BasicAliasAnalysis.cpp revision c10ecd8f23ebb4541acbe18563b7f19c4f79e721
1//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===// 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 file defines the primary stateless implementation of the 11// Alias Analysis interface that implements identities (two different 12// globals cannot alias, etc), but does no stateful analysis. 13// 14//===----------------------------------------------------------------------===// 15 16#include "llvm/Analysis/AliasAnalysis.h" 17#include "llvm/Analysis/Passes.h" 18#include "llvm/Constants.h" 19#include "llvm/DerivedTypes.h" 20#include "llvm/Function.h" 21#include "llvm/GlobalAlias.h" 22#include "llvm/GlobalVariable.h" 23#include "llvm/Instructions.h" 24#include "llvm/IntrinsicInst.h" 25#include "llvm/LLVMContext.h" 26#include "llvm/Operator.h" 27#include "llvm/Pass.h" 28#include "llvm/Analysis/CaptureTracking.h" 29#include "llvm/Analysis/MemoryBuiltins.h" 30#include "llvm/Analysis/InstructionSimplify.h" 31#include "llvm/Analysis/ValueTracking.h" 32#include "llvm/Target/TargetData.h" 33#include "llvm/ADT/SmallPtrSet.h" 34#include "llvm/ADT/SmallVector.h" 35#include "llvm/Support/ErrorHandling.h" 36#include "llvm/Support/GetElementPtrTypeIterator.h" 37#include <algorithm> 38using namespace llvm; 39 40//===----------------------------------------------------------------------===// 41// Useful predicates 42//===----------------------------------------------------------------------===// 43 44/// isKnownNonNull - Return true if we know that the specified value is never 45/// null. 46static bool isKnownNonNull(const Value *V) { 47 // Alloca never returns null, malloc might. 48 if (isa<AllocaInst>(V)) return true; 49 50 // A byval argument is never null. 51 if (const Argument *A = dyn_cast<Argument>(V)) 52 return A->hasByValAttr(); 53 54 // Global values are not null unless extern weak. 55 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) 56 return !GV->hasExternalWeakLinkage(); 57 return false; 58} 59 60/// isNonEscapingLocalObject - Return true if the pointer is to a function-local 61/// object that never escapes from the function. 62static bool isNonEscapingLocalObject(const Value *V) { 63 // If this is a local allocation, check to see if it escapes. 64 if (isa<AllocaInst>(V) || isNoAliasCall(V)) 65 // Set StoreCaptures to True so that we can assume in our callers that the 66 // pointer is not the result of a load instruction. Currently 67 // PointerMayBeCaptured doesn't have any special analysis for the 68 // StoreCaptures=false case; if it did, our callers could be refined to be 69 // more precise. 70 return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); 71 72 // If this is an argument that corresponds to a byval or noalias argument, 73 // then it has not escaped before entering the function. Check if it escapes 74 // inside the function. 75 if (const Argument *A = dyn_cast<Argument>(V)) 76 if (A->hasByValAttr() || A->hasNoAliasAttr()) { 77 // Don't bother analyzing arguments already known not to escape. 78 if (A->hasNoCaptureAttr()) 79 return true; 80 return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); 81 } 82 return false; 83} 84 85/// isEscapeSource - Return true if the pointer is one which would have 86/// been considered an escape by isNonEscapingLocalObject. 87static bool isEscapeSource(const Value *V) { 88 if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V)) 89 return true; 90 91 // The load case works because isNonEscapingLocalObject considers all 92 // stores to be escapes (it passes true for the StoreCaptures argument 93 // to PointerMayBeCaptured). 94 if (isa<LoadInst>(V)) 95 return true; 96 97 return false; 98} 99 100/// getObjectSize - Return the size of the object specified by V, or 101/// UnknownSize if unknown. 102static uint64_t getObjectSize(const Value *V, const TargetData &TD) { 103 const Type *AccessTy; 104 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) { 105 if (!GV->hasDefinitiveInitializer()) 106 return AliasAnalysis::UnknownSize; 107 AccessTy = GV->getType()->getElementType(); 108 } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 109 if (!AI->isArrayAllocation()) 110 AccessTy = AI->getType()->getElementType(); 111 else 112 return AliasAnalysis::UnknownSize; 113 } else if (const CallInst* CI = extractMallocCall(V)) { 114 if (!isArrayMalloc(V, &TD)) 115 // The size is the argument to the malloc call. 116 if (const ConstantInt* C = dyn_cast<ConstantInt>(CI->getArgOperand(0))) 117 return C->getZExtValue(); 118 return AliasAnalysis::UnknownSize; 119 } else if (const Argument *A = dyn_cast<Argument>(V)) { 120 if (A->hasByValAttr()) 121 AccessTy = cast<PointerType>(A->getType())->getElementType(); 122 else 123 return AliasAnalysis::UnknownSize; 124 } else { 125 return AliasAnalysis::UnknownSize; 126 } 127 128 if (AccessTy->isSized()) 129 return TD.getTypeAllocSize(AccessTy); 130 return AliasAnalysis::UnknownSize; 131} 132 133/// isObjectSmallerThan - Return true if we can prove that the object specified 134/// by V is smaller than Size. 135static bool isObjectSmallerThan(const Value *V, uint64_t Size, 136 const TargetData &TD) { 137 uint64_t ObjectSize = getObjectSize(V, TD); 138 return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size; 139} 140 141/// isObjectSize - Return true if we can prove that the object specified 142/// by V has size Size. 143static bool isObjectSize(const Value *V, uint64_t Size, 144 const TargetData &TD) { 145 uint64_t ObjectSize = getObjectSize(V, TD); 146 return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size; 147} 148 149//===----------------------------------------------------------------------===// 150// GetElementPtr Instruction Decomposition and Analysis 151//===----------------------------------------------------------------------===// 152 153namespace { 154 enum ExtensionKind { 155 EK_NotExtended, 156 EK_SignExt, 157 EK_ZeroExt 158 }; 159 160 struct VariableGEPIndex { 161 const Value *V; 162 ExtensionKind Extension; 163 int64_t Scale; 164 }; 165} 166 167 168/// GetLinearExpression - Analyze the specified value as a linear expression: 169/// "A*V + B", where A and B are constant integers. Return the scale and offset 170/// values as APInts and return V as a Value*, and return whether we looked 171/// through any sign or zero extends. The incoming Value is known to have 172/// IntegerType and it may already be sign or zero extended. 173/// 174/// Note that this looks through extends, so the high bits may not be 175/// represented in the result. 176static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, 177 ExtensionKind &Extension, 178 const TargetData &TD, unsigned Depth) { 179 assert(V->getType()->isIntegerTy() && "Not an integer value"); 180 181 // Limit our recursion depth. 182 if (Depth == 6) { 183 Scale = 1; 184 Offset = 0; 185 return V; 186 } 187 188 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) { 189 if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) { 190 switch (BOp->getOpcode()) { 191 default: break; 192 case Instruction::Or: 193 // X|C == X+C if all the bits in C are unset in X. Otherwise we can't 194 // analyze it. 195 if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &TD)) 196 break; 197 // FALL THROUGH. 198 case Instruction::Add: 199 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, 200 TD, Depth+1); 201 Offset += RHSC->getValue(); 202 return V; 203 case Instruction::Mul: 204 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, 205 TD, Depth+1); 206 Offset *= RHSC->getValue(); 207 Scale *= RHSC->getValue(); 208 return V; 209 case Instruction::Shl: 210 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, 211 TD, Depth+1); 212 Offset <<= RHSC->getValue().getLimitedValue(); 213 Scale <<= RHSC->getValue().getLimitedValue(); 214 return V; 215 } 216 } 217 } 218 219 // Since GEP indices are sign extended anyway, we don't care about the high 220 // bits of a sign or zero extended value - just scales and offsets. The 221 // extensions have to be consistent though. 222 if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) || 223 (isa<ZExtInst>(V) && Extension != EK_SignExt)) { 224 Value *CastOp = cast<CastInst>(V)->getOperand(0); 225 unsigned OldWidth = Scale.getBitWidth(); 226 unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits(); 227 Scale = Scale.trunc(SmallWidth); 228 Offset = Offset.trunc(SmallWidth); 229 Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt; 230 231 Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension, 232 TD, Depth+1); 233 Scale = Scale.zext(OldWidth); 234 Offset = Offset.zext(OldWidth); 235 236 return Result; 237 } 238 239 Scale = 1; 240 Offset = 0; 241 return V; 242} 243 244/// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it 245/// into a base pointer with a constant offset and a number of scaled symbolic 246/// offsets. 247/// 248/// The scaled symbolic offsets (represented by pairs of a Value* and a scale in 249/// the VarIndices vector) are Value*'s that are known to be scaled by the 250/// specified amount, but which may have other unrepresented high bits. As such, 251/// the gep cannot necessarily be reconstructed from its decomposed form. 252/// 253/// When TargetData is around, this function is capable of analyzing everything 254/// that GetUnderlyingObject can look through. When not, it just looks 255/// through pointer casts. 256/// 257static const Value * 258DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, 259 SmallVectorImpl<VariableGEPIndex> &VarIndices, 260 const TargetData *TD) { 261 // Limit recursion depth to limit compile time in crazy cases. 262 unsigned MaxLookup = 6; 263 264 BaseOffs = 0; 265 do { 266 // See if this is a bitcast or GEP. 267 const Operator *Op = dyn_cast<Operator>(V); 268 if (Op == 0) { 269 // The only non-operator case we can handle are GlobalAliases. 270 if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { 271 if (!GA->mayBeOverridden()) { 272 V = GA->getAliasee(); 273 continue; 274 } 275 } 276 return V; 277 } 278 279 if (Op->getOpcode() == Instruction::BitCast) { 280 V = Op->getOperand(0); 281 continue; 282 } 283 284 if (const Instruction *I = dyn_cast<Instruction>(V)) 285 // TODO: Get a DominatorTree and use it here. 286 if (const Value *Simplified = 287 SimplifyInstruction(const_cast<Instruction *>(I), TD)) { 288 V = Simplified; 289 continue; 290 } 291 292 const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op); 293 if (GEPOp == 0) 294 return V; 295 296 // Don't attempt to analyze GEPs over unsized objects. 297 if (!cast<PointerType>(GEPOp->getOperand(0)->getType()) 298 ->getElementType()->isSized()) 299 return V; 300 301 // If we are lacking TargetData information, we can't compute the offets of 302 // elements computed by GEPs. However, we can handle bitcast equivalent 303 // GEPs. 304 if (TD == 0) { 305 if (!GEPOp->hasAllZeroIndices()) 306 return V; 307 V = GEPOp->getOperand(0); 308 continue; 309 } 310 311 // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices. 312 gep_type_iterator GTI = gep_type_begin(GEPOp); 313 for (User::const_op_iterator I = GEPOp->op_begin()+1, 314 E = GEPOp->op_end(); I != E; ++I) { 315 Value *Index = *I; 316 // Compute the (potentially symbolic) offset in bytes for this index. 317 if (const StructType *STy = dyn_cast<StructType>(*GTI++)) { 318 // For a struct, add the member offset. 319 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue(); 320 if (FieldNo == 0) continue; 321 322 BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo); 323 continue; 324 } 325 326 // For an array/pointer, add the element offset, explicitly scaled. 327 if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) { 328 if (CIdx->isZero()) continue; 329 BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue(); 330 continue; 331 } 332 333 uint64_t Scale = TD->getTypeAllocSize(*GTI); 334 ExtensionKind Extension = EK_NotExtended; 335 336 // If the integer type is smaller than the pointer size, it is implicitly 337 // sign extended to pointer size. 338 unsigned Width = cast<IntegerType>(Index->getType())->getBitWidth(); 339 if (TD->getPointerSizeInBits() > Width) 340 Extension = EK_SignExt; 341 342 // Use GetLinearExpression to decompose the index into a C1*V+C2 form. 343 APInt IndexScale(Width, 0), IndexOffset(Width, 0); 344 Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension, 345 *TD, 0); 346 347 // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale. 348 // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale. 349 BaseOffs += IndexOffset.getSExtValue()*Scale; 350 Scale *= IndexScale.getSExtValue(); 351 352 353 // If we already had an occurrence of this index variable, merge this 354 // scale into it. For example, we want to handle: 355 // A[x][x] -> x*16 + x*4 -> x*20 356 // This also ensures that 'x' only appears in the index list once. 357 for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) { 358 if (VarIndices[i].V == Index && 359 VarIndices[i].Extension == Extension) { 360 Scale += VarIndices[i].Scale; 361 VarIndices.erase(VarIndices.begin()+i); 362 break; 363 } 364 } 365 366 // Make sure that we have a scale that makes sense for this target's 367 // pointer size. 368 if (unsigned ShiftBits = 64-TD->getPointerSizeInBits()) { 369 Scale <<= ShiftBits; 370 Scale = (int64_t)Scale >> ShiftBits; 371 } 372 373 if (Scale) { 374 VariableGEPIndex Entry = {Index, Extension, Scale}; 375 VarIndices.push_back(Entry); 376 } 377 } 378 379 // Analyze the base pointer next. 380 V = GEPOp->getOperand(0); 381 } while (--MaxLookup); 382 383 // If the chain of expressions is too deep, just return early. 384 return V; 385} 386 387/// GetIndexDifference - Dest and Src are the variable indices from two 388/// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base 389/// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic 390/// difference between the two pointers. 391static void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest, 392 const SmallVectorImpl<VariableGEPIndex> &Src) { 393 if (Src.empty()) return; 394 395 for (unsigned i = 0, e = Src.size(); i != e; ++i) { 396 const Value *V = Src[i].V; 397 ExtensionKind Extension = Src[i].Extension; 398 int64_t Scale = Src[i].Scale; 399 400 // Find V in Dest. This is N^2, but pointer indices almost never have more 401 // than a few variable indexes. 402 for (unsigned j = 0, e = Dest.size(); j != e; ++j) { 403 if (Dest[j].V != V || Dest[j].Extension != Extension) continue; 404 405 // If we found it, subtract off Scale V's from the entry in Dest. If it 406 // goes to zero, remove the entry. 407 if (Dest[j].Scale != Scale) 408 Dest[j].Scale -= Scale; 409 else 410 Dest.erase(Dest.begin()+j); 411 Scale = 0; 412 break; 413 } 414 415 // If we didn't consume this entry, add it to the end of the Dest list. 416 if (Scale) { 417 VariableGEPIndex Entry = { V, Extension, -Scale }; 418 Dest.push_back(Entry); 419 } 420 } 421} 422 423//===----------------------------------------------------------------------===// 424// BasicAliasAnalysis Pass 425//===----------------------------------------------------------------------===// 426 427#ifndef NDEBUG 428static const Function *getParent(const Value *V) { 429 if (const Instruction *inst = dyn_cast<Instruction>(V)) 430 return inst->getParent()->getParent(); 431 432 if (const Argument *arg = dyn_cast<Argument>(V)) 433 return arg->getParent(); 434 435 return NULL; 436} 437 438static bool notDifferentParent(const Value *O1, const Value *O2) { 439 440 const Function *F1 = getParent(O1); 441 const Function *F2 = getParent(O2); 442 443 return !F1 || !F2 || F1 == F2; 444} 445#endif 446 447namespace { 448 /// BasicAliasAnalysis - This is the primary alias analysis implementation. 449 struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis { 450 static char ID; // Class identification, replacement for typeinfo 451 BasicAliasAnalysis() : ImmutablePass(ID) { 452 initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry()); 453 } 454 455 virtual void initializePass() { 456 InitializeAliasAnalysis(this); 457 } 458 459 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 460 AU.addRequired<AliasAnalysis>(); 461 } 462 463 virtual AliasResult alias(const Location &LocA, 464 const Location &LocB) { 465 assert(Visited.empty() && "Visited must be cleared after use!"); 466 assert(notDifferentParent(LocA.Ptr, LocB.Ptr) && 467 "BasicAliasAnalysis doesn't support interprocedural queries."); 468 AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag, 469 LocB.Ptr, LocB.Size, LocB.TBAATag); 470 Visited.clear(); 471 return Alias; 472 } 473 474 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 475 const Location &Loc); 476 477 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 478 ImmutableCallSite CS2) { 479 // The AliasAnalysis base class has some smarts, lets use them. 480 return AliasAnalysis::getModRefInfo(CS1, CS2); 481 } 482 483 /// pointsToConstantMemory - Chase pointers until we find a (constant 484 /// global) or not. 485 virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal); 486 487 /// getModRefBehavior - Return the behavior when calling the given 488 /// call site. 489 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 490 491 /// getModRefBehavior - Return the behavior when calling the given function. 492 /// For use when the call site is not known. 493 virtual ModRefBehavior getModRefBehavior(const Function *F); 494 495 /// getAdjustedAnalysisPointer - This method is used when a pass implements 496 /// an analysis interface through multiple inheritance. If needed, it 497 /// should override this to adjust the this pointer as needed for the 498 /// specified pass info. 499 virtual void *getAdjustedAnalysisPointer(const void *ID) { 500 if (ID == &AliasAnalysis::ID) 501 return (AliasAnalysis*)this; 502 return this; 503 } 504 505 private: 506 // Visited - Track instructions visited by a aliasPHI, aliasSelect(), and aliasGEP(). 507 SmallPtrSet<const Value*, 16> Visited; 508 509 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP 510 // instruction against another. 511 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size, 512 const Value *V2, uint64_t V2Size, 513 const MDNode *V2TBAAInfo, 514 const Value *UnderlyingV1, const Value *UnderlyingV2); 515 516 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI 517 // instruction against another. 518 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize, 519 const MDNode *PNTBAAInfo, 520 const Value *V2, uint64_t V2Size, 521 const MDNode *V2TBAAInfo); 522 523 /// aliasSelect - Disambiguate a Select instruction against another value. 524 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize, 525 const MDNode *SITBAAInfo, 526 const Value *V2, uint64_t V2Size, 527 const MDNode *V2TBAAInfo); 528 529 AliasResult aliasCheck(const Value *V1, uint64_t V1Size, 530 const MDNode *V1TBAATag, 531 const Value *V2, uint64_t V2Size, 532 const MDNode *V2TBAATag); 533 }; 534} // End of anonymous namespace 535 536// Register this pass... 537char BasicAliasAnalysis::ID = 0; 538INITIALIZE_AG_PASS(BasicAliasAnalysis, AliasAnalysis, "basicaa", 539 "Basic Alias Analysis (stateless AA impl)", 540 false, true, false) 541 542ImmutablePass *llvm::createBasicAliasAnalysisPass() { 543 return new BasicAliasAnalysis(); 544} 545 546/// pointsToConstantMemory - Returns whether the given pointer value 547/// points to memory that is local to the function, with global constants being 548/// considered local to all functions. 549bool 550BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) { 551 assert(Visited.empty() && "Visited must be cleared after use!"); 552 553 unsigned MaxLookup = 8; 554 SmallVector<const Value *, 16> Worklist; 555 Worklist.push_back(Loc.Ptr); 556 do { 557 const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), TD); 558 if (!Visited.insert(V)) { 559 Visited.clear(); 560 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); 561 } 562 563 // An alloca instruction defines local memory. 564 if (OrLocal && isa<AllocaInst>(V)) 565 continue; 566 567 // A global constant counts as local memory for our purposes. 568 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) { 569 // Note: this doesn't require GV to be "ODR" because it isn't legal for a 570 // global to be marked constant in some modules and non-constant in 571 // others. GV may even be a declaration, not a definition. 572 if (!GV->isConstant()) { 573 Visited.clear(); 574 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); 575 } 576 continue; 577 } 578 579 // If both select values point to local memory, then so does the select. 580 if (const SelectInst *SI = dyn_cast<SelectInst>(V)) { 581 Worklist.push_back(SI->getTrueValue()); 582 Worklist.push_back(SI->getFalseValue()); 583 continue; 584 } 585 586 // If all values incoming to a phi node point to local memory, then so does 587 // the phi. 588 if (const PHINode *PN = dyn_cast<PHINode>(V)) { 589 // Don't bother inspecting phi nodes with many operands. 590 if (PN->getNumIncomingValues() > MaxLookup) { 591 Visited.clear(); 592 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); 593 } 594 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 595 Worklist.push_back(PN->getIncomingValue(i)); 596 continue; 597 } 598 599 // Otherwise be conservative. 600 Visited.clear(); 601 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); 602 603 } while (!Worklist.empty() && --MaxLookup); 604 605 Visited.clear(); 606 return Worklist.empty(); 607} 608 609/// getModRefBehavior - Return the behavior when calling the given call site. 610AliasAnalysis::ModRefBehavior 611BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { 612 if (CS.doesNotAccessMemory()) 613 // Can't do better than this. 614 return DoesNotAccessMemory; 615 616 ModRefBehavior Min = UnknownModRefBehavior; 617 618 // If the callsite knows it only reads memory, don't return worse 619 // than that. 620 if (CS.onlyReadsMemory()) 621 Min = OnlyReadsMemory; 622 623 // The AliasAnalysis base class has some smarts, lets use them. 624 return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min); 625} 626 627/// getModRefBehavior - Return the behavior when calling the given function. 628/// For use when the call site is not known. 629AliasAnalysis::ModRefBehavior 630BasicAliasAnalysis::getModRefBehavior(const Function *F) { 631 // If the function declares it doesn't access memory, we can't do better. 632 if (F->doesNotAccessMemory()) 633 return DoesNotAccessMemory; 634 635 // For intrinsics, we can check the table. 636 if (unsigned iid = F->getIntrinsicID()) { 637#define GET_INTRINSIC_MODREF_BEHAVIOR 638#include "llvm/Intrinsics.gen" 639#undef GET_INTRINSIC_MODREF_BEHAVIOR 640 } 641 642 ModRefBehavior Min = UnknownModRefBehavior; 643 644 // If the function declares it only reads memory, go with that. 645 if (F->onlyReadsMemory()) 646 Min = OnlyReadsMemory; 647 648 // Otherwise be conservative. 649 return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min); 650} 651 652/// getModRefInfo - Check to see if the specified callsite can clobber the 653/// specified memory object. Since we only look at local properties of this 654/// function, we really can't say much about this query. We do, however, use 655/// simple "address taken" analysis on local objects. 656AliasAnalysis::ModRefResult 657BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, 658 const Location &Loc) { 659 assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) && 660 "AliasAnalysis query involving multiple functions!"); 661 662 const Value *Object = GetUnderlyingObject(Loc.Ptr, TD); 663 664 // If this is a tail call and Loc.Ptr points to a stack location, we know that 665 // the tail call cannot access or modify the local stack. 666 // We cannot exclude byval arguments here; these belong to the caller of 667 // the current function not to the current function, and a tail callee 668 // may reference them. 669 if (isa<AllocaInst>(Object)) 670 if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction())) 671 if (CI->isTailCall()) 672 return NoModRef; 673 674 // If the pointer is to a locally allocated object that does not escape, 675 // then the call can not mod/ref the pointer unless the call takes the pointer 676 // as an argument, and itself doesn't capture it. 677 if (!isa<Constant>(Object) && CS.getInstruction() != Object && 678 isNonEscapingLocalObject(Object)) { 679 bool PassedAsArg = false; 680 unsigned ArgNo = 0; 681 for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end(); 682 CI != CE; ++CI, ++ArgNo) { 683 // Only look at the no-capture or byval pointer arguments. If this 684 // pointer were passed to arguments that were neither of these, then it 685 // couldn't be no-capture. 686 if (!(*CI)->getType()->isPointerTy() || 687 (!CS.paramHasAttr(ArgNo+1, Attribute::NoCapture) && 688 !CS.paramHasAttr(ArgNo+1, Attribute::ByVal))) 689 continue; 690 691 // If this is a no-capture pointer argument, see if we can tell that it 692 // is impossible to alias the pointer we're checking. If not, we have to 693 // assume that the call could touch the pointer, even though it doesn't 694 // escape. 695 if (!isNoAlias(Location(cast<Value>(CI)), Loc)) { 696 PassedAsArg = true; 697 break; 698 } 699 } 700 701 if (!PassedAsArg) 702 return NoModRef; 703 } 704 705 ModRefResult Min = ModRef; 706 707 // Finally, handle specific knowledge of intrinsics. 708 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction()); 709 if (II != 0) 710 switch (II->getIntrinsicID()) { 711 default: break; 712 case Intrinsic::memcpy: 713 case Intrinsic::memmove: { 714 uint64_t Len = UnknownSize; 715 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2))) 716 Len = LenCI->getZExtValue(); 717 Value *Dest = II->getArgOperand(0); 718 Value *Src = II->getArgOperand(1); 719 // If it can't overlap the source dest, then it doesn't modref the loc. 720 if (isNoAlias(Location(Dest, Len), Loc)) { 721 if (isNoAlias(Location(Src, Len), Loc)) 722 return NoModRef; 723 // If it can't overlap the dest, then worst case it reads the loc. 724 Min = Ref; 725 } else if (isNoAlias(Location(Src, Len), Loc)) { 726 // If it can't overlap the source, then worst case it mutates the loc. 727 Min = Mod; 728 } 729 break; 730 } 731 case Intrinsic::memset: 732 // Since memset is 'accesses arguments' only, the AliasAnalysis base class 733 // will handle it for the variable length case. 734 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2))) { 735 uint64_t Len = LenCI->getZExtValue(); 736 Value *Dest = II->getArgOperand(0); 737 if (isNoAlias(Location(Dest, Len), Loc)) 738 return NoModRef; 739 } 740 // We know that memset doesn't load anything. 741 Min = Mod; 742 break; 743 case Intrinsic::atomic_cmp_swap: 744 case Intrinsic::atomic_swap: 745 case Intrinsic::atomic_load_add: 746 case Intrinsic::atomic_load_sub: 747 case Intrinsic::atomic_load_and: 748 case Intrinsic::atomic_load_nand: 749 case Intrinsic::atomic_load_or: 750 case Intrinsic::atomic_load_xor: 751 case Intrinsic::atomic_load_max: 752 case Intrinsic::atomic_load_min: 753 case Intrinsic::atomic_load_umax: 754 case Intrinsic::atomic_load_umin: 755 if (TD) { 756 Value *Op1 = II->getArgOperand(0); 757 uint64_t Op1Size = TD->getTypeStoreSize(Op1->getType()); 758 MDNode *Tag = II->getMetadata(LLVMContext::MD_tbaa); 759 if (isNoAlias(Location(Op1, Op1Size, Tag), Loc)) 760 return NoModRef; 761 } 762 break; 763 case Intrinsic::lifetime_start: 764 case Intrinsic::lifetime_end: 765 case Intrinsic::invariant_start: { 766 uint64_t PtrSize = 767 cast<ConstantInt>(II->getArgOperand(0))->getZExtValue(); 768 if (isNoAlias(Location(II->getArgOperand(1), 769 PtrSize, 770 II->getMetadata(LLVMContext::MD_tbaa)), 771 Loc)) 772 return NoModRef; 773 break; 774 } 775 case Intrinsic::invariant_end: { 776 uint64_t PtrSize = 777 cast<ConstantInt>(II->getArgOperand(1))->getZExtValue(); 778 if (isNoAlias(Location(II->getArgOperand(2), 779 PtrSize, 780 II->getMetadata(LLVMContext::MD_tbaa)), 781 Loc)) 782 return NoModRef; 783 break; 784 } 785 case Intrinsic::arm_neon_vld1: { 786 // LLVM's vld1 and vst1 intrinsics currently only support a single 787 // vector register. 788 uint64_t Size = 789 TD ? TD->getTypeStoreSize(II->getType()) : UnknownSize; 790 if (isNoAlias(Location(II->getArgOperand(0), Size, 791 II->getMetadata(LLVMContext::MD_tbaa)), 792 Loc)) 793 return NoModRef; 794 break; 795 } 796 case Intrinsic::arm_neon_vst1: { 797 uint64_t Size = 798 TD ? TD->getTypeStoreSize(II->getArgOperand(1)->getType()) : UnknownSize; 799 if (isNoAlias(Location(II->getArgOperand(0), Size, 800 II->getMetadata(LLVMContext::MD_tbaa)), 801 Loc)) 802 return NoModRef; 803 break; 804 } 805 } 806 807 // The AliasAnalysis base class has some smarts, lets use them. 808 return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min); 809} 810 811/// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction 812/// against another pointer. We know that V1 is a GEP, but we don't know 813/// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, TD), 814/// UnderlyingV2 is the same for V2. 815/// 816AliasAnalysis::AliasResult 817BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, 818 const Value *V2, uint64_t V2Size, 819 const MDNode *V2TBAAInfo, 820 const Value *UnderlyingV1, 821 const Value *UnderlyingV2) { 822 // If this GEP has been visited before, we're on a use-def cycle. 823 // Such cycles are only valid when PHI nodes are involved or in unreachable 824 // code. The visitPHI function catches cycles containing PHIs, but there 825 // could still be a cycle without PHIs in unreachable code. 826 if (!Visited.insert(GEP1)) 827 return MayAlias; 828 829 int64_t GEP1BaseOffset; 830 SmallVector<VariableGEPIndex, 4> GEP1VariableIndices; 831 832 // If we have two gep instructions with must-alias'ing base pointers, figure 833 // out if the indexes to the GEP tell us anything about the derived pointer. 834 if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) { 835 // Do the base pointers alias? 836 AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0, 837 UnderlyingV2, UnknownSize, 0); 838 839 // If we get a No or May, then return it immediately, no amount of analysis 840 // will improve this situation. 841 if (BaseAlias != MustAlias) return BaseAlias; 842 843 // Otherwise, we have a MustAlias. Since the base pointers alias each other 844 // exactly, see if the computed offset from the common pointer tells us 845 // about the relation of the resulting pointer. 846 const Value *GEP1BasePtr = 847 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); 848 849 int64_t GEP2BaseOffset; 850 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices; 851 const Value *GEP2BasePtr = 852 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD); 853 854 // If DecomposeGEPExpression isn't able to look all the way through the 855 // addressing operation, we must not have TD and this is too complex for us 856 // to handle without it. 857 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { 858 assert(TD == 0 && 859 "DecomposeGEPExpression and GetUnderlyingObject disagree!"); 860 return MayAlias; 861 } 862 863 // Subtract the GEP2 pointer from the GEP1 pointer to find out their 864 // symbolic difference. 865 GEP1BaseOffset -= GEP2BaseOffset; 866 GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices); 867 868 } else { 869 // Check to see if these two pointers are related by the getelementptr 870 // instruction. If one pointer is a GEP with a non-zero index of the other 871 // pointer, we know they cannot alias. 872 873 // If both accesses are unknown size, we can't do anything useful here. 874 if (V1Size == UnknownSize && V2Size == UnknownSize) 875 return MayAlias; 876 877 AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, 0, 878 V2, V2Size, V2TBAAInfo); 879 if (R != MustAlias) 880 // If V2 may alias GEP base pointer, conservatively returns MayAlias. 881 // If V2 is known not to alias GEP base pointer, then the two values 882 // cannot alias per GEP semantics: "A pointer value formed from a 883 // getelementptr instruction is associated with the addresses associated 884 // with the first operand of the getelementptr". 885 return R; 886 887 const Value *GEP1BasePtr = 888 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); 889 890 // If DecomposeGEPExpression isn't able to look all the way through the 891 // addressing operation, we must not have TD and this is too complex for us 892 // to handle without it. 893 if (GEP1BasePtr != UnderlyingV1) { 894 assert(TD == 0 && 895 "DecomposeGEPExpression and GetUnderlyingObject disagree!"); 896 return MayAlias; 897 } 898 } 899 900 // In the two GEP Case, if there is no difference in the offsets of the 901 // computed pointers, the resultant pointers are a must alias. This 902 // hapens when we have two lexically identical GEP's (for example). 903 // 904 // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 905 // must aliases the GEP, the end result is a must alias also. 906 if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty()) 907 return MustAlias; 908 909 // If there is a difference between the pointers, but the difference is 910 // less than the size of the associated memory object, then we know 911 // that the objects are partially overlapping. 912 if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) { 913 if (GEP1BaseOffset >= 0 ? 914 (V2Size != UnknownSize && (uint64_t)GEP1BaseOffset < V2Size) : 915 (V1Size != UnknownSize && -(uint64_t)GEP1BaseOffset < V1Size && 916 GEP1BaseOffset != INT64_MIN)) 917 return PartialAlias; 918 } 919 920 // If we have a known constant offset, see if this offset is larger than the 921 // access size being queried. If so, and if no variable indices can remove 922 // pieces of this constant, then we know we have a no-alias. For example, 923 // &A[100] != &A. 924 925 // In order to handle cases like &A[100][i] where i is an out of range 926 // subscript, we have to ignore all constant offset pieces that are a multiple 927 // of a scaled index. Do this by removing constant offsets that are a 928 // multiple of any of our variable indices. This allows us to transform 929 // things like &A[i][1] because i has a stride of (e.g.) 8 bytes but the 1 930 // provides an offset of 4 bytes (assuming a <= 4 byte access). 931 for (unsigned i = 0, e = GEP1VariableIndices.size(); 932 i != e && GEP1BaseOffset;++i) 933 if (int64_t RemovedOffset = GEP1BaseOffset/GEP1VariableIndices[i].Scale) 934 GEP1BaseOffset -= RemovedOffset*GEP1VariableIndices[i].Scale; 935 936 // If our known offset is bigger than the access size, we know we don't have 937 // an alias. 938 if (GEP1BaseOffset) { 939 if (GEP1BaseOffset >= 0 ? 940 (V2Size != UnknownSize && (uint64_t)GEP1BaseOffset >= V2Size) : 941 (V1Size != UnknownSize && -(uint64_t)GEP1BaseOffset >= V1Size && 942 GEP1BaseOffset != INT64_MIN)) 943 return NoAlias; 944 } 945 946 return MayAlias; 947} 948 949/// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select 950/// instruction against another. 951AliasAnalysis::AliasResult 952BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize, 953 const MDNode *SITBAAInfo, 954 const Value *V2, uint64_t V2Size, 955 const MDNode *V2TBAAInfo) { 956 // If this select has been visited before, we're on a use-def cycle. 957 // Such cycles are only valid when PHI nodes are involved or in unreachable 958 // code. The visitPHI function catches cycles containing PHIs, but there 959 // could still be a cycle without PHIs in unreachable code. 960 if (!Visited.insert(SI)) 961 return MayAlias; 962 963 // If the values are Selects with the same condition, we can do a more precise 964 // check: just check for aliases between the values on corresponding arms. 965 if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2)) 966 if (SI->getCondition() == SI2->getCondition()) { 967 AliasResult Alias = 968 aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo, 969 SI2->getTrueValue(), V2Size, V2TBAAInfo); 970 if (Alias == MayAlias) 971 return MayAlias; 972 AliasResult ThisAlias = 973 aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo, 974 SI2->getFalseValue(), V2Size, V2TBAAInfo); 975 if (ThisAlias != Alias) 976 return MayAlias; 977 return Alias; 978 } 979 980 // If both arms of the Select node NoAlias or MustAlias V2, then returns 981 // NoAlias / MustAlias. Otherwise, returns MayAlias. 982 AliasResult Alias = 983 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo); 984 if (Alias == MayAlias) 985 return MayAlias; 986 987 // If V2 is visited, the recursive case will have been caught in the 988 // above aliasCheck call, so these subsequent calls to aliasCheck 989 // don't need to assume that V2 is being visited recursively. 990 Visited.erase(V2); 991 992 AliasResult ThisAlias = 993 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo); 994 if (ThisAlias != Alias) 995 return MayAlias; 996 return Alias; 997} 998 999// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction 1000// against another. 1001AliasAnalysis::AliasResult 1002BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, 1003 const MDNode *PNTBAAInfo, 1004 const Value *V2, uint64_t V2Size, 1005 const MDNode *V2TBAAInfo) { 1006 // The PHI node has already been visited, avoid recursion any further. 1007 if (!Visited.insert(PN)) 1008 return MayAlias; 1009 1010 // If the values are PHIs in the same block, we can do a more precise 1011 // as well as efficient check: just check for aliases between the values 1012 // on corresponding edges. 1013 if (const PHINode *PN2 = dyn_cast<PHINode>(V2)) 1014 if (PN2->getParent() == PN->getParent()) { 1015 AliasResult Alias = 1016 aliasCheck(PN->getIncomingValue(0), PNSize, PNTBAAInfo, 1017 PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)), 1018 V2Size, V2TBAAInfo); 1019 if (Alias == MayAlias) 1020 return MayAlias; 1021 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) { 1022 AliasResult ThisAlias = 1023 aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo, 1024 PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), 1025 V2Size, V2TBAAInfo); 1026 if (ThisAlias != Alias) 1027 return MayAlias; 1028 } 1029 return Alias; 1030 } 1031 1032 SmallPtrSet<Value*, 4> UniqueSrc; 1033 SmallVector<Value*, 4> V1Srcs; 1034 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1035 Value *PV1 = PN->getIncomingValue(i); 1036 if (isa<PHINode>(PV1)) 1037 // If any of the source itself is a PHI, return MayAlias conservatively 1038 // to avoid compile time explosion. The worst possible case is if both 1039 // sides are PHI nodes. In which case, this is O(m x n) time where 'm' 1040 // and 'n' are the number of PHI sources. 1041 return MayAlias; 1042 if (UniqueSrc.insert(PV1)) 1043 V1Srcs.push_back(PV1); 1044 } 1045 1046 AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo, 1047 V1Srcs[0], PNSize, PNTBAAInfo); 1048 // Early exit if the check of the first PHI source against V2 is MayAlias. 1049 // Other results are not possible. 1050 if (Alias == MayAlias) 1051 return MayAlias; 1052 1053 // If all sources of the PHI node NoAlias or MustAlias V2, then returns 1054 // NoAlias / MustAlias. Otherwise, returns MayAlias. 1055 for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) { 1056 Value *V = V1Srcs[i]; 1057 1058 // If V2 is visited, the recursive case will have been caught in the 1059 // above aliasCheck call, so these subsequent calls to aliasCheck 1060 // don't need to assume that V2 is being visited recursively. 1061 Visited.erase(V2); 1062 1063 AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo, 1064 V, PNSize, PNTBAAInfo); 1065 if (ThisAlias != Alias || ThisAlias == MayAlias) 1066 return MayAlias; 1067 } 1068 1069 return Alias; 1070} 1071 1072// aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases, 1073// such as array references. 1074// 1075AliasAnalysis::AliasResult 1076BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, 1077 const MDNode *V1TBAAInfo, 1078 const Value *V2, uint64_t V2Size, 1079 const MDNode *V2TBAAInfo) { 1080 // If either of the memory references is empty, it doesn't matter what the 1081 // pointer values are. 1082 if (V1Size == 0 || V2Size == 0) 1083 return NoAlias; 1084 1085 // Strip off any casts if they exist. 1086 V1 = V1->stripPointerCasts(); 1087 V2 = V2->stripPointerCasts(); 1088 1089 // Are we checking for alias of the same value? 1090 if (V1 == V2) return MustAlias; 1091 1092 if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy()) 1093 return NoAlias; // Scalars cannot alias each other 1094 1095 // Figure out what objects these things are pointing to if we can. 1096 const Value *O1 = GetUnderlyingObject(V1, TD); 1097 const Value *O2 = GetUnderlyingObject(V2, TD); 1098 1099 // Null values in the default address space don't point to any object, so they 1100 // don't alias any other pointer. 1101 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1)) 1102 if (CPN->getType()->getAddressSpace() == 0) 1103 return NoAlias; 1104 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2)) 1105 if (CPN->getType()->getAddressSpace() == 0) 1106 return NoAlias; 1107 1108 if (O1 != O2) { 1109 // If V1/V2 point to two different objects we know that we have no alias. 1110 if (isIdentifiedObject(O1) && isIdentifiedObject(O2)) 1111 return NoAlias; 1112 1113 // Constant pointers can't alias with non-const isIdentifiedObject objects. 1114 if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) || 1115 (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1))) 1116 return NoAlias; 1117 1118 // Arguments can't alias with local allocations or noalias calls 1119 // in the same function. 1120 if (((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) || 1121 (isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1))))) 1122 return NoAlias; 1123 1124 // Most objects can't alias null. 1125 if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) || 1126 (isa<ConstantPointerNull>(O1) && isKnownNonNull(O2))) 1127 return NoAlias; 1128 1129 // If one pointer is the result of a call/invoke or load and the other is a 1130 // non-escaping local object within the same function, then we know the 1131 // object couldn't escape to a point where the call could return it. 1132 // 1133 // Note that if the pointers are in different functions, there are a 1134 // variety of complications. A call with a nocapture argument may still 1135 // temporary store the nocapture argument's value in a temporary memory 1136 // location if that memory location doesn't escape. Or it may pass a 1137 // nocapture value to other functions as long as they don't capture it. 1138 if (isEscapeSource(O1) && isNonEscapingLocalObject(O2)) 1139 return NoAlias; 1140 if (isEscapeSource(O2) && isNonEscapingLocalObject(O1)) 1141 return NoAlias; 1142 } 1143 1144 // If the size of one access is larger than the entire object on the other 1145 // side, then we know such behavior is undefined and can assume no alias. 1146 if (TD) 1147 if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD)) || 1148 (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD))) 1149 return NoAlias; 1150 1151 // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the 1152 // GEP can't simplify, we don't even look at the PHI cases. 1153 if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) { 1154 std::swap(V1, V2); 1155 std::swap(V1Size, V2Size); 1156 std::swap(O1, O2); 1157 } 1158 if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) { 1159 AliasResult Result = aliasGEP(GV1, V1Size, V2, V2Size, V2TBAAInfo, O1, O2); 1160 if (Result != MayAlias) return Result; 1161 } 1162 1163 if (isa<PHINode>(V2) && !isa<PHINode>(V1)) { 1164 std::swap(V1, V2); 1165 std::swap(V1Size, V2Size); 1166 } 1167 if (const PHINode *PN = dyn_cast<PHINode>(V1)) { 1168 AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo, 1169 V2, V2Size, V2TBAAInfo); 1170 if (Result != MayAlias) return Result; 1171 } 1172 1173 if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) { 1174 std::swap(V1, V2); 1175 std::swap(V1Size, V2Size); 1176 } 1177 if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) { 1178 AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo, 1179 V2, V2Size, V2TBAAInfo); 1180 if (Result != MayAlias) return Result; 1181 } 1182 1183 // If both pointers are pointing into the same object and one of them 1184 // accesses is accessing the entire object, then the accesses must 1185 // overlap in some way. 1186 if (TD && O1 == O2) 1187 if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD)) || 1188 (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD))) 1189 return PartialAlias; 1190 1191 return AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo), 1192 Location(V2, V2Size, V2TBAAInfo)); 1193} 1194