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

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

On 28/03/24 11:51, H.J. Lu wrote:
> 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?

Because the new fmod@GLIBC_2.40 for i386 won't have the SVID handling,
similar to what has been done for other architectures with
16439f419b270184ec501c531bf20d83b6745fb0;