Default-addressspace null pointers don't alias anything. This allows
GVN to be more aggressive. Patch by Hans Wennborg! (with a comment added by me)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86582 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 2f46635..ea10a83 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -646,6 +646,15 @@
const Value *O1 = V1->getUnderlyingObject();
const Value *O2 = V2->getUnderlyingObject();
+ // Null values in the default address space don't point to any object, so they
+ // don't alias any other pointer.
+ if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
+ if (CPN->getType()->getAddressSpace() == 0)
+ return NoAlias;
+ if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
+ if (CPN->getType()->getAddressSpace() == 0)
+ return NoAlias;
+
if (O1 != O2) {
// If V1/V2 point to two different objects we know that we have no alias.
if (isIdentifiedObject(O1) && isIdentifiedObject(O2))