X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FBasicAliasAnalysis.cpp;h=116076ce2a993f7e9c6b38aeff3eeb759140bf5f;hb=39b5abf507b43da6b92f68b86406e0015ead18e9;hp=fb6b9df608d1985181a8cab7da84e832f6602b34;hpb=f6ac4d9dadaa62959e04a0281e3bc5f4270fc260;p=oota-llvm.git diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp index fb6b9df608d..116076ce2a9 100644 --- a/lib/Analysis/BasicAliasAnalysis.cpp +++ b/lib/Analysis/BasicAliasAnalysis.cpp @@ -1,4 +1,4 @@ -//===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===// +//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===// // // The LLVM Compiler Infrastructure // @@ -7,15 +7,13 @@ // //===----------------------------------------------------------------------===// // -// This file defines the default implementation of the Alias Analysis interface -// that simply implements a few identities (two different globals cannot alias, -// etc), but otherwise does no analysis. +// This file defines the primary stateless implementation of the +// Alias Analysis interface that implements identities (two different +// globals cannot alias, etc), but does no stateful analysis. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/AliasAnalysis.h" -#include "llvm/Analysis/CaptureTracking.h" -#include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Analysis/Passes.h" #include "llvm/Constants.h" #include "llvm/DerivedTypes.h" @@ -24,12 +22,16 @@ #include "llvm/GlobalVariable.h" #include "llvm/Instructions.h" #include "llvm/IntrinsicInst.h" +#include "llvm/LLVMContext.h" #include "llvm/Operator.h" #include "llvm/Pass.h" +#include "llvm/Analysis/CaptureTracking.h" +#include "llvm/Analysis/MemoryBuiltins.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/ValueTracking.h" #include "llvm/Target/TargetData.h" -#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallVector.h" -#include "llvm/ADT/STLExtras.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include @@ -80,323 +82,160 @@ static bool isNonEscapingLocalObject(const Value *V) { return false; } +/// isEscapeSource - Return true if the pointer is one which would have +/// been considered an escape by isNonEscapingLocalObject. +static bool isEscapeSource(const Value *V) { + if (isa(V) || isa(V) || isa(V)) + return true; -/// isObjectSmallerThan - Return true if we can prove that the object specified -/// by V is smaller than Size. -static bool isObjectSmallerThan(const Value *V, unsigned Size, - const TargetData &TD) { - const Type *AccessTy; + // The load case works because isNonEscapingLocalObject considers all + // stores to be escapes (it passes true for the StoreCaptures argument + // to PointerMayBeCaptured). + if (isa(V)) + return true; + + return false; +} + +/// getObjectSize - Return the size of the object specified by V, or +/// UnknownSize if unknown. +static uint64_t getObjectSize(const Value *V, const TargetData &TD) { + Type *AccessTy; if (const GlobalVariable *GV = dyn_cast(V)) { + if (!GV->hasDefinitiveInitializer()) + return AliasAnalysis::UnknownSize; AccessTy = GV->getType()->getElementType(); } else if (const AllocaInst *AI = dyn_cast(V)) { if (!AI->isArrayAllocation()) AccessTy = AI->getType()->getElementType(); else - return false; + return AliasAnalysis::UnknownSize; } else if (const CallInst* CI = extractMallocCall(V)) { if (!isArrayMalloc(V, &TD)) // The size is the argument to the malloc call. - if (const ConstantInt* C = dyn_cast(CI->getOperand(1))) - return (C->getZExtValue() < Size); - return false; + if (const ConstantInt* C = dyn_cast(CI->getArgOperand(0))) + return C->getZExtValue(); + return AliasAnalysis::UnknownSize; } else if (const Argument *A = dyn_cast(V)) { if (A->hasByValAttr()) AccessTy = cast(A->getType())->getElementType(); else - return false; + return AliasAnalysis::UnknownSize; } else { - return false; + return AliasAnalysis::UnknownSize; } if (AccessTy->isSized()) - return TD.getTypeAllocSize(AccessTy) < Size; - return false; + return TD.getTypeAllocSize(AccessTy); + return AliasAnalysis::UnknownSize; } -//===----------------------------------------------------------------------===// -// NoAA Pass -//===----------------------------------------------------------------------===// - -namespace { - /// NoAA - This class implements the -no-aa pass, which always returns "I - /// don't know" for alias queries. NoAA is unlike other alias analysis - /// implementations, in that it does not chain to a previous analysis. As - /// such it doesn't follow many of the rules that other alias analyses must. - /// - struct NoAA : public ImmutablePass, public AliasAnalysis { - static char ID; // Class identification, replacement for typeinfo - NoAA() : ImmutablePass(&ID) {} - explicit NoAA(void *PID) : ImmutablePass(PID) { } - - virtual void getAnalysisUsage(AnalysisUsage &AU) const { - } - - virtual void initializePass() { - TD = getAnalysisIfAvailable(); - } - - virtual AliasResult alias(const Value *V1, unsigned V1Size, - const Value *V2, unsigned V2Size) { - return MayAlias; - } - - virtual void getArgumentAccesses(Function *F, CallSite CS, - std::vector &Info) { - llvm_unreachable("This method may not be called on this function!"); - } - - virtual bool pointsToConstantMemory(const Value *P) { return false; } - virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) { - return ModRef; - } - virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { - return ModRef; - } - - virtual void deleteValue(Value *V) {} - virtual void copyValue(Value *From, Value *To) {} - }; -} // End of anonymous namespace - -// Register this pass... -char NoAA::ID = 0; -static RegisterPass -U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true); - -// Declare that we implement the AliasAnalysis interface -static RegisterAnalysisGroup V(U); +/// isObjectSmallerThan - Return true if we can prove that the object specified +/// by V is smaller than Size. +static bool isObjectSmallerThan(const Value *V, uint64_t Size, + const TargetData &TD) { + uint64_t ObjectSize = getObjectSize(V, TD); + return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size; +} -ImmutablePass *llvm::createNoAAPass() { return new NoAA(); } +/// isObjectSize - Return true if we can prove that the object specified +/// by V has size Size. +static bool isObjectSize(const Value *V, uint64_t Size, + const TargetData &TD) { + uint64_t ObjectSize = getObjectSize(V, TD); + return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size; +} //===----------------------------------------------------------------------===// -// BasicAA Pass +// GetElementPtr Instruction Decomposition and Analysis //===----------------------------------------------------------------------===// namespace { - /// BasicAliasAnalysis - This is the default alias analysis implementation. - /// Because it doesn't chain to a previous alias analysis (like -no-aa), it - /// derives from the NoAA class. - struct BasicAliasAnalysis : public NoAA { - static char ID; // Class identification, replacement for typeinfo - BasicAliasAnalysis() : NoAA(&ID) {} - AliasResult alias(const Value *V1, unsigned V1Size, - const Value *V2, unsigned V2Size) { - assert(VisitedPHIs.empty() && "VisitedPHIs must be cleared after use!"); - AliasResult Alias = aliasCheck(V1, V1Size, V2, V2Size); - VisitedPHIs.clear(); - return Alias; - } - - ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); - ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); - - /// pointsToConstantMemory - Chase pointers until we find a (constant - /// global) or not. - bool pointsToConstantMemory(const Value *P); - - private: - // VisitedPHIs - Track PHI nodes visited by a aliasCheck() call. - SmallPtrSet VisitedPHIs; - - // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP - // instruction against another. - AliasResult aliasGEP(const GEPOperator *V1, unsigned V1Size, - const Value *V2, unsigned V2Size, - const Value *UnderlyingV1, const Value *UnderlyingV2); - - // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI - // instruction against another. - AliasResult aliasPHI(const PHINode *PN, unsigned PNSize, - const Value *V2, unsigned V2Size); - - /// aliasSelect - Disambiguate a Select instruction against another value. - AliasResult aliasSelect(const SelectInst *SI, unsigned SISize, - const Value *V2, unsigned V2Size); - - AliasResult aliasCheck(const Value *V1, unsigned V1Size, - const Value *V2, unsigned V2Size); + enum ExtensionKind { + EK_NotExtended, + EK_SignExt, + EK_ZeroExt }; -} // End of anonymous namespace - -// Register this pass... -char BasicAliasAnalysis::ID = 0; -static RegisterPass -X("basicaa", "Basic Alias Analysis (default AA impl)", false, true); - -// Declare that we implement the AliasAnalysis interface -static RegisterAnalysisGroup Y(X); - -ImmutablePass *llvm::createBasicAliasAnalysisPass() { - return new BasicAliasAnalysis(); -} - - -/// pointsToConstantMemory - Chase pointers until we find a (constant -/// global) or not. -bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) { - if (const GlobalVariable *GV = - dyn_cast(P->getUnderlyingObject())) - // Note: this doesn't require GV to be "ODR" because it isn't legal for a - // global to be marked constant in some modules and non-constant in others. - // GV may even be a declaration, not a definition. - return GV->isConstant(); - return false; -} - - -/// getModRefInfo - Check to see if the specified callsite can clobber the -/// specified memory object. Since we only look at local properties of this -/// function, we really can't say much about this query. We do, however, use -/// simple "address taken" analysis on local objects. -AliasAnalysis::ModRefResult -BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { - const Value *Object = P->getUnderlyingObject(); - // If this is a tail call and P points to a stack location, we know that - // the tail call cannot access or modify the local stack. - // We cannot exclude byval arguments here; these belong to the caller of - // the current function not to the current function, and a tail callee - // may reference them. - if (isa(Object)) - if (CallInst *CI = dyn_cast(CS.getInstruction())) - if (CI->isTailCall()) - return NoModRef; - - // If the pointer is to a locally allocated object that does not escape, - // then the call can not mod/ref the pointer unless the call takes the pointer - // as an argument, and itself doesn't capture it. - if (!isa(Object) && CS.getInstruction() != Object && - isNonEscapingLocalObject(Object)) { - bool PassedAsArg = false; - unsigned ArgNo = 0; - for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end(); - CI != CE; ++CI, ++ArgNo) { - // Only look at the no-capture pointer arguments. - if (!isa((*CI)->getType()) || - !CS.paramHasAttr(ArgNo+1, Attribute::NoCapture)) - continue; - - // If this is a no-capture pointer argument, see if we can tell that it - // is impossible to alias the pointer we're checking. If not, we have to - // assume that the call could touch the pointer, even though it doesn't - // escape. - if (!isNoAlias(cast(CI), ~0U, P, ~0U)) { - PassedAsArg = true; - break; - } - } - - if (!PassedAsArg) - return NoModRef; - } - - // Finally, handle specific knowledge of intrinsics. - IntrinsicInst *II = dyn_cast(CS.getInstruction()); - if (II == 0) - return AliasAnalysis::getModRefInfo(CS, P, Size); - - switch (II->getIntrinsicID()) { - default: break; - case Intrinsic::memcpy: - case Intrinsic::memmove: { - unsigned Len = ~0U; - if (ConstantInt *LenCI = dyn_cast(II->getOperand(3))) - Len = LenCI->getZExtValue(); - Value *Dest = II->getOperand(1); - Value *Src = II->getOperand(2); - if (isNoAlias(Dest, Len, P, Size)) { - if (isNoAlias(Src, Len, P, Size)) - return NoModRef; - return Ref; - } - break; - } - case Intrinsic::memset: - // Since memset is 'accesses arguments' only, the AliasAnalysis base class - // will handle it for the variable length case. - if (ConstantInt *LenCI = dyn_cast(II->getOperand(3))) { - unsigned Len = LenCI->getZExtValue(); - Value *Dest = II->getOperand(1); - if (isNoAlias(Dest, Len, P, Size)) - return NoModRef; - } - break; - case Intrinsic::atomic_cmp_swap: - case Intrinsic::atomic_swap: - case Intrinsic::atomic_load_add: - case Intrinsic::atomic_load_sub: - case Intrinsic::atomic_load_and: - case Intrinsic::atomic_load_nand: - case Intrinsic::atomic_load_or: - case Intrinsic::atomic_load_xor: - case Intrinsic::atomic_load_max: - case Intrinsic::atomic_load_min: - case Intrinsic::atomic_load_umax: - case Intrinsic::atomic_load_umin: - if (TD) { - Value *Op1 = II->getOperand(1); - unsigned Op1Size = TD->getTypeStoreSize(Op1->getType()); - if (isNoAlias(Op1, Op1Size, P, Size)) - return NoModRef; - } - break; - case Intrinsic::lifetime_start: - case Intrinsic::lifetime_end: - case Intrinsic::invariant_start: { - unsigned PtrSize = cast(II->getOperand(1))->getZExtValue(); - if (isNoAlias(II->getOperand(2), PtrSize, P, Size)) - return NoModRef; - break; - } - case Intrinsic::invariant_end: { - unsigned PtrSize = cast(II->getOperand(2))->getZExtValue(); - if (isNoAlias(II->getOperand(3), PtrSize, P, Size)) - return NoModRef; - break; - } - } - - // The AliasAnalysis base class has some smarts, lets use them. - return AliasAnalysis::getModRefInfo(CS, P, Size); + struct VariableGEPIndex { + const Value *V; + ExtensionKind Extension; + int64_t Scale; + }; } -AliasAnalysis::ModRefResult -BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) { - // If CS1 or CS2 are readnone, they don't interact. - ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1); - if (CS1B == DoesNotAccessMemory) return NoModRef; - - ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2); - if (CS2B == DoesNotAccessMemory) return NoModRef; - - // If they both only read from memory, just return ref. - if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory) - return Ref; - - // Otherwise, fall back to NoAA (mod+ref). - return NoAA::getModRefInfo(CS1, CS2); -} - /// GetLinearExpression - Analyze the specified value as a linear expression: -/// "A*V + B". Return the scale and offset values as APInts and return V as a -/// Value*. The incoming Value is known to be a scalar integer. -static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset) { - assert(isa(V->getType()) && "Not an integer value"); +/// "A*V + B", where A and B are constant integers. Return the scale and offset +/// values as APInts and return V as a Value*, and return whether we looked +/// through any sign or zero extends. The incoming Value is known to have +/// IntegerType and it may already be sign or zero extended. +/// +/// Note that this looks through extends, so the high bits may not be +/// represented in the result. +static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, + ExtensionKind &Extension, + const TargetData &TD, unsigned Depth) { + assert(V->getType()->isIntegerTy() && "Not an integer value"); + + // Limit our recursion depth. + if (Depth == 6) { + Scale = 1; + Offset = 0; + return V; + } if (BinaryOperator *BOp = dyn_cast(V)) { if (ConstantInt *RHSC = dyn_cast(BOp->getOperand(1))) { switch (BOp->getOpcode()) { default: break; + case Instruction::Or: + // X|C == X+C if all the bits in C are unset in X. Otherwise we can't + // analyze it. + if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &TD)) + break; + // FALL THROUGH. case Instruction::Add: - V = GetLinearExpression(BOp->getOperand(0), Scale, Offset); + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, + TD, Depth+1); Offset += RHSC->getValue(); return V; - // TODO: SHL, MUL, OR. + case Instruction::Mul: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, + TD, Depth+1); + Offset *= RHSC->getValue(); + Scale *= RHSC->getValue(); + return V; + case Instruction::Shl: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, + TD, Depth+1); + Offset <<= RHSC->getValue().getLimitedValue(); + Scale <<= RHSC->getValue().getLimitedValue(); + return V; } } } - + + // Since GEP indices are sign extended anyway, we don't care about the high + // bits of a sign or zero extended value - just scales and offsets. The + // extensions have to be consistent though. + if ((isa(V) && Extension != EK_ZeroExt) || + (isa(V) && Extension != EK_SignExt)) { + Value *CastOp = cast(V)->getOperand(0); + unsigned OldWidth = Scale.getBitWidth(); + unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits(); + Scale = Scale.trunc(SmallWidth); + Offset = Offset.trunc(SmallWidth); + Extension = isa(V) ? EK_SignExt : EK_ZeroExt; + + Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension, + TD, Depth+1); + Scale = Scale.zext(OldWidth); + Offset = Offset.zext(OldWidth); + + return Result; + } + Scale = 1; Offset = 0; return V; @@ -406,18 +245,24 @@ static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset) { /// into a base pointer with a constant offset and a number of scaled symbolic /// offsets. /// +/// The scaled symbolic offsets (represented by pairs of a Value* and a scale in +/// the VarIndices vector) are Value*'s that are known to be scaled by the +/// specified amount, but which may have other unrepresented high bits. As such, +/// the gep cannot necessarily be reconstructed from its decomposed form. +/// /// When TargetData is around, this function is capable of analyzing everything -/// that Value::getUnderlyingObject() can look through. When not, it just looks +/// that GetUnderlyingObject can look through. When not, it just looks /// through pointer casts. /// -/// FIXME: Move this out to ValueTracking.cpp -/// -static const Value *DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, - SmallVectorImpl > &VarIndices, - const TargetData *TD) { - // FIXME: Should limit depth like getUnderlyingObject? +static const Value * +DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, + SmallVectorImpl &VarIndices, + const TargetData *TD) { + // Limit recursion depth to limit compile time in crazy cases. + unsigned MaxLookup = 6; + BaseOffs = 0; - while (1) { + do { // See if this is a bitcast or GEP. const Operator *Op = dyn_cast(V); if (Op == 0) { @@ -435,20 +280,31 @@ static const Value *DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, V = Op->getOperand(0); continue; } - + const GEPOperator *GEPOp = dyn_cast(Op); - if (GEPOp == 0) + if (GEPOp == 0) { + // If it's not a GEP, hand it off to SimplifyInstruction to see if it + // can come up with something. This matches what GetUnderlyingObject does. + if (const Instruction *I = dyn_cast(V)) + // TODO: Get a DominatorTree and use it here. + if (const Value *Simplified = + SimplifyInstruction(const_cast(I), TD)) { + V = Simplified; + continue; + } + return V; + } // Don't attempt to analyze GEPs over unsized objects. if (!cast(GEPOp->getOperand(0)->getType()) - ->getElementType()->isSized()) + ->getElementType()->isSized()) return V; - + // If we are lacking TargetData information, we can't compute the offets of // elements computed by GEPs. However, we can handle bitcast equivalent // GEPs. - if (!TD) { + if (TD == 0) { if (!GEPOp->hasAllZeroIndices()) return V; V = GEPOp->getOperand(0); @@ -457,11 +313,11 @@ static const Value *DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices. gep_type_iterator GTI = gep_type_begin(GEPOp); - for (User::const_op_iterator I = next(GEPOp->op_begin()), + for (User::const_op_iterator I = GEPOp->op_begin()+1, E = GEPOp->op_end(); I != E; ++I) { Value *Index = *I; // Compute the (potentially symbolic) offset in bytes for this index. - if (const StructType *STy = dyn_cast(*GTI++)) { + if (StructType *STy = dyn_cast(*GTI++)) { // For a struct, add the member offset. unsigned FieldNo = cast(Index)->getZExtValue(); if (FieldNo == 0) continue; @@ -477,24 +333,34 @@ static const Value *DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, continue; } - // TODO: Could handle linear expressions here like A[X+1], also A[X*4|1]. uint64_t Scale = TD->getTypeAllocSize(*GTI); + ExtensionKind Extension = EK_NotExtended; + // If the integer type is smaller than the pointer size, it is implicitly + // sign extended to pointer size. unsigned Width = cast(Index->getType())->getBitWidth(); + if (TD->getPointerSizeInBits() > Width) + Extension = EK_SignExt; + + // Use GetLinearExpression to decompose the index into a C1*V+C2 form. APInt IndexScale(Width, 0), IndexOffset(Width, 0); - Index = GetLinearExpression(Index, IndexScale, IndexOffset); + Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension, + *TD, 0); - Scale *= IndexScale.getZExtValue(); - BaseOffs += IndexOffset.getZExtValue()*Scale; + // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale. + // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale. + BaseOffs += IndexOffset.getSExtValue()*Scale; + Scale *= IndexScale.getSExtValue(); - // If we already had an occurrance of this index variable, merge this + // If we already had an occurrence of this index variable, merge this // scale into it. For example, we want to handle: // A[x][x] -> x*16 + x*4 -> x*20 // This also ensures that 'x' only appears in the index list once. for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) { - if (VarIndices[i].first == Index) { - Scale += VarIndices[i].second; + if (VarIndices[i].V == Index && + VarIndices[i].Extension == Extension) { + Scale += VarIndices[i].Scale; VarIndices.erase(VarIndices.begin()+i); break; } @@ -504,40 +370,45 @@ static const Value *DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, // pointer size. if (unsigned ShiftBits = 64-TD->getPointerSizeInBits()) { Scale <<= ShiftBits; - Scale >>= ShiftBits; + Scale = (int64_t)Scale >> ShiftBits; } - if (Scale) - VarIndices.push_back(std::make_pair(Index, Scale)); + if (Scale) { + VariableGEPIndex Entry = {Index, Extension, Scale}; + VarIndices.push_back(Entry); + } } // Analyze the base pointer next. V = GEPOp->getOperand(0); - } + } while (--MaxLookup); + + // If the chain of expressions is too deep, just return early. + return V; } -/// GetIndiceDifference - Dest and Src are the variable indices from two +/// GetIndexDifference - Dest and Src are the variable indices from two /// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic /// difference between the two pointers. -static void GetIndiceDifference( - SmallVectorImpl > &Dest, - const SmallVectorImpl > &Src) { +static void GetIndexDifference(SmallVectorImpl &Dest, + const SmallVectorImpl &Src) { if (Src.empty()) return; for (unsigned i = 0, e = Src.size(); i != e; ++i) { - const Value *V = Src[i].first; - int64_t Scale = Src[i].second; + const Value *V = Src[i].V; + ExtensionKind Extension = Src[i].Extension; + int64_t Scale = Src[i].Scale; // Find V in Dest. This is N^2, but pointer indices almost never have more // than a few variable indexes. for (unsigned j = 0, e = Dest.size(); j != e; ++j) { - if (Dest[j].first != V) continue; + if (Dest[j].V != V || Dest[j].Extension != Extension) continue; // If we found it, subtract off Scale V's from the entry in Dest. If it // goes to zero, remove the entry. - if (Dest[j].second != Scale) - Dest[j].second -= Scale; + if (Dest[j].Scale != Scale) + Dest[j].Scale -= Scale; else Dest.erase(Dest.begin()+j); Scale = 0; @@ -545,29 +416,432 @@ static void GetIndiceDifference( } // If we didn't consume this entry, add it to the end of the Dest list. - if (Scale) - Dest.push_back(std::make_pair(V, -Scale)); + if (Scale) { + VariableGEPIndex Entry = { V, Extension, -Scale }; + Dest.push_back(Entry); + } + } +} + +//===----------------------------------------------------------------------===// +// BasicAliasAnalysis Pass +//===----------------------------------------------------------------------===// + +#ifndef NDEBUG +static const Function *getParent(const Value *V) { + if (const Instruction *inst = dyn_cast(V)) + return inst->getParent()->getParent(); + + if (const Argument *arg = dyn_cast(V)) + return arg->getParent(); + + return NULL; +} + +static bool notDifferentParent(const Value *O1, const Value *O2) { + + const Function *F1 = getParent(O1); + const Function *F2 = getParent(O2); + + return !F1 || !F2 || F1 == F2; +} +#endif + +namespace { + /// BasicAliasAnalysis - This is the primary alias analysis implementation. + struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis { + static char ID; // Class identification, replacement for typeinfo + BasicAliasAnalysis() : ImmutablePass(ID), + // AliasCache rarely has more than 1 or 2 elements, + // so start it off fairly small so that clear() + // doesn't have to tromp through 64 (the default) + // elements on each alias query. This really wants + // something like a SmallDenseMap. + AliasCache(8) { + initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry()); + } + + virtual void initializePass() { + InitializeAliasAnalysis(this); + } + + virtual void getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired(); + } + + virtual AliasResult alias(const Location &LocA, + const Location &LocB) { + assert(AliasCache.empty() && "AliasCache must be cleared after use!"); + assert(notDifferentParent(LocA.Ptr, LocB.Ptr) && + "BasicAliasAnalysis doesn't support interprocedural queries."); + AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag, + LocB.Ptr, LocB.Size, LocB.TBAATag); + AliasCache.clear(); + return Alias; + } + + virtual ModRefResult getModRefInfo(ImmutableCallSite CS, + const Location &Loc); + + virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, + ImmutableCallSite CS2) { + // The AliasAnalysis base class has some smarts, lets use them. + return AliasAnalysis::getModRefInfo(CS1, CS2); + } + + /// pointsToConstantMemory - Chase pointers until we find a (constant + /// global) or not. + virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal); + + /// getModRefBehavior - Return the behavior when calling the given + /// call site. + virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); + + /// getModRefBehavior - Return the behavior when calling the given function. + /// For use when the call site is not known. + virtual ModRefBehavior getModRefBehavior(const Function *F); + + /// getAdjustedAnalysisPointer - This method is used when a pass implements + /// an analysis interface through multiple inheritance. If needed, it + /// should override this to adjust the this pointer as needed for the + /// specified pass info. + virtual void *getAdjustedAnalysisPointer(const void *ID) { + if (ID == &AliasAnalysis::ID) + return (AliasAnalysis*)this; + return this; + } + + private: + // AliasCache - Track alias queries to guard against recursion. + typedef std::pair LocPair; + typedef DenseMap AliasCacheTy; + AliasCacheTy AliasCache; + + // Visited - Track instructions visited by pointsToConstantMemory. + SmallPtrSet Visited; + + // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP + // instruction against another. + AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size, + const Value *V2, uint64_t V2Size, + const MDNode *V2TBAAInfo, + const Value *UnderlyingV1, const Value *UnderlyingV2); + + // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI + // instruction against another. + AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize, + const MDNode *PNTBAAInfo, + const Value *V2, uint64_t V2Size, + const MDNode *V2TBAAInfo); + + /// aliasSelect - Disambiguate a Select instruction against another value. + AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize, + const MDNode *SITBAAInfo, + const Value *V2, uint64_t V2Size, + const MDNode *V2TBAAInfo); + + AliasResult aliasCheck(const Value *V1, uint64_t V1Size, + const MDNode *V1TBAATag, + const Value *V2, uint64_t V2Size, + const MDNode *V2TBAATag); + }; +} // End of anonymous namespace + +// Register this pass... +char BasicAliasAnalysis::ID = 0; +INITIALIZE_AG_PASS(BasicAliasAnalysis, AliasAnalysis, "basicaa", + "Basic Alias Analysis (stateless AA impl)", + false, true, false) + +ImmutablePass *llvm::createBasicAliasAnalysisPass() { + return new BasicAliasAnalysis(); +} + +/// pointsToConstantMemory - Returns whether the given pointer value +/// points to memory that is local to the function, with global constants being +/// considered local to all functions. +bool +BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) { + assert(Visited.empty() && "Visited must be cleared after use!"); + + unsigned MaxLookup = 8; + SmallVector Worklist; + Worklist.push_back(Loc.Ptr); + do { + const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), TD); + if (!Visited.insert(V)) { + Visited.clear(); + return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); + } + + // An alloca instruction defines local memory. + if (OrLocal && isa(V)) + continue; + + // A global constant counts as local memory for our purposes. + if (const GlobalVariable *GV = dyn_cast(V)) { + // Note: this doesn't require GV to be "ODR" because it isn't legal for a + // global to be marked constant in some modules and non-constant in + // others. GV may even be a declaration, not a definition. + if (!GV->isConstant()) { + Visited.clear(); + return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); + } + continue; + } + + // If both select values point to local memory, then so does the select. + if (const SelectInst *SI = dyn_cast(V)) { + Worklist.push_back(SI->getTrueValue()); + Worklist.push_back(SI->getFalseValue()); + continue; + } + + // If all values incoming to a phi node point to local memory, then so does + // the phi. + if (const PHINode *PN = dyn_cast(V)) { + // Don't bother inspecting phi nodes with many operands. + if (PN->getNumIncomingValues() > MaxLookup) { + Visited.clear(); + return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); + } + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) + Worklist.push_back(PN->getIncomingValue(i)); + continue; + } + + // Otherwise be conservative. + Visited.clear(); + return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); + + } while (!Worklist.empty() && --MaxLookup); + + Visited.clear(); + return Worklist.empty(); +} + +/// getModRefBehavior - Return the behavior when calling the given call site. +AliasAnalysis::ModRefBehavior +BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { + if (CS.doesNotAccessMemory()) + // Can't do better than this. + return DoesNotAccessMemory; + + ModRefBehavior Min = UnknownModRefBehavior; + + // If the callsite knows it only reads memory, don't return worse + // than that. + if (CS.onlyReadsMemory()) + Min = OnlyReadsMemory; + + // The AliasAnalysis base class has some smarts, lets use them. + return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min); +} + +/// getModRefBehavior - Return the behavior when calling the given function. +/// For use when the call site is not known. +AliasAnalysis::ModRefBehavior +BasicAliasAnalysis::getModRefBehavior(const Function *F) { + // If the function declares it doesn't access memory, we can't do better. + if (F->doesNotAccessMemory()) + return DoesNotAccessMemory; + + // For intrinsics, we can check the table. + if (unsigned iid = F->getIntrinsicID()) { +#define GET_INTRINSIC_MODREF_BEHAVIOR +#include "llvm/Intrinsics.gen" +#undef GET_INTRINSIC_MODREF_BEHAVIOR } + + ModRefBehavior Min = UnknownModRefBehavior; + + // If the function declares it only reads memory, go with that. + if (F->onlyReadsMemory()) + Min = OnlyReadsMemory; + + // Otherwise be conservative. + return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min); +} + +/// getModRefInfo - Check to see if the specified callsite can clobber the +/// specified memory object. Since we only look at local properties of this +/// function, we really can't say much about this query. We do, however, use +/// simple "address taken" analysis on local objects. +AliasAnalysis::ModRefResult +BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, + const Location &Loc) { + assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) && + "AliasAnalysis query involving multiple functions!"); + + const Value *Object = GetUnderlyingObject(Loc.Ptr, TD); + + // If this is a tail call and Loc.Ptr points to a stack location, we know that + // the tail call cannot access or modify the local stack. + // We cannot exclude byval arguments here; these belong to the caller of + // the current function not to the current function, and a tail callee + // may reference them. + if (isa(Object)) + if (const CallInst *CI = dyn_cast(CS.getInstruction())) + if (CI->isTailCall()) + return NoModRef; + + // If the pointer is to a locally allocated object that does not escape, + // then the call can not mod/ref the pointer unless the call takes the pointer + // as an argument, and itself doesn't capture it. + if (!isa(Object) && CS.getInstruction() != Object && + isNonEscapingLocalObject(Object)) { + bool PassedAsArg = false; + unsigned ArgNo = 0; + for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end(); + CI != CE; ++CI, ++ArgNo) { + // Only look at the no-capture or byval pointer arguments. If this + // pointer were passed to arguments that were neither of these, then it + // couldn't be no-capture. + if (!(*CI)->getType()->isPointerTy() || + (!CS.paramHasAttr(ArgNo+1, Attribute::NoCapture) && + !CS.paramHasAttr(ArgNo+1, Attribute::ByVal))) + continue; + + // If this is a no-capture pointer argument, see if we can tell that it + // is impossible to alias the pointer we're checking. If not, we have to + // assume that the call could touch the pointer, even though it doesn't + // escape. + if (!isNoAlias(Location(cast(CI)), Loc)) { + PassedAsArg = true; + break; + } + } + + if (!PassedAsArg) + return NoModRef; + } + + ModRefResult Min = ModRef; + + // Finally, handle specific knowledge of intrinsics. + const IntrinsicInst *II = dyn_cast(CS.getInstruction()); + if (II != 0) + switch (II->getIntrinsicID()) { + default: break; + case Intrinsic::memcpy: + case Intrinsic::memmove: { + uint64_t Len = UnknownSize; + if (ConstantInt *LenCI = dyn_cast(II->getArgOperand(2))) + Len = LenCI->getZExtValue(); + Value *Dest = II->getArgOperand(0); + Value *Src = II->getArgOperand(1); + // If it can't overlap the source dest, then it doesn't modref the loc. + if (isNoAlias(Location(Dest, Len), Loc)) { + if (isNoAlias(Location(Src, Len), Loc)) + return NoModRef; + // If it can't overlap the dest, then worst case it reads the loc. + Min = Ref; + } else if (isNoAlias(Location(Src, Len), Loc)) { + // If it can't overlap the source, then worst case it mutates the loc. + Min = Mod; + } + break; + } + case Intrinsic::memset: + // Since memset is 'accesses arguments' only, the AliasAnalysis base class + // will handle it for the variable length case. + if (ConstantInt *LenCI = dyn_cast(II->getArgOperand(2))) { + uint64_t Len = LenCI->getZExtValue(); + Value *Dest = II->getArgOperand(0); + if (isNoAlias(Location(Dest, Len), Loc)) + return NoModRef; + } + // We know that memset doesn't load anything. + Min = Mod; + break; + case Intrinsic::atomic_cmp_swap: + case Intrinsic::atomic_swap: + case Intrinsic::atomic_load_add: + case Intrinsic::atomic_load_sub: + case Intrinsic::atomic_load_and: + case Intrinsic::atomic_load_nand: + case Intrinsic::atomic_load_or: + case Intrinsic::atomic_load_xor: + case Intrinsic::atomic_load_max: + case Intrinsic::atomic_load_min: + case Intrinsic::atomic_load_umax: + case Intrinsic::atomic_load_umin: + if (TD) { + Value *Op1 = II->getArgOperand(0); + uint64_t Op1Size = TD->getTypeStoreSize(Op1->getType()); + MDNode *Tag = II->getMetadata(LLVMContext::MD_tbaa); + if (isNoAlias(Location(Op1, Op1Size, Tag), Loc)) + return NoModRef; + } + break; + case Intrinsic::lifetime_start: + case Intrinsic::lifetime_end: + case Intrinsic::invariant_start: { + uint64_t PtrSize = + cast(II->getArgOperand(0))->getZExtValue(); + if (isNoAlias(Location(II->getArgOperand(1), + PtrSize, + II->getMetadata(LLVMContext::MD_tbaa)), + Loc)) + return NoModRef; + break; + } + case Intrinsic::invariant_end: { + uint64_t PtrSize = + cast(II->getArgOperand(1))->getZExtValue(); + if (isNoAlias(Location(II->getArgOperand(2), + PtrSize, + II->getMetadata(LLVMContext::MD_tbaa)), + Loc)) + return NoModRef; + break; + } + case Intrinsic::arm_neon_vld1: { + // LLVM's vld1 and vst1 intrinsics currently only support a single + // vector register. + uint64_t Size = + TD ? TD->getTypeStoreSize(II->getType()) : UnknownSize; + if (isNoAlias(Location(II->getArgOperand(0), Size, + II->getMetadata(LLVMContext::MD_tbaa)), + Loc)) + return NoModRef; + break; + } + case Intrinsic::arm_neon_vst1: { + uint64_t Size = + TD ? TD->getTypeStoreSize(II->getArgOperand(1)->getType()) : UnknownSize; + if (isNoAlias(Location(II->getArgOperand(0), Size, + II->getMetadata(LLVMContext::MD_tbaa)), + Loc)) + return NoModRef; + break; + } + } + + // The AliasAnalysis base class has some smarts, lets use them. + return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min); } /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction /// against another pointer. We know that V1 is a GEP, but we don't know -/// anything about V2. UnderlyingV1 is GEP1->getUnderlyingObject(), +/// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, TD), /// UnderlyingV2 is the same for V2. /// AliasAnalysis::AliasResult -BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size, - const Value *V2, unsigned V2Size, +BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, + const Value *V2, uint64_t V2Size, + const MDNode *V2TBAAInfo, const Value *UnderlyingV1, const Value *UnderlyingV2) { int64_t GEP1BaseOffset; - SmallVector, 4> GEP1VariableIndices; + SmallVector GEP1VariableIndices; // If we have two gep instructions with must-alias'ing base pointers, figure // out if the indexes to the GEP tell us anything about the derived pointer. if (const GEPOperator *GEP2 = dyn_cast(V2)) { // Do the base pointers alias? - AliasResult BaseAlias = aliasCheck(UnderlyingV1, ~0U, UnderlyingV2, ~0U); + AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0, + UnderlyingV2, UnknownSize, 0); // If we get a No or May, then return it immediately, no amount of analysis // will improve this situation. @@ -580,7 +854,7 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size, DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); int64_t GEP2BaseOffset; - SmallVector, 4> GEP2VariableIndices; + SmallVector GEP2VariableIndices; const Value *GEP2BasePtr = DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD); @@ -589,26 +863,26 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size, // to handle without it. if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { assert(TD == 0 && - "DecomposeGEPExpression and getUnderlyingObject disagree!"); + "DecomposeGEPExpression and GetUnderlyingObject disagree!"); return MayAlias; } // Subtract the GEP2 pointer from the GEP1 pointer to find out their // symbolic difference. GEP1BaseOffset -= GEP2BaseOffset; - GetIndiceDifference(GEP1VariableIndices, GEP2VariableIndices); + GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices); } else { // Check to see if these two pointers are related by the getelementptr // instruction. If one pointer is a GEP with a non-zero index of the other // pointer, we know they cannot alias. - // - // FIXME: The check below only looks at the size of one of the pointers, not - // both, this may cause us to miss things. - if (V1Size == ~0U || V2Size == ~0U) + + // If both accesses are unknown size, we can't do anything useful here. + if (V1Size == UnknownSize && V2Size == UnknownSize) return MayAlias; - AliasResult R = aliasCheck(UnderlyingV1, ~0U, V2, V2Size); + AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, 0, + V2, V2Size, V2TBAAInfo); if (R != MustAlias) // If V2 may alias GEP base pointer, conservatively returns MayAlias. // If V2 is known not to alias GEP base pointer, then the two values @@ -625,7 +899,7 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size, // to handle without it. if (GEP1BasePtr != UnderlyingV1) { assert(TD == 0 && - "DecomposeGEPExpression and getUnderlyingObject disagree!"); + "DecomposeGEPExpression and GetUnderlyingObject disagree!"); return MayAlias; } } @@ -639,6 +913,17 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size, if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty()) return MustAlias; + // If there is a difference between the pointers, but the difference is + // less than the size of the associated memory object, then we know + // that the objects are partially overlapping. + if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) { + if (GEP1BaseOffset >= 0 ? + (V2Size != UnknownSize && (uint64_t)GEP1BaseOffset < V2Size) : + (V1Size != UnknownSize && -(uint64_t)GEP1BaseOffset < V1Size && + GEP1BaseOffset != INT64_MIN)) + return PartialAlias; + } + // If we have a known constant offset, see if this offset is larger than the // access size being queried. If so, and if no variable indices can remove // pieces of this constant, then we know we have a no-alias. For example, @@ -652,82 +937,105 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size, // provides an offset of 4 bytes (assuming a <= 4 byte access). for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e && GEP1BaseOffset;++i) - if (int64_t RemovedOffset = GEP1BaseOffset/GEP1VariableIndices[i].second) - GEP1BaseOffset -= RemovedOffset*GEP1VariableIndices[i].second; + if (int64_t RemovedOffset = GEP1BaseOffset/GEP1VariableIndices[i].Scale) + GEP1BaseOffset -= RemovedOffset*GEP1VariableIndices[i].Scale; // If our known offset is bigger than the access size, we know we don't have // an alias. if (GEP1BaseOffset) { - if (GEP1BaseOffset >= (int64_t)V2Size || - GEP1BaseOffset <= -(int64_t)V1Size) + if (GEP1BaseOffset >= 0 ? + (V2Size != UnknownSize && (uint64_t)GEP1BaseOffset >= V2Size) : + (V1Size != UnknownSize && -(uint64_t)GEP1BaseOffset >= V1Size && + GEP1BaseOffset != INT64_MIN)) return NoAlias; } - return MayAlias; + // Statically, we can see that the base objects are the same, but the + // pointers have dynamic offsets which we can't resolve. And none of our + // little tricks above worked. + // + // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the + // practical effect of this is protecting TBAA in the case of dynamic + // indices into arrays of unions. An alternative way to solve this would + // be to have clang emit extra metadata for unions and/or union accesses. + // A union-specific solution wouldn't handle the problem for malloc'd + // memory however. + return PartialAlias; +} + +static AliasAnalysis::AliasResult +MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) { + // If the results agree, take it. + if (A == B) + return A; + // A mix of PartialAlias and MustAlias is PartialAlias. + if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) || + (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias)) + return AliasAnalysis::PartialAlias; + // Otherwise, we don't know anything. + return AliasAnalysis::MayAlias; } /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select /// instruction against another. AliasAnalysis::AliasResult -BasicAliasAnalysis::aliasSelect(const SelectInst *SI, unsigned SISize, - const Value *V2, unsigned V2Size) { +BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize, + const MDNode *SITBAAInfo, + const Value *V2, uint64_t V2Size, + const MDNode *V2TBAAInfo) { // If the values are Selects with the same condition, we can do a more precise // check: just check for aliases between the values on corresponding arms. if (const SelectInst *SI2 = dyn_cast(V2)) if (SI->getCondition() == SI2->getCondition()) { AliasResult Alias = - aliasCheck(SI->getTrueValue(), SISize, - SI2->getTrueValue(), V2Size); + aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo, + SI2->getTrueValue(), V2Size, V2TBAAInfo); if (Alias == MayAlias) return MayAlias; AliasResult ThisAlias = - aliasCheck(SI->getFalseValue(), SISize, - SI2->getFalseValue(), V2Size); - if (ThisAlias != Alias) - return MayAlias; - return Alias; + aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo, + SI2->getFalseValue(), V2Size, V2TBAAInfo); + return MergeAliasResults(ThisAlias, Alias); } // If both arms of the Select node NoAlias or MustAlias V2, then returns // NoAlias / MustAlias. Otherwise, returns MayAlias. AliasResult Alias = - aliasCheck(SI->getTrueValue(), SISize, V2, V2Size); + aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo); if (Alias == MayAlias) return MayAlias; + AliasResult ThisAlias = - aliasCheck(SI->getFalseValue(), SISize, V2, V2Size); - if (ThisAlias != Alias) - return MayAlias; - return Alias; + aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo); + return MergeAliasResults(ThisAlias, Alias); } // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction // against another. AliasAnalysis::AliasResult -BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize, - const Value *V2, unsigned V2Size) { - // The PHI node has already been visited, avoid recursion any further. - if (!VisitedPHIs.insert(PN)) - return MayAlias; - +BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, + const MDNode *PNTBAAInfo, + const Value *V2, uint64_t V2Size, + const MDNode *V2TBAAInfo) { // If the values are PHIs in the same block, we can do a more precise // as well as efficient check: just check for aliases between the values // on corresponding edges. if (const PHINode *PN2 = dyn_cast(V2)) if (PN2->getParent() == PN->getParent()) { AliasResult Alias = - aliasCheck(PN->getIncomingValue(0), PNSize, + aliasCheck(PN->getIncomingValue(0), PNSize, PNTBAAInfo, PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)), - V2Size); + V2Size, V2TBAAInfo); if (Alias == MayAlias) return MayAlias; for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) { AliasResult ThisAlias = - aliasCheck(PN->getIncomingValue(i), PNSize, + aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo, PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), - V2Size); - if (ThisAlias != Alias) - return MayAlias; + V2Size, V2TBAAInfo); + Alias = MergeAliasResults(ThisAlias, Alias); + if (Alias == MayAlias) + break; } return Alias; } @@ -746,7 +1054,8 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize, V1Srcs.push_back(PV1); } - AliasResult Alias = aliasCheck(V2, V2Size, V1Srcs[0], PNSize); + AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo, + V1Srcs[0], PNSize, PNTBAAInfo); // Early exit if the check of the first PHI source against V2 is MayAlias. // Other results are not possible. if (Alias == MayAlias) @@ -757,14 +1066,11 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize, for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) { Value *V = V1Srcs[i]; - // If V2 is a PHI, the recursive case will have been caught in the - // above aliasCheck call, so these subsequent calls to aliasCheck - // don't need to assume that V2 is being visited recursively. - VisitedPHIs.erase(V2); - - AliasResult ThisAlias = aliasCheck(V2, V2Size, V, PNSize); - if (ThisAlias != Alias || ThisAlias == MayAlias) - return MayAlias; + AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo, + V, PNSize, PNTBAAInfo); + Alias = MergeAliasResults(ThisAlias, Alias); + if (Alias == MayAlias) + break; } return Alias; @@ -774,8 +1080,15 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize, // such as array references. // AliasAnalysis::AliasResult -BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size, - const Value *V2, unsigned V2Size) { +BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, + const MDNode *V1TBAAInfo, + const Value *V2, uint64_t V2Size, + const MDNode *V2TBAAInfo) { + // If either of the memory references is empty, it doesn't matter what the + // pointer values are. + if (V1Size == 0 || V2Size == 0) + return NoAlias; + // Strip off any casts if they exist. V1 = V1->stripPointerCasts(); V2 = V2->stripPointerCasts(); @@ -783,12 +1096,12 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size, // Are we checking for alias of the same value? if (V1 == V2) return MustAlias; - if (!isa(V1->getType()) || !isa(V2->getType())) + if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy()) return NoAlias; // Scalars cannot alias each other // Figure out what objects these things are pointing to if we can. - const Value *O1 = V1->getUnderlyingObject(); - const Value *O2 = V2->getUnderlyingObject(); + const Value *O1 = GetUnderlyingObject(V1, TD); + const Value *O2 = GetUnderlyingObject(V2, TD); // Null values in the default address space don't point to any object, so they // don't alias any other pointer. @@ -809,39 +1122,49 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size, (isa(O2) && isIdentifiedObject(O1) && !isa(O1))) return NoAlias; - // Arguments can't alias with local allocations or noalias calls. - if ((isa(O1) && (isa(O2) || isNoAliasCall(O2))) || - (isa(O2) && (isa(O1) || isNoAliasCall(O1)))) + // Arguments can't alias with local allocations or noalias calls + // in the same function. + if (((isa(O1) && (isa(O2) || isNoAliasCall(O2))) || + (isa(O2) && (isa(O1) || isNoAliasCall(O1))))) return NoAlias; // Most objects can't alias null. - if ((isa(V2) && isKnownNonNull(O1)) || - (isa(V1) && isKnownNonNull(O2))) + if ((isa(O2) && isKnownNonNull(O1)) || + (isa(O1) && isKnownNonNull(O2))) return NoAlias; - } + // If one pointer is the result of a call/invoke or load and the other is a + // non-escaping local object within the same function, then we know the + // object couldn't escape to a point where the call could return it. + // + // Note that if the pointers are in different functions, there are a + // variety of complications. A call with a nocapture argument may still + // temporary store the nocapture argument's value in a temporary memory + // location if that memory location doesn't escape. Or it may pass a + // nocapture value to other functions as long as they don't capture it. + if (isEscapeSource(O1) && isNonEscapingLocalObject(O2)) + return NoAlias; + if (isEscapeSource(O2) && isNonEscapingLocalObject(O1)) + return NoAlias; + } + // If the size of one access is larger than the entire object on the other // side, then we know such behavior is undefined and can assume no alias. if (TD) - if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, *TD)) || - (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, *TD))) + if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD)) || + (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD))) return NoAlias; - // If one pointer is the result of a call/invoke or load and the other is a - // non-escaping local object, then we know the object couldn't escape to a - // point where the call could return it. The load case works because - // isNonEscapingLocalObject considers all stores to be escapes (it - // passes true for the StoreCaptures argument to PointerMayBeCaptured). - if (O1 != O2) { - if ((isa(O1) || isa(O1) || isa(O1) || - isa(O1)) && - isNonEscapingLocalObject(O2)) - return NoAlias; - if ((isa(O2) || isa(O2) || isa(O2) || - isa(O2)) && - isNonEscapingLocalObject(O1)) - return NoAlias; - } + // Check the cache before climbing up use-def chains. This also terminates + // otherwise infinitely recursive queries. + LocPair Locs(Location(V1, V1Size, V1TBAAInfo), + Location(V2, V2Size, V2TBAAInfo)); + if (V1 > V2) + std::swap(Locs.first, Locs.second); + std::pair Pair = + AliasCache.insert(std::make_pair(Locs, MayAlias)); + if (!Pair.second) + return Pair.first->second; // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the // GEP can't simplify, we don't even look at the PHI cases. @@ -850,25 +1173,41 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size, std::swap(V1Size, V2Size); std::swap(O1, O2); } - if (const GEPOperator *GV1 = dyn_cast(V1)) - return aliasGEP(GV1, V1Size, V2, V2Size, O1, O2); + if (const GEPOperator *GV1 = dyn_cast(V1)) { + AliasResult Result = aliasGEP(GV1, V1Size, V2, V2Size, V2TBAAInfo, O1, O2); + if (Result != MayAlias) return AliasCache[Locs] = Result; + } if (isa(V2) && !isa(V1)) { std::swap(V1, V2); std::swap(V1Size, V2Size); } - if (const PHINode *PN = dyn_cast(V1)) - return aliasPHI(PN, V1Size, V2, V2Size); + if (const PHINode *PN = dyn_cast(V1)) { + AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo, + V2, V2Size, V2TBAAInfo); + if (Result != MayAlias) return AliasCache[Locs] = Result; + } if (isa(V2) && !isa(V1)) { std::swap(V1, V2); std::swap(V1Size, V2Size); } - if (const SelectInst *S1 = dyn_cast(V1)) - return aliasSelect(S1, V1Size, V2, V2Size); + if (const SelectInst *S1 = dyn_cast(V1)) { + AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo, + V2, V2Size, V2TBAAInfo); + if (Result != MayAlias) return AliasCache[Locs] = Result; + } - return MayAlias; + // If both pointers are pointing into the same object and one of them + // accesses is accessing the entire object, then the accesses must + // overlap in some way. + if (TD && O1 == O2) + if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD)) || + (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD))) + return AliasCache[Locs] = PartialAlias; + + AliasResult Result = + AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo), + Location(V2, V2Size, V2TBAAInfo)); + return AliasCache[Locs] = Result; } - -// Make sure that anything that uses AliasAnalysis pulls in this file. -DEFINING_FILE_FOR(BasicAliasAnalysis)