When doing SLP reduction a needlessy marked IV update causes hybrid
SLP and thus pointless unrolling to happen. The following avoids
vectorizing the IV update when not otherwise necessary. Currently
we're creating a dead vector stmt for all inductions that are vectorized.
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.
Richard.
2017-06-02 Richard Biener <rguent...@suse.de>
* tree-vect-loop.c (vect_analyze_loop_operations): Not relevant
PHIs are ok.
* tree-vect-stmts.c (process_use): Do not mark backedge defs
for inductions as relevant.
Index: gcc/tree-vect-loop.c
===================================================================
--- gcc/tree-vect-loop.c (revision 248788)
+++ gcc/tree-vect-loop.c (working copy)
@@ -1708,8 +1708,7 @@ vect_analyze_loop_operations (loop_vec_i
are not used in the outerloop (unless it is double reduction,
i.e., this phi is vect_reduction_def), cause this case
requires to actually do something here. */
- if ((!STMT_VINFO_RELEVANT_P (stmt_info)
- || STMT_VINFO_LIVE_P (stmt_info))
+ if (STMT_VINFO_LIVE_P (stmt_info)
&& STMT_VINFO_DEF_TYPE (stmt_info)
!= vect_double_reduction_def)
{
Index: gcc/tree-vect-stmts.c
===================================================================
--- gcc/tree-vect-stmts.c (revision 248788)
+++ gcc/tree-vect-stmts.c (working copy)
@@ -579,6 +579,20 @@ process_use (gimple *stmt, tree use, loo
gcc_unreachable ();
}
}
+ /* We are also not interested in uses on loop PHI backedges that are
+ inductions. Otherwise we'll needlessly vectorize the IV increment
+ and cause hybrid SLP for SLP inductions. */
+ else if (gimple_code (stmt) == GIMPLE_PHI
+ && STMT_VINFO_DEF_TYPE (stmt_vinfo) == vect_induction_def
+ && (PHI_ARG_DEF_FROM_EDGE (stmt, loop_latch_edge (bb->loop_father))
+ == use))
+ {
+ if (dump_enabled_p ())
+ dump_printf_loc (MSG_NOTE, vect_location,
+ "induction value on backedge.\n");
+ return true;
+ }
+
vect_mark_relevant (worklist, def_stmt, relevant, false);
return true;
