[PATCH v2] math: Fix x86_64 build for -Os (BZ 33367)

[Adhemerval Zanella Netto]

On 09/09/25 09:25, H.J. Lu wrote:
> On Tue, Sep 9, 2025 at 5:21 AM Adhemerval Zanella Netto
> <adhemerval.zanella@linaro.org> wrote:
>>
>>
>>
>> On 09/09/25 01:11, H.J. Lu wrote:
>>> On Mon, Sep 8, 2025 at 1:47 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>
>>>> On Mon, Sep 8, 2025 at 1:11 PM Adhemerval Zanella Netto
>>>> <adhemerval.zanella@linaro.org> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 08/09/25 17:09, H.J. Lu wrote:
>>>>>> On Mon, Sep 8, 2025 at 12:56 PM Adhemerval Zanella
>>>>>> <adhemerval.zanella@linaro.org> wrote:
>>>>>>>
>>>>>>> The compiler might not inline the trunc function call for
>>>>>>> USE_TRUNC_BUILTIN [1].
>>>>>>>
>>>>>>> This patch adds an optimized __trunc/__truncf for x86 used
>>>>>>> on modf ifunc variant to avoid the trunc libcall.
>>>>>>>
>>>>>>> Checked on x86_64, x86_64-v2, x86_64-v3, and x86_64-v4. Used -O2 and
>>>>>>> -Os options. Performed a full make check on x86_64 with both
>>>>>>>  optimizations.
>>>>>>>
>>>>>>> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121861
>>>>>>> ---
>>>>>>>  sysdeps/x86/fpu/math_private.h                | 27 +++++++++++++++++++
>>>>>>>  sysdeps/x86_64/fpu/multiarch/s_modf-avx.c     |  4 +++
>>>>>>>  sysdeps/x86_64/fpu/multiarch/s_modf-sse4_1.c  |  4 +++
>>>>>>>  sysdeps/x86_64/fpu/multiarch/s_modf.c         |  3 ++-
>>>>>>>  sysdeps/x86_64/fpu/multiarch/s_modff-avx.c    |  4 +++
>>>>>>>  sysdeps/x86_64/fpu/multiarch/s_modff-sse4_1.c |  4 +++
>>>>>>>  sysdeps/x86_64/fpu/multiarch/s_modff.c        |  3 ++-
>>>>>>>  7 files changed, 47 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/sysdeps/x86/fpu/math_private.h b/sysdeps/x86/fpu/math_private.h
>>>>>>> index 132f011809..d30d580cea 100644
>>>>>>> --- a/sysdeps/x86/fpu/math_private.h
>>>>>>> +++ b/sysdeps/x86/fpu/math_private.h
>>>>>>> @@ -19,6 +19,7 @@
>>>>>>>  #ifndef X86_MATH_PRIVATE_H
>>>>>>>  #define X86_MATH_PRIVATE_H 1
>>>>>>>
>>>>>>> +#include <math.h>
>>>>>>>  #include_next <math_private.h>
>>>>>>>
>>>>>>>  __extern_always_inline long double
>>>>>>> @@ -29,4 +30,30 @@ __NTH (__ieee754_atan2l (long double y, long double x))
>>>>>>>    return ret;
>>>>>>>  }
>>>>>>>
>>>>>>> +__extern_always_inline double
>>>>>>> +__trunc (double x)
>>>>>>> +{
>>>>>>> +#ifdef __AVX__
>>>>>>> +  asm ("vroundsd $11, %1, %1, %0" : "=v" (x) : "v" (x));
>>>>>>> +#elif defined __SSE4_1__
>>>>>>> +  asm ("roundsd $11, %1, %0" : "=x" (x) : "x" (x));
>>>>>>> +#else
>>>>>>> +  x = trunc (x);
>>>>>>> +#endif
>>>>>>> +  return x;
>>>>>>> +}
>>>>>>
>>>>>> I will fix GCC 16.   Please make sure that inline asm isn't used for
>>>>>> GCC 16 or above.
>>>>>
>>>>> Would it make a lot of difference on modf implementation to add this extra
>>>>> switch?
>>>>
>>>> I think an extra
>>>>
>>>> #if GCC_COMPAT(16, 1)
>>>>
>>>> is simple enough.  But it can wait.
>>>
>>> GCC 16 is fixed.  But -fno-trapping-math doesn't work well due to
>>>
>>> https://sourceware.org/bugzilla/show_bug.cgi?id=33405
>>>
>>> since -fsignaling-nans takes precedence over -fno-trapping-math.
>>>
>>> We should add a configure test to check if the GCC bug is fixed.
>>
>> I am not sure which direction to use, both your patch enable -fno-trapping-math [1]
>> or this one works.  Your changes adds some generic Makefile rules, and the extra
>> use-builtins-trunc* which eventually we will need to remove since it is already
>> fixed upstream; the inline version at least is more clear of what tried to
>> accomplish and do not mess with the math flags.
> 
> Your patch works better.  But it needs some adjustments as I have suggested.
> 

Ok, I will reinstate the NO_MATH_REDIRECT. It is leftover from some experiments.