From: "Xiao Zeng" <zengxiao@eswincomputing.com>
To: "Jeff Johnston" <jjohnstn@redhat.com>
Cc: "newlib@sourceware.org" <newlib@sourceware.org>,
"palmer@rivosinc.com" <palmer@rivosinc.com>,
jeffreyalaw <jeffreyalaw@gmail.com>,
"Torbjorn SVENSSON" <torbjorn.svensson@foss.st.com>
Subject: Re: Re: [PATCH] newlib: libc: Improved the readability of strpbrk with minor optimization
Date: Fri, 22 Dec 2023 09:21:54 +0800 [thread overview]
Message-ID: <202312220921541052082@eswincomputing.com> (raw)
In-Reply-To: <CAOox84tuPPEvAX3zrQ4N3gGcq_ONdLg7hwpbeub_8z8xyCRK+A@mail.gmail.com>
2023-12-22 03:05 Jeff Johnston <jjohnstn@redhat.com> wrote:
>
>Patch merged. Thanks.
Thank you, Jeff.
Perhaps the two emails are too similar, I would like to remind you that there is a similar optimization on
<https://sourceware.org/pipermail/newlib/2023/020771.html>.
>
>-- Jeff J.
>
>On Wed, Dec 20, 2023 at 8:16 PM Xiao Zeng <zengxiao@eswincomputing.com>
>wrote:
>
>> 2023-12-21 06:48 Jeff Johnston <jjohnstn@redhat.com> wrote:
>> >
>>
>> >Unless I am missing something, I think the code could be made even simpler
>> >to return the pointer when found and return NULL otherwise.
>> Yes, you have found a more efficient method.
>> After my testing, fewer assembly instructions were generated. This is
>> really exciting.
>>
>> Xiao's 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>
>> ---------------------------------------------------------
>>
>> Jeff's patch
>> ---------------------------------------------------------
>> libc_a-strpbrk.o: file format elf64-littleriscv
>>
>>
>> Disassembly of section .text:
>>
>> 0000000000000000 <strpbrk>:
>> 0: 00054683 lbu a3,0(a0)
>> 4: 02068c63 beqz a3,3c <.L8>
>> 8: 0005c603 lbu a2,0(a1)
>> c: 02060c63 beqz a2,44 <.L12>
>>
>> 0000000000000010 <.L5>:
>> 10: 00058793 mv a5,a1
>> 14: 00060713 mv a4,a2
>> 18: 00c0006f j 24 <.L4>
>>
>> 000000000000001c <.L15>:
>> 1c: 0007c703 lbu a4,0(a5)
>> 20: 00070863 beqz a4,30 <.L14>
>>
>> 0000000000000024 <.L4>:
>> 24: 00178793 addi a5,a5,1
>>
>> 0000000000000028 <.LVL4>:
>> 28: fed71ae3 bne a4,a3,1c <.L15>
>> 2c: 00008067 ret
>>
>> 0000000000000030 <.L14>:
>> 30: 00154683 lbu a3,1(a0)
>> 34: 00150513 addi a0,a0,1
>>
>> 0000000000000038 <.LVL6>:
>> 38: fc069ce3 bnez a3,10 <.L5>
>>
>> 000000000000003c <.L8>:
>> 3c: 00000513 li a0,0
>>
>> 0000000000000040 <.LVL7>:
>> 40: 00008067 ret
>>
>> 0000000000000044 <.L12>:
>> 44: 00154683 lbu a3,1(a0)
>> 48: 00150513 addi a0,a0,1
>> 4c: fe069ce3 bnez a3,44 <.L12>
>> 50: fedff06f j 3c <.L8>
>> ---------------------------------------------------------
>> After careful comparison, it was found that there are fewer assembly
>> instructions after the Jeff's patch.
>>
>> >
>> >index 774db1e..d984745 100644
>> >--- a/newlib/libc/string/strpbrk.c
>> >+++ b/newlib/libc/string/strpbrk.c
>> >@@ -29,23 +29,16 @@ strpbrk (const char *s1,
>> > const char *s2)
>> > {
>> > const char *c = s2;
>> >- if (!*s1)
>> >- return (char *) NULL;
>> >
>> > while (*s1)
>> > {
>> > for (c = s2; *c; c++)
>> > {
>> > if (*s1 == *c)
>> >- break;
>> >+ return (char *) s1;
>> > }
>> >- if (*c)
>> >- break;
>> > s1++;
>> > }
>> >
>> >- if (*c == '\0')
>> >- s1 = NULL;
>> >-
>> >- return (char *) s1;
>> >+ return (char *) NULL;
>> > }
>> >
>> >On Wed, Dec 20, 2023 at 1:12 AM 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
>>
>>
Thanks
Xiao Zeng
prev parent reply other threads:[~2023-12-22 1:22 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
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 [this message]
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