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 /// isIdentifiedFunctionLocal - Return true if V is umabigously identified
160 /// at the function-level. Different IdentifiedFunctionLocals can't alias.
161 /// Further, an IdentifiedFunctionLocal can not alias with any function
162 /// arguments other than itself, which is not necessarily true for
163 /// IdentifiedObjects.
164 static bool isIdentifiedFunctionLocal(const Value *V)
166 return isa<AllocaInst>(V) || isNoAliasCall(V) || isNoAliasArgument(V);
170 //===----------------------------------------------------------------------===//
171 // GetElementPtr Instruction Decomposition and Analysis
172 //===----------------------------------------------------------------------===//
181 struct VariableGEPIndex {
183 ExtensionKind Extension;
186 bool operator==(const VariableGEPIndex &Other) const {
187 return V == Other.V && Extension == Other.Extension &&
188 Scale == Other.Scale;
191 bool operator!=(const VariableGEPIndex &Other) const {
192 return !operator==(Other);
198 /// GetLinearExpression - Analyze the specified value as a linear expression:
199 /// "A*V + B", where A and B are constant integers. Return the scale and offset
200 /// values as APInts and return V as a Value*, and return whether we looked
201 /// through any sign or zero extends. The incoming Value is known to have
202 /// IntegerType and it may already be sign or zero extended.
204 /// Note that this looks through extends, so the high bits may not be
205 /// represented in the result.
206 static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
207 ExtensionKind &Extension,
208 const DataLayout &DL, unsigned Depth) {
209 assert(V->getType()->isIntegerTy() && "Not an integer value");
211 // Limit our recursion depth.
218 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
219 if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
220 switch (BOp->getOpcode()) {
222 case Instruction::Or:
223 // X|C == X+C if all the bits in C are unset in X. Otherwise we can't
225 if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &DL))
228 case Instruction::Add:
229 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
231 Offset += RHSC->getValue();
233 case Instruction::Mul:
234 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
236 Offset *= RHSC->getValue();
237 Scale *= RHSC->getValue();
239 case Instruction::Shl:
240 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
242 Offset <<= RHSC->getValue().getLimitedValue();
243 Scale <<= RHSC->getValue().getLimitedValue();
249 // Since GEP indices are sign extended anyway, we don't care about the high
250 // bits of a sign or zero extended value - just scales and offsets. The
251 // extensions have to be consistent though.
252 if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) ||
253 (isa<ZExtInst>(V) && Extension != EK_SignExt)) {
254 Value *CastOp = cast<CastInst>(V)->getOperand(0);
255 unsigned OldWidth = Scale.getBitWidth();
256 unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
257 Scale = Scale.trunc(SmallWidth);
258 Offset = Offset.trunc(SmallWidth);
259 Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
261 Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension,
263 Scale = Scale.zext(OldWidth);
264 Offset = Offset.zext(OldWidth);
274 /// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it
275 /// into a base pointer with a constant offset and a number of scaled symbolic
278 /// The scaled symbolic offsets (represented by pairs of a Value* and a scale in
279 /// the VarIndices vector) are Value*'s that are known to be scaled by the
280 /// specified amount, but which may have other unrepresented high bits. As such,
281 /// the gep cannot necessarily be reconstructed from its decomposed form.
283 /// When DataLayout is around, this function is capable of analyzing everything
284 /// that GetUnderlyingObject can look through. To be able to do that
285 /// GetUnderlyingObject and DecomposeGEPExpression must use the same search
286 /// depth (MaxLookupSearchDepth).
287 /// When DataLayout not is around, it just looks through pointer casts.
290 DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
291 SmallVectorImpl<VariableGEPIndex> &VarIndices,
292 bool &MaxLookupReached, const DataLayout *DL) {
293 // Limit recursion depth to limit compile time in crazy cases.
294 unsigned MaxLookup = MaxLookupSearchDepth;
295 MaxLookupReached = false;
299 // See if this is a bitcast or GEP.
300 const Operator *Op = dyn_cast<Operator>(V);
302 // The only non-operator case we can handle are GlobalAliases.
303 if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
304 if (!GA->mayBeOverridden()) {
305 V = GA->getAliasee();
312 if (Op->getOpcode() == Instruction::BitCast ||
313 Op->getOpcode() == Instruction::AddrSpaceCast) {
314 V = Op->getOperand(0);
318 const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
320 // If it's not a GEP, hand it off to SimplifyInstruction to see if it
321 // can come up with something. This matches what GetUnderlyingObject does.
322 if (const Instruction *I = dyn_cast<Instruction>(V))
323 // TODO: Get a DominatorTree and use it here.
324 if (const Value *Simplified =
325 SimplifyInstruction(const_cast<Instruction *>(I), DL)) {
333 // Don't attempt to analyze GEPs over unsized objects.
334 if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized())
337 // If we are lacking DataLayout information, we can't compute the offets of
338 // elements computed by GEPs. However, we can handle bitcast equivalent
341 if (!GEPOp->hasAllZeroIndices())
343 V = GEPOp->getOperand(0);
347 unsigned AS = GEPOp->getPointerAddressSpace();
348 // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
349 gep_type_iterator GTI = gep_type_begin(GEPOp);
350 for (User::const_op_iterator I = GEPOp->op_begin()+1,
351 E = GEPOp->op_end(); I != E; ++I) {
353 // Compute the (potentially symbolic) offset in bytes for this index.
354 if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
355 // For a struct, add the member offset.
356 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
357 if (FieldNo == 0) continue;
359 BaseOffs += DL->getStructLayout(STy)->getElementOffset(FieldNo);
363 // For an array/pointer, add the element offset, explicitly scaled.
364 if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
365 if (CIdx->isZero()) continue;
366 BaseOffs += DL->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
370 uint64_t Scale = DL->getTypeAllocSize(*GTI);
371 ExtensionKind Extension = EK_NotExtended;
373 // If the integer type is smaller than the pointer size, it is implicitly
374 // sign extended to pointer size.
375 unsigned Width = Index->getType()->getIntegerBitWidth();
376 if (DL->getPointerSizeInBits(AS) > Width)
377 Extension = EK_SignExt;
379 // Use GetLinearExpression to decompose the index into a C1*V+C2 form.
380 APInt IndexScale(Width, 0), IndexOffset(Width, 0);
381 Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension,
384 // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
385 // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
386 BaseOffs += IndexOffset.getSExtValue()*Scale;
387 Scale *= IndexScale.getSExtValue();
389 // If we already had an occurrence of this index variable, merge this
390 // scale into it. For example, we want to handle:
391 // A[x][x] -> x*16 + x*4 -> x*20
392 // This also ensures that 'x' only appears in the index list once.
393 for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
394 if (VarIndices[i].V == Index &&
395 VarIndices[i].Extension == Extension) {
396 Scale += VarIndices[i].Scale;
397 VarIndices.erase(VarIndices.begin()+i);
402 // Make sure that we have a scale that makes sense for this target's
404 if (unsigned ShiftBits = 64 - DL->getPointerSizeInBits(AS)) {
406 Scale = (int64_t)Scale >> ShiftBits;
410 VariableGEPIndex Entry = {Index, Extension,
411 static_cast<int64_t>(Scale)};
412 VarIndices.push_back(Entry);
416 // Analyze the base pointer next.
417 V = GEPOp->getOperand(0);
418 } while (--MaxLookup);
420 // If the chain of expressions is too deep, just return early.
421 MaxLookupReached = true;
425 //===----------------------------------------------------------------------===//
426 // BasicAliasAnalysis Pass
427 //===----------------------------------------------------------------------===//
430 static const Function *getParent(const Value *V) {
431 if (const Instruction *inst = dyn_cast<Instruction>(V))
432 return inst->getParent()->getParent();
434 if (const Argument *arg = dyn_cast<Argument>(V))
435 return arg->getParent();
440 static bool notDifferentParent(const Value *O1, const Value *O2) {
442 const Function *F1 = getParent(O1);
443 const Function *F2 = getParent(O2);
445 return !F1 || !F2 || F1 == F2;
450 /// BasicAliasAnalysis - This is the primary alias analysis implementation.
451 struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
452 static char ID; // Class identification, replacement for typeinfo
453 BasicAliasAnalysis() : ImmutablePass(ID) {
454 initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
457 void initializePass() override {
458 InitializeAliasAnalysis(this);
461 void getAnalysisUsage(AnalysisUsage &AU) const override {
462 AU.addRequired<AliasAnalysis>();
463 AU.addRequired<TargetLibraryInfo>();
466 AliasResult alias(const Location &LocA, const Location &LocB) override {
467 assert(AliasCache.empty() && "AliasCache must be cleared after use!");
468 assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
469 "BasicAliasAnalysis doesn't support interprocedural queries.");
470 AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag,
471 LocB.Ptr, LocB.Size, LocB.TBAATag);
472 // AliasCache rarely has more than 1 or 2 elements, always use
473 // shrink_and_clear so it quickly returns to the inline capacity of the
474 // SmallDenseMap if it ever grows larger.
475 // FIXME: This should really be shrink_to_inline_capacity_and_clear().
476 AliasCache.shrink_and_clear();
477 VisitedPhiBBs.clear();
481 ModRefResult getModRefInfo(ImmutableCallSite CS,
482 const Location &Loc) override;
484 ModRefResult getModRefInfo(ImmutableCallSite CS1,
485 ImmutableCallSite CS2) override {
486 // The AliasAnalysis base class has some smarts, lets use them.
487 return AliasAnalysis::getModRefInfo(CS1, CS2);
490 /// pointsToConstantMemory - Chase pointers until we find a (constant
492 bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override;
494 /// getModRefBehavior - Return the behavior when calling the given
496 ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override;
498 /// getModRefBehavior - Return the behavior when calling the given function.
499 /// For use when the call site is not known.
500 ModRefBehavior getModRefBehavior(const Function *F) override;
502 /// getAdjustedAnalysisPointer - This method is used when a pass implements
503 /// an analysis interface through multiple inheritance. If needed, it
504 /// should override this to adjust the this pointer as needed for the
505 /// specified pass info.
506 void *getAdjustedAnalysisPointer(const void *ID) override {
507 if (ID == &AliasAnalysis::ID)
508 return (AliasAnalysis*)this;
513 // AliasCache - Track alias queries to guard against recursion.
514 typedef std::pair<Location, Location> LocPair;
515 typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
516 AliasCacheTy AliasCache;
518 /// \brief Track phi nodes we have visited. When interpret "Value" pointer
519 /// equality as value equality we need to make sure that the "Value" is not
520 /// part of a cycle. Otherwise, two uses could come from different
521 /// "iterations" of a cycle and see different values for the same "Value"
523 /// The following example shows the problem:
524 /// %p = phi(%alloca1, %addr2)
526 /// %addr1 = gep, %alloca2, 0, %l
527 /// %addr2 = gep %alloca2, 0, (%l + 1)
528 /// alias(%p, %addr1) -> MayAlias !
530 SmallPtrSet<const BasicBlock*, 8> VisitedPhiBBs;
532 // Visited - Track instructions visited by pointsToConstantMemory.
533 SmallPtrSet<const Value*, 16> Visited;
535 /// \brief Check whether two Values can be considered equivalent.
537 /// In addition to pointer equivalence of \p V1 and \p V2 this checks
538 /// whether they can not be part of a cycle in the value graph by looking at
539 /// all visited phi nodes an making sure that the phis cannot reach the
540 /// value. We have to do this because we are looking through phi nodes (That
541 /// is we say noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB).
542 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
544 /// \brief Dest and Src are the variable indices from two decomposed
545 /// GetElementPtr instructions GEP1 and GEP2 which have common base
546 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
547 /// difference between the two pointers.
548 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
549 const SmallVectorImpl<VariableGEPIndex> &Src);
551 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
552 // instruction against another.
553 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
554 const MDNode *V1TBAAInfo,
555 const Value *V2, uint64_t V2Size,
556 const MDNode *V2TBAAInfo,
557 const Value *UnderlyingV1, const Value *UnderlyingV2);
559 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
560 // instruction against another.
561 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
562 const MDNode *PNTBAAInfo,
563 const Value *V2, uint64_t V2Size,
564 const MDNode *V2TBAAInfo);
566 /// aliasSelect - Disambiguate a Select instruction against another value.
567 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
568 const MDNode *SITBAAInfo,
569 const Value *V2, uint64_t V2Size,
570 const MDNode *V2TBAAInfo);
572 AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
573 const MDNode *V1TBAATag,
574 const Value *V2, uint64_t V2Size,
575 const MDNode *V2TBAATag);
577 } // End of anonymous namespace
579 // Register this pass...
580 char BasicAliasAnalysis::ID = 0;
581 INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
582 "Basic Alias Analysis (stateless AA impl)",
584 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
585 INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
586 "Basic Alias Analysis (stateless AA impl)",
590 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
591 return new BasicAliasAnalysis();
594 /// pointsToConstantMemory - Returns whether the given pointer value
595 /// points to memory that is local to the function, with global constants being
596 /// considered local to all functions.
598 BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
599 assert(Visited.empty() && "Visited must be cleared after use!");
601 unsigned MaxLookup = 8;
602 SmallVector<const Value *, 16> Worklist;
603 Worklist.push_back(Loc.Ptr);
605 const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), DL);
606 if (!Visited.insert(V)) {
608 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
611 // An alloca instruction defines local memory.
612 if (OrLocal && isa<AllocaInst>(V))
615 // A global constant counts as local memory for our purposes.
616 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
617 // Note: this doesn't require GV to be "ODR" because it isn't legal for a
618 // global to be marked constant in some modules and non-constant in
619 // others. GV may even be a declaration, not a definition.
620 if (!GV->isConstant()) {
622 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
627 // If both select values point to local memory, then so does the select.
628 if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
629 Worklist.push_back(SI->getTrueValue());
630 Worklist.push_back(SI->getFalseValue());
634 // If all values incoming to a phi node point to local memory, then so does
636 if (const PHINode *PN = dyn_cast<PHINode>(V)) {
637 // Don't bother inspecting phi nodes with many operands.
638 if (PN->getNumIncomingValues() > MaxLookup) {
640 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
642 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
643 Worklist.push_back(PN->getIncomingValue(i));
647 // Otherwise be conservative.
649 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
651 } while (!Worklist.empty() && --MaxLookup);
654 return Worklist.empty();
657 /// getModRefBehavior - Return the behavior when calling the given call site.
658 AliasAnalysis::ModRefBehavior
659 BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
660 if (CS.doesNotAccessMemory())
661 // Can't do better than this.
662 return DoesNotAccessMemory;
664 ModRefBehavior Min = UnknownModRefBehavior;
666 // If the callsite knows it only reads memory, don't return worse
668 if (CS.onlyReadsMemory())
669 Min = OnlyReadsMemory;
671 // The AliasAnalysis base class has some smarts, lets use them.
672 return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
675 /// getModRefBehavior - Return the behavior when calling the given function.
676 /// For use when the call site is not known.
677 AliasAnalysis::ModRefBehavior
678 BasicAliasAnalysis::getModRefBehavior(const Function *F) {
679 // If the function declares it doesn't access memory, we can't do better.
680 if (F->doesNotAccessMemory())
681 return DoesNotAccessMemory;
683 // For intrinsics, we can check the table.
684 if (unsigned iid = F->getIntrinsicID()) {
685 #define GET_INTRINSIC_MODREF_BEHAVIOR
686 #include "llvm/IR/Intrinsics.gen"
687 #undef GET_INTRINSIC_MODREF_BEHAVIOR
690 ModRefBehavior Min = UnknownModRefBehavior;
692 // If the function declares it only reads memory, go with that.
693 if (F->onlyReadsMemory())
694 Min = OnlyReadsMemory;
696 // Otherwise be conservative.
697 return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
700 /// getModRefInfo - Check to see if the specified callsite can clobber the
701 /// specified memory object. Since we only look at local properties of this
702 /// function, we really can't say much about this query. We do, however, use
703 /// simple "address taken" analysis on local objects.
704 AliasAnalysis::ModRefResult
705 BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
706 const Location &Loc) {
707 assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
708 "AliasAnalysis query involving multiple functions!");
710 const Value *Object = GetUnderlyingObject(Loc.Ptr, DL);
712 // If this is a tail call and Loc.Ptr points to a stack location, we know that
713 // the tail call cannot access or modify the local stack.
714 // We cannot exclude byval arguments here; these belong to the caller of
715 // the current function not to the current function, and a tail callee
716 // may reference them.
717 if (isa<AllocaInst>(Object))
718 if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
719 if (CI->isTailCall())
722 // If the pointer is to a locally allocated object that does not escape,
723 // then the call can not mod/ref the pointer unless the call takes the pointer
724 // as an argument, and itself doesn't capture it.
725 if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
726 isNonEscapingLocalObject(Object)) {
727 bool PassedAsArg = false;
729 for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
730 CI != CE; ++CI, ++ArgNo) {
731 // Only look at the no-capture or byval pointer arguments. If this
732 // pointer were passed to arguments that were neither of these, then it
733 // couldn't be no-capture.
734 if (!(*CI)->getType()->isPointerTy() ||
735 (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
738 // If this is a no-capture pointer argument, see if we can tell that it
739 // is impossible to alias the pointer we're checking. If not, we have to
740 // assume that the call could touch the pointer, even though it doesn't
742 if (!isNoAlias(Location(*CI), Location(Object))) {
752 const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
753 ModRefResult Min = ModRef;
755 // Finally, handle specific knowledge of intrinsics.
756 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
758 switch (II->getIntrinsicID()) {
760 case Intrinsic::memcpy:
761 case Intrinsic::memmove: {
762 uint64_t Len = UnknownSize;
763 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
764 Len = LenCI->getZExtValue();
765 Value *Dest = II->getArgOperand(0);
766 Value *Src = II->getArgOperand(1);
767 // If it can't overlap the source dest, then it doesn't modref the loc.
768 if (isNoAlias(Location(Dest, Len), Loc)) {
769 if (isNoAlias(Location(Src, Len), Loc))
771 // If it can't overlap the dest, then worst case it reads the loc.
773 } else if (isNoAlias(Location(Src, Len), Loc)) {
774 // If it can't overlap the source, then worst case it mutates the loc.
779 case Intrinsic::memset:
780 // Since memset is 'accesses arguments' only, the AliasAnalysis base class
781 // will handle it for the variable length case.
782 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2))) {
783 uint64_t Len = LenCI->getZExtValue();
784 Value *Dest = II->getArgOperand(0);
785 if (isNoAlias(Location(Dest, Len), Loc))
788 // We know that memset doesn't load anything.
791 case Intrinsic::lifetime_start:
792 case Intrinsic::lifetime_end:
793 case Intrinsic::invariant_start: {
795 cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
796 if (isNoAlias(Location(II->getArgOperand(1),
798 II->getMetadata(LLVMContext::MD_tbaa)),
803 case Intrinsic::invariant_end: {
805 cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
806 if (isNoAlias(Location(II->getArgOperand(2),
808 II->getMetadata(LLVMContext::MD_tbaa)),
813 case Intrinsic::arm_neon_vld1: {
814 // LLVM's vld1 and vst1 intrinsics currently only support a single
817 DL ? DL->getTypeStoreSize(II->getType()) : UnknownSize;
818 if (isNoAlias(Location(II->getArgOperand(0), Size,
819 II->getMetadata(LLVMContext::MD_tbaa)),
824 case Intrinsic::arm_neon_vst1: {
826 DL ? DL->getTypeStoreSize(II->getArgOperand(1)->getType()) : UnknownSize;
827 if (isNoAlias(Location(II->getArgOperand(0), Size,
828 II->getMetadata(LLVMContext::MD_tbaa)),
835 // We can bound the aliasing properties of memset_pattern16 just as we can
836 // for memcpy/memset. This is particularly important because the
837 // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
838 // whenever possible.
839 else if (TLI.has(LibFunc::memset_pattern16) &&
840 CS.getCalledFunction() &&
841 CS.getCalledFunction()->getName() == "memset_pattern16") {
842 const Function *MS = CS.getCalledFunction();
843 FunctionType *MemsetType = MS->getFunctionType();
844 if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
845 isa<PointerType>(MemsetType->getParamType(0)) &&
846 isa<PointerType>(MemsetType->getParamType(1)) &&
847 isa<IntegerType>(MemsetType->getParamType(2))) {
848 uint64_t Len = UnknownSize;
849 if (const ConstantInt *LenCI = dyn_cast<ConstantInt>(CS.getArgument(2)))
850 Len = LenCI->getZExtValue();
851 const Value *Dest = CS.getArgument(0);
852 const Value *Src = CS.getArgument(1);
853 // If it can't overlap the source dest, then it doesn't modref the loc.
854 if (isNoAlias(Location(Dest, Len), Loc)) {
855 // Always reads 16 bytes of the source.
856 if (isNoAlias(Location(Src, 16), Loc))
858 // If it can't overlap the dest, then worst case it reads the loc.
860 // Always reads 16 bytes of the source.
861 } else if (isNoAlias(Location(Src, 16), Loc)) {
862 // If it can't overlap the source, then worst case it mutates the loc.
868 // The AliasAnalysis base class has some smarts, lets use them.
869 return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min);
872 /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
873 /// against another pointer. We know that V1 is a GEP, but we don't know
874 /// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, DL),
875 /// UnderlyingV2 is the same for V2.
877 AliasAnalysis::AliasResult
878 BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
879 const MDNode *V1TBAAInfo,
880 const Value *V2, uint64_t V2Size,
881 const MDNode *V2TBAAInfo,
882 const Value *UnderlyingV1,
883 const Value *UnderlyingV2) {
884 int64_t GEP1BaseOffset;
885 bool GEP1MaxLookupReached;
886 SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
888 // If we have two gep instructions with must-alias or not-alias'ing base
889 // pointers, figure out if the indexes to the GEP tell us anything about the
891 if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
892 // Do the base pointers alias?
893 AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, nullptr,
894 UnderlyingV2, UnknownSize, nullptr);
896 // Check for geps of non-aliasing underlying pointers where the offsets are
898 if ((BaseAlias == MayAlias) && V1Size == V2Size) {
899 // Do the base pointers alias assuming type and size.
900 AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
901 V1TBAAInfo, UnderlyingV2,
903 if (PreciseBaseAlias == NoAlias) {
904 // See if the computed offset from the common pointer tells us about the
905 // relation of the resulting pointer.
906 int64_t GEP2BaseOffset;
907 bool GEP2MaxLookupReached;
908 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
909 const Value *GEP2BasePtr =
910 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
911 GEP2MaxLookupReached, DL);
912 const Value *GEP1BasePtr =
913 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
914 GEP1MaxLookupReached, DL);
915 // DecomposeGEPExpression and GetUnderlyingObject should return the
916 // same result except when DecomposeGEPExpression has no DataLayout.
917 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
919 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
922 // If the max search depth is reached the result is undefined
923 if (GEP2MaxLookupReached || GEP1MaxLookupReached)
927 if (GEP1BaseOffset == GEP2BaseOffset &&
928 GEP1VariableIndices == GEP2VariableIndices)
930 GEP1VariableIndices.clear();
934 // If we get a No or May, then return it immediately, no amount of analysis
935 // will improve this situation.
936 if (BaseAlias != MustAlias) return BaseAlias;
938 // Otherwise, we have a MustAlias. Since the base pointers alias each other
939 // exactly, see if the computed offset from the common pointer tells us
940 // about the relation of the resulting pointer.
941 const Value *GEP1BasePtr =
942 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
943 GEP1MaxLookupReached, DL);
945 int64_t GEP2BaseOffset;
946 bool GEP2MaxLookupReached;
947 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
948 const Value *GEP2BasePtr =
949 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
950 GEP2MaxLookupReached, DL);
952 // DecomposeGEPExpression and GetUnderlyingObject should return the
953 // same result except when DecomposeGEPExpression has no DataLayout.
954 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
956 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
959 // If the max search depth is reached the result is undefined
960 if (GEP2MaxLookupReached || GEP1MaxLookupReached)
963 // Subtract the GEP2 pointer from the GEP1 pointer to find out their
964 // symbolic difference.
965 GEP1BaseOffset -= GEP2BaseOffset;
966 GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
969 // Check to see if these two pointers are related by the getelementptr
970 // instruction. If one pointer is a GEP with a non-zero index of the other
971 // pointer, we know they cannot alias.
973 // If both accesses are unknown size, we can't do anything useful here.
974 if (V1Size == UnknownSize && V2Size == UnknownSize)
977 AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, nullptr,
978 V2, V2Size, V2TBAAInfo);
980 // If V2 may alias GEP base pointer, conservatively returns MayAlias.
981 // If V2 is known not to alias GEP base pointer, then the two values
982 // cannot alias per GEP semantics: "A pointer value formed from a
983 // getelementptr instruction is associated with the addresses associated
984 // with the first operand of the getelementptr".
987 const Value *GEP1BasePtr =
988 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
989 GEP1MaxLookupReached, DL);
991 // DecomposeGEPExpression and GetUnderlyingObject should return the
992 // same result except when DecomposeGEPExpression has no DataLayout.
993 if (GEP1BasePtr != UnderlyingV1) {
995 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
998 // If the max search depth is reached the result is undefined
999 if (GEP1MaxLookupReached)
1003 // In the two GEP Case, if there is no difference in the offsets of the
1004 // computed pointers, the resultant pointers are a must alias. This
1005 // hapens when we have two lexically identical GEP's (for example).
1007 // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
1008 // must aliases the GEP, the end result is a must alias also.
1009 if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
1012 // If there is a constant difference between the pointers, but the difference
1013 // is less than the size of the associated memory object, then we know
1014 // that the objects are partially overlapping. If the difference is
1015 // greater, we know they do not overlap.
1016 if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
1017 if (GEP1BaseOffset >= 0) {
1018 if (V2Size != UnknownSize) {
1019 if ((uint64_t)GEP1BaseOffset < V2Size)
1020 return PartialAlias;
1024 // We have the situation where:
1027 // ---------------->|
1028 // |-->V1Size |-------> V2Size
1030 // We need to know that V2Size is not unknown, otherwise we might have
1031 // stripped a gep with negative index ('gep <ptr>, -1, ...).
1032 if (V1Size != UnknownSize && V2Size != UnknownSize) {
1033 if (-(uint64_t)GEP1BaseOffset < V1Size)
1034 return PartialAlias;
1040 // Try to distinguish something like &A[i][1] against &A[42][0].
1041 // Grab the least significant bit set in any of the scales.
1042 if (!GEP1VariableIndices.empty()) {
1043 uint64_t Modulo = 0;
1044 for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
1045 Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
1046 Modulo = Modulo ^ (Modulo & (Modulo - 1));
1048 // We can compute the difference between the two addresses
1049 // mod Modulo. Check whether that difference guarantees that the
1050 // two locations do not alias.
1051 uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
1052 if (V1Size != UnknownSize && V2Size != UnknownSize &&
1053 ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
1057 // Statically, we can see that the base objects are the same, but the
1058 // pointers have dynamic offsets which we can't resolve. And none of our
1059 // little tricks above worked.
1061 // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
1062 // practical effect of this is protecting TBAA in the case of dynamic
1063 // indices into arrays of unions or malloc'd memory.
1064 return PartialAlias;
1067 static AliasAnalysis::AliasResult
1068 MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
1069 // If the results agree, take it.
1072 // A mix of PartialAlias and MustAlias is PartialAlias.
1073 if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
1074 (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
1075 return AliasAnalysis::PartialAlias;
1076 // Otherwise, we don't know anything.
1077 return AliasAnalysis::MayAlias;
1080 /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
1081 /// instruction against another.
1082 AliasAnalysis::AliasResult
1083 BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
1084 const MDNode *SITBAAInfo,
1085 const Value *V2, uint64_t V2Size,
1086 const MDNode *V2TBAAInfo) {
1087 // If the values are Selects with the same condition, we can do a more precise
1088 // check: just check for aliases between the values on corresponding arms.
1089 if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
1090 if (SI->getCondition() == SI2->getCondition()) {
1092 aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo,
1093 SI2->getTrueValue(), V2Size, V2TBAAInfo);
1094 if (Alias == MayAlias)
1096 AliasResult ThisAlias =
1097 aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
1098 SI2->getFalseValue(), V2Size, V2TBAAInfo);
1099 return MergeAliasResults(ThisAlias, Alias);
1102 // If both arms of the Select node NoAlias or MustAlias V2, then returns
1103 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1105 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo);
1106 if (Alias == MayAlias)
1109 AliasResult ThisAlias =
1110 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
1111 return MergeAliasResults(ThisAlias, Alias);
1114 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
1116 AliasAnalysis::AliasResult
1117 BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
1118 const MDNode *PNTBAAInfo,
1119 const Value *V2, uint64_t V2Size,
1120 const MDNode *V2TBAAInfo) {
1121 // Track phi nodes we have visited. We use this information when we determine
1122 // value equivalence.
1123 VisitedPhiBBs.insert(PN->getParent());
1125 // If the values are PHIs in the same block, we can do a more precise
1126 // as well as efficient check: just check for aliases between the values
1127 // on corresponding edges.
1128 if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
1129 if (PN2->getParent() == PN->getParent()) {
1130 LocPair Locs(Location(PN, PNSize, PNTBAAInfo),
1131 Location(V2, V2Size, V2TBAAInfo));
1133 std::swap(Locs.first, Locs.second);
1134 // Analyse the PHIs' inputs under the assumption that the PHIs are
1136 // If the PHIs are May/MustAlias there must be (recursively) an input
1137 // operand from outside the PHIs' cycle that is MayAlias/MustAlias or
1138 // there must be an operation on the PHIs within the PHIs' value cycle
1139 // that causes a MayAlias.
1140 // Pretend the phis do not alias.
1141 AliasResult Alias = NoAlias;
1142 assert(AliasCache.count(Locs) &&
1143 "There must exist an entry for the phi node");
1144 AliasResult OrigAliasResult = AliasCache[Locs];
1145 AliasCache[Locs] = NoAlias;
1147 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1148 AliasResult ThisAlias =
1149 aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
1150 PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
1151 V2Size, V2TBAAInfo);
1152 Alias = MergeAliasResults(ThisAlias, Alias);
1153 if (Alias == MayAlias)
1157 // Reset if speculation failed.
1158 if (Alias != NoAlias)
1159 AliasCache[Locs] = OrigAliasResult;
1164 SmallPtrSet<Value*, 4> UniqueSrc;
1165 SmallVector<Value*, 4> V1Srcs;
1166 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1167 Value *PV1 = PN->getIncomingValue(i);
1168 if (isa<PHINode>(PV1))
1169 // If any of the source itself is a PHI, return MayAlias conservatively
1170 // to avoid compile time explosion. The worst possible case is if both
1171 // sides are PHI nodes. In which case, this is O(m x n) time where 'm'
1172 // and 'n' are the number of PHI sources.
1174 if (UniqueSrc.insert(PV1))
1175 V1Srcs.push_back(PV1);
1178 AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo,
1179 V1Srcs[0], PNSize, PNTBAAInfo);
1180 // Early exit if the check of the first PHI source against V2 is MayAlias.
1181 // Other results are not possible.
1182 if (Alias == MayAlias)
1185 // If all sources of the PHI node NoAlias or MustAlias V2, then returns
1186 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1187 for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
1188 Value *V = V1Srcs[i];
1190 AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
1191 V, PNSize, PNTBAAInfo);
1192 Alias = MergeAliasResults(ThisAlias, Alias);
1193 if (Alias == MayAlias)
1200 // aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
1201 // such as array references.
1203 AliasAnalysis::AliasResult
1204 BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
1205 const MDNode *V1TBAAInfo,
1206 const Value *V2, uint64_t V2Size,
1207 const MDNode *V2TBAAInfo) {
1208 // If either of the memory references is empty, it doesn't matter what the
1209 // pointer values are.
1210 if (V1Size == 0 || V2Size == 0)
1213 // Strip off any casts if they exist.
1214 V1 = V1->stripPointerCasts();
1215 V2 = V2->stripPointerCasts();
1217 // Are we checking for alias of the same value?
1218 // Because we look 'through' phi nodes we could look at "Value" pointers from
1219 // different iterations. We must therefore make sure that this is not the
1220 // case. The function isValueEqualInPotentialCycles ensures that this cannot
1221 // happen by looking at the visited phi nodes and making sure they cannot
1223 if (isValueEqualInPotentialCycles(V1, V2))
1226 if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
1227 return NoAlias; // Scalars cannot alias each other
1229 // Figure out what objects these things are pointing to if we can.
1230 const Value *O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth);
1231 const Value *O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth);
1233 // Null values in the default address space don't point to any object, so they
1234 // don't alias any other pointer.
1235 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
1236 if (CPN->getType()->getAddressSpace() == 0)
1238 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
1239 if (CPN->getType()->getAddressSpace() == 0)
1243 // If V1/V2 point to two different objects we know that we have no alias.
1244 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
1247 // Constant pointers can't alias with non-const isIdentifiedObject objects.
1248 if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
1249 (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
1252 // Function arguments can't alias with things that are known to be
1253 // unambigously identified at the function level.
1254 if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
1255 (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
1258 // Most objects can't alias null.
1259 if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
1260 (isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
1263 // If one pointer is the result of a call/invoke or load and the other is a
1264 // non-escaping local object within the same function, then we know the
1265 // object couldn't escape to a point where the call could return it.
1267 // Note that if the pointers are in different functions, there are a
1268 // variety of complications. A call with a nocapture argument may still
1269 // temporary store the nocapture argument's value in a temporary memory
1270 // location if that memory location doesn't escape. Or it may pass a
1271 // nocapture value to other functions as long as they don't capture it.
1272 if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
1274 if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
1278 // If the size of one access is larger than the entire object on the other
1279 // side, then we know such behavior is undefined and can assume no alias.
1281 if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *DL, *TLI)) ||
1282 (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *DL, *TLI)))
1285 // Check the cache before climbing up use-def chains. This also terminates
1286 // otherwise infinitely recursive queries.
1287 LocPair Locs(Location(V1, V1Size, V1TBAAInfo),
1288 Location(V2, V2Size, V2TBAAInfo));
1290 std::swap(Locs.first, Locs.second);
1291 std::pair<AliasCacheTy::iterator, bool> Pair =
1292 AliasCache.insert(std::make_pair(Locs, MayAlias));
1294 return Pair.first->second;
1296 // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
1297 // GEP can't simplify, we don't even look at the PHI cases.
1298 if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
1300 std::swap(V1Size, V2Size);
1302 std::swap(V1TBAAInfo, V2TBAAInfo);
1304 if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
1305 AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2);
1306 if (Result != MayAlias) return AliasCache[Locs] = Result;
1309 if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
1311 std::swap(V1Size, V2Size);
1312 std::swap(V1TBAAInfo, V2TBAAInfo);
1314 if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
1315 AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
1316 V2, V2Size, V2TBAAInfo);
1317 if (Result != MayAlias) return AliasCache[Locs] = Result;
1320 if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
1322 std::swap(V1Size, V2Size);
1323 std::swap(V1TBAAInfo, V2TBAAInfo);
1325 if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
1326 AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
1327 V2, V2Size, V2TBAAInfo);
1328 if (Result != MayAlias) return AliasCache[Locs] = Result;
1331 // If both pointers are pointing into the same object and one of them
1332 // accesses is accessing the entire object, then the accesses must
1333 // overlap in some way.
1335 if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *DL, *TLI)) ||
1336 (V2Size != UnknownSize && isObjectSize(O2, V2Size, *DL, *TLI)))
1337 return AliasCache[Locs] = PartialAlias;
1339 AliasResult Result =
1340 AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
1341 Location(V2, V2Size, V2TBAAInfo));
1342 return AliasCache[Locs] = Result;
1345 bool BasicAliasAnalysis::isValueEqualInPotentialCycles(const Value *V,
1350 const Instruction *Inst = dyn_cast<Instruction>(V);
1354 if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck)
1357 // Use dominance or loop info if available.
1358 DominatorTreeWrapperPass *DTWP =
1359 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
1360 DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
1361 LoopInfo *LI = getAnalysisIfAvailable<LoopInfo>();
1363 // Make sure that the visited phis cannot reach the Value. This ensures that
1364 // the Values cannot come from different iterations of a potential cycle the
1365 // phi nodes could be involved in.
1366 for (SmallPtrSet<const BasicBlock *, 8>::iterator PI = VisitedPhiBBs.begin(),
1367 PE = VisitedPhiBBs.end();
1369 if (isPotentiallyReachable((*PI)->begin(), Inst, DT, LI))
1375 /// GetIndexDifference - Dest and Src are the variable indices from two
1376 /// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
1377 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
1378 /// difference between the two pointers.
1379 void BasicAliasAnalysis::GetIndexDifference(
1380 SmallVectorImpl<VariableGEPIndex> &Dest,
1381 const SmallVectorImpl<VariableGEPIndex> &Src) {
1385 for (unsigned i = 0, e = Src.size(); i != e; ++i) {
1386 const Value *V = Src[i].V;
1387 ExtensionKind Extension = Src[i].Extension;
1388 int64_t Scale = Src[i].Scale;
1390 // Find V in Dest. This is N^2, but pointer indices almost never have more
1391 // than a few variable indexes.
1392 for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
1393 if (!isValueEqualInPotentialCycles(Dest[j].V, V) ||
1394 Dest[j].Extension != Extension)
1397 // If we found it, subtract off Scale V's from the entry in Dest. If it
1398 // goes to zero, remove the entry.
1399 if (Dest[j].Scale != Scale)
1400 Dest[j].Scale -= Scale;
1402 Dest.erase(Dest.begin() + j);
1407 // If we didn't consume this entry, add it to the end of the Dest list.
1409 VariableGEPIndex Entry = { V, Extension, -Scale };
1410 Dest.push_back(Entry);