/// getLocForWrite - Return a Location stored to by the specified instruction.
/// If isRemovable returns true, this function and getLocForRead completely
/// describe the memory operations for this instruction.
static AliasAnalysis::Location
getLocForWrite(Instruction *Inst, AliasAnalysis &AA) {
if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
return AA.getLocation(SI);
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(Inst)) {
// memcpy/memmove/memset.
AliasAnalysis::Location Loc = AA.getLocationForDest(MI);
// If we don't have target data around, an unknown size in Location means
// that we should use the size of the pointee type. This isn't valid for
// memset/memcpy, which writes more than an i8.
if (Loc.Size == AliasAnalysis::UnknownSize && AA.getTargetData() == 0)
return AliasAnalysis::Location();
return Loc;
}
IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst);
if (II == 0) return AliasAnalysis::Location();
switch (II->getIntrinsicID()) {
default: return AliasAnalysis::Location(); // Unhandled intrinsic.
case Intrinsic::init_trampoline:
// If we don't have target data around, an unknown size in Location means
// that we should use the size of the pointee type. This isn't valid for
// init.trampoline, which writes more than an i8.
if (AA.getTargetData() == 0) return AliasAnalysis::Location();
// FIXME: We don't know the size of the trampoline, so we can't really
// handle it here.
return AliasAnalysis::Location(II->getArgOperand(0));
case Intrinsic::lifetime_end: {
uint64_t Len = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
return AliasAnalysis::Location(II->getArgOperand(1), Len);
}
}
}
static uint64_t getPointerSize(Value *V, AliasAnalysis &AA) {
const TargetData *TD = AA.getTargetData();
if (TD == 0)
return AliasAnalysis::UnknownSize;
if (AllocaInst *A = dyn_cast<AllocaInst>(V)) {
// Get size information for the alloca
if (ConstantInt *C = dyn_cast<ConstantInt>(A->getArraySize()))
return C->getZExtValue() * TD->getTypeAllocSize(A->getAllocatedType());
return AliasAnalysis::UnknownSize;
}
assert(isa<Argument>(V) && "Expected AllocaInst or Argument!");
const PointerType *PT = cast<PointerType>(V->getType());
return TD->getTypeAllocSize(PT->getElementType());
}
static uint64_t getPointerSize(const Value *V, AliasAnalysis &AA) {
const TargetData *TD = AA.getTargetData();
if (const CallInst *CI = extractMallocCall(V)) {
if (const ConstantInt *C = dyn_cast<ConstantInt>(CI->getArgOperand(0)))
return C->getZExtValue();
}
if (const CallInst *CI = extractCallocCall(V)) {
if (const ConstantInt *C1 = dyn_cast<ConstantInt>(CI->getArgOperand(0)))
if (const ConstantInt *C2 = dyn_cast<ConstantInt>(CI->getArgOperand(1)))
return (C1->getValue() * C2->getValue()).getZExtValue();
}
if (TD == 0)
return AliasAnalysis::UnknownSize;
if (const AllocaInst *A = dyn_cast<AllocaInst>(V)) {
// Get size information for the alloca
if (const ConstantInt *C = dyn_cast<ConstantInt>(A->getArraySize()))
return C->getZExtValue() * TD->getTypeAllocSize(A->getAllocatedType());
}
if (const Argument *A = dyn_cast<Argument>(V)) {
if (A->hasByValAttr())
if (PointerType *PT = dyn_cast<PointerType>(A->getType()))
return TD->getTypeAllocSize(PT->getElementType());
}
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
if (!GV->mayBeOverridden())
return TD->getTypeAllocSize(GV->getType()->getElementType());
}
return AliasAnalysis::UnknownSize;
}
/// isOverwrite - Return 'OverwriteComplete' if a store to the 'Later' location
/// completely overwrites a store to the 'Earlier' location.
/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
/// overwritten by 'Later', or 'OverwriteUnknown' if nothing can be determined
static OverwriteResult isOverwrite(const AliasAnalysis::Location &Later,
const AliasAnalysis::Location &Earlier,
AliasAnalysis &AA,
int64_t &EarlierOff,
int64_t &LaterOff) {
const Value *P1 = Earlier.Ptr->stripPointerCasts();
const Value *P2 = Later.Ptr->stripPointerCasts();
// If the start pointers are the same, we just have to compare sizes to see if
// the later store was larger than the earlier store.
if (P1 == P2) {
// If we don't know the sizes of either access, then we can't do a
// comparison.
if (Later.Size == AliasAnalysis::UnknownSize ||
Earlier.Size == AliasAnalysis::UnknownSize) {
// If we have no TargetData information around, then the size of the store
// is inferrable from the pointee type. If they are the same type, then
// we know that the store is safe.
if (AA.getTargetData() == 0 &&
Later.Ptr->getType() == Earlier.Ptr->getType())
return OverwriteComplete;
return OverwriteUnknown;
}
// Make sure that the Later size is >= the Earlier size.
if (Later.Size >= Earlier.Size)
return OverwriteComplete;
}
// Otherwise, we have to have size information, and the later store has to be
// larger than the earlier one.
if (Later.Size == AliasAnalysis::UnknownSize ||
Earlier.Size == AliasAnalysis::UnknownSize ||
AA.getTargetData() == 0)
return OverwriteUnknown;
// Check to see if the later store is to the entire object (either a global,
// an alloca, or a byval argument). If so, then it clearly overwrites any
// other store to the same object.
const TargetData &TD = *AA.getTargetData();
const Value *UO1 = GetUnderlyingObject(P1, &TD),
*UO2 = GetUnderlyingObject(P2, &TD);
// If we can't resolve the same pointers to the same object, then we can't
// analyze them at all.
if (UO1 != UO2)
return OverwriteUnknown;
// If the "Later" store is to a recognizable object, get its size.
uint64_t ObjectSize = getPointerSize(UO2, AA);
if (ObjectSize != AliasAnalysis::UnknownSize)
if (ObjectSize == Later.Size && ObjectSize >= Earlier.Size)
return OverwriteComplete;
// Okay, we have stores to two completely different pointers. Try to
// decompose the pointer into a "base + constant_offset" form. If the base
// pointers are equal, then we can reason about the two stores.
EarlierOff = 0;
LaterOff = 0;
const Value *BP1 = GetPointerBaseWithConstantOffset(P1, EarlierOff, TD);
const Value *BP2 = GetPointerBaseWithConstantOffset(P2, LaterOff, TD);
// If the base pointers still differ, we have two completely different stores.
if (BP1 != BP2)
return OverwriteUnknown;
// The later store completely overlaps the earlier store if:
//
// 1. Both start at the same offset and the later one's size is greater than
// or equal to the earlier one's, or
//
// |--earlier--|
// |-- later --|
//
// 2. The earlier store has an offset greater than the later offset, but which
// still lies completely within the later store.
//
// |--earlier--|
// |----- later ------|
//
// We have to be careful here as *Off is signed while *.Size is unsigned.
if (EarlierOff >= LaterOff &&
Later.Size > Earlier.Size &&
uint64_t(EarlierOff - LaterOff) + Earlier.Size <= Later.Size)
return OverwriteComplete;
// The other interesting case is if the later store overwrites the end of
// the earlier store
//
// |--earlier--|
// |-- later --|
//
// In this case we may want to trim the size of earlier to avoid generating
// writes to addresses which will definitely be overwritten later
if (LaterOff > EarlierOff &&
LaterOff < int64_t(EarlierOff + Earlier.Size) &&
int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size))
return OverwriteEnd;
// Otherwise, they don't completely overlap.
return OverwriteUnknown;
}
/// isCompleteOverwrite - Return true if a store to the 'Later' location
/// completely overwrites a store to the 'Earlier' location.
static bool isCompleteOverwrite(const AliasAnalysis::Location &Later,
const AliasAnalysis::Location &Earlier,
AliasAnalysis &AA) {
const Value *P1 = Earlier.Ptr->stripPointerCasts();
const Value *P2 = Later.Ptr->stripPointerCasts();
// If the start pointers are the same, we just have to compare sizes to see if
// the later store was larger than the earlier store.
if (P1 == P2) {
// If we don't know the sizes of either access, then we can't do a
// comparison.
if (Later.Size == AliasAnalysis::UnknownSize ||
Earlier.Size == AliasAnalysis::UnknownSize) {
// If we have no TargetData information around, then the size of the store
// is inferrable from the pointee type. If they are the same type, then
// we know that the store is safe.
if (AA.getTargetData() == 0)
return Later.Ptr->getType() == Earlier.Ptr->getType();
return false;
}
// Make sure that the Later size is >= the Earlier size.
if (Later.Size < Earlier.Size)
return false;
return true;
}
// Otherwise, we have to have size information, and the later store has to be
// larger than the earlier one.
if (Later.Size == AliasAnalysis::UnknownSize ||
Earlier.Size == AliasAnalysis::UnknownSize ||
Later.Size <= Earlier.Size || AA.getTargetData() == 0)
return false;
// Check to see if the later store is to the entire object (either a global,
// an alloca, or a byval argument). If so, then it clearly overwrites any
// other store to the same object.
const TargetData &TD = *AA.getTargetData();
const Value *UO1 = P1->getUnderlyingObject(), *UO2 = P2->getUnderlyingObject();
// If we can't resolve the same pointers to the same object, then we can't
// analyze them at all.
if (UO1 != UO2)
return false;
// If the "Later" store is to a recognizable object, get its size.
if (isObjectPointerWithTrustworthySize(UO2)) {
uint64_t ObjectSize =
TD.getTypeAllocSize(cast<PointerType>(UO2->getType())->getElementType());
if (ObjectSize == Later.Size)
return true;
}
// Okay, we have stores to two completely different pointers. Try to
// decompose the pointer into a "base + constant_offset" form. If the base
// pointers are equal, then we can reason about the two stores.
int64_t Off1 = 0, Off2 = 0;
const Value *BP1 = GetPointerBaseWithConstantOffset(P1, Off1, TD);
const Value *BP2 = GetPointerBaseWithConstantOffset(P2, Off2, TD);
// If the base pointers still differ, we have two completely different stores.
if (BP1 != BP2)
return false;
// Otherwise, we might have a situation like:
// store i16 -> P + 1 Byte
// store i32 -> P
// In this case, we see if the later store completely overlaps all bytes
// stored by the previous store.
if (Off1 < Off2 || // Earlier starts before Later.
Off1+Earlier.Size > Off2+Later.Size) // Earlier goes beyond Later.
return false;
// Otherwise, we have complete overlap.
return true;
}
