[PATCH v3] x86: Define __HAVE_FLOAT128 for Clang and use __builtin_*f128 code path

[Khem Raj]

I am seeing compiler errors with this patch when compiling the mpfr
package with clang. see
https://0x0.st/8sHM.73658

On Fri, Dec 20, 2024 at 1:23 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> From: Fangrui Song <i@maskray.me>
>
> Clang supports __builtin_fabsf128 (despite not supporting _Float128) but
> it does not support __builtin_fabsq.  Fallback to back to
> `typedef __float128 _Float128;` it clang is used.
>
> Originally developed by Fangrui Song <maskray@google.com>.
> Co-Authored-By: H.J. Lu <hjl.tools@gmail.com>
> ---
>  sysdeps/x86/bits/floatn.h | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/sysdeps/x86/bits/floatn.h b/sysdeps/x86/bits/floatn.h
> index e661abaea4..ba030d270a 100644
> --- a/sysdeps/x86/bits/floatn.h
> +++ b/sysdeps/x86/bits/floatn.h
> @@ -28,7 +28,8 @@
>     support, for x86_64 and x86.  */
>  #if (defined __x86_64__                                                        \
>       ? __GNUC_PREREQ (4, 3)                                            \
> -     : (defined __GNU__ ? __GNUC_PREREQ (4, 5) : __GNUC_PREREQ (4, 4)))
> +     : (defined __GNU__ ? __GNUC_PREREQ (4, 5) : __GNUC_PREREQ (4, 4))) \
> +    || __glibc_clang_prereq (3, 4)
>  # define __HAVE_FLOAT128 1
>  #else
>  # define __HAVE_FLOAT128 0
> @@ -58,7 +59,9 @@
>  /* Defined to concatenate the literal suffix to be used with _Float128
>     types, if __HAVE_FLOAT128 is 1. */
>  # if __HAVE_FLOAT128
> -#  if !__GNUC_PREREQ (7, 0) || (defined __cplusplus && !__GNUC_PREREQ (13, 0))
> +#  if !__GNUC_PREREQ (7, 0) \
> +      || (defined __cplusplus && !__GNUC_PREREQ (13, 0)) \
> +      || defined __clang__
>  /* The literal suffix f128 exists only since GCC 7.0.  */
>  #   define __f128(x) x##q
>  #  else
> @@ -68,7 +71,9 @@
>
>  /* Defined to a complex binary128 type if __HAVE_FLOAT128 is 1.  */
>  # if __HAVE_FLOAT128
> -#  if !__GNUC_PREREQ (7, 0) || (defined __cplusplus && !__GNUC_PREREQ (13, 0))
> +#  if !__GNUC_PREREQ (7, 0) \
> +      || (defined __cplusplus && !__GNUC_PREREQ (13, 0)) \
> +      || defined __clang__
>  /* Add a typedef for older GCC compilers which don't natively support
>     _Complex _Float128.  */
>  typedef _Complex float __cfloat128 __attribute__ ((__mode__ (__TC__)));
> @@ -82,12 +87,14 @@ typedef _Complex float __cfloat128 __attribute__ ((__mode__ (__TC__)));
>  # if __HAVE_FLOAT128
>
>  /* The type _Float128 exists only since GCC 7.0.  */
> -#  if !__GNUC_PREREQ (7, 0) || (defined __cplusplus && !__GNUC_PREREQ (13, 0))
> +#  if !__GNUC_PREREQ (7, 0) \
> +      || (defined __cplusplus && !__GNUC_PREREQ (13, 0)) \
> +      || __glibc_clang_prereq (3, 4)
>  typedef __float128 _Float128;
>  #  endif
>
> -/* __builtin_huge_valf128 doesn't exist before GCC 7.0.  */
> -#  if !__GNUC_PREREQ (7, 0)
> +/* __builtin_huge_valf128 doesn't exist before GCC 7.0 nor Clang 7.0.  */
> +#  if !__GNUC_PREREQ (7, 0) && !__glibc_clang_prereq (7, 0)
>  #   define __builtin_huge_valf128() ((_Float128) __builtin_huge_val ())
>  #  endif
>
> @@ -96,7 +103,7 @@ typedef __float128 _Float128;
>     Converting a narrower sNaN to _Float128 produces a quiet NaN, so
>     attempts to use _Float128 sNaNs will not work properly with older
>     compilers.  */
> -#  if !__GNUC_PREREQ (7, 0)
> +#  if !__GNUC_PREREQ (7, 0) && !defined __clang__
>  #   define __builtin_copysignf128 __builtin_copysignq
>  #   define __builtin_fabsf128 __builtin_fabsq
>  #   define __builtin_inff128() ((_Float128) __builtin_inf ())
> @@ -107,7 +114,8 @@ typedef __float128 _Float128;
>  /* In math/math.h, __MATH_TG will expand signbit to __builtin_signbit*,
>     e.g.: __builtin_signbitf128, before GCC 6.  However, there has never
>     been a __builtin_signbitf128 in GCC and the type-generic builtin is
> -   only available since GCC 6.  */
> +   only available since GCC 6.  signbit is expanded to __builtin_signbit
> +   after Clang 3.3.  */
>  #  if !__GNUC_PREREQ (6, 0)
>  #   define __builtin_signbitf128 __signbitf128
>  #  endif
> --
> 2.47.1
>