[PATCH] D129572: [X86] initial -mfunction-return=thunk-extern support

[Erich Keane via Phabricator via llvm-commits]

erichkeane added a comment.

In D129572#3646004 <https://reviews.llvm.org/D129572#3646004>, @nickdesaulniers wrote:

> In D129572#3645934 <https://reviews.llvm.org/D129572#3645934>, @erichkeane wrote:
>
>> Our typical rule is to keep the 1st one I think, and reject the 2nd.
>
> But then the _codegen_ will differ from GCC.  And we _want_ clang to be a drop in replacement, so differing in behavior there is unacceptable.

Right, I get that, which is why I said we need a different diagnostic than is 'typical' attribute merging.

> https://godbolt.org/z/rf16T83Kj
>
> IMO, the standards bodies focusing on standardizing attributes should clarify the semantics of attribute merging, _then_ compiler vendors should fix their compilers.

They HAVE FWIW, by not creating attributes that have a 'merge' problem(yet).  They end up being able to be completely additive (with the exception of the 'reason' ones like nodiscard/deprecated, at which point the standards decide that is implementation defined IIRC).


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