BasicAliasAnalysis.cpp revision 207618
1193323Sed//===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===// 2193323Sed// 3193323Sed// The LLVM Compiler Infrastructure 4193323Sed// 5193323Sed// This file is distributed under the University of Illinois Open Source 6193323Sed// License. See LICENSE.TXT for details. 7193323Sed// 8193323Sed//===----------------------------------------------------------------------===// 9193323Sed// 10193323Sed// This file defines the default implementation of the Alias Analysis interface 11193323Sed// that simply implements a few identities (two different globals cannot alias, 12193323Sed// etc), but otherwise does no analysis. 13193323Sed// 14193323Sed//===----------------------------------------------------------------------===// 15193323Sed 16193323Sed#include "llvm/Analysis/AliasAnalysis.h" 17193323Sed#include "llvm/Analysis/Passes.h" 18193323Sed#include "llvm/Constants.h" 19193323Sed#include "llvm/DerivedTypes.h" 20193323Sed#include "llvm/Function.h" 21193323Sed#include "llvm/GlobalVariable.h" 22193323Sed#include "llvm/Instructions.h" 23193323Sed#include "llvm/IntrinsicInst.h" 24198090Srdivacky#include "llvm/Operator.h" 25193323Sed#include "llvm/Pass.h" 26199989Srdivacky#include "llvm/Analysis/CaptureTracking.h" 27199989Srdivacky#include "llvm/Analysis/MemoryBuiltins.h" 28199989Srdivacky#include "llvm/Analysis/ValueTracking.h" 29193323Sed#include "llvm/Target/TargetData.h" 30199989Srdivacky#include "llvm/ADT/SmallPtrSet.h" 31193323Sed#include "llvm/ADT/SmallVector.h" 32198090Srdivacky#include "llvm/Support/ErrorHandling.h" 33193323Sed#include <algorithm> 34193323Sedusing namespace llvm; 35193323Sed 36193323Sed//===----------------------------------------------------------------------===// 37193323Sed// Useful predicates 38193323Sed//===----------------------------------------------------------------------===// 39193323Sed 40193323Sed/// isKnownNonNull - Return true if we know that the specified value is never 41193323Sed/// null. 42193323Sedstatic bool isKnownNonNull(const Value *V) { 43193323Sed // Alloca never returns null, malloc might. 44193323Sed if (isa<AllocaInst>(V)) return true; 45193323Sed 46193323Sed // A byval argument is never null. 47193323Sed if (const Argument *A = dyn_cast<Argument>(V)) 48193323Sed return A->hasByValAttr(); 49193323Sed 50193323Sed // Global values are not null unless extern weak. 51193323Sed if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) 52193323Sed return !GV->hasExternalWeakLinkage(); 53193323Sed return false; 54193323Sed} 55193323Sed 56193323Sed/// isNonEscapingLocalObject - Return true if the pointer is to a function-local 57193323Sed/// object that never escapes from the function. 58193323Sedstatic bool isNonEscapingLocalObject(const Value *V) { 59193323Sed // If this is a local allocation, check to see if it escapes. 60198892Srdivacky if (isa<AllocaInst>(V) || isNoAliasCall(V)) 61199989Srdivacky // Set StoreCaptures to True so that we can assume in our callers that the 62199989Srdivacky // pointer is not the result of a load instruction. Currently 63199989Srdivacky // PointerMayBeCaptured doesn't have any special analysis for the 64199989Srdivacky // StoreCaptures=false case; if it did, our callers could be refined to be 65199989Srdivacky // more precise. 66199989Srdivacky return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); 67193323Sed 68193323Sed // If this is an argument that corresponds to a byval or noalias argument, 69193323Sed // then it has not escaped before entering the function. Check if it escapes 70193323Sed // inside the function. 71193323Sed if (const Argument *A = dyn_cast<Argument>(V)) 72193323Sed if (A->hasByValAttr() || A->hasNoAliasAttr()) { 73193323Sed // Don't bother analyzing arguments already known not to escape. 74193323Sed if (A->hasNoCaptureAttr()) 75193323Sed return true; 76199989Srdivacky return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); 77193323Sed } 78193323Sed return false; 79193323Sed} 80193323Sed 81193323Sed 82193323Sed/// isObjectSmallerThan - Return true if we can prove that the object specified 83193323Sed/// by V is smaller than Size. 84193323Sedstatic bool isObjectSmallerThan(const Value *V, unsigned Size, 85199481Srdivacky const TargetData &TD) { 86193323Sed const Type *AccessTy; 87193323Sed if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) { 88193323Sed AccessTy = GV->getType()->getElementType(); 89198892Srdivacky } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 90193323Sed if (!AI->isArrayAllocation()) 91193323Sed AccessTy = AI->getType()->getElementType(); 92193323Sed else 93193323Sed return false; 94198090Srdivacky } else if (const CallInst* CI = extractMallocCall(V)) { 95199481Srdivacky if (!isArrayMalloc(V, &TD)) 96198090Srdivacky // The size is the argument to the malloc call. 97198090Srdivacky if (const ConstantInt* C = dyn_cast<ConstantInt>(CI->getOperand(1))) 98198090Srdivacky return (C->getZExtValue() < Size); 99198090Srdivacky return false; 100193323Sed } else if (const Argument *A = dyn_cast<Argument>(V)) { 101193323Sed if (A->hasByValAttr()) 102193323Sed AccessTy = cast<PointerType>(A->getType())->getElementType(); 103193323Sed else 104193323Sed return false; 105193323Sed } else { 106193323Sed return false; 107193323Sed } 108193323Sed 109193323Sed if (AccessTy->isSized()) 110193323Sed return TD.getTypeAllocSize(AccessTy) < Size; 111193323Sed return false; 112193323Sed} 113193323Sed 114193323Sed//===----------------------------------------------------------------------===// 115193323Sed// NoAA Pass 116193323Sed//===----------------------------------------------------------------------===// 117193323Sed 118193323Sednamespace { 119193323Sed /// NoAA - This class implements the -no-aa pass, which always returns "I 120193323Sed /// don't know" for alias queries. NoAA is unlike other alias analysis 121193323Sed /// implementations, in that it does not chain to a previous analysis. As 122193323Sed /// such it doesn't follow many of the rules that other alias analyses must. 123193323Sed /// 124198892Srdivacky struct NoAA : public ImmutablePass, public AliasAnalysis { 125193323Sed static char ID; // Class identification, replacement for typeinfo 126193323Sed NoAA() : ImmutablePass(&ID) {} 127193323Sed explicit NoAA(void *PID) : ImmutablePass(PID) { } 128193323Sed 129193323Sed virtual void getAnalysisUsage(AnalysisUsage &AU) const { 130193323Sed } 131193323Sed 132193323Sed virtual void initializePass() { 133198090Srdivacky TD = getAnalysisIfAvailable<TargetData>(); 134193323Sed } 135193323Sed 136193323Sed virtual AliasResult alias(const Value *V1, unsigned V1Size, 137193323Sed const Value *V2, unsigned V2Size) { 138193323Sed return MayAlias; 139193323Sed } 140193323Sed 141193323Sed virtual void getArgumentAccesses(Function *F, CallSite CS, 142193323Sed std::vector<PointerAccessInfo> &Info) { 143198090Srdivacky llvm_unreachable("This method may not be called on this function!"); 144193323Sed } 145193323Sed 146193323Sed virtual bool pointsToConstantMemory(const Value *P) { return false; } 147193323Sed virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) { 148193323Sed return ModRef; 149193323Sed } 150193323Sed virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { 151193323Sed return ModRef; 152193323Sed } 153193323Sed 154193323Sed virtual void deleteValue(Value *V) {} 155193323Sed virtual void copyValue(Value *From, Value *To) {} 156202878Srdivacky 157202878Srdivacky /// getAdjustedAnalysisPointer - This method is used when a pass implements 158202878Srdivacky /// an analysis interface through multiple inheritance. If needed, it should 159202878Srdivacky /// override this to adjust the this pointer as needed for the specified pass 160202878Srdivacky /// info. 161202878Srdivacky virtual void *getAdjustedAnalysisPointer(const PassInfo *PI) { 162202878Srdivacky if (PI->isPassID(&AliasAnalysis::ID)) 163202878Srdivacky return (AliasAnalysis*)this; 164202878Srdivacky return this; 165202878Srdivacky } 166193323Sed }; 167193323Sed} // End of anonymous namespace 168193323Sed 169193323Sed// Register this pass... 170193323Sedchar NoAA::ID = 0; 171193323Sedstatic RegisterPass<NoAA> 172193323SedU("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true); 173193323Sed 174193323Sed// Declare that we implement the AliasAnalysis interface 175193323Sedstatic RegisterAnalysisGroup<AliasAnalysis> V(U); 176193323Sed 177193323SedImmutablePass *llvm::createNoAAPass() { return new NoAA(); } 178193323Sed 179193323Sed//===----------------------------------------------------------------------===// 180193323Sed// BasicAA Pass 181193323Sed//===----------------------------------------------------------------------===// 182193323Sed 183193323Sednamespace { 184193323Sed /// BasicAliasAnalysis - This is the default alias analysis implementation. 185193323Sed /// Because it doesn't chain to a previous alias analysis (like -no-aa), it 186193323Sed /// derives from the NoAA class. 187198892Srdivacky struct BasicAliasAnalysis : public NoAA { 188193323Sed static char ID; // Class identification, replacement for typeinfo 189193323Sed BasicAliasAnalysis() : NoAA(&ID) {} 190193323Sed AliasResult alias(const Value *V1, unsigned V1Size, 191198090Srdivacky const Value *V2, unsigned V2Size) { 192198090Srdivacky assert(VisitedPHIs.empty() && "VisitedPHIs must be cleared after use!"); 193198090Srdivacky AliasResult Alias = aliasCheck(V1, V1Size, V2, V2Size); 194198090Srdivacky VisitedPHIs.clear(); 195198090Srdivacky return Alias; 196198090Srdivacky } 197193323Sed 198193323Sed ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 199193323Sed ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 200193323Sed 201193323Sed /// pointsToConstantMemory - Chase pointers until we find a (constant 202193323Sed /// global) or not. 203193323Sed bool pointsToConstantMemory(const Value *P); 204193323Sed 205202878Srdivacky /// getAdjustedAnalysisPointer - This method is used when a pass implements 206202878Srdivacky /// an analysis interface through multiple inheritance. If needed, it should 207202878Srdivacky /// override this to adjust the this pointer as needed for the specified pass 208202878Srdivacky /// info. 209202878Srdivacky virtual void *getAdjustedAnalysisPointer(const PassInfo *PI) { 210202878Srdivacky if (PI->isPassID(&AliasAnalysis::ID)) 211202878Srdivacky return (AliasAnalysis*)this; 212202878Srdivacky return this; 213202878Srdivacky } 214202878Srdivacky 215193323Sed private: 216198090Srdivacky // VisitedPHIs - Track PHI nodes visited by a aliasCheck() call. 217198892Srdivacky SmallPtrSet<const Value*, 16> VisitedPHIs; 218198090Srdivacky 219199989Srdivacky // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP 220199989Srdivacky // instruction against another. 221199989Srdivacky AliasResult aliasGEP(const GEPOperator *V1, unsigned V1Size, 222199989Srdivacky const Value *V2, unsigned V2Size, 223199989Srdivacky const Value *UnderlyingV1, const Value *UnderlyingV2); 224198090Srdivacky 225199989Srdivacky // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI 226199989Srdivacky // instruction against another. 227198090Srdivacky AliasResult aliasPHI(const PHINode *PN, unsigned PNSize, 228198090Srdivacky const Value *V2, unsigned V2Size); 229198090Srdivacky 230198892Srdivacky /// aliasSelect - Disambiguate a Select instruction against another value. 231198892Srdivacky AliasResult aliasSelect(const SelectInst *SI, unsigned SISize, 232198892Srdivacky const Value *V2, unsigned V2Size); 233198892Srdivacky 234198090Srdivacky AliasResult aliasCheck(const Value *V1, unsigned V1Size, 235198090Srdivacky const Value *V2, unsigned V2Size); 236193323Sed }; 237193323Sed} // End of anonymous namespace 238193323Sed 239193323Sed// Register this pass... 240193323Sedchar BasicAliasAnalysis::ID = 0; 241193323Sedstatic RegisterPass<BasicAliasAnalysis> 242193323SedX("basicaa", "Basic Alias Analysis (default AA impl)", false, true); 243193323Sed 244193323Sed// Declare that we implement the AliasAnalysis interface 245193323Sedstatic RegisterAnalysisGroup<AliasAnalysis, true> Y(X); 246193323Sed 247193323SedImmutablePass *llvm::createBasicAliasAnalysisPass() { 248193323Sed return new BasicAliasAnalysis(); 249193323Sed} 250193323Sed 251193323Sed 252193323Sed/// pointsToConstantMemory - Chase pointers until we find a (constant 253193323Sed/// global) or not. 254193323Sedbool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) { 255193323Sed if (const GlobalVariable *GV = 256193323Sed dyn_cast<GlobalVariable>(P->getUnderlyingObject())) 257199989Srdivacky // Note: this doesn't require GV to be "ODR" because it isn't legal for a 258199989Srdivacky // global to be marked constant in some modules and non-constant in others. 259199989Srdivacky // GV may even be a declaration, not a definition. 260193323Sed return GV->isConstant(); 261193323Sed return false; 262193323Sed} 263193323Sed 264193323Sed 265199989Srdivacky/// getModRefInfo - Check to see if the specified callsite can clobber the 266199989Srdivacky/// specified memory object. Since we only look at local properties of this 267199989Srdivacky/// function, we really can't say much about this query. We do, however, use 268199989Srdivacky/// simple "address taken" analysis on local objects. 269193323SedAliasAnalysis::ModRefResult 270193323SedBasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { 271199989Srdivacky const Value *Object = P->getUnderlyingObject(); 272199989Srdivacky 273199989Srdivacky // If this is a tail call and P points to a stack location, we know that 274199989Srdivacky // the tail call cannot access or modify the local stack. 275199989Srdivacky // We cannot exclude byval arguments here; these belong to the caller of 276199989Srdivacky // the current function not to the current function, and a tail callee 277199989Srdivacky // may reference them. 278199989Srdivacky if (isa<AllocaInst>(Object)) 279199989Srdivacky if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction())) 280199989Srdivacky if (CI->isTailCall()) 281199989Srdivacky return NoModRef; 282199989Srdivacky 283199989Srdivacky // If the pointer is to a locally allocated object that does not escape, 284199989Srdivacky // then the call can not mod/ref the pointer unless the call takes the pointer 285199989Srdivacky // as an argument, and itself doesn't capture it. 286199989Srdivacky if (!isa<Constant>(Object) && CS.getInstruction() != Object && 287199989Srdivacky isNonEscapingLocalObject(Object)) { 288199989Srdivacky bool PassedAsArg = false; 289199989Srdivacky unsigned ArgNo = 0; 290199989Srdivacky for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end(); 291199989Srdivacky CI != CE; ++CI, ++ArgNo) { 292199989Srdivacky // Only look at the no-capture pointer arguments. 293204642Srdivacky if (!(*CI)->getType()->isPointerTy() || 294199989Srdivacky !CS.paramHasAttr(ArgNo+1, Attribute::NoCapture)) 295199989Srdivacky continue; 296193323Sed 297199989Srdivacky // If this is a no-capture pointer argument, see if we can tell that it 298199989Srdivacky // is impossible to alias the pointer we're checking. If not, we have to 299199989Srdivacky // assume that the call could touch the pointer, even though it doesn't 300199989Srdivacky // escape. 301199989Srdivacky if (!isNoAlias(cast<Value>(CI), ~0U, P, ~0U)) { 302199989Srdivacky PassedAsArg = true; 303198113Srdivacky break; 304198090Srdivacky } 305198090Srdivacky } 306199989Srdivacky 307199989Srdivacky if (!PassedAsArg) 308199989Srdivacky return NoModRef; 309193323Sed } 310193323Sed 311199989Srdivacky // Finally, handle specific knowledge of intrinsics. 312199989Srdivacky IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction()); 313199989Srdivacky if (II == 0) 314199989Srdivacky return AliasAnalysis::getModRefInfo(CS, P, Size); 315199989Srdivacky 316199989Srdivacky switch (II->getIntrinsicID()) { 317199989Srdivacky default: break; 318199989Srdivacky case Intrinsic::memcpy: 319199989Srdivacky case Intrinsic::memmove: { 320199989Srdivacky unsigned Len = ~0U; 321199989Srdivacky if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getOperand(3))) 322199989Srdivacky Len = LenCI->getZExtValue(); 323199989Srdivacky Value *Dest = II->getOperand(1); 324199989Srdivacky Value *Src = II->getOperand(2); 325199989Srdivacky if (isNoAlias(Dest, Len, P, Size)) { 326199989Srdivacky if (isNoAlias(Src, Len, P, Size)) 327199989Srdivacky return NoModRef; 328199989Srdivacky return Ref; 329199989Srdivacky } 330199989Srdivacky break; 331199989Srdivacky } 332199989Srdivacky case Intrinsic::memset: 333199989Srdivacky // Since memset is 'accesses arguments' only, the AliasAnalysis base class 334199989Srdivacky // will handle it for the variable length case. 335199989Srdivacky if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getOperand(3))) { 336199989Srdivacky unsigned Len = LenCI->getZExtValue(); 337199989Srdivacky Value *Dest = II->getOperand(1); 338199989Srdivacky if (isNoAlias(Dest, Len, P, Size)) 339199989Srdivacky return NoModRef; 340199989Srdivacky } 341199989Srdivacky break; 342199989Srdivacky case Intrinsic::atomic_cmp_swap: 343199989Srdivacky case Intrinsic::atomic_swap: 344199989Srdivacky case Intrinsic::atomic_load_add: 345199989Srdivacky case Intrinsic::atomic_load_sub: 346199989Srdivacky case Intrinsic::atomic_load_and: 347199989Srdivacky case Intrinsic::atomic_load_nand: 348199989Srdivacky case Intrinsic::atomic_load_or: 349199989Srdivacky case Intrinsic::atomic_load_xor: 350199989Srdivacky case Intrinsic::atomic_load_max: 351199989Srdivacky case Intrinsic::atomic_load_min: 352199989Srdivacky case Intrinsic::atomic_load_umax: 353199989Srdivacky case Intrinsic::atomic_load_umin: 354199989Srdivacky if (TD) { 355199989Srdivacky Value *Op1 = II->getOperand(1); 356199989Srdivacky unsigned Op1Size = TD->getTypeStoreSize(Op1->getType()); 357199989Srdivacky if (isNoAlias(Op1, Op1Size, P, Size)) 358199989Srdivacky return NoModRef; 359199989Srdivacky } 360199989Srdivacky break; 361199989Srdivacky case Intrinsic::lifetime_start: 362199989Srdivacky case Intrinsic::lifetime_end: 363199989Srdivacky case Intrinsic::invariant_start: { 364199989Srdivacky unsigned PtrSize = cast<ConstantInt>(II->getOperand(1))->getZExtValue(); 365199989Srdivacky if (isNoAlias(II->getOperand(2), PtrSize, P, Size)) 366199989Srdivacky return NoModRef; 367199989Srdivacky break; 368199989Srdivacky } 369199989Srdivacky case Intrinsic::invariant_end: { 370199989Srdivacky unsigned PtrSize = cast<ConstantInt>(II->getOperand(2))->getZExtValue(); 371199989Srdivacky if (isNoAlias(II->getOperand(3), PtrSize, P, Size)) 372199989Srdivacky return NoModRef; 373199989Srdivacky break; 374199989Srdivacky } 375199989Srdivacky } 376199989Srdivacky 377193323Sed // The AliasAnalysis base class has some smarts, lets use them. 378193323Sed return AliasAnalysis::getModRefInfo(CS, P, Size); 379193323Sed} 380193323Sed 381193323Sed 382193323SedAliasAnalysis::ModRefResult 383193323SedBasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) { 384193323Sed // If CS1 or CS2 are readnone, they don't interact. 385193323Sed ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1); 386193323Sed if (CS1B == DoesNotAccessMemory) return NoModRef; 387193323Sed 388193323Sed ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2); 389193323Sed if (CS2B == DoesNotAccessMemory) return NoModRef; 390193323Sed 391193323Sed // If they both only read from memory, just return ref. 392193323Sed if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory) 393193323Sed return Ref; 394193323Sed 395193323Sed // Otherwise, fall back to NoAA (mod+ref). 396193323Sed return NoAA::getModRefInfo(CS1, CS2); 397193323Sed} 398193323Sed 399199989Srdivacky/// GetIndiceDifference - Dest and Src are the variable indices from two 400199989Srdivacky/// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base 401199989Srdivacky/// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic 402199989Srdivacky/// difference between the two pointers. 403199989Srdivackystatic void GetIndiceDifference( 404199989Srdivacky SmallVectorImpl<std::pair<const Value*, int64_t> > &Dest, 405199989Srdivacky const SmallVectorImpl<std::pair<const Value*, int64_t> > &Src) { 406199989Srdivacky if (Src.empty()) return; 407199989Srdivacky 408199989Srdivacky for (unsigned i = 0, e = Src.size(); i != e; ++i) { 409199989Srdivacky const Value *V = Src[i].first; 410199989Srdivacky int64_t Scale = Src[i].second; 411199989Srdivacky 412199989Srdivacky // Find V in Dest. This is N^2, but pointer indices almost never have more 413199989Srdivacky // than a few variable indexes. 414199989Srdivacky for (unsigned j = 0, e = Dest.size(); j != e; ++j) { 415199989Srdivacky if (Dest[j].first != V) continue; 416199989Srdivacky 417199989Srdivacky // If we found it, subtract off Scale V's from the entry in Dest. If it 418199989Srdivacky // goes to zero, remove the entry. 419199989Srdivacky if (Dest[j].second != Scale) 420199989Srdivacky Dest[j].second -= Scale; 421199989Srdivacky else 422199989Srdivacky Dest.erase(Dest.begin()+j); 423199989Srdivacky Scale = 0; 424199989Srdivacky break; 425199989Srdivacky } 426199989Srdivacky 427199989Srdivacky // If we didn't consume this entry, add it to the end of the Dest list. 428199989Srdivacky if (Scale) 429199989Srdivacky Dest.push_back(std::make_pair(V, -Scale)); 430199989Srdivacky } 431199989Srdivacky} 432199989Srdivacky 433199989Srdivacky/// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction 434199989Srdivacky/// against another pointer. We know that V1 is a GEP, but we don't know 435199989Srdivacky/// anything about V2. UnderlyingV1 is GEP1->getUnderlyingObject(), 436199989Srdivacky/// UnderlyingV2 is the same for V2. 437199989Srdivacky/// 438193323SedAliasAnalysis::AliasResult 439199989SrdivackyBasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size, 440199989Srdivacky const Value *V2, unsigned V2Size, 441199989Srdivacky const Value *UnderlyingV1, 442199989Srdivacky const Value *UnderlyingV2) { 443199989Srdivacky int64_t GEP1BaseOffset; 444199989Srdivacky SmallVector<std::pair<const Value*, int64_t>, 4> GEP1VariableIndices; 445199989Srdivacky 446193323Sed // If we have two gep instructions with must-alias'ing base pointers, figure 447193323Sed // out if the indexes to the GEP tell us anything about the derived pointer. 448199989Srdivacky if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) { 449199989Srdivacky // Do the base pointers alias? 450199989Srdivacky AliasResult BaseAlias = aliasCheck(UnderlyingV1, ~0U, UnderlyingV2, ~0U); 451193323Sed 452199989Srdivacky // If we get a No or May, then return it immediately, no amount of analysis 453199989Srdivacky // will improve this situation. 454199989Srdivacky if (BaseAlias != MustAlias) return BaseAlias; 455193323Sed 456199989Srdivacky // Otherwise, we have a MustAlias. Since the base pointers alias each other 457199989Srdivacky // exactly, see if the computed offset from the common pointer tells us 458199989Srdivacky // about the relation of the resulting pointer. 459199989Srdivacky const Value *GEP1BasePtr = 460199989Srdivacky DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); 461199989Srdivacky 462199989Srdivacky int64_t GEP2BaseOffset; 463199989Srdivacky SmallVector<std::pair<const Value*, int64_t>, 4> GEP2VariableIndices; 464199989Srdivacky const Value *GEP2BasePtr = 465199989Srdivacky DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD); 466199989Srdivacky 467199989Srdivacky // If DecomposeGEPExpression isn't able to look all the way through the 468199989Srdivacky // addressing operation, we must not have TD and this is too complex for us 469199989Srdivacky // to handle without it. 470199989Srdivacky if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { 471199989Srdivacky assert(TD == 0 && 472199989Srdivacky "DecomposeGEPExpression and getUnderlyingObject disagree!"); 473199989Srdivacky return MayAlias; 474199989Srdivacky } 475199989Srdivacky 476199989Srdivacky // Subtract the GEP2 pointer from the GEP1 pointer to find out their 477199989Srdivacky // symbolic difference. 478199989Srdivacky GEP1BaseOffset -= GEP2BaseOffset; 479199989Srdivacky GetIndiceDifference(GEP1VariableIndices, GEP2VariableIndices); 480199989Srdivacky 481199989Srdivacky } else { 482199989Srdivacky // Check to see if these two pointers are related by the getelementptr 483199989Srdivacky // instruction. If one pointer is a GEP with a non-zero index of the other 484199989Srdivacky // pointer, we know they cannot alias. 485193323Sed 486199989Srdivacky // If both accesses are unknown size, we can't do anything useful here. 487199989Srdivacky if (V1Size == ~0U && V2Size == ~0U) 488199989Srdivacky return MayAlias; 489193323Sed 490199989Srdivacky AliasResult R = aliasCheck(UnderlyingV1, ~0U, V2, V2Size); 491199989Srdivacky if (R != MustAlias) 492199989Srdivacky // If V2 may alias GEP base pointer, conservatively returns MayAlias. 493199989Srdivacky // If V2 is known not to alias GEP base pointer, then the two values 494199989Srdivacky // cannot alias per GEP semantics: "A pointer value formed from a 495199989Srdivacky // getelementptr instruction is associated with the addresses associated 496199989Srdivacky // with the first operand of the getelementptr". 497199989Srdivacky return R; 498193323Sed 499199989Srdivacky const Value *GEP1BasePtr = 500199989Srdivacky DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); 501199989Srdivacky 502199989Srdivacky // If DecomposeGEPExpression isn't able to look all the way through the 503199989Srdivacky // addressing operation, we must not have TD and this is too complex for us 504199989Srdivacky // to handle without it. 505199989Srdivacky if (GEP1BasePtr != UnderlyingV1) { 506199989Srdivacky assert(TD == 0 && 507199989Srdivacky "DecomposeGEPExpression and getUnderlyingObject disagree!"); 508199989Srdivacky return MayAlias; 509193323Sed } 510193323Sed } 511199989Srdivacky 512199989Srdivacky // In the two GEP Case, if there is no difference in the offsets of the 513199989Srdivacky // computed pointers, the resultant pointers are a must alias. This 514199989Srdivacky // hapens when we have two lexically identical GEP's (for example). 515193323Sed // 516199989Srdivacky // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 517199989Srdivacky // must aliases the GEP, the end result is a must alias also. 518199989Srdivacky if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty()) 519198090Srdivacky return MustAlias; 520193323Sed 521199989Srdivacky // If we have a known constant offset, see if this offset is larger than the 522199989Srdivacky // access size being queried. If so, and if no variable indices can remove 523199989Srdivacky // pieces of this constant, then we know we have a no-alias. For example, 524199989Srdivacky // &A[100] != &A. 525199989Srdivacky 526199989Srdivacky // In order to handle cases like &A[100][i] where i is an out of range 527199989Srdivacky // subscript, we have to ignore all constant offset pieces that are a multiple 528199989Srdivacky // of a scaled index. Do this by removing constant offsets that are a 529199989Srdivacky // multiple of any of our variable indices. This allows us to transform 530199989Srdivacky // things like &A[i][1] because i has a stride of (e.g.) 8 bytes but the 1 531199989Srdivacky // provides an offset of 4 bytes (assuming a <= 4 byte access). 532199989Srdivacky for (unsigned i = 0, e = GEP1VariableIndices.size(); 533199989Srdivacky i != e && GEP1BaseOffset;++i) 534199989Srdivacky if (int64_t RemovedOffset = GEP1BaseOffset/GEP1VariableIndices[i].second) 535199989Srdivacky GEP1BaseOffset -= RemovedOffset*GEP1VariableIndices[i].second; 536199989Srdivacky 537199989Srdivacky // If our known offset is bigger than the access size, we know we don't have 538199989Srdivacky // an alias. 539199989Srdivacky if (GEP1BaseOffset) { 540199989Srdivacky if (GEP1BaseOffset >= (int64_t)V2Size || 541199989Srdivacky GEP1BaseOffset <= -(int64_t)V1Size) 542198090Srdivacky return NoAlias; 543198090Srdivacky } 544199989Srdivacky 545193323Sed return MayAlias; 546193323Sed} 547193323Sed 548199989Srdivacky/// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select 549199989Srdivacky/// instruction against another. 550198892SrdivackyAliasAnalysis::AliasResult 551198892SrdivackyBasicAliasAnalysis::aliasSelect(const SelectInst *SI, unsigned SISize, 552198892Srdivacky const Value *V2, unsigned V2Size) { 553198892Srdivacky // If the values are Selects with the same condition, we can do a more precise 554198892Srdivacky // check: just check for aliases between the values on corresponding arms. 555198892Srdivacky if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2)) 556198892Srdivacky if (SI->getCondition() == SI2->getCondition()) { 557198892Srdivacky AliasResult Alias = 558198892Srdivacky aliasCheck(SI->getTrueValue(), SISize, 559198892Srdivacky SI2->getTrueValue(), V2Size); 560198892Srdivacky if (Alias == MayAlias) 561198892Srdivacky return MayAlias; 562198892Srdivacky AliasResult ThisAlias = 563198892Srdivacky aliasCheck(SI->getFalseValue(), SISize, 564198892Srdivacky SI2->getFalseValue(), V2Size); 565198892Srdivacky if (ThisAlias != Alias) 566198892Srdivacky return MayAlias; 567198892Srdivacky return Alias; 568198892Srdivacky } 569198892Srdivacky 570198892Srdivacky // If both arms of the Select node NoAlias or MustAlias V2, then returns 571198892Srdivacky // NoAlias / MustAlias. Otherwise, returns MayAlias. 572198892Srdivacky AliasResult Alias = 573198892Srdivacky aliasCheck(SI->getTrueValue(), SISize, V2, V2Size); 574198892Srdivacky if (Alias == MayAlias) 575198892Srdivacky return MayAlias; 576198892Srdivacky AliasResult ThisAlias = 577198892Srdivacky aliasCheck(SI->getFalseValue(), SISize, V2, V2Size); 578198892Srdivacky if (ThisAlias != Alias) 579198892Srdivacky return MayAlias; 580198892Srdivacky return Alias; 581198892Srdivacky} 582198892Srdivacky 583198090Srdivacky// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction 584198090Srdivacky// against another. 585198090SrdivackyAliasAnalysis::AliasResult 586198090SrdivackyBasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize, 587198090Srdivacky const Value *V2, unsigned V2Size) { 588198090Srdivacky // The PHI node has already been visited, avoid recursion any further. 589198090Srdivacky if (!VisitedPHIs.insert(PN)) 590198090Srdivacky return MayAlias; 591198090Srdivacky 592198892Srdivacky // If the values are PHIs in the same block, we can do a more precise 593198892Srdivacky // as well as efficient check: just check for aliases between the values 594198892Srdivacky // on corresponding edges. 595198892Srdivacky if (const PHINode *PN2 = dyn_cast<PHINode>(V2)) 596198892Srdivacky if (PN2->getParent() == PN->getParent()) { 597198892Srdivacky AliasResult Alias = 598198892Srdivacky aliasCheck(PN->getIncomingValue(0), PNSize, 599198892Srdivacky PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)), 600198892Srdivacky V2Size); 601198892Srdivacky if (Alias == MayAlias) 602198892Srdivacky return MayAlias; 603198892Srdivacky for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) { 604198892Srdivacky AliasResult ThisAlias = 605198892Srdivacky aliasCheck(PN->getIncomingValue(i), PNSize, 606198892Srdivacky PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), 607198892Srdivacky V2Size); 608198892Srdivacky if (ThisAlias != Alias) 609198892Srdivacky return MayAlias; 610198892Srdivacky } 611198892Srdivacky return Alias; 612198892Srdivacky } 613198892Srdivacky 614198396Srdivacky SmallPtrSet<Value*, 4> UniqueSrc; 615198090Srdivacky SmallVector<Value*, 4> V1Srcs; 616198090Srdivacky for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 617198090Srdivacky Value *PV1 = PN->getIncomingValue(i); 618198090Srdivacky if (isa<PHINode>(PV1)) 619198090Srdivacky // If any of the source itself is a PHI, return MayAlias conservatively 620198090Srdivacky // to avoid compile time explosion. The worst possible case is if both 621198090Srdivacky // sides are PHI nodes. In which case, this is O(m x n) time where 'm' 622198090Srdivacky // and 'n' are the number of PHI sources. 623198090Srdivacky return MayAlias; 624198090Srdivacky if (UniqueSrc.insert(PV1)) 625198090Srdivacky V1Srcs.push_back(PV1); 626198090Srdivacky } 627198090Srdivacky 628198892Srdivacky AliasResult Alias = aliasCheck(V2, V2Size, V1Srcs[0], PNSize); 629198090Srdivacky // Early exit if the check of the first PHI source against V2 is MayAlias. 630198090Srdivacky // Other results are not possible. 631198090Srdivacky if (Alias == MayAlias) 632198090Srdivacky return MayAlias; 633198090Srdivacky 634198090Srdivacky // If all sources of the PHI node NoAlias or MustAlias V2, then returns 635198090Srdivacky // NoAlias / MustAlias. Otherwise, returns MayAlias. 636198090Srdivacky for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) { 637198090Srdivacky Value *V = V1Srcs[i]; 638198892Srdivacky 639198892Srdivacky // If V2 is a PHI, the recursive case will have been caught in the 640198892Srdivacky // above aliasCheck call, so these subsequent calls to aliasCheck 641198892Srdivacky // don't need to assume that V2 is being visited recursively. 642198892Srdivacky VisitedPHIs.erase(V2); 643198892Srdivacky 644198396Srdivacky AliasResult ThisAlias = aliasCheck(V2, V2Size, V, PNSize); 645198090Srdivacky if (ThisAlias != Alias || ThisAlias == MayAlias) 646198090Srdivacky return MayAlias; 647198090Srdivacky } 648198090Srdivacky 649198090Srdivacky return Alias; 650198090Srdivacky} 651198090Srdivacky 652198090Srdivacky// aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases, 653198090Srdivacky// such as array references. 654198090Srdivacky// 655198090SrdivackyAliasAnalysis::AliasResult 656198090SrdivackyBasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size, 657198090Srdivacky const Value *V2, unsigned V2Size) { 658207618Srdivacky // If either of the memory references is empty, it doesn't matter what the 659207618Srdivacky // pointer values are. 660207618Srdivacky if (V1Size == 0 || V2Size == 0) 661207618Srdivacky return NoAlias; 662207618Srdivacky 663198090Srdivacky // Strip off any casts if they exist. 664198090Srdivacky V1 = V1->stripPointerCasts(); 665198090Srdivacky V2 = V2->stripPointerCasts(); 666198090Srdivacky 667198090Srdivacky // Are we checking for alias of the same value? 668198090Srdivacky if (V1 == V2) return MustAlias; 669198090Srdivacky 670204642Srdivacky if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy()) 671198090Srdivacky return NoAlias; // Scalars cannot alias each other 672198090Srdivacky 673198090Srdivacky // Figure out what objects these things are pointing to if we can. 674198090Srdivacky const Value *O1 = V1->getUnderlyingObject(); 675198090Srdivacky const Value *O2 = V2->getUnderlyingObject(); 676198090Srdivacky 677199481Srdivacky // Null values in the default address space don't point to any object, so they 678199481Srdivacky // don't alias any other pointer. 679199481Srdivacky if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1)) 680199481Srdivacky if (CPN->getType()->getAddressSpace() == 0) 681199481Srdivacky return NoAlias; 682199481Srdivacky if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2)) 683199481Srdivacky if (CPN->getType()->getAddressSpace() == 0) 684199481Srdivacky return NoAlias; 685199481Srdivacky 686198090Srdivacky if (O1 != O2) { 687198090Srdivacky // If V1/V2 point to two different objects we know that we have no alias. 688198090Srdivacky if (isIdentifiedObject(O1) && isIdentifiedObject(O2)) 689198090Srdivacky return NoAlias; 690199481Srdivacky 691199481Srdivacky // Constant pointers can't alias with non-const isIdentifiedObject objects. 692199481Srdivacky if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) || 693199481Srdivacky (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1))) 694199481Srdivacky return NoAlias; 695199481Srdivacky 696198090Srdivacky // Arguments can't alias with local allocations or noalias calls. 697198892Srdivacky if ((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) || 698198892Srdivacky (isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1)))) 699198090Srdivacky return NoAlias; 700198090Srdivacky 701198090Srdivacky // Most objects can't alias null. 702198090Srdivacky if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) || 703198090Srdivacky (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2))) 704198090Srdivacky return NoAlias; 705198090Srdivacky } 706198090Srdivacky 707198090Srdivacky // If the size of one access is larger than the entire object on the other 708198090Srdivacky // side, then we know such behavior is undefined and can assume no alias. 709198090Srdivacky if (TD) 710199481Srdivacky if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, *TD)) || 711199481Srdivacky (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, *TD))) 712198090Srdivacky return NoAlias; 713198090Srdivacky 714199989Srdivacky // If one pointer is the result of a call/invoke or load and the other is a 715198090Srdivacky // non-escaping local object, then we know the object couldn't escape to a 716199989Srdivacky // point where the call could return it. The load case works because 717199989Srdivacky // isNonEscapingLocalObject considers all stores to be escapes (it 718199989Srdivacky // passes true for the StoreCaptures argument to PointerMayBeCaptured). 719199989Srdivacky if (O1 != O2) { 720199989Srdivacky if ((isa<CallInst>(O1) || isa<InvokeInst>(O1) || isa<LoadInst>(O1) || 721199989Srdivacky isa<Argument>(O1)) && 722199989Srdivacky isNonEscapingLocalObject(O2)) 723199989Srdivacky return NoAlias; 724199989Srdivacky if ((isa<CallInst>(O2) || isa<InvokeInst>(O2) || isa<LoadInst>(O2) || 725199989Srdivacky isa<Argument>(O2)) && 726199989Srdivacky isNonEscapingLocalObject(O1)) 727199989Srdivacky return NoAlias; 728199989Srdivacky } 729198090Srdivacky 730199989Srdivacky // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the 731199989Srdivacky // GEP can't simplify, we don't even look at the PHI cases. 732198396Srdivacky if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) { 733198090Srdivacky std::swap(V1, V2); 734198090Srdivacky std::swap(V1Size, V2Size); 735199989Srdivacky std::swap(O1, O2); 736198090Srdivacky } 737199989Srdivacky if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) 738199989Srdivacky return aliasGEP(GV1, V1Size, V2, V2Size, O1, O2); 739198090Srdivacky 740198090Srdivacky if (isa<PHINode>(V2) && !isa<PHINode>(V1)) { 741198090Srdivacky std::swap(V1, V2); 742198090Srdivacky std::swap(V1Size, V2Size); 743198090Srdivacky } 744198090Srdivacky if (const PHINode *PN = dyn_cast<PHINode>(V1)) 745198090Srdivacky return aliasPHI(PN, V1Size, V2, V2Size); 746198090Srdivacky 747198892Srdivacky if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) { 748198892Srdivacky std::swap(V1, V2); 749198892Srdivacky std::swap(V1Size, V2Size); 750198892Srdivacky } 751198892Srdivacky if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) 752198892Srdivacky return aliasSelect(S1, V1Size, V2, V2Size); 753198892Srdivacky 754198090Srdivacky return MayAlias; 755198090Srdivacky} 756198090Srdivacky 757199989Srdivacky// Make sure that anything that uses AliasAnalysis pulls in this file. 758193323SedDEFINING_FILE_FOR(BasicAliasAnalysis) 759