[PATCH] math: Fix x86_64 build for -Os (BZ 33367)
H.J. Lu
hjl.tools@gmail.com
Mon Sep 8 21:01:58 GMT 2025
On Mon, Sep 8, 2025 at 12:55 PM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 08/09/25 16:34, H.J. Lu wrote:
> > On Mon, Sep 8, 2025 at 12:09 PM Adhemerval Zanella Netto
> > <adhemerval.zanella@linaro.org> wrote:
> >>
> >>
> >>
> >> On 08/09/25 15:59, H.J. Lu wrote:
> >>> 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
> >>>
> >>
> >> Thanks, using inline resulted in a simpler patch. I will send a new version.
> >
> > Will adding -fno-trapping-math with -mavx/-msse4.1 break these 2 functions?
> > If not, we can add -fno-trapping-math with -mavx/-msse4.1.
> >
>
> The -fno-trapping-math forces the roundss/vroundss; however I am not if this is the
But roundss/vroundss are exactly what compiler generates for
trunc/truncf with -O2.
> best approach since it seems to be a unrelated flag.
--
H.J.
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