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Default-addressspace null pointers don't alias anything. This allows

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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
This commit is contained in:
Dan Gohman
2009-11-09 19:29:11 +00:00
parent 980d494ab6
commit f75ef668a7
2 changed files with 29 additions and 0 deletions
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9
lib/Analysis/BasicAliasAnalysis.cpp
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@ -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<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))