Implement knowledge in BasicAA that &A->field != &A and (P+1) != P
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@5519 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/AliasAnalysis.cpp b/lib/Analysis/AliasAnalysis.cpp
index 510db57..57867dd 100644
--- a/lib/Analysis/AliasAnalysis.cpp
+++ b/lib/Analysis/AliasAnalysis.cpp
@@ -220,5 +220,22 @@
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;
}