diff mbox series

[v1,2/2] x86: Remove unnecessary overflow check from wcsnlen-sse4_1.S

Message ID 20210623235902.1614933-2-goldstein.w.n@gmail.com
State Committed
Commit 08cbcd4dbc686bb38ec3093aff2f919fbff5ec17
Headers show
Series [v1,1/2] String: Add three more overflow tests cases to test-strnlen.c | expand

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent
dj/TryBot-32bit success Build for i686

Commit Message

Noah Goldstein June 23, 2021, 11:59 p.m. UTC
No bug. The way wcsnlen will check if near the end of maxlen
is the following macro:

	mov	%r11, %rsi;	\
	subq	%rax, %rsi;	\
	andq	$-64, %rax;	\
	testq	$-64, %rsi;	\
	je	L(strnlen_ret)

Which words independently of s + maxlen overflowing. So the
second overflow check is unnecissary for correctness and
just extra overhead in the common no overflow case.

test-strlen.c, test-wcslen.c, test-strnlen.c and test-wcsnlen.c are
all passing

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
---
Sorry I didn't notice this earlier before my last commit. As
of submitting this patch

	a775a7a3eb1e85b54af0b4ee5ff4dcf66772a1fb

Is HEAD of master to maybe rebase so commit history isnt messy?

        
 sysdeps/x86_64/multiarch/strlen-vec.S | 7 -------
 1 file changed, 7 deletions(-)

Comments

H.J. Lu June 24, 2021, 12:41 a.m. UTC | #1
On Wed, Jun 23, 2021 at 5:00 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> No bug. The way wcsnlen will check if near the end of maxlen
> is the following macro:
>
>         mov     %r11, %rsi;     \
>         subq    %rax, %rsi;     \
>         andq    $-64, %rax;     \
>         testq   $-64, %rsi;     \
>         je      L(strnlen_ret)
>
> Which words independently of s + maxlen overflowing. So the
> second overflow check is unnecissary for correctness and
> just extra overhead in the common no overflow case.
>
> test-strlen.c, test-wcslen.c, test-strnlen.c and test-wcsnlen.c are
> all passing
>
> Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> ---
> Sorry I didn't notice this earlier before my last commit. As
> of submitting this patch
>
>         a775a7a3eb1e85b54af0b4ee5ff4dcf66772a1fb
>
> Is HEAD of master to maybe rebase so commit history isnt messy?
>
>
>  sysdeps/x86_64/multiarch/strlen-vec.S | 7 -------
>  1 file changed, 7 deletions(-)
>
> diff --git a/sysdeps/x86_64/multiarch/strlen-vec.S b/sysdeps/x86_64/multiarch/strlen-vec.S
> index 439e486a43..b7657282bd 100644
> --- a/sysdeps/x86_64/multiarch/strlen-vec.S
> +++ b/sysdeps/x86_64/multiarch/strlen-vec.S
> @@ -71,19 +71,12 @@ L(n_nonzero):
>     suffice.  */
>         mov     %RSI_LP, %R10_LP
>         sar     $62, %R10_LP
> -       test    %R10_LP, %R10_LP
>         jnz     __wcslen_sse4_1
>         sal     $2, %RSI_LP
>  # endif
>
> -
>  /* Initialize long lived registers.  */
> -
>         add     %RDI_LP, %RSI_LP
> -# ifdef AS_WCSLEN
> -/* Check for overflow again from s + maxlen * sizeof(wchar_t).  */
> -       jbe     __wcslen_sse4_1
> -# endif
>         mov     %RSI_LP, %R10_LP
>         and     $-64, %R10_LP
>         mov     %RSI_LP, %R11_LP
> --
> 2.25.1
>

LGTM.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

Thanks.
Sunil Pandey April 28, 2022, 12:08 a.m. UTC | #2
On Wed, Jun 23, 2021 at 5:42 PM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Wed, Jun 23, 2021 at 5:00 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > No bug. The way wcsnlen will check if near the end of maxlen
> > is the following macro:
> >
> >         mov     %r11, %rsi;     \
> >         subq    %rax, %rsi;     \
> >         andq    $-64, %rax;     \
> >         testq   $-64, %rsi;     \
> >         je      L(strnlen_ret)
> >
> > Which words independently of s + maxlen overflowing. So the
> > second overflow check is unnecissary for correctness and
> > just extra overhead in the common no overflow case.
> >
> > test-strlen.c, test-wcslen.c, test-strnlen.c and test-wcsnlen.c are
> > all passing
> >
> > Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> > ---
> > Sorry I didn't notice this earlier before my last commit. As
> > of submitting this patch
> >
> >         a775a7a3eb1e85b54af0b4ee5ff4dcf66772a1fb
> >
> > Is HEAD of master to maybe rebase so commit history isnt messy?
> >
> >
> >  sysdeps/x86_64/multiarch/strlen-vec.S | 7 -------
> >  1 file changed, 7 deletions(-)
> >
> > diff --git a/sysdeps/x86_64/multiarch/strlen-vec.S b/sysdeps/x86_64/multiarch/strlen-vec.S
> > index 439e486a43..b7657282bd 100644
> > --- a/sysdeps/x86_64/multiarch/strlen-vec.S
> > +++ b/sysdeps/x86_64/multiarch/strlen-vec.S
> > @@ -71,19 +71,12 @@ L(n_nonzero):
> >     suffice.  */
> >         mov     %RSI_LP, %R10_LP
> >         sar     $62, %R10_LP
> > -       test    %R10_LP, %R10_LP
> >         jnz     __wcslen_sse4_1
> >         sal     $2, %RSI_LP
> >  # endif
> >
> > -
> >  /* Initialize long lived registers.  */
> > -
> >         add     %RDI_LP, %RSI_LP
> > -# ifdef AS_WCSLEN
> > -/* Check for overflow again from s + maxlen * sizeof(wchar_t).  */
> > -       jbe     __wcslen_sse4_1
> > -# endif
> >         mov     %RSI_LP, %R10_LP
> >         and     $-64, %R10_LP
> >         mov     %RSI_LP, %R11_LP
> > --
> > 2.25.1
> >
>
> LGTM.
>
> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
>
> Thanks.
>
> --
> H.J.

I would like to backport this patch to release branches.
Any comments or objections?

--Sunil
diff mbox series

Patch

diff --git a/sysdeps/x86_64/multiarch/strlen-vec.S b/sysdeps/x86_64/multiarch/strlen-vec.S
index 439e486a43..b7657282bd 100644
--- a/sysdeps/x86_64/multiarch/strlen-vec.S
+++ b/sysdeps/x86_64/multiarch/strlen-vec.S
@@ -71,19 +71,12 @@  L(n_nonzero):
    suffice.  */
 	mov	%RSI_LP, %R10_LP
 	sar	$62, %R10_LP
-	test	%R10_LP, %R10_LP
 	jnz	__wcslen_sse4_1
 	sal	$2, %RSI_LP
 # endif
 
-
 /* Initialize long lived registers.  */
-
 	add	%RDI_LP, %RSI_LP
-# ifdef AS_WCSLEN
-/* Check for overflow again from s + maxlen * sizeof(wchar_t).  */
-	jbe	__wcslen_sse4_1
-# endif
 	mov	%RSI_LP, %R10_LP
 	and	$-64, %R10_LP
 	mov	%RSI_LP, %R11_LP