How to inline string.h function on linux?

问题

I want to optimize some code such that all the functions in string.h will be inlined. I'm on x86_64.

I've tried -O3, -minline-all-stringops and when I do "nm a.out" it shows it is calling the glibc version.

Checking with gcc -S, I see the calls.

What am I missing? There are dozens of #ifdef _SOME_SETTING_ in string.h, and bits/string3.h shows the inline version, but I don't know how to get there.

for example:

$ cat test.c
#include <string.h>

main() {
    char *a, *b;
    strcpy(b,a);
}
/*

When compiled with:

gcc -minline-all-stringops -O6 -I. -S -o test.S test.c

Produces:

    .file   "test.c"
    .text
    .p2align 4,,15
.globl main
    .type   main, @function
main:
.LFB12:
    .cfi_startproc
    subq    $8, %rsp
    .cfi_def_cfa_offset 16
    xorl    %esi, %esi
    xorl    %edi, %edi
    call    strcpy
    addq    $8, %rsp
    .cfi_def_cfa_offset 8
    ret
    .cfi_endproc
.LFE12:
    .size   main, .-main
    .ident  "GCC: (GNU) 4.5.1 20100924 (Red Hat 4.5.1-4)"
    .section    .note.GNU-stack,"",@progbits
*/

回答1:

If a function implementation is not in the header file and in a separate compilation unit, it cannot be inlined unless you have a compiler that can do LTCG.

Sounds like you'll need to write the implementation yourself.

来源：https://stackoverflow.com/questions/5187735/how-to-inline-string-h-function-on-linux