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Be more robust in the face of undefined behavior.

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Fixes bug: BasicAA/2003-06-01-AliasCrash.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6538 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2003-06-02 05:42:39 +00:00
parent 4bf00c10d5
commit 920bd79f34
1 changed files with 30 additions and 5 deletions
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35
lib/Analysis/BasicAliasAnalysis.cpp
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@ -182,6 +182,22 @@ BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
return MayAlias;
}
static Value *CheckArrayIndicesForOverflow(const Type *PtrTy,
const std::vector<Value*> &Indices,
const ConstantInt *Idx) {
if (const ConstantSInt *IdxS = dyn_cast<ConstantSInt>(Idx)) {
if (IdxS->getValue() < 0) // Underflow on the array subscript?
return Constant::getNullValue(Type::LongTy);
else { // Check for overflow
const ArrayType *ATy =
cast<ArrayType>(GetElementPtrInst::getIndexedType(PtrTy, Indices,true));
if (IdxS->getValue() >= (int64_t)ATy->getNumElements())
return ConstantSInt::get(Type::LongTy, ATy->getNumElements()-1);
}
}
return (Value*)Idx; // Everything is acceptable.
}
// CheckGEPInstructions - Check two GEP instructions of compatible types and
// equal number of arguments. This checks to see if the index expressions
// preclude the pointers from aliasing...
@ -214,7 +230,7 @@ BasicAliasAnalysis::CheckGEPInstructions(GetElementPtrInst *GEP1, unsigned G1S,
//
unsigned SizeMax = std::max(G1S, G2S);
if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work...
// Scan for the first operand that is constant and unequal in the
// two getelemenptrs...
unsigned FirstConstantOper = UnequalOper;
@ -262,16 +278,20 @@ BasicAliasAnalysis::CheckGEPInstructions(GetElementPtrInst *GEP1, unsigned G1S,
const Type *GEPPointerTy = GEP1->getOperand(0)->getType();
// Loop over the rest of the operands...
for (unsigned i = FirstConstantOper+1; i!=NumGEPOperands; ++i){
for (unsigned i = FirstConstantOper+1; i != NumGEPOperands; ++i) {
const Value *Op1 = GEP1->getOperand(i);
const Value *Op2 = GEP2->getOperand(i);
if (Op1 == Op2) { // If they are equal, use a zero index...
Indices1.push_back(Constant::getNullValue(Op1->getType()));
Indices2.push_back(Indices1.back());
} else {
if (isa<Constant>(Op1))
if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// If this is an array index, make sure the array element is in range...
if (i != 1) // The pointer index can be "out of range"
Op1 = CheckArrayIndicesForOverflow(GEPPointerTy, Indices1, Op1C);
Indices1.push_back((Value*)Op1);
else {
} else {
// GEP1 is known to produce a value less than GEP2. To be
// conservatively correct, we must assume the largest possible constant
// is used in this position. This cannot be the initial index to the
@ -287,8 +307,13 @@ BasicAliasAnalysis::CheckGEPInstructions(GetElementPtrInst *GEP1, unsigned G1S,
ElTy->getNumElements()-1));
}
if (isa<Constant>(Op2))
if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op2)) {
// If this is an array index, make sure the array element is in range...
if (i != 1) // The pointer index can be "out of range"
Op1 = CheckArrayIndicesForOverflow(GEPPointerTy, Indices2, Op1C);
Indices2.push_back((Value*)Op2);
}
else // Conservatively assume the minimum value for this index
Indices2.push_back(Constant::getNullValue(Op2->getType()));
}