[Ada] Document attribute Has_Tagged_Values in GNAT RM

gcc/ada/

	* doc/gnat_rm/implementation_defined_attributes.rst
	(Has_Tagged_Values): Document based on the existing description
	of Has_Access_Type and the comment for Has_Tagged_Component,
	which is where frontend evaluates this attribute.
	* gnat_rm.texi: Regenerate.
	* sem_attr.adb (Analyze_Attribute): Merge processing of
	Has_Access_Type and Has_Tagged_Component attributes.
	* sem_util.adb (Has_Access_Type): Fix casing in comment.
	* sem_util.ads (Has_Tagged_Component): Remove wrong (or
	outdated) comment about the use of this routine to implement the
	equality operator.

gcc/ada/doc/gnat_rm/implementation_defined_attributes.rst

@@ -483,6 +483,19 @@ otherwise.  The intended use of this attribute is in conjunction with generic
 definitions.  If the attribute is applied to a generic private type, it
 indicates whether or not the corresponding actual type has discriminants.
 
+Attribute Has_Tagged_Values
+===========================
+.. index:: Tagged values, testing for
+
+.. index:: Has_Tagged_Values
+
+The prefix of the ``Has_Tagged_Values`` attribute is a type. The result is a
+Boolean value which is True if the type is a composite type (array or record)
+that is either a tagged type or has a subcomponent that is tagged, and is False
+otherwise. The intended use of this attribute is in conjunction with generic
+definitions. If the attribute is applied to a generic private type, it
+indicates whether or not the corresponding actual type has access values.
+
 Attribute Img
 =============
 .. index:: Img

gcc/ada/sem_attr.adb

@@ -3868,7 +3868,7 @@ package body Sem_Attr is
       -- Elab_Spec --
       ---------------
 
-      --  Shares processing with Elab_Body
+      --  Shares processing with Elab_Body attribute
 
       ----------------
       -- Elaborated --
@@ -4118,7 +4118,9 @@ package body Sem_Attr is
       -- Has_Access_Values --
       -----------------------
 
-      when Attribute_Has_Access_Values =>
+      when Attribute_Has_Access_Values
+         | Attribute_Has_Tagged_Values
+      =>
          Check_Type;
          Check_E0;
          Set_Etype (N, Standard_Boolean);
@@ -4142,10 +4144,7 @@ package body Sem_Attr is
       -- Has_Tagged_Values --
       -----------------------
 
-      when Attribute_Has_Tagged_Values =>
-         Check_Type;
-         Check_E0;
-         Set_Etype (N, Standard_Boolean);
+      --  Shares processing with Has_Access_Values attribute
 
       -----------------------
       -- Has_Discriminants --

gcc/ada/sem_util.adb

@@ -11396,7 +11396,7 @@ package body Sem_Util is
             Comp : Entity_Id;
 
          begin
-            --  Loop to Check components
+            --  Loop to check components
 
             Comp := First_Component_Or_Discriminant (Typ);
             while Present (Comp) loop

gcc/ada/sem_util.ads

@@ -1503,9 +1503,7 @@ package Sem_Util is
    function Has_Tagged_Component (Typ : Entity_Id) return Boolean;
    --  Returns True if Typ is a composite type (array or record) that is either
    --  a tagged type or has a subcomponent that is tagged. Returns False for a
-   --  noncomposite type, or if no tagged subcomponents are present. This
-   --  function is used to check if "=" has to be expanded into a bunch
-   --  component comparisons.
+   --  noncomposite type, or if no tagged subcomponents are present.
 
    function Has_Unconstrained_Access_Discriminants
      (Subtyp : Entity_Id) return Boolean;