llvm/lib/Analysis/AliasAnalysis.cpp - toolchain/llvm-project - Gitiles

 //===- 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/Pass.h"
 #include "llvm/BasicBlock.h"
 #include "llvm/Function.h"
 #include "llvm/IntrinsicInst.h"
 #include "llvm/Instructions.h"
 #include "llvm/LLVMContext.h"
 #include "llvm/Type.h"
 #include "llvm/Target/TargetData.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::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.
   if (L->isVolatile())
     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.
   if (S->isVolatile())
     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 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<TargetData>();
   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 TargetData store size for the given type,
 /// if known, or a conservative value otherwise.
 ///
 uint64_t AliasAnalysis::getTypeStoreSize(const 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;
 }

 /// 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;
 }
	//===- 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/Pass.h"
	#include "llvm/BasicBlock.h"
	#include "llvm/Function.h"
	#include "llvm/IntrinsicInst.h"
	#include "llvm/Instructions.h"
	#include "llvm/LLVMContext.h"
	#include "llvm/Type.h"
	#include "llvm/Target/TargetData.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::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.
	if (L->isVolatile())
	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.
	if (S->isVolatile())
	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 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<TargetData>();
	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 TargetData store size for the given type,
	/// if known, or a conservative value otherwise.
	///
	uint64_t AliasAnalysis::getTypeStoreSize(const 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;
	}

	/// 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;
	}