vec.h (vNULL): Extend comment to say = vNULL initialization isn't needed for static vars.

	* vec.h (vNULL): Extend comment to say = vNULL initialization
	isn't needed for static vars.

From-SVN: r240445

gcc/ChangeLog

 2016-09-23  Jakub Jelinek  <jakub@redhat.com>
 
+	* vec.h (vNULL): Extend comment to say = vNULL initialization
+	isn't needed for static vars.
+
 	* sel-sched-ir.c (sel_global_bb_info, sel_region_bb_info,
 	loop_nests, s_i_d, last_added_blocks): Remove unnecessary
 	= vNULL initialization of file scope vec.

gcc/vec.h

@@ -410,7 +410,9 @@ struct GTY((user)) vec
 /* Type to provide NULL values for vec<T, A, L>.  This is used to
    provide nil initializers for vec instances.  Since vec must be
    a POD, we cannot have proper ctor/dtor for it.  To initialize
-   a vec instance, you can assign it the value vNULL.  */
+   a vec instance, you can assign it the value vNULL.  This isn't
+   needed for file-scope and function-local static vectors, which
+   are zero-initialized by default.  */
 struct vnull
 {
   template <typename T, typename A, typename L>