From: Jeff Johnston <jjohnstn@redhat.com>
To: Xiao Zeng <zengxiao@eswincomputing.com>
Cc: Torbjorn SVENSSON <torbjorn.svensson@foss.st.com>,
"newlib@sourceware.org" <newlib@sourceware.org>,
"vapier@gentoo.org" <vapier@gentoo.org>,
"palmer@rivosinc.com" <palmer@rivosinc.com>,
jeffreyalaw <jeffreyalaw@gmail.com>
Subject: Re: Re: [PATCH] newlib: libc: Improved the readability of strcspn with minor optimization
Date: Tue, 19 Dec 2023 23:24:27 -0500 [thread overview]
Message-ID: <CAOox84tJ3nakbUFtAM6dNdPqcRkOZz=7ToJvhGt0XrrywA7CQg@mail.gmail.com> (raw)
In-Reply-To: <202312161730500900107@eswincomputing.com>
[-- Attachment #1: Type: text/plain, Size: 5632 bytes --]
Patch merged to master.
-- Jeff J.
On Sat, Dec 16, 2023 at 4:31 AM Xiao Zeng <zengxiao@eswincomputing.com>
wrote:
> 2023-12-15 18:28 Torbjorn SVENSSON <torbjorn.svensson@foss.st.com> wrote:
> >
>
> >Hello Xiao,
> >
> >On 2023-12-15 09:31, Xiao Zeng wrote:
> >> Signed-off-by: Xiao Zeng <zengxiao@eswincomputing.com>
> >> ---
> >> newlib/libc/string/strcspn.c | 6 ++----
> >> 1 file changed, 2 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/newlib/libc/string/strcspn.c b/newlib/libc/string/strcspn.c
> >> index abaa93ad6..8ac0bf10c 100644
> >> --- a/newlib/libc/string/strcspn.c
> >> +++ b/newlib/libc/string/strcspn.c
> >> @@ -37,12 +37,10 @@ strcspn (const char *s1,
> >> for (c = s2; *c; c++)
> >> {
> >> if (*s1 == *c)
> >> - break;
> >> + goto end;
> >> }
> >> - if (*c)
> >> - break;
> >> s1++;
> >> }
> >> -
> >> +end:
> >> return s1 - s;
> >> }
> >
> >Just looking at this small snippet of code, I would say that the
> >previous code and your suggestion won't do the same thing.
> >
> >Do you have unit tests that confirm that the behavior is identical with
> >the current implementation and your suggested change?
> >
> >When I run your suggestion, I get return value 0, but with the current
> >implementation it's 3 for this call: strspn("129th", "1234567890").
> >
> >Kind regards,
> >Torbjörn
>
> After applying this patch, provide a comparison of assembly code
> under the risc-v architecture, with default compilation parameters
> used in both of them:
>
> no-patch:
> ---------------------------------------------------------
> libc_a-strcspn.o: file format elf64-littleriscv
>
>
> Disassembly of section .text:
>
> 0000000000000000 <strcspn>:
> 0: 00054683 lbu a3,0(a0)
> 4: 06068263 beqz a3,68 <.L9>
> 8: 0005c803 lbu a6,0(a1)
> c: 00050613 mv a2,a0
>
> 0000000000000010 <.LVL1>:
> 10: 02080463 beqz a6,38 <.L14>
>
> 0000000000000014 <.L6>:
> 14: 00058793 mv a5,a1
> 18: 00080713 mv a4,a6
> 1c: 00c0006f j 28 <.L5>
>
> 0000000000000020 <.L4>:
> 20: 0007c703 lbu a4,0(a5)
> 24: 02070863 beqz a4,54 <.L17>
>
> 0000000000000028 <.L5>:
> 28: 00178793 addi a5,a5,1
>
> 000000000000002c <.LVL5>:
> 2c: fee69ae3 bne a3,a4,20 <.L4>
>
> 0000000000000030 <.L7>:
> 30: 40a60533 sub a0,a2,a0
>
> 0000000000000034 <.LVL7>:
> 34: 00008067 ret
>
> 0000000000000038 <.L14>:
> 38: 00164683 lbu a3,1(a2)
> 3c: 00160613 addi a2,a2,1
> 40: fe0688e3 beqz a3,30 <.L7>
> 44: 00164683 lbu a3,1(a2)
> 48: 00160613 addi a2,a2,1
> 4c: fe0696e3 bnez a3,38 <.L14>
> 50: fe1ff06f j 30 <.L7>
>
> 0000000000000054 <.L17>:
> 54: 00164683 lbu a3,1(a2)
> 58: 00160613 addi a2,a2,1
> 5c: fa069ce3 bnez a3,14 <.L6>
> 60: 40a60533 sub a0,a2,a0
>
> 0000000000000064 <.LVL13>:
> 64: 00008067 ret
>
> 0000000000000068 <.L9>:
> 68: 00000513 li a0,0
>
> 000000000000006c <.LVL15>:
> 6c: 00008067 ret
> ---------------------------------------------------------
>
> patch
> ---------------------------------------------------------
> libc_a-strcspn.o: file format elf64-littleriscv
>
>
> Disassembly of section .text:
>
> 0000000000000000 <strcspn>:
> 0: 00054683 lbu a3,0(a0)
> 4: 04068a63 beqz a3,58 <.L2>
> 8: 0005c803 lbu a6,0(a1)
> c: 00050613 mv a2,a0
>
> 0000000000000010 <.LVL1>:
> 10: 02080c63 beqz a6,48 <.L14>
>
> 0000000000000014 <.L6>:
> 14: 00058793 mv a5,a1
> 18: 00080713 mv a4,a6
> 1c: 00c0006f j 28 <.L5>
>
> 0000000000000020 <.L4>:
> 20: 0007c703 lbu a4,0(a5)
> 24: 00070a63 beqz a4,38 <.L16>
>
> 0000000000000028 <.L5>:
> 28: 00178793 addi a5,a5,1
>
> 000000000000002c <.LVL5>:
> 2c: fee69ae3 bne a3,a4,20 <.L4>
>
> 0000000000000030 <.L7>:
> 30: 40a60533 sub a0,a2,a0
>
> 0000000000000034 <.LVL7>:
> 34: 00008067 ret
>
> 0000000000000038 <.L16>:
> 38: 00164683 lbu a3,1(a2)
> 3c: 00160613 addi a2,a2,1
> 40: fc069ae3 bnez a3,14 <.L6>
> 44: fedff06f j 30 <.L7>
>
> 0000000000000048 <.L14>:
> 48: 00164683 lbu a3,1(a2)
> 4c: 00160613 addi a2,a2,1
> 50: fe069ce3 bnez a3,48 <.L14>
> 54: fddff06f j 30 <.L7>
>
> 0000000000000058 <.L2>:
> 58: 00000513 li a0,0
>
> 000000000000005c <.LVL12>:
> 5c: 00008067 ret
> ---------------------------------------------------------
> After careful comparison, it was found that there are fewer assembly
> instructions after the patch.
>
> Thanks
> Xiao Zeng
>
>
next prev parent reply other threads:[~2023-12-20 4:24 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-15 8:31 Xiao Zeng
2023-12-15 10:28 ` Torbjorn SVENSSON
2023-12-16 4:45 ` Xiao Zeng
2023-12-16 4:56 ` Xiao Zeng
2023-12-20 15:08 ` Torbjorn SVENSSON
2023-12-21 1:22 ` Xiao Zeng
2023-12-16 9:30 ` Xiao Zeng
2023-12-20 4:24 ` Jeff Johnston [this message]
2023-12-20 5:51 ` Xiao Zeng
2023-12-20 22:24 ` Brian Inglis
2023-12-21 8:00 ` Stefan Tauner
2023-12-21 17:47 ` Brian Inglis
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