On 26. 03. 20, 11:59, Arnaud POULIQUEN wrote:
>
>
> On 3/26/20 1:01 AM, Joe Perches wrote:
>> On Wed, 2020-03-25 at 14:31 +0100, Jiri Slaby wrote:
>>> The question was exactly about that: can a compiler optimize it to a
>>> bare number or will strlen call remain there?
>>
>> $ cat str.c
>> #include <string.h>
>>
>> int foo(void)
>> {
>> return strlen("abc");
>> }
>>
>> $ gcc -c -O2 str.c
>> $ objdump -d str.o
>> str.o: file format elf64-x86-64
>>
>>
>> Disassembly of section .text:
>>
>> 0000000000000000 <foo>:
>> 0: f3 0f 1e fa endbr64
>> 4: b8 03 00 00 00 mov $0x3,%eax
>> 9: c3 retq
>>
>>
> same result with arm gcc using -O1 or -Og:
>
> str.o: file format elf32-littlearm
>
>
> Disassembly of section .text:
>
> 00000000 <foo>:
> 0: e3a00003 mov r0, #3
> 4: e12fff1e bx lr
>
> So in conclusion replacing sizeof by srlen even if not optimized in -o0, right?
Right, gcc guys just confirmed, that it's constant-folded during parsing
already. I asked them as I tried to dump the tree.original and the
constant was already there.
So we are safe to use strlen, at least for gcc :P. Others should adapt
if they don't follow.
thanks,
--
js
suse labs
