------- Comment #5 from ubizjak at gmail dot com 2008-08-04 11:43 -------
Hm, following testcase doesn't vectorize due to vect cost model
(-O2 -msse3 -ftree-vectorize -ffast-math) on i686 target:
--cut here--
void testf(void)
{
int i;
for (i = 0; i < 16; i++)
cf[i] = af[i] + bf[i];
}
--cut here--
Compilation reports:
pr30211.c:8: note: vectorization_factor = 2, niters = 16
pr30211.c:8: note: === vect_update_slp_costs_according_to_vf ===
pr30211.c:8: note: cost model: vector iteration cost = 16 is divisible by
scalar iteration cost = 8 by a factor greater than or equal to the
vectorization factor = 2 .
pr30211.c:8: note: not vectorized: vectorization not profitable.
pr30211.c:8: note: not vectorized: vector version will never be profitable.
However, without cost model the loop in this testcase compiles to:
.L2:
movaps bf(%eax), %xmm0
addps af(%eax), %xmm0
movaps %xmm0, cf(%eax)
addl $16, %eax
cmpl $128, %eax
jne .L2
which is IMO faster than equivalent scalar version:
.L2:
movss bf+4(,%eax,8), %xmm1
addss af+4(,%eax,8), %xmm1
movss bf(,%eax,8), %xmm0
addss af(,%eax,8), %xmm0
movss %xmm0, cf(,%eax,8)
movss %xmm1, cf+4(,%eax,8)
addl $1, %eax
cmpl $16, %eax
jne .L2
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35252
