Re: Improve things for PR71724, in combine/if_then_else_cond

[Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>]

On 25/01/17 08:53, Christophe Lyon wrote:
> On 24 January 2017 at 18:15, Bernd Schmidt <bschmidt@redhat.com> wrote:
> > On 01/24/2017 06:03 PM, Christophe Lyon wrote:
> > > Ha... the regression occurred between r 244818  and r 244816,
> > > and I read r 244816 ChangeLog too quickly and did not notice
> > > it was modifying ifcvt.c in addition to x86-only files.
> > >
> > > So it's likely that it's your other patch for pr78634
> > > that caused the regression I mentioned. Does it make
> > > more sense?
> >
> > That's possible. That added a missing cost check, so the question becomes -
> > is the change in generated assembly sensible, given the selected CPU type?
> I can now confirm that the change is indeed caused by r244816 (pr78634).
> The difference in the generated asm is:
> -       vmov    d17, r0, r1
> -       vmov    d16, r2, r3
> -       vcmp.f64        d17, d16
> +       vmov    d16, r0, r1
> +       vmov    d17, r2, r3
> +       vcmp.f64        d16, d17
>          vmrs    APSR_nzcv, FPSCR
> -       vselvs.f64      d16, d16, d17
> +       vmovvs.f64      d16, d17
>
> which, besides swapping d16 and d17, summarizes to
> -       vselvs.f64      d16, d16, d17
> +       vmovvs.f64      d16, d17
>
> I'm not sure if there is a "best" one ?

The test is supposed to test the generation of the vsel instruction.
I believe adding an -mcpu=cortex-a57 to the testcases would be best, as
VSEL isn't actually available on Cortex-A5, it's just enabled by the -mfpu=fp-armv8 option.
A more realistic configuration would target an ARMv8-A CPU like the Cortex-A57.

Thanks,
Kyrill

> > Bernd