[MemoryBuiltins] Fix an issue with hasNoAliasAttr
Summary:
`hasNoAliasAttr` is buggy: it checks to see if the called function has
a `noalias` attribute, which is incorrect since functions are not even
allowed to have the `noalias` attribute. The comment on its only
caller, `llvm::isNoAliasFn`, makes it pretty clear that the intention
to do the `noalias` check on the return value, and not the callee.
Unfortunately I couldn't find a way to test this upstream -- fixing
this does not change the observable behavior of any of the passes that
use this. This is not very surprising, since `noalias` does not tell
anything about the contents of the allocated memory (so, e.g., you
still cannot fold loads). I'll be happy to be proven wrong though.
Reviewers: chandlerc, reames
Subscribers: mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D17037
llvm-svn: 260298
diff --git a/llvm/lib/Analysis/MemoryBuiltins.cpp b/llvm/lib/Analysis/MemoryBuiltins.cpp
index 480ab5c..b181292 100644
--- a/llvm/lib/Analysis/MemoryBuiltins.cpp
+++ b/llvm/lib/Analysis/MemoryBuiltins.cpp
@@ -144,7 +144,7 @@
static bool hasNoAliasAttr(const Value *V, bool LookThroughBitCast) {
ImmutableCallSite CS(LookThroughBitCast ? V->stripPointerCasts() : V);
- return CS && CS.hasFnAttr(Attribute::NoAlias);
+ return CS && CS.paramHasAttr(AttributeSet::ReturnIndex, Attribute::NoAlias);
}