https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78205
Bug ID: 78205
Summary: BB vectorization confused by too large load groups
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Blocks: 53947
Target Milestone: ---
double x, a[4], b[4], c[5];
void foo ()
{
a[0] = c[0];
a[1] = c[1];
a[2] = c[0];
a[3] = c[1];
b[0] = c[2];
b[1] = c[3];
b[2] = c[2];
b[3] = c[3];
x = c[4];
}
if you comment the load from c[4] the testcase will be vectorized. If not the
we run into
/* ??? The following is overly pessimistic (as well as the loop
case above) in the case we can statically determine the excess
elements loaded are within the bounds of a decl that is accessed.
Likewise for BB vectorizations using masked loads is a possibility.
*/
if (bb_vinfo && slp_perm && group_size % nunits != 0)
{
dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
"BB vectorization with gaps at the end of a load "
"is not supported\n");
return false;
}
I do have a hackish patch.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations
