------- Comment #1 from rguenth at gcc dot gnu dot org 2007-04-25 15:38 -------
Because it calls into libgcc and that without tail-calling:
_Z5func1y:
.LFB2:
pushl %ebp
.LCFI2:
movl %esp, %ebp
.LCFI3:
subl $24, %esp
.LCFI4:
movl 8(%ebp), %eax
movl 12(%ebp), %edx
movl %eax, (%esp)
movl %edx, 4(%esp)
call __ctzdi2
leave
ret
libgcc implements it as
int
__ctzDI2 (UDWtype x)
{
const DWunion uu = {.ll = x};
UWtype word;
Wtype ret, add;
if (uu.s.low)
word = uu.s.low, add = 0;
else
word = uu.s.high, add = W_TYPE_SIZE;
count_trailing_zeros (ret, word);
return ret + add;
}
(count_trailing_zeros is expanded to asm bsfl on x86, that's ok)
The question remains why we don't tailcall. And we could expand the
long-long version inline.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2007-04-25 15:38:21
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31695
