[Ada] Warning on use of predefined operations on an actual fixed-point type

[Pierre-Marie de Rodat <derodat at adacore dot com>]

The compiler warns when a generic actual is a fixed-point type, because
arithmetic operations in the instance will use the predefined operations on
it, even if the type has user-defined primitive operations (unless formsl
surprograms for these operations appear in the generic). This patch refines
this warning to exclude the case where the formsal type is private, because
in this case there can be no suspicious arithmetic operastions in the generic
unit.

Tested on x86_64-pc-linux-gnu, committed on trunk

2018-01-11  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch12.adb (Check_Fixed_Point_Type): Do not apply check if the
	formsl type corresponding to the actual fixed point type is private,
	because in this case there can be no suspicious arithmetic operations
	in the generic unless they reference a formal subprogram.  Clarify
	warning.

gcc/testsuite/

	* gnat.dg/fixedpnt2.adb, gnat.dg/fixedpnt2.ads: New testcase.

--- gcc/ada/sem_ch12.adb
+++ gcc/ada/sem_ch12.adb
@@ -1279,7 +1279,8 @@ package body Sem_Ch12 is
                if No (Formal) then
                   Error_Msg_Sloc := Sloc (Node (Elem));
                   Error_Msg_NE
-                    ("?instance does not use primitive operation&#",
+                    ("?instance uses predefined operation, "
+                      & "not primitive operation&#",
                       Actual, Node (Elem));
                end if;
             end if;
@@ -1717,7 +1718,16 @@ package body Sem_Ch12 is
                           (Formal, Match, Analyzed_Formal, Assoc_List),
                         Assoc_List);
 
-                     if Is_Fixed_Point_Type (Entity (Match)) then
+                     --  Warn when an actual is a fixed-point with user-
+                     --  defined promitives. The warning is superfluous
+                     --  if the fornal is private, because there can be
+                     --  no arithmetic operations in the generic so there
+                     --  no danger of confusion.
+
+                     if Is_Fixed_Point_Type (Entity (Match))
+                       and then not Is_Private_Type
+                         (Defining_Identifier (Analyzed_Formal))
+                     then
                         Check_Fixed_Point_Actual (Match);
                      end if;
 --- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/fixedpnt2.adb
@@ -0,0 +1,25 @@
+--  { dg-do compile }
+
+with Ada.Unchecked_Conversion;
+
+package body Fixedpnt2 is
+
+   function To_Integer_64 is
+      new Ada.Unchecked_Conversion (Source => My_Type,
+                                    Target => T_Integer_64);
+
+   function To_T is
+      new Ada.Unchecked_Conversion (Source => T_Integer_64,
+                                    Target => My_Type);
+
+   function "*" (Left  : in T_Integer_32;
+                 Right : in My_Type)
+      return My_Type is
+         (To_T (S => T_Integer_64 (Left) * To_Integer_64 (S => Right)));
+
+   function "*" (Left  : in My_Type;
+                 Right : in T_Integer_32)
+      return My_Type is
+         (To_T (S => To_Integer_64 (S => Left) * T_Integer_64 (Right)));
+
+end Fixedpnt2;--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/fixedpnt2.ads
@@ -0,0 +1,23 @@
+package Fixedpnt2 is
+
+   type T_Integer_32 is range -2 ** 31 .. 2 ** 31 - 1
+      with Size => 32;
+
+   type T_Integer_64 is range -2 ** 63 .. 2 ** 63 - 1
+      with Size => 64;
+
+   C_Unit  : constant := 0.001; -- One millisecond.
+   C_First : constant := (-2 ** 63) * C_Unit;
+   C_Last  : constant := (2 ** 63 - 1) * C_Unit;
+
+   type My_Type is
+      delta C_Unit range C_First .. C_Last
+      with Size  => 64,
+           Small => C_Unit;
+
+   function "*" (Left : in T_Integer_32; Right : in My_Type)
+     return My_Type;
+   function "*" (Left : in My_Type;      Right : in T_Integer_32)
+     return My_Type;
+
+end Fixedpnt2;