Re: gcc feature request / RFC: extra clobbered regs

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: gcc feature request / RFC: extra clobbered regs
Date	2015-06-30 23:50 +0200
Message-ID	<pHbzH-5V3-11@gated-at.bofh.it> (permalink)
References	<pHbgo-5xn-41@gated-at.bofh.it> <pHbq2-5IH-17@gated-at.bofh.it> <pHbzH-5V3-1@gated-at.bofh.it>
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On Tue, Jun 30, 2015 at 2:41 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 06/30/2015 02:37 PM, Jakub Jelinek wrote:
>> I'd say the most natural API for this would be to allow
>> f{fixed,call-{used,saved}}-REG in target attribute.
>
> Either that or
>
>         __attribute__((fixed(rbp,rcx),used(rax,rbx),saved(r11)))
>
> ... just to be shorter.  Either way, I would consider this to be
> desirable -- I have myself used this to good effect in a past life
> (*cough* Transmeta *cough*) -- but not a high priority feature.

I think I mean the per-function equivalent of -fcall-used-reg, so
hpa's "used" suggestion would do the trick.

I guess that clobbering the frame pointer is a non-starter, but five
out of six isn't so bad.  It would be nice to error out instead of
producing "disastrous results", though, if another bad reg is chosen.
(Presumably the PIC register on PIC builds would be an example of
that.)

--Andy
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Thread

gcc feature request / RFC: extra clobbered regs Andy Lutomirski <luto@kernel.org> - 2015-06-30 23:30 +0200
  Re: gcc feature request / RFC: extra clobbered regs Jakub Jelinek <jakub@redhat.com> - 2015-06-30 23:40 +0200
    Re: gcc feature request / RFC: extra clobbered regs "H. Peter Anvin" <hpa@zytor.com> - 2015-06-30 23:50 +0200
      Re: gcc feature request / RFC: extra clobbered regs Andy Lutomirski <luto@amacapital.net> - 2015-06-30 23:50 +0200
        Re: gcc feature request / RFC: extra clobbered regs "H. Peter Anvin" <hpa@zytor.com> - 2015-07-01 00:00 +0200
          Re: gcc feature request / RFC: extra clobbered regs Andy Lutomirski <luto@amacapital.net> - 2015-07-01 00:00 +0200
            Re: gcc feature request / RFC: extra clobbered regs "H. Peter Anvin" <hpa@zytor.com> - 2015-07-01 00:10 +0200
  Re: gcc feature request / RFC: extra clobbered regs "H. Peter Anvin" <hpa@zytor.com> - 2015-06-30 23:40 +0200

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