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/IR/Constants.h"
25 #include "llvm/IR/DataLayout.h"
26 #include "llvm/IR/DerivedTypes.h"
27 #include "llvm/IR/Function.h"
28 #include "llvm/IR/GlobalAlias.h"
29 #include "llvm/IR/GlobalVariable.h"
30 #include "llvm/IR/Instructions.h"
31 #include "llvm/IR/IntrinsicInst.h"
32 #include "llvm/IR/LLVMContext.h"
33 #include "llvm/IR/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 // Note that the meanings of the "object" are slightly different in the
102 // following contexts:
103 // c1: llvm::getObjectSize()
104 // c2: llvm.objectsize() intrinsic
105 // c3: isObjectSmallerThan()
106 // c1 and c2 share the same meaning; however, the meaning of "object" in c3
107 // refers to the "entire object".
109 // Consider this example:
110 // char *p = (char*)malloc(100)
113 // In the context of c1 and c2, the "object" pointed by q refers to the
114 // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
116 // However, in the context of c3, the "object" refers to the chunk of memory
117 // being allocated. So, the "object" has 100 bytes, and q points to the middle
118 // the "object". In case q is passed to isObjectSmallerThan() as the 1st
119 // parameter, before the llvm::getObjectSize() is called to get the size of
120 // entire object, we should:
121 // - either rewind the pointer q to the base-address of the object in
122 // question (in this case rewind to p), or
123 // - just give up. It is up to caller to make sure the pointer is pointing
124 // to the base address the object.
126 // We go for 2nd option for simplicity.
127 if (!isIdentifiedObject(V))
130 // This function needs to use the aligned object size because we allow
131 // reads a bit past the end given sufficient alignment.
132 uint64_t ObjectSize = getObjectSize(V, TD, TLI, /*RoundToAlign*/true);
134 return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size;
137 /// isObjectSize - Return true if we can prove that the object specified
138 /// by V has size Size.
139 static bool isObjectSize(const Value *V, uint64_t Size,
140 const DataLayout &TD, const TargetLibraryInfo &TLI) {
141 uint64_t ObjectSize = getObjectSize(V, TD, TLI);
142 return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size;
145 //===----------------------------------------------------------------------===//
146 // GetElementPtr Instruction Decomposition and Analysis
147 //===----------------------------------------------------------------------===//
156 struct VariableGEPIndex {
158 ExtensionKind Extension;
161 bool operator==(const VariableGEPIndex &Other) const {
162 return V == Other.V && Extension == Other.Extension &&
163 Scale == Other.Scale;
166 bool operator!=(const VariableGEPIndex &Other) const {
167 return !operator==(Other);
173 /// GetLinearExpression - Analyze the specified value as a linear expression:
174 /// "A*V + B", where A and B are constant integers. Return the scale and offset
175 /// values as APInts and return V as a Value*, and return whether we looked
176 /// through any sign or zero extends. The incoming Value is known to have
177 /// IntegerType and it may already be sign or zero extended.
179 /// Note that this looks through extends, so the high bits may not be
180 /// represented in the result.
181 static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
182 ExtensionKind &Extension,
183 const DataLayout &TD, unsigned Depth) {
184 assert(V->getType()->isIntegerTy() && "Not an integer value");
186 // Limit our recursion depth.
193 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
194 if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
195 switch (BOp->getOpcode()) {
197 case Instruction::Or:
198 // X|C == X+C if all the bits in C are unset in X. Otherwise we can't
200 if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &TD))
203 case Instruction::Add:
204 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
206 Offset += RHSC->getValue();
208 case Instruction::Mul:
209 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
211 Offset *= RHSC->getValue();
212 Scale *= RHSC->getValue();
214 case Instruction::Shl:
215 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
217 Offset <<= RHSC->getValue().getLimitedValue();
218 Scale <<= RHSC->getValue().getLimitedValue();
224 // Since GEP indices are sign extended anyway, we don't care about the high
225 // bits of a sign or zero extended value - just scales and offsets. The
226 // extensions have to be consistent though.
227 if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) ||
228 (isa<ZExtInst>(V) && Extension != EK_SignExt)) {
229 Value *CastOp = cast<CastInst>(V)->getOperand(0);
230 unsigned OldWidth = Scale.getBitWidth();
231 unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
232 Scale = Scale.trunc(SmallWidth);
233 Offset = Offset.trunc(SmallWidth);
234 Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
236 Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension,
238 Scale = Scale.zext(OldWidth);
239 Offset = Offset.zext(OldWidth);
249 /// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it
250 /// into a base pointer with a constant offset and a number of scaled symbolic
253 /// The scaled symbolic offsets (represented by pairs of a Value* and a scale in
254 /// the VarIndices vector) are Value*'s that are known to be scaled by the
255 /// specified amount, but which may have other unrepresented high bits. As such,
256 /// the gep cannot necessarily be reconstructed from its decomposed form.
258 /// When DataLayout is around, this function is capable of analyzing everything
259 /// that GetUnderlyingObject can look through. When not, it just looks
260 /// through pointer casts.
263 DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
264 SmallVectorImpl<VariableGEPIndex> &VarIndices,
265 const DataLayout *TD) {
266 // Limit recursion depth to limit compile time in crazy cases.
267 unsigned MaxLookup = 6;
271 // See if this is a bitcast or GEP.
272 const Operator *Op = dyn_cast<Operator>(V);
274 // The only non-operator case we can handle are GlobalAliases.
275 if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
276 if (!GA->mayBeOverridden()) {
277 V = GA->getAliasee();
284 if (Op->getOpcode() == Instruction::BitCast) {
285 V = Op->getOperand(0);
289 const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
291 // If it's not a GEP, hand it off to SimplifyInstruction to see if it
292 // can come up with something. This matches what GetUnderlyingObject does.
293 if (const Instruction *I = dyn_cast<Instruction>(V))
294 // TODO: Get a DominatorTree and use it here.
295 if (const Value *Simplified =
296 SimplifyInstruction(const_cast<Instruction *>(I), TD)) {
304 // Don't attempt to analyze GEPs over unsized objects.
305 if (!cast<PointerType>(GEPOp->getOperand(0)->getType())
306 ->getElementType()->isSized())
309 // If we are lacking DataLayout information, we can't compute the offets of
310 // elements computed by GEPs. However, we can handle bitcast equivalent
313 if (!GEPOp->hasAllZeroIndices())
315 V = GEPOp->getOperand(0);
319 // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
320 gep_type_iterator GTI = gep_type_begin(GEPOp);
321 for (User::const_op_iterator I = GEPOp->op_begin()+1,
322 E = GEPOp->op_end(); I != E; ++I) {
324 // Compute the (potentially symbolic) offset in bytes for this index.
325 if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
326 // For a struct, add the member offset.
327 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
328 if (FieldNo == 0) continue;
330 BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo);
334 // For an array/pointer, add the element offset, explicitly scaled.
335 if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
336 if (CIdx->isZero()) continue;
337 BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
341 uint64_t Scale = TD->getTypeAllocSize(*GTI);
342 ExtensionKind Extension = EK_NotExtended;
344 // If the integer type is smaller than the pointer size, it is implicitly
345 // sign extended to pointer size.
346 unsigned Width = cast<IntegerType>(Index->getType())->getBitWidth();
347 if (TD->getPointerSizeInBits() > Width)
348 Extension = EK_SignExt;
350 // Use GetLinearExpression to decompose the index into a C1*V+C2 form.
351 APInt IndexScale(Width, 0), IndexOffset(Width, 0);
352 Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension,
355 // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
356 // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
357 BaseOffs += IndexOffset.getSExtValue()*Scale;
358 Scale *= IndexScale.getSExtValue();
361 // If we already had an occurrence of this index variable, merge this
362 // scale into it. For example, we want to handle:
363 // A[x][x] -> x*16 + x*4 -> x*20
364 // This also ensures that 'x' only appears in the index list once.
365 for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
366 if (VarIndices[i].V == Index &&
367 VarIndices[i].Extension == Extension) {
368 Scale += VarIndices[i].Scale;
369 VarIndices.erase(VarIndices.begin()+i);
374 // Make sure that we have a scale that makes sense for this target's
376 if (unsigned ShiftBits = 64-TD->getPointerSizeInBits()) {
378 Scale = (int64_t)Scale >> ShiftBits;
382 VariableGEPIndex Entry = {Index, Extension,
383 static_cast<int64_t>(Scale)};
384 VarIndices.push_back(Entry);
388 // Analyze the base pointer next.
389 V = GEPOp->getOperand(0);
390 } while (--MaxLookup);
392 // If the chain of expressions is too deep, just return early.
396 /// GetIndexDifference - Dest and Src are the variable indices from two
397 /// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
398 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
399 /// difference between the two pointers.
400 static void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
401 const SmallVectorImpl<VariableGEPIndex> &Src) {
402 if (Src.empty()) return;
404 for (unsigned i = 0, e = Src.size(); i != e; ++i) {
405 const Value *V = Src[i].V;
406 ExtensionKind Extension = Src[i].Extension;
407 int64_t Scale = Src[i].Scale;
409 // Find V in Dest. This is N^2, but pointer indices almost never have more
410 // than a few variable indexes.
411 for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
412 if (Dest[j].V != V || Dest[j].Extension != Extension) continue;
414 // If we found it, subtract off Scale V's from the entry in Dest. If it
415 // goes to zero, remove the entry.
416 if (Dest[j].Scale != Scale)
417 Dest[j].Scale -= Scale;
419 Dest.erase(Dest.begin()+j);
424 // If we didn't consume this entry, add it to the end of the Dest list.
426 VariableGEPIndex Entry = { V, Extension, -Scale };
427 Dest.push_back(Entry);
432 //===----------------------------------------------------------------------===//
433 // BasicAliasAnalysis Pass
434 //===----------------------------------------------------------------------===//
437 static const Function *getParent(const Value *V) {
438 if (const Instruction *inst = dyn_cast<Instruction>(V))
439 return inst->getParent()->getParent();
441 if (const Argument *arg = dyn_cast<Argument>(V))
442 return arg->getParent();
447 static bool notDifferentParent(const Value *O1, const Value *O2) {
449 const Function *F1 = getParent(O1);
450 const Function *F2 = getParent(O2);
452 return !F1 || !F2 || F1 == F2;
457 /// BasicAliasAnalysis - This is the primary alias analysis implementation.
458 struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
459 static char ID; // Class identification, replacement for typeinfo
460 BasicAliasAnalysis() : ImmutablePass(ID) {
461 initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
464 virtual void initializePass() {
465 InitializeAliasAnalysis(this);
468 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
469 AU.addRequired<AliasAnalysis>();
470 AU.addRequired<TargetLibraryInfo>();
473 virtual AliasResult alias(const Location &LocA,
474 const Location &LocB) {
475 assert(AliasCache.empty() && "AliasCache must be cleared after use!");
476 assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
477 "BasicAliasAnalysis doesn't support interprocedural queries.");
478 AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag,
479 LocB.Ptr, LocB.Size, LocB.TBAATag);
480 // AliasCache rarely has more than 1 or 2 elements, always use
481 // shrink_and_clear so it quickly returns to the inline capacity of the
482 // SmallDenseMap if it ever grows larger.
483 // FIXME: This should really be shrink_to_inline_capacity_and_clear().
484 AliasCache.shrink_and_clear();
488 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
489 const Location &Loc);
491 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
492 ImmutableCallSite CS2) {
493 // The AliasAnalysis base class has some smarts, lets use them.
494 return AliasAnalysis::getModRefInfo(CS1, CS2);
497 /// pointsToConstantMemory - Chase pointers until we find a (constant
499 virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal);
501 /// getModRefBehavior - Return the behavior when calling the given
503 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
505 /// getModRefBehavior - Return the behavior when calling the given function.
506 /// For use when the call site is not known.
507 virtual ModRefBehavior getModRefBehavior(const Function *F);
509 /// getAdjustedAnalysisPointer - This method is used when a pass implements
510 /// an analysis interface through multiple inheritance. If needed, it
511 /// should override this to adjust the this pointer as needed for the
512 /// specified pass info.
513 virtual void *getAdjustedAnalysisPointer(const void *ID) {
514 if (ID == &AliasAnalysis::ID)
515 return (AliasAnalysis*)this;
520 // AliasCache - Track alias queries to guard against recursion.
521 typedef std::pair<Location, Location> LocPair;
522 typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
523 AliasCacheTy AliasCache;
525 // Visited - Track instructions visited by pointsToConstantMemory.
526 SmallPtrSet<const Value*, 16> Visited;
528 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
529 // instruction against another.
530 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
531 const MDNode *V1TBAAInfo,
532 const Value *V2, uint64_t V2Size,
533 const MDNode *V2TBAAInfo,
534 const Value *UnderlyingV1, const Value *UnderlyingV2);
536 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
537 // instruction against another.
538 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
539 const MDNode *PNTBAAInfo,
540 const Value *V2, uint64_t V2Size,
541 const MDNode *V2TBAAInfo);
543 /// aliasSelect - Disambiguate a Select instruction against another value.
544 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
545 const MDNode *SITBAAInfo,
546 const Value *V2, uint64_t V2Size,
547 const MDNode *V2TBAAInfo);
549 AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
550 const MDNode *V1TBAATag,
551 const Value *V2, uint64_t V2Size,
552 const MDNode *V2TBAATag);
554 } // End of anonymous namespace
556 // Register this pass...
557 char BasicAliasAnalysis::ID = 0;
558 INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
559 "Basic Alias Analysis (stateless AA impl)",
561 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
562 INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
563 "Basic Alias Analysis (stateless AA impl)",
567 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
568 return new BasicAliasAnalysis();
571 /// pointsToConstantMemory - Returns whether the given pointer value
572 /// points to memory that is local to the function, with global constants being
573 /// considered local to all functions.
575 BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
576 assert(Visited.empty() && "Visited must be cleared after use!");
578 unsigned MaxLookup = 8;
579 SmallVector<const Value *, 16> Worklist;
580 Worklist.push_back(Loc.Ptr);
582 const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), TD);
583 if (!Visited.insert(V)) {
585 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
588 // An alloca instruction defines local memory.
589 if (OrLocal && isa<AllocaInst>(V))
592 // A global constant counts as local memory for our purposes.
593 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
594 // Note: this doesn't require GV to be "ODR" because it isn't legal for a
595 // global to be marked constant in some modules and non-constant in
596 // others. GV may even be a declaration, not a definition.
597 if (!GV->isConstant()) {
599 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
604 // If both select values point to local memory, then so does the select.
605 if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
606 Worklist.push_back(SI->getTrueValue());
607 Worklist.push_back(SI->getFalseValue());
611 // If all values incoming to a phi node point to local memory, then so does
613 if (const PHINode *PN = dyn_cast<PHINode>(V)) {
614 // Don't bother inspecting phi nodes with many operands.
615 if (PN->getNumIncomingValues() > MaxLookup) {
617 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
619 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
620 Worklist.push_back(PN->getIncomingValue(i));
624 // Otherwise be conservative.
626 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
628 } while (!Worklist.empty() && --MaxLookup);
631 return Worklist.empty();
634 /// getModRefBehavior - Return the behavior when calling the given call site.
635 AliasAnalysis::ModRefBehavior
636 BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
637 if (CS.doesNotAccessMemory())
638 // Can't do better than this.
639 return DoesNotAccessMemory;
641 ModRefBehavior Min = UnknownModRefBehavior;
643 // If the callsite knows it only reads memory, don't return worse
645 if (CS.onlyReadsMemory())
646 Min = OnlyReadsMemory;
648 // The AliasAnalysis base class has some smarts, lets use them.
649 return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
652 /// getModRefBehavior - Return the behavior when calling the given function.
653 /// For use when the call site is not known.
654 AliasAnalysis::ModRefBehavior
655 BasicAliasAnalysis::getModRefBehavior(const Function *F) {
656 // If the function declares it doesn't access memory, we can't do better.
657 if (F->doesNotAccessMemory())
658 return DoesNotAccessMemory;
660 // For intrinsics, we can check the table.
661 if (unsigned iid = F->getIntrinsicID()) {
662 #define GET_INTRINSIC_MODREF_BEHAVIOR
663 #include "llvm/IR/Intrinsics.gen"
664 #undef GET_INTRINSIC_MODREF_BEHAVIOR
667 ModRefBehavior Min = UnknownModRefBehavior;
669 // If the function declares it only reads memory, go with that.
670 if (F->onlyReadsMemory())
671 Min = OnlyReadsMemory;
673 // Otherwise be conservative.
674 return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
677 /// getModRefInfo - Check to see if the specified callsite can clobber the
678 /// specified memory object. Since we only look at local properties of this
679 /// function, we really can't say much about this query. We do, however, use
680 /// simple "address taken" analysis on local objects.
681 AliasAnalysis::ModRefResult
682 BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
683 const Location &Loc) {
684 assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
685 "AliasAnalysis query involving multiple functions!");
687 const Value *Object = GetUnderlyingObject(Loc.Ptr, TD);
689 // If this is a tail call and Loc.Ptr points to a stack location, we know that
690 // the tail call cannot access or modify the local stack.
691 // We cannot exclude byval arguments here; these belong to the caller of
692 // the current function not to the current function, and a tail callee
693 // may reference them.
694 if (isa<AllocaInst>(Object))
695 if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
696 if (CI->isTailCall())
699 // If the pointer is to a locally allocated object that does not escape,
700 // then the call can not mod/ref the pointer unless the call takes the pointer
701 // as an argument, and itself doesn't capture it.
702 if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
703 isNonEscapingLocalObject(Object)) {
704 bool PassedAsArg = false;
706 for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
707 CI != CE; ++CI, ++ArgNo) {
708 // Only look at the no-capture or byval pointer arguments. If this
709 // pointer were passed to arguments that were neither of these, then it
710 // couldn't be no-capture.
711 if (!(*CI)->getType()->isPointerTy() ||
712 (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
715 // If this is a no-capture pointer argument, see if we can tell that it
716 // is impossible to alias the pointer we're checking. If not, we have to
717 // assume that the call could touch the pointer, even though it doesn't
719 if (!isNoAlias(Location(*CI), Location(Object))) {
729 const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
730 ModRefResult Min = ModRef;
732 // Finally, handle specific knowledge of intrinsics.
733 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
735 switch (II->getIntrinsicID()) {
737 case Intrinsic::memcpy:
738 case Intrinsic::memmove: {
739 uint64_t Len = UnknownSize;
740 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
741 Len = LenCI->getZExtValue();
742 Value *Dest = II->getArgOperand(0);
743 Value *Src = II->getArgOperand(1);
744 // If it can't overlap the source dest, then it doesn't modref the loc.
745 if (isNoAlias(Location(Dest, Len), Loc)) {
746 if (isNoAlias(Location(Src, Len), Loc))
748 // If it can't overlap the dest, then worst case it reads the loc.
750 } else if (isNoAlias(Location(Src, Len), Loc)) {
751 // If it can't overlap the source, then worst case it mutates the loc.
756 case Intrinsic::memset:
757 // Since memset is 'accesses arguments' only, the AliasAnalysis base class
758 // will handle it for the variable length case.
759 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2))) {
760 uint64_t Len = LenCI->getZExtValue();
761 Value *Dest = II->getArgOperand(0);
762 if (isNoAlias(Location(Dest, Len), Loc))
765 // We know that memset doesn't load anything.
768 case Intrinsic::lifetime_start:
769 case Intrinsic::lifetime_end:
770 case Intrinsic::invariant_start: {
772 cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
773 if (isNoAlias(Location(II->getArgOperand(1),
775 II->getMetadata(LLVMContext::MD_tbaa)),
780 case Intrinsic::invariant_end: {
782 cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
783 if (isNoAlias(Location(II->getArgOperand(2),
785 II->getMetadata(LLVMContext::MD_tbaa)),
790 case Intrinsic::arm_neon_vld1: {
791 // LLVM's vld1 and vst1 intrinsics currently only support a single
794 TD ? TD->getTypeStoreSize(II->getType()) : UnknownSize;
795 if (isNoAlias(Location(II->getArgOperand(0), Size,
796 II->getMetadata(LLVMContext::MD_tbaa)),
801 case Intrinsic::arm_neon_vst1: {
803 TD ? TD->getTypeStoreSize(II->getArgOperand(1)->getType()) : UnknownSize;
804 if (isNoAlias(Location(II->getArgOperand(0), Size,
805 II->getMetadata(LLVMContext::MD_tbaa)),
812 // We can bound the aliasing properties of memset_pattern16 just as we can
813 // for memcpy/memset. This is particularly important because the
814 // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
815 // whenever possible.
816 else if (TLI.has(LibFunc::memset_pattern16) &&
817 CS.getCalledFunction() &&
818 CS.getCalledFunction()->getName() == "memset_pattern16") {
819 const Function *MS = CS.getCalledFunction();
820 FunctionType *MemsetType = MS->getFunctionType();
821 if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
822 isa<PointerType>(MemsetType->getParamType(0)) &&
823 isa<PointerType>(MemsetType->getParamType(1)) &&
824 isa<IntegerType>(MemsetType->getParamType(2))) {
825 uint64_t Len = UnknownSize;
826 if (const ConstantInt *LenCI = dyn_cast<ConstantInt>(CS.getArgument(2)))
827 Len = LenCI->getZExtValue();
828 const Value *Dest = CS.getArgument(0);
829 const Value *Src = CS.getArgument(1);
830 // If it can't overlap the source dest, then it doesn't modref the loc.
831 if (isNoAlias(Location(Dest, Len), Loc)) {
832 // Always reads 16 bytes of the source.
833 if (isNoAlias(Location(Src, 16), Loc))
835 // If it can't overlap the dest, then worst case it reads the loc.
837 // Always reads 16 bytes of the source.
838 } else if (isNoAlias(Location(Src, 16), Loc)) {
839 // If it can't overlap the source, then worst case it mutates the loc.
845 // The AliasAnalysis base class has some smarts, lets use them.
846 return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min);
849 static bool areVarIndicesEqual(SmallVector<VariableGEPIndex, 4> &Indices1,
850 SmallVector<VariableGEPIndex, 4> &Indices2) {
851 unsigned Size1 = Indices1.size();
852 unsigned Size2 = Indices2.size();
857 for (unsigned I = 0; I != Size1; ++I)
858 if (Indices1[I] != Indices2[I])
864 /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
865 /// against another pointer. We know that V1 is a GEP, but we don't know
866 /// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, TD),
867 /// UnderlyingV2 is the same for V2.
869 AliasAnalysis::AliasResult
870 BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
871 const MDNode *V1TBAAInfo,
872 const Value *V2, uint64_t V2Size,
873 const MDNode *V2TBAAInfo,
874 const Value *UnderlyingV1,
875 const Value *UnderlyingV2) {
876 int64_t GEP1BaseOffset;
877 SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
879 // If we have two gep instructions with must-alias or not-alias'ing base
880 // pointers, figure out if the indexes to the GEP tell us anything about the
882 if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
883 // Check for geps of non-aliasing underlying pointers where the offsets are
885 if (V1Size == V2Size) {
886 // Do the base pointers alias assuming type and size.
887 AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
888 V1TBAAInfo, UnderlyingV2,
890 if (PreciseBaseAlias == NoAlias) {
891 // See if the computed offset from the common pointer tells us about the
892 // relation of the resulting pointer.
893 int64_t GEP2BaseOffset;
894 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
895 const Value *GEP2BasePtr =
896 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
897 const Value *GEP1BasePtr =
898 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
899 // DecomposeGEPExpression and GetUnderlyingObject should return the
900 // same result except when DecomposeGEPExpression has no DataLayout.
901 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
903 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
907 if (GEP1BaseOffset == GEP2BaseOffset &&
908 areVarIndicesEqual(GEP1VariableIndices, GEP2VariableIndices))
910 GEP1VariableIndices.clear();
914 // Do the base pointers alias?
915 AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0,
916 UnderlyingV2, UnknownSize, 0);
918 // If we get a No or May, then return it immediately, no amount of analysis
919 // will improve this situation.
920 if (BaseAlias != MustAlias) return BaseAlias;
922 // Otherwise, we have a MustAlias. Since the base pointers alias each other
923 // exactly, see if the computed offset from the common pointer tells us
924 // about the relation of the resulting pointer.
925 const Value *GEP1BasePtr =
926 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
928 int64_t GEP2BaseOffset;
929 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
930 const Value *GEP2BasePtr =
931 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
933 // DecomposeGEPExpression and GetUnderlyingObject should return the
934 // same result except when DecomposeGEPExpression has no DataLayout.
935 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
937 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
941 // Subtract the GEP2 pointer from the GEP1 pointer to find out their
942 // symbolic difference.
943 GEP1BaseOffset -= GEP2BaseOffset;
944 GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
947 // Check to see if these two pointers are related by the getelementptr
948 // instruction. If one pointer is a GEP with a non-zero index of the other
949 // pointer, we know they cannot alias.
951 // If both accesses are unknown size, we can't do anything useful here.
952 if (V1Size == UnknownSize && V2Size == UnknownSize)
955 AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, 0,
956 V2, V2Size, V2TBAAInfo);
958 // If V2 may alias GEP base pointer, conservatively returns MayAlias.
959 // If V2 is known not to alias GEP base pointer, then the two values
960 // cannot alias per GEP semantics: "A pointer value formed from a
961 // getelementptr instruction is associated with the addresses associated
962 // with the first operand of the getelementptr".
965 const Value *GEP1BasePtr =
966 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
968 // DecomposeGEPExpression and GetUnderlyingObject should return the
969 // same result except when DecomposeGEPExpression has no DataLayout.
970 if (GEP1BasePtr != UnderlyingV1) {
972 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
977 // In the two GEP Case, if there is no difference in the offsets of the
978 // computed pointers, the resultant pointers are a must alias. This
979 // hapens when we have two lexically identical GEP's (for example).
981 // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
982 // must aliases the GEP, the end result is a must alias also.
983 if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
986 // If there is a constant difference between the pointers, but the difference
987 // is less than the size of the associated memory object, then we know
988 // that the objects are partially overlapping. If the difference is
989 // greater, we know they do not overlap.
990 if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
991 if (GEP1BaseOffset >= 0) {
992 if (V2Size != UnknownSize) {
993 if ((uint64_t)GEP1BaseOffset < V2Size)
998 if (V1Size != UnknownSize) {
999 if (-(uint64_t)GEP1BaseOffset < V1Size)
1000 return PartialAlias;
1006 // Try to distinguish something like &A[i][1] against &A[42][0].
1007 // Grab the least significant bit set in any of the scales.
1008 if (!GEP1VariableIndices.empty()) {
1009 uint64_t Modulo = 0;
1010 for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
1011 Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
1012 Modulo = Modulo ^ (Modulo & (Modulo - 1));
1014 // We can compute the difference between the two addresses
1015 // mod Modulo. Check whether that difference guarantees that the
1016 // two locations do not alias.
1017 uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
1018 if (V1Size != UnknownSize && V2Size != UnknownSize &&
1019 ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
1023 // Statically, we can see that the base objects are the same, but the
1024 // pointers have dynamic offsets which we can't resolve. And none of our
1025 // little tricks above worked.
1027 // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
1028 // practical effect of this is protecting TBAA in the case of dynamic
1029 // indices into arrays of unions or malloc'd memory.
1030 return PartialAlias;
1033 static AliasAnalysis::AliasResult
1034 MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
1035 // If the results agree, take it.
1038 // A mix of PartialAlias and MustAlias is PartialAlias.
1039 if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
1040 (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
1041 return AliasAnalysis::PartialAlias;
1042 // Otherwise, we don't know anything.
1043 return AliasAnalysis::MayAlias;
1046 /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
1047 /// instruction against another.
1048 AliasAnalysis::AliasResult
1049 BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
1050 const MDNode *SITBAAInfo,
1051 const Value *V2, uint64_t V2Size,
1052 const MDNode *V2TBAAInfo) {
1053 // If the values are Selects with the same condition, we can do a more precise
1054 // check: just check for aliases between the values on corresponding arms.
1055 if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
1056 if (SI->getCondition() == SI2->getCondition()) {
1058 aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo,
1059 SI2->getTrueValue(), V2Size, V2TBAAInfo);
1060 if (Alias == MayAlias)
1062 AliasResult ThisAlias =
1063 aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
1064 SI2->getFalseValue(), V2Size, V2TBAAInfo);
1065 return MergeAliasResults(ThisAlias, Alias);
1068 // If both arms of the Select node NoAlias or MustAlias V2, then returns
1069 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1071 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo);
1072 if (Alias == MayAlias)
1075 AliasResult ThisAlias =
1076 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
1077 return MergeAliasResults(ThisAlias, Alias);
1080 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
1082 AliasAnalysis::AliasResult
1083 BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
1084 const MDNode *PNTBAAInfo,
1085 const Value *V2, uint64_t V2Size,
1086 const MDNode *V2TBAAInfo) {
1087 // If the values are PHIs in the same block, we can do a more precise
1088 // as well as efficient check: just check for aliases between the values
1089 // on corresponding edges.
1090 if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
1091 if (PN2->getParent() == PN->getParent()) {
1092 LocPair Locs(Location(PN, PNSize, PNTBAAInfo),
1093 Location(V2, V2Size, V2TBAAInfo));
1095 std::swap(Locs.first, Locs.second);
1096 // Analyse the PHIs' inputs under the assumption that the PHIs are
1098 // If the PHIs are May/MustAlias there must be (recursively) an input
1099 // operand from outside the PHIs' cycle that is MayAlias/MustAlias or
1100 // there must be an operation on the PHIs within the PHIs' value cycle
1101 // that causes a MayAlias.
1102 // Pretend the phis do not alias.
1103 AliasResult Alias = NoAlias;
1104 assert(AliasCache.count(Locs) &&
1105 "There must exist an entry for the phi node");
1106 AliasResult OrigAliasResult = AliasCache[Locs];
1107 AliasCache[Locs] = NoAlias;
1109 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1110 AliasResult ThisAlias =
1111 aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
1112 PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
1113 V2Size, V2TBAAInfo);
1114 Alias = MergeAliasResults(ThisAlias, Alias);
1115 if (Alias == MayAlias)
1119 // Reset if speculation failed.
1120 if (Alias != NoAlias)
1121 AliasCache[Locs] = OrigAliasResult;
1126 SmallPtrSet<Value*, 4> UniqueSrc;
1127 SmallVector<Value*, 4> V1Srcs;
1128 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1129 Value *PV1 = PN->getIncomingValue(i);
1130 if (isa<PHINode>(PV1))
1131 // If any of the source itself is a PHI, return MayAlias conservatively
1132 // to avoid compile time explosion. The worst possible case is if both
1133 // sides are PHI nodes. In which case, this is O(m x n) time where 'm'
1134 // and 'n' are the number of PHI sources.
1136 if (UniqueSrc.insert(PV1))
1137 V1Srcs.push_back(PV1);
1140 AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo,
1141 V1Srcs[0], PNSize, PNTBAAInfo);
1142 // Early exit if the check of the first PHI source against V2 is MayAlias.
1143 // Other results are not possible.
1144 if (Alias == MayAlias)
1147 // If all sources of the PHI node NoAlias or MustAlias V2, then returns
1148 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1149 for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
1150 Value *V = V1Srcs[i];
1152 AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
1153 V, PNSize, PNTBAAInfo);
1154 Alias = MergeAliasResults(ThisAlias, Alias);
1155 if (Alias == MayAlias)
1162 // aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
1163 // such as array references.
1165 AliasAnalysis::AliasResult
1166 BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
1167 const MDNode *V1TBAAInfo,
1168 const Value *V2, uint64_t V2Size,
1169 const MDNode *V2TBAAInfo) {
1170 // If either of the memory references is empty, it doesn't matter what the
1171 // pointer values are.
1172 if (V1Size == 0 || V2Size == 0)
1175 // Strip off any casts if they exist.
1176 V1 = V1->stripPointerCasts();
1177 V2 = V2->stripPointerCasts();
1179 // Are we checking for alias of the same value?
1180 if (V1 == V2) return MustAlias;
1182 if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
1183 return NoAlias; // Scalars cannot alias each other
1185 // Figure out what objects these things are pointing to if we can.
1186 const Value *O1 = GetUnderlyingObject(V1, TD);
1187 const Value *O2 = GetUnderlyingObject(V2, TD);
1189 // Null values in the default address space don't point to any object, so they
1190 // don't alias any other pointer.
1191 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
1192 if (CPN->getType()->getAddressSpace() == 0)
1194 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
1195 if (CPN->getType()->getAddressSpace() == 0)
1199 // If V1/V2 point to two different objects we know that we have no alias.
1200 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
1203 // Constant pointers can't alias with non-const isIdentifiedObject objects.
1204 if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
1205 (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
1208 // Arguments can't alias with local allocations or noalias calls
1209 // in the same function.
1210 if (((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) ||
1211 (isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1)))))
1214 // Most objects can't alias null.
1215 if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
1216 (isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
1219 // If one pointer is the result of a call/invoke or load and the other is a
1220 // non-escaping local object within the same function, then we know the
1221 // object couldn't escape to a point where the call could return it.
1223 // Note that if the pointers are in different functions, there are a
1224 // variety of complications. A call with a nocapture argument may still
1225 // temporary store the nocapture argument's value in a temporary memory
1226 // location if that memory location doesn't escape. Or it may pass a
1227 // nocapture value to other functions as long as they don't capture it.
1228 if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
1230 if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
1234 // If the size of one access is larger than the entire object on the other
1235 // side, then we know such behavior is undefined and can assume no alias.
1237 if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD, *TLI)) ||
1238 (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD, *TLI)))
1241 // Check the cache before climbing up use-def chains. This also terminates
1242 // otherwise infinitely recursive queries.
1243 LocPair Locs(Location(V1, V1Size, V1TBAAInfo),
1244 Location(V2, V2Size, V2TBAAInfo));
1246 std::swap(Locs.first, Locs.second);
1247 std::pair<AliasCacheTy::iterator, bool> Pair =
1248 AliasCache.insert(std::make_pair(Locs, MayAlias));
1250 return Pair.first->second;
1252 // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
1253 // GEP can't simplify, we don't even look at the PHI cases.
1254 if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
1256 std::swap(V1Size, V2Size);
1258 std::swap(V1TBAAInfo, V2TBAAInfo);
1260 if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
1261 AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2);
1262 if (Result != MayAlias) return AliasCache[Locs] = Result;
1265 if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
1267 std::swap(V1Size, V2Size);
1268 std::swap(V1TBAAInfo, V2TBAAInfo);
1270 if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
1271 AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
1272 V2, V2Size, V2TBAAInfo);
1273 if (Result != MayAlias) return AliasCache[Locs] = Result;
1276 if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
1278 std::swap(V1Size, V2Size);
1279 std::swap(V1TBAAInfo, V2TBAAInfo);
1281 if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
1282 AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
1283 V2, V2Size, V2TBAAInfo);
1284 if (Result != MayAlias) return AliasCache[Locs] = Result;
1287 // If both pointers are pointing into the same object and one of them
1288 // accesses is accessing the entire object, then the accesses must
1289 // overlap in some way.
1291 if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD, *TLI)) ||
1292 (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD, *TLI)))
1293 return AliasCache[Locs] = PartialAlias;
1295 AliasResult Result =
1296 AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
1297 Location(V2, V2Size, V2TBAAInfo));
1298 return AliasCache[Locs] = Result;