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

[H.J. Lu]

On Mon, Sep 8, 2025 at 9:04 AM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 08/09/25 12:56, H.J. Lu wrote:
> > On Mon, Sep 8, 2025 at 8:27 AM Adhemerval Zanella Netto
> > <adhemerval.zanella@linaro.org> wrote:
> >>
> >>
> >>
> >> On 08/09/25 12:22, H.J. Lu wrote:
> >>> On Mon, Sep 8, 2025 at 7:26 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> >>>>
> >>>> On Sat, Sep 6, 2025 at 3:22 PM Adhemerval Zanella
> >>>> <adhemerval.zanella@linaro.org> wrote:
> >>>>>
> >>>>> The compiler might not inline the trunc function call for
> >>>>> USE_TRUNC_BUILTIN, which requires adding the required objects.
> >>>>>
> >>>>> Route trunc calls for the optimized modf variants to thei
> >>>>> ABI-compatible version. This avoids invoking the ifunc variant
> >>>>> for x86_64-v1 and requires fewer objects to be added.
> >>>>>
> >>>>> 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.
> >>>>> ---
> >>>>>  sysdeps/x86_64/fpu/multiarch/Makefile         | 19 ++++++++++++-------
> >>>>>  sysdeps/x86_64/fpu/multiarch/s_modf-avx.c     |  5 +++++
> >>>>>  sysdeps/x86_64/fpu/multiarch/s_modf-sse4_1.c  |  5 +++++
> >>>>>  sysdeps/x86_64/fpu/multiarch/s_modf.c         |  1 -
> >>>>>  sysdeps/x86_64/fpu/multiarch/s_modff-avx.c    |  5 +++++
> >>>>>  sysdeps/x86_64/fpu/multiarch/s_modff-sse4_1.c |  5 +++++
> >>>>>  sysdeps/x86_64/fpu/multiarch/s_modff.c        |  1 -
> >>>>>  7 files changed, 32 insertions(+), 9 deletions(-)
> >>>>>
> >>>>> diff --git a/sysdeps/x86_64/fpu/multiarch/Makefile b/sysdeps/x86_64/fpu/multiarch/Makefile
> >>>>> index 708b14297f..baefe8dd07 100644
> >>>>> --- a/sysdeps/x86_64/fpu/multiarch/Makefile
> >>>>> +++ b/sysdeps/x86_64/fpu/multiarch/Makefile
> >>>>> @@ -26,6 +26,11 @@ CFLAGS-s_sinf-fma.c = -mfma -mavx2
> >>>>>  CFLAGS-s_cosf-fma.c = -mfma -mavx2
> >>>>>  CFLAGS-s_sincosf-fma.c = -mfma -mavx2
> >>>>>
> >>>>> +sysdep_calls += \
> >>>>> +  s_trunc-sse4_1 \
> >>>>> +  s_truncf-sse4_1 \
> >>>>> +# sysdep_calls
> >>>>> +
> >>>>>  # Check if ISA level is 2 or above.
> >>>>>  ifeq (,$(filter $(have-x86-isa-level),$(x86-isa-level-2-or-above)))
> >>>>>  sysdep_calls += \
> >>>>> @@ -36,6 +41,10 @@ endif
> >>>>>
> >>>>>  # Check if ISA level is 3 or above.
> >>>>>  ifneq (,$(filter $(have-x86-isa-level),$(x86-isa-level-3-or-above)))
> >>>>> +sysdep_calls += \
> >>>>> +  s_trunc-avx \
> >>>>> +  s_truncf-avx \
> >>>>> +# sysdep_calls
> >>>>>  libm-sysdep_routines += \
> >>>>>    s_ceil-avx \
> >>>>>    s_ceilf-avx \
> >>>>> @@ -47,8 +56,6 @@ libm-sysdep_routines += \
> >>>>>    s_rintf-avx \
> >>>>>    s_roundeven-avx \
> >>>>>    s_roundevenf-avx \
> >>>>> -  s_trunc-avx \
> >>>>> -  s_truncf-avx \
> >>>>>  # libm-sysdep_routines
> >>>>>  else
> >>>>>  sysdep_calls += \
> >>>>> @@ -114,8 +121,6 @@ libm-sysdep_routines += \
> >>>>>    s_tan-avx \
> >>>>>    s_tan-fma \
> >>>>>    s_tanh-fma \
> >>>>> -  s_trunc-sse4_1 \
> >>>>> -  s_truncf-sse4_1 \
> >>>>>  # libm-sysdep_routines
> >>>>>  ifeq ($(have-x86-isa-level),baseline)
> >>>>>  libm-sysdep_routines += \
> >>>>> @@ -132,13 +137,13 @@ libm-sysdep_routines += \
> >>>>>    s_trunc-c \
> >>>>>    s_truncf-c \
> >>>>>  # libm-sysdep_routines
> >>>>> -endif
> >>>>> +endif # ($(have-x86-isa-level),baseline)
> >>>>> +endif # (,$(filter $(have-x86-isa-level),$(x86-isa-level-3-or-above)))
> >>>>>
> >>>>>  # $(sysdep_calls) functions are built both for libc and libm.  While the
> >>>>>  # libc objects have the prefix s_, the libm ones are prefixed with m_.
> >>>>> -sysdep_routines += $(sysdep_calls)
> >>>>> +sysdep_routines +=  $(sysdep_calls)
> >>>>>  libm-sysdep_routines += $(sysdep_calls:s_%=m_%)
> >>>>> -endif
> >>>>>
> >>>>>  CFLAGS-e_asin-fma4.c = -mfma4
> >>>>>  CFLAGS-e_atan2-fma4.c = -mfma4
> >>>>> diff --git a/sysdeps/x86_64/fpu/multiarch/s_modf-avx.c b/sysdeps/x86_64/fpu/multiarch/s_modf-avx.c
> >>>>> index ab4f03db0e..25617c4fdc 100644
> >>>>> --- a/sysdeps/x86_64/fpu/multiarch/s_modf-avx.c
> >>>>> +++ b/sysdeps/x86_64/fpu/multiarch/s_modf-avx.c
> >>>>> @@ -1,3 +1,8 @@
> >>>>> +#include <sysdeps/x86/isa-level.h>
> >>>>> +#if MINIMUM_X86_ISA_LEVEL < SSE4_1_X86_ISA_LEVEL
> >>>>> +asm ("__trunc = __trunc_sse41");
> >>>>
> >>>> It looks odd for __modf_avx to call __trunc_sse41.   But this is a
> >>>> separate issue.
> >>>> We do have s_truncf-avx.S, but it isn't used by default.  I think we should
> >>>> make it available for s_modf.c and s_modf-avx.c first.
> >>>
> >>> Can we use inline functions?
> >>
> >> It might an option, and I think it simplified the Makefile requirement.
> >> I will update the patch with this.
> >>
> >> Do we have a way to force compiler always expand the builin
> >> regardless of the optimization level?
> >
> > #include <math.h>
> > #include <x86intrin.h>
> >
> > 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;
> > }
> >
> Yeah, that was my idea to change it.  But my question was if there is an extra
> compiler option to avoid the libcall generation for -Os if the builtin lowering
> does allow to use an instruction.

I don't know.

> As a side note, I think it is a missed optimization that gcc is creating a
> libcall for x86_64-v2 and forward.

Can you open a GCC bug and CC me?

-- 
H.J.