[PATCH 11/11] libstdc++: Fix ODR issues with different -m flags

Matthias Kretz m.kretz@gsi.de
Mon Nov 15 08:57:39 GMT 2021


ping. OK to push?

On Tuesday, 8 June 2021 14:12:23 CET Matthias Kretz wrote:
> From: Matthias Kretz <kretz@kde.org>
> 
> Explicitly support use of the stdx::simd implementation in situations
> where the user links TUs that were compiled with different -m flags. In
> general, this is always a (quasi) ODR violation for inline functions
> because at least codegen may differ in important ways. However, in the
> resulting executable only one (unspecified which one) of them might be
> used. For simd we want to support users to compile code multiple times,
> with different -m flags and have a runtime dispatch to the TU matching
> the target CPU. But if internal functions are not inlined this may lead
> to unexpected performance loss or execution of illegal instructions.
> Therefore, inline functions that are not marked as always_inline must
> use an additional template parameter somewhere in their name, to
> disambiguate between the different -m translations.
> 
> Signed-off-by: Matthias Kretz <m.kretz@gsi.de>
> 
> libstdc++-v3/ChangeLog:
> 
> 	* include/experimental/bits/simd.h: Move feature detection bools
> 	and add __have_avx512bitalg, __have_avx512vbmi2,
> 	__have_avx512vbmi, __have_avx512ifma, __have_avx512cd,
> 	__have_avx512vnni, __have_avx512vpopcntdq.
> 	(__detail::__machine_flags): New function which returns a unique
> 	uint64 depending on relevant -m and -f flags.
> 	(__detail::__odr_helper): New type alias for either an anonymous
> 	type or a type specialized with the __machine_flags number.
> 	(_SimdIntOperators): Change template parameters from _Impl to
> 	_Tp, _Abi because _Impl now has an __odr_helper parameter which
> 	may be _OdrEnforcer from the anonymous namespace, which makes
> 	for a bad base class.
> 	(many): Either add __odr_helper template parameter or mark as
> 	always_inline.
> 	* include/experimental/bits/simd_detail.h: Add defines for
> 	AVX512BITALG, AVX512VBMI2, AVX512VBMI, AVX512IFMA, AVX512CD,
> 	AVX512VNNI, AVX512VPOPCNTDQ, and AVX512VP2INTERSECT.
> 	* include/experimental/bits/simd_builtin.h: Add __odr_helper
> 	template parameter or mark as always_inline.
> 	* include/experimental/bits/simd_fixed_size.h: Ditto.
> 	* include/experimental/bits/simd_math.h: Ditto.
> 	* include/experimental/bits/simd_scalar.h: Ditto.
> 	* include/experimental/bits/simd_neon.h: Add __odr_helper
> 	template parameter.
> 	* include/experimental/bits/simd_ppc.h: Ditto.
> 	* include/experimental/bits/simd_x86.h: Ditto.
> ---
>  libstdc++-v3/include/experimental/bits/simd.h | 380 ++++++++++++------
>  .../include/experimental/bits/simd_builtin.h  |  41 +-
>  .../include/experimental/bits/simd_detail.h   |  40 ++
>  .../experimental/bits/simd_fixed_size.h       |  39 +-
>  .../include/experimental/bits/simd_math.h     |  45 ++-
>  .../include/experimental/bits/simd_neon.h     |   4 +-
>  .../include/experimental/bits/simd_ppc.h      |   4 +-
>  .../include/experimental/bits/simd_scalar.h   |  71 +++-
>  .../include/experimental/bits/simd_x86.h      |   4 +-
>  9 files changed, 440 insertions(+), 188 deletions(-)

-- 
──────────────────────────────────────────────────────────────────────────
 Dr. Matthias Kretz                           https://mattkretz.github.io
 GSI Helmholtz Centre for Heavy Ion Research               https://gsi.de
 stdₓ::simd
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