// Useful predicates
//===----------------------------------------------------------------------===//
-/// isKnownNonNull - Return true if we know that the specified value is never
-/// null.
-static bool isKnownNonNull(const Value *V) {
- // Alloca never returns null, malloc might.
- if (isa<AllocaInst>(V)) return true;
-
- // A byval argument is never null.
- if (const Argument *A = dyn_cast<Argument>(V))
- return A->hasByValAttr();
-
- // Global values are not null unless extern weak.
- if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
- return !GV->hasExternalWeakLinkage();
- return false;
-}
-
/// isNonEscapingLocalObject - Return true if the pointer is to a function-local
/// object that never escapes from the function.
static bool isNonEscapingLocalObject(const Value *V) {
/// getObjectSize - Return the size of the object specified by V, or
/// UnknownSize if unknown.
-static uint64_t getObjectSize(const Value *V, const TargetData &TD) {
+static uint64_t getObjectSize(const Value *V, const TargetData &TD,
+ bool RoundToAlign = false) {
Type *AccessTy;
+ unsigned Align;
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
if (!GV->hasDefinitiveInitializer())
return AliasAnalysis::UnknownSize;
AccessTy = GV->getType()->getElementType();
+ Align = GV->getAlignment();
} else if (const AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
if (!AI->isArrayAllocation())
AccessTy = AI->getType()->getElementType();
else
return AliasAnalysis::UnknownSize;
+ Align = AI->getAlignment();
} else if (const CallInst* CI = extractMallocCall(V)) {
- if (!isArrayMalloc(V, &TD))
+ if (!RoundToAlign && !isArrayMalloc(V, &TD))
// The size is the argument to the malloc call.
if (const ConstantInt* C = dyn_cast<ConstantInt>(CI->getArgOperand(0)))
return C->getZExtValue();
return AliasAnalysis::UnknownSize;
} else if (const Argument *A = dyn_cast<Argument>(V)) {
- if (A->hasByValAttr())
+ if (A->hasByValAttr()) {
AccessTy = cast<PointerType>(A->getType())->getElementType();
- else
+ Align = A->getParamAlignment();
+ } else {
return AliasAnalysis::UnknownSize;
+ }
} else {
return AliasAnalysis::UnknownSize;
}
-
- if (AccessTy->isSized())
- return TD.getTypeAllocSize(AccessTy);
- return AliasAnalysis::UnknownSize;
+
+ if (!AccessTy->isSized())
+ return AliasAnalysis::UnknownSize;
+
+ uint64_t Size = TD.getTypeAllocSize(AccessTy);
+ // If there is an explicitly specified alignment, and we need to
+ // take alignment into account, round up the size. (If the alignment
+ // is implicit, getTypeAllocSize is sufficient.)
+ if (RoundToAlign && Align)
+ Size = RoundUpToAlignment(Size, Align);
+
+ return Size;
}
/// isObjectSmallerThan - Return true if we can prove that the object specified
/// by V is smaller than Size.
static bool isObjectSmallerThan(const Value *V, uint64_t Size,
const TargetData &TD) {
- uint64_t ObjectSize = getObjectSize(V, TD);
+ // This function needs to use the aligned object size because we allow
+ // reads a bit past the end given sufficient alignment.
+ uint64_t ObjectSize = getObjectSize(V, TD, /*RoundToAlign*/true);
+
return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size;
}
// pointer were passed to arguments that were neither of these, then it
// couldn't be no-capture.
if (!(*CI)->getType()->isPointerTy() ||
- (!CS.paramHasAttr(ArgNo+1, Attribute::NoCapture) &&
- !CS.paramHasAttr(ArgNo+1, Attribute::ByVal)))
+ (!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(Location(cast<Value>(CI)), Loc)) {
+ if (!isNoAlias(Location(*CI), Location(Object))) {
PassedAsArg = true;
break;
}
// We know that memset doesn't load anything.
Min = Mod;
break;
- case Intrinsic::atomic_cmp_swap:
- case Intrinsic::atomic_swap:
- case Intrinsic::atomic_load_add:
- case Intrinsic::atomic_load_sub:
- case Intrinsic::atomic_load_and:
- case Intrinsic::atomic_load_nand:
- case Intrinsic::atomic_load_or:
- case Intrinsic::atomic_load_xor:
- case Intrinsic::atomic_load_max:
- case Intrinsic::atomic_load_min:
- case Intrinsic::atomic_load_umax:
- case Intrinsic::atomic_load_umin:
- if (TD) {
- Value *Op1 = II->getArgOperand(0);
- uint64_t Op1Size = TD->getTypeStoreSize(Op1->getType());
- MDNode *Tag = II->getMetadata(LLVMContext::MD_tbaa);
- if (isNoAlias(Location(Op1, Op1Size, Tag), Loc))
- return NoModRef;
- }
- break;
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
case Intrinsic::invariant_start: {
const Value *Src = CS.getArgument(1);
// If it can't overlap the source dest, then it doesn't modref the loc.
if (isNoAlias(Location(Dest, Len), Loc)) {
- if (isNoAlias(Location(Src, 2), Loc))
+ // Always reads 16 bytes of the source.
+ if (isNoAlias(Location(Src, 16), Loc))
return NoModRef;
// If it can't overlap the dest, then worst case it reads the loc.
Min = Ref;
- } else if (isNoAlias(Location(Src, 2), Loc)) {
+ // Always reads 16 bytes of the source.
+ } else if (isNoAlias(Location(Src, 16), Loc)) {
// If it can't overlap the source, then worst case it mutates the loc.
Min = Mod;
}
if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
return MustAlias;
- // If there is a difference between the pointers, but the difference is
- // less than the size of the associated memory object, then we know
- // that the objects are partially overlapping.
+ // If there is a constant difference between the pointers, but the difference
+ // is less than the size of the associated memory object, then we know
+ // that the objects are partially overlapping. If the difference is
+ // greater, we know they do not overlap.
if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
- if (GEP1BaseOffset >= 0 ?
- (V2Size != UnknownSize && (uint64_t)GEP1BaseOffset < V2Size) :
- (V1Size != UnknownSize && -(uint64_t)GEP1BaseOffset < V1Size &&
- GEP1BaseOffset != INT64_MIN))
- return PartialAlias;
+ if (GEP1BaseOffset >= 0) {
+ if (V2Size != UnknownSize) {
+ if ((uint64_t)GEP1BaseOffset < V2Size)
+ return PartialAlias;
+ return NoAlias;
+ }
+ } else {
+ if (V1Size != UnknownSize) {
+ if (-(uint64_t)GEP1BaseOffset < V1Size)
+ return PartialAlias;
+ return NoAlias;
+ }
+ }
}
- // If we have a known constant offset, see if this offset is larger than the
- // access size being queried. If so, and if no variable indices can remove
- // pieces of this constant, then we know we have a no-alias. For example,
- // &A[100] != &A.
-
- // In order to handle cases like &A[100][i] where i is an out of range
- // subscript, we have to ignore all constant offset pieces that are a multiple
- // of a scaled index. Do this by removing constant offsets that are a
- // multiple of any of our variable indices. This allows us to transform
- // things like &A[i][1] because i has a stride of (e.g.) 8 bytes but the 1
- // provides an offset of 4 bytes (assuming a <= 4 byte access).
- for (unsigned i = 0, e = GEP1VariableIndices.size();
- i != e && GEP1BaseOffset;++i)
- if (int64_t RemovedOffset = GEP1BaseOffset/GEP1VariableIndices[i].Scale)
- GEP1BaseOffset -= RemovedOffset*GEP1VariableIndices[i].Scale;
-
- // If our known offset is bigger than the access size, we know we don't have
- // an alias.
- if (GEP1BaseOffset) {
- if (GEP1BaseOffset >= 0 ?
- (V2Size != UnknownSize && (uint64_t)GEP1BaseOffset >= V2Size) :
- (V1Size != UnknownSize && -(uint64_t)GEP1BaseOffset >= V1Size &&
- GEP1BaseOffset != INT64_MIN))
+ // Try to distinguish something like &A[i][1] against &A[42][0].
+ // Grab the least significant bit set in any of the scales.
+ if (!GEP1VariableIndices.empty()) {
+ uint64_t Modulo = 0;
+ for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
+ Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
+ Modulo = Modulo ^ (Modulo & (Modulo - 1));
+
+ // We can compute the difference between the two addresses
+ // mod Modulo. Check whether that difference guarantees that the
+ // two locations do not alias.
+ uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
+ if (V1Size != UnknownSize && V2Size != UnknownSize &&
+ ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
return NoAlias;
}
-
+
// Statically, we can see that the base objects are the same, but the
// pointers have dynamic offsets which we can't resolve. And none of our
// little tricks above worked.
//
// TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
// practical effect of this is protecting TBAA in the case of dynamic
- // indices into arrays of unions. An alternative way to solve this would
- // be to have clang emit extra metadata for unions and/or union accesses.
- // A union-specific solution wouldn't handle the problem for malloc'd
- // memory however.
+ // indices into arrays of unions or malloc'd memory.
return PartialAlias;
}
projects / oota-llvm.git / blobdiff