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/Passes.h"
17 #include "llvm/ADT/SmallPtrSet.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/Analysis/AliasAnalysis.h"
20 #include "llvm/Analysis/CaptureTracking.h"
21 #include "llvm/Analysis/InstructionSimplify.h"
22 #include "llvm/Analysis/MemoryBuiltins.h"
23 #include "llvm/Analysis/ValueTracking.h"
24 #include "llvm/Constants.h"
25 #include "llvm/DataLayout.h"
26 #include "llvm/DerivedTypes.h"
27 #include "llvm/Function.h"
28 #include "llvm/GlobalAlias.h"
29 #include "llvm/GlobalVariable.h"
30 #include "llvm/Instructions.h"
31 #include "llvm/IntrinsicInst.h"
32 #include "llvm/LLVMContext.h"
33 #include "llvm/Operator.h"
34 #include "llvm/Pass.h"
35 #include "llvm/Support/ErrorHandling.h"
36 #include "llvm/Support/GetElementPtrTypeIterator.h"
37 #include "llvm/Target/TargetLibraryInfo.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 // Note even if the argument is marked nocapture we still need to check
63 // for copies made inside the function. The nocapture attribute only
64 // specifies that there are no copies made that outlive the function.
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 // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
291 gep_type_iterator GTI = gep_type_begin(GEPOp);
292 for (User::const_op_iterator I = GEPOp->op_begin()+1,
293 E = GEPOp->op_end(); I != E; ++I) {
295 // Compute the (potentially symbolic) offset in bytes for this index.
296 if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
297 // For a struct, add the member offset.
298 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
299 if (FieldNo == 0) continue;
301 BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo);
305 // For an array/pointer, add the element offset, explicitly scaled.
306 if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
307 if (CIdx->isZero()) continue;
308 BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
312 uint64_t Scale = TD->getTypeAllocSize(*GTI);
313 ExtensionKind Extension = EK_NotExtended;
315 // If the integer type is smaller than the pointer size, it is implicitly
316 // sign extended to pointer size.
317 unsigned Width = cast<IntegerType>(Index->getType())->getBitWidth();
318 if (TD->getPointerSizeInBits() > Width)
319 Extension = EK_SignExt;
321 // Use GetLinearExpression to decompose the index into a C1*V+C2 form.
322 APInt IndexScale(Width, 0), IndexOffset(Width, 0);
323 Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension,
326 // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
327 // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
328 BaseOffs += IndexOffset.getSExtValue()*Scale;
329 Scale *= IndexScale.getSExtValue();
332 // If we already had an occurrence of this index variable, merge this
333 // scale into it. For example, we want to handle:
334 // A[x][x] -> x*16 + x*4 -> x*20
335 // This also ensures that 'x' only appears in the index list once.
336 for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
337 if (VarIndices[i].V == Index &&
338 VarIndices[i].Extension == Extension) {
339 Scale += VarIndices[i].Scale;
340 VarIndices.erase(VarIndices.begin()+i);
345 // Make sure that we have a scale that makes sense for this target's
347 if (unsigned ShiftBits = 64-TD->getPointerSizeInBits()) {
349 Scale = (int64_t)Scale >> ShiftBits;
353 VariableGEPIndex Entry = {Index, Extension,
354 static_cast<int64_t>(Scale)};
355 VarIndices.push_back(Entry);
359 // Analyze the base pointer next.
360 V = GEPOp->getOperand(0);
361 } while (--MaxLookup);
363 // If the chain of expressions is too deep, just return early.
367 /// GetIndexDifference - Dest and Src are the variable indices from two
368 /// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
369 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
370 /// difference between the two pointers.
371 static void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
372 const SmallVectorImpl<VariableGEPIndex> &Src) {
373 if (Src.empty()) return;
375 for (unsigned i = 0, e = Src.size(); i != e; ++i) {
376 const Value *V = Src[i].V;
377 ExtensionKind Extension = Src[i].Extension;
378 int64_t Scale = Src[i].Scale;
380 // Find V in Dest. This is N^2, but pointer indices almost never have more
381 // than a few variable indexes.
382 for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
383 if (Dest[j].V != V || Dest[j].Extension != Extension) continue;
385 // If we found it, subtract off Scale V's from the entry in Dest. If it
386 // goes to zero, remove the entry.
387 if (Dest[j].Scale != Scale)
388 Dest[j].Scale -= Scale;
390 Dest.erase(Dest.begin()+j);
395 // If we didn't consume this entry, add it to the end of the Dest list.
397 VariableGEPIndex Entry = { V, Extension, -Scale };
398 Dest.push_back(Entry);
403 //===----------------------------------------------------------------------===//
404 // BasicAliasAnalysis Pass
405 //===----------------------------------------------------------------------===//
408 static const Function *getParent(const Value *V) {
409 if (const Instruction *inst = dyn_cast<Instruction>(V))
410 return inst->getParent()->getParent();
412 if (const Argument *arg = dyn_cast<Argument>(V))
413 return arg->getParent();
418 static bool notDifferentParent(const Value *O1, const Value *O2) {
420 const Function *F1 = getParent(O1);
421 const Function *F2 = getParent(O2);
423 return !F1 || !F2 || F1 == F2;
428 /// BasicAliasAnalysis - This is the primary alias analysis implementation.
429 struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
430 static char ID; // Class identification, replacement for typeinfo
431 BasicAliasAnalysis() : ImmutablePass(ID) {
432 initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
435 virtual void initializePass() {
436 InitializeAliasAnalysis(this);
439 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
440 AU.addRequired<AliasAnalysis>();
441 AU.addRequired<TargetLibraryInfo>();
444 virtual AliasResult alias(const Location &LocA,
445 const Location &LocB) {
446 assert(AliasCache.empty() && "AliasCache must be cleared after use!");
447 assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
448 "BasicAliasAnalysis doesn't support interprocedural queries.");
449 AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag,
450 LocB.Ptr, LocB.Size, LocB.TBAATag);
451 // AliasCache rarely has more than 1 or 2 elements, always use
452 // shrink_and_clear so it quickly returns to the inline capacity of the
453 // SmallDenseMap if it ever grows larger.
454 // FIXME: This should really be shrink_to_inline_capacity_and_clear().
455 AliasCache.shrink_and_clear();
459 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
460 const Location &Loc);
462 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
463 ImmutableCallSite CS2) {
464 // The AliasAnalysis base class has some smarts, lets use them.
465 return AliasAnalysis::getModRefInfo(CS1, CS2);
468 /// pointsToConstantMemory - Chase pointers until we find a (constant
470 virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal);
472 /// getModRefBehavior - Return the behavior when calling the given
474 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
476 /// getModRefBehavior - Return the behavior when calling the given function.
477 /// For use when the call site is not known.
478 virtual ModRefBehavior getModRefBehavior(const Function *F);
480 /// getAdjustedAnalysisPointer - This method is used when a pass implements
481 /// an analysis interface through multiple inheritance. If needed, it
482 /// should override this to adjust the this pointer as needed for the
483 /// specified pass info.
484 virtual void *getAdjustedAnalysisPointer(const void *ID) {
485 if (ID == &AliasAnalysis::ID)
486 return (AliasAnalysis*)this;
491 // AliasCache - Track alias queries to guard against recursion.
492 typedef std::pair<Location, Location> LocPair;
493 typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
494 AliasCacheTy AliasCache;
496 // Visited - Track instructions visited by pointsToConstantMemory.
497 SmallPtrSet<const Value*, 16> Visited;
499 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
500 // instruction against another.
501 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
502 const MDNode *V1TBAAInfo,
503 const Value *V2, uint64_t V2Size,
504 const MDNode *V2TBAAInfo,
505 const Value *UnderlyingV1, const Value *UnderlyingV2);
507 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
508 // instruction against another.
509 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
510 const MDNode *PNTBAAInfo,
511 const Value *V2, uint64_t V2Size,
512 const MDNode *V2TBAAInfo);
514 /// aliasSelect - Disambiguate a Select instruction against another value.
515 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
516 const MDNode *SITBAAInfo,
517 const Value *V2, uint64_t V2Size,
518 const MDNode *V2TBAAInfo);
520 AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
521 const MDNode *V1TBAATag,
522 const Value *V2, uint64_t V2Size,
523 const MDNode *V2TBAATag);
525 } // End of anonymous namespace
527 // Register this pass...
528 char BasicAliasAnalysis::ID = 0;
529 INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
530 "Basic Alias Analysis (stateless AA impl)",
532 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
533 INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
534 "Basic Alias Analysis (stateless AA impl)",
538 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
539 return new BasicAliasAnalysis();
542 /// pointsToConstantMemory - Returns whether the given pointer value
543 /// points to memory that is local to the function, with global constants being
544 /// considered local to all functions.
546 BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
547 assert(Visited.empty() && "Visited must be cleared after use!");
549 unsigned MaxLookup = 8;
550 SmallVector<const Value *, 16> Worklist;
551 Worklist.push_back(Loc.Ptr);
553 const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), TD);
554 if (!Visited.insert(V)) {
556 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
559 // An alloca instruction defines local memory.
560 if (OrLocal && isa<AllocaInst>(V))
563 // A global constant counts as local memory for our purposes.
564 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
565 // Note: this doesn't require GV to be "ODR" because it isn't legal for a
566 // global to be marked constant in some modules and non-constant in
567 // others. GV may even be a declaration, not a definition.
568 if (!GV->isConstant()) {
570 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
575 // If both select values point to local memory, then so does the select.
576 if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
577 Worklist.push_back(SI->getTrueValue());
578 Worklist.push_back(SI->getFalseValue());
582 // If all values incoming to a phi node point to local memory, then so does
584 if (const PHINode *PN = dyn_cast<PHINode>(V)) {
585 // Don't bother inspecting phi nodes with many operands.
586 if (PN->getNumIncomingValues() > MaxLookup) {
588 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
590 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
591 Worklist.push_back(PN->getIncomingValue(i));
595 // Otherwise be conservative.
597 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
599 } while (!Worklist.empty() && --MaxLookup);
602 return Worklist.empty();
605 /// getModRefBehavior - Return the behavior when calling the given call site.
606 AliasAnalysis::ModRefBehavior
607 BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
608 if (CS.doesNotAccessMemory())
609 // Can't do better than this.
610 return DoesNotAccessMemory;
612 ModRefBehavior Min = UnknownModRefBehavior;
614 // If the callsite knows it only reads memory, don't return worse
616 if (CS.onlyReadsMemory())
617 Min = OnlyReadsMemory;
619 // The AliasAnalysis base class has some smarts, lets use them.
620 return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
623 /// getModRefBehavior - Return the behavior when calling the given function.
624 /// For use when the call site is not known.
625 AliasAnalysis::ModRefBehavior
626 BasicAliasAnalysis::getModRefBehavior(const Function *F) {
627 // If the function declares it doesn't access memory, we can't do better.
628 if (F->doesNotAccessMemory())
629 return DoesNotAccessMemory;
631 // For intrinsics, we can check the table.
632 if (unsigned iid = F->getIntrinsicID()) {
633 #define GET_INTRINSIC_MODREF_BEHAVIOR
634 #include "llvm/Intrinsics.gen"
635 #undef GET_INTRINSIC_MODREF_BEHAVIOR
638 ModRefBehavior Min = UnknownModRefBehavior;
640 // If the function declares it only reads memory, go with that.
641 if (F->onlyReadsMemory())
642 Min = OnlyReadsMemory;
644 // Otherwise be conservative.
645 return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
648 /// getModRefInfo - Check to see if the specified callsite can clobber the
649 /// specified memory object. Since we only look at local properties of this
650 /// function, we really can't say much about this query. We do, however, use
651 /// simple "address taken" analysis on local objects.
652 AliasAnalysis::ModRefResult
653 BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
654 const Location &Loc) {
655 assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
656 "AliasAnalysis query involving multiple functions!");
658 const Value *Object = GetUnderlyingObject(Loc.Ptr, TD);
660 // If this is a tail call and Loc.Ptr points to a stack location, we know that
661 // the tail call cannot access or modify the local stack.
662 // We cannot exclude byval arguments here; these belong to the caller of
663 // the current function not to the current function, and a tail callee
664 // may reference them.
665 if (isa<AllocaInst>(Object))
666 if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
667 if (CI->isTailCall())
670 // If the pointer is to a locally allocated object that does not escape,
671 // then the call can not mod/ref the pointer unless the call takes the pointer
672 // as an argument, and itself doesn't capture it.
673 if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
674 isNonEscapingLocalObject(Object)) {
675 bool PassedAsArg = false;
677 for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
678 CI != CE; ++CI, ++ArgNo) {
679 // Only look at the no-capture or byval pointer arguments. If this
680 // pointer were passed to arguments that were neither of these, then it
681 // couldn't be no-capture.
682 if (!(*CI)->getType()->isPointerTy() ||
683 (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
686 // If this is a no-capture pointer argument, see if we can tell that it
687 // is impossible to alias the pointer we're checking. If not, we have to
688 // assume that the call could touch the pointer, even though it doesn't
690 if (!isNoAlias(Location(*CI), Location(Object))) {
700 const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
701 ModRefResult Min = ModRef;
703 // Finally, handle specific knowledge of intrinsics.
704 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
706 switch (II->getIntrinsicID()) {
708 case Intrinsic::memcpy:
709 case Intrinsic::memmove: {
710 uint64_t Len = UnknownSize;
711 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
712 Len = LenCI->getZExtValue();
713 Value *Dest = II->getArgOperand(0);
714 Value *Src = II->getArgOperand(1);
715 // If it can't overlap the source dest, then it doesn't modref the loc.
716 if (isNoAlias(Location(Dest, Len), Loc)) {
717 if (isNoAlias(Location(Src, Len), Loc))
719 // If it can't overlap the dest, then worst case it reads the loc.
721 } else if (isNoAlias(Location(Src, Len), Loc)) {
722 // If it can't overlap the source, then worst case it mutates the loc.
727 case Intrinsic::memset:
728 // Since memset is 'accesses arguments' only, the AliasAnalysis base class
729 // will handle it for the variable length case.
730 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2))) {
731 uint64_t Len = LenCI->getZExtValue();
732 Value *Dest = II->getArgOperand(0);
733 if (isNoAlias(Location(Dest, Len), Loc))
736 // We know that memset doesn't load anything.
739 case Intrinsic::lifetime_start:
740 case Intrinsic::lifetime_end:
741 case Intrinsic::invariant_start: {
743 cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
744 if (isNoAlias(Location(II->getArgOperand(1),
746 II->getMetadata(LLVMContext::MD_tbaa)),
751 case Intrinsic::invariant_end: {
753 cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
754 if (isNoAlias(Location(II->getArgOperand(2),
756 II->getMetadata(LLVMContext::MD_tbaa)),
761 case Intrinsic::arm_neon_vld1: {
762 // LLVM's vld1 and vst1 intrinsics currently only support a single
765 TD ? TD->getTypeStoreSize(II->getType()) : UnknownSize;
766 if (isNoAlias(Location(II->getArgOperand(0), Size,
767 II->getMetadata(LLVMContext::MD_tbaa)),
772 case Intrinsic::arm_neon_vst1: {
774 TD ? TD->getTypeStoreSize(II->getArgOperand(1)->getType()) : UnknownSize;
775 if (isNoAlias(Location(II->getArgOperand(0), Size,
776 II->getMetadata(LLVMContext::MD_tbaa)),
783 // We can bound the aliasing properties of memset_pattern16 just as we can
784 // for memcpy/memset. This is particularly important because the
785 // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
786 // whenever possible.
787 else if (TLI.has(LibFunc::memset_pattern16) &&
788 CS.getCalledFunction() &&
789 CS.getCalledFunction()->getName() == "memset_pattern16") {
790 const Function *MS = CS.getCalledFunction();
791 FunctionType *MemsetType = MS->getFunctionType();
792 if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
793 isa<PointerType>(MemsetType->getParamType(0)) &&
794 isa<PointerType>(MemsetType->getParamType(1)) &&
795 isa<IntegerType>(MemsetType->getParamType(2))) {
796 uint64_t Len = UnknownSize;
797 if (const ConstantInt *LenCI = dyn_cast<ConstantInt>(CS.getArgument(2)))
798 Len = LenCI->getZExtValue();
799 const Value *Dest = CS.getArgument(0);
800 const Value *Src = CS.getArgument(1);
801 // If it can't overlap the source dest, then it doesn't modref the loc.
802 if (isNoAlias(Location(Dest, Len), Loc)) {
803 // Always reads 16 bytes of the source.
804 if (isNoAlias(Location(Src, 16), Loc))
806 // If it can't overlap the dest, then worst case it reads the loc.
808 // Always reads 16 bytes of the source.
809 } else if (isNoAlias(Location(Src, 16), Loc)) {
810 // If it can't overlap the source, then worst case it mutates the loc.
816 // The AliasAnalysis base class has some smarts, lets use them.
817 return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min);
820 static bool areVarIndicesEqual(SmallVector<VariableGEPIndex, 4> &Indices1,
821 SmallVector<VariableGEPIndex, 4> &Indices2) {
822 unsigned Size1 = Indices1.size();
823 unsigned Size2 = Indices2.size();
828 for (unsigned I = 0; I != Size1; ++I)
829 if (Indices1[I] != Indices2[I])
835 /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
836 /// against another pointer. We know that V1 is a GEP, but we don't know
837 /// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, TD),
838 /// UnderlyingV2 is the same for V2.
840 AliasAnalysis::AliasResult
841 BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
842 const MDNode *V1TBAAInfo,
843 const Value *V2, uint64_t V2Size,
844 const MDNode *V2TBAAInfo,
845 const Value *UnderlyingV1,
846 const Value *UnderlyingV2) {
847 int64_t GEP1BaseOffset;
848 SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
850 // If we have two gep instructions with must-alias or not-alias'ing base
851 // pointers, figure out if the indexes to the GEP tell us anything about the
853 if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
854 // Check for geps of non-aliasing underlying pointers where the offsets are
856 if (V1Size == V2Size) {
857 // Do the base pointers alias assuming type and size.
858 AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
859 V1TBAAInfo, UnderlyingV2,
861 if (PreciseBaseAlias == NoAlias) {
862 // See if the computed offset from the common pointer tells us about the
863 // relation of the resulting pointer.
864 int64_t GEP2BaseOffset;
865 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
866 const Value *GEP2BasePtr =
867 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
868 const Value *GEP1BasePtr =
869 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
870 // DecomposeGEPExpression and GetUnderlyingObject should return the
871 // same result except when DecomposeGEPExpression has no DataLayout.
872 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
874 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
878 if (GEP1BaseOffset == GEP2BaseOffset &&
879 areVarIndicesEqual(GEP1VariableIndices, GEP2VariableIndices))
881 GEP1VariableIndices.clear();
885 // Do the base pointers alias?
886 AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0,
887 UnderlyingV2, UnknownSize, 0);
889 // If we get a No or May, then return it immediately, no amount of analysis
890 // will improve this situation.
891 if (BaseAlias != MustAlias) return BaseAlias;
893 // Otherwise, we have a MustAlias. Since the base pointers alias each other
894 // exactly, see if the computed offset from the common pointer tells us
895 // about the relation of the resulting pointer.
896 const Value *GEP1BasePtr =
897 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
899 int64_t GEP2BaseOffset;
900 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
901 const Value *GEP2BasePtr =
902 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
904 // DecomposeGEPExpression and GetUnderlyingObject should return the
905 // same result except when DecomposeGEPExpression has no DataLayout.
906 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
908 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
912 // Subtract the GEP2 pointer from the GEP1 pointer to find out their
913 // symbolic difference.
914 GEP1BaseOffset -= GEP2BaseOffset;
915 GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
918 // Check to see if these two pointers are related by the getelementptr
919 // instruction. If one pointer is a GEP with a non-zero index of the other
920 // pointer, we know they cannot alias.
922 // If both accesses are unknown size, we can't do anything useful here.
923 if (V1Size == UnknownSize && V2Size == UnknownSize)
926 AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, 0,
927 V2, V2Size, V2TBAAInfo);
929 // If V2 may alias GEP base pointer, conservatively returns MayAlias.
930 // If V2 is known not to alias GEP base pointer, then the two values
931 // cannot alias per GEP semantics: "A pointer value formed from a
932 // getelementptr instruction is associated with the addresses associated
933 // with the first operand of the getelementptr".
936 const Value *GEP1BasePtr =
937 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
939 // DecomposeGEPExpression and GetUnderlyingObject should return the
940 // same result except when DecomposeGEPExpression has no DataLayout.
941 if (GEP1BasePtr != UnderlyingV1) {
943 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
948 // In the two GEP Case, if there is no difference in the offsets of the
949 // computed pointers, the resultant pointers are a must alias. This
950 // hapens when we have two lexically identical GEP's (for example).
952 // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
953 // must aliases the GEP, the end result is a must alias also.
954 if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
957 // If there is a constant difference between the pointers, but the difference
958 // is less than the size of the associated memory object, then we know
959 // that the objects are partially overlapping. If the difference is
960 // greater, we know they do not overlap.
961 if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
962 if (GEP1BaseOffset >= 0) {
963 if (V2Size != UnknownSize) {
964 if ((uint64_t)GEP1BaseOffset < V2Size)
969 if (V1Size != UnknownSize) {
970 if (-(uint64_t)GEP1BaseOffset < V1Size)
977 // Try to distinguish something like &A[i][1] against &A[42][0].
978 // Grab the least significant bit set in any of the scales.
979 if (!GEP1VariableIndices.empty()) {
981 for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
982 Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
983 Modulo = Modulo ^ (Modulo & (Modulo - 1));
985 // We can compute the difference between the two addresses
986 // mod Modulo. Check whether that difference guarantees that the
987 // two locations do not alias.
988 uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
989 if (V1Size != UnknownSize && V2Size != UnknownSize &&
990 ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
994 // Statically, we can see that the base objects are the same, but the
995 // pointers have dynamic offsets which we can't resolve. And none of our
996 // little tricks above worked.
998 // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
999 // practical effect of this is protecting TBAA in the case of dynamic
1000 // indices into arrays of unions or malloc'd memory.
1001 return PartialAlias;
1004 static AliasAnalysis::AliasResult
1005 MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
1006 // If the results agree, take it.
1009 // A mix of PartialAlias and MustAlias is PartialAlias.
1010 if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
1011 (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
1012 return AliasAnalysis::PartialAlias;
1013 // Otherwise, we don't know anything.
1014 return AliasAnalysis::MayAlias;
1017 /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
1018 /// instruction against another.
1019 AliasAnalysis::AliasResult
1020 BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
1021 const MDNode *SITBAAInfo,
1022 const Value *V2, uint64_t V2Size,
1023 const MDNode *V2TBAAInfo) {
1024 // If the values are Selects with the same condition, we can do a more precise
1025 // check: just check for aliases between the values on corresponding arms.
1026 if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
1027 if (SI->getCondition() == SI2->getCondition()) {
1029 aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo,
1030 SI2->getTrueValue(), V2Size, V2TBAAInfo);
1031 if (Alias == MayAlias)
1033 AliasResult ThisAlias =
1034 aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
1035 SI2->getFalseValue(), V2Size, V2TBAAInfo);
1036 return MergeAliasResults(ThisAlias, Alias);
1039 // If both arms of the Select node NoAlias or MustAlias V2, then returns
1040 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1042 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo);
1043 if (Alias == MayAlias)
1046 AliasResult ThisAlias =
1047 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
1048 return MergeAliasResults(ThisAlias, Alias);
1051 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
1053 AliasAnalysis::AliasResult
1054 BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
1055 const MDNode *PNTBAAInfo,
1056 const Value *V2, uint64_t V2Size,
1057 const MDNode *V2TBAAInfo) {
1058 // If the values are PHIs in the same block, we can do a more precise
1059 // as well as efficient check: just check for aliases between the values
1060 // on corresponding edges.
1061 if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
1062 if (PN2->getParent() == PN->getParent()) {
1063 LocPair Locs(Location(PN, PNSize, PNTBAAInfo),
1064 Location(V2, V2Size, V2TBAAInfo));
1066 std::swap(Locs.first, Locs.second);
1068 // Find the first incoming phi value not from its parent.
1070 while (PN->getIncomingBlock(f) == PN->getParent() &&
1071 f < PN->getNumIncomingValues()-1)
1075 aliasCheck(PN->getIncomingValue(f), PNSize, PNTBAAInfo,
1076 PN2->getIncomingValueForBlock(PN->getIncomingBlock(f)),
1077 V2Size, V2TBAAInfo);
1078 if (Alias == MayAlias)
1081 // If the first source of the PHI nodes NoAlias and the other inputs are
1082 // the PHI node itself through some amount of recursion this does not add
1083 // any new information so just return NoAlias.
1087 // ptr_phi = phi [bb, ptr], [loop, ptr_plus_one]
1088 // ptr2_phi = phi [bb, ptr2], [loop, ptr2_plus_one]
1090 // ptr_plus_one = gep ptr_phi, 1
1091 // ptr2_plus_one = gep ptr2_phi, 1
1092 // We assume for the recursion that the the phis (ptr_phi, ptr2_phi) do
1093 // not alias each other.
1094 bool ArePhisAssumedNoAlias = false;
1095 AliasResult OrigAliasResult = NoAlias;
1096 if (Alias == NoAlias) {
1097 // Pretend the phis do not alias.
1098 assert(AliasCache.count(Locs) &&
1099 "There must exist an entry for the phi node");
1100 OrigAliasResult = AliasCache[Locs];
1101 AliasCache[Locs] = NoAlias;
1102 ArePhisAssumedNoAlias = true;
1105 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1109 AliasResult ThisAlias =
1110 aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
1111 PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
1112 V2Size, V2TBAAInfo);
1113 Alias = MergeAliasResults(ThisAlias, Alias);
1114 if (Alias == MayAlias)
1118 // Reset if speculation failed.
1119 if (ArePhisAssumedNoAlias && Alias != NoAlias)
1120 AliasCache[Locs] = OrigAliasResult;
1125 SmallPtrSet<Value*, 4> UniqueSrc;
1126 SmallVector<Value*, 4> V1Srcs;
1127 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1128 Value *PV1 = PN->getIncomingValue(i);
1129 if (isa<PHINode>(PV1))
1130 // If any of the source itself is a PHI, return MayAlias conservatively
1131 // to avoid compile time explosion. The worst possible case is if both
1132 // sides are PHI nodes. In which case, this is O(m x n) time where 'm'
1133 // and 'n' are the number of PHI sources.
1135 if (UniqueSrc.insert(PV1))
1136 V1Srcs.push_back(PV1);
1139 AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo,
1140 V1Srcs[0], PNSize, PNTBAAInfo);
1141 // Early exit if the check of the first PHI source against V2 is MayAlias.
1142 // Other results are not possible.
1143 if (Alias == MayAlias)
1146 // If all sources of the PHI node NoAlias or MustAlias V2, then returns
1147 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1148 for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
1149 Value *V = V1Srcs[i];
1151 AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
1152 V, PNSize, PNTBAAInfo);
1153 Alias = MergeAliasResults(ThisAlias, Alias);
1154 if (Alias == MayAlias)
1161 // aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
1162 // such as array references.
1164 AliasAnalysis::AliasResult
1165 BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
1166 const MDNode *V1TBAAInfo,
1167 const Value *V2, uint64_t V2Size,
1168 const MDNode *V2TBAAInfo) {
1169 // If either of the memory references is empty, it doesn't matter what the
1170 // pointer values are.
1171 if (V1Size == 0 || V2Size == 0)
1174 // Strip off any casts if they exist.
1175 V1 = V1->stripPointerCasts();
1176 V2 = V2->stripPointerCasts();
1178 // Are we checking for alias of the same value?
1179 if (V1 == V2) return MustAlias;
1181 if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
1182 return NoAlias; // Scalars cannot alias each other
1184 // Figure out what objects these things are pointing to if we can.
1185 const Value *O1 = GetUnderlyingObject(V1, TD);
1186 const Value *O2 = GetUnderlyingObject(V2, TD);
1188 // Null values in the default address space don't point to any object, so they
1189 // don't alias any other pointer.
1190 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
1191 if (CPN->getType()->getAddressSpace() == 0)
1193 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
1194 if (CPN->getType()->getAddressSpace() == 0)
1198 // If V1/V2 point to two different objects we know that we have no alias.
1199 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
1202 // Constant pointers can't alias with non-const isIdentifiedObject objects.
1203 if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
1204 (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
1207 // Arguments can't alias with local allocations or noalias calls
1208 // in the same function.
1209 if (((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) ||
1210 (isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1)))))
1213 // Most objects can't alias null.
1214 if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
1215 (isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
1218 // If one pointer is the result of a call/invoke or load and the other is a
1219 // non-escaping local object within the same function, then we know the
1220 // object couldn't escape to a point where the call could return it.
1222 // Note that if the pointers are in different functions, there are a
1223 // variety of complications. A call with a nocapture argument may still
1224 // temporary store the nocapture argument's value in a temporary memory
1225 // location if that memory location doesn't escape. Or it may pass a
1226 // nocapture value to other functions as long as they don't capture it.
1227 if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
1229 if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
1233 // If the size of one access is larger than the entire object on the other
1234 // side, then we know such behavior is undefined and can assume no alias.
1236 if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD, *TLI)) ||
1237 (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD, *TLI)))
1240 // Check the cache before climbing up use-def chains. This also terminates
1241 // otherwise infinitely recursive queries.
1242 LocPair Locs(Location(V1, V1Size, V1TBAAInfo),
1243 Location(V2, V2Size, V2TBAAInfo));
1245 std::swap(Locs.first, Locs.second);
1246 std::pair<AliasCacheTy::iterator, bool> Pair =
1247 AliasCache.insert(std::make_pair(Locs, MayAlias));
1249 return Pair.first->second;
1251 // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
1252 // GEP can't simplify, we don't even look at the PHI cases.
1253 if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
1255 std::swap(V1Size, V2Size);
1257 std::swap(V1TBAAInfo, V2TBAAInfo);
1259 if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
1260 AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2);
1261 if (Result != MayAlias) return AliasCache[Locs] = Result;
1264 if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
1266 std::swap(V1Size, V2Size);
1267 std::swap(V1TBAAInfo, V2TBAAInfo);
1269 if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
1270 AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
1271 V2, V2Size, V2TBAAInfo);
1272 if (Result != MayAlias) return AliasCache[Locs] = Result;
1275 if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
1277 std::swap(V1Size, V2Size);
1278 std::swap(V1TBAAInfo, V2TBAAInfo);
1280 if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
1281 AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
1282 V2, V2Size, V2TBAAInfo);
1283 if (Result != MayAlias) return AliasCache[Locs] = Result;
1286 // If both pointers are pointing into the same object and one of them
1287 // accesses is accessing the entire object, then the accesses must
1288 // overlap in some way.
1290 if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD, *TLI)) ||
1291 (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD, *TLI)))
1292 return AliasCache[Locs] = PartialAlias;
1294 AliasResult Result =
1295 AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
1296 Location(V2, V2Size, V2TBAAInfo));
1297 return AliasCache[Locs] = Result;