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

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

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).