[PATCH] math: Fix x86_64 build for -Os (BZ 33367)
H.J. Lu
hjl.tools@gmail.com
Mon Sep 8 18:59:30 GMT 2025
On Mon, Sep 8, 2025 at 9:30 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> 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?
>
I opened:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121861
--
H.J.
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