[PATCH 3/8] x86: Do not use __builtin_isinf_sign for _Float64x/long double

[H.J. Lu]

On Thu, Dec 18, 2025 at 1:56 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
> Neither gcc [1] nor clang [2] handles pseudo-normal numbers correctly
> with the __builtin_isinf_sign, so disable its usage for _Float64x and
> long double types.
>
> This only affects x86, so add a new define __FP_BUILTIN_ISINF_SIGN_DENORMAL
> to gate long double and related types to the libc function instead.
>
> It fixes the regression on test-ldouble-isinf when built with clang:

Why don't they fail with GCC?

> Failure: isinf (pseudo_zero): Exception "Invalid operation" set
> Failure: isinf (pseudo_inf): Exception "Invalid operation" set
> Failure: isinf (pseudo_qnan): Exception "Invalid operation" set
> Failure: isinf (pseudo_snan): Exception "Invalid operation" set
> Failure: isinf (pseudo_unnormal): Exception "Invalid operation" set
> Failure: isinf_downward (pseudo_zero): Exception "Invalid operation" set
> Failure: isinf_downward (pseudo_inf): Exception "Invalid operation" set
> Failure: isinf_downward (pseudo_qnan): Exception "Invalid operation" set
> Failure: isinf_downward (pseudo_snan): Exception "Invalid operation" set
> Failure: isinf_downward (pseudo_unnormal): Exception "Invalid operation" set
> Failure: isinf_towardzero (pseudo_zero): Exception "Invalid operation" set
> Failure: isinf_towardzero (pseudo_inf): Exception "Invalid operation" set
> Failure: isinf_towardzero (pseudo_qnan): Exception "Invalid operation" set
> Failure: isinf_towardzero (pseudo_snan): Exception "Invalid operation" set
> Failure: isinf_towardzero (pseudo_unnormal): Exception "Invalid operation" set
> Failure: isinf_upward (pseudo_zero): Exception "Invalid operation" set
> Failure: isinf_upward (pseudo_inf): Exception "Invalid operation" set
> Failure: isinf_upward (pseudo_qnan): Exception "Invalid operation" set
> Failure: isinf_upward (pseudo_snan): Exception "Invalid operation" set
> Failure: isinf_upward (pseudo_unnormal): Exception "Invalid operation" set
>
> Checked on x86_64-linux-gnu with gcc-15 and clang-18.
>
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123173
> [2] https://github.com/llvm/llvm-project/issues/172651
> ---
>  bits/fp-builtin-denormal.h             | 4 ++++
>  math/math.h                            | 5 ++++-
>  sysdeps/x86/bits/fp-builtin-denormal.h | 4 ++++
>  3 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/bits/fp-builtin-denormal.h b/bits/fp-builtin-denormal.h
> index 77b7184975..5748eb86f0 100644
> --- a/bits/fp-builtin-denormal.h
> +++ b/bits/fp-builtin-denormal.h
> @@ -26,3 +26,7 @@
>      Intel double extended-precision (long double).  By default assume 1 to
>      enable the usage of compiler builtin on math.h.  */
>  #define __FP_BUILTIN_FPCLASSIFY_DENORMAL 1
> +
> +/* __FP_BUILTIN_ISINF_SIGN_DENORMAL is defined to 1 if compiler supports
> +   handling pseudo-dernormal numbers with isinf_sign builtin.  */
> +#define __FP_BUILTIN_ISINF_SIGN_DENORMAL 1
> diff --git a/math/math.h b/math/math.h
> index cbec2f406a..96b64379f7 100644
> --- a/math/math.h
> +++ b/math/math.h
> @@ -1249,7 +1249,10 @@ enum
>       ? __isinff128 (x) : __builtin_isinf_sign (x))
>  # elif (__GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__) \
>         || __glibc_clang_prereq (3,7)
> -#  define isinf(x) __builtin_isinf_sign (x)
> +#  define isinf(x) __MATH_TG_BUILTIN_CLASSIFY ((x),                          \
> +                                              __builtin_isinf_sign, (x),     \
> +                                              isinf, (x),                    \
> +                                              __FP_BUILTIN_ISINF_SIGN_DENORMAL)
>  # else
>  #  define isinf(x) __MATH_TG ((x), __isinf, (x))
>  # endif
> diff --git a/sysdeps/x86/bits/fp-builtin-denormal.h b/sysdeps/x86/bits/fp-builtin-denormal.h
> index bfb8f54237..2f9a5c7b66 100644
> --- a/sysdeps/x86/bits/fp-builtin-denormal.h
> +++ b/sysdeps/x86/bits/fp-builtin-denormal.h
> @@ -23,3 +23,7 @@
>  /* Neither GCC (bug 123161) nor clang (issue 172533) handles pseudo-normal
>     numbers correctly with fpclassify builtin.  */
>  #define __FP_BUILTIN_FPCLASSIFY_DENORMAL 0
> +
> +/* Neither GCC (bug 123173) nor clang (issue 172651) handles pseudo-normal
> +   numbers correctly with isinf_sign builtin.  */
> +#define __FP_BUILTIN_ISINF_SIGN_DENORMAL 0
> --
> 2.43.0
>


-- 
H.J.