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 /// Get the location associated with a pointer argument of a callsite.
495 Location getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
496 ModRefResult &Mask) override;
498 /// getModRefBehavior - Return the behavior when calling the given
500 ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override;
502 /// getModRefBehavior - Return the behavior when calling the given function.
503 /// For use when the call site is not known.
504 ModRefBehavior getModRefBehavior(const Function *F) override;
506 /// getAdjustedAnalysisPointer - This method is used when a pass implements
507 /// an analysis interface through multiple inheritance. If needed, it
508 /// should override this to adjust the this pointer as needed for the
509 /// specified pass info.
510 void *getAdjustedAnalysisPointer(const void *ID) override {
511 if (ID == &AliasAnalysis::ID)
512 return (AliasAnalysis*)this;
517 // AliasCache - Track alias queries to guard against recursion.
518 typedef std::pair<Location, Location> LocPair;
519 typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
520 AliasCacheTy AliasCache;
522 /// \brief Track phi nodes we have visited. When interpret "Value" pointer
523 /// equality as value equality we need to make sure that the "Value" is not
524 /// part of a cycle. Otherwise, two uses could come from different
525 /// "iterations" of a cycle and see different values for the same "Value"
527 /// The following example shows the problem:
528 /// %p = phi(%alloca1, %addr2)
530 /// %addr1 = gep, %alloca2, 0, %l
531 /// %addr2 = gep %alloca2, 0, (%l + 1)
532 /// alias(%p, %addr1) -> MayAlias !
534 SmallPtrSet<const BasicBlock*, 8> VisitedPhiBBs;
536 // Visited - Track instructions visited by pointsToConstantMemory.
537 SmallPtrSet<const Value*, 16> Visited;
539 /// \brief Check whether two Values can be considered equivalent.
541 /// In addition to pointer equivalence of \p V1 and \p V2 this checks
542 /// whether they can not be part of a cycle in the value graph by looking at
543 /// all visited phi nodes an making sure that the phis cannot reach the
544 /// value. We have to do this because we are looking through phi nodes (That
545 /// is we say noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB).
546 bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
548 /// \brief Dest and Src are the variable indices from two decomposed
549 /// GetElementPtr instructions GEP1 and GEP2 which have common base
550 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
551 /// difference between the two pointers.
552 void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
553 const SmallVectorImpl<VariableGEPIndex> &Src);
555 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
556 // instruction against another.
557 AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
558 const MDNode *V1TBAAInfo,
559 const Value *V2, uint64_t V2Size,
560 const MDNode *V2TBAAInfo,
561 const Value *UnderlyingV1, const Value *UnderlyingV2);
563 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
564 // instruction against another.
565 AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
566 const MDNode *PNTBAAInfo,
567 const Value *V2, uint64_t V2Size,
568 const MDNode *V2TBAAInfo);
570 /// aliasSelect - Disambiguate a Select instruction against another value.
571 AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
572 const MDNode *SITBAAInfo,
573 const Value *V2, uint64_t V2Size,
574 const MDNode *V2TBAAInfo);
576 AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
577 const MDNode *V1TBAATag,
578 const Value *V2, uint64_t V2Size,
579 const MDNode *V2TBAATag);
581 } // End of anonymous namespace
583 // Register this pass...
584 char BasicAliasAnalysis::ID = 0;
585 INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
586 "Basic Alias Analysis (stateless AA impl)",
588 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
589 INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
590 "Basic Alias Analysis (stateless AA impl)",
594 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
595 return new BasicAliasAnalysis();
598 /// pointsToConstantMemory - Returns whether the given pointer value
599 /// points to memory that is local to the function, with global constants being
600 /// considered local to all functions.
602 BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
603 assert(Visited.empty() && "Visited must be cleared after use!");
605 unsigned MaxLookup = 8;
606 SmallVector<const Value *, 16> Worklist;
607 Worklist.push_back(Loc.Ptr);
609 const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), DL);
610 if (!Visited.insert(V)) {
612 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
615 // An alloca instruction defines local memory.
616 if (OrLocal && isa<AllocaInst>(V))
619 // A global constant counts as local memory for our purposes.
620 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
621 // Note: this doesn't require GV to be "ODR" because it isn't legal for a
622 // global to be marked constant in some modules and non-constant in
623 // others. GV may even be a declaration, not a definition.
624 if (!GV->isConstant()) {
626 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
631 // If both select values point to local memory, then so does the select.
632 if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
633 Worklist.push_back(SI->getTrueValue());
634 Worklist.push_back(SI->getFalseValue());
638 // If all values incoming to a phi node point to local memory, then so does
640 if (const PHINode *PN = dyn_cast<PHINode>(V)) {
641 // Don't bother inspecting phi nodes with many operands.
642 if (PN->getNumIncomingValues() > MaxLookup) {
644 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
646 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
647 Worklist.push_back(PN->getIncomingValue(i));
651 // Otherwise be conservative.
653 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
655 } while (!Worklist.empty() && --MaxLookup);
658 return Worklist.empty();
661 static bool isMemsetPattern16(const Function *MS,
662 const TargetLibraryInfo &TLI) {
663 if (TLI.has(LibFunc::memset_pattern16) &&
664 MS->getName() == "memset_pattern16") {
665 FunctionType *MemsetType = MS->getFunctionType();
666 if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
667 isa<PointerType>(MemsetType->getParamType(0)) &&
668 isa<PointerType>(MemsetType->getParamType(1)) &&
669 isa<IntegerType>(MemsetType->getParamType(2)))
676 /// getModRefBehavior - Return the behavior when calling the given call site.
677 AliasAnalysis::ModRefBehavior
678 BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
679 if (CS.doesNotAccessMemory())
680 // Can't do better than this.
681 return DoesNotAccessMemory;
683 ModRefBehavior Min = UnknownModRefBehavior;
685 // If the callsite knows it only reads memory, don't return worse
687 if (CS.onlyReadsMemory())
688 Min = OnlyReadsMemory;
690 // The AliasAnalysis base class has some smarts, lets use them.
691 return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
694 /// getModRefBehavior - Return the behavior when calling the given function.
695 /// For use when the call site is not known.
696 AliasAnalysis::ModRefBehavior
697 BasicAliasAnalysis::getModRefBehavior(const Function *F) {
698 // If the function declares it doesn't access memory, we can't do better.
699 if (F->doesNotAccessMemory())
700 return DoesNotAccessMemory;
702 // For intrinsics, we can check the table.
703 if (unsigned iid = F->getIntrinsicID()) {
704 #define GET_INTRINSIC_MODREF_BEHAVIOR
705 #include "llvm/IR/Intrinsics.gen"
706 #undef GET_INTRINSIC_MODREF_BEHAVIOR
709 ModRefBehavior Min = UnknownModRefBehavior;
711 // If the function declares it only reads memory, go with that.
712 if (F->onlyReadsMemory())
713 Min = OnlyReadsMemory;
715 const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
716 if (isMemsetPattern16(F, TLI))
717 Min = OnlyAccessesArgumentPointees;
719 // Otherwise be conservative.
720 return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
723 AliasAnalysis::Location
724 BasicAliasAnalysis::getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
725 ModRefResult &Mask) {
726 Location Loc = AliasAnalysis::getArgLocation(CS, ArgIdx, Mask);
727 const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
728 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
730 switch (II->getIntrinsicID()) {
732 case Intrinsic::memset:
733 case Intrinsic::memcpy:
734 case Intrinsic::memmove: {
735 assert((ArgIdx == 0 || ArgIdx == 1) &&
736 "Invalid argument index for memory intrinsic");
737 if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
738 Loc.Size = LenCI->getZExtValue();
739 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
740 "Memory intrinsic location pointer not argument?");
741 Mask = ArgIdx ? Ref : Mod;
744 case Intrinsic::lifetime_start:
745 case Intrinsic::lifetime_end:
746 case Intrinsic::invariant_start: {
747 assert(ArgIdx == 1 && "Invalid argument index");
748 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
749 "Intrinsic location pointer not argument?");
750 Loc.Size = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
753 case Intrinsic::invariant_end: {
754 assert(ArgIdx == 2 && "Invalid argument index");
755 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
756 "Intrinsic location pointer not argument?");
757 Loc.Size = cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
760 case Intrinsic::arm_neon_vld1: {
761 assert(ArgIdx == 0 && "Invalid argument index");
762 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
763 "Intrinsic location pointer not argument?");
764 // LLVM's vld1 and vst1 intrinsics currently only support a single
767 Loc.Size = DL->getTypeStoreSize(II->getType());
770 case Intrinsic::arm_neon_vst1: {
771 assert(ArgIdx == 0 && "Invalid argument index");
772 assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
773 "Intrinsic location pointer not argument?");
775 Loc.Size = DL->getTypeStoreSize(II->getArgOperand(1)->getType());
780 // We can bound the aliasing properties of memset_pattern16 just as we can
781 // for memcpy/memset. This is particularly important because the
782 // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
783 // whenever possible.
784 else if (CS.getCalledFunction() &&
785 isMemsetPattern16(CS.getCalledFunction(), TLI)) {
786 assert((ArgIdx == 0 || ArgIdx == 1) &&
787 "Invalid argument index for memset_pattern16");
790 else if (const ConstantInt *LenCI =
791 dyn_cast<ConstantInt>(CS.getArgument(2)))
792 Loc.Size = LenCI->getZExtValue();
793 assert(Loc.Ptr == CS.getArgument(ArgIdx) &&
794 "memset_pattern16 location pointer not argument?");
795 Mask = ArgIdx ? Ref : Mod;
797 // FIXME: Handle memset_pattern4 and memset_pattern8 also.
802 /// getModRefInfo - Check to see if the specified callsite can clobber the
803 /// specified memory object. Since we only look at local properties of this
804 /// function, we really can't say much about this query. We do, however, use
805 /// simple "address taken" analysis on local objects.
806 AliasAnalysis::ModRefResult
807 BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
808 const Location &Loc) {
809 assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
810 "AliasAnalysis query involving multiple functions!");
812 const Value *Object = GetUnderlyingObject(Loc.Ptr, DL);
814 // If this is a tail call and Loc.Ptr points to a stack location, we know that
815 // the tail call cannot access or modify the local stack.
816 // We cannot exclude byval arguments here; these belong to the caller of
817 // the current function not to the current function, and a tail callee
818 // may reference them.
819 if (isa<AllocaInst>(Object))
820 if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
821 if (CI->isTailCall())
824 // If the pointer is to a locally allocated object that does not escape,
825 // then the call can not mod/ref the pointer unless the call takes the pointer
826 // as an argument, and itself doesn't capture it.
827 if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
828 isNonEscapingLocalObject(Object)) {
829 bool PassedAsArg = false;
831 for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
832 CI != CE; ++CI, ++ArgNo) {
833 // Only look at the no-capture or byval pointer arguments. If this
834 // pointer were passed to arguments that were neither of these, then it
835 // couldn't be no-capture.
836 if (!(*CI)->getType()->isPointerTy() ||
837 (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
840 // If this is a no-capture pointer argument, see if we can tell that it
841 // is impossible to alias the pointer we're checking. If not, we have to
842 // assume that the call could touch the pointer, even though it doesn't
844 if (!isNoAlias(Location(*CI), Location(Object))) {
854 // The AliasAnalysis base class has some smarts, lets use them.
855 return AliasAnalysis::getModRefInfo(CS, Loc);
858 /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
859 /// against another pointer. We know that V1 is a GEP, but we don't know
860 /// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, DL),
861 /// UnderlyingV2 is the same for V2.
863 AliasAnalysis::AliasResult
864 BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
865 const MDNode *V1TBAAInfo,
866 const Value *V2, uint64_t V2Size,
867 const MDNode *V2TBAAInfo,
868 const Value *UnderlyingV1,
869 const Value *UnderlyingV2) {
870 int64_t GEP1BaseOffset;
871 bool GEP1MaxLookupReached;
872 SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
874 // If we have two gep instructions with must-alias or not-alias'ing base
875 // pointers, figure out if the indexes to the GEP tell us anything about the
877 if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
878 // Do the base pointers alias?
879 AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, nullptr,
880 UnderlyingV2, UnknownSize, nullptr);
882 // Check for geps of non-aliasing underlying pointers where the offsets are
884 if ((BaseAlias == MayAlias) && V1Size == V2Size) {
885 // Do the base pointers alias assuming type and size.
886 AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
887 V1TBAAInfo, UnderlyingV2,
889 if (PreciseBaseAlias == NoAlias) {
890 // See if the computed offset from the common pointer tells us about the
891 // relation of the resulting pointer.
892 int64_t GEP2BaseOffset;
893 bool GEP2MaxLookupReached;
894 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
895 const Value *GEP2BasePtr =
896 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
897 GEP2MaxLookupReached, DL);
898 const Value *GEP1BasePtr =
899 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
900 GEP1MaxLookupReached, DL);
901 // DecomposeGEPExpression and GetUnderlyingObject should return the
902 // same result except when DecomposeGEPExpression has no DataLayout.
903 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
905 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
908 // If the max search depth is reached the result is undefined
909 if (GEP2MaxLookupReached || GEP1MaxLookupReached)
913 if (GEP1BaseOffset == GEP2BaseOffset &&
914 GEP1VariableIndices == GEP2VariableIndices)
916 GEP1VariableIndices.clear();
920 // If we get a No or May, then return it immediately, no amount of analysis
921 // will improve this situation.
922 if (BaseAlias != MustAlias) return BaseAlias;
924 // Otherwise, we have a MustAlias. Since the base pointers alias each other
925 // exactly, see if the computed offset from the common pointer tells us
926 // about the relation of the resulting pointer.
927 const Value *GEP1BasePtr =
928 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
929 GEP1MaxLookupReached, DL);
931 int64_t GEP2BaseOffset;
932 bool GEP2MaxLookupReached;
933 SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
934 const Value *GEP2BasePtr =
935 DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
936 GEP2MaxLookupReached, DL);
938 // DecomposeGEPExpression and GetUnderlyingObject should return the
939 // same result except when DecomposeGEPExpression has no DataLayout.
940 if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
942 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
945 // If the max search depth is reached the result is undefined
946 if (GEP2MaxLookupReached || GEP1MaxLookupReached)
949 // Subtract the GEP2 pointer from the GEP1 pointer to find out their
950 // symbolic difference.
951 GEP1BaseOffset -= GEP2BaseOffset;
952 GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
955 // Check to see if these two pointers are related by the getelementptr
956 // instruction. If one pointer is a GEP with a non-zero index of the other
957 // pointer, we know they cannot alias.
959 // If both accesses are unknown size, we can't do anything useful here.
960 if (V1Size == UnknownSize && V2Size == UnknownSize)
963 AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, nullptr,
964 V2, V2Size, V2TBAAInfo);
966 // If V2 may alias GEP base pointer, conservatively returns MayAlias.
967 // If V2 is known not to alias GEP base pointer, then the two values
968 // cannot alias per GEP semantics: "A pointer value formed from a
969 // getelementptr instruction is associated with the addresses associated
970 // with the first operand of the getelementptr".
973 const Value *GEP1BasePtr =
974 DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
975 GEP1MaxLookupReached, DL);
977 // DecomposeGEPExpression and GetUnderlyingObject should return the
978 // same result except when DecomposeGEPExpression has no DataLayout.
979 if (GEP1BasePtr != UnderlyingV1) {
981 "DecomposeGEPExpression and GetUnderlyingObject disagree!");
984 // If the max search depth is reached the result is undefined
985 if (GEP1MaxLookupReached)
989 // In the two GEP Case, if there is no difference in the offsets of the
990 // computed pointers, the resultant pointers are a must alias. This
991 // hapens when we have two lexically identical GEP's (for example).
993 // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
994 // must aliases the GEP, the end result is a must alias also.
995 if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
998 // If there is a constant difference between the pointers, but the difference
999 // is less than the size of the associated memory object, then we know
1000 // that the objects are partially overlapping. If the difference is
1001 // greater, we know they do not overlap.
1002 if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
1003 if (GEP1BaseOffset >= 0) {
1004 if (V2Size != UnknownSize) {
1005 if ((uint64_t)GEP1BaseOffset < V2Size)
1006 return PartialAlias;
1010 // We have the situation where:
1013 // ---------------->|
1014 // |-->V1Size |-------> V2Size
1016 // We need to know that V2Size is not unknown, otherwise we might have
1017 // stripped a gep with negative index ('gep <ptr>, -1, ...).
1018 if (V1Size != UnknownSize && V2Size != UnknownSize) {
1019 if (-(uint64_t)GEP1BaseOffset < V1Size)
1020 return PartialAlias;
1026 // Try to distinguish something like &A[i][1] against &A[42][0].
1027 // Grab the least significant bit set in any of the scales.
1028 if (!GEP1VariableIndices.empty()) {
1029 uint64_t Modulo = 0;
1030 for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
1031 Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
1032 Modulo = Modulo ^ (Modulo & (Modulo - 1));
1034 // We can compute the difference between the two addresses
1035 // mod Modulo. Check whether that difference guarantees that the
1036 // two locations do not alias.
1037 uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
1038 if (V1Size != UnknownSize && V2Size != UnknownSize &&
1039 ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
1043 // Statically, we can see that the base objects are the same, but the
1044 // pointers have dynamic offsets which we can't resolve. And none of our
1045 // little tricks above worked.
1047 // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
1048 // practical effect of this is protecting TBAA in the case of dynamic
1049 // indices into arrays of unions or malloc'd memory.
1050 return PartialAlias;
1053 static AliasAnalysis::AliasResult
1054 MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
1055 // If the results agree, take it.
1058 // A mix of PartialAlias and MustAlias is PartialAlias.
1059 if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
1060 (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
1061 return AliasAnalysis::PartialAlias;
1062 // Otherwise, we don't know anything.
1063 return AliasAnalysis::MayAlias;
1066 /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
1067 /// instruction against another.
1068 AliasAnalysis::AliasResult
1069 BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
1070 const MDNode *SITBAAInfo,
1071 const Value *V2, uint64_t V2Size,
1072 const MDNode *V2TBAAInfo) {
1073 // If the values are Selects with the same condition, we can do a more precise
1074 // check: just check for aliases between the values on corresponding arms.
1075 if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
1076 if (SI->getCondition() == SI2->getCondition()) {
1078 aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo,
1079 SI2->getTrueValue(), V2Size, V2TBAAInfo);
1080 if (Alias == MayAlias)
1082 AliasResult ThisAlias =
1083 aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
1084 SI2->getFalseValue(), V2Size, V2TBAAInfo);
1085 return MergeAliasResults(ThisAlias, Alias);
1088 // If both arms of the Select node NoAlias or MustAlias V2, then returns
1089 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1091 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo);
1092 if (Alias == MayAlias)
1095 AliasResult ThisAlias =
1096 aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
1097 return MergeAliasResults(ThisAlias, Alias);
1100 // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
1102 AliasAnalysis::AliasResult
1103 BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
1104 const MDNode *PNTBAAInfo,
1105 const Value *V2, uint64_t V2Size,
1106 const MDNode *V2TBAAInfo) {
1107 // Track phi nodes we have visited. We use this information when we determine
1108 // value equivalence.
1109 VisitedPhiBBs.insert(PN->getParent());
1111 // If the values are PHIs in the same block, we can do a more precise
1112 // as well as efficient check: just check for aliases between the values
1113 // on corresponding edges.
1114 if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
1115 if (PN2->getParent() == PN->getParent()) {
1116 LocPair Locs(Location(PN, PNSize, PNTBAAInfo),
1117 Location(V2, V2Size, V2TBAAInfo));
1119 std::swap(Locs.first, Locs.second);
1120 // Analyse the PHIs' inputs under the assumption that the PHIs are
1122 // If the PHIs are May/MustAlias there must be (recursively) an input
1123 // operand from outside the PHIs' cycle that is MayAlias/MustAlias or
1124 // there must be an operation on the PHIs within the PHIs' value cycle
1125 // that causes a MayAlias.
1126 // Pretend the phis do not alias.
1127 AliasResult Alias = NoAlias;
1128 assert(AliasCache.count(Locs) &&
1129 "There must exist an entry for the phi node");
1130 AliasResult OrigAliasResult = AliasCache[Locs];
1131 AliasCache[Locs] = NoAlias;
1133 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1134 AliasResult ThisAlias =
1135 aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
1136 PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
1137 V2Size, V2TBAAInfo);
1138 Alias = MergeAliasResults(ThisAlias, Alias);
1139 if (Alias == MayAlias)
1143 // Reset if speculation failed.
1144 if (Alias != NoAlias)
1145 AliasCache[Locs] = OrigAliasResult;
1150 SmallPtrSet<Value*, 4> UniqueSrc;
1151 SmallVector<Value*, 4> V1Srcs;
1152 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1153 Value *PV1 = PN->getIncomingValue(i);
1154 if (isa<PHINode>(PV1))
1155 // If any of the source itself is a PHI, return MayAlias conservatively
1156 // to avoid compile time explosion. The worst possible case is if both
1157 // sides are PHI nodes. In which case, this is O(m x n) time where 'm'
1158 // and 'n' are the number of PHI sources.
1160 if (UniqueSrc.insert(PV1))
1161 V1Srcs.push_back(PV1);
1164 AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo,
1165 V1Srcs[0], PNSize, PNTBAAInfo);
1166 // Early exit if the check of the first PHI source against V2 is MayAlias.
1167 // Other results are not possible.
1168 if (Alias == MayAlias)
1171 // If all sources of the PHI node NoAlias or MustAlias V2, then returns
1172 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1173 for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
1174 Value *V = V1Srcs[i];
1176 AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
1177 V, PNSize, PNTBAAInfo);
1178 Alias = MergeAliasResults(ThisAlias, Alias);
1179 if (Alias == MayAlias)
1186 // aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
1187 // such as array references.
1189 AliasAnalysis::AliasResult
1190 BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
1191 const MDNode *V1TBAAInfo,
1192 const Value *V2, uint64_t V2Size,
1193 const MDNode *V2TBAAInfo) {
1194 // If either of the memory references is empty, it doesn't matter what the
1195 // pointer values are.
1196 if (V1Size == 0 || V2Size == 0)
1199 // Strip off any casts if they exist.
1200 V1 = V1->stripPointerCasts();
1201 V2 = V2->stripPointerCasts();
1203 // Are we checking for alias of the same value?
1204 // Because we look 'through' phi nodes we could look at "Value" pointers from
1205 // different iterations. We must therefore make sure that this is not the
1206 // case. The function isValueEqualInPotentialCycles ensures that this cannot
1207 // happen by looking at the visited phi nodes and making sure they cannot
1209 if (isValueEqualInPotentialCycles(V1, V2))
1212 if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
1213 return NoAlias; // Scalars cannot alias each other
1215 // Figure out what objects these things are pointing to if we can.
1216 const Value *O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth);
1217 const Value *O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth);
1219 // Null values in the default address space don't point to any object, so they
1220 // don't alias any other pointer.
1221 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
1222 if (CPN->getType()->getAddressSpace() == 0)
1224 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
1225 if (CPN->getType()->getAddressSpace() == 0)
1229 // If V1/V2 point to two different objects we know that we have no alias.
1230 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
1233 // Constant pointers can't alias with non-const isIdentifiedObject objects.
1234 if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
1235 (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
1238 // Function arguments can't alias with things that are known to be
1239 // unambigously identified at the function level.
1240 if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
1241 (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
1244 // Most objects can't alias null.
1245 if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
1246 (isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
1249 // If one pointer is the result of a call/invoke or load and the other is a
1250 // non-escaping local object within the same function, then we know the
1251 // object couldn't escape to a point where the call could return it.
1253 // Note that if the pointers are in different functions, there are a
1254 // variety of complications. A call with a nocapture argument may still
1255 // temporary store the nocapture argument's value in a temporary memory
1256 // location if that memory location doesn't escape. Or it may pass a
1257 // nocapture value to other functions as long as they don't capture it.
1258 if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
1260 if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
1264 // If the size of one access is larger than the entire object on the other
1265 // side, then we know such behavior is undefined and can assume no alias.
1267 if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *DL, *TLI)) ||
1268 (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *DL, *TLI)))
1271 // Check the cache before climbing up use-def chains. This also terminates
1272 // otherwise infinitely recursive queries.
1273 LocPair Locs(Location(V1, V1Size, V1TBAAInfo),
1274 Location(V2, V2Size, V2TBAAInfo));
1276 std::swap(Locs.first, Locs.second);
1277 std::pair<AliasCacheTy::iterator, bool> Pair =
1278 AliasCache.insert(std::make_pair(Locs, MayAlias));
1280 return Pair.first->second;
1282 // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
1283 // GEP can't simplify, we don't even look at the PHI cases.
1284 if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
1286 std::swap(V1Size, V2Size);
1288 std::swap(V1TBAAInfo, V2TBAAInfo);
1290 if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
1291 AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2);
1292 if (Result != MayAlias) return AliasCache[Locs] = Result;
1295 if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
1297 std::swap(V1Size, V2Size);
1298 std::swap(V1TBAAInfo, V2TBAAInfo);
1300 if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
1301 AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
1302 V2, V2Size, V2TBAAInfo);
1303 if (Result != MayAlias) return AliasCache[Locs] = Result;
1306 if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
1308 std::swap(V1Size, V2Size);
1309 std::swap(V1TBAAInfo, V2TBAAInfo);
1311 if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
1312 AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
1313 V2, V2Size, V2TBAAInfo);
1314 if (Result != MayAlias) return AliasCache[Locs] = Result;
1317 // If both pointers are pointing into the same object and one of them
1318 // accesses is accessing the entire object, then the accesses must
1319 // overlap in some way.
1321 if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *DL, *TLI)) ||
1322 (V2Size != UnknownSize && isObjectSize(O2, V2Size, *DL, *TLI)))
1323 return AliasCache[Locs] = PartialAlias;
1325 AliasResult Result =
1326 AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
1327 Location(V2, V2Size, V2TBAAInfo));
1328 return AliasCache[Locs] = Result;
1331 bool BasicAliasAnalysis::isValueEqualInPotentialCycles(const Value *V,
1336 const Instruction *Inst = dyn_cast<Instruction>(V);
1340 if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck)
1343 // Use dominance or loop info if available.
1344 DominatorTreeWrapperPass *DTWP =
1345 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
1346 DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
1347 LoopInfo *LI = getAnalysisIfAvailable<LoopInfo>();
1349 // Make sure that the visited phis cannot reach the Value. This ensures that
1350 // the Values cannot come from different iterations of a potential cycle the
1351 // phi nodes could be involved in.
1352 for (SmallPtrSet<const BasicBlock *, 8>::iterator PI = VisitedPhiBBs.begin(),
1353 PE = VisitedPhiBBs.end();
1355 if (isPotentiallyReachable((*PI)->begin(), Inst, DT, LI))
1361 /// GetIndexDifference - Dest and Src are the variable indices from two
1362 /// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
1363 /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
1364 /// difference between the two pointers.
1365 void BasicAliasAnalysis::GetIndexDifference(
1366 SmallVectorImpl<VariableGEPIndex> &Dest,
1367 const SmallVectorImpl<VariableGEPIndex> &Src) {
1371 for (unsigned i = 0, e = Src.size(); i != e; ++i) {
1372 const Value *V = Src[i].V;
1373 ExtensionKind Extension = Src[i].Extension;
1374 int64_t Scale = Src[i].Scale;
1376 // Find V in Dest. This is N^2, but pointer indices almost never have more
1377 // than a few variable indexes.
1378 for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
1379 if (!isValueEqualInPotentialCycles(Dest[j].V, V) ||
1380 Dest[j].Extension != Extension)
1383 // If we found it, subtract off Scale V's from the entry in Dest. If it
1384 // goes to zero, remove the entry.
1385 if (Dest[j].Scale != Scale)
1386 Dest[j].Scale -= Scale;
1388 Dest.erase(Dest.begin() + j);
1393 // If we didn't consume this entry, add it to the end of the Dest list.
1395 VariableGEPIndex Entry = { V, Extension, -Scale };
1396 Dest.push_back(Entry);