From ccb4584eddd133ff90fc0e19929c8ce4089a33ae Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Mon, 9 Nov 2009 19:29:11 +0000 Subject: 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) llvm-svn: 86582 --- llvm/lib/Analysis/BasicAliasAnalysis.cpp | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'llvm/lib/Analysis/BasicAliasAnalysis.cpp') diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp index 2f4663531ae..ea10a830547 100644 --- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp +++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp @@ -646,6 +646,15 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size, 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(O1)) + if (CPN->getType()->getAddressSpace() == 0) + return NoAlias; + if (const ConstantPointerNull *CPN = dyn_cast(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)) -- cgit v1.2.3