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

Adhemerval Zanella Netto adhemerval.zanella@linaro.org
Mon Sep 8 19:55:03 GMT 2025 


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
best approach since it seems to be a unrelated flag.

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