https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65660
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2015-04-07
Ever confirmed|0 |1
--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> ---
Indeed g++.dg/vect/slp-pr56812.cc FAILs with -march=bdver2 because we loop
vectorize the testcase (not wrong, but wrong is that we vectorize it by
applying peeling for alignment).
On the tester I tested a "simple"
Index: gcc/tree-vect-data-refs.c
===================================================================
--- gcc/tree-vect-data-refs.c (revision 221808)
+++ gcc/tree-vect-data-refs.c (working copy)
@@ -1548,7 +1548,7 @@ vect_enhance_data_refs_alignment (loop_v
&& all_misalignments_unknown
&& LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
&& (LOOP_VINFO_INT_NITERS (loop_vinfo)
- < 2 * (unsigned) LOOP_VINFO_VECT_FACTOR (loop_vinfo) - 1))
+ < 3 * (unsigned) LOOP_VINFO_VECT_FACTOR (loop_vinfo) - 1))
do_peeling = false;
if (do_peeling
but at this stage this will have too much testsuite fallout (in archs I
did not test).
The "real" fix is to apply similar cost considerations as the final cost model
does when deciding peeling for alignment (which is hardly profitable on most
archs).
A good fix restricted to bdver2 is to increase the suspiciously low cost of
taken/not taken branches. I am going to propose a patch doing that.
