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Teach BasicAA about the LLVM IR rules that allow reading past the end of an object given sufficient alignment. Fixes PR12098.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151553 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman
2012-02-27 20:46:07 +00:00
parent 9e2a79c287
commit 1680a24e53
3 changed files with 52 additions and 10 deletions
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35
lib/Analysis/BasicAliasAnalysis.cpp
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@ -84,42 +84,59 @@ static bool isEscapeSource(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 (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;
}