Christopher Layne writes:
> Given this simple toy code:
>
> /* */
> #include <unistd.h>
> #include <stdlib.h>
> #include <stdio.h>
>
> typedef struct cbt__ cbt;
> typedef void (*cbt_cb_display)(cbt *);
>
> struct cbt__ {
> char *text;
> cbt_cb_display display;
> };
>
> static void cbt_display(cbt *c)
> {
> fprintf(stdout, "c->text == %s\n", c->text);
>
> return;
> }
>
> extern cbt *cbt_new(void)
> {
> cbt *c;
>
> c = malloc(sizeof *c);
> c->text = NULL;
> c->display = cbt_display;
>
> return c;
> }
>
> int main(int argc, char **argv)
> {
> cbt *c;
>
> if (argc <= 1) return EXIT_FAILURE;
>
> c = cbt_new();
> c->text = argv[1];
> #ifdef CB
> c->display(c);
> #else
> cbt_display(c);
> #endif
>
> return 0;
> }
> /* */
>
> I notice that it seems impossible to get that callback to ever be inlined.
>
> $ gcc -DCB -W -Wall -pedantic -O2 -S -o /dev/stdout cb.c
> [...]
> movl %eax, (%esp)
> call *4(%eax)
> xorl %eax, %eax
> [...]
>
> $ gcc -DCB -W -Wall -pedantic -O3 -S -o /dev/stdout cb.c
> [...]
> movl %eax, (%esp)
> call cbt_display
> xorl %eax, %eax
> [...]
With your unaltered source code, I get this at -O3:
main:
.LFB28:
subl $1, %edi
pushq %rbx
.LCFI1:
movl $1, %eax
movq %rsi, %rbx
jle .L8
movl $16, %edi
call malloc
movq 8(%rbx), %rdx
movq stdout(%rip), %rdi
movl $.LC0, %esi
movq $cbt_display, 8(%rax)
movq %rdx, (%rax)
xorl %eax, %eax
call fprintf
xorl %eax, %eax
.L8:
popq %rbx
ret
What version of gcc are you using?
Andrew.
