[Ada] Suppress warnings on unreferenced parameters of dispatching ops

If the -gnatwf switch is used to activate warnings on unreferenced
formal parameters, the warning is no longer given if the subprogram is
dispatching, because such warnings tend to be noise. It is quite common
to have a parameter that is necessary just because the subprogram is
overriding, or just because we need a controlling parameter for the
dispatch.

2019-08-19  Bob Duff  <duff@adacore.com>

gcc/ada/

	* sem_warn.adb (Warn_On_Unreferenced_Entity): Suppress warning
	on formal parameters of dispatching operations.

gcc/testsuite/

	* gnat.dg/warn29.adb, gnat.dg/warn29.ads: New testcase.

From-SVN: r274663

gcc/ada/ChangeLog

@@ -1,3 +1,8 @@
+2019-08-19  Bob Duff  <duff@adacore.com>
+
+	* sem_warn.adb (Warn_On_Unreferenced_Entity): Suppress warning
+	on formal parameters of dispatching operations.
+
 2019-08-19  Ed Schonberg  <schonberg@adacore.com>
 
 	* sem_res.adb (Resolve_Call): A call to an expression function

gcc/ada/sem_warn.adb

@@ -4407,11 +4407,31 @@ package body Sem_Warn is
                         E := Body_E;
                      end if;
 
-                     if not Is_Trivial_Subprogram (Scope (E)) then
-                        Error_Msg_NE -- CODEFIX
-                          ("?u?formal parameter & is not referenced!",
-                           E, Spec_E);
-                     end if;
+                     declare
+                        B : constant Node_Id := Parent (Parent (Scope (E)));
+                        S : Entity_Id := Empty;
+                     begin
+                        if Nkind_In (B,
+                                     N_Expression_Function,
+                                     N_Subprogram_Body,
+                                     N_Subprogram_Renaming_Declaration)
+                        then
+                           S := Corresponding_Spec (B);
+                        end if;
+
+                        --  Do not warn for dispatching operations, because
+                        --  that causes too much noise. Also do not warn for
+                        --  trivial subprograms.
+
+                        if (not Present (S)
+                            or else not Is_Dispatching_Operation (S))
+                          and then not Is_Trivial_Subprogram (Scope (E))
+                        then
+                           Error_Msg_NE -- CODEFIX
+                             ("?u?formal parameter & is not referenced!",
+                              E, Spec_E);
+                        end if;
+                     end;
                   end if;
                end if;
 

gcc/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2019-08-19  Bob Duff  <duff@adacore.com>
+
+	* gnat.dg/warn29.adb, gnat.dg/warn29.ads: New testcase.
+
 2019-08-19  Ed Schonberg  <schonberg@adacore.com>
 
 	* gnat.dg/expr_func9.adb: New testcase.

gcc/testsuite/gnat.dg/warn29.adb

@@ -0,0 +1,11 @@
+--  { dg-do compile }
+--  { dg-options "-gnatwa" }
+
+with Text_IO; use Text_IO;
+
+package body Warn29 is
+   procedure P (X : T; Y : Integer) is
+   begin
+      Put_Line ("hello");
+   end P;
+end Warn29;

gcc/testsuite/gnat.dg/warn29.ads

@@ -0,0 +1,4 @@
+package Warn29 is
+   type T is tagged null record;
+   procedure P (X : T; Y : Integer);
+end Warn29;