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

[Adhemerval Zanella Netto]

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.

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