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/BasicAliasAnalysis.h"
17 #include "llvm/ADT/APInt.h"
18 #include "llvm/ADT/SmallPtrSet.h"
19 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/ADT/Statistic.h"
21 #include "llvm/Analysis/AliasAnalysis.h"
22 #include "llvm/Analysis/AssumptionCache.h"
23 #include "llvm/Analysis/CFG.h"
24 #include "llvm/Analysis/CaptureTracking.h"
25 #include "llvm/Analysis/InstructionSimplify.h"
26 #include "llvm/Analysis/LoopInfo.h"
27 #include "llvm/Analysis/MemoryBuiltins.h"
28 #include "llvm/Analysis/MemoryLocation.h"
29 #include "llvm/Analysis/TargetLibraryInfo.h"
30 #include "llvm/Analysis/ValueTracking.h"
31 #include "llvm/IR/Argument.h"
32 #include "llvm/IR/Attributes.h"
33 #include "llvm/IR/CallSite.h"
34 #include "llvm/IR/Constant.h"
35 #include "llvm/IR/Constants.h"
36 #include "llvm/IR/DataLayout.h"
37 #include "llvm/IR/DerivedTypes.h"
38 #include "llvm/IR/Dominators.h"
39 #include "llvm/IR/Function.h"
40 #include "llvm/IR/GetElementPtrTypeIterator.h"
41 #include "llvm/IR/GlobalAlias.h"
42 #include "llvm/IR/GlobalVariable.h"
43 #include "llvm/IR/InstrTypes.h"
44 #include "llvm/IR/Instruction.h"
45 #include "llvm/IR/Instructions.h"
46 #include "llvm/IR/IntrinsicInst.h"
47 #include "llvm/IR/Intrinsics.h"
48 #include "llvm/IR/Metadata.h"
49 #include "llvm/IR/Operator.h"
50 #include "llvm/IR/Type.h"
51 #include "llvm/IR/User.h"
52 #include "llvm/IR/Value.h"
53 #include "llvm/Pass.h"
54 #include "llvm/Support/Casting.h"
55 #include "llvm/Support/CommandLine.h"
56 #include "llvm/Support/Compiler.h"
57 #include "llvm/Support/KnownBits.h"
63 #define DEBUG_TYPE "basicaa"
67 /// Enable analysis of recursive PHI nodes.
68 static cl::opt<bool> EnableRecPhiAnalysis("basicaa-recphi", cl::Hidden,
70 /// SearchLimitReached / SearchTimes shows how often the limit of
71 /// to decompose GEPs is reached. It will affect the precision
72 /// of basic alias analysis.
73 STATISTIC(SearchLimitReached, "Number of times the limit to "
74 "decompose GEPs is reached");
75 STATISTIC(SearchTimes, "Number of times a GEP is decomposed");
77 /// Cutoff after which to stop analysing a set of phi nodes potentially involved
78 /// in a cycle. Because we are analysing 'through' phi nodes, we need to be
79 /// careful with value equivalence. We use reachability to make sure a value
80 /// cannot be involved in a cycle.
81 const unsigned MaxNumPhiBBsValueReachabilityCheck = 20;
83 // The max limit of the search depth in DecomposeGEPExpression() and
84 // GetUnderlyingObject(), both functions need to use the same search
85 // depth otherwise the algorithm in aliasGEP will assert.
86 static const unsigned MaxLookupSearchDepth = 6;
88 bool BasicAAResult::invalidate(Function &F, const PreservedAnalyses &PA,
89 FunctionAnalysisManager::Invalidator &Inv) {
90 // We don't care if this analysis itself is preserved, it has no state. But
91 // we need to check that the analyses it depends on have been. Note that we
92 // may be created without handles to some analyses and in that case don't
94 if (Inv.invalidate<AssumptionAnalysis>(F, PA) ||
95 (DT && Inv.invalidate<DominatorTreeAnalysis>(F, PA)) ||
96 (LI && Inv.invalidate<LoopAnalysis>(F, PA)))
99 // Otherwise this analysis result remains valid.
103 //===----------------------------------------------------------------------===//
105 //===----------------------------------------------------------------------===//
107 /// Returns true if the pointer is to a function-local object that never
108 /// escapes from the function.
109 static bool isNonEscapingLocalObject(const Value *V) {
110 // If this is a local allocation, check to see if it escapes.
111 if (isa<AllocaInst>(V) || isNoAliasCall(V))
112 // Set StoreCaptures to True so that we can assume in our callers that the
113 // pointer is not the result of a load instruction. Currently
114 // PointerMayBeCaptured doesn't have any special analysis for the
115 // StoreCaptures=false case; if it did, our callers could be refined to be
117 return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
119 // If this is an argument that corresponds to a byval or noalias argument,
120 // then it has not escaped before entering the function. Check if it escapes
121 // inside the function.
122 if (const Argument *A = dyn_cast<Argument>(V))
123 if (A->hasByValAttr() || A->hasNoAliasAttr())
124 // Note even if the argument is marked nocapture, we still need to check
125 // for copies made inside the function. The nocapture attribute only
126 // specifies that there are no copies made that outlive the function.
127 return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
132 /// Returns true if the pointer is one which would have been considered an
133 /// escape by isNonEscapingLocalObject.
134 static bool isEscapeSource(const Value *V) {
135 if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V))
138 // The load case works because isNonEscapingLocalObject considers all
139 // stores to be escapes (it passes true for the StoreCaptures argument
140 // to PointerMayBeCaptured).
141 if (isa<LoadInst>(V))
147 /// Returns the size of the object specified by V or UnknownSize if unknown.
148 static uint64_t getObjectSize(const Value *V, const DataLayout &DL,
149 const TargetLibraryInfo &TLI,
150 bool RoundToAlign = false) {
153 Opts.RoundToAlign = RoundToAlign;
154 if (getObjectSize(V, Size, DL, &TLI, Opts))
156 return MemoryLocation::UnknownSize;
159 /// Returns true if we can prove that the object specified by V is smaller than
161 static bool isObjectSmallerThan(const Value *V, uint64_t Size,
162 const DataLayout &DL,
163 const TargetLibraryInfo &TLI) {
164 // Note that the meanings of the "object" are slightly different in the
165 // following contexts:
166 // c1: llvm::getObjectSize()
167 // c2: llvm.objectsize() intrinsic
168 // c3: isObjectSmallerThan()
169 // c1 and c2 share the same meaning; however, the meaning of "object" in c3
170 // refers to the "entire object".
172 // Consider this example:
173 // char *p = (char*)malloc(100)
176 // In the context of c1 and c2, the "object" pointed by q refers to the
177 // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
179 // However, in the context of c3, the "object" refers to the chunk of memory
180 // being allocated. So, the "object" has 100 bytes, and q points to the middle
181 // the "object". In case q is passed to isObjectSmallerThan() as the 1st
182 // parameter, before the llvm::getObjectSize() is called to get the size of
183 // entire object, we should:
184 // - either rewind the pointer q to the base-address of the object in
185 // question (in this case rewind to p), or
186 // - just give up. It is up to caller to make sure the pointer is pointing
187 // to the base address the object.
189 // We go for 2nd option for simplicity.
190 if (!isIdentifiedObject(V))
193 // This function needs to use the aligned object size because we allow
194 // reads a bit past the end given sufficient alignment.
195 uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/ true);
197 return ObjectSize != MemoryLocation::UnknownSize && ObjectSize < Size;
200 /// Returns true if we can prove that the object specified by V has size Size.
201 static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
202 const TargetLibraryInfo &TLI) {
203 uint64_t ObjectSize = getObjectSize(V, DL, TLI);
204 return ObjectSize != MemoryLocation::UnknownSize && ObjectSize == Size;
207 //===----------------------------------------------------------------------===//
208 // GetElementPtr Instruction Decomposition and Analysis
209 //===----------------------------------------------------------------------===//
211 /// Analyzes the specified value as a linear expression: "A*V + B", where A and
212 /// B are constant integers.
214 /// Returns the scale and offset values as APInts and return V as a Value*, and
215 /// return whether we looked through any sign or zero extends. The incoming
216 /// Value is known to have IntegerType, and it may already be sign or zero
219 /// Note that this looks through extends, so the high bits may not be
220 /// represented in the result.
221 /*static*/ const Value *BasicAAResult::GetLinearExpression(
222 const Value *V, APInt &Scale, APInt &Offset, unsigned &ZExtBits,
223 unsigned &SExtBits, const DataLayout &DL, unsigned Depth,
224 AssumptionCache *AC, DominatorTree *DT, bool &NSW, bool &NUW) {
225 assert(V->getType()->isIntegerTy() && "Not an integer value");
227 // Limit our recursion depth.
234 if (const ConstantInt *Const = dyn_cast<ConstantInt>(V)) {
235 // If it's a constant, just convert it to an offset and remove the variable.
236 // If we've been called recursively, the Offset bit width will be greater
237 // than the constant's (the Offset's always as wide as the outermost call),
238 // so we'll zext here and process any extension in the isa<SExtInst> &
239 // isa<ZExtInst> cases below.
240 Offset += Const->getValue().zextOrSelf(Offset.getBitWidth());
241 assert(Scale == 0 && "Constant values don't have a scale");
245 if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
246 if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
247 // If we've been called recursively, then Offset and Scale will be wider
248 // than the BOp operands. We'll always zext it here as we'll process sign
249 // extensions below (see the isa<SExtInst> / isa<ZExtInst> cases).
250 APInt RHS = RHSC->getValue().zextOrSelf(Offset.getBitWidth());
252 switch (BOp->getOpcode()) {
254 // We don't understand this instruction, so we can't decompose it any
259 case Instruction::Or:
260 // X|C == X+C if all the bits in C are unset in X. Otherwise we can't
262 if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), DL, 0, AC,
269 case Instruction::Add:
270 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
271 SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
274 case Instruction::Sub:
275 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
276 SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
279 case Instruction::Mul:
280 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
281 SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
285 case Instruction::Shl:
286 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
287 SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
288 Offset <<= RHS.getLimitedValue();
289 Scale <<= RHS.getLimitedValue();
290 // the semantics of nsw and nuw for left shifts don't match those of
291 // multiplications, so we won't propagate them.
296 if (isa<OverflowingBinaryOperator>(BOp)) {
297 NUW &= BOp->hasNoUnsignedWrap();
298 NSW &= BOp->hasNoSignedWrap();
304 // Since GEP indices are sign extended anyway, we don't care about the high
305 // bits of a sign or zero extended value - just scales and offsets. The
306 // extensions have to be consistent though.
307 if (isa<SExtInst>(V) || isa<ZExtInst>(V)) {
308 Value *CastOp = cast<CastInst>(V)->getOperand(0);
309 unsigned NewWidth = V->getType()->getPrimitiveSizeInBits();
310 unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
311 unsigned OldZExtBits = ZExtBits, OldSExtBits = SExtBits;
312 const Value *Result =
313 GetLinearExpression(CastOp, Scale, Offset, ZExtBits, SExtBits, DL,
314 Depth + 1, AC, DT, NSW, NUW);
316 // zext(zext(%x)) == zext(%x), and similarly for sext; we'll handle this
317 // by just incrementing the number of bits we've extended by.
318 unsigned ExtendedBy = NewWidth - SmallWidth;
320 if (isa<SExtInst>(V) && ZExtBits == 0) {
321 // sext(sext(%x, a), b) == sext(%x, a + b)
324 // We haven't sign-wrapped, so it's valid to decompose sext(%x + c)
325 // into sext(%x) + sext(c). We'll sext the Offset ourselves:
326 unsigned OldWidth = Offset.getBitWidth();
327 Offset = Offset.trunc(SmallWidth).sext(NewWidth).zextOrSelf(OldWidth);
329 // We may have signed-wrapped, so don't decompose sext(%x + c) into
330 // sext(%x) + sext(c)
334 ZExtBits = OldZExtBits;
335 SExtBits = OldSExtBits;
337 SExtBits += ExtendedBy;
339 // sext(zext(%x, a), b) = zext(zext(%x, a), b) = zext(%x, a + b)
342 // We may have unsigned-wrapped, so don't decompose zext(%x + c) into
343 // zext(%x) + zext(c)
347 ZExtBits = OldZExtBits;
348 SExtBits = OldSExtBits;
350 ZExtBits += ExtendedBy;
361 /// To ensure a pointer offset fits in an integer of size PointerSize
362 /// (in bits) when that size is smaller than 64. This is an issue in
363 /// particular for 32b programs with negative indices that rely on two's
364 /// complement wrap-arounds for precise alias information.
365 static int64_t adjustToPointerSize(int64_t Offset, unsigned PointerSize) {
366 assert(PointerSize <= 64 && "Invalid PointerSize!");
367 unsigned ShiftBits = 64 - PointerSize;
368 return (int64_t)((uint64_t)Offset << ShiftBits) >> ShiftBits;
371 /// If V is a symbolic pointer expression, decompose it into a base pointer
372 /// with a constant offset and a number of scaled symbolic offsets.
374 /// The scaled symbolic offsets (represented by pairs of a Value* and a scale
375 /// in the VarIndices vector) are Value*'s that are known to be scaled by the
376 /// specified amount, but which may have other unrepresented high bits. As
377 /// such, the gep cannot necessarily be reconstructed from its decomposed form.
379 /// When DataLayout is around, this function is capable of analyzing everything
380 /// that GetUnderlyingObject can look through. To be able to do that
381 /// GetUnderlyingObject and DecomposeGEPExpression must use the same search
382 /// depth (MaxLookupSearchDepth). When DataLayout not is around, it just looks
383 /// through pointer casts.
384 bool BasicAAResult::DecomposeGEPExpression(const Value *V,
385 DecomposedGEP &Decomposed, const DataLayout &DL, AssumptionCache *AC,
387 // Limit recursion depth to limit compile time in crazy cases.
388 unsigned MaxLookup = MaxLookupSearchDepth;
391 Decomposed.StructOffset = 0;
392 Decomposed.OtherOffset = 0;
393 Decomposed.VarIndices.clear();
395 // See if this is a bitcast or GEP.
396 const Operator *Op = dyn_cast<Operator>(V);
398 // The only non-operator case we can handle are GlobalAliases.
399 if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
400 if (!GA->isInterposable()) {
401 V = GA->getAliasee();
409 if (Op->getOpcode() == Instruction::BitCast ||
410 Op->getOpcode() == Instruction::AddrSpaceCast) {
411 V = Op->getOperand(0);
415 const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
417 if (auto CS = ImmutableCallSite(V))
418 if (const Value *RV = CS.getReturnedArgOperand()) {
423 // If it's not a GEP, hand it off to SimplifyInstruction to see if it
424 // can come up with something. This matches what GetUnderlyingObject does.
425 if (const Instruction *I = dyn_cast<Instruction>(V))
426 // TODO: Get a DominatorTree and AssumptionCache and use them here
427 // (these are both now available in this function, but this should be
428 // updated when GetUnderlyingObject is updated). TLI should be
430 if (const Value *Simplified =
431 SimplifyInstruction(const_cast<Instruction *>(I), DL)) {
440 // Don't attempt to analyze GEPs over unsized objects.
441 if (!GEPOp->getSourceElementType()->isSized()) {
446 unsigned AS = GEPOp->getPointerAddressSpace();
447 // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
448 gep_type_iterator GTI = gep_type_begin(GEPOp);
449 unsigned PointerSize = DL.getPointerSizeInBits(AS);
450 // Assume all GEP operands are constants until proven otherwise.
451 bool GepHasConstantOffset = true;
452 for (User::const_op_iterator I = GEPOp->op_begin() + 1, E = GEPOp->op_end();
453 I != E; ++I, ++GTI) {
454 const Value *Index = *I;
455 // Compute the (potentially symbolic) offset in bytes for this index.
456 if (StructType *STy = GTI.getStructTypeOrNull()) {
457 // For a struct, add the member offset.
458 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
462 Decomposed.StructOffset +=
463 DL.getStructLayout(STy)->getElementOffset(FieldNo);
467 // For an array/pointer, add the element offset, explicitly scaled.
468 if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
471 Decomposed.OtherOffset +=
472 DL.getTypeAllocSize(GTI.getIndexedType()) * CIdx->getSExtValue();
476 GepHasConstantOffset = false;
478 uint64_t Scale = DL.getTypeAllocSize(GTI.getIndexedType());
479 unsigned ZExtBits = 0, SExtBits = 0;
481 // If the integer type is smaller than the pointer size, it is implicitly
482 // sign extended to pointer size.
483 unsigned Width = Index->getType()->getIntegerBitWidth();
484 if (PointerSize > Width)
485 SExtBits += PointerSize - Width;
487 // Use GetLinearExpression to decompose the index into a C1*V+C2 form.
488 APInt IndexScale(Width, 0), IndexOffset(Width, 0);
489 bool NSW = true, NUW = true;
490 Index = GetLinearExpression(Index, IndexScale, IndexOffset, ZExtBits,
491 SExtBits, DL, 0, AC, DT, NSW, NUW);
493 // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
494 // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
495 Decomposed.OtherOffset += IndexOffset.getSExtValue() * Scale;
496 Scale *= IndexScale.getSExtValue();
498 // If we already had an occurrence of this index variable, merge this
499 // scale into it. For example, we want to handle:
500 // A[x][x] -> x*16 + x*4 -> x*20
501 // This also ensures that 'x' only appears in the index list once.
502 for (unsigned i = 0, e = Decomposed.VarIndices.size(); i != e; ++i) {
503 if (Decomposed.VarIndices[i].V == Index &&
504 Decomposed.VarIndices[i].ZExtBits == ZExtBits &&
505 Decomposed.VarIndices[i].SExtBits == SExtBits) {
506 Scale += Decomposed.VarIndices[i].Scale;
507 Decomposed.VarIndices.erase(Decomposed.VarIndices.begin() + i);
512 // Make sure that we have a scale that makes sense for this target's
514 Scale = adjustToPointerSize(Scale, PointerSize);
517 VariableGEPIndex Entry = {Index, ZExtBits, SExtBits,
518 static_cast<int64_t>(Scale)};
519 Decomposed.VarIndices.push_back(Entry);
523 // Take care of wrap-arounds
524 if (GepHasConstantOffset) {
525 Decomposed.StructOffset =
526 adjustToPointerSize(Decomposed.StructOffset, PointerSize);
527 Decomposed.OtherOffset =
528 adjustToPointerSize(Decomposed.OtherOffset, PointerSize);
531 // Analyze the base pointer next.
532 V = GEPOp->getOperand(0);
533 } while (--MaxLookup);
535 // If the chain of expressions is too deep, just return early.
537 SearchLimitReached++;
541 /// Returns whether the given pointer value points to memory that is local to
542 /// the function, with global constants being considered local to all
544 bool BasicAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
546 assert(Visited.empty() && "Visited must be cleared after use!");
548 unsigned MaxLookup = 8;
549 SmallVector<const Value *, 16> Worklist;
550 Worklist.push_back(Loc.Ptr);
552 const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), DL);
553 if (!Visited.insert(V).second) {
555 return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
558 // An alloca instruction defines local memory.
559 if (OrLocal && isa<AllocaInst>(V))
562 // A global constant counts as local memory for our purposes.
563 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
564 // Note: this doesn't require GV to be "ODR" because it isn't legal for a
565 // global to be marked constant in some modules and non-constant in
566 // others. GV may even be a declaration, not a definition.
567 if (!GV->isConstant()) {
569 return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
574 // If both select values point to local memory, then so does the select.
575 if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
576 Worklist.push_back(SI->getTrueValue());
577 Worklist.push_back(SI->getFalseValue());
581 // If all values incoming to a phi node point to local memory, then so does
583 if (const PHINode *PN = dyn_cast<PHINode>(V)) {
584 // Don't bother inspecting phi nodes with many operands.
585 if (PN->getNumIncomingValues() > MaxLookup) {
587 return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
589 for (Value *IncValue : PN->incoming_values())
590 Worklist.push_back(IncValue);
594 // Otherwise be conservative.
596 return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
597 } while (!Worklist.empty() && --MaxLookup);
600 return Worklist.empty();
603 /// Returns the behavior when calling the given call site.
604 FunctionModRefBehavior BasicAAResult::getModRefBehavior(ImmutableCallSite CS) {
605 if (CS.doesNotAccessMemory())
606 // Can't do better than this.
607 return FMRB_DoesNotAccessMemory;
609 FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
611 // If the callsite knows it only reads memory, don't return worse
613 if (CS.onlyReadsMemory())
614 Min = FMRB_OnlyReadsMemory;
615 else if (CS.doesNotReadMemory())
616 Min = FMRB_DoesNotReadMemory;
618 if (CS.onlyAccessesArgMemory())
619 Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees);
620 else if (CS.onlyAccessesInaccessibleMemory())
621 Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleMem);
622 else if (CS.onlyAccessesInaccessibleMemOrArgMem())
623 Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleOrArgMem);
625 // If CS has operand bundles then aliasing attributes from the function it
626 // calls do not directly apply to the CallSite. This can be made more
627 // precise in the future.
628 if (!CS.hasOperandBundles())
629 if (const Function *F = CS.getCalledFunction())
631 FunctionModRefBehavior(Min & getBestAAResults().getModRefBehavior(F));
636 /// Returns the behavior when calling the given function. For use when the call
637 /// site is not known.
638 FunctionModRefBehavior BasicAAResult::getModRefBehavior(const Function *F) {
639 // If the function declares it doesn't access memory, we can't do better.
640 if (F->doesNotAccessMemory())
641 return FMRB_DoesNotAccessMemory;
643 FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
645 // If the function declares it only reads memory, go with that.
646 if (F->onlyReadsMemory())
647 Min = FMRB_OnlyReadsMemory;
648 else if (F->doesNotReadMemory())
649 Min = FMRB_DoesNotReadMemory;
651 if (F->onlyAccessesArgMemory())
652 Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees);
653 else if (F->onlyAccessesInaccessibleMemory())
654 Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleMem);
655 else if (F->onlyAccessesInaccessibleMemOrArgMem())
656 Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleOrArgMem);
661 /// Returns true if this is a writeonly (i.e Mod only) parameter.
662 static bool isWriteOnlyParam(ImmutableCallSite CS, unsigned ArgIdx,
663 const TargetLibraryInfo &TLI) {
664 if (CS.paramHasAttr(ArgIdx, Attribute::WriteOnly))
667 // We can bound the aliasing properties of memset_pattern16 just as we can
668 // for memcpy/memset. This is particularly important because the
669 // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
670 // whenever possible.
671 // FIXME Consider handling this in InferFunctionAttr.cpp together with other
674 if (CS.getCalledFunction() && TLI.getLibFunc(*CS.getCalledFunction(), F) &&
675 F == LibFunc_memset_pattern16 && TLI.has(F))
679 // TODO: memset_pattern4, memset_pattern8
680 // TODO: _chk variants
681 // TODO: strcmp, strcpy
686 ModRefInfo BasicAAResult::getArgModRefInfo(ImmutableCallSite CS,
688 // Checking for known builtin intrinsics and target library functions.
689 if (isWriteOnlyParam(CS, ArgIdx, TLI))
690 return ModRefInfo::Mod;
692 if (CS.paramHasAttr(ArgIdx, Attribute::ReadOnly))
693 return ModRefInfo::Ref;
695 if (CS.paramHasAttr(ArgIdx, Attribute::ReadNone))
696 return ModRefInfo::NoModRef;
698 return AAResultBase::getArgModRefInfo(CS, ArgIdx);
701 static bool isIntrinsicCall(ImmutableCallSite CS, Intrinsic::ID IID) {
702 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
703 return II && II->getIntrinsicID() == IID;
707 static const Function *getParent(const Value *V) {
708 if (const Instruction *inst = dyn_cast<Instruction>(V)) {
709 if (!inst->getParent())
711 return inst->getParent()->getParent();
714 if (const Argument *arg = dyn_cast<Argument>(V))
715 return arg->getParent();
720 static bool notDifferentParent(const Value *O1, const Value *O2) {
722 const Function *F1 = getParent(O1);
723 const Function *F2 = getParent(O2);
725 return !F1 || !F2 || F1 == F2;
729 AliasResult BasicAAResult::alias(const MemoryLocation &LocA,
730 const MemoryLocation &LocB) {
731 assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
732 "BasicAliasAnalysis doesn't support interprocedural queries.");
734 // If we have a directly cached entry for these locations, we have recursed
735 // through this once, so just return the cached results. Notably, when this
736 // happens, we don't clear the cache.
737 auto CacheIt = AliasCache.find(LocPair(LocA, LocB));
738 if (CacheIt != AliasCache.end())
739 return CacheIt->second;
741 AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.AATags, LocB.Ptr,
742 LocB.Size, LocB.AATags);
743 // AliasCache rarely has more than 1 or 2 elements, always use
744 // shrink_and_clear so it quickly returns to the inline capacity of the
745 // SmallDenseMap if it ever grows larger.
746 // FIXME: This should really be shrink_to_inline_capacity_and_clear().
747 AliasCache.shrink_and_clear();
748 VisitedPhiBBs.clear();
752 /// Checks to see if the specified callsite can clobber the specified memory
755 /// Since we only look at local properties of this function, we really can't
756 /// say much about this query. We do, however, use simple "address taken"
757 /// analysis on local objects.
758 ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS,
759 const MemoryLocation &Loc) {
760 assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
761 "AliasAnalysis query involving multiple functions!");
763 const Value *Object = GetUnderlyingObject(Loc.Ptr, DL);
765 // If this is a tail call and Loc.Ptr points to a stack location, we know that
766 // the tail call cannot access or modify the local stack.
767 // We cannot exclude byval arguments here; these belong to the caller of
768 // the current function not to the current function, and a tail callee
769 // may reference them.
770 if (isa<AllocaInst>(Object))
771 if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
772 if (CI->isTailCall())
773 return ModRefInfo::NoModRef;
775 // If the pointer is to a locally allocated object that does not escape,
776 // then the call can not mod/ref the pointer unless the call takes the pointer
777 // as an argument, and itself doesn't capture it.
778 if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
779 isNonEscapingLocalObject(Object)) {
781 // Optimistically assume that call doesn't touch Object and check this
782 // assumption in the following loop.
783 ModRefInfo Result = ModRefInfo::NoModRef;
785 unsigned OperandNo = 0;
786 for (auto CI = CS.data_operands_begin(), CE = CS.data_operands_end();
787 CI != CE; ++CI, ++OperandNo) {
788 // Only look at the no-capture or byval pointer arguments. If this
789 // pointer were passed to arguments that were neither of these, then it
790 // couldn't be no-capture.
791 if (!(*CI)->getType()->isPointerTy() ||
792 (!CS.doesNotCapture(OperandNo) &&
793 OperandNo < CS.getNumArgOperands() && !CS.isByValArgument(OperandNo)))
796 // Call doesn't access memory through this operand, so we don't care
797 // if it aliases with Object.
798 if (CS.doesNotAccessMemory(OperandNo))
801 // If this is a no-capture pointer argument, see if we can tell that it
802 // is impossible to alias the pointer we're checking.
804 getBestAAResults().alias(MemoryLocation(*CI), MemoryLocation(Object));
806 // Operand doesnt alias 'Object', continue looking for other aliases
809 // Operand aliases 'Object', but call doesn't modify it. Strengthen
810 // initial assumption and keep looking in case if there are more aliases.
811 if (CS.onlyReadsMemory(OperandNo)) {
812 Result = setRef(Result);
815 // Operand aliases 'Object' but call only writes into it.
816 if (CS.doesNotReadMemory(OperandNo)) {
817 Result = setMod(Result);
820 // This operand aliases 'Object' and call reads and writes into it.
821 Result = ModRefInfo::ModRef;
825 // Early return if we improved mod ref information
826 if (!isModAndRefSet(Result))
830 // If the CallSite is to malloc or calloc, we can assume that it doesn't
831 // modify any IR visible value. This is only valid because we assume these
832 // routines do not read values visible in the IR. TODO: Consider special
833 // casing realloc and strdup routines which access only their arguments as
834 // well. Or alternatively, replace all of this with inaccessiblememonly once
835 // that's implemented fully.
836 auto *Inst = CS.getInstruction();
837 if (isMallocOrCallocLikeFn(Inst, &TLI)) {
838 // Be conservative if the accessed pointer may alias the allocation -
839 // fallback to the generic handling below.
840 if (getBestAAResults().alias(MemoryLocation(Inst), Loc) == NoAlias)
841 return ModRefInfo::NoModRef;
844 // The semantics of memcpy intrinsics forbid overlap between their respective
845 // operands, i.e., source and destination of any given memcpy must no-alias.
846 // If Loc must-aliases either one of these two locations, then it necessarily
847 // no-aliases the other.
848 if (auto *Inst = dyn_cast<MemCpyInst>(CS.getInstruction())) {
849 AliasResult SrcAA, DestAA;
851 if ((SrcAA = getBestAAResults().alias(MemoryLocation::getForSource(Inst),
853 // Loc is exactly the memcpy source thus disjoint from memcpy dest.
854 return ModRefInfo::Ref;
855 if ((DestAA = getBestAAResults().alias(MemoryLocation::getForDest(Inst),
857 // The converse case.
858 return ModRefInfo::Mod;
860 // It's also possible for Loc to alias both src and dest, or neither.
861 ModRefInfo rv = ModRefInfo::NoModRef;
862 if (SrcAA != NoAlias)
864 if (DestAA != NoAlias)
869 // While the assume intrinsic is marked as arbitrarily writing so that
870 // proper control dependencies will be maintained, it never aliases any
871 // particular memory location.
872 if (isIntrinsicCall(CS, Intrinsic::assume))
873 return ModRefInfo::NoModRef;
875 // Like assumes, guard intrinsics are also marked as arbitrarily writing so
876 // that proper control dependencies are maintained but they never mods any
877 // particular memory location.
879 // *Unlike* assumes, guard intrinsics are modeled as reading memory since the
880 // heap state at the point the guard is issued needs to be consistent in case
881 // the guard invokes the "deopt" continuation.
882 if (isIntrinsicCall(CS, Intrinsic::experimental_guard))
883 return ModRefInfo::Ref;
885 // Like assumes, invariant.start intrinsics were also marked as arbitrarily
886 // writing so that proper control dependencies are maintained but they never
887 // mod any particular memory location visible to the IR.
888 // *Unlike* assumes (which are now modeled as NoModRef), invariant.start
889 // intrinsic is now modeled as reading memory. This prevents hoisting the
890 // invariant.start intrinsic over stores. Consider:
893 // invariant_start(ptr)
897 // This cannot be transformed to:
900 // invariant_start(ptr)
905 // The transformation will cause the second store to be ignored (based on
906 // rules of invariant.start) and print 40, while the first program always
908 if (isIntrinsicCall(CS, Intrinsic::invariant_start))
909 return ModRefInfo::Ref;
911 // The AAResultBase base class has some smarts, lets use them.
912 return AAResultBase::getModRefInfo(CS, Loc);
915 ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS1,
916 ImmutableCallSite CS2) {
917 // While the assume intrinsic is marked as arbitrarily writing so that
918 // proper control dependencies will be maintained, it never aliases any
919 // particular memory location.
920 if (isIntrinsicCall(CS1, Intrinsic::assume) ||
921 isIntrinsicCall(CS2, Intrinsic::assume))
922 return ModRefInfo::NoModRef;
924 // Like assumes, guard intrinsics are also marked as arbitrarily writing so
925 // that proper control dependencies are maintained but they never mod any
926 // particular memory location.
928 // *Unlike* assumes, guard intrinsics are modeled as reading memory since the
929 // heap state at the point the guard is issued needs to be consistent in case
930 // the guard invokes the "deopt" continuation.
932 // NB! This function is *not* commutative, so we specical case two
933 // possibilities for guard intrinsics.
935 if (isIntrinsicCall(CS1, Intrinsic::experimental_guard))
936 return isModSet(createModRefInfo(getModRefBehavior(CS2)))
938 : ModRefInfo::NoModRef;
940 if (isIntrinsicCall(CS2, Intrinsic::experimental_guard))
941 return isModSet(createModRefInfo(getModRefBehavior(CS1)))
943 : ModRefInfo::NoModRef;
945 // The AAResultBase base class has some smarts, lets use them.
946 return AAResultBase::getModRefInfo(CS1, CS2);
949 /// Provide ad-hoc rules to disambiguate accesses through two GEP operators,
950 /// both having the exact same pointer operand.
951 static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1,
953 const GEPOperator *GEP2,
955 const DataLayout &DL) {
956 assert(GEP1->getPointerOperand()->stripPointerCastsAndBarriers() ==
957 GEP2->getPointerOperand()->stripPointerCastsAndBarriers() &&
958 GEP1->getPointerOperandType() == GEP2->getPointerOperandType() &&
959 "Expected GEPs with the same pointer operand");
961 // Try to determine whether GEP1 and GEP2 index through arrays, into structs,
962 // such that the struct field accesses provably cannot alias.
963 // We also need at least two indices (the pointer, and the struct field).
964 if (GEP1->getNumIndices() != GEP2->getNumIndices() ||
965 GEP1->getNumIndices() < 2)
968 // If we don't know the size of the accesses through both GEPs, we can't
969 // determine whether the struct fields accessed can't alias.
970 if (V1Size == MemoryLocation::UnknownSize ||
971 V2Size == MemoryLocation::UnknownSize)
975 dyn_cast<ConstantInt>(GEP1->getOperand(GEP1->getNumOperands() - 1));
977 dyn_cast<ConstantInt>(GEP2->getOperand(GEP2->getNumOperands() - 1));
979 // If the last (struct) indices are constants and are equal, the other indices
980 // might be also be dynamically equal, so the GEPs can alias.
981 if (C1 && C2 && C1->getSExtValue() == C2->getSExtValue())
984 // Find the last-indexed type of the GEP, i.e., the type you'd get if
985 // you stripped the last index.
986 // On the way, look at each indexed type. If there's something other
987 // than an array, different indices can lead to different final types.
988 SmallVector<Value *, 8> IntermediateIndices;
990 // Insert the first index; we don't need to check the type indexed
991 // through it as it only drops the pointer indirection.
992 assert(GEP1->getNumIndices() > 1 && "Not enough GEP indices to examine");
993 IntermediateIndices.push_back(GEP1->getOperand(1));
995 // Insert all the remaining indices but the last one.
996 // Also, check that they all index through arrays.
997 for (unsigned i = 1, e = GEP1->getNumIndices() - 1; i != e; ++i) {
998 if (!isa<ArrayType>(GetElementPtrInst::getIndexedType(
999 GEP1->getSourceElementType(), IntermediateIndices)))
1001 IntermediateIndices.push_back(GEP1->getOperand(i + 1));
1004 auto *Ty = GetElementPtrInst::getIndexedType(
1005 GEP1->getSourceElementType(), IntermediateIndices);
1006 StructType *LastIndexedStruct = dyn_cast<StructType>(Ty);
1008 if (isa<SequentialType>(Ty)) {
1010 // - both GEPs begin indexing from the exact same pointer;
1011 // - the last indices in both GEPs are constants, indexing into a sequential
1012 // type (array or pointer);
1013 // - both GEPs only index through arrays prior to that.
1015 // Because array indices greater than the number of elements are valid in
1016 // GEPs, unless we know the intermediate indices are identical between
1017 // GEP1 and GEP2 we cannot guarantee that the last indexed arrays don't
1018 // partially overlap. We also need to check that the loaded size matches
1019 // the element size, otherwise we could still have overlap.
1020 const uint64_t ElementSize =
1021 DL.getTypeStoreSize(cast<SequentialType>(Ty)->getElementType());
1022 if (V1Size != ElementSize || V2Size != ElementSize)
1025 for (unsigned i = 0, e = GEP1->getNumIndices() - 1; i != e; ++i)
1026 if (GEP1->getOperand(i + 1) != GEP2->getOperand(i + 1))
1029 // Now we know that the array/pointer that GEP1 indexes into and that
1030 // that GEP2 indexes into must either precisely overlap or be disjoint.
1031 // Because they cannot partially overlap and because fields in an array
1032 // cannot overlap, if we can prove the final indices are different between
1033 // GEP1 and GEP2, we can conclude GEP1 and GEP2 don't alias.
1035 // If the last indices are constants, we've already checked they don't
1036 // equal each other so we can exit early.
1040 Value *GEP1LastIdx = GEP1->getOperand(GEP1->getNumOperands() - 1);
1041 Value *GEP2LastIdx = GEP2->getOperand(GEP2->getNumOperands() - 1);
1042 if (isa<PHINode>(GEP1LastIdx) || isa<PHINode>(GEP2LastIdx)) {
1043 // If one of the indices is a PHI node, be safe and only use
1044 // computeKnownBits so we don't make any assumptions about the
1045 // relationships between the two indices. This is important if we're
1046 // asking about values from different loop iterations. See PR32314.
1047 // TODO: We may be able to change the check so we only do this when
1048 // we definitely looked through a PHINode.
1049 if (GEP1LastIdx != GEP2LastIdx &&
1050 GEP1LastIdx->getType() == GEP2LastIdx->getType()) {
1051 KnownBits Known1 = computeKnownBits(GEP1LastIdx, DL);
1052 KnownBits Known2 = computeKnownBits(GEP2LastIdx, DL);
1053 if (Known1.Zero.intersects(Known2.One) ||
1054 Known1.One.intersects(Known2.Zero))
1057 } else if (isKnownNonEqual(GEP1LastIdx, GEP2LastIdx, DL))
1061 } else if (!LastIndexedStruct || !C1 || !C2) {
1066 // - both GEPs begin indexing from the exact same pointer;
1067 // - the last indices in both GEPs are constants, indexing into a struct;
1068 // - said indices are different, hence, the pointed-to fields are different;
1069 // - both GEPs only index through arrays prior to that.
1071 // This lets us determine that the struct that GEP1 indexes into and the
1072 // struct that GEP2 indexes into must either precisely overlap or be
1073 // completely disjoint. Because they cannot partially overlap, indexing into
1074 // different non-overlapping fields of the struct will never alias.
1076 // Therefore, the only remaining thing needed to show that both GEPs can't
1077 // alias is that the fields are not overlapping.
1078 const StructLayout *SL = DL.getStructLayout(LastIndexedStruct);
1079 const uint64_t StructSize = SL->getSizeInBytes();
1080 const uint64_t V1Off = SL->getElementOffset(C1->getZExtValue());
1081 const uint64_t V2Off = SL->getElementOffset(C2->getZExtValue());
1083 auto EltsDontOverlap = [StructSize](uint64_t V1Off, uint64_t V1Size,
1084 uint64_t V2Off, uint64_t V2Size) {
1085 return V1Off < V2Off && V1Off + V1Size <= V2Off &&
1086 ((V2Off + V2Size <= StructSize) ||
1087 (V2Off + V2Size - StructSize <= V1Off));
1090 if (EltsDontOverlap(V1Off, V1Size, V2Off, V2Size) ||
1091 EltsDontOverlap(V2Off, V2Size, V1Off, V1Size))
1097 // If a we have (a) a GEP and (b) a pointer based on an alloca, and the
1098 // beginning of the object the GEP points would have a negative offset with
1099 // repsect to the alloca, that means the GEP can not alias pointer (b).
1100 // Note that the pointer based on the alloca may not be a GEP. For
1101 // example, it may be the alloca itself.
1102 // The same applies if (b) is based on a GlobalVariable. Note that just being
1103 // based on isIdentifiedObject() is not enough - we need an identified object
1104 // that does not permit access to negative offsets. For example, a negative
1105 // offset from a noalias argument or call can be inbounds w.r.t the actual
1106 // underlying object.
1108 // For example, consider:
1110 // struct { int f0, int f1, ...} foo;
1112 // foo* random = bar(alloca);
1113 // int *f0 = &alloca.f0
1114 // int *f1 = &random->f1;
1116 // Which is lowered, approximately, to:
1118 // %alloca = alloca %struct.foo
1119 // %random = call %struct.foo* @random(%struct.foo* %alloca)
1120 // %f0 = getelementptr inbounds %struct, %struct.foo* %alloca, i32 0, i32 0
1121 // %f1 = getelementptr inbounds %struct, %struct.foo* %random, i32 0, i32 1
1123 // Assume %f1 and %f0 alias. Then %f1 would point into the object allocated
1124 // by %alloca. Since the %f1 GEP is inbounds, that means %random must also
1125 // point into the same object. But since %f0 points to the beginning of %alloca,
1126 // the highest %f1 can be is (%alloca + 3). This means %random can not be higher
1127 // than (%alloca - 1), and so is not inbounds, a contradiction.
1128 bool BasicAAResult::isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
1129 const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
1130 uint64_t ObjectAccessSize) {
1131 // If the object access size is unknown, or the GEP isn't inbounds, bail.
1132 if (ObjectAccessSize == MemoryLocation::UnknownSize || !GEPOp->isInBounds())
1135 // We need the object to be an alloca or a globalvariable, and want to know
1136 // the offset of the pointer from the object precisely, so no variable
1137 // indices are allowed.
1138 if (!(isa<AllocaInst>(DecompObject.Base) ||
1139 isa<GlobalVariable>(DecompObject.Base)) ||
1140 !DecompObject.VarIndices.empty())
1143 int64_t ObjectBaseOffset = DecompObject.StructOffset +
1144 DecompObject.OtherOffset;
1146 // If the GEP has no variable indices, we know the precise offset
1147 // from the base, then use it. If the GEP has variable indices, we're in
1148 // a bit more trouble: we can't count on the constant offsets that come
1149 // from non-struct sources, since these can be "rewound" by a negative
1150 // variable offset. So use only offsets that came from structs.
1151 int64_t GEPBaseOffset = DecompGEP.StructOffset;
1152 if (DecompGEP.VarIndices.empty())
1153 GEPBaseOffset += DecompGEP.OtherOffset;
1155 return (GEPBaseOffset >= ObjectBaseOffset + (int64_t)ObjectAccessSize);
1158 /// Provides a bunch of ad-hoc rules to disambiguate a GEP instruction against
1159 /// another pointer.
1161 /// We know that V1 is a GEP, but we don't know anything about V2.
1162 /// UnderlyingV1 is GetUnderlyingObject(GEP1, DL), UnderlyingV2 is the same for
1164 AliasResult BasicAAResult::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
1165 const AAMDNodes &V1AAInfo, const Value *V2,
1166 uint64_t V2Size, const AAMDNodes &V2AAInfo,
1167 const Value *UnderlyingV1,
1168 const Value *UnderlyingV2) {
1169 DecomposedGEP DecompGEP1, DecompGEP2;
1170 bool GEP1MaxLookupReached =
1171 DecomposeGEPExpression(GEP1, DecompGEP1, DL, &AC, DT);
1172 bool GEP2MaxLookupReached =
1173 DecomposeGEPExpression(V2, DecompGEP2, DL, &AC, DT);
1175 int64_t GEP1BaseOffset = DecompGEP1.StructOffset + DecompGEP1.OtherOffset;
1176 int64_t GEP2BaseOffset = DecompGEP2.StructOffset + DecompGEP2.OtherOffset;
1178 assert(DecompGEP1.Base == UnderlyingV1 && DecompGEP2.Base == UnderlyingV2 &&
1179 "DecomposeGEPExpression returned a result different from "
1180 "GetUnderlyingObject");
1182 // If the GEP's offset relative to its base is such that the base would
1183 // fall below the start of the object underlying V2, then the GEP and V2
1185 if (!GEP1MaxLookupReached && !GEP2MaxLookupReached &&
1186 isGEPBaseAtNegativeOffset(GEP1, DecompGEP1, DecompGEP2, V2Size))
1188 // If we have two gep instructions with must-alias or not-alias'ing base
1189 // pointers, figure out if the indexes to the GEP tell us anything about the
1191 if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
1192 // Check for the GEP base being at a negative offset, this time in the other
1194 if (!GEP1MaxLookupReached && !GEP2MaxLookupReached &&
1195 isGEPBaseAtNegativeOffset(GEP2, DecompGEP2, DecompGEP1, V1Size))
1197 // Do the base pointers alias?
1198 AliasResult BaseAlias =
1199 aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize, AAMDNodes(),
1200 UnderlyingV2, MemoryLocation::UnknownSize, AAMDNodes());
1202 // Check for geps of non-aliasing underlying pointers where the offsets are
1204 if ((BaseAlias == MayAlias) && V1Size == V2Size) {
1205 // Do the base pointers alias assuming type and size.
1206 AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size, V1AAInfo,
1207 UnderlyingV2, V2Size, V2AAInfo);
1208 if (PreciseBaseAlias == NoAlias) {
1209 // See if the computed offset from the common pointer tells us about the
1210 // relation of the resulting pointer.
1211 // If the max search depth is reached the result is undefined
1212 if (GEP2MaxLookupReached || GEP1MaxLookupReached)
1216 if (GEP1BaseOffset == GEP2BaseOffset &&
1217 DecompGEP1.VarIndices == DecompGEP2.VarIndices)
1222 // If we get a No or May, then return it immediately, no amount of analysis
1223 // will improve this situation.
1224 if (BaseAlias != MustAlias) {
1225 assert(BaseAlias == NoAlias || BaseAlias == MayAlias);
1229 // Otherwise, we have a MustAlias. Since the base pointers alias each other
1230 // exactly, see if the computed offset from the common pointer tells us
1231 // about the relation of the resulting pointer.
1232 // If we know the two GEPs are based off of the exact same pointer (and not
1233 // just the same underlying object), see if that tells us anything about
1234 // the resulting pointers.
1235 if (GEP1->getPointerOperand()->stripPointerCastsAndBarriers() ==
1236 GEP2->getPointerOperand()->stripPointerCastsAndBarriers() &&
1237 GEP1->getPointerOperandType() == GEP2->getPointerOperandType()) {
1238 AliasResult R = aliasSameBasePointerGEPs(GEP1, V1Size, GEP2, V2Size, DL);
1239 // If we couldn't find anything interesting, don't abandon just yet.
1244 // If the max search depth is reached, the result is undefined
1245 if (GEP2MaxLookupReached || GEP1MaxLookupReached)
1248 // Subtract the GEP2 pointer from the GEP1 pointer to find out their
1249 // symbolic difference.
1250 GEP1BaseOffset -= GEP2BaseOffset;
1251 GetIndexDifference(DecompGEP1.VarIndices, DecompGEP2.VarIndices);
1254 // Check to see if these two pointers are related by the getelementptr
1255 // instruction. If one pointer is a GEP with a non-zero index of the other
1256 // pointer, we know they cannot alias.
1258 // If both accesses are unknown size, we can't do anything useful here.
1259 if (V1Size == MemoryLocation::UnknownSize &&
1260 V2Size == MemoryLocation::UnknownSize)
1263 AliasResult R = aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize,
1264 AAMDNodes(), V2, MemoryLocation::UnknownSize,
1265 V2AAInfo, nullptr, UnderlyingV2);
1266 if (R != MustAlias) {
1267 // If V2 may alias GEP base pointer, conservatively returns MayAlias.
1268 // If V2 is known not to alias GEP base pointer, then the two values
1269 // cannot alias per GEP semantics: "Any memory access must be done through
1270 // a pointer value associated with an address range of the memory access,
1271 // otherwise the behavior is undefined.".
1272 assert(R == NoAlias || R == MayAlias);
1276 // If the max search depth is reached the result is undefined
1277 if (GEP1MaxLookupReached)
1281 // In the two GEP Case, if there is no difference in the offsets of the
1282 // computed pointers, the resultant pointers are a must alias. This
1283 // happens when we have two lexically identical GEP's (for example).
1285 // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
1286 // must aliases the GEP, the end result is a must alias also.
1287 if (GEP1BaseOffset == 0 && DecompGEP1.VarIndices.empty())
1290 // If there is a constant difference between the pointers, but the difference
1291 // is less than the size of the associated memory object, then we know
1292 // that the objects are partially overlapping. If the difference is
1293 // greater, we know they do not overlap.
1294 if (GEP1BaseOffset != 0 && DecompGEP1.VarIndices.empty()) {
1295 if (GEP1BaseOffset >= 0) {
1296 if (V2Size != MemoryLocation::UnknownSize) {
1297 if ((uint64_t)GEP1BaseOffset < V2Size)
1298 return PartialAlias;
1302 // We have the situation where:
1305 // ---------------->|
1306 // |-->V1Size |-------> V2Size
1308 // We need to know that V2Size is not unknown, otherwise we might have
1309 // stripped a gep with negative index ('gep <ptr>, -1, ...).
1310 if (V1Size != MemoryLocation::UnknownSize &&
1311 V2Size != MemoryLocation::UnknownSize) {
1312 if (-(uint64_t)GEP1BaseOffset < V1Size)
1313 return PartialAlias;
1319 if (!DecompGEP1.VarIndices.empty()) {
1320 uint64_t Modulo = 0;
1321 bool AllPositive = true;
1322 for (unsigned i = 0, e = DecompGEP1.VarIndices.size(); i != e; ++i) {
1324 // Try to distinguish something like &A[i][1] against &A[42][0].
1325 // Grab the least significant bit set in any of the scales. We
1326 // don't need std::abs here (even if the scale's negative) as we'll
1327 // be ^'ing Modulo with itself later.
1328 Modulo |= (uint64_t)DecompGEP1.VarIndices[i].Scale;
1331 // If the Value could change between cycles, then any reasoning about
1332 // the Value this cycle may not hold in the next cycle. We'll just
1333 // give up if we can't determine conditions that hold for every cycle:
1334 const Value *V = DecompGEP1.VarIndices[i].V;
1336 KnownBits Known = computeKnownBits(V, DL, 0, &AC, nullptr, DT);
1337 bool SignKnownZero = Known.isNonNegative();
1338 bool SignKnownOne = Known.isNegative();
1340 // Zero-extension widens the variable, and so forces the sign
1342 bool IsZExt = DecompGEP1.VarIndices[i].ZExtBits > 0 || isa<ZExtInst>(V);
1343 SignKnownZero |= IsZExt;
1344 SignKnownOne &= !IsZExt;
1346 // If the variable begins with a zero then we know it's
1347 // positive, regardless of whether the value is signed or
1349 int64_t Scale = DecompGEP1.VarIndices[i].Scale;
1351 (SignKnownZero && Scale >= 0) || (SignKnownOne && Scale < 0);
1355 Modulo = Modulo ^ (Modulo & (Modulo - 1));
1357 // We can compute the difference between the two addresses
1358 // mod Modulo. Check whether that difference guarantees that the
1359 // two locations do not alias.
1360 uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
1361 if (V1Size != MemoryLocation::UnknownSize &&
1362 V2Size != MemoryLocation::UnknownSize && ModOffset >= V2Size &&
1363 V1Size <= Modulo - ModOffset)
1366 // If we know all the variables are positive, then GEP1 >= GEP1BasePtr.
1367 // If GEP1BasePtr > V2 (GEP1BaseOffset > 0) then we know the pointers
1368 // don't alias if V2Size can fit in the gap between V2 and GEP1BasePtr.
1369 if (AllPositive && GEP1BaseOffset > 0 && V2Size <= (uint64_t)GEP1BaseOffset)
1372 if (constantOffsetHeuristic(DecompGEP1.VarIndices, V1Size, V2Size,
1373 GEP1BaseOffset, &AC, DT))
1377 // Statically, we can see that the base objects are the same, but the
1378 // pointers have dynamic offsets which we can't resolve. And none of our
1379 // little tricks above worked.
1383 static AliasResult MergeAliasResults(AliasResult A, AliasResult B) {
1384 // If the results agree, take it.
1387 // A mix of PartialAlias and MustAlias is PartialAlias.
1388 if ((A == PartialAlias && B == MustAlias) ||
1389 (B == PartialAlias && A == MustAlias))
1390 return PartialAlias;
1391 // Otherwise, we don't know anything.
1395 /// Provides a bunch of ad-hoc rules to disambiguate a Select instruction
1396 /// against another.
1397 AliasResult BasicAAResult::aliasSelect(const SelectInst *SI, uint64_t SISize,
1398 const AAMDNodes &SIAAInfo,
1399 const Value *V2, uint64_t V2Size,
1400 const AAMDNodes &V2AAInfo,
1401 const Value *UnderV2) {
1402 // If the values are Selects with the same condition, we can do a more precise
1403 // check: just check for aliases between the values on corresponding arms.
1404 if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
1405 if (SI->getCondition() == SI2->getCondition()) {
1406 AliasResult Alias = aliasCheck(SI->getTrueValue(), SISize, SIAAInfo,
1407 SI2->getTrueValue(), V2Size, V2AAInfo);
1408 if (Alias == MayAlias)
1410 AliasResult ThisAlias =
1411 aliasCheck(SI->getFalseValue(), SISize, SIAAInfo,
1412 SI2->getFalseValue(), V2Size, V2AAInfo);
1413 return MergeAliasResults(ThisAlias, Alias);
1416 // If both arms of the Select node NoAlias or MustAlias V2, then returns
1417 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1419 aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(),
1420 SISize, SIAAInfo, UnderV2);
1421 if (Alias == MayAlias)
1424 AliasResult ThisAlias =
1425 aliasCheck(V2, V2Size, V2AAInfo, SI->getFalseValue(), SISize, SIAAInfo,
1427 return MergeAliasResults(ThisAlias, Alias);
1430 /// Provide a bunch of ad-hoc rules to disambiguate a PHI instruction against
1432 AliasResult BasicAAResult::aliasPHI(const PHINode *PN, uint64_t PNSize,
1433 const AAMDNodes &PNAAInfo, const Value *V2,
1434 uint64_t V2Size, const AAMDNodes &V2AAInfo,
1435 const Value *UnderV2) {
1436 // Track phi nodes we have visited. We use this information when we determine
1437 // value equivalence.
1438 VisitedPhiBBs.insert(PN->getParent());
1440 // If the values are PHIs in the same block, we can do a more precise
1441 // as well as efficient check: just check for aliases between the values
1442 // on corresponding edges.
1443 if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
1444 if (PN2->getParent() == PN->getParent()) {
1445 LocPair Locs(MemoryLocation(PN, PNSize, PNAAInfo),
1446 MemoryLocation(V2, V2Size, V2AAInfo));
1448 std::swap(Locs.first, Locs.second);
1449 // Analyse the PHIs' inputs under the assumption that the PHIs are
1451 // If the PHIs are May/MustAlias there must be (recursively) an input
1452 // operand from outside the PHIs' cycle that is MayAlias/MustAlias or
1453 // there must be an operation on the PHIs within the PHIs' value cycle
1454 // that causes a MayAlias.
1455 // Pretend the phis do not alias.
1456 AliasResult Alias = NoAlias;
1457 assert(AliasCache.count(Locs) &&
1458 "There must exist an entry for the phi node");
1459 AliasResult OrigAliasResult = AliasCache[Locs];
1460 AliasCache[Locs] = NoAlias;
1462 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1463 AliasResult ThisAlias =
1464 aliasCheck(PN->getIncomingValue(i), PNSize, PNAAInfo,
1465 PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
1467 Alias = MergeAliasResults(ThisAlias, Alias);
1468 if (Alias == MayAlias)
1472 // Reset if speculation failed.
1473 if (Alias != NoAlias)
1474 AliasCache[Locs] = OrigAliasResult;
1479 SmallPtrSet<Value *, 4> UniqueSrc;
1480 SmallVector<Value *, 4> V1Srcs;
1481 bool isRecursive = false;
1482 for (Value *PV1 : PN->incoming_values()) {
1483 if (isa<PHINode>(PV1))
1484 // If any of the source itself is a PHI, return MayAlias conservatively
1485 // to avoid compile time explosion. The worst possible case is if both
1486 // sides are PHI nodes. In which case, this is O(m x n) time where 'm'
1487 // and 'n' are the number of PHI sources.
1490 if (EnableRecPhiAnalysis)
1491 if (GEPOperator *PV1GEP = dyn_cast<GEPOperator>(PV1)) {
1492 // Check whether the incoming value is a GEP that advances the pointer
1493 // result of this PHI node (e.g. in a loop). If this is the case, we
1494 // would recurse and always get a MayAlias. Handle this case specially
1496 if (PV1GEP->getPointerOperand() == PN && PV1GEP->getNumIndices() == 1 &&
1497 isa<ConstantInt>(PV1GEP->idx_begin())) {
1503 if (UniqueSrc.insert(PV1).second)
1504 V1Srcs.push_back(PV1);
1507 // If this PHI node is recursive, set the size of the accessed memory to
1508 // unknown to represent all the possible values the GEP could advance the
1511 PNSize = MemoryLocation::UnknownSize;
1514 aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0],
1515 PNSize, PNAAInfo, UnderV2);
1517 // Early exit if the check of the first PHI source against V2 is MayAlias.
1518 // Other results are not possible.
1519 if (Alias == MayAlias)
1522 // If all sources of the PHI node NoAlias or MustAlias V2, then returns
1523 // NoAlias / MustAlias. Otherwise, returns MayAlias.
1524 for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
1525 Value *V = V1Srcs[i];
1527 AliasResult ThisAlias =
1528 aliasCheck(V2, V2Size, V2AAInfo, V, PNSize, PNAAInfo, UnderV2);
1529 Alias = MergeAliasResults(ThisAlias, Alias);
1530 if (Alias == MayAlias)
1537 /// Provides a bunch of ad-hoc rules to disambiguate in common cases, such as
1538 /// array references.
1539 AliasResult BasicAAResult::aliasCheck(const Value *V1, uint64_t V1Size,
1540 AAMDNodes V1AAInfo, const Value *V2,
1541 uint64_t V2Size, AAMDNodes V2AAInfo,
1542 const Value *O1, const Value *O2) {
1543 // If either of the memory references is empty, it doesn't matter what the
1544 // pointer values are.
1545 if (V1Size == 0 || V2Size == 0)
1548 // Strip off any casts if they exist.
1549 V1 = V1->stripPointerCastsAndBarriers();
1550 V2 = V2->stripPointerCastsAndBarriers();
1552 // If V1 or V2 is undef, the result is NoAlias because we can always pick a
1553 // value for undef that aliases nothing in the program.
1554 if (isa<UndefValue>(V1) || isa<UndefValue>(V2))
1557 // Are we checking for alias of the same value?
1558 // Because we look 'through' phi nodes, we could look at "Value" pointers from
1559 // different iterations. We must therefore make sure that this is not the
1560 // case. The function isValueEqualInPotentialCycles ensures that this cannot
1561 // happen by looking at the visited phi nodes and making sure they cannot
1563 if (isValueEqualInPotentialCycles(V1, V2))
1566 if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
1567 return NoAlias; // Scalars cannot alias each other
1569 // Figure out what objects these things are pointing to if we can.
1571 O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth);
1574 O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth);
1576 // Null values in the default address space don't point to any object, so they
1577 // don't alias any other pointer.
1578 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
1579 if (CPN->getType()->getAddressSpace() == 0)
1581 if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
1582 if (CPN->getType()->getAddressSpace() == 0)
1586 // If V1/V2 point to two different objects, we know that we have no alias.
1587 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
1590 // Constant pointers can't alias with non-const isIdentifiedObject objects.
1591 if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
1592 (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
1595 // Function arguments can't alias with things that are known to be
1596 // unambigously identified at the function level.
1597 if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
1598 (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
1601 // If one pointer is the result of a call/invoke or load and the other is a
1602 // non-escaping local object within the same function, then we know the
1603 // object couldn't escape to a point where the call could return it.
1605 // Note that if the pointers are in different functions, there are a
1606 // variety of complications. A call with a nocapture argument may still
1607 // temporary store the nocapture argument's value in a temporary memory
1608 // location if that memory location doesn't escape. Or it may pass a
1609 // nocapture value to other functions as long as they don't capture it.
1610 if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
1612 if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
1616 // If the size of one access is larger than the entire object on the other
1617 // side, then we know such behavior is undefined and can assume no alias.
1618 if ((V1Size != MemoryLocation::UnknownSize &&
1619 isObjectSmallerThan(O2, V1Size, DL, TLI)) ||
1620 (V2Size != MemoryLocation::UnknownSize &&
1621 isObjectSmallerThan(O1, V2Size, DL, TLI)))
1624 // Check the cache before climbing up use-def chains. This also terminates
1625 // otherwise infinitely recursive queries.
1626 LocPair Locs(MemoryLocation(V1, V1Size, V1AAInfo),
1627 MemoryLocation(V2, V2Size, V2AAInfo));
1629 std::swap(Locs.first, Locs.second);
1630 std::pair<AliasCacheTy::iterator, bool> Pair =
1631 AliasCache.insert(std::make_pair(Locs, MayAlias));
1633 return Pair.first->second;
1635 // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
1636 // GEP can't simplify, we don't even look at the PHI cases.
1637 if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
1639 std::swap(V1Size, V2Size);
1641 std::swap(V1AAInfo, V2AAInfo);
1643 if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
1644 AliasResult Result =
1645 aliasGEP(GV1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O1, O2);
1646 if (Result != MayAlias)
1647 return AliasCache[Locs] = Result;
1650 if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
1653 std::swap(V1Size, V2Size);
1654 std::swap(V1AAInfo, V2AAInfo);
1656 if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
1657 AliasResult Result = aliasPHI(PN, V1Size, V1AAInfo,
1658 V2, V2Size, V2AAInfo, O2);
1659 if (Result != MayAlias)
1660 return AliasCache[Locs] = Result;
1663 if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
1666 std::swap(V1Size, V2Size);
1667 std::swap(V1AAInfo, V2AAInfo);
1669 if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
1670 AliasResult Result =
1671 aliasSelect(S1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O2);
1672 if (Result != MayAlias)
1673 return AliasCache[Locs] = Result;
1676 // If both pointers are pointing into the same object and one of them
1677 // accesses the entire object, then the accesses must overlap in some way.
1679 if (V1Size != MemoryLocation::UnknownSize &&
1680 V2Size != MemoryLocation::UnknownSize &&
1681 (isObjectSize(O1, V1Size, DL, TLI) ||
1682 isObjectSize(O2, V2Size, DL, TLI)))
1683 return AliasCache[Locs] = PartialAlias;
1685 // Recurse back into the best AA results we have, potentially with refined
1686 // memory locations. We have already ensured that BasicAA has a MayAlias
1687 // cache result for these, so any recursion back into BasicAA won't loop.
1688 AliasResult Result = getBestAAResults().alias(Locs.first, Locs.second);
1689 return AliasCache[Locs] = Result;
1692 /// Check whether two Values can be considered equivalent.
1694 /// In addition to pointer equivalence of \p V1 and \p V2 this checks whether
1695 /// they can not be part of a cycle in the value graph by looking at all
1696 /// visited phi nodes an making sure that the phis cannot reach the value. We
1697 /// have to do this because we are looking through phi nodes (That is we say
1698 /// noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB).
1699 bool BasicAAResult::isValueEqualInPotentialCycles(const Value *V,
1704 const Instruction *Inst = dyn_cast<Instruction>(V);
1708 if (VisitedPhiBBs.empty())
1711 if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck)
1714 // Make sure that the visited phis cannot reach the Value. This ensures that
1715 // the Values cannot come from different iterations of a potential cycle the
1716 // phi nodes could be involved in.
1717 for (auto *P : VisitedPhiBBs)
1718 if (isPotentiallyReachable(&P->front(), Inst, DT, LI))
1724 /// Computes the symbolic difference between two de-composed GEPs.
1726 /// Dest and Src are the variable indices from two decomposed GetElementPtr
1727 /// instructions GEP1 and GEP2 which have common base pointers.
1728 void BasicAAResult::GetIndexDifference(
1729 SmallVectorImpl<VariableGEPIndex> &Dest,
1730 const SmallVectorImpl<VariableGEPIndex> &Src) {
1734 for (unsigned i = 0, e = Src.size(); i != e; ++i) {
1735 const Value *V = Src[i].V;
1736 unsigned ZExtBits = Src[i].ZExtBits, SExtBits = Src[i].SExtBits;
1737 int64_t Scale = Src[i].Scale;
1739 // Find V in Dest. This is N^2, but pointer indices almost never have more
1740 // than a few variable indexes.
1741 for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
1742 if (!isValueEqualInPotentialCycles(Dest[j].V, V) ||
1743 Dest[j].ZExtBits != ZExtBits || Dest[j].SExtBits != SExtBits)
1746 // If we found it, subtract off Scale V's from the entry in Dest. If it
1747 // goes to zero, remove the entry.
1748 if (Dest[j].Scale != Scale)
1749 Dest[j].Scale -= Scale;
1751 Dest.erase(Dest.begin() + j);
1756 // If we didn't consume this entry, add it to the end of the Dest list.
1758 VariableGEPIndex Entry = {V, ZExtBits, SExtBits, -Scale};
1759 Dest.push_back(Entry);
1764 bool BasicAAResult::constantOffsetHeuristic(
1765 const SmallVectorImpl<VariableGEPIndex> &VarIndices, uint64_t V1Size,
1766 uint64_t V2Size, int64_t BaseOffset, AssumptionCache *AC,
1767 DominatorTree *DT) {
1768 if (VarIndices.size() != 2 || V1Size == MemoryLocation::UnknownSize ||
1769 V2Size == MemoryLocation::UnknownSize)
1772 const VariableGEPIndex &Var0 = VarIndices[0], &Var1 = VarIndices[1];
1774 if (Var0.ZExtBits != Var1.ZExtBits || Var0.SExtBits != Var1.SExtBits ||
1775 Var0.Scale != -Var1.Scale)
1778 unsigned Width = Var1.V->getType()->getIntegerBitWidth();
1780 // We'll strip off the Extensions of Var0 and Var1 and do another round
1781 // of GetLinearExpression decomposition. In the example above, if Var0
1782 // is zext(%x + 1) we should get V1 == %x and V1Offset == 1.
1784 APInt V0Scale(Width, 0), V0Offset(Width, 0), V1Scale(Width, 0),
1786 bool NSW = true, NUW = true;
1787 unsigned V0ZExtBits = 0, V0SExtBits = 0, V1ZExtBits = 0, V1SExtBits = 0;
1788 const Value *V0 = GetLinearExpression(Var0.V, V0Scale, V0Offset, V0ZExtBits,
1789 V0SExtBits, DL, 0, AC, DT, NSW, NUW);
1792 const Value *V1 = GetLinearExpression(Var1.V, V1Scale, V1Offset, V1ZExtBits,
1793 V1SExtBits, DL, 0, AC, DT, NSW, NUW);
1795 if (V0Scale != V1Scale || V0ZExtBits != V1ZExtBits ||
1796 V0SExtBits != V1SExtBits || !isValueEqualInPotentialCycles(V0, V1))
1799 // We have a hit - Var0 and Var1 only differ by a constant offset!
1801 // If we've been sext'ed then zext'd the maximum difference between Var0 and
1802 // Var1 is possible to calculate, but we're just interested in the absolute
1803 // minimum difference between the two. The minimum distance may occur due to
1804 // wrapping; consider "add i3 %i, 5": if %i == 7 then 7 + 5 mod 8 == 4, and so
1805 // the minimum distance between %i and %i + 5 is 3.
1806 APInt MinDiff = V0Offset - V1Offset, Wrapped = -MinDiff;
1807 MinDiff = APIntOps::umin(MinDiff, Wrapped);
1808 uint64_t MinDiffBytes = MinDiff.getZExtValue() * std::abs(Var0.Scale);
1810 // We can't definitely say whether GEP1 is before or after V2 due to wrapping
1811 // arithmetic (i.e. for some values of GEP1 and V2 GEP1 < V2, and for other
1812 // values GEP1 > V2). We'll therefore only declare NoAlias if both V1Size and
1813 // V2Size can fit in the MinDiffBytes gap.
1814 return V1Size + std::abs(BaseOffset) <= MinDiffBytes &&
1815 V2Size + std::abs(BaseOffset) <= MinDiffBytes;
1818 //===----------------------------------------------------------------------===//
1819 // BasicAliasAnalysis Pass
1820 //===----------------------------------------------------------------------===//
1822 AnalysisKey BasicAA::Key;
1824 BasicAAResult BasicAA::run(Function &F, FunctionAnalysisManager &AM) {
1825 return BasicAAResult(F.getParent()->getDataLayout(),
1826 AM.getResult<TargetLibraryAnalysis>(F),
1827 AM.getResult<AssumptionAnalysis>(F),
1828 &AM.getResult<DominatorTreeAnalysis>(F),
1829 AM.getCachedResult<LoopAnalysis>(F));
1832 BasicAAWrapperPass::BasicAAWrapperPass() : FunctionPass(ID) {
1833 initializeBasicAAWrapperPassPass(*PassRegistry::getPassRegistry());
1836 char BasicAAWrapperPass::ID = 0;
1838 void BasicAAWrapperPass::anchor() {}
1840 INITIALIZE_PASS_BEGIN(BasicAAWrapperPass, "basicaa",
1841 "Basic Alias Analysis (stateless AA impl)", true, true)
1842 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
1843 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
1844 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
1845 INITIALIZE_PASS_END(BasicAAWrapperPass, "basicaa",
1846 "Basic Alias Analysis (stateless AA impl)", true, true)
1848 FunctionPass *llvm::createBasicAAWrapperPass() {
1849 return new BasicAAWrapperPass();
1852 bool BasicAAWrapperPass::runOnFunction(Function &F) {
1853 auto &ACT = getAnalysis<AssumptionCacheTracker>();
1854 auto &TLIWP = getAnalysis<TargetLibraryInfoWrapperPass>();
1855 auto &DTWP = getAnalysis<DominatorTreeWrapperPass>();
1856 auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
1858 Result.reset(new BasicAAResult(F.getParent()->getDataLayout(), TLIWP.getTLI(),
1859 ACT.getAssumptionCache(F), &DTWP.getDomTree(),
1860 LIWP ? &LIWP->getLoopInfo() : nullptr));
1865 void BasicAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
1866 AU.setPreservesAll();
1867 AU.addRequired<AssumptionCacheTracker>();
1868 AU.addRequired<DominatorTreeWrapperPass>();
1869 AU.addRequired<TargetLibraryInfoWrapperPass>();
1872 BasicAAResult llvm::createLegacyPMBasicAAResult(Pass &P, Function &F) {
1873 return BasicAAResult(
1874 F.getParent()->getDataLayout(),
1875 P.getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
1876 P.getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F));