Occured to me when looking into PR81028.
Bootstrap and regtest running on x86_64-unknown-linux-gnu.
Richard.
2017-06-09 Richard Biener <rguent...@suse.de>
* tree-ssa-loop-im.c (execute_sm): Do not force multi-threaded
model if the ref is always written to.
Index: gcc/tree-ssa-loop-im.c
===================================================================
--- gcc/tree-ssa-loop-im.c (revision 249053)
+++ gcc/tree-ssa-loop-im.c (working copy)
@@ -198,6 +198,7 @@ static bitmap_obstack lim_bitmap_obstack
static obstack mem_ref_obstack;
static bool ref_indep_loop_p (struct loop *, im_mem_ref *, struct loop *);
+static bool ref_always_accessed_p (struct loop *, im_mem_ref *, bool);
/* Minimum cost of an expensive expression. */
#define LIM_EXPENSIVE ((unsigned) PARAM_VALUE (PARAM_LIM_EXPENSIVE))
@@ -2025,7 +2026,8 @@ execute_sm (struct loop *loop, vec<edge>
for_each_index (&ref->mem.ref, force_move_till, &fmt_data);
if (bb_in_transaction (loop_preheader_edge (loop)->src)
- || !PARAM_VALUE (PARAM_ALLOW_STORE_DATA_RACES))
+ || (! PARAM_VALUE (PARAM_ALLOW_STORE_DATA_RACES)
+ && ! ref_always_accessed_p (loop, ref, true)))
multi_threaded_model_p = true;
if (multi_threaded_model_p)
