/3rd_party/llvm/lib/Analysis/AliasAnalysis.cpp
https://code.google.com/p/softart/ · C++ · 556 lines · 342 code · 84 blank · 130 comment · 101 complexity · 1c83b975edafd8386967221d667f7b03 MD5 · raw file
- //===- 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.
- //
- // This file also implements the default version of the AliasAnalysis interface
- // that is to be used when no other implementation is specified. This does some
- // simple tests that detect obvious cases: two different global pointers cannot
- // alias, a global cannot alias a malloc, two different mallocs cannot alias,
- // etc.
- //
- // This alias analysis implementation really isn't very good for anything, but
- // it is very fast, and makes a nice clean default implementation. Because it
- // handles lots of little corner cases, other, more complex, alias analysis
- // implementations may choose to rely on this pass to resolve these simple and
- // easy cases.
- //
- //===----------------------------------------------------------------------===//
- #include "llvm/Analysis/AliasAnalysis.h"
- #include "llvm/Analysis/CaptureTracking.h"
- #include "llvm/Analysis/CFG.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.
- 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);
- }
- 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);
- }
- 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;
- }
- }
- }
- 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;
- }
- }
- 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<ConstantInt>(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<ConstantInt>(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;
- // 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 {
- /// 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<Instruction>(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;
- }
- bool captured(Use *U) {
- Instruction *I = cast<Instruction>(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;
- }
- 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<GlobalValue>(Object) ||
- isa<Constant>(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
- // support to not be included in the tool correctly!
- //
- AliasAnalysis::~AliasAnalysis() {}
- /// InitializeAliasAnalysis - Subclasses must call this method to initialize the
- /// AliasAnalysis interface before any other methods are called.
- ///
- void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
- TD = P->getAnalysisIfAvailable<DataLayout>();
- TLI = P->getAnalysisIfAvailable<TargetLibraryInfo>();
- AA = &P->getAnalysis<AliasAnalysis>();
- }
- // getAnalysisUsage - All alias analysis implementations should invoke this
- // directly (using AliasAnalysis::getAnalysisUsage(AU)).
- void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<AliasAnalysis>(); // 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 Location &Loc) {
- return canInstructionRangeModify(BB.front(), BB.back(), Loc);
- }
- /// canInstructionRangeModify - Return true if it is possible for the execution
- /// of the specified instructions to modify the value pointed to by Ptr. The
- /// instructions to consider are all of the instructions in the range of [I1,I2]
- /// INCLUSIVE. I1 and I2 must be in the same basic block.
- ///
- bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
- const Instruction &I2,
- const Location &Loc) {
- assert(I1.getParent() == I2.getParent() &&
- "Instructions not in same basic block!");
- 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, Loc) & Mod)
- return true;
- return false;
- }
- /// isNoAliasCall - Return true if this pointer is returned by a noalias
- /// function.
- bool llvm::isNoAliasCall(const Value *V) {
- if (isa<CallInst>(V) || isa<InvokeInst>(V))
- return ImmutableCallSite(cast<Instruction>(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<Argument>(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<AllocaInst>(V))
- return true;
- if (isa<GlobalValue>(V) && !isa<GlobalAlias>(V))
- return true;
- if (isNoAliasCall(V))
- return true;
- if (const Argument *A = dyn_cast<Argument>(V))
- return A->hasNoAliasAttr() || A->hasByValAttr();
- return false;
- }