X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FAliasAnalysis.cpp;h=b8085cdd8190b863bc4bf7f560044c77fc85a681;hb=974a445bd90795248274493eda5cdbf6721910f7;hp=f1b0f56b847cff79aa065c9e2a8b9ad443f47961;hpb=954da37bb492b519f5c31dc360f2a142567e08b4;p=oota-llvm.git diff --git a/lib/Analysis/AliasAnalysis.cpp b/lib/Analysis/AliasAnalysis.cpp index f1b0f56b847..b8085cdd819 100644 --- a/lib/Analysis/AliasAnalysis.cpp +++ b/lib/Analysis/AliasAnalysis.cpp @@ -1,10 +1,10 @@ //===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==// -// +// // The LLVM Compiler Infrastructure // -// This file was developed by the LLVM research group and is distributed under -// the University of Illinois Open Source License. See LICENSE.TXT for details. -// +// 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 @@ -25,111 +25,440 @@ //===----------------------------------------------------------------------===// #include "llvm/Analysis/AliasAnalysis.h" -#include "llvm/BasicBlock.h" -#include "llvm/iMemory.h" -#include "llvm/Target/TargetData.h" -#include +#include "llvm/Analysis/CFG.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 Value *V1, unsigned V1Size, - const Value *V2, unsigned V2Size) { +AliasAnalysis::alias(const Location &LocA, const Location &LocB) { assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); - return AA->alias(V1, V1Size, V2, V2Size); + return AA->alias(LocA, LocB); } -void AliasAnalysis::getMustAliases(Value *P, std::vector &RetVals) { +bool AliasAnalysis::pointsToConstantMemory(const Location &Loc, + bool OrLocal) { assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); - return AA->getMustAliases(P, RetVals); + return AA->pointsToConstantMemory(Loc, OrLocal); } -bool AliasAnalysis::pointsToConstantMemory(const Value *P) { +void AliasAnalysis::deleteValue(Value *V) { assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); - return AA->pointsToConstantMemory(P); + AA->deleteValue(V); } -bool AliasAnalysis::doesNotAccessMemory(Function *F) { +void AliasAnalysis::copyValue(Value *From, Value *To) { assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); - return AA->doesNotAccessMemory(F); + AA->copyValue(From, To); } -bool AliasAnalysis::onlyReadsMemory(Function *F) { +void AliasAnalysis::addEscapingUse(Use &U) { assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); - return doesNotAccessMemory(F) || AA->onlyReadsMemory(F); + AA->addEscapingUse(U); } -bool AliasAnalysis::hasNoModRefInfoForCalls() const { + +AliasAnalysis::ModRefResult +AliasAnalysis::getModRefInfo(ImmutableCallSite CS, + const Location &Loc) { assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); - return AA->hasNoModRefInfoForCalls(); + + 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; + } + } + } + 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); } -void AliasAnalysis::deleteValue(Value *V) { +AliasAnalysis::ModRefResult +AliasAnalysis::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) { assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); - AA->deleteValue(V); + + // 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; + } + } + 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); } -void AliasAnalysis::copyValue(Value *From, Value *To) { +AliasAnalysis::ModRefBehavior +AliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); - AA->copyValue(From, To); + + 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::ModRefResult -AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) { - // FIXME: we can do better. +AliasAnalysis::ModRefBehavior +AliasAnalysis::getModRefBehavior(const Function *F) { assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!"); - return AA->getModRefInfo(CS1, CS2); + 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(LoadInst *L, Value *P, unsigned Size) { - return alias(L->getOperand(0), TD->getTypeSize(L->getType()), - P, Size) ? Ref : NoModRef; +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(StoreInst *S, Value *P, unsigned Size) { - // If the stored address cannot alias the pointer in question, then the - // pointer cannot be modified by the store. - if (!alias(S->getOperand(1), TD->getTypeSize(S->getOperand(0)->getType()), - P, Size)) +AliasAnalysis::getModRefInfo(const StoreInst *S, const Location &Loc) { + // Be conservative in the face of volatile/atomic. + if (!S->isUnordered()) + return ModRef; + + // 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. - return pointsToConstantMemory(P) ? NoModRef : Mod; + if (pointsToConstantMemory(Loc)) + return NoModRef; + + // Otherwise, a store just writes. + return Mod; } AliasAnalysis::ModRefResult -AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { - ModRefResult Mask = ModRef; - if (Function *F = CS.getCalledFunction()) - if (onlyReadsMemory(F)) { - if (doesNotAccessMemory(F)) return NoModRef; - Mask = Ref; +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 { + /// 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) && + !isPotentiallyReachable(I, BeforeHere, DT)) + return false; + return true; } - if (!AA) return Mask; + 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) && + !isPotentiallyReachable(I, BeforeHere, DT)) + return false; + Captured = true; + return true; + } - // If P points to a constant memory location, the call definitely could not - // modify the memory location. - if ((Mask & Mod) && AA->pointsToConstantMemory(P)) - Mask = Ref; + 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; - return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size)); + 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 @@ -139,28 +468,34 @@ AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { // AliasAnalysis::~AliasAnalysis() {} -/// setTargetData - Subclasses must call this method to initialize the +/// InitializeAliasAnalysis - Subclasses must call this method to initialize the /// AliasAnalysis interface before any other methods are called. /// void AliasAnalysis::InitializeAliasAnalysis(Pass *P) { - TD = &P->getAnalysis(); + TD = P->getAnalysisIfAvailable(); + TLI = P->getAnalysisIfAvailable(); AA = &P->getAnalysis(); } // getAnalysisUsage - All alias analysis implementations should invoke this -// directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that -// TargetData is required by the pass. +// directly (using AliasAnalysis::getAnalysisUsage(AU)). void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { - AU.addRequired(); // All AA's need TargetData. AU.addRequired(); // All AA's chain } +/// 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 Value *Ptr, unsigned Size) { - return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size); + const Location &Loc) { + return canInstructionRangeModify(BB.front(), BB.back(), Loc); } /// canInstructionRangeModify - Return true if it is possible for the execution @@ -170,23 +505,52 @@ bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB, /// bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1, const Instruction &I2, - const Value *Ptr, unsigned Size) { + const Location &Loc) { assert(I1.getParent() == I2.getParent() && "Instructions not in same basic block!"); - 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) // Check every instruction in range - if (getModRefInfo(I, const_cast(Ptr), Size) & Mod) + if (getModRefInfo(I, Loc) & Mod) return true; return false; } -// Because of the way .a files work, we must force the BasicAA implementation to -// be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run -// the risk of AliasAnalysis being used, but the default implementation not -// being linked into the tool that uses it. -// -extern void llvm::BasicAAStub(); -static IncludeFile INCLUDE_BASICAA_CPP((void*)&BasicAAStub); +/// 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; +} + +/// 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; +} + +/// 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; +}