The existing vector costs stop some beneficial vectorization.

The existing vector costs stop some beneficial vectorization.  This is mostly
due to vector statement cost being set to 3 as well as vector loads having a
higher cost than scalar loads.  This means that even when we vectorize 4x, it
is possible that the cost of a vectorized loop is similar to the scalar
version, and we fail to vectorize.

Using a cost of 3 for a vector operation suggests they are 3 times as
expensive as scalar operations.  Since most vector operations have a
similar throughput as scalar operations, this is not correct.

Using slightly lower values for these heuristics now allows this loop
and many others to be vectorized.  On a proprietary benchmark the gain
from vectorizing this loop is around 15-30% which shows vectorizing it is
indeed beneficial.

	* config/aarch64/aarch64.c (cortexa57_vector_cost):
	Change vec_stmt_cost, vec_align_load_cost and vec_unalign_load_cost.

From-SVN: r242383

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a4f6a34f8f15c2db53aa6fd8cb1fb8324c93ee95..b3967a245dea075e7dfa7dd55625c83512ecf110 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2016-11-14  Wilco Dijkstra  <wdijkstr@arm.com>
+
+       * config/aarch64/aarch64.c (cortexa57_vector_cost):
+       Change vec_stmt_cost, vec_align_load_cost and vec_unalign_load_cost.
+
 2016-11-14  Richard Biener  <rguenther@suse.de>
 
        PR tree-optimization/78312

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index b7d4640826ac1eb8f67642a41fc19419caee9641..bd97c5b701cacc1ccc8481b5249ab657f1258be6 100644 (file)
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -398,12 +398,12 @@ static const struct cpu_vector_cost cortexa57_vector_cost =
   1, /* scalar_stmt_cost  */
   4, /* scalar_load_cost  */
   1, /* scalar_store_cost  */
-  3, /* vec_stmt_cost  */
+  2, /* vec_stmt_cost  */
   3, /* vec_permute_cost  */
   8, /* vec_to_scalar_cost  */
   8, /* scalar_to_vec_cost  */
-  5, /* vec_align_load_cost  */
-  5, /* vec_unalign_load_cost  */
+  4, /* vec_align_load_cost  */
+  4, /* vec_unalign_load_cost  */
   1, /* vec_unalign_store_cost  */
   1, /* vec_store_cost  */
   1, /* cond_taken_branch_cost  */