diff options
Diffstat (limited to 'contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp')
| -rw-r--r-- | contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp | 1309 |
1 files changed, 1309 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp new file mode 100644 index 000000000000..b2c20110e90e --- /dev/null +++ b/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp @@ -0,0 +1,1309 @@ +//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// 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/Passes.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/CaptureTracking.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/MemoryBuiltins.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GlobalAlias.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Operator.h" +#include "llvm/Pass.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/GetElementPtrTypeIterator.h" +#include "llvm/Target/TargetLibraryInfo.h" +#include <algorithm> +using namespace llvm; + +//===----------------------------------------------------------------------===// +// Useful predicates +//===----------------------------------------------------------------------===// + +/// isNonEscapingLocalObject - Return true if the pointer is to a function-local +/// object that never escapes from the function. +static bool isNonEscapingLocalObject(const Value *V) { + // If this is a local allocation, check to see if it escapes. + if (isa<AllocaInst>(V) || isNoAliasCall(V)) + // Set StoreCaptures to True so that we can assume in our callers that the + // pointer is not the result of a load instruction. Currently + // PointerMayBeCaptured doesn't have any special analysis for the + // StoreCaptures=false case; if it did, our callers could be refined to be + // more precise. + return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); + + // If this is an argument that corresponds to a byval or noalias argument, + // then it has not escaped before entering the function. Check if it escapes + // inside the function. + if (const Argument *A = dyn_cast<Argument>(V)) + if (A->hasByValAttr() || A->hasNoAliasAttr()) + // Note even if the argument is marked nocapture we still need to check + // for copies made inside the function. The nocapture attribute only + // specifies that there are no copies made that outlive the function. + return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); + + 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<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V)) + return true; + + // The load case works because isNonEscapingLocalObject considers all + // stores to be escapes (it passes true for the StoreCaptures argument + // to PointerMayBeCaptured). + if (isa<LoadInst>(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 DataLayout &TD, + const TargetLibraryInfo &TLI, + bool RoundToAlign = false) { + uint64_t Size; + if (getObjectSize(V, Size, &TD, &TLI, RoundToAlign)) + return Size; + return AliasAnalysis::UnknownSize; +} + +/// 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 DataLayout &TD, + const TargetLibraryInfo &TLI) { + // Note that the meanings of the "object" are slightly different in the + // following contexts: + // c1: llvm::getObjectSize() + // c2: llvm.objectsize() intrinsic + // c3: isObjectSmallerThan() + // c1 and c2 share the same meaning; however, the meaning of "object" in c3 + // refers to the "entire object". + // + // Consider this example: + // char *p = (char*)malloc(100) + // char *q = p+80; + // + // In the context of c1 and c2, the "object" pointed by q refers to the + // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20. + // + // However, in the context of c3, the "object" refers to the chunk of memory + // being allocated. So, the "object" has 100 bytes, and q points to the middle + // the "object". In case q is passed to isObjectSmallerThan() as the 1st + // parameter, before the llvm::getObjectSize() is called to get the size of + // entire object, we should: + // - either rewind the pointer q to the base-address of the object in + // question (in this case rewind to p), or + // - just give up. It is up to caller to make sure the pointer is pointing + // to the base address the object. + // + // We go for 2nd option for simplicity. + if (!isIdentifiedObject(V)) + return false; + + // This function needs to use the aligned object size because we allow + // reads a bit past the end given sufficient alignment. + uint64_t ObjectSize = getObjectSize(V, TD, TLI, /*RoundToAlign*/true); + + return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size; +} + +/// 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 DataLayout &TD, const TargetLibraryInfo &TLI) { + uint64_t ObjectSize = getObjectSize(V, TD, TLI); + return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size; +} + +/// isIdentifiedFunctionLocal - Return true if V is umabigously identified +/// at the function-level. Different IdentifiedFunctionLocals can't alias. +/// Further, an IdentifiedFunctionLocal can not alias with any function +/// arguments other than itself, which is not neccessarily true for +/// IdentifiedObjects. +static bool isIdentifiedFunctionLocal(const Value *V) +{ + return isa<AllocaInst>(V) || isNoAliasCall(V) || isNoAliasArgument(V); +} + + +//===----------------------------------------------------------------------===// +// GetElementPtr Instruction Decomposition and Analysis +//===----------------------------------------------------------------------===// + +namespace { + enum ExtensionKind { + EK_NotExtended, + EK_SignExt, + EK_ZeroExt + }; + + struct VariableGEPIndex { + const Value *V; + ExtensionKind Extension; + int64_t Scale; + + bool operator==(const VariableGEPIndex &Other) const { + return V == Other.V && Extension == Other.Extension && + Scale == Other.Scale; + } + + bool operator!=(const VariableGEPIndex &Other) const { + return !operator==(Other); + } + }; +} + + +/// GetLinearExpression - Analyze the specified value as a linear expression: +/// "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 DataLayout &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<BinaryOperator>(V)) { + if (ConstantInt *RHSC = dyn_cast<ConstantInt>(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, Extension, + TD, Depth+1); + Offset += RHSC->getValue(); + return V; + 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<SExtInst>(V) && Extension != EK_ZeroExt) || + (isa<ZExtInst>(V) && Extension != EK_SignExt)) { + Value *CastOp = cast<CastInst>(V)->getOperand(0); + unsigned OldWidth = Scale.getBitWidth(); + unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits(); + Scale = Scale.trunc(SmallWidth); + Offset = Offset.trunc(SmallWidth); + Extension = isa<SExtInst>(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; +} + +/// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it +/// 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 DataLayout is around, this function is capable of analyzing everything +/// that GetUnderlyingObject can look through. When not, it just looks +/// through pointer casts. +/// +static const Value * +DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, + SmallVectorImpl<VariableGEPIndex> &VarIndices, + const DataLayout *TD) { + // Limit recursion depth to limit compile time in crazy cases. + unsigned MaxLookup = 6; + + BaseOffs = 0; + do { + // See if this is a bitcast or GEP. + const Operator *Op = dyn_cast<Operator>(V); + if (Op == 0) { + // The only non-operator case we can handle are GlobalAliases. + if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { + if (!GA->mayBeOverridden()) { + V = GA->getAliasee(); + continue; + } + } + return V; + } + + if (Op->getOpcode() == Instruction::BitCast) { + V = Op->getOperand(0); + continue; + } + + const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op); + 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<Instruction>(V)) + // TODO: Get a DominatorTree and use it here. + if (const Value *Simplified = + SimplifyInstruction(const_cast<Instruction *>(I), TD)) { + V = Simplified; + continue; + } + + return V; + } + + // Don't attempt to analyze GEPs over unsized objects. + if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized()) + return V; + + // If we are lacking DataLayout information, we can't compute the offets of + // elements computed by GEPs. However, we can handle bitcast equivalent + // GEPs. + if (TD == 0) { + if (!GEPOp->hasAllZeroIndices()) + return V; + V = GEPOp->getOperand(0); + continue; + } + + unsigned AS = GEPOp->getPointerAddressSpace(); + // 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 = 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 (StructType *STy = dyn_cast<StructType>(*GTI++)) { + // For a struct, add the member offset. + unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue(); + if (FieldNo == 0) continue; + + BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo); + continue; + } + + // For an array/pointer, add the element offset, explicitly scaled. + if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) { + if (CIdx->isZero()) continue; + BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue(); + continue; + } + + 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 = Index->getType()->getIntegerBitWidth(); + if (TD->getPointerSizeInBits(AS) > 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, Extension, + *TD, 0); + + // 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 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].V == Index && + VarIndices[i].Extension == Extension) { + Scale += VarIndices[i].Scale; + VarIndices.erase(VarIndices.begin()+i); + break; + } + } + + // Make sure that we have a scale that makes sense for this target's + // pointer size. + if (unsigned ShiftBits = 64 - TD->getPointerSizeInBits(AS)) { + Scale <<= ShiftBits; + Scale = (int64_t)Scale >> ShiftBits; + } + + if (Scale) { + VariableGEPIndex Entry = {Index, Extension, + static_cast<int64_t>(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; +} + +/// 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 GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest, + const SmallVectorImpl<VariableGEPIndex> &Src) { + if (Src.empty()) return; + + for (unsigned i = 0, e = Src.size(); i != e; ++i) { + 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].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].Scale != Scale) + Dest[j].Scale -= Scale; + else + Dest.erase(Dest.begin()+j); + Scale = 0; + break; + } + + // If we didn't consume this entry, add it to the end of the Dest list. + 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<Instruction>(V)) + return inst->getParent()->getParent(); + + if (const Argument *arg = dyn_cast<Argument>(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) { + initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry()); + } + + virtual void initializePass() { + InitializeAliasAnalysis(this); + } + + virtual void getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired<AliasAnalysis>(); + AU.addRequired<TargetLibraryInfo>(); + } + + 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 rarely has more than 1 or 2 elements, always use + // shrink_and_clear so it quickly returns to the inline capacity of the + // SmallDenseMap if it ever grows larger. + // FIXME: This should really be shrink_to_inline_capacity_and_clear(). + AliasCache.shrink_and_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<Location, Location> LocPair; + typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy; + AliasCacheTy AliasCache; + + // Visited - Track instructions visited by pointsToConstantMemory. + SmallPtrSet<const Value*, 16> 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 MDNode *V1TBAAInfo, + 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_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa", + "Basic Alias Analysis (stateless AA impl)", + false, true, false) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) +INITIALIZE_AG_PASS_END(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<const Value *, 16> 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<AllocaInst>(V)) + continue; + + // A global constant counts as local memory for our purposes. + if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(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<SelectInst>(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<PHINode>(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/IR/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<AllocaInst>(Object)) + if (const CallInst *CI = dyn_cast<CallInst>(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<Constant>(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.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo))) + 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(*CI), Location(Object))) { + PassedAsArg = true; + break; + } + } + + if (!PassedAsArg) + return NoModRef; + } + + const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>(); + ModRefResult Min = ModRef; + + // Finally, handle specific knowledge of intrinsics. + const IntrinsicInst *II = dyn_cast<IntrinsicInst>(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<ConstantInt>(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<ConstantInt>(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::lifetime_start: + case Intrinsic::lifetime_end: + case Intrinsic::invariant_start: { + uint64_t PtrSize = + cast<ConstantInt>(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<ConstantInt>(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; + } + } + + // We can bound the aliasing properties of memset_pattern16 just as we can + // for memcpy/memset. This is particularly important because the + // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16 + // whenever possible. + else if (TLI.has(LibFunc::memset_pattern16) && + CS.getCalledFunction() && + CS.getCalledFunction()->getName() == "memset_pattern16") { + const Function *MS = CS.getCalledFunction(); + FunctionType *MemsetType = MS->getFunctionType(); + if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 && + isa<PointerType>(MemsetType->getParamType(0)) && + isa<PointerType>(MemsetType->getParamType(1)) && + isa<IntegerType>(MemsetType->getParamType(2))) { + uint64_t Len = UnknownSize; + if (const ConstantInt *LenCI = dyn_cast<ConstantInt>(CS.getArgument(2))) + Len = LenCI->getZExtValue(); + const Value *Dest = CS.getArgument(0); + const Value *Src = CS.getArgument(1); + // If it can't overlap the source dest, then it doesn't modref the loc. + if (isNoAlias(Location(Dest, Len), Loc)) { + // Always reads 16 bytes of the source. + if (isNoAlias(Location(Src, 16), Loc)) + return NoModRef; + // If it can't overlap the dest, then worst case it reads the loc. + Min = Ref; + // Always reads 16 bytes of the source. + } else if (isNoAlias(Location(Src, 16), Loc)) { + // If it can't overlap the source, then worst case it mutates the loc. + Min = Mod; + } + } + } + + // The AliasAnalysis base class has some smarts, lets use them. + return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min); +} + +static bool areVarIndicesEqual(SmallVectorImpl<VariableGEPIndex> &Indices1, + SmallVectorImpl<VariableGEPIndex> &Indices2) { + unsigned Size1 = Indices1.size(); + unsigned Size2 = Indices2.size(); + + if (Size1 != Size2) + return false; + + for (unsigned I = 0; I != Size1; ++I) + if (Indices1[I] != Indices2[I]) + return false; + + return true; +} + +/// 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 GetUnderlyingObject(GEP1, TD), +/// UnderlyingV2 is the same for V2. +/// +AliasAnalysis::AliasResult +BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, + const MDNode *V1TBAAInfo, + const Value *V2, uint64_t V2Size, + const MDNode *V2TBAAInfo, + const Value *UnderlyingV1, + const Value *UnderlyingV2) { + int64_t GEP1BaseOffset; + SmallVector<VariableGEPIndex, 4> GEP1VariableIndices; + + // If we have two gep instructions with must-alias or not-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<GEPOperator>(V2)) { + // Do the base pointers alias? + AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0, + UnderlyingV2, UnknownSize, 0); + + // Check for geps of non-aliasing underlying pointers where the offsets are + // identical. + if ((BaseAlias == MayAlias) && V1Size == V2Size) { + // Do the base pointers alias assuming type and size. + AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size, + V1TBAAInfo, UnderlyingV2, + V2Size, V2TBAAInfo); + if (PreciseBaseAlias == NoAlias) { + // See if the computed offset from the common pointer tells us about the + // relation of the resulting pointer. + int64_t GEP2BaseOffset; + SmallVector<VariableGEPIndex, 4> GEP2VariableIndices; + const Value *GEP2BasePtr = + DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD); + const Value *GEP1BasePtr = + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. + if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { + assert(TD == 0 && + "DecomposeGEPExpression and GetUnderlyingObject disagree!"); + return MayAlias; + } + // Same offsets. + if (GEP1BaseOffset == GEP2BaseOffset && + areVarIndicesEqual(GEP1VariableIndices, GEP2VariableIndices)) + return NoAlias; + GEP1VariableIndices.clear(); + } + } + + // If we get a No or May, then return it immediately, no amount of analysis + // will improve this situation. + if (BaseAlias != MustAlias) return BaseAlias; + + // Otherwise, we have a MustAlias. Since the base pointers alias each other + // exactly, see if the computed offset from the common pointer tells us + // about the relation of the resulting pointer. + const Value *GEP1BasePtr = + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); + + int64_t GEP2BaseOffset; + SmallVector<VariableGEPIndex, 4> GEP2VariableIndices; + const Value *GEP2BasePtr = + DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD); + + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. + if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { + assert(TD == 0 && + "DecomposeGEPExpression and GetUnderlyingObject disagree!"); + return MayAlias; + } + + // Subtract the GEP2 pointer from the GEP1 pointer to find out their + // symbolic difference. + GEP1BaseOffset -= GEP2BaseOffset; + 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. + + // If both accesses are unknown size, we can't do anything useful here. + if (V1Size == UnknownSize && V2Size == UnknownSize) + return MayAlias; + + 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 + // cannot alias per GEP semantics: "A pointer value formed from a + // getelementptr instruction is associated with the addresses associated + // with the first operand of the getelementptr". + return R; + + const Value *GEP1BasePtr = + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); + + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. + if (GEP1BasePtr != UnderlyingV1) { + assert(TD == 0 && + "DecomposeGEPExpression and GetUnderlyingObject disagree!"); + return MayAlias; + } + } + + // In the two GEP Case, if there is no difference in the offsets of the + // computed pointers, the resultant pointers are a must alias. This + // hapens when we have two lexically identical GEP's (for example). + // + // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 + // must aliases the GEP, the end result is a must alias also. + if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty()) + return MustAlias; + + // If there is a constant 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 the difference is + // greater, we know they do not overlap. + if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) { + if (GEP1BaseOffset >= 0) { + if (V2Size != UnknownSize) { + if ((uint64_t)GEP1BaseOffset < V2Size) + return PartialAlias; + return NoAlias; + } + } else { + if (V1Size != UnknownSize) { + if (-(uint64_t)GEP1BaseOffset < V1Size) + return PartialAlias; + return NoAlias; + } + } + } + + // Try to distinguish something like &A[i][1] against &A[42][0]. + // Grab the least significant bit set in any of the scales. + if (!GEP1VariableIndices.empty()) { + uint64_t Modulo = 0; + for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i) + Modulo |= (uint64_t)GEP1VariableIndices[i].Scale; + Modulo = Modulo ^ (Modulo & (Modulo - 1)); + + // We can compute the difference between the two addresses + // mod Modulo. Check whether that difference guarantees that the + // two locations do not alias. + uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1); + if (V1Size != UnknownSize && V2Size != UnknownSize && + ModOffset >= V2Size && V1Size <= Modulo - ModOffset) + return NoAlias; + } + + // 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 or malloc'd memory. + 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, 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<SelectInst>(V2)) + if (SI->getCondition() == SI2->getCondition()) { + AliasResult Alias = + aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo, + SI2->getTrueValue(), V2Size, V2TBAAInfo); + if (Alias == MayAlias) + return MayAlias; + AliasResult ThisAlias = + 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(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo); + if (Alias == MayAlias) + return MayAlias; + + AliasResult ThisAlias = + 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, 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<PHINode>(V2)) + if (PN2->getParent() == PN->getParent()) { + LocPair Locs(Location(PN, PNSize, PNTBAAInfo), + Location(V2, V2Size, V2TBAAInfo)); + if (PN > V2) + std::swap(Locs.first, Locs.second); + // Analyse the PHIs' inputs under the assumption that the PHIs are + // NoAlias. + // If the PHIs are May/MustAlias there must be (recursively) an input + // operand from outside the PHIs' cycle that is MayAlias/MustAlias or + // there must be an operation on the PHIs within the PHIs' value cycle + // that causes a MayAlias. + // Pretend the phis do not alias. + AliasResult Alias = NoAlias; + assert(AliasCache.count(Locs) && + "There must exist an entry for the phi node"); + AliasResult OrigAliasResult = AliasCache[Locs]; + AliasCache[Locs] = NoAlias; + + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + AliasResult ThisAlias = + aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo, + PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), + V2Size, V2TBAAInfo); + Alias = MergeAliasResults(ThisAlias, Alias); + if (Alias == MayAlias) + break; + } + + // Reset if speculation failed. + if (Alias != NoAlias) + AliasCache[Locs] = OrigAliasResult; + + return Alias; + } + + SmallPtrSet<Value*, 4> UniqueSrc; + SmallVector<Value*, 4> V1Srcs; + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + Value *PV1 = PN->getIncomingValue(i); + if (isa<PHINode>(PV1)) + // If any of the source itself is a PHI, return MayAlias conservatively + // to avoid compile time explosion. The worst possible case is if both + // sides are PHI nodes. In which case, this is O(m x n) time where 'm' + // and 'n' are the number of PHI sources. + return MayAlias; + if (UniqueSrc.insert(PV1)) + V1Srcs.push_back(PV1); + } + + 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) + return MayAlias; + + // If all sources of the PHI node NoAlias or MustAlias V2, then returns + // NoAlias / MustAlias. Otherwise, returns MayAlias. + for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) { + Value *V = V1Srcs[i]; + + AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo, + V, PNSize, PNTBAAInfo); + Alias = MergeAliasResults(ThisAlias, Alias); + if (Alias == MayAlias) + break; + } + + return Alias; +} + +// aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases, +// such as array references. +// +AliasAnalysis::AliasResult +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(); + + // Are we checking for alias of the same value? + if (V1 == V2) return MustAlias; + + 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 = 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. + if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1)) + if (CPN->getType()->getAddressSpace() == 0) + return NoAlias; + if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2)) + if (CPN->getType()->getAddressSpace() == 0) + return NoAlias; + + if (O1 != O2) { + // If V1/V2 point to two different objects we know that we have no alias. + if (isIdentifiedObject(O1) && isIdentifiedObject(O2)) + return NoAlias; + + // Constant pointers can't alias with non-const isIdentifiedObject objects. + if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) || + (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1))) + return NoAlias; + + // Function arguments can't alias with things that are known to be + // unambigously identified at the function level. + if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) || + (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1))) + return NoAlias; + + // Most objects can't alias null. + if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) || + (isa<ConstantPointerNull>(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 != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD, *TLI)) || + (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD, *TLI))) + 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<AliasCacheTy::iterator, bool> 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. + if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) { + std::swap(V1, V2); + std::swap(V1Size, V2Size); + std::swap(O1, O2); + std::swap(V1TBAAInfo, V2TBAAInfo); + } + if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) { + AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2); + if (Result != MayAlias) return AliasCache[Locs] = Result; + } + + if (isa<PHINode>(V2) && !isa<PHINode>(V1)) { + std::swap(V1, V2); + std::swap(V1Size, V2Size); + std::swap(V1TBAAInfo, V2TBAAInfo); + } + if (const PHINode *PN = dyn_cast<PHINode>(V1)) { + AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo, + V2, V2Size, V2TBAAInfo); + if (Result != MayAlias) return AliasCache[Locs] = Result; + } + + if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) { + std::swap(V1, V2); + std::swap(V1Size, V2Size); + std::swap(V1TBAAInfo, V2TBAAInfo); + } + if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) { + AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo, + V2, V2Size, V2TBAAInfo); + if (Result != MayAlias) return AliasCache[Locs] = Result; + } + + // 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, *TLI)) || + (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD, *TLI))) + return AliasCache[Locs] = PartialAlias; + + AliasResult Result = + AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo), + Location(V2, V2Size, V2TBAAInfo)); + return AliasCache[Locs] = Result; +} |