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Implement knowledge in BasicAA that &A->field != &A and (P+1) != P

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llvm-svn: 5519
This commit is contained in:
Chris Lattner 2003-02-09 19:38:11 +00:00
parent f3627e3ee3
commit 471d708ae0
1 changed files with 17 additions and 0 deletions
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17
lib/Analysis/AliasAnalysis.cpp
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@ -220,5 +220,22 @@ AliasAnalysis::Result BasicAliasAnalysis::alias(const Value *V1,
return NoAlias; // Unique values don't alias null
}
// Check to see if these two pointers are related by a getelementptr
// instruction. If one pointer is a GEP with a non-zero index of the other
// pointer, we know they cannot alias.
//
if (isa<GetElementPtrInst>(V2))
std::swap(V1, V2);
if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V1))
if (GEP->getOperand(0) == V2) {
// If there is at least one non-zero constant index, we know they cannot
// alias.
for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
if (const Constant *C = dyn_cast<Constant>(GEP->getOperand(i)))
if (!C->isNullValue())
return NoAlias;
}
return MayAlias;
}