[Bug rtl-optimization/107013] New: Add fmin/fmax to RTL codes

["guihaoc at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107013

            Bug ID: 107013
           Summary: Add fmin/fmax to RTL codes
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: guihaoc at gcc dot gnu.org
  Target Milestone: ---

Could we add fmin/fmax to RTL codes so that the C standard fmin/fmax can be
represented in RTL without UNSPECs? Currently we only have smin/smax that are
not valid for NaNs, or when the sign of zeros is relevant.

C standard for fmax
F.10.9.2 The fmax functions
1 If just one argument is a NaN, the fmax functions return the other argument
(if both arguments are NaNs, the functions return a NaN).

2 The returned value is exact and is independent of the current rounding
direction mode.

3 The body of the fmax function might be374)

        { return (isgreaterequal(x, y) ||
             isnan(y)) ? x : y; }
Footnotes

374) Ideally, fmax would be sensitive to the sign of zero, for example
fmax(-0.0, +0.0) would return +0; however, implementation in software might be
impractical.