Re: [PATCH v2 03/10] i386: Use generic fmod

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Mar 28, 2024 at 7:11 AM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 27/03/24 18:38, H.J. Lu wrote:
> > On Wed, Mar 27, 2024 at 1:37 PM Adhemerval Zanella Netto
> > <adhemerval.zanella@linaro.org> wrote:
> >>
> >>
> >>
> >> On 27/03/24 16:55, H.J. Lu wrote:
> >>> On Wed, Mar 27, 2024 at 12:40 PM Adhemerval Zanella
> >>> <adhemerval.zanella@linaro.org> wrote:
> >>>>
> >>>> The benchtest results shows a slight improvement (Ryzen 5900, gcc
> >>>> 13.2.1):
> >>>>
> >>>> * sysdeps/i386/fpu/e_fmod.S:
> >>>>   "fmod": {
> >>>>    "subnormals": {
> >>>>     "duration": 3.68855e+09,
> >>>>     "iterations": 2.12608e+08,
> >>>>     "max": 62.012,
> >>>>     "min": 16.798,
> >>>>     "mean": 17.349
> >>>>    },
> >>>>    "normal": {
> >>>>     "duration": 3.88459e+09,
> >>>>     "iterations": 7.168e+06,
> >>>>     "max": 2879.12,
> >>>>     "min": 16.909,
> >>>>     "mean": 541.934
> >>>>    },
> >>>>    "close-exponents": {
> >>>>     "duration": 3.692e+09,
> >>>>     "iterations": 1.96608e+08,
> >>>>     "max": 66.452,
> >>>>     "min": 16.835,
> >>>>     "mean": 18.7785
> >>>>    }
> >>>>   }
> >>>>
> >>>> * generic
> >>>>   "fmod": {
> >>>>    "subnormals": {
> >>>>     "duration": 3.68645e+09,
> >>>>     "iterations": 2.2848e+08,
> >>>>     "max": 66.896,
> >>>>     "min": 15.91,
> >>>>     "mean": 16.1347
> >>>>    },
> >>>>    "normal": {
> >>>>     "duration": 4.1455e+09,
> >>>>     "iterations": 8.192e+06,
> >>>>     "max": 3376.18,
> >>>>     "min": 15.873,
> >>>>     "mean": 506.043
> >>>>    },
> >>>>    "close-exponents": {
> >>>>     "duration": 3.70197e+09,
> >>>>     "iterations": 2.08896e+08,
> >>>>     "max": 69.597,
> >>>>     "min": 15.947,
> >>>>     "mean": 17.7216
> >>>>    }
> >>>>   }
> >>>> ---
> >>>>  sysdeps/i386/fpu/Versions                 |  4 ++++
> >>>>  sysdeps/i386/fpu/e_fmod.S                 | 18 ------------------
> >>>>  sysdeps/i386/fpu/e_fmod.c                 |  2 ++
> >>>>  sysdeps/i386/fpu/math_err.c               |  1 -
> >>>>  sysdeps/i386/fpu/w_fmod_compat.c          | 15 ---------------
> >>>>  sysdeps/ieee754/dbl-64/e_fmod.c           |  5 ++++-
> >>>>  sysdeps/mach/hurd/i386/libm.abilist       |  1 +
> >>>>  sysdeps/unix/sysv/linux/i386/libm.abilist |  1 +
> >>>>  8 files changed, 12 insertions(+), 35 deletions(-)
> >>>>  delete mode 100644 sysdeps/i386/fpu/e_fmod.S
> >>>>  create mode 100644 sysdeps/i386/fpu/e_fmod.c
> >>>>  delete mode 100644 sysdeps/i386/fpu/math_err.c
> >>>>  delete mode 100644 sysdeps/i386/fpu/w_fmod_compat.c
> >>>>
> >>>> diff --git a/sysdeps/i386/fpu/Versions b/sysdeps/i386/fpu/Versions
> >>>> index a2eec371f1..d37bc1eae6 100644
> >>>> --- a/sysdeps/i386/fpu/Versions
> >>>> +++ b/sysdeps/i386/fpu/Versions
> >>>> @@ -3,4 +3,8 @@ libm {
> >>>>      # functions used in inline functions or macros
> >>>>      __expl; __expm1l;
> >>>>    }
> >>>> +  GLIBC_2.40 {
> >>>> +    # No SVID compatible error handling.
> >>>> +    fmod;
> >>>> +  }
> >>>
> >>> This changes the ABI.  I assume that it fixes a real bug.   Is there a bug
> >>> report open for this?
> >>>
> >>
> >> The new version is the way to provide the system without the SVID compat
> >> support, which we for all ABIs but i386 on 2.38. For instance:
> >>
> >> find . -iname libm.abilist | xargs grep -w fmod
> >> ./sysdeps/unix/sysv/linux/sparc/sparc32/libm.abilist:GLIBC_2.0 fmod F
> >> ./sysdeps/unix/sysv/linux/sparc/sparc32/libm.abilist:GLIBC_2.38 fmod F
> >> [...]
> >>
> >> For i386 specifically, the old SVID symbol will be kept as fmod@GLIBC_2.0.
> >>
> >
> > Does it fix a run-time test which fails without the fix?
> >
>
> Not really, but it is one less assembly implementation in favor a generic one
> (which also shows a slight improvement on recent chips) and it sync i386
> with generic code (so less possible issues, such as the static lib in this
> patchset).

Why do we need a new symbol?

-- 
H.J.