[PATCH v2] math: Fix x86_64 build for -Os (BZ 33367)
H.J. Lu
hjl.tools@gmail.com
Tue Sep 9 04:11:51 GMT 2025
On Mon, Sep 8, 2025 at 1:47 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Sep 8, 2025 at 1:11 PM Adhemerval Zanella Netto
> <adhemerval.zanella@linaro.org> wrote:
> >
> >
> >
> > On 08/09/25 17:09, H.J. Lu wrote:
> > > 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.
> >
> > Would it make a lot of difference on modf implementation to add this extra
> > switch?
>
> I think an extra
>
> #if GCC_COMPAT(16, 1)
>
> is simple enough. But it can wait.
GCC 16 is fixed. But -fno-trapping-math doesn't work well due to
https://sourceware.org/bugzilla/show_bug.cgi?id=33405
since -fsignaling-nans takes precedence over -fno-trapping-math.
We should add a configure test to check if the GCC bug is fixed.
> > >
> > >> +__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
>
> Why is this needed?
>
> > >> # 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
>
> Why is this needed?
>
> > >> # 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.
--
H.J.
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