1 //===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the primary stateless implementation of the
11 // Alias Analysis interface that implements identities (two different
12 // globals cannot alias, etc), but does no stateful analysis.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Analysis/AliasAnalysis.h"
17 #include "llvm/Analysis/Passes.h"
18 #include "llvm/Constants.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Function.h"
21 #include "llvm/GlobalAlias.h"
22 #include "llvm/GlobalVariable.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/IntrinsicInst.h"
25 #include "llvm/LLVMContext.h"
26 #include "llvm/Operator.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Analysis/CaptureTracking.h"
29 #include "llvm/Analysis/MemoryBuiltins.h"
30 #include "llvm/Analysis/InstructionSimplify.h"
31 #include "llvm/Analysis/ValueTracking.h"
32 #include "llvm/DataLayout.h"
33 #include "llvm/Target/TargetLibraryInfo.h"
34 #include "llvm/ADT/SmallPtrSet.h"
35 #include "llvm/ADT/SmallVector.h"
36 #include "llvm/Support/ErrorHandling.h"
37 #include "llvm/Support/GetElementPtrTypeIterator.h"
41 //===----------------------------------------------------------------------===//
43 //===----------------------------------------------------------------------===//
45 /// isNonEscapingLocalObject - Return true if the pointer is to a function-local
46 /// object that never escapes from the function.
47 static bool isNonEscapingLocalObject(const Value *V) {
48 // If this is a local allocation, check to see if it escapes.
49 if (isa<AllocaInst>(V) || isNoAliasCall(V))
50 // Set StoreCaptures to True so that we can assume in our callers that the
51 // pointer is not the result of a load instruction. Currently
52 // PointerMayBeCaptured doesn't have any special analysis for the
53 // StoreCaptures=false case; if it did, our callers could be refined to be
55 return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
57 // If this is an argument that corresponds to a byval or noalias argument,
58 // then it has not escaped before entering the function. Check if it escapes
59 // inside the function.
60 if (const Argument *A = dyn_cast<Argument>(V))
61 if (A->hasByValAttr() || A->hasNoAliasAttr()) {
62 // Don't bother analyzing arguments already known not to escape.
63 if (A->hasNoCaptureAttr())
65 return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
70 /// isEscapeSource - Return true if the pointer is one which would have
71 /// been considered an escape by isNonEscapingLocalObject.
72 static bool isEscapeSource(const Value *V) {
73 if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V))
76 // The load case works because isNonEscapingLocalObject considers all
77 // stores to be escapes (it passes true for the StoreCaptures argument
78 // to PointerMayBeCaptured).
85 /// getObjectSize - Return the size of the object specified by V, or
86 /// UnknownSize if unknown.
87 static uint64_t getObjectSize(const Value *V, const DataLayout &TD,
88 const TargetLibraryInfo &TLI,
89 bool RoundToAlign = false) {
91 if (getObjectSize(V, Size, &TD, &TLI, RoundToAlign))
93 return AliasAnalysis::UnknownSize;
96 /// isObjectSmallerThan - Return true if we can prove that the object specified
97 /// by V is smaller than Size.
98 static bool isObjectSmallerThan(const Value *V, uint64_t Size,
100 const TargetLibraryInfo &TLI) {
101 // This function needs to use the aligned object size because we allow
102 // reads a bit past the end given sufficient alignment.
103 uint64_t ObjectSize = getObjectSize(V, TD, TLI, /*RoundToAlign*/true);
105 return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size;
108 /// isObjectSize - Return true if we can prove that the object specified
109 /// by V has size Size.
110 static bool isObjectSize(const Value *V, uint64_t Size,
111 const DataLayout &TD, const TargetLibraryInfo &TLI) {
112 uint64_t ObjectSize = getObjectSize(V, TD, TLI);
113 return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size;
116 //===----------------------------------------------------------------------===//
117 // GetElementPtr Instruction Decomposition and Analysis
118 //===----------------------------------------------------------------------===//
127 struct VariableGEPIndex {
129 ExtensionKind Extension;
132 bool operator==(const VariableGEPIndex &Other) const {
133 return V == Other.V && Extension == Other.Extension &&
134 Scale == Other.Scale;
137 bool operator!=(const VariableGEPIndex &Other) const {
138 return !operator==(Other);
144 /// GetLinearExpression - Analyze the specified value as a linear expression:
145 /// "A*V + B", where A and B are constant integers. Return the scale and offset
146 /// values as APInts and return V as a Value*, and return whether we looked
147 /// through any sign or zero extends. The incoming Value is known to have
148 /// IntegerType and it may already be sign or zero extended.
150 /// Note that this looks through extends, so the high bits may not be
151 /// represented in the result.
152 static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
153 ExtensionKind &Extension,
154 const DataLayout &TD, unsigned Depth) {
155 assert(V->getType()->isIntegerTy() && "Not an integer value");
157 // Limit our recursion depth.
164 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
165 if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
166 switch (BOp->getOpcode()) {
168 case Instruction::Or:
169 // X|C == X+C if all the bits in C are unset in X. Otherwise we can't
171 if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &TD))
174 case Instruction::Add:
175 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
177 Offset += RHSC->getValue();
179 case Instruction::Mul:
180 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
182 Offset *= RHSC->getValue();
183 Scale *= RHSC->getValue();
185 case Instruction::Shl:
186 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
188 Offset <<= RHSC->getValue().getLimitedValue();
189 Scale <<= RHSC->getValue().getLimitedValue();
195 // Since GEP indices are sign extended anyway, we don't care about the high
196 // bits of a sign or zero extended value - just scales and offsets. The
197 // extensions have to be consistent though.
198 if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) ||
199 (isa<ZExtInst>(V) && Extension != EK_SignExt)) {
200 Value *CastOp = cast<CastInst>(V)->getOperand(0);
201 unsigned OldWidth = Scale.getBitWidth();
202 unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
203 Scale = Scale.trunc(SmallWidth);
204 Offset = Offset.trunc(SmallWidth);
205 Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
207 Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension,
209 Scale = Scale.zext(OldWidth);
210 Offset = Offset.zext(OldWidth);
220 /// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it
221 /// into a base pointer with a constant offset and a number of scaled symbolic
224 /// The scaled symbolic offsets (represented by pairs of a Value* and a scale in
225 /// the VarIndices vector) are Value*'s that are known to be scaled by the
226 /// specified amount, but which may have other unrepresented high bits. As such,
227 /// the gep cannot necessarily be reconstructed from its decomposed form.
229 /// When DataLayout is around, this function is capable of analyzing everything
230 /// that GetUnderlyingObject can look through. When not, it just looks
231 /// through pointer casts.
234 DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
235 SmallVectorImpl<VariableGEPIndex> &VarIndices,
236 const DataLayout *TD) {
237 // Limit recursion depth to limit compile time in crazy cases.
238 unsigned MaxLookup = 6;
242 // See if this is a bitcast or GEP.
243 const Operator *Op = dyn_cast<Operator>(V);
245 // The only non-operator case we can handle are GlobalAliases.
246 if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
247 if (!GA->mayBeOverridden()) {
248 V = GA->getAliasee();
255 if (Op->getOpcode() == Instruction::BitCast) {
256 V = Op->getOperand(0);
260 const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
262 // If it's not a GEP, hand it off to SimplifyInstruction to see if it
263 // can come up with something. This matches what GetUnderlyingObject does.
264 if (const Instruction *I = dyn_cast<Instruction>(V))
265 // TODO: Get a DominatorTree and use it here.
266 if (const Value *Simplified =
267 SimplifyInstruction(const_cast<Instruction *>(I), TD)) {
275 // Don't attempt to analyze GEPs over unsized objects.
276 if (!cast<PointerType>(GEPOp->getOperand(0)->getType())
277 ->getElementType()->isSized())
280 // If we are lacking DataLayout information, we can't compute the offets of
281 // elements computed by GEPs. However, we can handle bitcast equivalent
284 if (!GEPOp->hasAllZeroIndices())
286 V = GEPOp->getOperand(0);
290 unsigned AS = GEPOp->getPointerAddressSpace();
291 // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
292 gep_type_iterator GTI = gep_type_begin(GEPOp);
293 for (User::const_op_iterator I = GEPOp->op_begin()+1,
294 E = GEPOp->op_end(); I != E; ++I) {
296 // Compute the (potentially symbolic) offset in bytes for this index.
297 if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
298 // For a struct, add the member offset.
299 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
300 if (FieldNo == 0) continue;
302 BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo);
306 // For an array/pointer, add the element offset, explicitly scaled.
307 if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
308 if (CIdx->isZero()) continue;
309 BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
313 uint64_t Scale = TD->getTypeAllocSize(*GTI);
314 ExtensionKind Extension = EK_NotExtended;
316 // If the integer type is smaller than the pointer size, it is implicitly
317 // sign extended to pointer size.
318 unsigned Width = cast<IntegerType>(Index->getType())->getBitWidth();
319 if (TD->getPointerSizeInBits(AS) > Width)
320 Extension = EK_SignExt;
322 // Use GetLinearExpression to decompose the index into a C1*V+C2 form.
323 APInt IndexScale(Width, 0), IndexOffset(Width, 0);
324 Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension,
327 // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
328 // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
329 BaseOffs += IndexOffset.getSExtValue()*Scale;
330 Scale *= IndexScale.getSExtValue();
333 // If we already had an occurrence of this index variable, merge this
334 // scale into it. For example, we want to handle:
335 // A[x][x] -> x*16 + x*4 -> x*20
336 // This also ensures that 'x' only appears in the index list once.
337 for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
338 if (VarIndices[i].V == Index &&
339 VarIndices[i].Extension == Extension) {
340 Scale += VarIndices[i].Scale;
341 VarIndices.erase(VarIndices.begin()+i);
346 // Make sure that we have a scale that makes sense for this target's
348 if (unsigned ShiftBits = 64-TD->getPointerSizeInBits(AS)) {
350 Scale = (int64_t)Scale >> ShiftBits;
354 VariableGEPIndex Entry = {Index, Extension,
355 static_cast<int64_t>(Scale)};
356 VarIndices.push_back(Entry);
360 // Analyze the base pointer next.
361 V = GEPOp->getOperand(0);
362 } while (--MaxLookup);
364 // If the chain of expressions is too deep, just return early.
368 /// GetIndexDifference - Dest and Src are the variable indices from two
369 /// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
370 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
371 /// difference between the two pointers.
372 static void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
373 const SmallVectorImpl<VariableGEPIndex> &Src) {
374 if (Src.empty()) return;
376 for (unsigned i = 0, e = Src.size(); i != e; ++i) {
377 const Value *V = Src[i].V;
378 ExtensionKind Extension = Src[i].Extension;
379 int64_t Scale = Src[i].Scale;
381 // Find V in Dest. This is N^2, but pointer indices almost never have more
382 // than a few variable indexes.
383 for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
384 if (Dest[j].V != V || Dest[j].Extension != Extension) continue;
386 // If we found it, subtract off Scale V's from the entry in Dest. If it
387 // goes to zero, remove the entry.
388 if (Dest[j].Scale != Scale)
389 Dest[j].Scale -= Scale;
391 Dest.erase(Dest.begin()+j);
396 // If we didn't consume this entry, add it to the end of the Dest list.
398 VariableGEPIndex Entry = { V, Extension, -Scale };
399 Dest.push_back(Entry);
404 //===----------------------------------------------------------------------===//
405 // BasicAliasAnalysis Pass
406 //===----------------------------------------------------------------------===//
409 static const Function *getParent(const Value *V) {
410 if (const Instruction *inst = dyn_cast<Instruction>(V))
411 return inst->getParent()->getParent();
413 if (const Argument *arg = dyn_cast<Argument>(V))
414 return arg->getParent();
419 static bool notDifferentParent(const Value *O1, const Value *O2) {
421 const Function *F1 = getParent(O1);
422 const Function *F2 = getParent(O2);
424 return !F1 || !F2 || F1 == F2;
429 /// BasicAliasAnalysis - This is the primary alias analysis implementation.
430 struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
431 static char ID; // Class identification, replacement for typeinfo
432 BasicAliasAnalysis() : ImmutablePass(ID) {
433 initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
436 virtual void initializePass() {
437 InitializeAliasAnalysis(this);
440 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
441 AU.addRequired<AliasAnalysis>();
442 AU.addRequired<TargetLibraryInfo>();
445 virtual AliasResult alias(const Location &LocA,
446 const Location &LocB) {
447 assert(AliasCache.empty() && "AliasCache must be cleared after use!");
448 assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
449 "BasicAliasAnalysis doesn't support interprocedural queries.");
450 AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag,
451 LocB.Ptr, LocB.Size, LocB.TBAATag);
452 // AliasCache rarely has more than 1 or 2 elements, always use
453 // shrink_and_clear so it quickly returns to the inline capacity of the
454 // SmallDenseMap if it ever grows larger.
455 // FIXME: This should really be shrink_to_inline_capacity_and_clear().
456 AliasCache.shrink_and_clear();
460 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
461 const Location &Loc);
463 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
464 ImmutableCallSite CS2) {
465 // The AliasAnalysis base class has some smarts, lets use them.
466 return AliasAnalysis::getModRefInfo(CS1, CS2);
469 /// pointsToConstantMemory - Chase pointers until we find a (constant
471 virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal);
473 /// getModRefBehavior - Return the behavior when calling the given
475 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
477 /// getModRefBehavior - Return the behavior when calling the given function.
478 /// For use when the call site is not known.
479 virtual ModRefBehavior getModRefBehavior(const Function *F);
481 /// getAdjustedAnalysisPointer - This method is used when a pass implements
482 /// an analysis interface through multiple inheritance. If needed, it
483 /// should override this to adjust the this pointer as needed for the
484 /// specified pass info.
485 virtual void *getAdjustedAnalysisPointer(const void *ID) {
486 if (ID == &AliasAnalysis::ID)
487 return (AliasAnalysis*)this;
492 // AliasCache - Track alias queries to guard against recursion.
493 typedef std::pair<Location, Location> LocPair;
494 typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
495 AliasCacheTy AliasCache;
497 // Visited - Track instructions visited by pointsToConstantMemory.
498 SmallPtrSet<const Value*, 16> Visited;
500 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
501 // instruction against another.
502 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
503 const MDNode *V1TBAAInfo,
504 const Value *V2, uint64_t V2Size,
505 const MDNode *V2TBAAInfo,
506 const Value *UnderlyingV1, const Value *UnderlyingV2);
508 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
509 // instruction against another.
510 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
511 const MDNode *PNTBAAInfo,
512 const Value *V2, uint64_t V2Size,
513 const MDNode *V2TBAAInfo);
515 /// aliasSelect - Disambiguate a Select instruction against another value.
516 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
517 const MDNode *SITBAAInfo,
518 const Value *V2, uint64_t V2Size,
519 const MDNode *V2TBAAInfo);
521 AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
522 const MDNode *V1TBAATag,
523 const Value *V2, uint64_t V2Size,
524 const MDNode *V2TBAATag);
526 } // End of anonymous namespace
528 // Register this pass...
529 char BasicAliasAnalysis::ID = 0;
530 INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
531 "Basic Alias Analysis (stateless AA impl)",
533 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
534 INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
535 "Basic Alias Analysis (stateless AA impl)",
539 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
540 return new BasicAliasAnalysis();
543 /// pointsToConstantMemory - Returns whether the given pointer value
544 /// points to memory that is local to the function, with global constants being
545 /// considered local to all functions.
547 BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
548 assert(Visited.empty() && "Visited must be cleared after use!");
550 unsigned MaxLookup = 8;
551 SmallVector<const Value *, 16> Worklist;
552 Worklist.push_back(Loc.Ptr);
554 const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), TD);
555 if (!Visited.insert(V)) {
557 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
560 // An alloca instruction defines local memory.
561 if (OrLocal && isa<AllocaInst>(V))
564 // A global constant counts as local memory for our purposes.
565 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
566 // Note: this doesn't require GV to be "ODR" because it isn't legal for a
567 // global to be marked constant in some modules and non-constant in
568 // others. GV may even be a declaration, not a definition.
569 if (!GV->isConstant()) {
571 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
576 // If both select values point to local memory, then so does the select.
577 if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
578 Worklist.push_back(SI->getTrueValue());
579 Worklist.push_back(SI->getFalseValue());
583 // If all values incoming to a phi node point to local memory, then so does
585 if (const PHINode *PN = dyn_cast<PHINode>(V)) {
586 // Don't bother inspecting phi nodes with many operands.
587 if (PN->getNumIncomingValues() > MaxLookup) {
589 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
591 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
592 Worklist.push_back(PN->getIncomingValue(i));
596 // Otherwise be conservative.
598 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
600 } while (!Worklist.empty() && --MaxLookup);
603 return Worklist.empty();
606 /// getModRefBehavior - Return the behavior when calling the given call site.
607 AliasAnalysis::ModRefBehavior
608 BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
609 if (CS.doesNotAccessMemory())
610 // Can't do better than this.
611 return DoesNotAccessMemory;
613 ModRefBehavior Min = UnknownModRefBehavior;
615 // If the callsite knows it only reads memory, don't return worse
617 if (CS.onlyReadsMemory())
618 Min = OnlyReadsMemory;
620 // The AliasAnalysis base class has some smarts, lets use them.
621 return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
624 /// getModRefBehavior - Return the behavior when calling the given function.
625 /// For use when the call site is not known.
626 AliasAnalysis::ModRefBehavior
627 BasicAliasAnalysis::getModRefBehavior(const Function *F) {
628 // If the function declares it doesn't access memory, we can't do better.
629 if (F->doesNotAccessMemory())
630 return DoesNotAccessMemory;
632 // For intrinsics, we can check the table.
633 if (unsigned iid = F->getIntrinsicID()) {
634 #define GET_INTRINSIC_MODREF_BEHAVIOR
635 #include "llvm/Intrinsics.gen"
636 #undef GET_INTRINSIC_MODREF_BEHAVIOR
639 ModRefBehavior Min = UnknownModRefBehavior;
641 // If the function declares it only reads memory, go with that.
642 if (F->onlyReadsMemory())
643 Min = OnlyReadsMemory;
645 // Otherwise be conservative.
646 return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
649 /// getModRefInfo - Check to see if the specified callsite can clobber the
650 /// specified memory object. Since we only look at local properties of this
651 /// function, we really can't say much about this query. We do, however, use
652 /// simple "address taken" analysis on local objects.
653 AliasAnalysis::ModRefResult
654 BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
655 const Location &Loc) {
656 assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
657 "AliasAnalysis query involving multiple functions!");
659 const Value *Object = GetUnderlyingObject(Loc.Ptr, TD);
661 // If this is a tail call and Loc.Ptr points to a stack location, we know that
662 // the tail call cannot access or modify the local stack.
663 // We cannot exclude byval arguments here; these belong to the caller of
664 // the current function not to the current function, and a tail callee
665 // may reference them.
666 if (isa<AllocaInst>(Object))
667 if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
668 if (CI->isTailCall())
671 // If the pointer is to a locally allocated object that does not escape,
672 // then the call can not mod/ref the pointer unless the call takes the pointer
673 // as an argument, and itself doesn't capture it.
674 if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
675 isNonEscapingLocalObject(Object)) {
676 bool PassedAsArg = false;
678 for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
679 CI != CE; ++CI, ++ArgNo) {
680 // Only look at the no-capture or byval pointer arguments. If this
681 // pointer were passed to arguments that were neither of these, then it
682 // couldn't be no-capture.
683 if (!(*CI)->getType()->isPointerTy() ||
684 (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
687 // If this is a no-capture pointer argument, see if we can tell that it
688 // is impossible to alias the pointer we're checking. If not, we have to
689 // assume that the call could touch the pointer, even though it doesn't
691 if (!isNoAlias(Location(*CI), Location(Object))) {
701 const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
702 ModRefResult Min = ModRef;
704 // Finally, handle specific knowledge of intrinsics.
705 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
707 switch (II->getIntrinsicID()) {
709 case Intrinsic::memcpy:
710 case Intrinsic::memmove: {
711 uint64_t Len = UnknownSize;
712 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
713 Len = LenCI->getZExtValue();
714 Value *Dest = II->getArgOperand(0);
715 Value *Src = II->getArgOperand(1);
716 // If it can't overlap the source dest, then it doesn't modref the loc.
717 if (isNoAlias(Location(Dest, Len), Loc)) {
718 if (isNoAlias(Location(Src, Len), Loc))
720 // If it can't overlap the dest, then worst case it reads the loc.
722 } else if (isNoAlias(Location(Src, Len), Loc)) {
723 // If it can't overlap the source, then worst case it mutates the loc.
728 case Intrinsic::memset:
729 // Since memset is 'accesses arguments' only, the AliasAnalysis base class
730 // will handle it for the variable length case.
731 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2))) {
732 uint64_t Len = LenCI->getZExtValue();
733 Value *Dest = II->getArgOperand(0);
734 if (isNoAlias(Location(Dest, Len), Loc))
737 // We know that memset doesn't load anything.
740 case Intrinsic::lifetime_start:
741 case Intrinsic::lifetime_end:
742 case Intrinsic::invariant_start: {
744 cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
745 if (isNoAlias(Location(II->getArgOperand(1),
747 II->getMetadata(LLVMContext::MD_tbaa)),
752 case Intrinsic::invariant_end: {
754 cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
755 if (isNoAlias(Location(II->getArgOperand(2),
757 II->getMetadata(LLVMContext::MD_tbaa)),
762 case Intrinsic::arm_neon_vld1: {
763 // LLVM's vld1 and vst1 intrinsics currently only support a single
766 TD ? TD->getTypeStoreSize(II->getType()) : UnknownSize;
767 if (isNoAlias(Location(II->getArgOperand(0), Size,
768 II->getMetadata(LLVMContext::MD_tbaa)),
773 case Intrinsic::arm_neon_vst1: {
775 TD ? TD->getTypeStoreSize(II->getArgOperand(1)->getType()) : UnknownSize;
776 if (isNoAlias(Location(II->getArgOperand(0), Size,
777 II->getMetadata(LLVMContext::MD_tbaa)),
784 // We can bound the aliasing properties of memset_pattern16 just as we can
785 // for memcpy/memset. This is particularly important because the
786 // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
787 // whenever possible.
788 else if (TLI.has(LibFunc::memset_pattern16) &&
789 CS.getCalledFunction() &&
790 CS.getCalledFunction()->getName() == "memset_pattern16") {
791 const Function *MS = CS.getCalledFunction();
792 FunctionType *MemsetType = MS->getFunctionType();
793 if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
794 isa<PointerType>(MemsetType->getParamType(0)) &&
795 isa<PointerType>(MemsetType->getParamType(1)) &&
796 isa<IntegerType>(MemsetType->getParamType(2))) {
797 uint64_t Len = UnknownSize;
798 if (const ConstantInt *LenCI = dyn_cast<ConstantInt>(CS.getArgument(2)))
799 Len = LenCI->getZExtValue();
800 const Value *Dest = CS.getArgument(0);
801 const Value *Src = CS.getArgument(1);
802 // If it can't overlap the source dest, then it doesn't modref the loc.
803 if (isNoAlias(Location(Dest, Len), Loc)) {
804 // Always reads 16 bytes of the source.
805 if (isNoAlias(Location(Src, 16), Loc))
807 // If it can't overlap the dest, then worst case it reads the loc.
809 // Always reads 16 bytes of the source.
810 } else if (isNoAlias(Location(Src, 16), Loc)) {
811 // If it can't overlap the source, then worst case it mutates the loc.
817 // The AliasAnalysis base class has some smarts, lets use them.
818 return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min);
821 static bool areVarIndicesEqual(SmallVector<VariableGEPIndex, 4> &Indices1,
822 SmallVector<VariableGEPIndex, 4> &Indices2) {
823 unsigned Size1 = Indices1.size();
824 unsigned Size2 = Indices2.size();
829 for (unsigned I = 0; I != Size1; ++I)
830 if (Indices1[I] != Indices2[I])
836 /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
837 /// against another pointer. We know that V1 is a GEP, but we don't know
838 /// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, TD),
839 /// UnderlyingV2 is the same for V2.
841 AliasAnalysis::AliasResult
842 BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
843 const MDNode *V1TBAAInfo,
844 const Value *V2, uint64_t V2Size,
845 const MDNode *V2TBAAInfo,
846 const Value *UnderlyingV1,
847 const Value *UnderlyingV2) {
848 int64_t GEP1BaseOffset;
849 SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
851 // If we have two gep instructions with must-alias or not-alias'ing base
852 // pointers, figure out if the indexes to the GEP tell us anything about the
854 if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
855 // Check for geps of non-aliasing underlying pointers where the offsets are
857 if (V1Size == V2Size) {
858 // Do the base pointers alias assuming type and size.
859 AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
860 V1TBAAInfo, UnderlyingV2,
862 if (PreciseBaseAlias == NoAlias) {
863 // See if the computed offset from the common pointer tells us about the
864 // relation of the resulting pointer.
865 int64_t GEP2BaseOffset;
866 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
867 const Value *GEP2BasePtr =
868 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
869 const Value *GEP1BasePtr =
870 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
871 // DecomposeGEPExpression and GetUnderlyingObject should return the
872 // same result except when DecomposeGEPExpression has no DataLayout.
873 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
875 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
879 if (GEP1BaseOffset == GEP2BaseOffset &&
880 areVarIndicesEqual(GEP1VariableIndices, GEP2VariableIndices))
882 GEP1VariableIndices.clear();
886 // Do the base pointers alias?
887 AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0,
888 UnderlyingV2, UnknownSize, 0);
890 // If we get a No or May, then return it immediately, no amount of analysis
891 // will improve this situation.
892 if (BaseAlias != MustAlias) return BaseAlias;
894 // Otherwise, we have a MustAlias. Since the base pointers alias each other
895 // exactly, see if the computed offset from the common pointer tells us
896 // about the relation of the resulting pointer.
897 const Value *GEP1BasePtr =
898 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
900 int64_t GEP2BaseOffset;
901 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
902 const Value *GEP2BasePtr =
903 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
905 // DecomposeGEPExpression and GetUnderlyingObject should return the
906 // same result except when DecomposeGEPExpression has no DataLayout.
907 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
909 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
913 // Subtract the GEP2 pointer from the GEP1 pointer to find out their
914 // symbolic difference.
915 GEP1BaseOffset -= GEP2BaseOffset;
916 GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
919 // Check to see if these two pointers are related by the getelementptr
920 // instruction. If one pointer is a GEP with a non-zero index of the other
921 // pointer, we know they cannot alias.
923 // If both accesses are unknown size, we can't do anything useful here.
924 if (V1Size == UnknownSize && V2Size == UnknownSize)
927 AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, 0,
928 V2, V2Size, V2TBAAInfo);
930 // If V2 may alias GEP base pointer, conservatively returns MayAlias.
931 // If V2 is known not to alias GEP base pointer, then the two values
932 // cannot alias per GEP semantics: "A pointer value formed from a
933 // getelementptr instruction is associated with the addresses associated
934 // with the first operand of the getelementptr".
937 const Value *GEP1BasePtr =
938 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
940 // DecomposeGEPExpression and GetUnderlyingObject should return the
941 // same result except when DecomposeGEPExpression has no DataLayout.
942 if (GEP1BasePtr != UnderlyingV1) {
944 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
949 // In the two GEP Case, if there is no difference in the offsets of the
950 // computed pointers, the resultant pointers are a must alias. This
951 // hapens when we have two lexically identical GEP's (for example).
953 // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
954 // must aliases the GEP, the end result is a must alias also.
955 if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
958 // If there is a constant difference between the pointers, but the difference
959 // is less than the size of the associated memory object, then we know
960 // that the objects are partially overlapping. If the difference is
961 // greater, we know they do not overlap.
962 if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
963 if (GEP1BaseOffset >= 0) {
964 if (V2Size != UnknownSize) {
965 if ((uint64_t)GEP1BaseOffset < V2Size)
970 if (V1Size != UnknownSize) {
971 if (-(uint64_t)GEP1BaseOffset < V1Size)
978 // Try to distinguish something like &A[i][1] against &A[42][0].
979 // Grab the least significant bit set in any of the scales.
980 if (!GEP1VariableIndices.empty()) {
982 for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
983 Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
984 Modulo = Modulo ^ (Modulo & (Modulo - 1));
986 // We can compute the difference between the two addresses
987 // mod Modulo. Check whether that difference guarantees that the
988 // two locations do not alias.
989 uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
990 if (V1Size != UnknownSize && V2Size != UnknownSize &&
991 ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
995 // Statically, we can see that the base objects are the same, but the
996 // pointers have dynamic offsets which we can't resolve. And none of our
997 // little tricks above worked.
999 // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
1000 // practical effect of this is protecting TBAA in the case of dynamic
1001 // indices into arrays of unions or malloc'd memory.
1002 return PartialAlias;
1005 static AliasAnalysis::AliasResult
1006 MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
1007 // If the results agree, take it.
1010 // A mix of PartialAlias and MustAlias is PartialAlias.
1011 if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
1012 (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
1013 return AliasAnalysis::PartialAlias;
1014 // Otherwise, we don't know anything.
1015 return AliasAnalysis::MayAlias;
1018 /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
1019 /// instruction against another.
1020 AliasAnalysis::AliasResult
1021 BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
1022 const MDNode *SITBAAInfo,
1023 const Value *V2, uint64_t V2Size,
1024 const MDNode *V2TBAAInfo) {
1025 // If the values are Selects with the same condition, we can do a more precise
1026 // check: just check for aliases between the values on corresponding arms.
1027 if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
1028 if (SI->getCondition() == SI2->getCondition()) {
1030 aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo,
1031 SI2->getTrueValue(), V2Size, V2TBAAInfo);
1032 if (Alias == MayAlias)
1034 AliasResult ThisAlias =
1035 aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
1036 SI2->getFalseValue(), V2Size, V2TBAAInfo);
1037 return MergeAliasResults(ThisAlias, Alias);
1040 // If both arms of the Select node NoAlias or MustAlias V2, then returns
1041 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1043 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo);
1044 if (Alias == MayAlias)
1047 AliasResult ThisAlias =
1048 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
1049 return MergeAliasResults(ThisAlias, Alias);
1052 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
1054 AliasAnalysis::AliasResult
1055 BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
1056 const MDNode *PNTBAAInfo,
1057 const Value *V2, uint64_t V2Size,
1058 const MDNode *V2TBAAInfo) {
1059 // If the values are PHIs in the same block, we can do a more precise
1060 // as well as efficient check: just check for aliases between the values
1061 // on corresponding edges.
1062 if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
1063 if (PN2->getParent() == PN->getParent()) {
1064 LocPair Locs(Location(PN, PNSize, PNTBAAInfo),
1065 Location(V2, V2Size, V2TBAAInfo));
1067 std::swap(Locs.first, Locs.second);
1070 aliasCheck(PN->getIncomingValue(0), PNSize, PNTBAAInfo,
1071 PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)),
1072 V2Size, V2TBAAInfo);
1073 if (Alias == MayAlias)
1076 // If the first source of the PHI nodes NoAlias and the other inputs are
1077 // the PHI node itself through some amount of recursion this does not add
1078 // any new information so just return NoAlias.
1082 // ptr_phi = phi [bb, ptr], [loop, ptr_plus_one]
1083 // ptr2_phi = phi [bb, ptr2], [loop, ptr2_plus_one]
1085 // ptr_plus_one = gep ptr_phi, 1
1086 // ptr2_plus_one = gep ptr2_phi, 1
1087 // We assume for the recursion that the the phis (ptr_phi, ptr2_phi) do
1088 // not alias each other.
1089 bool ArePhisAssumedNoAlias = false;
1090 AliasResult OrigAliasResult = NoAlias;
1091 if (Alias == NoAlias) {
1092 // Pretend the phis do not alias.
1093 assert(AliasCache.count(Locs) &&
1094 "There must exist an entry for the phi node");
1095 OrigAliasResult = AliasCache[Locs];
1096 AliasCache[Locs] = NoAlias;
1097 ArePhisAssumedNoAlias = true;
1100 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
1101 AliasResult ThisAlias =
1102 aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
1103 PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
1104 V2Size, V2TBAAInfo);
1105 Alias = MergeAliasResults(ThisAlias, Alias);
1106 if (Alias == MayAlias)
1110 // Reset if speculation failed.
1111 if (ArePhisAssumedNoAlias && Alias != NoAlias)
1112 AliasCache[Locs] = OrigAliasResult;
1117 SmallPtrSet<Value*, 4> UniqueSrc;
1118 SmallVector<Value*, 4> V1Srcs;
1119 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1120 Value *PV1 = PN->getIncomingValue(i);
1121 if (isa<PHINode>(PV1))
1122 // If any of the source itself is a PHI, return MayAlias conservatively
1123 // to avoid compile time explosion. The worst possible case is if both
1124 // sides are PHI nodes. In which case, this is O(m x n) time where 'm'
1125 // and 'n' are the number of PHI sources.
1127 if (UniqueSrc.insert(PV1))
1128 V1Srcs.push_back(PV1);
1131 AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo,
1132 V1Srcs[0], PNSize, PNTBAAInfo);
1133 // Early exit if the check of the first PHI source against V2 is MayAlias.
1134 // Other results are not possible.
1135 if (Alias == MayAlias)
1138 // If all sources of the PHI node NoAlias or MustAlias V2, then returns
1139 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1140 for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
1141 Value *V = V1Srcs[i];
1143 AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
1144 V, PNSize, PNTBAAInfo);
1145 Alias = MergeAliasResults(ThisAlias, Alias);
1146 if (Alias == MayAlias)
1153 // aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
1154 // such as array references.
1156 AliasAnalysis::AliasResult
1157 BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
1158 const MDNode *V1TBAAInfo,
1159 const Value *V2, uint64_t V2Size,
1160 const MDNode *V2TBAAInfo) {
1161 // If either of the memory references is empty, it doesn't matter what the
1162 // pointer values are.
1163 if (V1Size == 0 || V2Size == 0)
1166 // Strip off any casts if they exist.
1167 V1 = V1->stripPointerCasts();
1168 V2 = V2->stripPointerCasts();
1170 // Are we checking for alias of the same value?
1171 if (V1 == V2) return MustAlias;
1173 if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
1174 return NoAlias; // Scalars cannot alias each other
1176 // Figure out what objects these things are pointing to if we can.
1177 const Value *O1 = GetUnderlyingObject(V1, TD);
1178 const Value *O2 = GetUnderlyingObject(V2, TD);
1180 // Null values in the default address space don't point to any object, so they
1181 // don't alias any other pointer.
1182 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
1183 if (CPN->getType()->getAddressSpace() == 0)
1185 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
1186 if (CPN->getType()->getAddressSpace() == 0)
1190 // If V1/V2 point to two different objects we know that we have no alias.
1191 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
1194 // Constant pointers can't alias with non-const isIdentifiedObject objects.
1195 if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
1196 (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
1199 // Arguments can't alias with local allocations or noalias calls
1200 // in the same function.
1201 if (((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) ||
1202 (isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1)))))
1205 // Most objects can't alias null.
1206 if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
1207 (isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
1210 // If one pointer is the result of a call/invoke or load and the other is a
1211 // non-escaping local object within the same function, then we know the
1212 // object couldn't escape to a point where the call could return it.
1214 // Note that if the pointers are in different functions, there are a
1215 // variety of complications. A call with a nocapture argument may still
1216 // temporary store the nocapture argument's value in a temporary memory
1217 // location if that memory location doesn't escape. Or it may pass a
1218 // nocapture value to other functions as long as they don't capture it.
1219 if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
1221 if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
1225 // If the size of one access is larger than the entire object on the other
1226 // side, then we know such behavior is undefined and can assume no alias.
1228 if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD, *TLI)) ||
1229 (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD, *TLI)))
1232 // Check the cache before climbing up use-def chains. This also terminates
1233 // otherwise infinitely recursive queries.
1234 LocPair Locs(Location(V1, V1Size, V1TBAAInfo),
1235 Location(V2, V2Size, V2TBAAInfo));
1237 std::swap(Locs.first, Locs.second);
1238 std::pair<AliasCacheTy::iterator, bool> Pair =
1239 AliasCache.insert(std::make_pair(Locs, MayAlias));
1241 return Pair.first->second;
1243 // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
1244 // GEP can't simplify, we don't even look at the PHI cases.
1245 if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
1247 std::swap(V1Size, V2Size);
1250 if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
1251 AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2);
1252 if (Result != MayAlias) return AliasCache[Locs] = Result;
1255 if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
1257 std::swap(V1Size, V2Size);
1259 if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
1260 AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
1261 V2, V2Size, V2TBAAInfo);
1262 if (Result != MayAlias) return AliasCache[Locs] = Result;
1265 if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
1267 std::swap(V1Size, V2Size);
1269 if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
1270 AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
1271 V2, V2Size, V2TBAAInfo);
1272 if (Result != MayAlias) return AliasCache[Locs] = Result;
1275 // If both pointers are pointing into the same object and one of them
1276 // accesses is accessing the entire object, then the accesses must
1277 // overlap in some way.
1279 if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD, *TLI)) ||
1280 (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD, *TLI)))
1281 return AliasCache[Locs] = PartialAlias;
1283 AliasResult Result =
1284 AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
1285 Location(V2, V2Size, V2TBAAInfo));
1286 return AliasCache[Locs] = Result;