Teach BasicAA about the LLVM IR rules that allow reading past the end of an object given sufficient alignment. Fixes PR12098.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151553 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 4a55c21..23b89dd 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -84,42 +84,59 @@
/// 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 (RoundToAlign) {
+ if (!Align)
+ return AliasAnalysis::UnknownSize;
+ 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;
}