From: "Xiao Zeng" <zengxiao@eswincomputing.com>
To: "Xiao Zeng" <zengxiao@eswincomputing.com>,
"newlib@sourceware.org" <newlib@sourceware.org>
Cc: "Jeff Johnston" <jjohnstn@redhat.com>,
"palmer@rivosinc.com" <palmer@rivosinc.com>,
jeffreyalaw <jeffreyalaw@gmail.com>,
"Torbjorn SVENSSON" <torbjorn.svensson@foss.st.com>
Subject: Re: [PATCH] newlib: libc: Improved the readability of strpbrk with minor optimization
Date: Wed, 20 Dec 2023 14:25:45 +0800 [thread overview]
Message-ID: <202312201425448232416@eswincomputing.com> (raw)
In-Reply-To: <20231220061054.35685-1-zengxiao@eswincomputing.com>
As mentioned in [PATCH] newlib: libc: Improved the readability of strcspn with minor optimization: <https://sourceware.org/pipermail/newlib/2023/020766.html>
This patch did the same thing and passed the testcases.
Similarly, provide a comparison of risc-v assembly:
no-patch:
---------------------------------------------------------
libc_a-strpbrk.o: file format elf64-littleriscv
Disassembly of section .text:
0000000000000000 <strpbrk>:
0: 00054683 lbu a3,0(a0)
0000000000000004 <.LVL1>:
4: 06068463 beqz a3,6c <.L8>
8: 0005c603 lbu a2,0(a1)
000000000000000c <.LVL2>:
c: 02060e63 beqz a2,48 <.L14>
0000000000000010 <.L6>:
10: 00058713 mv a4,a1
14: 00060793 mv a5,a2
0000000000000018 <.L5>:
18: 00f68e63 beq a3,a5,34 <.L4>
1c: 00174783 lbu a5,1(a4)
20: 00170713 addi a4,a4,1
0000000000000024 <.LVL4>:
24: fe079ae3 bnez a5,18 <.L5>
28: 00154683 lbu a3,1(a0)
2c: 00150513 addi a0,a0,1
0000000000000030 <.LVL5>:
30: fe0690e3 bnez a3,10 <.L6>
0000000000000034 <.L4>:
34: 00074783 lbu a5,0(a4)
38: 00f037b3 snez a5,a5
3c: 40f007b3 neg a5,a5
40: 00f57533 and a0,a0,a5
44: 00008067 ret
0000000000000048 <.L14>:
48: 00154683 lbu a3,1(a0)
4c: 00150513 addi a0,a0,1
0000000000000050 <.LVL8>:
50: fe069ce3 bnez a3,48 <.L14>
54: 00058713 mv a4,a1
58: 00074783 lbu a5,0(a4)
5c: 00f037b3 snez a5,a5
60: 40f007b3 neg a5,a5
64: 00f57533 and a0,a0,a5
0000000000000068 <.LVL9>:
68: 00008067 ret
000000000000006c <.L8>:
6c: 00000513 li a0,0
0000000000000070 <.LVL11>:
70: 00008067 ret
---------------------------------------------------------
patch
---------------------------------------------------------
libc_a-strpbrk.o: file format elf64-littleriscv
Disassembly of section .text:
0000000000000000 <strpbrk>:
0: 00054683 lbu a3,0(a0)
0000000000000004 <.LVL1>:
4: 04068063 beqz a3,44 <.L10>
8: 0005c603 lbu a2,0(a1)
c: 04060063 beqz a2,4c <.L14>
0000000000000010 <.L5>:
10: 00058793 mv a5,a1
14: 00060713 mv a4,a2
18: 00c0006f j 24 <.L4>
000000000000001c <.L17>:
1c: 0007c703 lbu a4,0(a5)
20: 00070863 beqz a4,30 <.L16>
0000000000000024 <.L4>:
24: 00178793 addi a5,a5,1
0000000000000028 <.LVL5>:
28: fee69ae3 bne a3,a4,1c <.L17>
000000000000002c <.L1>:
2c: 00008067 ret
0000000000000030 <.L16>:
30: 00154683 lbu a3,1(a0)
34: 00150513 addi a0,a0,1
0000000000000038 <.LVL8>:
38: fc069ce3 bnez a3,10 <.L5>
000000000000003c <.L6>:
3c: 0007c783 lbu a5,0(a5)
0000000000000040 <.LVL9>:
40: fe0796e3 bnez a5,2c <.L1>
0000000000000044 <.L10>:
44: 00000513 li a0,0
0000000000000048 <.LVL11>:
48: 00008067 ret
000000000000004c <.L14>:
4c: 00154683 lbu a3,1(a0)
50: 00150513 addi a0,a0,1
54: fe069ce3 bnez a3,4c <.L14>
58: 00058793 mv a5,a1
5c: fe1ff06f j 3c <.L6>
---------------------------------------------------------
After careful comparison, it was found that there are fewer assembly
instructions after the patch.
2023-12-20 14:10 Xiao Zeng <zengxiao@eswincomputing.com> wrote:
>
>Signed-off-by: Xiao Zeng <zengxiao@eswincomputing.com>
>---
> newlib/libc/string/strpbrk.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
>diff --git a/newlib/libc/string/strpbrk.c b/newlib/libc/string/strpbrk.c
>index 774db1e6d..95e89c20c 100644
>--- a/newlib/libc/string/strpbrk.c
>+++ b/newlib/libc/string/strpbrk.c
>@@ -37,15 +37,14 @@ strpbrk (const char *s1,
> for (c = s2; *c; c++)
> {
> if (*s1 == *c)
>- break;
>+ goto end;
> }
>- if (*c)
>- break;
> s1++;
> }
>
> if (*c == '\0')
> s1 = NULL;
>
>+end:
> return (char *) s1;
> }
>--
>2.17.1
Thanks
Xiao Zeng
next prev parent reply other threads:[~2023-12-20 6:25 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-20 6:10 Xiao Zeng
2023-12-20 6:25 ` Xiao Zeng [this message]
2023-12-20 22:48 ` Jeff Johnston
2023-12-21 1:16 ` Xiao Zeng
2023-12-21 19:05 ` Jeff Johnston
2023-12-22 1:21 ` Xiao Zeng
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