Re: [PATCH v1 2/3] x86: Move and slightly improve memset_erms

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Wed, Jun 29, 2022 at 12:32 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> On Wed, Jun 29, 2022 at 12:26 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Tue, Jun 28, 2022 at 8:27 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> > >
> > > Implementation wise:
> > >     1. Remove the VZEROUPPER as memset_{impl}_unaligned_erms does not
> > >        use the L(stosb) label that was previously defined.
> > >
> > >     2. Don't give the hotpath (fallthrough) to zero size.
> > >
> > > Code positioning wise:
> > >
> > > Move L(memset_{chk}_erms) to its own file.  Leaving it in between the
> >
> >  It is ENTRY, not L.   Did you mean to move them to the end of file?
>
> Will fix L -> ENTRY for V2.

Fixed in V2.
>
> Yes it should be moved to new file in this patch. Was rebase mistake. The file
> change is in the isa raising patch. Will fix both for v2.
> >
> > > memset_{impl}_unaligned both adds unnecessary complexity to the
> > > file and wastes space in a relatively hot cache section.
> > > ---
> > >  .../multiarch/memset-vec-unaligned-erms.S     | 54 ++++++++-----------
> > >  1 file changed, 23 insertions(+), 31 deletions(-)
> > >
> > > diff --git a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> > > index abc12d9cda..d98c613651 100644
> > > --- a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> > > +++ b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> > > @@ -156,37 +156,6 @@ L(entry_from_wmemset):
> > >  #if defined USE_MULTIARCH && IS_IN (libc)
> > >  END (MEMSET_SYMBOL (__memset, unaligned))
> > >
> > > -# if VEC_SIZE == 16
> > > -ENTRY (__memset_chk_erms)
> > > -       cmp     %RDX_LP, %RCX_LP
> > > -       jb      HIDDEN_JUMPTARGET (__chk_fail)
> > > -END (__memset_chk_erms)
> > > -
> > > -/* Only used to measure performance of REP STOSB.  */
> > > -ENTRY (__memset_erms)
> > > -       /* Skip zero length.  */
> > > -       test    %RDX_LP, %RDX_LP
> > > -       jnz      L(stosb)
> > > -       movq    %rdi, %rax
> > > -       ret
> > > -# else
> > > -/* Provide a hidden symbol to debugger.  */
> > > -       .hidden MEMSET_SYMBOL (__memset, erms)
> > > -ENTRY (MEMSET_SYMBOL (__memset, erms))
> > > -# endif
> > > -L(stosb):
> > > -       mov     %RDX_LP, %RCX_LP
> > > -       movzbl  %sil, %eax
> > > -       mov     %RDI_LP, %RDX_LP
> > > -       rep stosb
> > > -       mov     %RDX_LP, %RAX_LP
> > > -       VZEROUPPER_RETURN
> > > -# if VEC_SIZE == 16
> > > -END (__memset_erms)
> > > -# else
> > > -END (MEMSET_SYMBOL (__memset, erms))
> > > -# endif
> > > -
> > >  # if defined SHARED && IS_IN (libc)
> > >  ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
> > >         cmp     %RDX_LP, %RCX_LP
> > > @@ -461,3 +430,26 @@ L(between_2_3):
> > >  #endif
> > >         ret
> > >  END (MEMSET_SYMBOL (__memset, unaligned_erms))
> > > +
> > > +#if defined USE_MULTIARCH && IS_IN (libc) && VEC_SIZE == 16
> > > +ENTRY (__memset_chk_erms)
> > > +       cmp     %RDX_LP, %RCX_LP
> > > +       jb      HIDDEN_JUMPTARGET (__chk_fail)
> > > +END (__memset_chk_erms)
> > > +
> > > +/* Only used to measure performance of REP STOSB.  */
> > > +ENTRY (__memset_erms)
> > > +       /* Skip zero length.  */
> > > +       test    %RDX_LP, %RDX_LP
> > > +       jz       L(stosb_return_zero)
> > > +       mov     %RDX_LP, %RCX_LP
> > > +       movzbl  %sil, %eax
> > > +       mov     %RDI_LP, %RDX_LP
> > > +       rep stosb
> > > +       mov     %RDX_LP, %RAX_LP
> > > +       ret
> > > +L(stosb_return_zero):
> > > +       movq    %rdi, %rax
> > > +       ret
> > > +END (__memset_erms)
> > > +#endif
> > > --
> > > 2.34.1
> > >
> >
> >
> > --
> > H.J.