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Be conservative about allocations that may alias the accessed pointer.

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If an allocation has a must-alias relation to the access pointer, we treat it
as a Def.  Otherwise, without this check, the code here was just skipping over
the allocation call and ignoring it.  I noticed this by inspection and don't
have a specific testcase that it breaks, but it seems like we need to treat
a may-alias allocation as a Clobber.

llvm-svn: 163127
This commit is contained in:
Bob Wilson 2012-09-04 03:30:13 +00:00
parent f24d0a24c7
commit 00bddec249
1 changed files with 3 additions and 0 deletions
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3
lib/Analysis/MemoryDependenceAnalysis.cpp
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@ -485,6 +485,9 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
if (AccessPtr == Inst || AA->isMustAlias(Inst, AccessPtr))
return MemDepResult::getDef(Inst);
// Be conservative if the accessed pointer may alias the allocation.
if (AA->alias(Inst, AccessPtr) != AliasAnalysis::NoAlias)
return MemDepResult::getClobber(Inst);
// If the allocation is not aliased and does not read memory (like
// strdup), it is safe to ignore.
if (isa<AllocaInst>(Inst) ||