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/CFG.h"
21 #include "llvm/Analysis/CaptureTracking.h"
22 #include "llvm/Analysis/InstructionSimplify.h"
23 #include "llvm/Analysis/LoopInfo.h"
24 #include "llvm/Analysis/MemoryBuiltins.h"
25 #include "llvm/Analysis/ValueTracking.h"
26 #include "llvm/IR/Constants.h"
27 #include "llvm/IR/DataLayout.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/Dominators.h"
30 #include "llvm/IR/Function.h"
31 #include "llvm/IR/GetElementPtrTypeIterator.h"
32 #include "llvm/IR/GlobalAlias.h"
33 #include "llvm/IR/GlobalVariable.h"
34 #include "llvm/IR/Instructions.h"
35 #include "llvm/IR/IntrinsicInst.h"
36 #include "llvm/IR/LLVMContext.h"
37 #include "llvm/IR/Operator.h"
38 #include "llvm/Pass.h"
39 #include "llvm/Support/ErrorHandling.h"
40 #include "llvm/Target/TargetLibraryInfo.h"
44 /// Cutoff after which to stop analysing a set of phi nodes potentially involved
45 /// in a cycle. Because we are analysing 'through' phi nodes we need to be
46 /// careful with value equivalence. We use reachability to make sure a value
47 /// cannot be involved in a cycle.
48 const unsigned MaxNumPhiBBsValueReachabilityCheck = 20;
50 // The max limit of the search depth in DecomposeGEPExpression() and
51 // GetUnderlyingObject(), both functions need to use the same search
52 // depth otherwise the algorithm in aliasGEP will assert.
53 static const unsigned MaxLookupSearchDepth = 6;
55 //===----------------------------------------------------------------------===//
57 //===----------------------------------------------------------------------===//
59 /// isNonEscapingLocalObject - Return true if the pointer is to a function-local
60 /// object that never escapes from the function.
61 static bool isNonEscapingLocalObject(const Value *V) {
62 // If this is a local allocation, check to see if it escapes.
63 if (isa<AllocaInst>(V) || isNoAliasCall(V))
64 // Set StoreCaptures to True so that we can assume in our callers that the
65 // pointer is not the result of a load instruction. Currently
66 // PointerMayBeCaptured doesn't have any special analysis for the
67 // StoreCaptures=false case; if it did, our callers could be refined to be
69 return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
71 // If this is an argument that corresponds to a byval or noalias argument,
72 // then it has not escaped before entering the function. Check if it escapes
73 // inside the function.
74 if (const Argument *A = dyn_cast<Argument>(V))
75 if (A->hasByValAttr() || A->hasNoAliasAttr())
76 // Note even if the argument is marked nocapture we still need to check
77 // for copies made inside the function. The nocapture attribute only
78 // specifies that there are no copies made that outlive the function.
79 return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
84 /// isEscapeSource - Return true if the pointer is one which would have
85 /// been considered an escape by isNonEscapingLocalObject.
86 static bool isEscapeSource(const Value *V) {
87 if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V))
90 // The load case works because isNonEscapingLocalObject considers all
91 // stores to be escapes (it passes true for the StoreCaptures argument
92 // to PointerMayBeCaptured).
99 /// getObjectSize - Return the size of the object specified by V, or
100 /// UnknownSize if unknown.
101 static uint64_t getObjectSize(const Value *V, const DataLayout &DL,
102 const TargetLibraryInfo &TLI,
103 bool RoundToAlign = false) {
105 if (getObjectSize(V, Size, &DL, &TLI, RoundToAlign))
107 return AliasAnalysis::UnknownSize;
110 /// isObjectSmallerThan - Return true if we can prove that the object specified
111 /// by V is smaller than Size.
112 static bool isObjectSmallerThan(const Value *V, uint64_t Size,
113 const DataLayout &DL,
114 const TargetLibraryInfo &TLI) {
115 // Note that the meanings of the "object" are slightly different in the
116 // following contexts:
117 // c1: llvm::getObjectSize()
118 // c2: llvm.objectsize() intrinsic
119 // c3: isObjectSmallerThan()
120 // c1 and c2 share the same meaning; however, the meaning of "object" in c3
121 // refers to the "entire object".
123 // Consider this example:
124 // char *p = (char*)malloc(100)
127 // In the context of c1 and c2, the "object" pointed by q refers to the
128 // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
130 // However, in the context of c3, the "object" refers to the chunk of memory
131 // being allocated. So, the "object" has 100 bytes, and q points to the middle
132 // the "object". In case q is passed to isObjectSmallerThan() as the 1st
133 // parameter, before the llvm::getObjectSize() is called to get the size of
134 // entire object, we should:
135 // - either rewind the pointer q to the base-address of the object in
136 // question (in this case rewind to p), or
137 // - just give up. It is up to caller to make sure the pointer is pointing
138 // to the base address the object.
140 // We go for 2nd option for simplicity.
141 if (!isIdentifiedObject(V))
144 // This function needs to use the aligned object size because we allow
145 // reads a bit past the end given sufficient alignment.
146 uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/true);
148 return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size;
151 /// isObjectSize - Return true if we can prove that the object specified
152 /// by V has size Size.
153 static bool isObjectSize(const Value *V, uint64_t Size,
154 const DataLayout &DL, const TargetLibraryInfo &TLI) {
155 uint64_t ObjectSize = getObjectSize(V, DL, TLI);
156 return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size;
159 //===----------------------------------------------------------------------===//
160 // GetElementPtr Instruction Decomposition and Analysis
161 //===----------------------------------------------------------------------===//
170 struct VariableGEPIndex {
172 ExtensionKind Extension;
175 bool operator==(const VariableGEPIndex &Other) const {
176 return V == Other.V && Extension == Other.Extension &&
177 Scale == Other.Scale;
180 bool operator!=(const VariableGEPIndex &Other) const {
181 return !operator==(Other);
187 /// GetLinearExpression - Analyze the specified value as a linear expression:
188 /// "A*V + B", where A and B are constant integers. Return the scale and offset
189 /// values as APInts and return V as a Value*, and return whether we looked
190 /// through any sign or zero extends. The incoming Value is known to have
191 /// IntegerType and it may already be sign or zero extended.
193 /// Note that this looks through extends, so the high bits may not be
194 /// represented in the result.
195 static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
196 ExtensionKind &Extension,
197 const DataLayout &DL, unsigned Depth) {
198 assert(V->getType()->isIntegerTy() && "Not an integer value");
200 // Limit our recursion depth.
207 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
208 if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
209 switch (BOp->getOpcode()) {
211 case Instruction::Or:
212 // X|C == X+C if all the bits in C are unset in X. Otherwise we can't
214 if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &DL))
217 case Instruction::Add:
218 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
220 Offset += RHSC->getValue();
222 case Instruction::Mul:
223 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
225 Offset *= RHSC->getValue();
226 Scale *= RHSC->getValue();
228 case Instruction::Shl:
229 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
231 Offset <<= RHSC->getValue().getLimitedValue();
232 Scale <<= RHSC->getValue().getLimitedValue();
238 // Since GEP indices are sign extended anyway, we don't care about the high
239 // bits of a sign or zero extended value - just scales and offsets. The
240 // extensions have to be consistent though.
241 if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) ||
242 (isa<ZExtInst>(V) && Extension != EK_SignExt)) {
243 Value *CastOp = cast<CastInst>(V)->getOperand(0);
244 unsigned OldWidth = Scale.getBitWidth();
245 unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
246 Scale = Scale.trunc(SmallWidth);
247 Offset = Offset.trunc(SmallWidth);
248 Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
250 Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension,
252 Scale = Scale.zext(OldWidth);
253 Offset = Offset.zext(OldWidth);
263 /// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it
264 /// into a base pointer with a constant offset and a number of scaled symbolic
267 /// The scaled symbolic offsets (represented by pairs of a Value* and a scale in
268 /// the VarIndices vector) are Value*'s that are known to be scaled by the
269 /// specified amount, but which may have other unrepresented high bits. As such,
270 /// the gep cannot necessarily be reconstructed from its decomposed form.
272 /// When DataLayout is around, this function is capable of analyzing everything
273 /// that GetUnderlyingObject can look through. To be able to do that
274 /// GetUnderlyingObject and DecomposeGEPExpression must use the same search
275 /// depth (MaxLookupSearchDepth).
276 /// When DataLayout not is around, it just looks through pointer casts.
279 DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
280 SmallVectorImpl<VariableGEPIndex> &VarIndices,
281 bool &MaxLookupReached, const DataLayout *DL) {
282 // Limit recursion depth to limit compile time in crazy cases.
283 unsigned MaxLookup = MaxLookupSearchDepth;
284 MaxLookupReached = false;
288 // See if this is a bitcast or GEP.
289 const Operator *Op = dyn_cast<Operator>(V);
291 // The only non-operator case we can handle are GlobalAliases.
292 if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
293 if (!GA->mayBeOverridden()) {
294 V = GA->getAliasee();
301 if (Op->getOpcode() == Instruction::BitCast ||
302 Op->getOpcode() == Instruction::AddrSpaceCast) {
303 V = Op->getOperand(0);
307 const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
309 // If it's not a GEP, hand it off to SimplifyInstruction to see if it
310 // can come up with something. This matches what GetUnderlyingObject does.
311 if (const Instruction *I = dyn_cast<Instruction>(V))
312 // TODO: Get a DominatorTree and use it here.
313 if (const Value *Simplified =
314 SimplifyInstruction(const_cast<Instruction *>(I), DL)) {
322 // Don't attempt to analyze GEPs over unsized objects.
323 if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized())
326 // If we are lacking DataLayout information, we can't compute the offets of
327 // elements computed by GEPs. However, we can handle bitcast equivalent
330 if (!GEPOp->hasAllZeroIndices())
332 V = GEPOp->getOperand(0);
336 unsigned AS = GEPOp->getPointerAddressSpace();
337 // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
338 gep_type_iterator GTI = gep_type_begin(GEPOp);
339 for (User::const_op_iterator I = GEPOp->op_begin()+1,
340 E = GEPOp->op_end(); I != E; ++I) {
342 // Compute the (potentially symbolic) offset in bytes for this index.
343 if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
344 // For a struct, add the member offset.
345 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
346 if (FieldNo == 0) continue;
348 BaseOffs += DL->getStructLayout(STy)->getElementOffset(FieldNo);
352 // For an array/pointer, add the element offset, explicitly scaled.
353 if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
354 if (CIdx->isZero()) continue;
355 BaseOffs += DL->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
359 uint64_t Scale = DL->getTypeAllocSize(*GTI);
360 ExtensionKind Extension = EK_NotExtended;
362 // If the integer type is smaller than the pointer size, it is implicitly
363 // sign extended to pointer size.
364 unsigned Width = Index->getType()->getIntegerBitWidth();
365 if (DL->getPointerSizeInBits(AS) > Width)
366 Extension = EK_SignExt;
368 // Use GetLinearExpression to decompose the index into a C1*V+C2 form.
369 APInt IndexScale(Width, 0), IndexOffset(Width, 0);
370 Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension,
373 // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
374 // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
375 BaseOffs += IndexOffset.getSExtValue()*Scale;
376 Scale *= IndexScale.getSExtValue();
378 // If we already had an occurrence of this index variable, merge this
379 // scale into it. For example, we want to handle:
380 // A[x][x] -> x*16 + x*4 -> x*20
381 // This also ensures that 'x' only appears in the index list once.
382 for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
383 if (VarIndices[i].V == Index &&
384 VarIndices[i].Extension == Extension) {
385 Scale += VarIndices[i].Scale;
386 VarIndices.erase(VarIndices.begin()+i);
391 // Make sure that we have a scale that makes sense for this target's
393 if (unsigned ShiftBits = 64 - DL->getPointerSizeInBits(AS)) {
395 Scale = (int64_t)Scale >> ShiftBits;
399 VariableGEPIndex Entry = {Index, Extension,
400 static_cast<int64_t>(Scale)};
401 VarIndices.push_back(Entry);
405 // Analyze the base pointer next.
406 V = GEPOp->getOperand(0);
407 } while (--MaxLookup);
409 // If the chain of expressions is too deep, just return early.
410 MaxLookupReached = true;
414 //===----------------------------------------------------------------------===//
415 // BasicAliasAnalysis Pass
416 //===----------------------------------------------------------------------===//
419 static const Function *getParent(const Value *V) {
420 if (const Instruction *inst = dyn_cast<Instruction>(V))
421 return inst->getParent()->getParent();
423 if (const Argument *arg = dyn_cast<Argument>(V))
424 return arg->getParent();
429 static bool notDifferentParent(const Value *O1, const Value *O2) {
431 const Function *F1 = getParent(O1);
432 const Function *F2 = getParent(O2);
434 return !F1 || !F2 || F1 == F2;
439 /// BasicAliasAnalysis - This is the primary alias analysis implementation.
440 struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
441 static char ID; // Class identification, replacement for typeinfo
442 BasicAliasAnalysis() : ImmutablePass(ID) {
443 initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
446 void initializePass() override {
447 InitializeAliasAnalysis(this);
450 void getAnalysisUsage(AnalysisUsage &AU) const override {
451 AU.addRequired<AliasAnalysis>();
452 AU.addRequired<TargetLibraryInfo>();
455 AliasResult alias(const Location &LocA, const Location &LocB) override {
456 assert(AliasCache.empty() && "AliasCache must be cleared after use!");
457 assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
458 "BasicAliasAnalysis doesn't support interprocedural queries.");
459 AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag,
460 LocB.Ptr, LocB.Size, LocB.TBAATag);
461 // AliasCache rarely has more than 1 or 2 elements, always use
462 // shrink_and_clear so it quickly returns to the inline capacity of the
463 // SmallDenseMap if it ever grows larger.
464 // FIXME: This should really be shrink_to_inline_capacity_and_clear().
465 AliasCache.shrink_and_clear();
466 VisitedPhiBBs.clear();
470 ModRefResult getModRefInfo(ImmutableCallSite CS,
471 const Location &Loc) override;
473 ModRefResult getModRefInfo(ImmutableCallSite CS1,
474 ImmutableCallSite CS2) override {
475 // The AliasAnalysis base class has some smarts, lets use them.
476 return AliasAnalysis::getModRefInfo(CS1, CS2);
479 /// pointsToConstantMemory - Chase pointers until we find a (constant
481 bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override;
483 /// Get the location associated with a pointer argument of a callsite.
484 Location getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
485 ModRefResult &Mask) override;
487 /// getModRefBehavior - Return the behavior when calling the given
489 ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override;
491 /// getModRefBehavior - Return the behavior when calling the given function.
492 /// For use when the call site is not known.
493 ModRefBehavior getModRefBehavior(const Function *F) override;
495 /// getAdjustedAnalysisPointer - This method is used when a pass implements
496 /// an analysis interface through multiple inheritance. If needed, it
497 /// should override this to adjust the this pointer as needed for the
498 /// specified pass info.
499 void *getAdjustedAnalysisPointer(const void *ID) override {
500 if (ID == &AliasAnalysis::ID)
501 return (AliasAnalysis*)this;
506 // AliasCache - Track alias queries to guard against recursion.
507 typedef std::pair<Location, Location> LocPair;
508 typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
509 AliasCacheTy AliasCache;
511 /// \brief Track phi nodes we have visited. When interpret "Value" pointer
512 /// equality as value equality we need to make sure that the "Value" is not
513 /// part of a cycle. Otherwise, two uses could come from different
514 /// "iterations" of a cycle and see different values for the same "Value"
516 /// The following example shows the problem:
517 /// %p = phi(%alloca1, %addr2)
519 /// %addr1 = gep, %alloca2, 0, %l
520 /// %addr2 = gep %alloca2, 0, (%l + 1)
521 /// alias(%p, %addr1) -> MayAlias !
523 SmallPtrSet<const BasicBlock*, 8> VisitedPhiBBs;
525 // Visited - Track instructions visited by pointsToConstantMemory.
526 SmallPtrSet<const Value*, 16> Visited;
528 /// \brief Check whether two Values can be considered equivalent.
530 /// In addition to pointer equivalence of \p V1 and \p V2 this checks
531 /// whether they can not be part of a cycle in the value graph by looking at
532 /// all visited phi nodes an making sure that the phis cannot reach the
533 /// value. We have to do this because we are looking through phi nodes (That
534 /// is we say noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB).
535 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
537 /// \brief Dest and Src are the variable indices from two decomposed
538 /// GetElementPtr instructions GEP1 and GEP2 which have common base
539 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
540 /// difference between the two pointers.
541 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
542 const SmallVectorImpl<VariableGEPIndex> &Src);
544 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
545 // instruction against another.
546 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
547 const MDNode *V1TBAAInfo,
548 const Value *V2, uint64_t V2Size,
549 const MDNode *V2TBAAInfo,
550 const Value *UnderlyingV1, const Value *UnderlyingV2);
552 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
553 // instruction against another.
554 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
555 const MDNode *PNTBAAInfo,
556 const Value *V2, uint64_t V2Size,
557 const MDNode *V2TBAAInfo);
559 /// aliasSelect - Disambiguate a Select instruction against another value.
560 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
561 const MDNode *SITBAAInfo,
562 const Value *V2, uint64_t V2Size,
563 const MDNode *V2TBAAInfo);
565 AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
566 const MDNode *V1TBAATag,
567 const Value *V2, uint64_t V2Size,
568 const MDNode *V2TBAATag);
570 } // End of anonymous namespace
572 // Register this pass...
573 char BasicAliasAnalysis::ID = 0;
574 INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
575 "Basic Alias Analysis (stateless AA impl)",
577 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
578 INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
579 "Basic Alias Analysis (stateless AA impl)",
583 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
584 return new BasicAliasAnalysis();
587 /// pointsToConstantMemory - Returns whether the given pointer value
588 /// points to memory that is local to the function, with global constants being
589 /// considered local to all functions.
591 BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
592 assert(Visited.empty() && "Visited must be cleared after use!");
594 unsigned MaxLookup = 8;
595 SmallVector<const Value *, 16> Worklist;
596 Worklist.push_back(Loc.Ptr);
598 const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), DL);
599 if (!Visited.insert(V)) {
601 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
604 // An alloca instruction defines local memory.
605 if (OrLocal && isa<AllocaInst>(V))
608 // A global constant counts as local memory for our purposes.
609 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
610 // Note: this doesn't require GV to be "ODR" because it isn't legal for a
611 // global to be marked constant in some modules and non-constant in
612 // others. GV may even be a declaration, not a definition.
613 if (!GV->isConstant()) {
615 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
620 // If both select values point to local memory, then so does the select.
621 if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
622 Worklist.push_back(SI->getTrueValue());
623 Worklist.push_back(SI->getFalseValue());
627 // If all values incoming to a phi node point to local memory, then so does
629 if (const PHINode *PN = dyn_cast<PHINode>(V)) {
630 // Don't bother inspecting phi nodes with many operands.
631 if (PN->getNumIncomingValues() > MaxLookup) {
633 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
635 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
636 Worklist.push_back(PN->getIncomingValue(i));
640 // Otherwise be conservative.
642 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
644 } while (!Worklist.empty() && --MaxLookup);
647 return Worklist.empty();
650 static bool isMemsetPattern16(const Function *MS,
651 const TargetLibraryInfo &TLI) {
652 if (TLI.has(LibFunc::memset_pattern16) &&
653 MS->getName() == "memset_pattern16") {
654 FunctionType *MemsetType = MS->getFunctionType();
655 if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
656 isa<PointerType>(MemsetType->getParamType(0)) &&
657 isa<PointerType>(MemsetType->getParamType(1)) &&
658 isa<IntegerType>(MemsetType->getParamType(2)))
665 /// getModRefBehavior - Return the behavior when calling the given call site.
666 AliasAnalysis::ModRefBehavior
667 BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
668 if (CS.doesNotAccessMemory())
669 // Can't do better than this.
670 return DoesNotAccessMemory;
672 ModRefBehavior Min = UnknownModRefBehavior;
674 // If the callsite knows it only reads memory, don't return worse
676 if (CS.onlyReadsMemory())
677 Min = OnlyReadsMemory;
679 // The AliasAnalysis base class has some smarts, lets use them.
680 return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
683 /// getModRefBehavior - Return the behavior when calling the given function.
684 /// For use when the call site is not known.
685 AliasAnalysis::ModRefBehavior
686 BasicAliasAnalysis::getModRefBehavior(const Function *F) {
687 // If the function declares it doesn't access memory, we can't do better.
688 if (F->doesNotAccessMemory())
689 return DoesNotAccessMemory;
691 // For intrinsics, we can check the table.
692 if (unsigned iid = F->getIntrinsicID()) {
693 #define GET_INTRINSIC_MODREF_BEHAVIOR
694 #include "llvm/IR/Intrinsics.gen"
695 #undef GET_INTRINSIC_MODREF_BEHAVIOR
698 ModRefBehavior Min = UnknownModRefBehavior;
700 // If the function declares it only reads memory, go with that.
701 if (F->onlyReadsMemory())
702 Min = OnlyReadsMemory;
704 const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
705 if (isMemsetPattern16(F, TLI))
706 Min = OnlyAccessesArgumentPointees;
708 // Otherwise be conservative.
709 return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
712 AliasAnalysis::Location
713 BasicAliasAnalysis::getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
714 ModRefResult &Mask) {
715 Location Loc = AliasAnalysis::getArgLocation(CS, ArgIdx, Mask);
716 const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
717 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
719 switch (II->getIntrinsicID()) {
721 case Intrinsic::memset:
722 case Intrinsic::memcpy:
723 case Intrinsic::memmove: {
724 assert((ArgIdx == 0 || ArgIdx == 1) &&
725 "Invalid argument index for memory intrinsic");
726 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
727 Loc.Size = LenCI->getZExtValue();
728 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
729 "Memory intrinsic location pointer not argument?");
730 Mask = ArgIdx ? Ref : Mod;
733 case Intrinsic::lifetime_start:
734 case Intrinsic::lifetime_end:
735 case Intrinsic::invariant_start: {
736 assert(ArgIdx == 1 && "Invalid argument index");
737 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
738 "Intrinsic location pointer not argument?");
739 Loc.Size = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
742 case Intrinsic::invariant_end: {
743 assert(ArgIdx == 2 && "Invalid argument index");
744 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
745 "Intrinsic location pointer not argument?");
746 Loc.Size = cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
749 case Intrinsic::arm_neon_vld1: {
750 assert(ArgIdx == 0 && "Invalid argument index");
751 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
752 "Intrinsic location pointer not argument?");
753 // LLVM's vld1 and vst1 intrinsics currently only support a single
756 Loc.Size = DL->getTypeStoreSize(II->getType());
759 case Intrinsic::arm_neon_vst1: {
760 assert(ArgIdx == 0 && "Invalid argument index");
761 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
762 "Intrinsic location pointer not argument?");
764 Loc.Size = DL->getTypeStoreSize(II->getArgOperand(1)->getType());
769 // We can bound the aliasing properties of memset_pattern16 just as we can
770 // for memcpy/memset. This is particularly important because the
771 // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
772 // whenever possible.
773 else if (CS.getCalledFunction() &&
774 isMemsetPattern16(CS.getCalledFunction(), TLI)) {
775 assert((ArgIdx == 0 || ArgIdx == 1) &&
776 "Invalid argument index for memset_pattern16");
779 else if (const ConstantInt *LenCI =
780 dyn_cast<ConstantInt>(CS.getArgument(2)))
781 Loc.Size = LenCI->getZExtValue();
782 assert(Loc.Ptr == CS.getArgument(ArgIdx) &&
783 "memset_pattern16 location pointer not argument?");
784 Mask = ArgIdx ? Ref : Mod;
786 // FIXME: Handle memset_pattern4 and memset_pattern8 also.
791 /// getModRefInfo - Check to see if the specified callsite can clobber the
792 /// specified memory object. Since we only look at local properties of this
793 /// function, we really can't say much about this query. We do, however, use
794 /// simple "address taken" analysis on local objects.
795 AliasAnalysis::ModRefResult
796 BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
797 const Location &Loc) {
798 assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
799 "AliasAnalysis query involving multiple functions!");
801 const Value *Object = GetUnderlyingObject(Loc.Ptr, DL);
803 // If this is a tail call and Loc.Ptr points to a stack location, we know that
804 // the tail call cannot access or modify the local stack.
805 // We cannot exclude byval arguments here; these belong to the caller of
806 // the current function not to the current function, and a tail callee
807 // may reference them.
808 if (isa<AllocaInst>(Object))
809 if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
810 if (CI->isTailCall())
813 // If the pointer is to a locally allocated object that does not escape,
814 // then the call can not mod/ref the pointer unless the call takes the pointer
815 // as an argument, and itself doesn't capture it.
816 if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
817 isNonEscapingLocalObject(Object)) {
818 bool PassedAsArg = false;
820 for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
821 CI != CE; ++CI, ++ArgNo) {
822 // Only look at the no-capture or byval pointer arguments. If this
823 // pointer were passed to arguments that were neither of these, then it
824 // couldn't be no-capture.
825 if (!(*CI)->getType()->isPointerTy() ||
826 (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
829 // If this is a no-capture pointer argument, see if we can tell that it
830 // is impossible to alias the pointer we're checking. If not, we have to
831 // assume that the call could touch the pointer, even though it doesn't
833 if (!isNoAlias(Location(*CI), Location(Object))) {
843 // The AliasAnalysis base class has some smarts, lets use them.
844 return AliasAnalysis::getModRefInfo(CS, Loc);
847 /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
848 /// against another pointer. We know that V1 is a GEP, but we don't know
849 /// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, DL),
850 /// UnderlyingV2 is the same for V2.
852 AliasAnalysis::AliasResult
853 BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
854 const MDNode *V1TBAAInfo,
855 const Value *V2, uint64_t V2Size,
856 const MDNode *V2TBAAInfo,
857 const Value *UnderlyingV1,
858 const Value *UnderlyingV2) {
859 int64_t GEP1BaseOffset;
860 bool GEP1MaxLookupReached;
861 SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
863 // If we have two gep instructions with must-alias or not-alias'ing base
864 // pointers, figure out if the indexes to the GEP tell us anything about the
866 if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
867 // Do the base pointers alias?
868 AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, nullptr,
869 UnderlyingV2, UnknownSize, nullptr);
871 // Check for geps of non-aliasing underlying pointers where the offsets are
873 if ((BaseAlias == MayAlias) && V1Size == V2Size) {
874 // Do the base pointers alias assuming type and size.
875 AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
876 V1TBAAInfo, UnderlyingV2,
878 if (PreciseBaseAlias == NoAlias) {
879 // See if the computed offset from the common pointer tells us about the
880 // relation of the resulting pointer.
881 int64_t GEP2BaseOffset;
882 bool GEP2MaxLookupReached;
883 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
884 const Value *GEP2BasePtr =
885 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
886 GEP2MaxLookupReached, DL);
887 const Value *GEP1BasePtr =
888 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
889 GEP1MaxLookupReached, DL);
890 // DecomposeGEPExpression and GetUnderlyingObject should return the
891 // same result except when DecomposeGEPExpression has no DataLayout.
892 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
894 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
897 // If the max search depth is reached the result is undefined
898 if (GEP2MaxLookupReached || GEP1MaxLookupReached)
902 if (GEP1BaseOffset == GEP2BaseOffset &&
903 GEP1VariableIndices == GEP2VariableIndices)
905 GEP1VariableIndices.clear();
909 // If we get a No or May, then return it immediately, no amount of analysis
910 // will improve this situation.
911 if (BaseAlias != MustAlias) return BaseAlias;
913 // Otherwise, we have a MustAlias. Since the base pointers alias each other
914 // exactly, see if the computed offset from the common pointer tells us
915 // about the relation of the resulting pointer.
916 const Value *GEP1BasePtr =
917 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
918 GEP1MaxLookupReached, DL);
920 int64_t GEP2BaseOffset;
921 bool GEP2MaxLookupReached;
922 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
923 const Value *GEP2BasePtr =
924 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
925 GEP2MaxLookupReached, DL);
927 // DecomposeGEPExpression and GetUnderlyingObject should return the
928 // same result except when DecomposeGEPExpression has no DataLayout.
929 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
931 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
934 // If the max search depth is reached the result is undefined
935 if (GEP2MaxLookupReached || GEP1MaxLookupReached)
938 // Subtract the GEP2 pointer from the GEP1 pointer to find out their
939 // symbolic difference.
940 GEP1BaseOffset -= GEP2BaseOffset;
941 GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
944 // Check to see if these two pointers are related by the getelementptr
945 // instruction. If one pointer is a GEP with a non-zero index of the other
946 // pointer, we know they cannot alias.
948 // If both accesses are unknown size, we can't do anything useful here.
949 if (V1Size == UnknownSize && V2Size == UnknownSize)
952 AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, nullptr,
953 V2, V2Size, V2TBAAInfo);
955 // If V2 may alias GEP base pointer, conservatively returns MayAlias.
956 // If V2 is known not to alias GEP base pointer, then the two values
957 // cannot alias per GEP semantics: "A pointer value formed from a
958 // getelementptr instruction is associated with the addresses associated
959 // with the first operand of the getelementptr".
962 const Value *GEP1BasePtr =
963 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
964 GEP1MaxLookupReached, DL);
966 // DecomposeGEPExpression and GetUnderlyingObject should return the
967 // same result except when DecomposeGEPExpression has no DataLayout.
968 if (GEP1BasePtr != UnderlyingV1) {
970 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
973 // If the max search depth is reached the result is undefined
974 if (GEP1MaxLookupReached)
978 // In the two GEP Case, if there is no difference in the offsets of the
979 // computed pointers, the resultant pointers are a must alias. This
980 // hapens when we have two lexically identical GEP's (for example).
982 // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
983 // must aliases the GEP, the end result is a must alias also.
984 if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
987 // If there is a constant difference between the pointers, but the difference
988 // is less than the size of the associated memory object, then we know
989 // that the objects are partially overlapping. If the difference is
990 // greater, we know they do not overlap.
991 if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
992 if (GEP1BaseOffset >= 0) {
993 if (V2Size != UnknownSize) {
994 if ((uint64_t)GEP1BaseOffset < V2Size)
999 // We have the situation where:
1002 // ---------------->|
1003 // |-->V1Size |-------> V2Size
1005 // We need to know that V2Size is not unknown, otherwise we might have
1006 // stripped a gep with negative index ('gep <ptr>, -1, ...).
1007 if (V1Size != UnknownSize && V2Size != UnknownSize) {
1008 if (-(uint64_t)GEP1BaseOffset < V1Size)
1009 return PartialAlias;
1015 // Try to distinguish something like &A[i][1] against &A[42][0].
1016 // Grab the least significant bit set in any of the scales.
1017 if (!GEP1VariableIndices.empty()) {
1018 uint64_t Modulo = 0;
1019 for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
1020 Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
1021 Modulo = Modulo ^ (Modulo & (Modulo - 1));
1023 // We can compute the difference between the two addresses
1024 // mod Modulo. Check whether that difference guarantees that the
1025 // two locations do not alias.
1026 uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
1027 if (V1Size != UnknownSize && V2Size != UnknownSize &&
1028 ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
1032 // Statically, we can see that the base objects are the same, but the
1033 // pointers have dynamic offsets which we can't resolve. And none of our
1034 // little tricks above worked.
1036 // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
1037 // practical effect of this is protecting TBAA in the case of dynamic
1038 // indices into arrays of unions or malloc'd memory.
1039 return PartialAlias;
1042 static AliasAnalysis::AliasResult
1043 MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
1044 // If the results agree, take it.
1047 // A mix of PartialAlias and MustAlias is PartialAlias.
1048 if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
1049 (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
1050 return AliasAnalysis::PartialAlias;
1051 // Otherwise, we don't know anything.
1052 return AliasAnalysis::MayAlias;
1055 /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
1056 /// instruction against another.
1057 AliasAnalysis::AliasResult
1058 BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
1059 const MDNode *SITBAAInfo,
1060 const Value *V2, uint64_t V2Size,
1061 const MDNode *V2TBAAInfo) {
1062 // If the values are Selects with the same condition, we can do a more precise
1063 // check: just check for aliases between the values on corresponding arms.
1064 if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
1065 if (SI->getCondition() == SI2->getCondition()) {
1067 aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo,
1068 SI2->getTrueValue(), V2Size, V2TBAAInfo);
1069 if (Alias == MayAlias)
1071 AliasResult ThisAlias =
1072 aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
1073 SI2->getFalseValue(), V2Size, V2TBAAInfo);
1074 return MergeAliasResults(ThisAlias, Alias);
1077 // If both arms of the Select node NoAlias or MustAlias V2, then returns
1078 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1080 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo);
1081 if (Alias == MayAlias)
1084 AliasResult ThisAlias =
1085 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
1086 return MergeAliasResults(ThisAlias, Alias);
1089 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
1091 AliasAnalysis::AliasResult
1092 BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
1093 const MDNode *PNTBAAInfo,
1094 const Value *V2, uint64_t V2Size,
1095 const MDNode *V2TBAAInfo) {
1096 // Track phi nodes we have visited. We use this information when we determine
1097 // value equivalence.
1098 VisitedPhiBBs.insert(PN->getParent());
1100 // If the values are PHIs in the same block, we can do a more precise
1101 // as well as efficient check: just check for aliases between the values
1102 // on corresponding edges.
1103 if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
1104 if (PN2->getParent() == PN->getParent()) {
1105 LocPair Locs(Location(PN, PNSize, PNTBAAInfo),
1106 Location(V2, V2Size, V2TBAAInfo));
1108 std::swap(Locs.first, Locs.second);
1109 // Analyse the PHIs' inputs under the assumption that the PHIs are
1111 // If the PHIs are May/MustAlias there must be (recursively) an input
1112 // operand from outside the PHIs' cycle that is MayAlias/MustAlias or
1113 // there must be an operation on the PHIs within the PHIs' value cycle
1114 // that causes a MayAlias.
1115 // Pretend the phis do not alias.
1116 AliasResult Alias = NoAlias;
1117 assert(AliasCache.count(Locs) &&
1118 "There must exist an entry for the phi node");
1119 AliasResult OrigAliasResult = AliasCache[Locs];
1120 AliasCache[Locs] = NoAlias;
1122 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1123 AliasResult ThisAlias =
1124 aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
1125 PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
1126 V2Size, V2TBAAInfo);
1127 Alias = MergeAliasResults(ThisAlias, Alias);
1128 if (Alias == MayAlias)
1132 // Reset if speculation failed.
1133 if (Alias != NoAlias)
1134 AliasCache[Locs] = OrigAliasResult;
1139 SmallPtrSet<Value*, 4> UniqueSrc;
1140 SmallVector<Value*, 4> V1Srcs;
1141 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1142 Value *PV1 = PN->getIncomingValue(i);
1143 if (isa<PHINode>(PV1))
1144 // If any of the source itself is a PHI, return MayAlias conservatively
1145 // to avoid compile time explosion. The worst possible case is if both
1146 // sides are PHI nodes. In which case, this is O(m x n) time where 'm'
1147 // and 'n' are the number of PHI sources.
1149 if (UniqueSrc.insert(PV1))
1150 V1Srcs.push_back(PV1);
1153 AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo,
1154 V1Srcs[0], PNSize, PNTBAAInfo);
1155 // Early exit if the check of the first PHI source against V2 is MayAlias.
1156 // Other results are not possible.
1157 if (Alias == MayAlias)
1160 // If all sources of the PHI node NoAlias or MustAlias V2, then returns
1161 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1162 for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
1163 Value *V = V1Srcs[i];
1165 AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
1166 V, PNSize, PNTBAAInfo);
1167 Alias = MergeAliasResults(ThisAlias, Alias);
1168 if (Alias == MayAlias)
1175 // aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
1176 // such as array references.
1178 AliasAnalysis::AliasResult
1179 BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
1180 const MDNode *V1TBAAInfo,
1181 const Value *V2, uint64_t V2Size,
1182 const MDNode *V2TBAAInfo) {
1183 // If either of the memory references is empty, it doesn't matter what the
1184 // pointer values are.
1185 if (V1Size == 0 || V2Size == 0)
1188 // Strip off any casts if they exist.
1189 V1 = V1->stripPointerCasts();
1190 V2 = V2->stripPointerCasts();
1192 // Are we checking for alias of the same value?
1193 // Because we look 'through' phi nodes we could look at "Value" pointers from
1194 // different iterations. We must therefore make sure that this is not the
1195 // case. The function isValueEqualInPotentialCycles ensures that this cannot
1196 // happen by looking at the visited phi nodes and making sure they cannot
1198 if (isValueEqualInPotentialCycles(V1, V2))
1201 if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
1202 return NoAlias; // Scalars cannot alias each other
1204 // Figure out what objects these things are pointing to if we can.
1205 const Value *O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth);
1206 const Value *O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth);
1208 // Null values in the default address space don't point to any object, so they
1209 // don't alias any other pointer.
1210 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
1211 if (CPN->getType()->getAddressSpace() == 0)
1213 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
1214 if (CPN->getType()->getAddressSpace() == 0)
1218 // If V1/V2 point to two different objects we know that we have no alias.
1219 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
1222 // Constant pointers can't alias with non-const isIdentifiedObject objects.
1223 if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
1224 (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
1227 // Function arguments can't alias with things that are known to be
1228 // unambigously identified at the function level.
1229 if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
1230 (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
1233 // Most objects can't alias null.
1234 if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
1235 (isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
1238 // If one pointer is the result of a call/invoke or load and the other is a
1239 // non-escaping local object within the same function, then we know the
1240 // object couldn't escape to a point where the call could return it.
1242 // Note that if the pointers are in different functions, there are a
1243 // variety of complications. A call with a nocapture argument may still
1244 // temporary store the nocapture argument's value in a temporary memory
1245 // location if that memory location doesn't escape. Or it may pass a
1246 // nocapture value to other functions as long as they don't capture it.
1247 if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
1249 if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
1253 // If the size of one access is larger than the entire object on the other
1254 // side, then we know such behavior is undefined and can assume no alias.
1256 if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *DL, *TLI)) ||
1257 (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *DL, *TLI)))
1260 // Check the cache before climbing up use-def chains. This also terminates
1261 // otherwise infinitely recursive queries.
1262 LocPair Locs(Location(V1, V1Size, V1TBAAInfo),
1263 Location(V2, V2Size, V2TBAAInfo));
1265 std::swap(Locs.first, Locs.second);
1266 std::pair<AliasCacheTy::iterator, bool> Pair =
1267 AliasCache.insert(std::make_pair(Locs, MayAlias));
1269 return Pair.first->second;
1271 // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
1272 // GEP can't simplify, we don't even look at the PHI cases.
1273 if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
1275 std::swap(V1Size, V2Size);
1277 std::swap(V1TBAAInfo, V2TBAAInfo);
1279 if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
1280 AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2);
1281 if (Result != MayAlias) return AliasCache[Locs] = Result;
1284 if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
1286 std::swap(V1Size, V2Size);
1287 std::swap(V1TBAAInfo, V2TBAAInfo);
1289 if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
1290 AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
1291 V2, V2Size, V2TBAAInfo);
1292 if (Result != MayAlias) return AliasCache[Locs] = Result;
1295 if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
1297 std::swap(V1Size, V2Size);
1298 std::swap(V1TBAAInfo, V2TBAAInfo);
1300 if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
1301 AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
1302 V2, V2Size, V2TBAAInfo);
1303 if (Result != MayAlias) return AliasCache[Locs] = Result;
1306 // If both pointers are pointing into the same object and one of them
1307 // accesses is accessing the entire object, then the accesses must
1308 // overlap in some way.
1310 if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *DL, *TLI)) ||
1311 (V2Size != UnknownSize && isObjectSize(O2, V2Size, *DL, *TLI)))
1312 return AliasCache[Locs] = PartialAlias;
1314 AliasResult Result =
1315 AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
1316 Location(V2, V2Size, V2TBAAInfo));
1317 return AliasCache[Locs] = Result;
1320 bool BasicAliasAnalysis::isValueEqualInPotentialCycles(const Value *V,
1325 const Instruction *Inst = dyn_cast<Instruction>(V);
1329 if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck)
1332 // Use dominance or loop info if available.
1333 DominatorTreeWrapperPass *DTWP =
1334 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
1335 DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
1336 LoopInfo *LI = getAnalysisIfAvailable<LoopInfo>();
1338 // Make sure that the visited phis cannot reach the Value. This ensures that
1339 // the Values cannot come from different iterations of a potential cycle the
1340 // phi nodes could be involved in.
1341 for (SmallPtrSet<const BasicBlock *, 8>::iterator PI = VisitedPhiBBs.begin(),
1342 PE = VisitedPhiBBs.end();
1344 if (isPotentiallyReachable((*PI)->begin(), Inst, DT, LI))
1350 /// GetIndexDifference - Dest and Src are the variable indices from two
1351 /// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
1352 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
1353 /// difference between the two pointers.
1354 void BasicAliasAnalysis::GetIndexDifference(
1355 SmallVectorImpl<VariableGEPIndex> &Dest,
1356 const SmallVectorImpl<VariableGEPIndex> &Src) {
1360 for (unsigned i = 0, e = Src.size(); i != e; ++i) {
1361 const Value *V = Src[i].V;
1362 ExtensionKind Extension = Src[i].Extension;
1363 int64_t Scale = Src[i].Scale;
1365 // Find V in Dest. This is N^2, but pointer indices almost never have more
1366 // than a few variable indexes.
1367 for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
1368 if (!isValueEqualInPotentialCycles(Dest[j].V, V) ||
1369 Dest[j].Extension != Extension)
1372 // If we found it, subtract off Scale V's from the entry in Dest. If it
1373 // goes to zero, remove the entry.
1374 if (Dest[j].Scale != Scale)
1375 Dest[j].Scale -= Scale;
1377 Dest.erase(Dest.begin() + j);
1382 // If we didn't consume this entry, add it to the end of the Dest list.
1384 VariableGEPIndex Entry = { V, Extension, -Scale };
1385 Dest.push_back(Entry);