[PATCH v2 03/10] i386: Use generic fmod
Adhemerval Zanella Netto
adhemerval.zanella@linaro.org
Thu Mar 28 15:14:46 GMT 2024
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;
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