[PATCH] newlib: libc: Improved the readability of strcspn with minor optimization
Xiao Zeng
zengxiao@eswincomputing.com
Wed Dec 20 05:51:23 GMT 2023
2023-12-20 12:24 Jeff Johnston <jjohnstn@redhat.com> wrote:
>
>Patch merged to master.
Thanks, Jeff.
There will be some similar patches in the future, and I will
submit them to the master immediately.
>
>-- 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
>>
>>
Thanks
Xiao Zeng
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