[PATCH 37/59] math: Fix modf{f} build on clang

[Adhemerval Zanella Netto]

On 20/10/25 19:09, H.J. Lu wrote:
> On Tue, Oct 21, 2025 at 1:58 AM Adhemerval Zanella Netto
> <adhemerval.zanella@linaro.org> wrote:
>>
>>
>>
>> On 18/10/25 03:28, H.J. Lu wrote:
>>> On Sat, Oct 18, 2025 at 3:58 AM Adhemerval Zanella
>>> <adhemerval.zanella@linaro.org> wrote:
>>>>
>>>> We need to disable the internal optimize for math builtins
>>>> (NO_MATH_REDIRECT) for the USE_TRUNC_BUILTIN case.
>>>
>>> Does it change GCC codegen?
>>
>> No, both with clang and gcc either the builtin is issues (on
>> aarch64 for instance) or the internal symbol is called.
> 
> Why does NO_MATH_REDIRECT make no difference here?
> Why is this macro needed?

With clang the internal optimization to avoid PLT usage for symbol
that might be inline will make clang to *not* emit the builtin:

include/math.h

177 MATH_REDIRECT (trunc, "__", MATH_REDIRECT_UNARY_ARGS)

Without NO_MATH_REDIRECT, which disables it; build with clang
fails:

>>> referenced by s_modf.c:34 ([...]/../sysdeps/ieee754/dbl-64/s_modf.c:34)
>>>               [...]/aarch64-linux-gnu-clang-21/libc_pic.os.clean:(__modf)
clang: error: linker command failed with exit code 1 (use -v to see invocation)

gcc is not affected by this, it will emit the 'frintz' regardless
of MATH_REDIRECT.