https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98365
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2021-01-05
Blocks| |53947
Ever confirmed|0 |1
Keywords| |missed-optimization
Status|UNCONFIRMED |NEW
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
The issue is that we hit
/* If this isn't a nested cycle or if the nested cycle reduction value
is used ouside of the inner loop we cannot handle uses of the reduction
value. */
if (nlatch_def_loop_uses > 1 || nphi_def_loop_uses > 1)
{
if (dump_enabled_p ())
dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
"reduction used in loop.\n");
return NULL;
}
because cnt_21 is used in both the update and the COND_EXPR. The reduction
doesn't fit the cond reductions we support but is a blend of a cond and
regular reduction. Making the COND-reduction support handle this case should
be possible though.
Using 'int' we arrive at handled IL:
# cnt_19 = PHI <cnt_8(7), 0(15)>
_ifc__32 = _4 == _7 ? 1 : 0;
cnt_8 = cnt_19 + _ifc__32;
so adjusting if-conversion can indeed help.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations
