on 2022/9/22 05:56, Segher Boessenkool wrote:
> Hi!
>
> On Fri, Jun 24, 2022 at 10:02:19AM +0800, HAO CHEN GUI wrote:
>> This patch also binds __builtin_vsx_xs[min/max]dp to fmin/max instead
>> of smin/max. So the builtins always generate xs[min/max]dp on all
>> platforms.
>
> But how does this not blow up with -ffast-math?
Indeed. Since it guards with "TARGET_VSX && !flag_finite_math_only",
the bifs seem to cause ICE at -ffast-math.
Haochen, could you double check it?
>
> In the other direction I am worried that the unspecs will degrade
> performance (relative to smin/smax) when -ffast-math *is* active (and
> this new builtin code and pattern doesn't blow up).
For fmin/fmax it would be fine, since they are transformed to {MAX,MIN}
EXPR in middle end, and yes, it can degrade for the bifs, although IMHO
the previous expansion to smin/smax contradicts with the bif names (users
expect to map them to xs{min,max}dp than others).
>
> I still think we should get RTL codes for this, to have access to proper
> floating point min/max semantics always and everywhere. "fmin" and
> "fmax" seem to be good names :-)
It would be good, especially if we have observed some uses of these bifs
and further opportunities around them. :)
BR,
Kewen
