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Teach BasicAA that a constant expression can't alias memory provably not

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allocated until runtime (such as an alloca). Patch by Hans Wennborg!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88760 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2009-11-14 06:15:14 +00:00
parent fae3e92345
commit 20162ac566
2 changed files with 45 additions and 1 deletions
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7
lib/Analysis/BasicAliasAnalysis.cpp
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@ -659,7 +659,12 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
// If V1/V2 point to two different objects we know that we have no alias.
if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
return NoAlias;
// Constant pointers can't alias with non-const isIdentifiedObject objects.
if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
(isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
return NoAlias;
// Arguments can't alias with local allocations or noalias calls.
if ((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) ||
(isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1))))