BasicAliasAnalysis.cpp revision 193323
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" 18193323Sed#include "llvm/Analysis/Passes.h" 19193323Sed#include "llvm/Constants.h" 20193323Sed#include "llvm/DerivedTypes.h" 21193323Sed#include "llvm/Function.h" 22193323Sed#include "llvm/GlobalVariable.h" 23193323Sed#include "llvm/Instructions.h" 24193323Sed#include "llvm/IntrinsicInst.h" 25193323Sed#include "llvm/Pass.h" 26193323Sed#include "llvm/Target/TargetData.h" 27193323Sed#include "llvm/ADT/SmallVector.h" 28193323Sed#include "llvm/ADT/STLExtras.h" 29193323Sed#include "llvm/Support/Compiler.h" 30193323Sed#include "llvm/Support/GetElementPtrTypeIterator.h" 31193323Sed#include "llvm/Support/ManagedStatic.h" 32193323Sed#include <algorithm> 33193323Sedusing namespace llvm; 34193323Sed 35193323Sed//===----------------------------------------------------------------------===// 36193323Sed// Useful predicates 37193323Sed//===----------------------------------------------------------------------===// 38193323Sed 39193323Sedstatic const User *isGEP(const Value *V) { 40193323Sed if (isa<GetElementPtrInst>(V) || 41193323Sed (isa<ConstantExpr>(V) && 42193323Sed cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr)) 43193323Sed return cast<User>(V); 44193323Sed return 0; 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, 107193323Sed 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; 116193323Sed } else if (const Argument *A = dyn_cast<Argument>(V)) { 117193323Sed if (A->hasByValAttr()) 118193323Sed AccessTy = cast<PointerType>(A->getType())->getElementType(); 119193323Sed else 120193323Sed return false; 121193323Sed } else { 122193323Sed return false; 123193323Sed } 124193323Sed 125193323Sed if (AccessTy->isSized()) 126193323Sed return TD.getTypeAllocSize(AccessTy) < Size; 127193323Sed return false; 128193323Sed} 129193323Sed 130193323Sed//===----------------------------------------------------------------------===// 131193323Sed// NoAA Pass 132193323Sed//===----------------------------------------------------------------------===// 133193323Sed 134193323Sednamespace { 135193323Sed /// NoAA - This class implements the -no-aa pass, which always returns "I 136193323Sed /// don't know" for alias queries. NoAA is unlike other alias analysis 137193323Sed /// implementations, in that it does not chain to a previous analysis. As 138193323Sed /// such it doesn't follow many of the rules that other alias analyses must. 139193323Sed /// 140193323Sed struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis { 141193323Sed static char ID; // Class identification, replacement for typeinfo 142193323Sed NoAA() : ImmutablePass(&ID) {} 143193323Sed explicit NoAA(void *PID) : ImmutablePass(PID) { } 144193323Sed 145193323Sed virtual void getAnalysisUsage(AnalysisUsage &AU) const { 146193323Sed AU.addRequired<TargetData>(); 147193323Sed } 148193323Sed 149193323Sed virtual void initializePass() { 150193323Sed TD = &getAnalysis<TargetData>(); 151193323Sed } 152193323Sed 153193323Sed virtual AliasResult alias(const Value *V1, unsigned V1Size, 154193323Sed const Value *V2, unsigned V2Size) { 155193323Sed return MayAlias; 156193323Sed } 157193323Sed 158193323Sed virtual void getArgumentAccesses(Function *F, CallSite CS, 159193323Sed std::vector<PointerAccessInfo> &Info) { 160193323Sed assert(0 && "This method may not be called on this function!"); 161193323Sed } 162193323Sed 163193323Sed virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { } 164193323Sed virtual bool pointsToConstantMemory(const Value *P) { return false; } 165193323Sed virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) { 166193323Sed return ModRef; 167193323Sed } 168193323Sed virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { 169193323Sed return ModRef; 170193323Sed } 171193323Sed virtual bool hasNoModRefInfoForCalls() const { return true; } 172193323Sed 173193323Sed virtual void deleteValue(Value *V) {} 174193323Sed virtual void copyValue(Value *From, Value *To) {} 175193323Sed }; 176193323Sed} // End of anonymous namespace 177193323Sed 178193323Sed// Register this pass... 179193323Sedchar NoAA::ID = 0; 180193323Sedstatic RegisterPass<NoAA> 181193323SedU("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true); 182193323Sed 183193323Sed// Declare that we implement the AliasAnalysis interface 184193323Sedstatic RegisterAnalysisGroup<AliasAnalysis> V(U); 185193323Sed 186193323SedImmutablePass *llvm::createNoAAPass() { return new NoAA(); } 187193323Sed 188193323Sed//===----------------------------------------------------------------------===// 189193323Sed// BasicAA Pass 190193323Sed//===----------------------------------------------------------------------===// 191193323Sed 192193323Sednamespace { 193193323Sed /// BasicAliasAnalysis - This is the default alias analysis implementation. 194193323Sed /// Because it doesn't chain to a previous alias analysis (like -no-aa), it 195193323Sed /// derives from the NoAA class. 196193323Sed struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA { 197193323Sed static char ID; // Class identification, replacement for typeinfo 198193323Sed BasicAliasAnalysis() : NoAA(&ID) {} 199193323Sed AliasResult alias(const Value *V1, unsigned V1Size, 200193323Sed const Value *V2, unsigned V2Size); 201193323Sed 202193323Sed ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 203193323Sed ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 204193323Sed 205193323Sed /// hasNoModRefInfoForCalls - We can provide mod/ref information against 206193323Sed /// non-escaping allocations. 207193323Sed virtual bool hasNoModRefInfoForCalls() const { return false; } 208193323Sed 209193323Sed /// pointsToConstantMemory - Chase pointers until we find a (constant 210193323Sed /// global) or not. 211193323Sed bool pointsToConstantMemory(const Value *P); 212193323Sed 213193323Sed private: 214193323Sed // CheckGEPInstructions - Check two GEP instructions with known 215193323Sed // must-aliasing base pointers. This checks to see if the index expressions 216193323Sed // preclude the pointers from aliasing... 217193323Sed AliasResult 218193323Sed CheckGEPInstructions(const Type* BasePtr1Ty, 219193323Sed Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size, 220193323Sed const Type *BasePtr2Ty, 221193323Sed Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size); 222193323Sed }; 223193323Sed} // End of anonymous namespace 224193323Sed 225193323Sed// Register this pass... 226193323Sedchar BasicAliasAnalysis::ID = 0; 227193323Sedstatic RegisterPass<BasicAliasAnalysis> 228193323SedX("basicaa", "Basic Alias Analysis (default AA impl)", false, true); 229193323Sed 230193323Sed// Declare that we implement the AliasAnalysis interface 231193323Sedstatic RegisterAnalysisGroup<AliasAnalysis, true> Y(X); 232193323Sed 233193323SedImmutablePass *llvm::createBasicAliasAnalysisPass() { 234193323Sed return new BasicAliasAnalysis(); 235193323Sed} 236193323Sed 237193323Sed 238193323Sed/// pointsToConstantMemory - Chase pointers until we find a (constant 239193323Sed/// global) or not. 240193323Sedbool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) { 241193323Sed if (const GlobalVariable *GV = 242193323Sed dyn_cast<GlobalVariable>(P->getUnderlyingObject())) 243193323Sed return GV->isConstant(); 244193323Sed return false; 245193323Sed} 246193323Sed 247193323Sed 248193323Sed// getModRefInfo - Check to see if the specified callsite can clobber the 249193323Sed// specified memory object. Since we only look at local properties of this 250193323Sed// function, we really can't say much about this query. We do, however, use 251193323Sed// simple "address taken" analysis on local objects. 252193323Sed// 253193323SedAliasAnalysis::ModRefResult 254193323SedBasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { 255193323Sed if (!isa<Constant>(P)) { 256193323Sed const Value *Object = P->getUnderlyingObject(); 257193323Sed 258193323Sed // If this is a tail call and P points to a stack location, we know that 259193323Sed // the tail call cannot access or modify the local stack. 260193323Sed // We cannot exclude byval arguments here; these belong to the caller of 261193323Sed // the current function not to the current function, and a tail callee 262193323Sed // may reference them. 263193323Sed if (isa<AllocaInst>(Object)) 264193323Sed if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction())) 265193323Sed if (CI->isTailCall()) 266193323Sed return NoModRef; 267193323Sed 268193323Sed // If the pointer is to a locally allocated object that does not escape, 269193323Sed // then the call can not mod/ref the pointer unless the call takes the 270193323Sed // argument without capturing it. 271193323Sed if (isNonEscapingLocalObject(Object) && CS.getInstruction() != Object) { 272193323Sed bool passedAsArg = false; 273193323Sed // TODO: Eventually only check 'nocapture' arguments. 274193323Sed for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end(); 275193323Sed CI != CE; ++CI) 276193323Sed if (isa<PointerType>((*CI)->getType()) && 277193323Sed alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias) 278193323Sed passedAsArg = true; 279193323Sed 280193323Sed if (!passedAsArg) 281193323Sed return NoModRef; 282193323Sed } 283193323Sed } 284193323Sed 285193323Sed // The AliasAnalysis base class has some smarts, lets use them. 286193323Sed return AliasAnalysis::getModRefInfo(CS, P, Size); 287193323Sed} 288193323Sed 289193323Sed 290193323SedAliasAnalysis::ModRefResult 291193323SedBasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) { 292193323Sed // If CS1 or CS2 are readnone, they don't interact. 293193323Sed ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1); 294193323Sed if (CS1B == DoesNotAccessMemory) return NoModRef; 295193323Sed 296193323Sed ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2); 297193323Sed if (CS2B == DoesNotAccessMemory) return NoModRef; 298193323Sed 299193323Sed // If they both only read from memory, just return ref. 300193323Sed if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory) 301193323Sed return Ref; 302193323Sed 303193323Sed // Otherwise, fall back to NoAA (mod+ref). 304193323Sed return NoAA::getModRefInfo(CS1, CS2); 305193323Sed} 306193323Sed 307193323Sed 308193323Sed// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such 309193323Sed// as array references. 310193323Sed// 311193323SedAliasAnalysis::AliasResult 312193323SedBasicAliasAnalysis::alias(const Value *V1, unsigned V1Size, 313193323Sed const Value *V2, unsigned V2Size) { 314193323Sed // Strip off any constant expression casts if they exist 315193323Sed if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1)) 316193323Sed if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType())) 317193323Sed V1 = CE->getOperand(0); 318193323Sed if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2)) 319193323Sed if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType())) 320193323Sed V2 = CE->getOperand(0); 321193323Sed 322193323Sed // Are we checking for alias of the same value? 323193323Sed if (V1 == V2) return MustAlias; 324193323Sed 325193323Sed if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) 326193323Sed return NoAlias; // Scalars cannot alias each other 327193323Sed 328193323Sed // Strip off cast instructions. Since V1 and V2 are pointers, they must be 329193323Sed // pointer<->pointer bitcasts. 330193323Sed if (const BitCastInst *I = dyn_cast<BitCastInst>(V1)) 331193323Sed return alias(I->getOperand(0), V1Size, V2, V2Size); 332193323Sed if (const BitCastInst *I = dyn_cast<BitCastInst>(V2)) 333193323Sed return alias(V1, V1Size, I->getOperand(0), V2Size); 334193323Sed 335193323Sed // Figure out what objects these things are pointing to if we can. 336193323Sed const Value *O1 = V1->getUnderlyingObject(); 337193323Sed const Value *O2 = V2->getUnderlyingObject(); 338193323Sed 339193323Sed if (O1 != O2) { 340193323Sed // If V1/V2 point to two different objects we know that we have no alias. 341193323Sed if (isIdentifiedObject(O1) && isIdentifiedObject(O2)) 342193323Sed return NoAlias; 343193323Sed 344193323Sed // Arguments can't alias with local allocations or noalias calls. 345193323Sed if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) || 346193323Sed (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1)))) 347193323Sed return NoAlias; 348193323Sed 349193323Sed // Most objects can't alias null. 350193323Sed if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) || 351193323Sed (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2))) 352193323Sed return NoAlias; 353193323Sed } 354193323Sed 355193323Sed // If the size of one access is larger than the entire object on the other 356193323Sed // side, then we know such behavior is undefined and can assume no alias. 357193323Sed const TargetData &TD = getTargetData(); 358193323Sed if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) || 359193323Sed (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD))) 360193323Sed return NoAlias; 361193323Sed 362193323Sed // If one pointer is the result of a call/invoke and the other is a 363193323Sed // non-escaping local object, then we know the object couldn't escape to a 364193323Sed // point where the call could return it. 365193323Sed if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) && 366193323Sed isNonEscapingLocalObject(O2) && O1 != O2) 367193323Sed return NoAlias; 368193323Sed if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) && 369193323Sed isNonEscapingLocalObject(O1) && O1 != O2) 370193323Sed return NoAlias; 371193323Sed 372193323Sed // If we have two gep instructions with must-alias'ing base pointers, figure 373193323Sed // out if the indexes to the GEP tell us anything about the derived pointer. 374193323Sed // Note that we also handle chains of getelementptr instructions as well as 375193323Sed // constant expression getelementptrs here. 376193323Sed // 377193323Sed if (isGEP(V1) && isGEP(V2)) { 378193323Sed const User *GEP1 = cast<User>(V1); 379193323Sed const User *GEP2 = cast<User>(V2); 380193323Sed 381193323Sed // If V1 and V2 are identical GEPs, just recurse down on both of them. 382193323Sed // This allows us to analyze things like: 383193323Sed // P = gep A, 0, i, 1 384193323Sed // Q = gep B, 0, i, 1 385193323Sed // by just analyzing A and B. This is even safe for variable indices. 386193323Sed if (GEP1->getType() == GEP2->getType() && 387193323Sed GEP1->getNumOperands() == GEP2->getNumOperands() && 388193323Sed GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() && 389193323Sed // All operands are the same, ignoring the base. 390193323Sed std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1)) 391193323Sed return alias(GEP1->getOperand(0), V1Size, GEP2->getOperand(0), V2Size); 392193323Sed 393193323Sed 394193323Sed // Drill down into the first non-gep value, to test for must-aliasing of 395193323Sed // the base pointers. 396193323Sed while (isGEP(GEP1->getOperand(0)) && 397193323Sed GEP1->getOperand(1) == 398193323Sed Constant::getNullValue(GEP1->getOperand(1)->getType())) 399193323Sed GEP1 = cast<User>(GEP1->getOperand(0)); 400193323Sed const Value *BasePtr1 = GEP1->getOperand(0); 401193323Sed 402193323Sed while (isGEP(GEP2->getOperand(0)) && 403193323Sed GEP2->getOperand(1) == 404193323Sed Constant::getNullValue(GEP2->getOperand(1)->getType())) 405193323Sed GEP2 = cast<User>(GEP2->getOperand(0)); 406193323Sed const Value *BasePtr2 = GEP2->getOperand(0); 407193323Sed 408193323Sed // Do the base pointers alias? 409193323Sed AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U); 410193323Sed if (BaseAlias == NoAlias) return NoAlias; 411193323Sed if (BaseAlias == MustAlias) { 412193323Sed // If the base pointers alias each other exactly, check to see if we can 413193323Sed // figure out anything about the resultant pointers, to try to prove 414193323Sed // non-aliasing. 415193323Sed 416193323Sed // Collect all of the chained GEP operands together into one simple place 417193323Sed SmallVector<Value*, 16> GEP1Ops, GEP2Ops; 418193323Sed BasePtr1 = GetGEPOperands(V1, GEP1Ops); 419193323Sed BasePtr2 = GetGEPOperands(V2, GEP2Ops); 420193323Sed 421193323Sed // If GetGEPOperands were able to fold to the same must-aliased pointer, 422193323Sed // do the comparison. 423193323Sed if (BasePtr1 == BasePtr2) { 424193323Sed AliasResult GAlias = 425193323Sed CheckGEPInstructions(BasePtr1->getType(), 426193323Sed &GEP1Ops[0], GEP1Ops.size(), V1Size, 427193323Sed BasePtr2->getType(), 428193323Sed &GEP2Ops[0], GEP2Ops.size(), V2Size); 429193323Sed if (GAlias != MayAlias) 430193323Sed return GAlias; 431193323Sed } 432193323Sed } 433193323Sed } 434193323Sed 435193323Sed // Check to see if these two pointers are related by a getelementptr 436193323Sed // instruction. If one pointer is a GEP with a non-zero index of the other 437193323Sed // pointer, we know they cannot alias. 438193323Sed // 439193323Sed if (isGEP(V2)) { 440193323Sed std::swap(V1, V2); 441193323Sed std::swap(V1Size, V2Size); 442193323Sed } 443193323Sed 444193323Sed if (V1Size != ~0U && V2Size != ~0U) 445193323Sed if (isGEP(V1)) { 446193323Sed SmallVector<Value*, 16> GEPOperands; 447193323Sed const Value *BasePtr = GetGEPOperands(V1, GEPOperands); 448193323Sed 449193323Sed AliasResult R = alias(BasePtr, V1Size, V2, V2Size); 450193323Sed if (R == MustAlias) { 451193323Sed // If there is at least one non-zero constant index, we know they cannot 452193323Sed // alias. 453193323Sed bool ConstantFound = false; 454193323Sed bool AllZerosFound = true; 455193323Sed for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i) 456193323Sed if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) { 457193323Sed if (!C->isNullValue()) { 458193323Sed ConstantFound = true; 459193323Sed AllZerosFound = false; 460193323Sed break; 461193323Sed } 462193323Sed } else { 463193323Sed AllZerosFound = false; 464193323Sed } 465193323Sed 466193323Sed // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases 467193323Sed // the ptr, the end result is a must alias also. 468193323Sed if (AllZerosFound) 469193323Sed return MustAlias; 470193323Sed 471193323Sed if (ConstantFound) { 472193323Sed if (V2Size <= 1 && V1Size <= 1) // Just pointer check? 473193323Sed return NoAlias; 474193323Sed 475193323Sed // Otherwise we have to check to see that the distance is more than 476193323Sed // the size of the argument... build an index vector that is equal to 477193323Sed // the arguments provided, except substitute 0's for any variable 478193323Sed // indexes we find... 479193323Sed if (cast<PointerType>( 480193323Sed BasePtr->getType())->getElementType()->isSized()) { 481193323Sed for (unsigned i = 0; i != GEPOperands.size(); ++i) 482193323Sed if (!isa<ConstantInt>(GEPOperands[i])) 483193323Sed GEPOperands[i] = 484193323Sed Constant::getNullValue(GEPOperands[i]->getType()); 485193323Sed int64_t Offset = 486193323Sed getTargetData().getIndexedOffset(BasePtr->getType(), 487193323Sed &GEPOperands[0], 488193323Sed GEPOperands.size()); 489193323Sed 490193323Sed if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size) 491193323Sed return NoAlias; 492193323Sed } 493193323Sed } 494193323Sed } 495193323Sed } 496193323Sed 497193323Sed return MayAlias; 498193323Sed} 499193323Sed 500193323Sed// This function is used to determine if the indices of two GEP instructions are 501193323Sed// equal. V1 and V2 are the indices. 502193323Sedstatic bool IndexOperandsEqual(Value *V1, Value *V2) { 503193323Sed if (V1->getType() == V2->getType()) 504193323Sed return V1 == V2; 505193323Sed if (Constant *C1 = dyn_cast<Constant>(V1)) 506193323Sed if (Constant *C2 = dyn_cast<Constant>(V2)) { 507193323Sed // Sign extend the constants to long types, if necessary 508193323Sed if (C1->getType() != Type::Int64Ty) 509193323Sed C1 = ConstantExpr::getSExt(C1, Type::Int64Ty); 510193323Sed if (C2->getType() != Type::Int64Ty) 511193323Sed C2 = ConstantExpr::getSExt(C2, Type::Int64Ty); 512193323Sed return C1 == C2; 513193323Sed } 514193323Sed return false; 515193323Sed} 516193323Sed 517193323Sed/// CheckGEPInstructions - Check two GEP instructions with known must-aliasing 518193323Sed/// base pointers. This checks to see if the index expressions preclude the 519193323Sed/// pointers from aliasing... 520193323SedAliasAnalysis::AliasResult 521193323SedBasicAliasAnalysis::CheckGEPInstructions( 522193323Sed const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S, 523193323Sed const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) { 524193323Sed // We currently can't handle the case when the base pointers have different 525193323Sed // primitive types. Since this is uncommon anyway, we are happy being 526193323Sed // extremely conservative. 527193323Sed if (BasePtr1Ty != BasePtr2Ty) 528193323Sed return MayAlias; 529193323Sed 530193323Sed const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty); 531193323Sed 532193323Sed // Find the (possibly empty) initial sequence of equal values... which are not 533193323Sed // necessarily constants. 534193323Sed unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops; 535193323Sed unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands); 536193323Sed unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands); 537193323Sed unsigned UnequalOper = 0; 538193323Sed while (UnequalOper != MinOperands && 539193323Sed IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) { 540193323Sed // Advance through the type as we go... 541193323Sed ++UnequalOper; 542193323Sed if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty)) 543193323Sed BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]); 544193323Sed else { 545193323Sed // If all operands equal each other, then the derived pointers must 546193323Sed // alias each other... 547193323Sed BasePtr1Ty = 0; 548193323Sed assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands && 549193323Sed "Ran out of type nesting, but not out of operands?"); 550193323Sed return MustAlias; 551193323Sed } 552193323Sed } 553193323Sed 554193323Sed // If we have seen all constant operands, and run out of indexes on one of the 555193323Sed // getelementptrs, check to see if the tail of the leftover one is all zeros. 556193323Sed // If so, return mustalias. 557193323Sed if (UnequalOper == MinOperands) { 558193323Sed if (NumGEP1Ops < NumGEP2Ops) { 559193323Sed std::swap(GEP1Ops, GEP2Ops); 560193323Sed std::swap(NumGEP1Ops, NumGEP2Ops); 561193323Sed } 562193323Sed 563193323Sed bool AllAreZeros = true; 564193323Sed for (unsigned i = UnequalOper; i != MaxOperands; ++i) 565193323Sed if (!isa<Constant>(GEP1Ops[i]) || 566193323Sed !cast<Constant>(GEP1Ops[i])->isNullValue()) { 567193323Sed AllAreZeros = false; 568193323Sed break; 569193323Sed } 570193323Sed if (AllAreZeros) return MustAlias; 571193323Sed } 572193323Sed 573193323Sed 574193323Sed // So now we know that the indexes derived from the base pointers, 575193323Sed // which are known to alias, are different. We can still determine a 576193323Sed // no-alias result if there are differing constant pairs in the index 577193323Sed // chain. For example: 578193323Sed // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S)) 579193323Sed // 580193323Sed // We have to be careful here about array accesses. In particular, consider: 581193323Sed // A[1][0] vs A[0][i] 582193323Sed // In this case, we don't *know* that the array will be accessed in bounds: 583193323Sed // the index could even be negative. Because of this, we have to 584193323Sed // conservatively *give up* and return may alias. We disregard differing 585193323Sed // array subscripts that are followed by a variable index without going 586193323Sed // through a struct. 587193323Sed // 588193323Sed unsigned SizeMax = std::max(G1S, G2S); 589193323Sed if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work. 590193323Sed 591193323Sed // Scan for the first operand that is constant and unequal in the 592193323Sed // two getelementptrs... 593193323Sed unsigned FirstConstantOper = UnequalOper; 594193323Sed for (; FirstConstantOper != MinOperands; ++FirstConstantOper) { 595193323Sed const Value *G1Oper = GEP1Ops[FirstConstantOper]; 596193323Sed const Value *G2Oper = GEP2Ops[FirstConstantOper]; 597193323Sed 598193323Sed if (G1Oper != G2Oper) // Found non-equal constant indexes... 599193323Sed if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper))) 600193323Sed if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){ 601193323Sed if (G1OC->getType() != G2OC->getType()) { 602193323Sed // Sign extend both operands to long. 603193323Sed if (G1OC->getType() != Type::Int64Ty) 604193323Sed G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty); 605193323Sed if (G2OC->getType() != Type::Int64Ty) 606193323Sed G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty); 607193323Sed GEP1Ops[FirstConstantOper] = G1OC; 608193323Sed GEP2Ops[FirstConstantOper] = G2OC; 609193323Sed } 610193323Sed 611193323Sed if (G1OC != G2OC) { 612193323Sed // Handle the "be careful" case above: if this is an array/vector 613193323Sed // subscript, scan for a subsequent variable array index. 614193323Sed if (const SequentialType *STy = 615193323Sed dyn_cast<SequentialType>(BasePtr1Ty)) { 616193323Sed const Type *NextTy = STy; 617193323Sed bool isBadCase = false; 618193323Sed 619193323Sed for (unsigned Idx = FirstConstantOper; 620193323Sed Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) { 621193323Sed const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx]; 622193323Sed if (!isa<Constant>(V1) || !isa<Constant>(V2)) { 623193323Sed isBadCase = true; 624193323Sed break; 625193323Sed } 626193323Sed // If the array is indexed beyond the bounds of the static type 627193323Sed // at this level, it will also fall into the "be careful" case. 628193323Sed // It would theoretically be possible to analyze these cases, 629193323Sed // but for now just be conservatively correct. 630193323Sed if (const ArrayType *ATy = dyn_cast<ArrayType>(STy)) 631193323Sed if (cast<ConstantInt>(G1OC)->getZExtValue() >= 632193323Sed ATy->getNumElements() || 633193323Sed cast<ConstantInt>(G2OC)->getZExtValue() >= 634193323Sed ATy->getNumElements()) { 635193323Sed isBadCase = true; 636193323Sed break; 637193323Sed } 638193323Sed if (const VectorType *VTy = dyn_cast<VectorType>(STy)) 639193323Sed if (cast<ConstantInt>(G1OC)->getZExtValue() >= 640193323Sed VTy->getNumElements() || 641193323Sed cast<ConstantInt>(G2OC)->getZExtValue() >= 642193323Sed VTy->getNumElements()) { 643193323Sed isBadCase = true; 644193323Sed break; 645193323Sed } 646193323Sed STy = cast<SequentialType>(NextTy); 647193323Sed NextTy = cast<SequentialType>(NextTy)->getElementType(); 648193323Sed } 649193323Sed 650193323Sed if (isBadCase) G1OC = 0; 651193323Sed } 652193323Sed 653193323Sed // Make sure they are comparable (ie, not constant expressions), and 654193323Sed // make sure the GEP with the smaller leading constant is GEP1. 655193323Sed if (G1OC) { 656193323Sed Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT, 657193323Sed G1OC, G2OC); 658193323Sed if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) { 659193323Sed if (CV->getZExtValue()) { // If they are comparable and G2 > G1 660193323Sed std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2 661193323Sed std::swap(NumGEP1Ops, NumGEP2Ops); 662193323Sed } 663193323Sed break; 664193323Sed } 665193323Sed } 666193323Sed } 667193323Sed } 668193323Sed BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper); 669193323Sed } 670193323Sed 671193323Sed // No shared constant operands, and we ran out of common operands. At this 672193323Sed // point, the GEP instructions have run through all of their operands, and we 673193323Sed // haven't found evidence that there are any deltas between the GEP's. 674193323Sed // However, one GEP may have more operands than the other. If this is the 675193323Sed // case, there may still be hope. Check this now. 676193323Sed if (FirstConstantOper == MinOperands) { 677193323Sed // Make GEP1Ops be the longer one if there is a longer one. 678193323Sed if (NumGEP1Ops < NumGEP2Ops) { 679193323Sed std::swap(GEP1Ops, GEP2Ops); 680193323Sed std::swap(NumGEP1Ops, NumGEP2Ops); 681193323Sed } 682193323Sed 683193323Sed // Is there anything to check? 684193323Sed if (NumGEP1Ops > MinOperands) { 685193323Sed for (unsigned i = FirstConstantOper; i != MaxOperands; ++i) 686193323Sed if (isa<ConstantInt>(GEP1Ops[i]) && 687193323Sed !cast<ConstantInt>(GEP1Ops[i])->isZero()) { 688193323Sed // Yup, there's a constant in the tail. Set all variables to 689193323Sed // constants in the GEP instruction to make it suitable for 690193323Sed // TargetData::getIndexedOffset. 691193323Sed for (i = 0; i != MaxOperands; ++i) 692193323Sed if (!isa<ConstantInt>(GEP1Ops[i])) 693193323Sed GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType()); 694193323Sed // Okay, now get the offset. This is the relative offset for the full 695193323Sed // instruction. 696193323Sed const TargetData &TD = getTargetData(); 697193323Sed int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops, 698193323Sed NumGEP1Ops); 699193323Sed 700193323Sed // Now check without any constants at the end. 701193323Sed int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops, 702193323Sed MinOperands); 703193323Sed 704193323Sed // Make sure we compare the absolute difference. 705193323Sed if (Offset1 > Offset2) 706193323Sed std::swap(Offset1, Offset2); 707193323Sed 708193323Sed // If the tail provided a bit enough offset, return noalias! 709193323Sed if ((uint64_t)(Offset2-Offset1) >= SizeMax) 710193323Sed return NoAlias; 711193323Sed // Otherwise break - we don't look for another constant in the tail. 712193323Sed break; 713193323Sed } 714193323Sed } 715193323Sed 716193323Sed // Couldn't find anything useful. 717193323Sed return MayAlias; 718193323Sed } 719193323Sed 720193323Sed // If there are non-equal constants arguments, then we can figure 721193323Sed // out a minimum known delta between the two index expressions... at 722193323Sed // this point we know that the first constant index of GEP1 is less 723193323Sed // than the first constant index of GEP2. 724193323Sed 725193323Sed // Advance BasePtr[12]Ty over this first differing constant operand. 726193323Sed BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)-> 727193323Sed getTypeAtIndex(GEP2Ops[FirstConstantOper]); 728193323Sed BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)-> 729193323Sed getTypeAtIndex(GEP1Ops[FirstConstantOper]); 730193323Sed 731193323Sed // We are going to be using TargetData::getIndexedOffset to determine the 732193323Sed // offset that each of the GEP's is reaching. To do this, we have to convert 733193323Sed // all variable references to constant references. To do this, we convert the 734193323Sed // initial sequence of array subscripts into constant zeros to start with. 735193323Sed const Type *ZeroIdxTy = GEPPointerTy; 736193323Sed for (unsigned i = 0; i != FirstConstantOper; ++i) { 737193323Sed if (!isa<StructType>(ZeroIdxTy)) 738193323Sed GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty); 739193323Sed 740193323Sed if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy)) 741193323Sed ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]); 742193323Sed } 743193323Sed 744193323Sed // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok 745193323Sed 746193323Sed // Loop over the rest of the operands... 747193323Sed for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) { 748193323Sed const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0; 749193323Sed const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0; 750193323Sed // If they are equal, use a zero index... 751193323Sed if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) { 752193323Sed if (!isa<ConstantInt>(Op1)) 753193323Sed GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType()); 754193323Sed // Otherwise, just keep the constants we have. 755193323Sed } else { 756193323Sed if (Op1) { 757193323Sed if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { 758193323Sed // If this is an array index, make sure the array element is in range. 759193323Sed if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) { 760193323Sed if (Op1C->getZExtValue() >= AT->getNumElements()) 761193323Sed return MayAlias; // Be conservative with out-of-range accesses 762193323Sed } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) { 763193323Sed if (Op1C->getZExtValue() >= VT->getNumElements()) 764193323Sed return MayAlias; // Be conservative with out-of-range accesses 765193323Sed } 766193323Sed 767193323Sed } else { 768193323Sed // GEP1 is known to produce a value less than GEP2. To be 769193323Sed // conservatively correct, we must assume the largest possible 770193323Sed // constant is used in this position. This cannot be the initial 771193323Sed // index to the GEP instructions (because we know we have at least one 772193323Sed // element before this one with the different constant arguments), so 773193323Sed // we know that the current index must be into either a struct or 774193323Sed // array. Because we know it's not constant, this cannot be a 775193323Sed // structure index. Because of this, we can calculate the maximum 776193323Sed // value possible. 777193323Sed // 778193323Sed if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) 779193323Sed GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1); 780193323Sed else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) 781193323Sed GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1); 782193323Sed } 783193323Sed } 784193323Sed 785193323Sed if (Op2) { 786193323Sed if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) { 787193323Sed // If this is an array index, make sure the array element is in range. 788193323Sed if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) { 789193323Sed if (Op2C->getZExtValue() >= AT->getNumElements()) 790193323Sed return MayAlias; // Be conservative with out-of-range accesses 791193323Sed } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) { 792193323Sed if (Op2C->getZExtValue() >= VT->getNumElements()) 793193323Sed return MayAlias; // Be conservative with out-of-range accesses 794193323Sed } 795193323Sed } else { // Conservatively assume the minimum value for this index 796193323Sed GEP2Ops[i] = Constant::getNullValue(Op2->getType()); 797193323Sed } 798193323Sed } 799193323Sed } 800193323Sed 801193323Sed if (BasePtr1Ty && Op1) { 802193323Sed if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty)) 803193323Sed BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]); 804193323Sed else 805193323Sed BasePtr1Ty = 0; 806193323Sed } 807193323Sed 808193323Sed if (BasePtr2Ty && Op2) { 809193323Sed if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty)) 810193323Sed BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]); 811193323Sed else 812193323Sed BasePtr2Ty = 0; 813193323Sed } 814193323Sed } 815193323Sed 816193323Sed if (GEPPointerTy->getElementType()->isSized()) { 817193323Sed int64_t Offset1 = 818193323Sed getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops); 819193323Sed int64_t Offset2 = 820193323Sed getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops); 821193323Sed assert(Offset1 != Offset2 && 822193323Sed "There is at least one different constant here!"); 823193323Sed 824193323Sed // Make sure we compare the absolute difference. 825193323Sed if (Offset1 > Offset2) 826193323Sed std::swap(Offset1, Offset2); 827193323Sed 828193323Sed if ((uint64_t)(Offset2-Offset1) >= SizeMax) { 829193323Sed //cerr << "Determined that these two GEP's don't alias [" 830193323Sed // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2; 831193323Sed return NoAlias; 832193323Sed } 833193323Sed } 834193323Sed return MayAlias; 835193323Sed} 836193323Sed 837193323Sed// Make sure that anything that uses AliasAnalysis pulls in this file... 838193323SedDEFINING_FILE_FOR(BasicAliasAnalysis) 839