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 /// isIdentifiedFunctionLocal - Return true if V is umabigously identified
146 /// at the function-level. Different IdentifiedFunctionLocals can't alias.
147 /// Further, an IdentifiedFunctionLocal can not alias with any function
148 /// arguments other than itself, which is not neccessarily true for
149 /// IdentifiedObjects.
150 static bool isIdentifiedFunctionLocal(const Value *V)
152 return isa<AllocaInst>(V) || isNoAliasCall(V) || isNoAliasArgument(V);
156 //===----------------------------------------------------------------------===//
157 // GetElementPtr Instruction Decomposition and Analysis
158 //===----------------------------------------------------------------------===//
167 struct VariableGEPIndex {
169 ExtensionKind Extension;
172 bool operator==(const VariableGEPIndex &Other) const {
173 return V == Other.V && Extension == Other.Extension &&
174 Scale == Other.Scale;
177 bool operator!=(const VariableGEPIndex &Other) const {
178 return !operator==(Other);
184 /// GetLinearExpression - Analyze the specified value as a linear expression:
185 /// "A*V + B", where A and B are constant integers. Return the scale and offset
186 /// values as APInts and return V as a Value*, and return whether we looked
187 /// through any sign or zero extends. The incoming Value is known to have
188 /// IntegerType and it may already be sign or zero extended.
190 /// Note that this looks through extends, so the high bits may not be
191 /// represented in the result.
192 static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
193 ExtensionKind &Extension,
194 const DataLayout &TD, unsigned Depth) {
195 assert(V->getType()->isIntegerTy() && "Not an integer value");
197 // Limit our recursion depth.
204 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
205 if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
206 switch (BOp->getOpcode()) {
208 case Instruction::Or:
209 // X|C == X+C if all the bits in C are unset in X. Otherwise we can't
211 if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &TD))
214 case Instruction::Add:
215 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
217 Offset += RHSC->getValue();
219 case Instruction::Mul:
220 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
222 Offset *= RHSC->getValue();
223 Scale *= RHSC->getValue();
225 case Instruction::Shl:
226 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
228 Offset <<= RHSC->getValue().getLimitedValue();
229 Scale <<= RHSC->getValue().getLimitedValue();
235 // Since GEP indices are sign extended anyway, we don't care about the high
236 // bits of a sign or zero extended value - just scales and offsets. The
237 // extensions have to be consistent though.
238 if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) ||
239 (isa<ZExtInst>(V) && Extension != EK_SignExt)) {
240 Value *CastOp = cast<CastInst>(V)->getOperand(0);
241 unsigned OldWidth = Scale.getBitWidth();
242 unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
243 Scale = Scale.trunc(SmallWidth);
244 Offset = Offset.trunc(SmallWidth);
245 Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
247 Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension,
249 Scale = Scale.zext(OldWidth);
250 Offset = Offset.zext(OldWidth);
260 /// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it
261 /// into a base pointer with a constant offset and a number of scaled symbolic
264 /// The scaled symbolic offsets (represented by pairs of a Value* and a scale in
265 /// the VarIndices vector) are Value*'s that are known to be scaled by the
266 /// specified amount, but which may have other unrepresented high bits. As such,
267 /// the gep cannot necessarily be reconstructed from its decomposed form.
269 /// When DataLayout is around, this function is capable of analyzing everything
270 /// that GetUnderlyingObject can look through. When not, it just looks
271 /// through pointer casts.
274 DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
275 SmallVectorImpl<VariableGEPIndex> &VarIndices,
276 const DataLayout *TD) {
277 // Limit recursion depth to limit compile time in crazy cases.
278 unsigned MaxLookup = 6;
282 // See if this is a bitcast or GEP.
283 const Operator *Op = dyn_cast<Operator>(V);
285 // The only non-operator case we can handle are GlobalAliases.
286 if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
287 if (!GA->mayBeOverridden()) {
288 V = GA->getAliasee();
295 if (Op->getOpcode() == Instruction::BitCast) {
296 V = Op->getOperand(0);
300 const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
302 // If it's not a GEP, hand it off to SimplifyInstruction to see if it
303 // can come up with something. This matches what GetUnderlyingObject does.
304 if (const Instruction *I = dyn_cast<Instruction>(V))
305 // TODO: Get a DominatorTree and use it here.
306 if (const Value *Simplified =
307 SimplifyInstruction(const_cast<Instruction *>(I), TD)) {
315 // Don't attempt to analyze GEPs over unsized objects.
316 if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized())
319 // If we are lacking DataLayout information, we can't compute the offets of
320 // elements computed by GEPs. However, we can handle bitcast equivalent
323 if (!GEPOp->hasAllZeroIndices())
325 V = GEPOp->getOperand(0);
329 unsigned AS = GEPOp->getPointerAddressSpace();
330 // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
331 gep_type_iterator GTI = gep_type_begin(GEPOp);
332 for (User::const_op_iterator I = GEPOp->op_begin()+1,
333 E = GEPOp->op_end(); I != E; ++I) {
335 // Compute the (potentially symbolic) offset in bytes for this index.
336 if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
337 // For a struct, add the member offset.
338 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
339 if (FieldNo == 0) continue;
341 BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo);
345 // For an array/pointer, add the element offset, explicitly scaled.
346 if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
347 if (CIdx->isZero()) continue;
348 BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
352 uint64_t Scale = TD->getTypeAllocSize(*GTI);
353 ExtensionKind Extension = EK_NotExtended;
355 // If the integer type is smaller than the pointer size, it is implicitly
356 // sign extended to pointer size.
357 unsigned Width = Index->getType()->getIntegerBitWidth();
358 if (TD->getPointerSizeInBits(AS) > Width)
359 Extension = EK_SignExt;
361 // Use GetLinearExpression to decompose the index into a C1*V+C2 form.
362 APInt IndexScale(Width, 0), IndexOffset(Width, 0);
363 Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension,
366 // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
367 // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
368 BaseOffs += IndexOffset.getSExtValue()*Scale;
369 Scale *= IndexScale.getSExtValue();
371 // If we already had an occurrence of this index variable, merge this
372 // scale into it. For example, we want to handle:
373 // A[x][x] -> x*16 + x*4 -> x*20
374 // This also ensures that 'x' only appears in the index list once.
375 for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
376 if (VarIndices[i].V == Index &&
377 VarIndices[i].Extension == Extension) {
378 Scale += VarIndices[i].Scale;
379 VarIndices.erase(VarIndices.begin()+i);
384 // Make sure that we have a scale that makes sense for this target's
386 if (unsigned ShiftBits = 64 - TD->getPointerSizeInBits(AS)) {
388 Scale = (int64_t)Scale >> ShiftBits;
392 VariableGEPIndex Entry = {Index, Extension,
393 static_cast<int64_t>(Scale)};
394 VarIndices.push_back(Entry);
398 // Analyze the base pointer next.
399 V = GEPOp->getOperand(0);
400 } while (--MaxLookup);
402 // If the chain of expressions is too deep, just return early.
406 /// GetIndexDifference - Dest and Src are the variable indices from two
407 /// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
408 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
409 /// difference between the two pointers.
410 static void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
411 const SmallVectorImpl<VariableGEPIndex> &Src) {
412 if (Src.empty()) return;
414 for (unsigned i = 0, e = Src.size(); i != e; ++i) {
415 const Value *V = Src[i].V;
416 ExtensionKind Extension = Src[i].Extension;
417 int64_t Scale = Src[i].Scale;
419 // Find V in Dest. This is N^2, but pointer indices almost never have more
420 // than a few variable indexes.
421 for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
422 if (Dest[j].V != V || Dest[j].Extension != Extension) continue;
424 // If we found it, subtract off Scale V's from the entry in Dest. If it
425 // goes to zero, remove the entry.
426 if (Dest[j].Scale != Scale)
427 Dest[j].Scale -= Scale;
429 Dest.erase(Dest.begin()+j);
434 // If we didn't consume this entry, add it to the end of the Dest list.
436 VariableGEPIndex Entry = { V, Extension, -Scale };
437 Dest.push_back(Entry);
442 //===----------------------------------------------------------------------===//
443 // BasicAliasAnalysis Pass
444 //===----------------------------------------------------------------------===//
447 static const Function *getParent(const Value *V) {
448 if (const Instruction *inst = dyn_cast<Instruction>(V))
449 return inst->getParent()->getParent();
451 if (const Argument *arg = dyn_cast<Argument>(V))
452 return arg->getParent();
457 static bool notDifferentParent(const Value *O1, const Value *O2) {
459 const Function *F1 = getParent(O1);
460 const Function *F2 = getParent(O2);
462 return !F1 || !F2 || F1 == F2;
467 /// BasicAliasAnalysis - This is the primary alias analysis implementation.
468 struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
469 static char ID; // Class identification, replacement for typeinfo
470 BasicAliasAnalysis() : ImmutablePass(ID) {
471 initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
474 virtual void initializePass() {
475 InitializeAliasAnalysis(this);
478 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
479 AU.addRequired<AliasAnalysis>();
480 AU.addRequired<TargetLibraryInfo>();
483 virtual AliasResult alias(const Location &LocA,
484 const Location &LocB) {
485 assert(AliasCache.empty() && "AliasCache must be cleared after use!");
486 assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
487 "BasicAliasAnalysis doesn't support interprocedural queries.");
488 AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag,
489 LocB.Ptr, LocB.Size, LocB.TBAATag);
490 // AliasCache rarely has more than 1 or 2 elements, always use
491 // shrink_and_clear so it quickly returns to the inline capacity of the
492 // SmallDenseMap if it ever grows larger.
493 // FIXME: This should really be shrink_to_inline_capacity_and_clear().
494 AliasCache.shrink_and_clear();
498 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
499 const Location &Loc);
501 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
502 ImmutableCallSite CS2) {
503 // The AliasAnalysis base class has some smarts, lets use them.
504 return AliasAnalysis::getModRefInfo(CS1, CS2);
507 /// pointsToConstantMemory - Chase pointers until we find a (constant
509 virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal);
511 /// getModRefBehavior - Return the behavior when calling the given
513 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
515 /// getModRefBehavior - Return the behavior when calling the given function.
516 /// For use when the call site is not known.
517 virtual ModRefBehavior getModRefBehavior(const Function *F);
519 /// getAdjustedAnalysisPointer - This method is used when a pass implements
520 /// an analysis interface through multiple inheritance. If needed, it
521 /// should override this to adjust the this pointer as needed for the
522 /// specified pass info.
523 virtual void *getAdjustedAnalysisPointer(const void *ID) {
524 if (ID == &AliasAnalysis::ID)
525 return (AliasAnalysis*)this;
530 // AliasCache - Track alias queries to guard against recursion.
531 typedef std::pair<Location, Location> LocPair;
532 typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
533 AliasCacheTy AliasCache;
535 // Visited - Track instructions visited by pointsToConstantMemory.
536 SmallPtrSet<const Value*, 16> Visited;
538 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
539 // instruction against another.
540 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
541 const MDNode *V1TBAAInfo,
542 const Value *V2, uint64_t V2Size,
543 const MDNode *V2TBAAInfo,
544 const Value *UnderlyingV1, const Value *UnderlyingV2);
546 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
547 // instruction against another.
548 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
549 const MDNode *PNTBAAInfo,
550 const Value *V2, uint64_t V2Size,
551 const MDNode *V2TBAAInfo);
553 /// aliasSelect - Disambiguate a Select instruction against another value.
554 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
555 const MDNode *SITBAAInfo,
556 const Value *V2, uint64_t V2Size,
557 const MDNode *V2TBAAInfo);
559 AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
560 const MDNode *V1TBAATag,
561 const Value *V2, uint64_t V2Size,
562 const MDNode *V2TBAATag);
564 } // End of anonymous namespace
566 // Register this pass...
567 char BasicAliasAnalysis::ID = 0;
568 INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
569 "Basic Alias Analysis (stateless AA impl)",
571 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
572 INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
573 "Basic Alias Analysis (stateless AA impl)",
577 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
578 return new BasicAliasAnalysis();
581 /// pointsToConstantMemory - Returns whether the given pointer value
582 /// points to memory that is local to the function, with global constants being
583 /// considered local to all functions.
585 BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
586 assert(Visited.empty() && "Visited must be cleared after use!");
588 unsigned MaxLookup = 8;
589 SmallVector<const Value *, 16> Worklist;
590 Worklist.push_back(Loc.Ptr);
592 const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), TD);
593 if (!Visited.insert(V)) {
595 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
598 // An alloca instruction defines local memory.
599 if (OrLocal && isa<AllocaInst>(V))
602 // A global constant counts as local memory for our purposes.
603 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
604 // Note: this doesn't require GV to be "ODR" because it isn't legal for a
605 // global to be marked constant in some modules and non-constant in
606 // others. GV may even be a declaration, not a definition.
607 if (!GV->isConstant()) {
609 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
614 // If both select values point to local memory, then so does the select.
615 if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
616 Worklist.push_back(SI->getTrueValue());
617 Worklist.push_back(SI->getFalseValue());
621 // If all values incoming to a phi node point to local memory, then so does
623 if (const PHINode *PN = dyn_cast<PHINode>(V)) {
624 // Don't bother inspecting phi nodes with many operands.
625 if (PN->getNumIncomingValues() > MaxLookup) {
627 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
629 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
630 Worklist.push_back(PN->getIncomingValue(i));
634 // Otherwise be conservative.
636 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
638 } while (!Worklist.empty() && --MaxLookup);
641 return Worklist.empty();
644 /// getModRefBehavior - Return the behavior when calling the given call site.
645 AliasAnalysis::ModRefBehavior
646 BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
647 if (CS.doesNotAccessMemory())
648 // Can't do better than this.
649 return DoesNotAccessMemory;
651 ModRefBehavior Min = UnknownModRefBehavior;
653 // If the callsite knows it only reads memory, don't return worse
655 if (CS.onlyReadsMemory())
656 Min = OnlyReadsMemory;
658 // The AliasAnalysis base class has some smarts, lets use them.
659 return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
662 /// getModRefBehavior - Return the behavior when calling the given function.
663 /// For use when the call site is not known.
664 AliasAnalysis::ModRefBehavior
665 BasicAliasAnalysis::getModRefBehavior(const Function *F) {
666 // If the function declares it doesn't access memory, we can't do better.
667 if (F->doesNotAccessMemory())
668 return DoesNotAccessMemory;
670 // For intrinsics, we can check the table.
671 if (unsigned iid = F->getIntrinsicID()) {
672 #define GET_INTRINSIC_MODREF_BEHAVIOR
673 #include "llvm/IR/Intrinsics.gen"
674 #undef GET_INTRINSIC_MODREF_BEHAVIOR
677 ModRefBehavior Min = UnknownModRefBehavior;
679 // If the function declares it only reads memory, go with that.
680 if (F->onlyReadsMemory())
681 Min = OnlyReadsMemory;
683 // Otherwise be conservative.
684 return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
687 /// getModRefInfo - Check to see if the specified callsite can clobber the
688 /// specified memory object. Since we only look at local properties of this
689 /// function, we really can't say much about this query. We do, however, use
690 /// simple "address taken" analysis on local objects.
691 AliasAnalysis::ModRefResult
692 BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
693 const Location &Loc) {
694 assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
695 "AliasAnalysis query involving multiple functions!");
697 const Value *Object = GetUnderlyingObject(Loc.Ptr, TD);
699 // If this is a tail call and Loc.Ptr points to a stack location, we know that
700 // the tail call cannot access or modify the local stack.
701 // We cannot exclude byval arguments here; these belong to the caller of
702 // the current function not to the current function, and a tail callee
703 // may reference them.
704 if (isa<AllocaInst>(Object))
705 if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
706 if (CI->isTailCall())
709 // If the pointer is to a locally allocated object that does not escape,
710 // then the call can not mod/ref the pointer unless the call takes the pointer
711 // as an argument, and itself doesn't capture it.
712 if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
713 isNonEscapingLocalObject(Object)) {
714 bool PassedAsArg = false;
716 for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
717 CI != CE; ++CI, ++ArgNo) {
718 // Only look at the no-capture or byval pointer arguments. If this
719 // pointer were passed to arguments that were neither of these, then it
720 // couldn't be no-capture.
721 if (!(*CI)->getType()->isPointerTy() ||
722 (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
725 // If this is a no-capture pointer argument, see if we can tell that it
726 // is impossible to alias the pointer we're checking. If not, we have to
727 // assume that the call could touch the pointer, even though it doesn't
729 if (!isNoAlias(Location(*CI), Location(Object))) {
739 const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
740 ModRefResult Min = ModRef;
742 // Finally, handle specific knowledge of intrinsics.
743 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
745 switch (II->getIntrinsicID()) {
747 case Intrinsic::memcpy:
748 case Intrinsic::memmove: {
749 uint64_t Len = UnknownSize;
750 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
751 Len = LenCI->getZExtValue();
752 Value *Dest = II->getArgOperand(0);
753 Value *Src = II->getArgOperand(1);
754 // If it can't overlap the source dest, then it doesn't modref the loc.
755 if (isNoAlias(Location(Dest, Len), Loc)) {
756 if (isNoAlias(Location(Src, Len), Loc))
758 // If it can't overlap the dest, then worst case it reads the loc.
760 } else if (isNoAlias(Location(Src, Len), Loc)) {
761 // If it can't overlap the source, then worst case it mutates the loc.
766 case Intrinsic::memset:
767 // Since memset is 'accesses arguments' only, the AliasAnalysis base class
768 // will handle it for the variable length case.
769 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2))) {
770 uint64_t Len = LenCI->getZExtValue();
771 Value *Dest = II->getArgOperand(0);
772 if (isNoAlias(Location(Dest, Len), Loc))
775 // We know that memset doesn't load anything.
778 case Intrinsic::lifetime_start:
779 case Intrinsic::lifetime_end:
780 case Intrinsic::invariant_start: {
782 cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
783 if (isNoAlias(Location(II->getArgOperand(1),
785 II->getMetadata(LLVMContext::MD_tbaa)),
790 case Intrinsic::invariant_end: {
792 cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
793 if (isNoAlias(Location(II->getArgOperand(2),
795 II->getMetadata(LLVMContext::MD_tbaa)),
800 case Intrinsic::arm_neon_vld1: {
801 // LLVM's vld1 and vst1 intrinsics currently only support a single
804 TD ? TD->getTypeStoreSize(II->getType()) : UnknownSize;
805 if (isNoAlias(Location(II->getArgOperand(0), Size,
806 II->getMetadata(LLVMContext::MD_tbaa)),
811 case Intrinsic::arm_neon_vst1: {
813 TD ? TD->getTypeStoreSize(II->getArgOperand(1)->getType()) : UnknownSize;
814 if (isNoAlias(Location(II->getArgOperand(0), Size,
815 II->getMetadata(LLVMContext::MD_tbaa)),
822 // We can bound the aliasing properties of memset_pattern16 just as we can
823 // for memcpy/memset. This is particularly important because the
824 // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
825 // whenever possible.
826 else if (TLI.has(LibFunc::memset_pattern16) &&
827 CS.getCalledFunction() &&
828 CS.getCalledFunction()->getName() == "memset_pattern16") {
829 const Function *MS = CS.getCalledFunction();
830 FunctionType *MemsetType = MS->getFunctionType();
831 if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
832 isa<PointerType>(MemsetType->getParamType(0)) &&
833 isa<PointerType>(MemsetType->getParamType(1)) &&
834 isa<IntegerType>(MemsetType->getParamType(2))) {
835 uint64_t Len = UnknownSize;
836 if (const ConstantInt *LenCI = dyn_cast<ConstantInt>(CS.getArgument(2)))
837 Len = LenCI->getZExtValue();
838 const Value *Dest = CS.getArgument(0);
839 const Value *Src = CS.getArgument(1);
840 // If it can't overlap the source dest, then it doesn't modref the loc.
841 if (isNoAlias(Location(Dest, Len), Loc)) {
842 // Always reads 16 bytes of the source.
843 if (isNoAlias(Location(Src, 16), Loc))
845 // If it can't overlap the dest, then worst case it reads the loc.
847 // Always reads 16 bytes of the source.
848 } else if (isNoAlias(Location(Src, 16), Loc)) {
849 // If it can't overlap the source, then worst case it mutates the loc.
855 // The AliasAnalysis base class has some smarts, lets use them.
856 return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min);
859 static bool areVarIndicesEqual(SmallVectorImpl<VariableGEPIndex> &Indices1,
860 SmallVectorImpl<VariableGEPIndex> &Indices2) {
861 unsigned Size1 = Indices1.size();
862 unsigned Size2 = Indices2.size();
867 for (unsigned I = 0; I != Size1; ++I)
868 if (Indices1[I] != Indices2[I])
874 /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
875 /// against another pointer. We know that V1 is a GEP, but we don't know
876 /// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, TD),
877 /// UnderlyingV2 is the same for V2.
879 AliasAnalysis::AliasResult
880 BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
881 const MDNode *V1TBAAInfo,
882 const Value *V2, uint64_t V2Size,
883 const MDNode *V2TBAAInfo,
884 const Value *UnderlyingV1,
885 const Value *UnderlyingV2) {
886 int64_t GEP1BaseOffset;
887 SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
889 // If we have two gep instructions with must-alias or not-alias'ing base
890 // pointers, figure out if the indexes to the GEP tell us anything about the
892 if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
893 // Do the base pointers alias?
894 AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0,
895 UnderlyingV2, UnknownSize, 0);
897 // Check for geps of non-aliasing underlying pointers where the offsets are
899 if ((BaseAlias == MayAlias) && V1Size == V2Size) {
900 // Do the base pointers alias assuming type and size.
901 AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
902 V1TBAAInfo, UnderlyingV2,
904 if (PreciseBaseAlias == NoAlias) {
905 // See if the computed offset from the common pointer tells us about the
906 // relation of the resulting pointer.
907 int64_t GEP2BaseOffset;
908 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
909 const Value *GEP2BasePtr =
910 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
911 const Value *GEP1BasePtr =
912 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
913 // DecomposeGEPExpression and GetUnderlyingObject should return the
914 // same result except when DecomposeGEPExpression has no DataLayout.
915 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
917 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
921 if (GEP1BaseOffset == GEP2BaseOffset &&
922 areVarIndicesEqual(GEP1VariableIndices, GEP2VariableIndices))
924 GEP1VariableIndices.clear();
928 // If we get a No or May, then return it immediately, no amount of analysis
929 // will improve this situation.
930 if (BaseAlias != MustAlias) return BaseAlias;
932 // Otherwise, we have a MustAlias. Since the base pointers alias each other
933 // exactly, see if the computed offset from the common pointer tells us
934 // about the relation of the resulting pointer.
935 const Value *GEP1BasePtr =
936 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
938 int64_t GEP2BaseOffset;
939 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
940 const Value *GEP2BasePtr =
941 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
943 // DecomposeGEPExpression and GetUnderlyingObject should return the
944 // same result except when DecomposeGEPExpression has no DataLayout.
945 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
947 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
951 // Subtract the GEP2 pointer from the GEP1 pointer to find out their
952 // symbolic difference.
953 GEP1BaseOffset -= GEP2BaseOffset;
954 GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
957 // Check to see if these two pointers are related by the getelementptr
958 // instruction. If one pointer is a GEP with a non-zero index of the other
959 // pointer, we know they cannot alias.
961 // If both accesses are unknown size, we can't do anything useful here.
962 if (V1Size == UnknownSize && V2Size == UnknownSize)
965 AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, 0,
966 V2, V2Size, V2TBAAInfo);
968 // If V2 may alias GEP base pointer, conservatively returns MayAlias.
969 // If V2 is known not to alias GEP base pointer, then the two values
970 // cannot alias per GEP semantics: "A pointer value formed from a
971 // getelementptr instruction is associated with the addresses associated
972 // with the first operand of the getelementptr".
975 const Value *GEP1BasePtr =
976 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
978 // DecomposeGEPExpression and GetUnderlyingObject should return the
979 // same result except when DecomposeGEPExpression has no DataLayout.
980 if (GEP1BasePtr != UnderlyingV1) {
982 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
987 // In the two GEP Case, if there is no difference in the offsets of the
988 // computed pointers, the resultant pointers are a must alias. This
989 // hapens when we have two lexically identical GEP's (for example).
991 // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
992 // must aliases the GEP, the end result is a must alias also.
993 if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
996 // If there is a constant difference between the pointers, but the difference
997 // is less than the size of the associated memory object, then we know
998 // that the objects are partially overlapping. If the difference is
999 // greater, we know they do not overlap.
1000 if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
1001 if (GEP1BaseOffset >= 0) {
1002 if (V2Size != UnknownSize) {
1003 if ((uint64_t)GEP1BaseOffset < V2Size)
1004 return PartialAlias;
1008 if (V1Size != UnknownSize) {
1009 if (-(uint64_t)GEP1BaseOffset < V1Size)
1010 return PartialAlias;
1016 // Try to distinguish something like &A[i][1] against &A[42][0].
1017 // Grab the least significant bit set in any of the scales.
1018 if (!GEP1VariableIndices.empty()) {
1019 uint64_t Modulo = 0;
1020 for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
1021 Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
1022 Modulo = Modulo ^ (Modulo & (Modulo - 1));
1024 // We can compute the difference between the two addresses
1025 // mod Modulo. Check whether that difference guarantees that the
1026 // two locations do not alias.
1027 uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
1028 if (V1Size != UnknownSize && V2Size != UnknownSize &&
1029 ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
1033 // Statically, we can see that the base objects are the same, but the
1034 // pointers have dynamic offsets which we can't resolve. And none of our
1035 // little tricks above worked.
1037 // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
1038 // practical effect of this is protecting TBAA in the case of dynamic
1039 // indices into arrays of unions or malloc'd memory.
1040 return PartialAlias;
1043 static AliasAnalysis::AliasResult
1044 MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
1045 // If the results agree, take it.
1048 // A mix of PartialAlias and MustAlias is PartialAlias.
1049 if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
1050 (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
1051 return AliasAnalysis::PartialAlias;
1052 // Otherwise, we don't know anything.
1053 return AliasAnalysis::MayAlias;
1056 /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
1057 /// instruction against another.
1058 AliasAnalysis::AliasResult
1059 BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
1060 const MDNode *SITBAAInfo,
1061 const Value *V2, uint64_t V2Size,
1062 const MDNode *V2TBAAInfo) {
1063 // If the values are Selects with the same condition, we can do a more precise
1064 // check: just check for aliases between the values on corresponding arms.
1065 if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
1066 if (SI->getCondition() == SI2->getCondition()) {
1068 aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo,
1069 SI2->getTrueValue(), V2Size, V2TBAAInfo);
1070 if (Alias == MayAlias)
1072 AliasResult ThisAlias =
1073 aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
1074 SI2->getFalseValue(), V2Size, V2TBAAInfo);
1075 return MergeAliasResults(ThisAlias, Alias);
1078 // If both arms of the Select node NoAlias or MustAlias V2, then returns
1079 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1081 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo);
1082 if (Alias == MayAlias)
1085 AliasResult ThisAlias =
1086 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
1087 return MergeAliasResults(ThisAlias, Alias);
1090 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
1092 AliasAnalysis::AliasResult
1093 BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
1094 const MDNode *PNTBAAInfo,
1095 const Value *V2, uint64_t V2Size,
1096 const MDNode *V2TBAAInfo) {
1097 // If the values are PHIs in the same block, we can do a more precise
1098 // as well as efficient check: just check for aliases between the values
1099 // on corresponding edges.
1100 if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
1101 if (PN2->getParent() == PN->getParent()) {
1102 LocPair Locs(Location(PN, PNSize, PNTBAAInfo),
1103 Location(V2, V2Size, V2TBAAInfo));
1105 std::swap(Locs.first, Locs.second);
1106 // Analyse the PHIs' inputs under the assumption that the PHIs are
1108 // If the PHIs are May/MustAlias there must be (recursively) an input
1109 // operand from outside the PHIs' cycle that is MayAlias/MustAlias or
1110 // there must be an operation on the PHIs within the PHIs' value cycle
1111 // that causes a MayAlias.
1112 // Pretend the phis do not alias.
1113 AliasResult Alias = NoAlias;
1114 assert(AliasCache.count(Locs) &&
1115 "There must exist an entry for the phi node");
1116 AliasResult OrigAliasResult = AliasCache[Locs];
1117 AliasCache[Locs] = NoAlias;
1119 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1120 AliasResult ThisAlias =
1121 aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
1122 PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
1123 V2Size, V2TBAAInfo);
1124 Alias = MergeAliasResults(ThisAlias, Alias);
1125 if (Alias == MayAlias)
1129 // Reset if speculation failed.
1130 if (Alias != NoAlias)
1131 AliasCache[Locs] = OrigAliasResult;
1136 SmallPtrSet<Value*, 4> UniqueSrc;
1137 SmallVector<Value*, 4> V1Srcs;
1138 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1139 Value *PV1 = PN->getIncomingValue(i);
1140 if (isa<PHINode>(PV1))
1141 // If any of the source itself is a PHI, return MayAlias conservatively
1142 // to avoid compile time explosion. The worst possible case is if both
1143 // sides are PHI nodes. In which case, this is O(m x n) time where 'm'
1144 // and 'n' are the number of PHI sources.
1146 if (UniqueSrc.insert(PV1))
1147 V1Srcs.push_back(PV1);
1150 AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo,
1151 V1Srcs[0], PNSize, PNTBAAInfo);
1152 // Early exit if the check of the first PHI source against V2 is MayAlias.
1153 // Other results are not possible.
1154 if (Alias == MayAlias)
1157 // If all sources of the PHI node NoAlias or MustAlias V2, then returns
1158 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1159 for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
1160 Value *V = V1Srcs[i];
1162 AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
1163 V, PNSize, PNTBAAInfo);
1164 Alias = MergeAliasResults(ThisAlias, Alias);
1165 if (Alias == MayAlias)
1172 // aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
1173 // such as array references.
1175 AliasAnalysis::AliasResult
1176 BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
1177 const MDNode *V1TBAAInfo,
1178 const Value *V2, uint64_t V2Size,
1179 const MDNode *V2TBAAInfo) {
1180 // If either of the memory references is empty, it doesn't matter what the
1181 // pointer values are.
1182 if (V1Size == 0 || V2Size == 0)
1185 // Strip off any casts if they exist.
1186 V1 = V1->stripPointerCasts();
1187 V2 = V2->stripPointerCasts();
1189 // Are we checking for alias of the same value?
1190 if (V1 == V2) return MustAlias;
1192 if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
1193 return NoAlias; // Scalars cannot alias each other
1195 // Figure out what objects these things are pointing to if we can.
1196 const Value *O1 = GetUnderlyingObject(V1, TD);
1197 const Value *O2 = GetUnderlyingObject(V2, TD);
1199 // Null values in the default address space don't point to any object, so they
1200 // don't alias any other pointer.
1201 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
1202 if (CPN->getType()->getAddressSpace() == 0)
1204 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
1205 if (CPN->getType()->getAddressSpace() == 0)
1209 // If V1/V2 point to two different objects we know that we have no alias.
1210 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
1213 // Constant pointers can't alias with non-const isIdentifiedObject objects.
1214 if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
1215 (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
1218 // Function arguments can't alias with things that are known to be
1219 // unambigously identified at the function level.
1220 if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
1221 (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
1224 // Most objects can't alias null.
1225 if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
1226 (isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
1229 // If one pointer is the result of a call/invoke or load and the other is a
1230 // non-escaping local object within the same function, then we know the
1231 // object couldn't escape to a point where the call could return it.
1233 // Note that if the pointers are in different functions, there are a
1234 // variety of complications. A call with a nocapture argument may still
1235 // temporary store the nocapture argument's value in a temporary memory
1236 // location if that memory location doesn't escape. Or it may pass a
1237 // nocapture value to other functions as long as they don't capture it.
1238 if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
1240 if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
1244 // If the size of one access is larger than the entire object on the other
1245 // side, then we know such behavior is undefined and can assume no alias.
1247 if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD, *TLI)) ||
1248 (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD, *TLI)))
1251 // Check the cache before climbing up use-def chains. This also terminates
1252 // otherwise infinitely recursive queries.
1253 LocPair Locs(Location(V1, V1Size, V1TBAAInfo),
1254 Location(V2, V2Size, V2TBAAInfo));
1256 std::swap(Locs.first, Locs.second);
1257 std::pair<AliasCacheTy::iterator, bool> Pair =
1258 AliasCache.insert(std::make_pair(Locs, MayAlias));
1260 return Pair.first->second;
1262 // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
1263 // GEP can't simplify, we don't even look at the PHI cases.
1264 if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
1266 std::swap(V1Size, V2Size);
1268 std::swap(V1TBAAInfo, V2TBAAInfo);
1270 if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
1271 AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2);
1272 if (Result != MayAlias) return AliasCache[Locs] = Result;
1275 if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
1277 std::swap(V1Size, V2Size);
1278 std::swap(V1TBAAInfo, V2TBAAInfo);
1280 if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
1281 AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
1282 V2, V2Size, V2TBAAInfo);
1283 if (Result != MayAlias) return AliasCache[Locs] = Result;
1286 if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
1288 std::swap(V1Size, V2Size);
1289 std::swap(V1TBAAInfo, V2TBAAInfo);
1291 if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
1292 AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
1293 V2, V2Size, V2TBAAInfo);
1294 if (Result != MayAlias) return AliasCache[Locs] = Result;
1297 // If both pointers are pointing into the same object and one of them
1298 // accesses is accessing the entire object, then the accesses must
1299 // overlap in some way.
1301 if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD, *TLI)) ||
1302 (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD, *TLI)))
1303 return AliasCache[Locs] = PartialAlias;
1305 AliasResult Result =
1306 AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
1307 Location(V2, V2Size, V2TBAAInfo));
1308 return AliasCache[Locs] = Result;