BasicAliasAnalysis.cpp revision 198113
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/CaptureTracking.h" 18198090Srdivacky#include "llvm/Analysis/MallocHelper.h" 19193323Sed#include "llvm/Analysis/Passes.h" 20193323Sed#include "llvm/Constants.h" 21193323Sed#include "llvm/DerivedTypes.h" 22193323Sed#include "llvm/Function.h" 23193323Sed#include "llvm/GlobalVariable.h" 24193323Sed#include "llvm/Instructions.h" 25193323Sed#include "llvm/IntrinsicInst.h" 26198090Srdivacky#include "llvm/LLVMContext.h" 27198090Srdivacky#include "llvm/Operator.h" 28193323Sed#include "llvm/Pass.h" 29193323Sed#include "llvm/Target/TargetData.h" 30198090Srdivacky#include "llvm/ADT/SmallSet.h" 31193323Sed#include "llvm/ADT/SmallVector.h" 32193323Sed#include "llvm/ADT/STLExtras.h" 33193323Sed#include "llvm/Support/Compiler.h" 34198090Srdivacky#include "llvm/Support/ErrorHandling.h" 35193323Sed#include "llvm/Support/GetElementPtrTypeIterator.h" 36193323Sed#include <algorithm> 37193323Sedusing namespace llvm; 38193323Sed 39193323Sed//===----------------------------------------------------------------------===// 40193323Sed// Useful predicates 41193323Sed//===----------------------------------------------------------------------===// 42193323Sed 43198090Srdivackystatic const GEPOperator *isGEP(const Value *V) { 44198090Srdivacky return dyn_cast<GEPOperator>(V); 45193323Sed} 46193323Sed 47193323Sedstatic const Value *GetGEPOperands(const Value *V, 48193323Sed SmallVector<Value*, 16> &GEPOps) { 49193323Sed assert(GEPOps.empty() && "Expect empty list to populate!"); 50193323Sed GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1, 51193323Sed cast<User>(V)->op_end()); 52193323Sed 53193323Sed // Accumulate all of the chained indexes into the operand array 54193323Sed V = cast<User>(V)->getOperand(0); 55193323Sed 56193323Sed while (const User *G = isGEP(V)) { 57193323Sed if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) || 58193323Sed !cast<Constant>(GEPOps[0])->isNullValue()) 59193323Sed break; // Don't handle folding arbitrary pointer offsets yet... 60193323Sed GEPOps.erase(GEPOps.begin()); // Drop the zero index 61193323Sed GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end()); 62193323Sed V = G->getOperand(0); 63193323Sed } 64193323Sed return V; 65193323Sed} 66193323Sed 67193323Sed/// isKnownNonNull - Return true if we know that the specified value is never 68193323Sed/// null. 69193323Sedstatic bool isKnownNonNull(const Value *V) { 70193323Sed // Alloca never returns null, malloc might. 71193323Sed if (isa<AllocaInst>(V)) return true; 72193323Sed 73193323Sed // A byval argument is never null. 74193323Sed if (const Argument *A = dyn_cast<Argument>(V)) 75193323Sed return A->hasByValAttr(); 76193323Sed 77193323Sed // Global values are not null unless extern weak. 78193323Sed if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) 79193323Sed return !GV->hasExternalWeakLinkage(); 80193323Sed return false; 81193323Sed} 82193323Sed 83193323Sed/// isNonEscapingLocalObject - Return true if the pointer is to a function-local 84193323Sed/// object that never escapes from the function. 85193323Sedstatic bool isNonEscapingLocalObject(const Value *V) { 86193323Sed // If this is a local allocation, check to see if it escapes. 87193323Sed if (isa<AllocationInst>(V) || isNoAliasCall(V)) 88193323Sed return !PointerMayBeCaptured(V, false); 89193323Sed 90193323Sed // If this is an argument that corresponds to a byval or noalias argument, 91193323Sed // then it has not escaped before entering the function. Check if it escapes 92193323Sed // inside the function. 93193323Sed if (const Argument *A = dyn_cast<Argument>(V)) 94193323Sed if (A->hasByValAttr() || A->hasNoAliasAttr()) { 95193323Sed // Don't bother analyzing arguments already known not to escape. 96193323Sed if (A->hasNoCaptureAttr()) 97193323Sed return true; 98193323Sed return !PointerMayBeCaptured(V, false); 99193323Sed } 100193323Sed return false; 101193323Sed} 102193323Sed 103193323Sed 104193323Sed/// isObjectSmallerThan - Return true if we can prove that the object specified 105193323Sed/// by V is smaller than Size. 106193323Sedstatic bool isObjectSmallerThan(const Value *V, unsigned Size, 107198090Srdivacky LLVMContext &Context, const TargetData &TD) { 108193323Sed const Type *AccessTy; 109193323Sed if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) { 110193323Sed AccessTy = GV->getType()->getElementType(); 111193323Sed } else if (const AllocationInst *AI = dyn_cast<AllocationInst>(V)) { 112193323Sed if (!AI->isArrayAllocation()) 113193323Sed AccessTy = AI->getType()->getElementType(); 114193323Sed else 115193323Sed return false; 116198090Srdivacky } else if (const CallInst* CI = extractMallocCall(V)) { 117198090Srdivacky if (!isArrayMalloc(V, Context, &TD)) 118198090Srdivacky // The size is the argument to the malloc call. 119198090Srdivacky if (const ConstantInt* C = dyn_cast<ConstantInt>(CI->getOperand(1))) 120198090Srdivacky return (C->getZExtValue() < Size); 121198090Srdivacky return false; 122193323Sed } else if (const Argument *A = dyn_cast<Argument>(V)) { 123193323Sed if (A->hasByValAttr()) 124193323Sed AccessTy = cast<PointerType>(A->getType())->getElementType(); 125193323Sed else 126193323Sed return false; 127193323Sed } else { 128193323Sed return false; 129193323Sed } 130193323Sed 131193323Sed if (AccessTy->isSized()) 132193323Sed return TD.getTypeAllocSize(AccessTy) < Size; 133193323Sed return false; 134193323Sed} 135193323Sed 136193323Sed//===----------------------------------------------------------------------===// 137193323Sed// NoAA Pass 138193323Sed//===----------------------------------------------------------------------===// 139193323Sed 140193323Sednamespace { 141193323Sed /// NoAA - This class implements the -no-aa pass, which always returns "I 142193323Sed /// don't know" for alias queries. NoAA is unlike other alias analysis 143193323Sed /// implementations, in that it does not chain to a previous analysis. As 144193323Sed /// such it doesn't follow many of the rules that other alias analyses must. 145193323Sed /// 146193323Sed struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis { 147193323Sed static char ID; // Class identification, replacement for typeinfo 148193323Sed NoAA() : ImmutablePass(&ID) {} 149193323Sed explicit NoAA(void *PID) : ImmutablePass(PID) { } 150193323Sed 151193323Sed virtual void getAnalysisUsage(AnalysisUsage &AU) const { 152193323Sed } 153193323Sed 154193323Sed virtual void initializePass() { 155198090Srdivacky TD = getAnalysisIfAvailable<TargetData>(); 156193323Sed } 157193323Sed 158193323Sed virtual AliasResult alias(const Value *V1, unsigned V1Size, 159193323Sed const Value *V2, unsigned V2Size) { 160193323Sed return MayAlias; 161193323Sed } 162193323Sed 163193323Sed virtual void getArgumentAccesses(Function *F, CallSite CS, 164193323Sed std::vector<PointerAccessInfo> &Info) { 165198090Srdivacky llvm_unreachable("This method may not be called on this function!"); 166193323Sed } 167193323Sed 168193323Sed virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { } 169193323Sed virtual bool pointsToConstantMemory(const Value *P) { return false; } 170193323Sed virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) { 171193323Sed return ModRef; 172193323Sed } 173193323Sed virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { 174193323Sed return ModRef; 175193323Sed } 176193323Sed virtual bool hasNoModRefInfoForCalls() const { return true; } 177193323Sed 178193323Sed virtual void deleteValue(Value *V) {} 179193323Sed virtual void copyValue(Value *From, Value *To) {} 180193323Sed }; 181193323Sed} // End of anonymous namespace 182193323Sed 183193323Sed// Register this pass... 184193323Sedchar NoAA::ID = 0; 185193323Sedstatic RegisterPass<NoAA> 186193323SedU("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true); 187193323Sed 188193323Sed// Declare that we implement the AliasAnalysis interface 189193323Sedstatic RegisterAnalysisGroup<AliasAnalysis> V(U); 190193323Sed 191193323SedImmutablePass *llvm::createNoAAPass() { return new NoAA(); } 192193323Sed 193193323Sed//===----------------------------------------------------------------------===// 194193323Sed// BasicAA Pass 195193323Sed//===----------------------------------------------------------------------===// 196193323Sed 197193323Sednamespace { 198193323Sed /// BasicAliasAnalysis - This is the default alias analysis implementation. 199193323Sed /// Because it doesn't chain to a previous alias analysis (like -no-aa), it 200193323Sed /// derives from the NoAA class. 201193323Sed struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA { 202193323Sed static char ID; // Class identification, replacement for typeinfo 203193323Sed BasicAliasAnalysis() : NoAA(&ID) {} 204193323Sed AliasResult alias(const Value *V1, unsigned V1Size, 205198090Srdivacky const Value *V2, unsigned V2Size) { 206198090Srdivacky assert(VisitedPHIs.empty() && "VisitedPHIs must be cleared after use!"); 207198090Srdivacky AliasResult Alias = aliasCheck(V1, V1Size, V2, V2Size); 208198090Srdivacky VisitedPHIs.clear(); 209198090Srdivacky return Alias; 210198090Srdivacky } 211193323Sed 212193323Sed ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 213193323Sed ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 214193323Sed 215193323Sed /// hasNoModRefInfoForCalls - We can provide mod/ref information against 216193323Sed /// non-escaping allocations. 217193323Sed virtual bool hasNoModRefInfoForCalls() const { return false; } 218193323Sed 219193323Sed /// pointsToConstantMemory - Chase pointers until we find a (constant 220193323Sed /// global) or not. 221193323Sed bool pointsToConstantMemory(const Value *P); 222193323Sed 223193323Sed private: 224198090Srdivacky // VisitedPHIs - Track PHI nodes visited by a aliasCheck() call. 225198090Srdivacky SmallSet<const PHINode*, 16> VisitedPHIs; 226198090Srdivacky 227198090Srdivacky // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction 228198090Srdivacky // against another. 229198090Srdivacky AliasResult aliasGEP(const Value *V1, unsigned V1Size, 230198090Srdivacky const Value *V2, unsigned V2Size); 231198090Srdivacky 232198090Srdivacky // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction 233198090Srdivacky // against another. 234198090Srdivacky AliasResult aliasPHI(const PHINode *PN, unsigned PNSize, 235198090Srdivacky const Value *V2, unsigned V2Size); 236198090Srdivacky 237198090Srdivacky AliasResult aliasCheck(const Value *V1, unsigned V1Size, 238198090Srdivacky const Value *V2, unsigned V2Size); 239198090Srdivacky 240193323Sed // CheckGEPInstructions - Check two GEP instructions with known 241193323Sed // must-aliasing base pointers. This checks to see if the index expressions 242193323Sed // preclude the pointers from aliasing... 243193323Sed AliasResult 244193323Sed CheckGEPInstructions(const Type* BasePtr1Ty, 245193323Sed Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size, 246193323Sed const Type *BasePtr2Ty, 247193323Sed Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size); 248193323Sed }; 249193323Sed} // End of anonymous namespace 250193323Sed 251193323Sed// Register this pass... 252193323Sedchar BasicAliasAnalysis::ID = 0; 253193323Sedstatic RegisterPass<BasicAliasAnalysis> 254193323SedX("basicaa", "Basic Alias Analysis (default AA impl)", false, true); 255193323Sed 256193323Sed// Declare that we implement the AliasAnalysis interface 257193323Sedstatic RegisterAnalysisGroup<AliasAnalysis, true> Y(X); 258193323Sed 259193323SedImmutablePass *llvm::createBasicAliasAnalysisPass() { 260193323Sed return new BasicAliasAnalysis(); 261193323Sed} 262193323Sed 263193323Sed 264193323Sed/// pointsToConstantMemory - Chase pointers until we find a (constant 265193323Sed/// global) or not. 266193323Sedbool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) { 267193323Sed if (const GlobalVariable *GV = 268193323Sed dyn_cast<GlobalVariable>(P->getUnderlyingObject())) 269193323Sed return GV->isConstant(); 270193323Sed return false; 271193323Sed} 272193323Sed 273193323Sed 274193323Sed// getModRefInfo - Check to see if the specified callsite can clobber the 275193323Sed// specified memory object. Since we only look at local properties of this 276193323Sed// function, we really can't say much about this query. We do, however, use 277193323Sed// simple "address taken" analysis on local objects. 278193323Sed// 279193323SedAliasAnalysis::ModRefResult 280193323SedBasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { 281193323Sed if (!isa<Constant>(P)) { 282193323Sed const Value *Object = P->getUnderlyingObject(); 283193323Sed 284193323Sed // If this is a tail call and P points to a stack location, we know that 285193323Sed // the tail call cannot access or modify the local stack. 286193323Sed // We cannot exclude byval arguments here; these belong to the caller of 287193323Sed // the current function not to the current function, and a tail callee 288193323Sed // may reference them. 289193323Sed if (isa<AllocaInst>(Object)) 290193323Sed if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction())) 291193323Sed if (CI->isTailCall()) 292193323Sed return NoModRef; 293193323Sed 294193323Sed // If the pointer is to a locally allocated object that does not escape, 295193323Sed // then the call can not mod/ref the pointer unless the call takes the 296193323Sed // argument without capturing it. 297193323Sed if (isNonEscapingLocalObject(Object) && CS.getInstruction() != Object) { 298193323Sed bool passedAsArg = false; 299193323Sed // TODO: Eventually only check 'nocapture' arguments. 300193323Sed for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end(); 301193323Sed CI != CE; ++CI) 302193323Sed if (isa<PointerType>((*CI)->getType()) && 303193323Sed alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias) 304193323Sed passedAsArg = true; 305193323Sed 306193323Sed if (!passedAsArg) 307193323Sed return NoModRef; 308193323Sed } 309198090Srdivacky 310198090Srdivacky if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) { 311198090Srdivacky switch (II->getIntrinsicID()) { 312198090Srdivacky default: break; 313198113Srdivacky case Intrinsic::memcpy: 314198113Srdivacky case Intrinsic::memmove: { 315198113Srdivacky unsigned Len = ~0U; 316198113Srdivacky if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getOperand(3))) 317198113Srdivacky Len = LenCI->getZExtValue(); 318198113Srdivacky Value *Dest = II->getOperand(1); 319198113Srdivacky Value *Src = II->getOperand(2); 320198113Srdivacky if (alias(Dest, Len, P, Size) == NoAlias) { 321198113Srdivacky if (alias(Src, Len, P, Size) == NoAlias) 322198113Srdivacky return NoModRef; 323198113Srdivacky return Ref; 324198113Srdivacky } 325198113Srdivacky } 326198113Srdivacky break; 327198113Srdivacky case Intrinsic::memset: 328198113Srdivacky if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getOperand(3))) { 329198113Srdivacky unsigned Len = LenCI->getZExtValue(); 330198113Srdivacky Value *Dest = II->getOperand(1); 331198113Srdivacky if (alias(Dest, Len, P, Size) == NoAlias) 332198113Srdivacky return NoModRef; 333198113Srdivacky } 334198113Srdivacky break; 335198090Srdivacky case Intrinsic::atomic_cmp_swap: 336198090Srdivacky case Intrinsic::atomic_swap: 337198090Srdivacky case Intrinsic::atomic_load_add: 338198090Srdivacky case Intrinsic::atomic_load_sub: 339198090Srdivacky case Intrinsic::atomic_load_and: 340198090Srdivacky case Intrinsic::atomic_load_nand: 341198090Srdivacky case Intrinsic::atomic_load_or: 342198090Srdivacky case Intrinsic::atomic_load_xor: 343198090Srdivacky case Intrinsic::atomic_load_max: 344198090Srdivacky case Intrinsic::atomic_load_min: 345198090Srdivacky case Intrinsic::atomic_load_umax: 346198090Srdivacky case Intrinsic::atomic_load_umin: 347198113Srdivacky if (TD) { 348198113Srdivacky Value *Op1 = II->getOperand(1); 349198113Srdivacky unsigned Op1Size = TD->getTypeStoreSize(Op1->getType()); 350198113Srdivacky if (alias(Op1, Op1Size, P, Size) == NoAlias) 351198113Srdivacky return NoModRef; 352198113Srdivacky } 353198113Srdivacky break; 354198113Srdivacky case Intrinsic::lifetime_start: 355198113Srdivacky case Intrinsic::lifetime_end: 356198113Srdivacky case Intrinsic::invariant_start: { 357198113Srdivacky unsigned PtrSize = cast<ConstantInt>(II->getOperand(1))->getZExtValue(); 358198113Srdivacky if (alias(II->getOperand(2), PtrSize, P, Size) == NoAlias) 359198090Srdivacky return NoModRef; 360198090Srdivacky } 361198113Srdivacky case Intrinsic::invariant_end: { 362198113Srdivacky unsigned PtrSize = cast<ConstantInt>(II->getOperand(2))->getZExtValue(); 363198113Srdivacky if (alias(II->getOperand(3), PtrSize, P, Size) == NoAlias) 364198113Srdivacky return NoModRef; 365198113Srdivacky } 366198113Srdivacky } 367198090Srdivacky } 368193323Sed } 369193323Sed 370193323Sed // The AliasAnalysis base class has some smarts, lets use them. 371193323Sed return AliasAnalysis::getModRefInfo(CS, P, Size); 372193323Sed} 373193323Sed 374193323Sed 375193323SedAliasAnalysis::ModRefResult 376193323SedBasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) { 377193323Sed // If CS1 or CS2 are readnone, they don't interact. 378193323Sed ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1); 379193323Sed if (CS1B == DoesNotAccessMemory) return NoModRef; 380193323Sed 381193323Sed ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2); 382193323Sed if (CS2B == DoesNotAccessMemory) return NoModRef; 383193323Sed 384193323Sed // If they both only read from memory, just return ref. 385193323Sed if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory) 386193323Sed return Ref; 387193323Sed 388193323Sed // Otherwise, fall back to NoAA (mod+ref). 389193323Sed return NoAA::getModRefInfo(CS1, CS2); 390193323Sed} 391193323Sed 392198090Srdivacky// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction 393198090Srdivacky// against another. 394193323Sed// 395193323SedAliasAnalysis::AliasResult 396198090SrdivackyBasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size, 397198090Srdivacky const Value *V2, unsigned V2Size) { 398193323Sed // If we have two gep instructions with must-alias'ing base pointers, figure 399193323Sed // out if the indexes to the GEP tell us anything about the derived pointer. 400193323Sed // Note that we also handle chains of getelementptr instructions as well as 401193323Sed // constant expression getelementptrs here. 402193323Sed // 403193323Sed if (isGEP(V1) && isGEP(V2)) { 404193323Sed const User *GEP1 = cast<User>(V1); 405193323Sed const User *GEP2 = cast<User>(V2); 406193323Sed 407193323Sed // If V1 and V2 are identical GEPs, just recurse down on both of them. 408193323Sed // This allows us to analyze things like: 409193323Sed // P = gep A, 0, i, 1 410193323Sed // Q = gep B, 0, i, 1 411193323Sed // by just analyzing A and B. This is even safe for variable indices. 412193323Sed if (GEP1->getType() == GEP2->getType() && 413193323Sed GEP1->getNumOperands() == GEP2->getNumOperands() && 414193323Sed GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() && 415193323Sed // All operands are the same, ignoring the base. 416193323Sed std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1)) 417198090Srdivacky return aliasCheck(GEP1->getOperand(0), V1Size, 418198090Srdivacky GEP2->getOperand(0), V2Size); 419193323Sed 420193323Sed // Drill down into the first non-gep value, to test for must-aliasing of 421193323Sed // the base pointers. 422193323Sed while (isGEP(GEP1->getOperand(0)) && 423193323Sed GEP1->getOperand(1) == 424193323Sed Constant::getNullValue(GEP1->getOperand(1)->getType())) 425193323Sed GEP1 = cast<User>(GEP1->getOperand(0)); 426193323Sed const Value *BasePtr1 = GEP1->getOperand(0); 427193323Sed 428193323Sed while (isGEP(GEP2->getOperand(0)) && 429193323Sed GEP2->getOperand(1) == 430193323Sed Constant::getNullValue(GEP2->getOperand(1)->getType())) 431193323Sed GEP2 = cast<User>(GEP2->getOperand(0)); 432193323Sed const Value *BasePtr2 = GEP2->getOperand(0); 433193323Sed 434193323Sed // Do the base pointers alias? 435198090Srdivacky AliasResult BaseAlias = aliasCheck(BasePtr1, ~0U, BasePtr2, ~0U); 436193323Sed if (BaseAlias == NoAlias) return NoAlias; 437193323Sed if (BaseAlias == MustAlias) { 438193323Sed // If the base pointers alias each other exactly, check to see if we can 439193323Sed // figure out anything about the resultant pointers, to try to prove 440193323Sed // non-aliasing. 441193323Sed 442193323Sed // Collect all of the chained GEP operands together into one simple place 443193323Sed SmallVector<Value*, 16> GEP1Ops, GEP2Ops; 444193323Sed BasePtr1 = GetGEPOperands(V1, GEP1Ops); 445193323Sed BasePtr2 = GetGEPOperands(V2, GEP2Ops); 446193323Sed 447193323Sed // If GetGEPOperands were able to fold to the same must-aliased pointer, 448193323Sed // do the comparison. 449193323Sed if (BasePtr1 == BasePtr2) { 450193323Sed AliasResult GAlias = 451193323Sed CheckGEPInstructions(BasePtr1->getType(), 452193323Sed &GEP1Ops[0], GEP1Ops.size(), V1Size, 453193323Sed BasePtr2->getType(), 454193323Sed &GEP2Ops[0], GEP2Ops.size(), V2Size); 455193323Sed if (GAlias != MayAlias) 456193323Sed return GAlias; 457193323Sed } 458193323Sed } 459193323Sed } 460193323Sed 461193323Sed // Check to see if these two pointers are related by a getelementptr 462193323Sed // instruction. If one pointer is a GEP with a non-zero index of the other 463193323Sed // pointer, we know they cannot alias. 464193323Sed // 465198090Srdivacky if (V1Size == ~0U || V2Size == ~0U) 466198090Srdivacky return MayAlias; 467193323Sed 468198090Srdivacky SmallVector<Value*, 16> GEPOperands; 469198090Srdivacky const Value *BasePtr = GetGEPOperands(V1, GEPOperands); 470193323Sed 471198090Srdivacky AliasResult R = aliasCheck(BasePtr, ~0U, V2, V2Size); 472198090Srdivacky if (R != MustAlias) 473198090Srdivacky // If V2 may alias GEP base pointer, conservatively returns MayAlias. 474198090Srdivacky // If V2 is known not to alias GEP base pointer, then the two values 475198090Srdivacky // cannot alias per GEP semantics: "A pointer value formed from a 476198090Srdivacky // getelementptr instruction is associated with the addresses associated 477198090Srdivacky // with the first operand of the getelementptr". 478198090Srdivacky return R; 479193323Sed 480198090Srdivacky // If there is at least one non-zero constant index, we know they cannot 481198090Srdivacky // alias. 482198090Srdivacky bool ConstantFound = false; 483198090Srdivacky bool AllZerosFound = true; 484198090Srdivacky for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i) 485198090Srdivacky if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) { 486198090Srdivacky if (!C->isNullValue()) { 487198090Srdivacky ConstantFound = true; 488198090Srdivacky AllZerosFound = false; 489198090Srdivacky break; 490198090Srdivacky } 491198090Srdivacky } else { 492198090Srdivacky AllZerosFound = false; 493198090Srdivacky } 494193323Sed 495198090Srdivacky // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases 496198090Srdivacky // the ptr, the end result is a must alias also. 497198090Srdivacky if (AllZerosFound) 498198090Srdivacky return MustAlias; 499193323Sed 500198090Srdivacky if (ConstantFound) { 501198090Srdivacky if (V2Size <= 1 && V1Size <= 1) // Just pointer check? 502198090Srdivacky return NoAlias; 503193323Sed 504198090Srdivacky // Otherwise we have to check to see that the distance is more than 505198090Srdivacky // the size of the argument... build an index vector that is equal to 506198090Srdivacky // the arguments provided, except substitute 0's for any variable 507198090Srdivacky // indexes we find... 508198090Srdivacky if (TD && 509198090Srdivacky cast<PointerType>(BasePtr->getType())->getElementType()->isSized()) { 510198090Srdivacky for (unsigned i = 0; i != GEPOperands.size(); ++i) 511198090Srdivacky if (!isa<ConstantInt>(GEPOperands[i])) 512198090Srdivacky GEPOperands[i] = Constant::getNullValue(GEPOperands[i]->getType()); 513198090Srdivacky int64_t Offset = TD->getIndexedOffset(BasePtr->getType(), 514198090Srdivacky &GEPOperands[0], 515198090Srdivacky GEPOperands.size()); 516198090Srdivacky 517198090Srdivacky if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size) 518198090Srdivacky return NoAlias; 519193323Sed } 520198090Srdivacky } 521193323Sed 522193323Sed return MayAlias; 523193323Sed} 524193323Sed 525198090Srdivacky// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction 526198090Srdivacky// against another. 527198090SrdivackyAliasAnalysis::AliasResult 528198090SrdivackyBasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize, 529198090Srdivacky const Value *V2, unsigned V2Size) { 530198090Srdivacky // The PHI node has already been visited, avoid recursion any further. 531198090Srdivacky if (!VisitedPHIs.insert(PN)) 532198090Srdivacky return MayAlias; 533198090Srdivacky 534198090Srdivacky SmallSet<Value*, 4> UniqueSrc; 535198090Srdivacky SmallVector<Value*, 4> V1Srcs; 536198090Srdivacky for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 537198090Srdivacky Value *PV1 = PN->getIncomingValue(i); 538198090Srdivacky if (isa<PHINode>(PV1)) 539198090Srdivacky // If any of the source itself is a PHI, return MayAlias conservatively 540198090Srdivacky // to avoid compile time explosion. The worst possible case is if both 541198090Srdivacky // sides are PHI nodes. In which case, this is O(m x n) time where 'm' 542198090Srdivacky // and 'n' are the number of PHI sources. 543198090Srdivacky return MayAlias; 544198090Srdivacky if (UniqueSrc.insert(PV1)) 545198090Srdivacky V1Srcs.push_back(PV1); 546198090Srdivacky } 547198090Srdivacky 548198090Srdivacky AliasResult Alias = aliasCheck(V1Srcs[0], PNSize, V2, V2Size); 549198090Srdivacky // Early exit if the check of the first PHI source against V2 is MayAlias. 550198090Srdivacky // Other results are not possible. 551198090Srdivacky if (Alias == MayAlias) 552198090Srdivacky return MayAlias; 553198090Srdivacky 554198090Srdivacky // If all sources of the PHI node NoAlias or MustAlias V2, then returns 555198090Srdivacky // NoAlias / MustAlias. Otherwise, returns MayAlias. 556198090Srdivacky for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) { 557198090Srdivacky Value *V = V1Srcs[i]; 558198090Srdivacky AliasResult ThisAlias = aliasCheck(V, PNSize, V2, V2Size); 559198090Srdivacky if (ThisAlias != Alias || ThisAlias == MayAlias) 560198090Srdivacky return MayAlias; 561198090Srdivacky } 562198090Srdivacky 563198090Srdivacky return Alias; 564198090Srdivacky} 565198090Srdivacky 566198090Srdivacky// aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases, 567198090Srdivacky// such as array references. 568198090Srdivacky// 569198090SrdivackyAliasAnalysis::AliasResult 570198090SrdivackyBasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size, 571198090Srdivacky const Value *V2, unsigned V2Size) { 572198090Srdivacky // Strip off any casts if they exist. 573198090Srdivacky V1 = V1->stripPointerCasts(); 574198090Srdivacky V2 = V2->stripPointerCasts(); 575198090Srdivacky 576198090Srdivacky // Are we checking for alias of the same value? 577198090Srdivacky if (V1 == V2) return MustAlias; 578198090Srdivacky 579198090Srdivacky if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) 580198090Srdivacky return NoAlias; // Scalars cannot alias each other 581198090Srdivacky 582198090Srdivacky // Figure out what objects these things are pointing to if we can. 583198090Srdivacky const Value *O1 = V1->getUnderlyingObject(); 584198090Srdivacky const Value *O2 = V2->getUnderlyingObject(); 585198090Srdivacky 586198090Srdivacky if (O1 != O2) { 587198090Srdivacky // If V1/V2 point to two different objects we know that we have no alias. 588198090Srdivacky if (isIdentifiedObject(O1) && isIdentifiedObject(O2)) 589198090Srdivacky return NoAlias; 590198090Srdivacky 591198090Srdivacky // Arguments can't alias with local allocations or noalias calls. 592198090Srdivacky if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) || 593198090Srdivacky (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1)))) 594198090Srdivacky return NoAlias; 595198090Srdivacky 596198090Srdivacky // Most objects can't alias null. 597198090Srdivacky if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) || 598198090Srdivacky (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2))) 599198090Srdivacky return NoAlias; 600198090Srdivacky } 601198090Srdivacky 602198090Srdivacky // If the size of one access is larger than the entire object on the other 603198090Srdivacky // side, then we know such behavior is undefined and can assume no alias. 604198090Srdivacky LLVMContext &Context = V1->getContext(); 605198090Srdivacky if (TD) 606198090Srdivacky if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, Context, *TD)) || 607198090Srdivacky (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, Context, *TD))) 608198090Srdivacky return NoAlias; 609198090Srdivacky 610198090Srdivacky // If one pointer is the result of a call/invoke and the other is a 611198090Srdivacky // non-escaping local object, then we know the object couldn't escape to a 612198090Srdivacky // point where the call could return it. 613198090Srdivacky if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) && 614198090Srdivacky isNonEscapingLocalObject(O2) && O1 != O2) 615198090Srdivacky return NoAlias; 616198090Srdivacky if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) && 617198090Srdivacky isNonEscapingLocalObject(O1) && O1 != O2) 618198090Srdivacky return NoAlias; 619198090Srdivacky 620198090Srdivacky if (!isGEP(V1) && isGEP(V2)) { 621198090Srdivacky std::swap(V1, V2); 622198090Srdivacky std::swap(V1Size, V2Size); 623198090Srdivacky } 624198090Srdivacky if (isGEP(V1)) 625198090Srdivacky return aliasGEP(V1, V1Size, V2, V2Size); 626198090Srdivacky 627198090Srdivacky if (isa<PHINode>(V2) && !isa<PHINode>(V1)) { 628198090Srdivacky std::swap(V1, V2); 629198090Srdivacky std::swap(V1Size, V2Size); 630198090Srdivacky } 631198090Srdivacky if (const PHINode *PN = dyn_cast<PHINode>(V1)) 632198090Srdivacky return aliasPHI(PN, V1Size, V2, V2Size); 633198090Srdivacky 634198090Srdivacky return MayAlias; 635198090Srdivacky} 636198090Srdivacky 637193323Sed// This function is used to determine if the indices of two GEP instructions are 638193323Sed// equal. V1 and V2 are the indices. 639198090Srdivackystatic bool IndexOperandsEqual(Value *V1, Value *V2, LLVMContext &Context) { 640193323Sed if (V1->getType() == V2->getType()) 641193323Sed return V1 == V2; 642193323Sed if (Constant *C1 = dyn_cast<Constant>(V1)) 643193323Sed if (Constant *C2 = dyn_cast<Constant>(V2)) { 644193323Sed // Sign extend the constants to long types, if necessary 645198090Srdivacky if (C1->getType() != Type::getInt64Ty(Context)) 646198090Srdivacky C1 = ConstantExpr::getSExt(C1, Type::getInt64Ty(Context)); 647198090Srdivacky if (C2->getType() != Type::getInt64Ty(Context)) 648198090Srdivacky C2 = ConstantExpr::getSExt(C2, Type::getInt64Ty(Context)); 649193323Sed return C1 == C2; 650193323Sed } 651193323Sed return false; 652193323Sed} 653193323Sed 654193323Sed/// CheckGEPInstructions - Check two GEP instructions with known must-aliasing 655193323Sed/// base pointers. This checks to see if the index expressions preclude the 656193323Sed/// pointers from aliasing... 657193323SedAliasAnalysis::AliasResult 658193323SedBasicAliasAnalysis::CheckGEPInstructions( 659193323Sed const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S, 660193323Sed const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) { 661193323Sed // We currently can't handle the case when the base pointers have different 662193323Sed // primitive types. Since this is uncommon anyway, we are happy being 663193323Sed // extremely conservative. 664193323Sed if (BasePtr1Ty != BasePtr2Ty) 665193323Sed return MayAlias; 666193323Sed 667193323Sed const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty); 668193323Sed 669198090Srdivacky LLVMContext &Context = GEPPointerTy->getContext(); 670198090Srdivacky 671193323Sed // Find the (possibly empty) initial sequence of equal values... which are not 672193323Sed // necessarily constants. 673193323Sed unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops; 674193323Sed unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands); 675193323Sed unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands); 676193323Sed unsigned UnequalOper = 0; 677193323Sed while (UnequalOper != MinOperands && 678198090Srdivacky IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper], 679198090Srdivacky Context)) { 680193323Sed // Advance through the type as we go... 681193323Sed ++UnequalOper; 682193323Sed if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty)) 683193323Sed BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]); 684193323Sed else { 685193323Sed // If all operands equal each other, then the derived pointers must 686193323Sed // alias each other... 687193323Sed BasePtr1Ty = 0; 688193323Sed assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands && 689193323Sed "Ran out of type nesting, but not out of operands?"); 690193323Sed return MustAlias; 691193323Sed } 692193323Sed } 693193323Sed 694193323Sed // If we have seen all constant operands, and run out of indexes on one of the 695193323Sed // getelementptrs, check to see if the tail of the leftover one is all zeros. 696193323Sed // If so, return mustalias. 697193323Sed if (UnequalOper == MinOperands) { 698193323Sed if (NumGEP1Ops < NumGEP2Ops) { 699193323Sed std::swap(GEP1Ops, GEP2Ops); 700193323Sed std::swap(NumGEP1Ops, NumGEP2Ops); 701193323Sed } 702193323Sed 703193323Sed bool AllAreZeros = true; 704193323Sed for (unsigned i = UnequalOper; i != MaxOperands; ++i) 705193323Sed if (!isa<Constant>(GEP1Ops[i]) || 706193323Sed !cast<Constant>(GEP1Ops[i])->isNullValue()) { 707193323Sed AllAreZeros = false; 708193323Sed break; 709193323Sed } 710193323Sed if (AllAreZeros) return MustAlias; 711193323Sed } 712193323Sed 713193323Sed 714193323Sed // So now we know that the indexes derived from the base pointers, 715193323Sed // which are known to alias, are different. We can still determine a 716193323Sed // no-alias result if there are differing constant pairs in the index 717193323Sed // chain. For example: 718193323Sed // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S)) 719193323Sed // 720193323Sed // We have to be careful here about array accesses. In particular, consider: 721193323Sed // A[1][0] vs A[0][i] 722193323Sed // In this case, we don't *know* that the array will be accessed in bounds: 723193323Sed // the index could even be negative. Because of this, we have to 724193323Sed // conservatively *give up* and return may alias. We disregard differing 725193323Sed // array subscripts that are followed by a variable index without going 726193323Sed // through a struct. 727193323Sed // 728193323Sed unsigned SizeMax = std::max(G1S, G2S); 729193323Sed if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work. 730193323Sed 731193323Sed // Scan for the first operand that is constant and unequal in the 732193323Sed // two getelementptrs... 733193323Sed unsigned FirstConstantOper = UnequalOper; 734193323Sed for (; FirstConstantOper != MinOperands; ++FirstConstantOper) { 735193323Sed const Value *G1Oper = GEP1Ops[FirstConstantOper]; 736193323Sed const Value *G2Oper = GEP2Ops[FirstConstantOper]; 737193323Sed 738193323Sed if (G1Oper != G2Oper) // Found non-equal constant indexes... 739193323Sed if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper))) 740193323Sed if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){ 741193323Sed if (G1OC->getType() != G2OC->getType()) { 742193323Sed // Sign extend both operands to long. 743198090Srdivacky if (G1OC->getType() != Type::getInt64Ty(Context)) 744198090Srdivacky G1OC = ConstantExpr::getSExt(G1OC, Type::getInt64Ty(Context)); 745198090Srdivacky if (G2OC->getType() != Type::getInt64Ty(Context)) 746198090Srdivacky G2OC = ConstantExpr::getSExt(G2OC, Type::getInt64Ty(Context)); 747193323Sed GEP1Ops[FirstConstantOper] = G1OC; 748193323Sed GEP2Ops[FirstConstantOper] = G2OC; 749193323Sed } 750193323Sed 751193323Sed if (G1OC != G2OC) { 752193323Sed // Handle the "be careful" case above: if this is an array/vector 753193323Sed // subscript, scan for a subsequent variable array index. 754193323Sed if (const SequentialType *STy = 755193323Sed dyn_cast<SequentialType>(BasePtr1Ty)) { 756193323Sed const Type *NextTy = STy; 757193323Sed bool isBadCase = false; 758193323Sed 759193323Sed for (unsigned Idx = FirstConstantOper; 760193323Sed Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) { 761193323Sed const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx]; 762193323Sed if (!isa<Constant>(V1) || !isa<Constant>(V2)) { 763193323Sed isBadCase = true; 764193323Sed break; 765193323Sed } 766193323Sed // If the array is indexed beyond the bounds of the static type 767193323Sed // at this level, it will also fall into the "be careful" case. 768193323Sed // It would theoretically be possible to analyze these cases, 769193323Sed // but for now just be conservatively correct. 770193323Sed if (const ArrayType *ATy = dyn_cast<ArrayType>(STy)) 771193323Sed if (cast<ConstantInt>(G1OC)->getZExtValue() >= 772193323Sed ATy->getNumElements() || 773193323Sed cast<ConstantInt>(G2OC)->getZExtValue() >= 774193323Sed ATy->getNumElements()) { 775193323Sed isBadCase = true; 776193323Sed break; 777193323Sed } 778193323Sed if (const VectorType *VTy = dyn_cast<VectorType>(STy)) 779193323Sed if (cast<ConstantInt>(G1OC)->getZExtValue() >= 780193323Sed VTy->getNumElements() || 781193323Sed cast<ConstantInt>(G2OC)->getZExtValue() >= 782193323Sed VTy->getNumElements()) { 783193323Sed isBadCase = true; 784193323Sed break; 785193323Sed } 786193323Sed STy = cast<SequentialType>(NextTy); 787193323Sed NextTy = cast<SequentialType>(NextTy)->getElementType(); 788193323Sed } 789193323Sed 790193323Sed if (isBadCase) G1OC = 0; 791193323Sed } 792193323Sed 793193323Sed // Make sure they are comparable (ie, not constant expressions), and 794193323Sed // make sure the GEP with the smaller leading constant is GEP1. 795193323Sed if (G1OC) { 796193323Sed Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT, 797193323Sed G1OC, G2OC); 798193323Sed if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) { 799193323Sed if (CV->getZExtValue()) { // If they are comparable and G2 > G1 800193323Sed std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2 801193323Sed std::swap(NumGEP1Ops, NumGEP2Ops); 802193323Sed } 803193323Sed break; 804193323Sed } 805193323Sed } 806193323Sed } 807193323Sed } 808193323Sed BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper); 809193323Sed } 810193323Sed 811193323Sed // No shared constant operands, and we ran out of common operands. At this 812193323Sed // point, the GEP instructions have run through all of their operands, and we 813193323Sed // haven't found evidence that there are any deltas between the GEP's. 814193323Sed // However, one GEP may have more operands than the other. If this is the 815193323Sed // case, there may still be hope. Check this now. 816193323Sed if (FirstConstantOper == MinOperands) { 817198090Srdivacky // Without TargetData, we won't know what the offsets are. 818198090Srdivacky if (!TD) 819198090Srdivacky return MayAlias; 820198090Srdivacky 821193323Sed // Make GEP1Ops be the longer one if there is a longer one. 822193323Sed if (NumGEP1Ops < NumGEP2Ops) { 823193323Sed std::swap(GEP1Ops, GEP2Ops); 824193323Sed std::swap(NumGEP1Ops, NumGEP2Ops); 825193323Sed } 826193323Sed 827193323Sed // Is there anything to check? 828193323Sed if (NumGEP1Ops > MinOperands) { 829193323Sed for (unsigned i = FirstConstantOper; i != MaxOperands; ++i) 830193323Sed if (isa<ConstantInt>(GEP1Ops[i]) && 831193323Sed !cast<ConstantInt>(GEP1Ops[i])->isZero()) { 832193323Sed // Yup, there's a constant in the tail. Set all variables to 833193323Sed // constants in the GEP instruction to make it suitable for 834193323Sed // TargetData::getIndexedOffset. 835193323Sed for (i = 0; i != MaxOperands; ++i) 836193323Sed if (!isa<ConstantInt>(GEP1Ops[i])) 837193323Sed GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType()); 838193323Sed // Okay, now get the offset. This is the relative offset for the full 839193323Sed // instruction. 840198090Srdivacky int64_t Offset1 = TD->getIndexedOffset(GEPPointerTy, GEP1Ops, 841198090Srdivacky NumGEP1Ops); 842193323Sed 843193323Sed // Now check without any constants at the end. 844198090Srdivacky int64_t Offset2 = TD->getIndexedOffset(GEPPointerTy, GEP1Ops, 845198090Srdivacky MinOperands); 846193323Sed 847193323Sed // Make sure we compare the absolute difference. 848193323Sed if (Offset1 > Offset2) 849193323Sed std::swap(Offset1, Offset2); 850193323Sed 851193323Sed // If the tail provided a bit enough offset, return noalias! 852193323Sed if ((uint64_t)(Offset2-Offset1) >= SizeMax) 853193323Sed return NoAlias; 854193323Sed // Otherwise break - we don't look for another constant in the tail. 855193323Sed break; 856193323Sed } 857193323Sed } 858193323Sed 859193323Sed // Couldn't find anything useful. 860193323Sed return MayAlias; 861193323Sed } 862193323Sed 863193323Sed // If there are non-equal constants arguments, then we can figure 864193323Sed // out a minimum known delta between the two index expressions... at 865193323Sed // this point we know that the first constant index of GEP1 is less 866193323Sed // than the first constant index of GEP2. 867193323Sed 868193323Sed // Advance BasePtr[12]Ty over this first differing constant operand. 869193323Sed BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)-> 870193323Sed getTypeAtIndex(GEP2Ops[FirstConstantOper]); 871193323Sed BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)-> 872193323Sed getTypeAtIndex(GEP1Ops[FirstConstantOper]); 873193323Sed 874193323Sed // We are going to be using TargetData::getIndexedOffset to determine the 875193323Sed // offset that each of the GEP's is reaching. To do this, we have to convert 876193323Sed // all variable references to constant references. To do this, we convert the 877193323Sed // initial sequence of array subscripts into constant zeros to start with. 878193323Sed const Type *ZeroIdxTy = GEPPointerTy; 879193323Sed for (unsigned i = 0; i != FirstConstantOper; ++i) { 880193323Sed if (!isa<StructType>(ZeroIdxTy)) 881198090Srdivacky GEP1Ops[i] = GEP2Ops[i] = 882198090Srdivacky Constant::getNullValue(Type::getInt32Ty(Context)); 883193323Sed 884193323Sed if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy)) 885193323Sed ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]); 886193323Sed } 887193323Sed 888193323Sed // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok 889193323Sed 890193323Sed // Loop over the rest of the operands... 891193323Sed for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) { 892193323Sed const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0; 893193323Sed const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0; 894193323Sed // If they are equal, use a zero index... 895193323Sed if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) { 896193323Sed if (!isa<ConstantInt>(Op1)) 897193323Sed GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType()); 898193323Sed // Otherwise, just keep the constants we have. 899193323Sed } else { 900193323Sed if (Op1) { 901193323Sed if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { 902193323Sed // If this is an array index, make sure the array element is in range. 903193323Sed if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) { 904193323Sed if (Op1C->getZExtValue() >= AT->getNumElements()) 905193323Sed return MayAlias; // Be conservative with out-of-range accesses 906193323Sed } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) { 907193323Sed if (Op1C->getZExtValue() >= VT->getNumElements()) 908193323Sed return MayAlias; // Be conservative with out-of-range accesses 909193323Sed } 910193323Sed 911193323Sed } else { 912193323Sed // GEP1 is known to produce a value less than GEP2. To be 913193323Sed // conservatively correct, we must assume the largest possible 914193323Sed // constant is used in this position. This cannot be the initial 915193323Sed // index to the GEP instructions (because we know we have at least one 916193323Sed // element before this one with the different constant arguments), so 917193323Sed // we know that the current index must be into either a struct or 918193323Sed // array. Because we know it's not constant, this cannot be a 919193323Sed // structure index. Because of this, we can calculate the maximum 920193323Sed // value possible. 921193323Sed // 922193323Sed if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) 923198090Srdivacky GEP1Ops[i] = 924198090Srdivacky ConstantInt::get(Type::getInt64Ty(Context), 925198090Srdivacky AT->getNumElements()-1); 926193323Sed else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) 927198090Srdivacky GEP1Ops[i] = 928198090Srdivacky ConstantInt::get(Type::getInt64Ty(Context), 929198090Srdivacky VT->getNumElements()-1); 930193323Sed } 931193323Sed } 932193323Sed 933193323Sed if (Op2) { 934193323Sed if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) { 935193323Sed // If this is an array index, make sure the array element is in range. 936193323Sed if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) { 937193323Sed if (Op2C->getZExtValue() >= AT->getNumElements()) 938193323Sed return MayAlias; // Be conservative with out-of-range accesses 939193323Sed } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) { 940193323Sed if (Op2C->getZExtValue() >= VT->getNumElements()) 941193323Sed return MayAlias; // Be conservative with out-of-range accesses 942193323Sed } 943193323Sed } else { // Conservatively assume the minimum value for this index 944193323Sed GEP2Ops[i] = Constant::getNullValue(Op2->getType()); 945193323Sed } 946193323Sed } 947193323Sed } 948193323Sed 949193323Sed if (BasePtr1Ty && Op1) { 950193323Sed if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty)) 951193323Sed BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]); 952193323Sed else 953193323Sed BasePtr1Ty = 0; 954193323Sed } 955193323Sed 956193323Sed if (BasePtr2Ty && Op2) { 957193323Sed if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty)) 958193323Sed BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]); 959193323Sed else 960193323Sed BasePtr2Ty = 0; 961193323Sed } 962193323Sed } 963193323Sed 964198090Srdivacky if (TD && GEPPointerTy->getElementType()->isSized()) { 965193323Sed int64_t Offset1 = 966198090Srdivacky TD->getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops); 967193323Sed int64_t Offset2 = 968198090Srdivacky TD->getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops); 969193323Sed assert(Offset1 != Offset2 && 970193323Sed "There is at least one different constant here!"); 971193323Sed 972193323Sed // Make sure we compare the absolute difference. 973193323Sed if (Offset1 > Offset2) 974193323Sed std::swap(Offset1, Offset2); 975193323Sed 976193323Sed if ((uint64_t)(Offset2-Offset1) >= SizeMax) { 977193323Sed //cerr << "Determined that these two GEP's don't alias [" 978193323Sed // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2; 979193323Sed return NoAlias; 980193323Sed } 981193323Sed } 982193323Sed return MayAlias; 983193323Sed} 984193323Sed 985193323Sed// Make sure that anything that uses AliasAnalysis pulls in this file... 986193323SedDEFINING_FILE_FOR(BasicAliasAnalysis) 987