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

[H.J. Lu]

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.

> +__extern_always_inline float
> +__truncf (float x)
> +{
> +#ifdef __AVX__
> +  asm ("vroundss $11, %1, %1, %0" : "=v" (x) : "v" (x));
> +#elif defined __SSE4_1__
> +  asm ("roundss $11, %1, %0" : "=x" (x) : "x" (x));
> +#else
> +  x = truncf (x);
> +#endif
> +  return x;
> +}
> +
>  #endif
> diff --git a/sysdeps/x86_64/fpu/multiarch/s_modf-avx.c b/sysdeps/x86_64/fpu/multiarch/s_modf-avx.c
> index ab4f03db0e..2f84d254a9 100644
> --- a/sysdeps/x86_64/fpu/multiarch/s_modf-avx.c
> +++ b/sysdeps/x86_64/fpu/multiarch/s_modf-avx.c
> @@ -1,3 +1,7 @@
> +#include <sysdeps/x86/isa-level.h>
> +#include <math_private.h>
> +
>  #define __modf __modf_avx
> +#define trunc __trunc
>
>  #include <sysdeps/ieee754/dbl-64/s_modf.c>
> diff --git a/sysdeps/x86_64/fpu/multiarch/s_modf-sse4_1.c b/sysdeps/x86_64/fpu/multiarch/s_modf-sse4_1.c
> index 00aa8cd736..dcf04097f2 100644
> --- a/sysdeps/x86_64/fpu/multiarch/s_modf-sse4_1.c
> +++ b/sysdeps/x86_64/fpu/multiarch/s_modf-sse4_1.c
> @@ -1,3 +1,7 @@
> +#include <sysdeps/x86/isa-level.h>
> +#include <math_private.h>
> +
>  #define __modf __modf_sse41
> +#define trunc __trunc
>
>  #include <sysdeps/ieee754/dbl-64/s_modf.c>
> diff --git a/sysdeps/x86_64/fpu/multiarch/s_modf.c b/sysdeps/x86_64/fpu/multiarch/s_modf.c
> index e365bfcef7..61f77566b1 100644
> --- a/sysdeps/x86_64/fpu/multiarch/s_modf.c
> +++ b/sysdeps/x86_64/fpu/multiarch/s_modf.c
> @@ -18,7 +18,6 @@
>
>  #include <sysdeps/x86/isa-level.h>
>  #if MINIMUM_X86_ISA_LEVEL < AVX_X86_ISA_LEVEL
> -# define NO_MATH_REDIRECT
>  # include <libm-alias-double.h>
>
>  # define modf __redirect_modf
> @@ -38,4 +37,6 @@ libm_alias_double (__modf, modf)
>  #  define __modf __modf_sse2
>  # endif
>  #endif
> +#include <math_private.h>
> +#define trunc __trunc
>  #include <sysdeps/ieee754/dbl-64/s_modf.c>
> diff --git a/sysdeps/x86_64/fpu/multiarch/s_modff-avx.c b/sysdeps/x86_64/fpu/multiarch/s_modff-avx.c
> index 07cb9c1036..c121ec26e2 100644
> --- a/sysdeps/x86_64/fpu/multiarch/s_modff-avx.c
> +++ b/sysdeps/x86_64/fpu/multiarch/s_modff-avx.c
> @@ -1,3 +1,7 @@
> +#include <sysdeps/x86/isa-level.h>
> +#include <math_private.h>
> +
>  #define __modff __modff_avx
> +#define truncf __truncf
>
>  #include <sysdeps/ieee754/flt-32/s_modff.c>
> diff --git a/sysdeps/x86_64/fpu/multiarch/s_modff-sse4_1.c b/sysdeps/x86_64/fpu/multiarch/s_modff-sse4_1.c
> index 060c5e3979..30a785d385 100644
> --- a/sysdeps/x86_64/fpu/multiarch/s_modff-sse4_1.c
> +++ b/sysdeps/x86_64/fpu/multiarch/s_modff-sse4_1.c
> @@ -1,3 +1,7 @@
> +#include <sysdeps/x86/isa-level.h>
> +#include <math_private.h>
> +
>  #define __modff __modff_sse41
> +#define truncf __truncf
>
>  #include <sysdeps/ieee754/flt-32/s_modff.c>
> diff --git a/sysdeps/x86_64/fpu/multiarch/s_modff.c b/sysdeps/x86_64/fpu/multiarch/s_modff.c
> index a4b5429037..ebf16777fd 100644
> --- a/sysdeps/x86_64/fpu/multiarch/s_modff.c
> +++ b/sysdeps/x86_64/fpu/multiarch/s_modff.c
> @@ -18,7 +18,6 @@
>
>  #include <sysdeps/x86/isa-level.h>
>  #if MINIMUM_X86_ISA_LEVEL < AVX_X86_ISA_LEVEL
> -# define NO_MATH_REDIRECT
>  # include <libm-alias-float.h>
>
>  # define modff __redirect_modff
> @@ -38,4 +37,6 @@ libm_alias_float (__modf, modf)
>  #  define __modff __modff_sse2
>  # endif
>  #endif
> +#include <math_private.h>
> +#define truncf __truncf
>  #include <sysdeps/ieee754/flt-32/s_modff.c>
> --
> 2.43.0
>


-- 
H.J.