On Mon, 06 Apr 2015, Joe Perches wrote:
> On Mon, 2015-04-06 at 08:40 +0200, Nicholas Mc Guire wrote:
> > #define msecs_to_jiffies(m) \
> > (__builtin_constant_p (m) \
> > ? ((m) * HZ / MSECS_PER_SEC ) : __msecs_to_jiffies(m))
> []
> > main:
> > .LFB12:
> > .cfi_startproc
> > subq $8, %rsp #,
> > .cfi_def_cfa_offset 16
> > movl $10, %esi #,
> > movl $.LC0, %edi #,
> > xorl %eax, %eax #
> > call printf #
>
> vs:
>
> > static inline unsigned long msecs_to_jiffies(int m)
> > {
> > return __builtin_constant_p (m) ?
> > (m) * HZ / MSECS_PER_SEC : __msecs_to_jiffies(m);
> > }
> []
> > main:
> > .LFB13:
> > .cfi_startproc
> > subq $8, %rsp #,
> > .cfi_def_cfa_offset 16
> > xorl %esi, %esi #
> > movl $.LC0, %edi #,
> > xorl %eax, %eax #
> > call printf #
> >
> > giving it another run from scratch somewhere I simply screwed up or
> > overlooked some detail.
>
> If the optimizer was doing it's job properly, wouldn't
> the macro and inline output object code be the same?
>
yes - and they are - that was my mistake I grabed the
wrong asm snippet - here is the complete test case
also made a mess of the code while trimming down
the mail - so here is the single test case showing,
I think, that inline works as well and as expected.
testi.h:
#define HZ 100
#define MSECS_PER_SEC 1000
#define TIMEOUT 100
extern inline unsigned long __msecs_to_jiffies(int m);
unsigned long msecs_to_jiffies(int m)
{
return __builtin_constant_p(m) ? ((m) * HZ / MSECS_PER_SEC ) :
__msecs_to_jiffies(m);
}
test.c:
#include <stdio.h>
#include "testi.h"
unsigned long __msecs_to_jiffies(int m)
{
return (m * HZ / MSECS_PER_SEC);
}
int main(int argc, char **argv) {
//int m = atoi(argv[1]);
int m = TIMEOUT;
printf("%lu\n",msecs_to_jiffies(m));
return 0;
}
compiled with:
gcc -O2 -S --verbose-asm test.c
<snip>
main:
.LFB13:
.cfi_startproc
subq $8, %rsp #,
.cfi_def_cfa_offset 16
movl $10, %esi #,
movl $.LC0, %edi #,
xorl %eax, %eax #
call printf #
<snip>
need to cleanup here :)
thx!
hofrat
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