Re: [PATCH 2/5] riscv: Optimize fmaximum and fminimum

On 06/08/26 07:25, Julian Zhu wrote:
> Add RISC-V float and double implementations for the NaN-propagating C23 maximum and minimum operations.  Handle NaN inputs explicitly, then use fmax or fmin for ordered operands.
> 
> Signed-off-by: Julian Zhu <[email protected]>

Can't you just USE_FMAX_BUILTIN/USE_FMAXF_BUILTIN on RISC-V instead?
Since a95db490b5acefda5dbb2ffbb1523af6b2d47dfa and with builtin available,
the code is essentially the same.

It should be something like since gcc has it for some time [1]:

#if __GNUC_PREREQ (13, 0)
# define USE_FMAX_BUILTIN 1
# define USE_FMAXF_BUILTIN 1
#else
# define USE_FMAX_BUILTIN 0
# define USE_FMAXF_BUILTIN 0
#endif
#define USE_FMAXL_BUILTIN 0
#define USE_FMAXF128_BUILTIN 0


[1] https://gcc.gnu.org/pipermail/gcc-patches/2022-May/594468.html

> ---
>  sysdeps/riscv/rvd/s_fmaximum.c  | 37 +++++++++++++++++++++++++++++++++
>  sysdeps/riscv/rvd/s_fminimum.c  | 37 +++++++++++++++++++++++++++++++++
>  sysdeps/riscv/rvf/s_fmaximumf.c | 34 ++++++++++++++++++++++++++++++
>  sysdeps/riscv/rvf/s_fminimumf.c | 34 ++++++++++++++++++++++++++++++
>  4 files changed, 142 insertions(+)
>  create mode 100644 sysdeps/riscv/rvd/s_fmaximum.c
>  create mode 100644 sysdeps/riscv/rvd/s_fminimum.c
>  create mode 100644 sysdeps/riscv/rvf/s_fmaximumf.c
>  create mode 100644 sysdeps/riscv/rvf/s_fminimumf.c
> 
> diff --git a/sysdeps/riscv/rvd/s_fmaximum.c b/sysdeps/riscv/rvd/s_fmaximum.c
> new file mode 100644
> index 0000000000..d514fb17a6
> --- /dev/null
> +++ b/sysdeps/riscv/rvd/s_fmaximum.c
> @@ -0,0 +1,37 @@
> +/* fmaximum().  RISC-V version.
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library.  If not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <math.h>
> +#include <libm-alias-double.h>
> +
> +/* fmaximum is the IEEE 754-2019 maximum operation: like fmaximum_num but
> +   NaN-propagating, so a NaN operand yields a quiet NaN result (and a
> +   signaling NaN also raises the invalid exception).  RISC-V's fmax.d gives
> +   the correct result whenever neither operand is NaN, so only the NaN case
> +   needs to be handled explicitly.  */
> +
> +double
> +__fmaximum (double x, double y)
> +{
> +  double res;
> +  if (__glibc_unlikely (isunordered (x, y)))
> +    return x + y;
> +  asm ("fmax.d %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
> +  return res;
> +}
> +libm_alias_double (__fmaximum, fmaximum)
> diff --git a/sysdeps/riscv/rvd/s_fminimum.c b/sysdeps/riscv/rvd/s_fminimum.c
> new file mode 100644
> index 0000000000..608b37bed5
> --- /dev/null
> +++ b/sysdeps/riscv/rvd/s_fminimum.c
> @@ -0,0 +1,37 @@
> +/* fminimum().  RISC-V version.
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library.  If not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <math.h>
> +#include <libm-alias-double.h>
> +
> +/* fminimum is the IEEE 754-2019 minimum operation: like fminimum_num but
> +   NaN-propagating, so a NaN operand yields a quiet NaN result (and a
> +   signaling NaN also raises the invalid exception).  RISC-V's fmin.d gives
> +   the correct result whenever neither operand is NaN, so only the NaN case
> +   needs to be handled explicitly.  */
> +
> +double
> +__fminimum (double x, double y)
> +{
> +  double res;
> +  if (__glibc_unlikely (isunordered (x, y)))
> +    return x + y;
> +  asm ("fmin.d %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
> +  return res;
> +}
> +libm_alias_double (__fminimum, fminimum)
> diff --git a/sysdeps/riscv/rvf/s_fmaximumf.c b/sysdeps/riscv/rvf/s_fmaximumf.c
> new file mode 100644
> index 0000000000..daa71f0f34
> --- /dev/null
> +++ b/sysdeps/riscv/rvf/s_fmaximumf.c
> @@ -0,0 +1,34 @@
> +/* fmaximumf().  RISC-V version.
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library.  If not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <math.h>
> +#include <libm-alias-float.h>
> +
> +/* See s_fmaximum.c for a description of the semantics.  RISC-V's fmax.s
> +   handles the ordered case, so only NaNs need explicit handling.  */
> +
> +float
> +__fmaximumf (float x, float y)
> +{
> +  float res;
> +  if (__glibc_unlikely (isunordered (x, y)))
> +    return x + y;
> +  asm ("fmax.s %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
> +  return res;
> +}
> +libm_alias_float (__fmaximum, fmaximum)
> diff --git a/sysdeps/riscv/rvf/s_fminimumf.c b/sysdeps/riscv/rvf/s_fminimumf.c
> new file mode 100644
> index 0000000000..2dba5412f8
> --- /dev/null
> +++ b/sysdeps/riscv/rvf/s_fminimumf.c
> @@ -0,0 +1,34 @@
> +/* fminimumf().  RISC-V version.
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library.  If not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <math.h>
> +#include <libm-alias-float.h>
> +
> +/* See s_fminimum.c for a description of the semantics.  RISC-V's fmin.s
> +   handles the ordered case, so only NaNs need explicit handling.  */
> +
> +float
> +__fminimumf (float x, float y)
> +{
> +  float res;
> +  if (__glibc_unlikely (isunordered (x, y)))
> +    return x + y;
> +  asm ("fmin.s %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
> +  return res;
> +}
> +libm_alias_float (__fminimum, fminimum)