Re: volatile qualifier hurts single-threaded optimized case

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 8/30/06, Benjamin Kosnik <bkoz@redhat.com> wrote:
> > bits/atomicity.h has volatile qualifiers on the _Atomic_word* arguments to
> > the __*_single and __*_dispatch variants of the atomic operations.  This
> > huts especially the single-threaded optimization variants which are usually
> > inlined.  Removing those qualifiers allows to reduce code size significantly
> > as can be seen in the following simple testcase
>
> I've been able to reproduce this with your example and the following
> patch. Thanks for looking at this.
>
> without volatile:
> 19: 00000000   546 FUNC    GLOBAL DEFAULT    2 _Z3fooPKcS0_
>
> with:
> 19: 00000000   578 FUNC    GLOBAL DEFAULT    2 _Z3fooPKcS0_
>
> I don't understand the ABI objections to your suggestion, and feel like
> there must be a misunderstanding somewhere. These helper functions are
> not exported at all, in fact. Also, the *_dispatch and *_single parts
> of the atomicity.h interface are new with 4.2, so I'd like to get the
> correct signatures in with their introduction, and not have to patch
> this up later.

Oh, indeed.  If the *_dispatch and *_single parts are new, we can change the
function signatures there.  The patch looks fine and should get us the runtime
and size improvements I saw.

Thanks for having a look!

Richard.