http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55742
davidxl <xinliangli at gmail dot com> changed:
What |Removed |Added
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CC| |xinliangli at gmail dot com
--- Comment #6 from davidxl <xinliangli at gmail dot com> 2012-12-20 19:52:32
UTC ---
Since target attribute merging/conflicts handling is not well specified nor
implemented, with the introduction of MV, it is a good opportunity to
straighten it out and document it.
MV helps providing diagnostics to detect the broken code (where the target
attribute is ignored) :)
David
(In reply to comment #5)
> (In reply to comment #4)
> > On Thu, Dec 20, 2012 at 1:21 PM, tmsriram at google dot com
> > <gcc-bugzi...@gcc.gnu.org> wrote:
> >
> > > However, with function multiversioning, this will become a problem as
> > > multiversioning does not treat two decls with different target attributes
> > > as
> > > identical. Since we are enabling multiversioning by default, atleast in
> > > C++
> > > front-end for now, IMO, it is better to insist that the definition and
> > > declaration contain identical target attributes.
> >
> > Unfortunately, we cannot do that. A lot of existing code relies on
> > this attribute merging. The cleanest approach here is probably to add
> > an additional 'mv' attribute to explicitly enable multiversioning.
> > Breaking the existing semantics is going to break a lot of code.
>
> Ok, just to be clear, there are two problems here:
>
> 1) Target attribute merging. If the assumption that the target attributes of
> the decls must be merged is valid, there is a bug. Also, this means that using
> target attributes to do multiversioning is wrong.
>
> 2) Function multiversioning is exposing the bug, via build failures, the
> problem of declarations and definitions not having identical target
> attributes.
>
>
> First, we need to decide if target attribute merging is a valid assumption. If
> so, we fix the bug and make function multiversioning use a new attribute.
>
> If the assumption is not valid, changing the source is the only solution. The
> source is invalid now since the intended behaviour is not happening.
>
>
> >
> >
> > Diego.
