[PATCH] x86-64: Optimize strlen/strnlen/wcslen/wcsnlen with AVX2

[H.J. Lu]

On Thu, Jun 1, 2017 at 11:12 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
> Optimize strlen/strnlen/wcslen/wcsnlen with AVX2 to check 32 bytes with
> a single vector compare instruction.  It is as fast as SSE2 versions for
> size <= 16 bytes and up to 1X faster for or size > 16 bytes on Haswell.
> Select AVX2 version on AVX2 machines where vzeroupper is preferred and
> AVX unaligned load is fast.
>
> NB: It uses TZCNT instead of BSF since TZCNT produces the same result
> as BSF for non-zero input.  TZCNT is faster than BSF and is executed
> as BSF if machine doesn't support TZCNT.
>
> Any comments?
>
> H.J.
> ---
>         * sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
>         strlen-avx2, strnlen-avx2 and wcslen-avx2 and wcsnlen-avx2.
>         * sysdeps/x86_64/multiarch/ifunc-impl-list.c
>         (__libc_ifunc_impl_list): Add tests for __strlen_avx2,
>         __strlen_sse2, __strnlen_avx2, __strnlen_sse2, __wcslen_avx2,
>         __wcslen_sse2, __wcsnlen_avx2 and __wcsnlen_sse2.
>         * sysdeps/x86_64/multiarch/strlen-avx2.S: New file.
>         * sysdeps/x86_64/multiarch/strlen.S: Likewise.
>         * sysdeps/x86_64/multiarch/strnlen-avx2.S: Likewise.
>         * sysdeps/x86_64/multiarch/strnlen.S: Likewise.
>         * sysdeps/x86_64/multiarch/wcslen-avx2.S: Likewise.
>         * sysdeps/x86_64/multiarch/wcslen.S: Likewise.
>         * sysdeps/x86_64/multiarch/wcsnlen-avx2.S: Likewise.
>         * sysdeps/x86_64/multiarch/wcsnlen.S: Likewise.

Updated patch with IFUNC selector in C.


-- 
H.J.
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