Fix gather/scatter check when updating a vector epilogue loop

update_epilogue_loop_vinfo applies SSA renmaing to the DR_REF of a
gather or scatter, so that vect_check_gather_scatter continues to work.
However, we sometimes also rely on vect_check_gather_scatter when
using gathers and scatters to implement strided accesses.

This showed up on existing tests when testing with fixed-length
-msve-vector-bits=128.

2020-01-10  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-loop.c (update_epilogue_loop_vinfo): Update DR_REF
	for any type of gather or scatter, including strided accesses.

From-SVN: r280111

gcc/ChangeLog

@@ -1,3 +1,8 @@
+2020-01-10  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* tree-vect-loop.c (update_epilogue_loop_vinfo): Update DR_REF
+	for any type of gather or scatter, including strided accesses.
+
 2020-01-10  Andre Vieira  <andre.simoesdiasvieira@arm.com>
 
 	* tree-vectorizer.h (get_dr_vinfo_offset): Add missing function

gcc/tree-vect-loop.c

@@ -8451,7 +8451,7 @@ update_epilogue_loop_vinfo (class loop *epilogue, tree advance)
 	 updated offset we set using ADVANCE.  Instead we have to make sure the
 	 reference in the data references point to the corresponding copy of
 	 the original in the epilogue.  */
-      if (STMT_VINFO_GATHER_SCATTER_P (stmt_vinfo))
+      if (STMT_VINFO_MEMORY_ACCESS_TYPE (stmt_vinfo) == VMAT_GATHER_SCATTER)
 	{
 	  DR_REF (dr)
 	    = simplify_replace_tree (DR_REF (dr), NULL_TREE, NULL_TREE,