* Re: [PATCH v1 2/2] x86: Small improvements for wcslen
[not found] ` <CAMe9rOo+mCgBdnhz4b9O52Cuy5GGmc08KB9XPuH0RDJpCrT5sg@mail.gmail.com>
@ 2022-05-12 19:55 ` Sunil Pandey
0 siblings, 0 replies; only message in thread
From: Sunil Pandey @ 2022-05-12 19:55 UTC (permalink / raw)
To: H.J. Lu, Libc-stable Mailing List; +Cc: Noah Goldstein, GNU C Library
On Mon, Mar 28, 2022 at 11:53 AM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Fri, Mar 25, 2022 at 3:13 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > Just a few QOL changes.
> > 1. Prefer `add` > `lea` as it has high execution units it can run
> > on.
> > 2. Don't break macro-fusion between `test` and `jcc`
> > 3. Reduce code size by removing gratuitous padding bytes (-90
> > bytes).
> >
> > geometric_mean(N=20) of all benchmarks New / Original: 0.959
> >
> > All string/memory tests pass.
> > ---
> > sysdeps/x86_64/wcslen.S | 86 ++++++++++++++++++++---------------------
> > 1 file changed, 41 insertions(+), 45 deletions(-)
> >
> > diff --git a/sysdeps/x86_64/wcslen.S b/sysdeps/x86_64/wcslen.S
> > index c9165dbf03..d641141d75 100644
> > --- a/sysdeps/x86_64/wcslen.S
> > +++ b/sysdeps/x86_64/wcslen.S
> > @@ -40,82 +40,82 @@ ENTRY (__wcslen)
> > pxor %xmm0, %xmm0
> >
> > lea 32(%rdi), %rax
> > - lea 16(%rdi), %rcx
> > + addq $16, %rdi
> > and $-16, %rax
> >
> > pcmpeqd (%rax), %xmm0
> > pmovmskb %xmm0, %edx
> > pxor %xmm1, %xmm1
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm1
> > pmovmskb %xmm1, %edx
> > pxor %xmm2, %xmm2
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm2
> > pmovmskb %xmm2, %edx
> > pxor %xmm3, %xmm3
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm3
> > pmovmskb %xmm3, %edx
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm0
> > pmovmskb %xmm0, %edx
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm1
> > pmovmskb %xmm1, %edx
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm2
> > pmovmskb %xmm2, %edx
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm3
> > pmovmskb %xmm3, %edx
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm0
> > pmovmskb %xmm0, %edx
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm1
> > pmovmskb %xmm1, %edx
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm2
> > pmovmskb %xmm2, %edx
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > pcmpeqd (%rax), %xmm3
> > pmovmskb %xmm3, %edx
> > + addq $16, %rax
> > test %edx, %edx
> > - lea 16(%rax), %rax
> > jnz L(exit)
> >
> > and $-0x40, %rax
> > @@ -132,104 +132,100 @@ L(aligned_64_loop):
> > pminub %xmm0, %xmm2
> > pcmpeqd %xmm3, %xmm2
> > pmovmskb %xmm2, %edx
> > + addq $64, %rax
> > test %edx, %edx
> > - lea 64(%rax), %rax
> > jz L(aligned_64_loop)
> >
> > pcmpeqd -64(%rax), %xmm3
> > pmovmskb %xmm3, %edx
> > + addq $48, %rdi
> > test %edx, %edx
> > - lea 48(%rcx), %rcx
> > jnz L(exit)
> >
> > pcmpeqd %xmm1, %xmm3
> > pmovmskb %xmm3, %edx
> > + addq $-16, %rdi
> > test %edx, %edx
> > - lea -16(%rcx), %rcx
> > jnz L(exit)
> >
> > pcmpeqd -32(%rax), %xmm3
> > pmovmskb %xmm3, %edx
> > + addq $-16, %rdi
> > test %edx, %edx
> > - lea -16(%rcx), %rcx
> > jnz L(exit)
> >
> > pcmpeqd %xmm6, %xmm3
> > pmovmskb %xmm3, %edx
> > + addq $-16, %rdi
> > test %edx, %edx
> > - lea -16(%rcx), %rcx
> > - jnz L(exit)
> > -
> > - jmp L(aligned_64_loop)
> > + jz L(aligned_64_loop)
> >
> > .p2align 4
> > L(exit):
> > - sub %rcx, %rax
> > + sub %rdi, %rax
> > shr $2, %rax
> > test %dl, %dl
> > jz L(exit_high)
> >
> > - mov %dl, %cl
> > - and $15, %cl
> > + andl $15, %edx
> > jz L(exit_1)
> > ret
> >
> > - .p2align 4
> > + /* No align here. Naturally aligned % 16 == 1. */
> > L(exit_high):
> > - mov %dh, %ch
> > - and $15, %ch
> > + andl $(15 << 8), %edx
> > jz L(exit_3)
> > add $2, %rax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_1):
> > add $1, %rax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_3):
> > add $3, %rax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_tail0):
> > - xor %rax, %rax
> > + xorl %eax, %eax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_tail1):
> > - mov $1, %rax
> > + movl $1, %eax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_tail2):
> > - mov $2, %rax
> > + movl $2, %eax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_tail3):
> > - mov $3, %rax
> > + movl $3, %eax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_tail4):
> > - mov $4, %rax
> > + movl $4, %eax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_tail5):
> > - mov $5, %rax
> > + movl $5, %eax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_tail6):
> > - mov $6, %rax
> > + movl $6, %eax
> > ret
> >
> > - .p2align 4
> > + .p2align 3
> > L(exit_tail7):
> > - mov $7, %rax
> > + movl $7, %eax
> > ret
> >
> > END (__wcslen)
> > --
> > 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
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