X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FAliasAnalysis.cpp;h=054930c0e1936c2ec64450dd89defbe6990b34e9;hb=55ec2218c448ef9e0d09b5534885b6d2a9786a73;hp=57867dd6eedd5466949419308d1fb1b0e0aeb907;hpb=762d2f0897a453bab92800b7aaadb0872e98aabd;p=oota-llvm.git diff --git a/lib/Analysis/AliasAnalysis.cpp b/lib/Analysis/AliasAnalysis.cpp index 57867dd6eed..054930c0e19 100644 --- a/lib/Analysis/AliasAnalysis.cpp +++ b/lib/Analysis/AliasAnalysis.cpp @@ -1,5 +1,12 @@ //===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==// // +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// // This file implements the generic AliasAnalysis interface which is used as the // common interface used by all clients and implementations of alias analysis. // @@ -17,46 +24,460 @@ // //===----------------------------------------------------------------------===// -#include "llvm/Analysis/BasicAliasAnalysis.h" -#include "llvm/BasicBlock.h" -#include "llvm/Support/InstVisitor.h" -#include "llvm/iMemory.h" -#include "llvm/iOther.h" -#include "llvm/Constants.h" -#include "llvm/GlobalValue.h" -#include "llvm/DerivedTypes.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/CaptureTracking.h" +#include "llvm/Analysis/Dominators.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Type.h" +#include "llvm/Pass.h" +#include "llvm/Target/TargetLibraryInfo.h" +using namespace llvm; // Register the AliasAnalysis interface, providing a nice name to refer to. -namespace { - RegisterAnalysisGroup Z("Alias Analysis"); +INITIALIZE_ANALYSIS_GROUP(AliasAnalysis, "Alias Analysis", NoAA) +char AliasAnalysis::ID = 0; + +//===----------------------------------------------------------------------===// +// Default chaining methods +//===----------------------------------------------------------------------===// + +AliasAnalysis::AliasResult +AliasAnalysis::alias(const Location &LocA, const Location &LocB) { + assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); + return AA->alias(LocA, LocB); } -// CanModify - Define a little visitor class that is used to check to see if -// arbitrary chunks of code can modify a specified pointer. -// -namespace { - struct CanModify : public InstVisitor { - AliasAnalysis &AA; - const Value *Ptr; +bool AliasAnalysis::pointsToConstantMemory(const Location &Loc, + bool OrLocal) { + assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); + return AA->pointsToConstantMemory(Loc, OrLocal); +} + +void AliasAnalysis::deleteValue(Value *V) { + assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); + AA->deleteValue(V); +} + +void AliasAnalysis::copyValue(Value *From, Value *To) { + assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); + AA->copyValue(From, To); +} + +void AliasAnalysis::addEscapingUse(Use &U) { + assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); + AA->addEscapingUse(U); +} - CanModify(AliasAnalysis *aa, const Value *ptr) - : AA(*aa), Ptr(ptr) {} - bool visitInvokeInst(InvokeInst &II) { - return AA.canInvokeModify(II, Ptr); +AliasAnalysis::ModRefResult +AliasAnalysis::getModRefInfo(ImmutableCallSite CS, + const Location &Loc) { + assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); + + ModRefBehavior MRB = getModRefBehavior(CS); + if (MRB == DoesNotAccessMemory) + return NoModRef; + + ModRefResult Mask = ModRef; + if (onlyReadsMemory(MRB)) + Mask = Ref; + + if (onlyAccessesArgPointees(MRB)) { + bool doesAlias = false; + if (doesAccessArgPointees(MRB)) { + MDNode *CSTag = CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa); + for (ImmutableCallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end(); + AI != AE; ++AI) { + const Value *Arg = *AI; + if (!Arg->getType()->isPointerTy()) + continue; + Location CSLoc(Arg, UnknownSize, CSTag); + if (!isNoAlias(CSLoc, Loc)) { + doesAlias = true; + break; + } + } } - bool visitCallInst(CallInst &CI) { - return AA.canCallModify(CI, Ptr); + if (!doesAlias) + return NoModRef; + } + + // If Loc is a constant memory location, the call definitely could not + // modify the memory location. + if ((Mask & Mod) && pointsToConstantMemory(Loc)) + Mask = ModRefResult(Mask & ~Mod); + + // If this is the end of the chain, don't forward. + if (!AA) return Mask; + + // Otherwise, fall back to the next AA in the chain. But we can merge + // in any mask we've managed to compute. + return ModRefResult(AA->getModRefInfo(CS, Loc) & Mask); +} + +AliasAnalysis::ModRefResult +AliasAnalysis::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) { + assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); + + // If CS1 or CS2 are readnone, they don't interact. + ModRefBehavior CS1B = getModRefBehavior(CS1); + if (CS1B == DoesNotAccessMemory) return NoModRef; + + ModRefBehavior CS2B = getModRefBehavior(CS2); + if (CS2B == DoesNotAccessMemory) return NoModRef; + + // If they both only read from memory, there is no dependence. + if (onlyReadsMemory(CS1B) && onlyReadsMemory(CS2B)) + return NoModRef; + + AliasAnalysis::ModRefResult Mask = ModRef; + + // If CS1 only reads memory, the only dependence on CS2 can be + // from CS1 reading memory written by CS2. + if (onlyReadsMemory(CS1B)) + Mask = ModRefResult(Mask & Ref); + + // If CS2 only access memory through arguments, accumulate the mod/ref + // information from CS1's references to the memory referenced by + // CS2's arguments. + if (onlyAccessesArgPointees(CS2B)) { + AliasAnalysis::ModRefResult R = NoModRef; + if (doesAccessArgPointees(CS2B)) { + MDNode *CS2Tag = CS2.getInstruction()->getMetadata(LLVMContext::MD_tbaa); + for (ImmutableCallSite::arg_iterator + I = CS2.arg_begin(), E = CS2.arg_end(); I != E; ++I) { + const Value *Arg = *I; + if (!Arg->getType()->isPointerTy()) + continue; + Location CS2Loc(Arg, UnknownSize, CS2Tag); + R = ModRefResult((R | getModRefInfo(CS1, CS2Loc)) & Mask); + if (R == Mask) + break; + } } - bool visitStoreInst(StoreInst &SI) { - return AA.alias(Ptr, SI.getOperand(1)); + return R; + } + + // If CS1 only accesses memory through arguments, check if CS2 references + // any of the memory referenced by CS1's arguments. If not, return NoModRef. + if (onlyAccessesArgPointees(CS1B)) { + AliasAnalysis::ModRefResult R = NoModRef; + if (doesAccessArgPointees(CS1B)) { + MDNode *CS1Tag = CS1.getInstruction()->getMetadata(LLVMContext::MD_tbaa); + for (ImmutableCallSite::arg_iterator + I = CS1.arg_begin(), E = CS1.arg_end(); I != E; ++I) { + const Value *Arg = *I; + if (!Arg->getType()->isPointerTy()) + continue; + Location CS1Loc(Arg, UnknownSize, CS1Tag); + if (getModRefInfo(CS2, CS1Loc) != NoModRef) { + R = Mask; + break; + } + } } + if (R == NoModRef) + return R; + } + + // If this is the end of the chain, don't forward. + if (!AA) return Mask; + + // Otherwise, fall back to the next AA in the chain. But we can merge + // in any mask we've managed to compute. + return ModRefResult(AA->getModRefInfo(CS1, CS2) & Mask); +} + +AliasAnalysis::ModRefBehavior +AliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { + assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); + + ModRefBehavior Min = UnknownModRefBehavior; + + // Call back into the alias analysis with the other form of getModRefBehavior + // to see if it can give a better response. + if (const Function *F = CS.getCalledFunction()) + Min = getModRefBehavior(F); + + // If this is the end of the chain, don't forward. + if (!AA) return Min; + + // Otherwise, fall back to the next AA in the chain. But we can merge + // in any result we've managed to compute. + return ModRefBehavior(AA->getModRefBehavior(CS) & Min); +} + +AliasAnalysis::ModRefBehavior +AliasAnalysis::getModRefBehavior(const Function *F) { + assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); + return AA->getModRefBehavior(F); +} + +//===----------------------------------------------------------------------===// +// AliasAnalysis non-virtual helper method implementation +//===----------------------------------------------------------------------===// + +AliasAnalysis::Location AliasAnalysis::getLocation(const LoadInst *LI) { + return Location(LI->getPointerOperand(), + getTypeStoreSize(LI->getType()), + LI->getMetadata(LLVMContext::MD_tbaa)); +} + +AliasAnalysis::Location AliasAnalysis::getLocation(const StoreInst *SI) { + return Location(SI->getPointerOperand(), + getTypeStoreSize(SI->getValueOperand()->getType()), + SI->getMetadata(LLVMContext::MD_tbaa)); +} + +AliasAnalysis::Location AliasAnalysis::getLocation(const VAArgInst *VI) { + return Location(VI->getPointerOperand(), + UnknownSize, + VI->getMetadata(LLVMContext::MD_tbaa)); +} + +AliasAnalysis::Location +AliasAnalysis::getLocation(const AtomicCmpXchgInst *CXI) { + return Location(CXI->getPointerOperand(), + getTypeStoreSize(CXI->getCompareOperand()->getType()), + CXI->getMetadata(LLVMContext::MD_tbaa)); +} + +AliasAnalysis::Location +AliasAnalysis::getLocation(const AtomicRMWInst *RMWI) { + return Location(RMWI->getPointerOperand(), + getTypeStoreSize(RMWI->getValOperand()->getType()), + RMWI->getMetadata(LLVMContext::MD_tbaa)); +} + +AliasAnalysis::Location +AliasAnalysis::getLocationForSource(const MemTransferInst *MTI) { + uint64_t Size = UnknownSize; + if (ConstantInt *C = dyn_cast(MTI->getLength())) + Size = C->getValue().getZExtValue(); + + // memcpy/memmove can have TBAA tags. For memcpy, they apply + // to both the source and the destination. + MDNode *TBAATag = MTI->getMetadata(LLVMContext::MD_tbaa); + + return Location(MTI->getRawSource(), Size, TBAATag); +} + +AliasAnalysis::Location +AliasAnalysis::getLocationForDest(const MemIntrinsic *MTI) { + uint64_t Size = UnknownSize; + if (ConstantInt *C = dyn_cast(MTI->getLength())) + Size = C->getValue().getZExtValue(); + + // memcpy/memmove can have TBAA tags. For memcpy, they apply + // to both the source and the destination. + MDNode *TBAATag = MTI->getMetadata(LLVMContext::MD_tbaa); + + return Location(MTI->getRawDest(), Size, TBAATag); +} + + + +AliasAnalysis::ModRefResult +AliasAnalysis::getModRefInfo(const LoadInst *L, const Location &Loc) { + // Be conservative in the face of volatile/atomic. + if (!L->isUnordered()) + return ModRef; + + // If the load address doesn't alias the given address, it doesn't read + // or write the specified memory. + if (!alias(getLocation(L), Loc)) + return NoModRef; + + // Otherwise, a load just reads. + return Ref; +} + +AliasAnalysis::ModRefResult +AliasAnalysis::getModRefInfo(const StoreInst *S, const Location &Loc) { + // Be conservative in the face of volatile/atomic. + if (!S->isUnordered()) + return ModRef; - // Other instructions do not alias anything. - bool visitInstruction(Instruction &I) { return false; } + // If the store address cannot alias the pointer in question, then the + // specified memory cannot be modified by the store. + if (!alias(getLocation(S), Loc)) + return NoModRef; + + // If the pointer is a pointer to constant memory, then it could not have been + // modified by this store. + if (pointsToConstantMemory(Loc)) + return NoModRef; + + // Otherwise, a store just writes. + return Mod; +} + +AliasAnalysis::ModRefResult +AliasAnalysis::getModRefInfo(const VAArgInst *V, const Location &Loc) { + // If the va_arg address cannot alias the pointer in question, then the + // specified memory cannot be accessed by the va_arg. + if (!alias(getLocation(V), Loc)) + return NoModRef; + + // If the pointer is a pointer to constant memory, then it could not have been + // modified by this va_arg. + if (pointsToConstantMemory(Loc)) + return NoModRef; + + // Otherwise, a va_arg reads and writes. + return ModRef; +} + +AliasAnalysis::ModRefResult +AliasAnalysis::getModRefInfo(const AtomicCmpXchgInst *CX, const Location &Loc) { + // Acquire/Release cmpxchg has properties that matter for arbitrary addresses. + if (CX->getOrdering() > Monotonic) + return ModRef; + + // If the cmpxchg address does not alias the location, it does not access it. + if (!alias(getLocation(CX), Loc)) + return NoModRef; + + return ModRef; +} + +AliasAnalysis::ModRefResult +AliasAnalysis::getModRefInfo(const AtomicRMWInst *RMW, const Location &Loc) { + // Acquire/Release atomicrmw has properties that matter for arbitrary addresses. + if (RMW->getOrdering() > Monotonic) + return ModRef; + + // If the atomicrmw address does not alias the location, it does not access it. + if (!alias(getLocation(RMW), Loc)) + return NoModRef; + + return ModRef; +} + +namespace { + // Conservatively return true. Return false, if there is a single path + // starting from "From" and the path does not reach "To". + static bool hasPath(const BasicBlock *From, const BasicBlock *To) { + const unsigned MaxCheck = 5; + const BasicBlock *Current = From; + for (unsigned I = 0; I < MaxCheck; I++) { + unsigned NumSuccs = Current->getTerminator()->getNumSuccessors(); + if (NumSuccs > 1) + return true; + if (NumSuccs == 0) + return false; + Current = Current->getTerminator()->getSuccessor(0); + if (Current == To) + return true; + } + return true; + } + + /// Only find pointer captures which happen before the given instruction. Uses + /// the dominator tree to determine whether one instruction is before another. + /// Only support the case where the Value is defined in the same basic block + /// as the given instruction and the use. + struct CapturesBefore : public CaptureTracker { + CapturesBefore(const Instruction *I, DominatorTree *DT) + : BeforeHere(I), DT(DT), Captured(false) {} + + void tooManyUses() { Captured = true; } + + bool shouldExplore(Use *U) { + Instruction *I = cast(U->getUser()); + BasicBlock *BB = I->getParent(); + // We explore this usage only if the usage can reach "BeforeHere". + // If use is not reachable from entry, there is no need to explore. + if (BeforeHere != I && !DT->isReachableFromEntry(BB)) + return false; + // If the value is defined in the same basic block as use and BeforeHere, + // there is no need to explore the use if BeforeHere dominates use. + // Check whether there is a path from I to BeforeHere. + if (BeforeHere != I && DT->dominates(BeforeHere, I) && + !hasPath(BB, BeforeHere->getParent())) + return false; + return true; + } + + bool captured(Use *U) { + Instruction *I = cast(U->getUser()); + BasicBlock *BB = I->getParent(); + // Same logic as in shouldExplore. + if (BeforeHere != I && !DT->isReachableFromEntry(BB)) + return false; + if (BeforeHere != I && DT->dominates(BeforeHere, I) && + !hasPath(BB, BeforeHere->getParent())) + return false; + Captured = true; + return true; + } + + const Instruction *BeforeHere; + DominatorTree *DT; + + bool Captured; }; } +// FIXME: this is really just shoring-up a deficiency in alias analysis. +// BasicAA isn't willing to spend linear time determining whether an alloca +// was captured before or after this particular call, while we are. However, +// with a smarter AA in place, this test is just wasting compile time. +AliasAnalysis::ModRefResult +AliasAnalysis::callCapturesBefore(const Instruction *I, + const AliasAnalysis::Location &MemLoc, + DominatorTree *DT) { + if (!DT || !TD) return AliasAnalysis::ModRef; + + const Value *Object = GetUnderlyingObject(MemLoc.Ptr, TD); + if (!isIdentifiedObject(Object) || isa(Object) || + isa(Object)) + return AliasAnalysis::ModRef; + + ImmutableCallSite CS(I); + if (!CS.getInstruction() || CS.getInstruction() == Object) + return AliasAnalysis::ModRef; + + CapturesBefore CB(I, DT); + llvm::PointerMayBeCaptured(Object, &CB); + if (CB.Captured) + return AliasAnalysis::ModRef; + + unsigned ArgNo = 0; + AliasAnalysis::ModRefResult R = AliasAnalysis::NoModRef; + 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(AliasAnalysis::Location(*CI), + AliasAnalysis::Location(Object))) + continue; + if (CS.doesNotAccessMemory(ArgNo)) + continue; + if (CS.onlyReadsMemory(ArgNo)) { + R = AliasAnalysis::Ref; + continue; + } + return AliasAnalysis::ModRef; + } + return R; +} + // AliasAnalysis destructor: DO NOT move this to the header file for // AliasAnalysis or else clients of the AliasAnalysis class may not depend on // the AliasAnalysis.o file in the current .a file, causing alias analysis @@ -64,19 +485,34 @@ namespace { // AliasAnalysis::~AliasAnalysis() {} -/// canBasicBlockModify - Return true if it is possible for execution of the -/// specified basic block to modify the value pointed to by Ptr. +/// InitializeAliasAnalysis - Subclasses must call this method to initialize the +/// AliasAnalysis interface before any other methods are called. /// -bool AliasAnalysis::canBasicBlockModify(const BasicBlock &bb, - const Value *Ptr) { - CanModify CM(this, Ptr); - BasicBlock &BB = const_cast(bb); +void AliasAnalysis::InitializeAliasAnalysis(Pass *P) { + TD = P->getAnalysisIfAvailable(); + TLI = P->getAnalysisIfAvailable(); + AA = &P->getAnalysis(); +} - for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) - if (CM.visit(I)) // Check every instruction in the basic block... - return true; +// getAnalysisUsage - All alias analysis implementations should invoke this +// directly (using AliasAnalysis::getAnalysisUsage(AU)). +void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired(); // All AA's chain +} - return false; +/// getTypeStoreSize - Return the DataLayout store size for the given type, +/// if known, or a conservative value otherwise. +/// +uint64_t AliasAnalysis::getTypeStoreSize(Type *Ty) { + return TD ? TD->getTypeStoreSize(Ty) : UnknownSize; +} + +/// canBasicBlockModify - Return true if it is possible for execution of the +/// specified basic block to modify the value pointed to by Ptr. +/// +bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB, + const Location &Loc) { + return canInstructionRangeModify(BB.front(), BB.back(), Loc); } /// canInstructionRangeModify - Return true if it is possible for the execution @@ -86,156 +522,52 @@ bool AliasAnalysis::canBasicBlockModify(const BasicBlock &bb, /// bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1, const Instruction &I2, - const Value *Ptr) { + const Location &Loc) { assert(I1.getParent() == I2.getParent() && "Instructions not in same basic block!"); - CanModify CM(this, Ptr); - BasicBlock::iterator I = const_cast(&I1); - BasicBlock::iterator E = const_cast(&I2); + BasicBlock::const_iterator I = &I1; + BasicBlock::const_iterator E = &I2; ++E; // Convert from inclusive to exclusive range. - for (; I != E; ++I) - if (CM.visit(I)) // Check every instruction in the basic block... + for (; I != E; ++I) // Check every instruction in range + if (getModRefInfo(I, Loc) & Mod) return true; - return false; } -//===----------------------------------------------------------------------===// -// BasicAliasAnalysis Pass Implementation -//===----------------------------------------------------------------------===// -// -// Because of the way .a files work, the implementation of the -// BasicAliasAnalysis class MUST be in the AliasAnalysis file itself, or else we -// run the risk of AliasAnalysis being used, but the default implementation not -// being linked into the tool that uses it. As such, we register and implement -// the class here. -// -namespace { - // Register this pass... - RegisterOpt - X("basicaa", "Basic Alias Analysis (default AA impl)"); - - // Declare that we implement the AliasAnalysis interface - RegisterAnalysisGroup Y; -} // End of anonymous namespace - - - -// hasUniqueAddress - Return true if the -static inline bool hasUniqueAddress(const Value *V) { - return isa(V) || isa(V) || isa(V); +/// isNoAliasCall - Return true if this pointer is returned by a noalias +/// function. +bool llvm::isNoAliasCall(const Value *V) { + if (isa(V) || isa(V)) + return ImmutableCallSite(cast(V)) + .paramHasAttr(0, Attribute::NoAlias); + return false; } -static const Value *getUnderlyingObject(const Value *V) { - if (!isa(V->getType())) return 0; - - // If we are at some type of object... return it. - if (hasUniqueAddress(V)) return V; - - // Traverse through different addressing mechanisms... - if (const Instruction *I = dyn_cast(V)) { - if (isa(I) || isa(I)) - return getUnderlyingObject(I->getOperand(0)); - } - return 0; +/// isNoAliasArgument - Return true if this is an argument with the noalias +/// attribute. +bool llvm::isNoAliasArgument(const Value *V) +{ + if (const Argument *A = dyn_cast(V)) + return A->hasNoAliasAttr(); + return false; } - -// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such -// as array references. Note that this function is heavily tail recursive. -// Hopefully we have a smart C++ compiler. :) -// -AliasAnalysis::Result BasicAliasAnalysis::alias(const Value *V1, - const Value *V2) { - // Strip off constant pointer refs if they exist - if (const ConstantPointerRef *CPR = dyn_cast(V1)) - V1 = CPR->getValue(); - if (const ConstantPointerRef *CPR = dyn_cast(V2)) - V2 = CPR->getValue(); - - // Are we checking for alias of the same value? - if (V1 == V2) return MustAlias; - - if ((!isa(V1->getType()) || !isa(V2->getType())) && - V1->getType() != Type::LongTy && V2->getType() != Type::LongTy) - return NoAlias; // Scalars cannot alias each other - - // Strip off cast instructions... - if (const Instruction *I = dyn_cast(V1)) - return alias(I->getOperand(0), V2); - if (const Instruction *I = dyn_cast(V2)) - return alias(V1, I->getOperand(0)); - - // If we have two gep instructions with identical indices, return an alias - // result equal to the alias result of the original pointer... - // - if (const GetElementPtrInst *GEP1 = dyn_cast(V1)) - if (const GetElementPtrInst *GEP2 = dyn_cast(V2)) - if (GEP1->getNumOperands() == GEP2->getNumOperands() && - GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType()) { - if (std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1)) - return alias(GEP1->getOperand(0), GEP2->getOperand(0)); - - // If all of the indexes to the getelementptr are constant, but - // different (well we already know they are different), then we know - // that there cannot be an alias here if the two base pointers DO alias. - // - bool AllConstant = true; - for (unsigned i = 1, e = GEP1->getNumOperands(); i != e; ++i) - if (!isa(GEP1->getOperand(i)) || - !isa(GEP2->getOperand(i))) { - AllConstant = false; - break; - } - - // If we are all constant, then look at where the the base pointers - // alias. If they are known not to alias, then we are dealing with two - // different arrays or something, so no alias is possible. If they are - // known to be the same object, then we cannot alias because we are - // indexing into a different part of the object. As usual, MayAlias - // doesn't tell us anything. - // - if (AllConstant && - alias(GEP1->getOperand(0), GEP2->getOperand(0)) != MayAlias) - return NoAlias; - } - - // Figure out what objects these things are pointing to if we can... - const Value *O1 = getUnderlyingObject(V1); - const Value *O2 = getUnderlyingObject(V2); - - // Pointing at a discernable object? - if (O1 && O2) { - // If they are two different objects, we know that we have no alias... - if (O1 != O2) return NoAlias; - - // If they are the same object, they we can look at the indexes. If they - // index off of the object is the same for both pointers, they must alias. - // If they are provably different, they must not alias. Otherwise, we can't - // tell anything. - } else if (O1 && isa(V2)) { - return NoAlias; // Unique values don't alias null - } else if (O2 && isa(V1)) { - return NoAlias; // Unique values don't alias null - } - - // Check to see if these two pointers are related by a getelementptr - // instruction. If one pointer is a GEP with a non-zero index of the other - // pointer, we know they cannot alias. - // - if (isa(V2)) - std::swap(V1, V2); - - if (const GetElementPtrInst *GEP = dyn_cast(V1)) - if (GEP->getOperand(0) == V2) { - // If there is at least one non-zero constant index, we know they cannot - // alias. - for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i) - if (const Constant *C = dyn_cast(GEP->getOperand(i))) - if (!C->isNullValue()) - return NoAlias; - } - - return MayAlias; +/// isIdentifiedObject - Return true if this pointer refers to a distinct and +/// identifiable object. This returns true for: +/// Global Variables and Functions (but not Global Aliases) +/// Allocas and Mallocs +/// ByVal and NoAlias Arguments +/// NoAlias returns +/// +bool llvm::isIdentifiedObject(const Value *V) { + if (isa(V)) + return true; + if (isa(V) && !isa(V)) + return true; + if (isNoAliasCall(V)) + return true; + if (const Argument *A = dyn_cast(V)) + return A->hasNoAliasAttr() || A->hasByValAttr(); + return false; }