1450 Value *LoadPtr = I->second; 1451 1452 Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1453 LI->getAlignment(), 1454 UnavailablePred->getTerminator()); 1455 1456 // Transfer the old load's TBAA tag to the new load. 1457 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) 1458 NewLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1459 1460 // Add the newly created load. 1461 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, 1462 NewLoad)); 1463 MD->invalidateCachedPointerInfo(LoadPtr); 1464 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); 1465 } 1466 1467 // Perform PHI construction. 1468 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1469 VN.getAliasAnalysis()); 1470 LI->replaceAllUsesWith(V); 1471 if (isa<PHINode>(V)) 1472 V->takeName(LI); 1473 if (V->getType()->isPointerTy()) 1474 MD->invalidateCachedPointerInfo(V); 1475 VN.erase(LI); 1476 toErase.push_back(LI); 1477 ++NumPRELoad; 1478 return true; 1479} 1480 1481/// processLoad - Attempt to eliminate a load, first by eliminating it 1482/// locally, and then attempting non-local elimination if that fails. 1483bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1484 if (!MD) 1485 return false; 1486 1487 if (L->isVolatile()) 1488 return false; 1489 1490 // ... to a pointer that has been loaded from before... 1491 MemDepResult Dep = MD->getDependency(L); 1492 1493 // If we have a clobber and target data is around, see if this is a clobber 1494 // that we can fix up through code synthesis. 1495 if (Dep.isClobber() && TD) { 1496 // Check to see if we have something like this: 1497 // store i32 123, i32* %P 1498 // %A = bitcast i32* %P to i8* 1499 // %B = gep i8* %A, i32 1 1500 // %C = load i8* %B 1501 // 1502 // We could do that by recognizing if the clobber instructions are obviously 1503 // a common base + constant offset, and if the previous store (or memset) 1504 // completely covers this load. This sort of thing can happen in bitfield 1505 // access code. 1506 Value *AvailVal = 0; 1507 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) { 1508 int Offset = AnalyzeLoadFromClobberingStore(L->getType(), 1509 L->getPointerOperand(), 1510 DepSI, *TD); 1511 if (Offset != -1) 1512 AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset, 1513 L->getType(), L, *TD); 1514 } 1515 1516 // Check to see if we have something like this: 1517 // load i32* P 1518 // load i8* (P+1) 1519 // if we have this, replace the later with an extraction from the former. 1520 if (LoadInst *DepLI = dyn_cast<LoadInst>(Dep.getInst())) { 1521 // If this is a clobber and L is the first instruction in its block, then 1522 // we have the first instruction in the entry block. 1523 if (DepLI == L) 1524 return false; 1525 1526 int Offset = AnalyzeLoadFromClobberingLoad(L->getType(), 1527 L->getPointerOperand(), 1528 DepLI, *TD); 1529 if (Offset != -1) 1530 AvailVal = GetStoreValueForLoad(DepLI, Offset, L->getType(), L, *TD); 1531 } 1532 1533 // If the clobbering value is a memset/memcpy/memmove, see if we can forward 1534 // a value on from it. 1535 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { 1536 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(), 1537 L->getPointerOperand(), 1538 DepMI, *TD); 1539 if (Offset != -1) 1540 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L, *TD); 1541 } 1542 1543 if (AvailVal) { 1544 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' 1545 << *AvailVal << '\n' << *L << "\n\n\n"); 1546 1547 // Replace the load! 1548 L->replaceAllUsesWith(AvailVal); 1549 if (AvailVal->getType()->isPointerTy()) 1550 MD->invalidateCachedPointerInfo(AvailVal); 1551 VN.erase(L); 1552 toErase.push_back(L); 1553 ++NumGVNLoad; 1554 return true; 1555 } 1556 } 1557 1558 // If the value isn't available, don't do anything! 1559 if (Dep.isClobber()) { 1560 DEBUG( 1561 // fast print dep, using operator<< on instruction is too slow. 1562 dbgs() << "GVN: load "; 1563 WriteAsOperand(dbgs(), L); 1564 Instruction *I = Dep.getInst(); 1565 dbgs() << " is clobbered by " << *I << '\n'; 1566 ); 1567 return false; 1568 } 1569 1570 // If it is defined in another block, try harder. 1571 if (Dep.isNonLocal()) 1572 return processNonLocalLoad(L, toErase); 1573 1574 Instruction *DepInst = Dep.getInst(); 1575 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1576 Value *StoredVal = DepSI->getValueOperand(); 1577 1578 // The store and load are to a must-aliased pointer, but they may not 1579 // actually have the same type. See if we know how to reuse the stored 1580 // value (depending on its type). 1581 if (StoredVal->getType() != L->getType()) { 1582 if (TD) { 1583 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1584 L, *TD); 1585 if (StoredVal == 0) 1586 return false; 1587 1588 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1589 << '\n' << *L << "\n\n\n"); 1590 } 1591 else 1592 return false; 1593 } 1594 1595 // Remove it! 1596 L->replaceAllUsesWith(StoredVal); 1597 if (StoredVal->getType()->isPointerTy()) 1598 MD->invalidateCachedPointerInfo(StoredVal); 1599 VN.erase(L); 1600 toErase.push_back(L); 1601 ++NumGVNLoad; 1602 return true; 1603 } 1604 1605 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1606 Value *AvailableVal = DepLI; 1607 1608 // The loads are of a must-aliased pointer, but they may not actually have 1609 // the same type. See if we know how to reuse the previously loaded value 1610 // (depending on its type). 1611 if (DepLI->getType() != L->getType()) { 1612 if (TD) { 1613 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), 1614 L, *TD); 1615 if (AvailableVal == 0) 1616 return false; 1617 1618 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1619 << "\n" << *L << "\n\n\n"); 1620 } 1621 else 1622 return false; 1623 } 1624 1625 // Remove it! 1626 L->replaceAllUsesWith(AvailableVal); 1627 if (DepLI->getType()->isPointerTy()) 1628 MD->invalidateCachedPointerInfo(DepLI); 1629 VN.erase(L); 1630 toErase.push_back(L); 1631 ++NumGVNLoad; 1632 return true; 1633 } 1634 1635 // If this load really doesn't depend on anything, then we must be loading an 1636 // undef value. This can happen when loading for a fresh allocation with no 1637 // intervening stores, for example. 1638 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) { 1639 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1640 VN.erase(L); 1641 toErase.push_back(L); 1642 ++NumGVNLoad; 1643 return true; 1644 } 1645 1646 // If this load occurs either right after a lifetime begin, 1647 // then the loaded value is undefined. 1648 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) { 1649 if (II->getIntrinsicID() == Intrinsic::lifetime_start) { 1650 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1651 VN.erase(L); 1652 toErase.push_back(L); 1653 ++NumGVNLoad; 1654 return true; 1655 } 1656 } 1657 1658 return false; 1659} 1660 1661// findLeader - In order to find a leader for a given value number at a 1662// specific basic block, we first obtain the list of all Values for that number, 1663// and then scan the list to find one whose block dominates the block in 1664// question. This is fast because dominator tree queries consist of only 1665// a few comparisons of DFS numbers. 1666Value *GVN::findLeader(BasicBlock *BB, uint32_t num) { 1667 LeaderTableEntry Vals = LeaderTable[num]; 1668 if (!Vals.Val) return 0; 1669 1670 Value *Val = 0; 1671 if (DT->dominates(Vals.BB, BB)) { 1672 Val = Vals.Val; 1673 if (isa<Constant>(Val)) return Val; 1674 } 1675 1676 LeaderTableEntry* Next = Vals.Next; 1677 while (Next) { 1678 if (DT->dominates(Next->BB, BB)) { 1679 if (isa<Constant>(Next->Val)) return Next->Val; 1680 if (!Val) Val = Next->Val; 1681 } 1682 1683 Next = Next->Next; 1684 } 1685 1686 return Val; 1687} 1688 1689 1690/// processInstruction - When calculating availability, handle an instruction 1691/// by inserting it into the appropriate sets 1692bool GVN::processInstruction(Instruction *I, 1693 SmallVectorImpl<Instruction*> &toErase) { 1694 // Ignore dbg info intrinsics. 1695 if (isa<DbgInfoIntrinsic>(I)) 1696 return false; 1697 1698 // If the instruction can be easily simplified then do so now in preference 1699 // to value numbering it. Value numbering often exposes redundancies, for 1700 // example if it determines that %y is equal to %x then the instruction 1701 // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. 1702 if (Value *V = SimplifyInstruction(I, TD, DT)) { 1703 I->replaceAllUsesWith(V); 1704 if (MD && V->getType()->isPointerTy()) 1705 MD->invalidateCachedPointerInfo(V); 1706 VN.erase(I); 1707 toErase.push_back(I); 1708 return true; 1709 } 1710 1711 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1712 bool Changed = processLoad(LI, toErase); 1713 1714 if (!Changed) { 1715 unsigned Num = VN.lookup_or_add(LI); 1716 addToLeaderTable(Num, LI, LI->getParent()); 1717 } 1718 1719 return Changed; 1720 } 1721 1722 // For conditions branches, we can perform simple conditional propagation on 1723 // the condition value itself. 1724 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1725 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1726 return false; 1727 1728 Value *BranchCond = BI->getCondition(); 1729 uint32_t CondVN = VN.lookup_or_add(BranchCond); 1730 1731 BasicBlock *TrueSucc = BI->getSuccessor(0); 1732 BasicBlock *FalseSucc = BI->getSuccessor(1); 1733 1734 if (TrueSucc->getSinglePredecessor()) 1735 addToLeaderTable(CondVN, 1736 ConstantInt::getTrue(TrueSucc->getContext()), 1737 TrueSucc); 1738 if (FalseSucc->getSinglePredecessor()) 1739 addToLeaderTable(CondVN, 1740 ConstantInt::getFalse(TrueSucc->getContext()), 1741 FalseSucc); 1742 1743 return false; 1744 } 1745 1746 // Instructions with void type don't return a value, so there's 1747 // no point in trying to find redudancies in them. 1748 if (I->getType()->isVoidTy()) return false; 1749 1750 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1751 unsigned Num = VN.lookup_or_add(I); 1752 1753 // Allocations are always uniquely numbered, so we can save time and memory 1754 // by fast failing them. 1755 if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) { 1756 addToLeaderTable(Num, I, I->getParent()); 1757 return false; 1758 } 1759 1760 // If the number we were assigned was a brand new VN, then we don't 1761 // need to do a lookup to see if the number already exists 1762 // somewhere in the domtree: it can't! 1763 if (Num == NextNum) { 1764 addToLeaderTable(Num, I, I->getParent()); 1765 return false; 1766 } 1767 1768 // Perform fast-path value-number based elimination of values inherited from 1769 // dominators. 1770 Value *repl = findLeader(I->getParent(), Num); 1771 if (repl == 0) { 1772 // Failure, just remember this instance for future use. 1773 addToLeaderTable(Num, I, I->getParent()); 1774 return false; 1775 } 1776 1777 // Remove it! 1778 VN.erase(I); 1779 I->replaceAllUsesWith(repl); 1780 if (MD && repl->getType()->isPointerTy()) 1781 MD->invalidateCachedPointerInfo(repl); 1782 toErase.push_back(I); 1783 return true; 1784} 1785 1786/// runOnFunction - This is the main transformation entry point for a function. 1787bool GVN::runOnFunction(Function& F) { 1788 if (!NoLoads) 1789 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1790 DT = &getAnalysis<DominatorTree>(); 1791 TD = getAnalysisIfAvailable<TargetData>(); 1792 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1793 VN.setMemDep(MD); 1794 VN.setDomTree(DT); 1795 1796 bool Changed = false; 1797 bool ShouldContinue = true; 1798 1799 // Merge unconditional branches, allowing PRE to catch more 1800 // optimization opportunities. 1801 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1802 BasicBlock *BB = FI++; 1803 1804 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1805 if (removedBlock) ++NumGVNBlocks; 1806 1807 Changed |= removedBlock; 1808 } 1809 1810 unsigned Iteration = 0; 1811 while (ShouldContinue) { 1812 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); 1813 ShouldContinue = iterateOnFunction(F); 1814 if (splitCriticalEdges()) 1815 ShouldContinue = true; 1816 Changed |= ShouldContinue; 1817 ++Iteration; 1818 } 1819 1820 if (EnablePRE) { 1821 bool PREChanged = true; 1822 while (PREChanged) { 1823 PREChanged = performPRE(F); 1824 Changed |= PREChanged; 1825 } 1826 } 1827 // FIXME: Should perform GVN again after PRE does something. PRE can move 1828 // computations into blocks where they become fully redundant. Note that 1829 // we can't do this until PRE's critical edge splitting updates memdep. 1830 // Actually, when this happens, we should just fully integrate PRE into GVN. 1831 1832 cleanupGlobalSets(); 1833 1834 return Changed; 1835} 1836 1837 1838bool GVN::processBlock(BasicBlock *BB) { 1839 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1840 // incrementing BI before processing an instruction). 1841 SmallVector<Instruction*, 8> toErase; 1842 bool ChangedFunction = false; 1843 1844 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1845 BI != BE;) { 1846 ChangedFunction |= processInstruction(BI, toErase); 1847 if (toErase.empty()) { 1848 ++BI; 1849 continue; 1850 } 1851 1852 // If we need some instructions deleted, do it now. 1853 NumGVNInstr += toErase.size(); 1854 1855 // Avoid iterator invalidation. 1856 bool AtStart = BI == BB->begin(); 1857 if (!AtStart) 1858 --BI; 1859 1860 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1861 E = toErase.end(); I != E; ++I) { 1862 DEBUG(dbgs() << "GVN removed: " << **I << '\n'); 1863 if (MD) MD->removeInstruction(*I); 1864 (*I)->eraseFromParent(); 1865 DEBUG(verifyRemoved(*I)); 1866 } 1867 toErase.clear(); 1868 1869 if (AtStart) 1870 BI = BB->begin(); 1871 else 1872 ++BI; 1873 } 1874 1875 return ChangedFunction; 1876} 1877 1878/// performPRE - Perform a purely local form of PRE that looks for diamond 1879/// control flow patterns and attempts to perform simple PRE at the join point. 1880bool GVN::performPRE(Function &F) { 1881 bool Changed = false; 1882 DenseMap<BasicBlock*, Value*> predMap; 1883 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1884 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1885 BasicBlock *CurrentBlock = *DI; 1886 1887 // Nothing to PRE in the entry block. 1888 if (CurrentBlock == &F.getEntryBlock()) continue; 1889 1890 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1891 BE = CurrentBlock->end(); BI != BE; ) { 1892 Instruction *CurInst = BI++; 1893 1894 if (isa<AllocaInst>(CurInst) || 1895 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 1896 CurInst->getType()->isVoidTy() || 1897 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 1898 isa<DbgInfoIntrinsic>(CurInst)) 1899 continue; 1900 1901 // We don't currently value number ANY inline asm calls. 1902 if (CallInst *CallI = dyn_cast<CallInst>(CurInst)) 1903 if (CallI->isInlineAsm()) 1904 continue; 1905 1906 uint32_t ValNo = VN.lookup(CurInst); 1907 1908 // Look for the predecessors for PRE opportunities. We're 1909 // only trying to solve the basic diamond case, where 1910 // a value is computed in the successor and one predecessor, 1911 // but not the other. We also explicitly disallow cases 1912 // where the successor is its own predecessor, because they're 1913 // more complicated to get right. 1914 unsigned NumWith = 0; 1915 unsigned NumWithout = 0; 1916 BasicBlock *PREPred = 0; 1917 predMap.clear(); 1918 1919 for (pred_iterator PI = pred_begin(CurrentBlock), 1920 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1921 BasicBlock *P = *PI; 1922 // We're not interested in PRE where the block is its 1923 // own predecessor, or in blocks with predecessors 1924 // that are not reachable. 1925 if (P == CurrentBlock) { 1926 NumWithout = 2; 1927 break; 1928 } else if (!DT->dominates(&F.getEntryBlock(), P)) { 1929 NumWithout = 2; 1930 break; 1931 } 1932 1933 Value* predV = findLeader(P, ValNo); 1934 if (predV == 0) { 1935 PREPred = P; 1936 ++NumWithout; 1937 } else if (predV == CurInst) { 1938 NumWithout = 2; 1939 } else { 1940 predMap[P] = predV; 1941 ++NumWith; 1942 } 1943 } 1944 1945 // Don't do PRE when it might increase code size, i.e. when 1946 // we would need to insert instructions in more than one pred. 1947 if (NumWithout != 1 || NumWith == 0) 1948 continue; 1949 1950 // Don't do PRE across indirect branch. 1951 if (isa<IndirectBrInst>(PREPred->getTerminator())) 1952 continue; 1953 1954 // We can't do PRE safely on a critical edge, so instead we schedule 1955 // the edge to be split and perform the PRE the next time we iterate 1956 // on the function. 1957 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); 1958 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 1959 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 1960 continue; 1961 } 1962 1963 // Instantiate the expression in the predecessor that lacked it. 1964 // Because we are going top-down through the block, all value numbers 1965 // will be available in the predecessor by the time we need them. Any 1966 // that weren't originally present will have been instantiated earlier 1967 // in this loop. 1968 Instruction *PREInstr = CurInst->clone(); 1969 bool success = true; 1970 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 1971 Value *Op = PREInstr->getOperand(i); 1972 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 1973 continue; 1974 1975 if (Value *V = findLeader(PREPred, VN.lookup(Op))) { 1976 PREInstr->setOperand(i, V); 1977 } else { 1978 success = false; 1979 break; 1980 } 1981 } 1982 1983 // Fail out if we encounter an operand that is not available in 1984 // the PRE predecessor. This is typically because of loads which 1985 // are not value numbered precisely. 1986 if (!success) { 1987 delete PREInstr; 1988 DEBUG(verifyRemoved(PREInstr)); 1989 continue; 1990 } 1991 1992 PREInstr->insertBefore(PREPred->getTerminator()); 1993 PREInstr->setName(CurInst->getName() + ".pre"); 1994 predMap[PREPred] = PREInstr; 1995 VN.add(PREInstr, ValNo); 1996 ++NumGVNPRE; 1997 1998 // Update the availability map to include the new instruction. 1999 addToLeaderTable(ValNo, PREInstr, PREPred); 2000 2001 // Create a PHI to make the value available in this block. 2002 pred_iterator PB = pred_begin(CurrentBlock), PE = pred_end(CurrentBlock); 2003 PHINode* Phi = PHINode::Create(CurInst->getType(), std::distance(PB, PE), 2004 CurInst->getName() + ".pre-phi", 2005 CurrentBlock->begin()); 2006 for (pred_iterator PI = PB; PI != PE; ++PI) { 2007 BasicBlock *P = *PI; 2008 Phi->addIncoming(predMap[P], P); 2009 } 2010 2011 VN.add(Phi, ValNo); 2012 addToLeaderTable(ValNo, Phi, CurrentBlock); 2013 2014 CurInst->replaceAllUsesWith(Phi); 2015 if (Phi->getType()->isPointerTy()) { 2016 // Because we have added a PHI-use of the pointer value, it has now 2017 // "escaped" from alias analysis' perspective. We need to inform 2018 // AA of this. 2019 for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee; ++ii) 2020 VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(2*ii)); 2021 2022 if (MD) 2023 MD->invalidateCachedPointerInfo(Phi); 2024 } 2025 VN.erase(CurInst); 2026 removeFromLeaderTable(ValNo, CurInst, CurrentBlock); 2027 2028 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); 2029 if (MD) MD->removeInstruction(CurInst); 2030 CurInst->eraseFromParent(); 2031 DEBUG(verifyRemoved(CurInst)); 2032 Changed = true; 2033 } 2034 } 2035 2036 if (splitCriticalEdges()) 2037 Changed = true; 2038 2039 return Changed; 2040} 2041 2042/// splitCriticalEdges - Split critical edges found during the previous 2043/// iteration that may enable further optimization. 2044bool GVN::splitCriticalEdges() { 2045 if (toSplit.empty()) 2046 return false; 2047 do { 2048 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); 2049 SplitCriticalEdge(Edge.first, Edge.second, this); 2050 } while (!toSplit.empty()); 2051 if (MD) MD->invalidateCachedPredecessors(); 2052 return true; 2053} 2054 2055/// iterateOnFunction - Executes one iteration of GVN 2056bool GVN::iterateOnFunction(Function &F) { 2057 cleanupGlobalSets(); 2058 2059 // Top-down walk of the dominator tree 2060 bool Changed = false; 2061#if 0 2062 // Needed for value numbering with phi construction to work. 2063 ReversePostOrderTraversal<Function*> RPOT(&F); 2064 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2065 RE = RPOT.end(); RI != RE; ++RI) 2066 Changed |= processBlock(*RI); 2067#else 2068 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2069 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2070 Changed |= processBlock(DI->getBlock()); 2071#endif 2072 2073 return Changed; 2074} 2075 2076void GVN::cleanupGlobalSets() { 2077 VN.clear(); 2078 LeaderTable.clear(); 2079 TableAllocator.Reset(); 2080} 2081 2082/// verifyRemoved - Verify that the specified instruction does not occur in our 2083/// internal data structures. 2084void GVN::verifyRemoved(const Instruction *Inst) const { 2085 VN.verifyRemoved(Inst); 2086 2087 // Walk through the value number scope to make sure the instruction isn't 2088 // ferreted away in it. 2089 for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator 2090 I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) { 2091 const LeaderTableEntry *Node = &I->second; 2092 assert(Node->Val != Inst && "Inst still in value numbering scope!"); 2093 2094 while (Node->Next) { 2095 Node = Node->Next; 2096 assert(Node->Val != Inst && "Inst still in value numbering scope!"); 2097 } 2098 } 2099} 2100