[2/6] Don't assign a cost to vectorizable_assignment

[Richard Sandiford <Richard.Sandiford@arm.com>]

vectorizable_assignment handles true SSA-to-SSA copies (which hopefully
we don't see in practice) and no-op conversions that are required
to maintain correct gimple, such as changes between signed and
unsigned types.  These cases shouldn't generate any code and so
shouldn't count against either the scalar or vector costs.

Later patches test this, but it seemed worth splitting out.


2019-11-04  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-stmts.c (vectorizable_assignment): Don't add a cost.

Index: gcc/tree-vect-stmts.c
===================================================================
--- gcc/tree-vect-stmts.c	2019-11-05 14:17:43.330141911 +0000
+++ gcc/tree-vect-stmts.c	2019-11-05 14:18:39.169752725 +0000
@@ -5305,7 +5305,7 @@ vectorizable_conversion (stmt_vec_info s
 static bool
 vectorizable_assignment (stmt_vec_info stmt_info, gimple_stmt_iterator *gsi,
 			 stmt_vec_info *vec_stmt, slp_tree slp_node,
-			 stmt_vector_for_cost *cost_vec)
+			 stmt_vector_for_cost *)
 {
   tree vec_dest;
   tree scalar_dest;
@@ -5313,7 +5313,6 @@ vectorizable_assignment (stmt_vec_info s
   loop_vec_info loop_vinfo = STMT_VINFO_LOOP_VINFO (stmt_info);
   tree new_temp;
   enum vect_def_type dt[1] = {vect_unknown_def_type};
-  int ndts = 1;
   int ncopies;
   int i, j;
   vec<tree> vec_oprnds = vNULL;
@@ -5409,7 +5408,8 @@ vectorizable_assignment (stmt_vec_info s
     {
       STMT_VINFO_TYPE (stmt_info) = assignment_vec_info_type;
       DUMP_VECT_SCOPE ("vectorizable_assignment");
-      vect_model_simple_cost (stmt_info, ncopies, dt, ndts, slp_node, cost_vec);
+      /* Don't add a cost here.  SSA copies and no-op conversions
+	 shouldn't generate any code in either scalar or vector form.  */
       return true;
     }