[PATCH, i386]: Do not limit the cost of moves to/from XMM register to minimum 8.

[Hongtao Liu]

On Fri, Aug 30, 2019 at 8:10 AM Hongtao Liu <crazylht@gmail.com> wrote:
>
> On Fri, Aug 30, 2019 at 2:09 AM Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> > 2019-08-28  Uroš Bizjak  <ubizjak@gmail.com>
> >
> >     * config/i386/i386.c (ix86_register_move_cost): Do not
> >     limit the cost of moves to/from XMM register to minimum 8.
> >
> > Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.
> >
> > Actually committed as r274994 with the wrong ChangeLog.
> >
> > Uros.
>
> There is 11% regression in 548.exchange_r of SPEC2017.
>
> Reason for the regression:
> For 548.exchange_r, a lot of movements between gpr and xmm are
> generated as expected,
> and it reduced  clocksticks by 3%.
> But  however maybe too many xmm registers are used,
> a frequency reduction issue is triggered(average frequency reduced by 13%).
> So totally it takes more time.
>
>
>
> --
> BR,
> Hongtao

Tested on skylake workstation.

-- 
BR,
Hongtao