[Ada] Remove misleading warning/suggestion in membership test

This patch removes a warning on a membership test whose right operand is
given by a range. In many cases the check can be replaced by the use of
attribute 'Valid, but if the bounds of range are type conversion this
replacement would be invorrect and the warning and suggestion are
misleading.

2019-07-22  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_ch4.adb (Expand_N_In): Do not suggest the use of attribute
	'Valid as a replacement for a range check on a discrete type
	when the bounds of the range are given by type conversions,
	because in such a case there are distinct types involved and the
	subbested attribute replacement would be misplaced.

gcc/testsuite/

	* gnat.dg/warn26.adb: New testcase.

From-SVN: r273694

gcc/ada/ChangeLog

+2019-07-22  Ed Schonberg  <schonberg@adacore.com>
+
+	* exp_ch4.adb (Expand_N_In): Do not suggest the use of attribute
+	'Valid as a replacement for a range check on a discrete type
+	when the bounds of the range are given by type conversions,
+	because in such a case there are distinct types involved and the
+	subbested attribute replacement would be misplaced.
+
 2019-07-22  Yannick Moy  <moy@adacore.com>
 
 	* sem_spark.adb (Get_Root_Object, Is_Path_Expression,

gcc/ada/exp_ch4.adb

@@ -6272,6 +6272,10 @@ package body Exp_Ch4 is
               --  Similarly, do not rewrite membership as a validity check if
               --  within the predicate function for the type.
 
+              --  Finally, if the original bounds are type conversions, even
+              --  if they have been folded into constants, there are different
+              --  types involved and 'Valid is not appropriate.
+
             then
                if In_Instance
                  or else (Ekind (Current_Scope) = E_Function
@@ -6279,6 +6283,11 @@ package body Exp_Ch4 is
                then
                   null;
 
+               elsif Nkind (Lo_Orig) = N_Type_Conversion
+                 or else Nkind (Hi_Orig) = N_Type_Conversion
+               then
+                  null;
+
                else
                   Substitute_Valid_Check;
                   goto Leave;

gcc/testsuite/ChangeLog

+2019-07-22  Ed Schonberg  <schonberg@adacore.com>
+
+	* gnat.dg/warn26.adb: New testcase.
+
 2019-07-22  Javier Miranda  <miranda@adacore.com>
 
 	* gnat.dg/class_wide5.adb: New testcase.

gcc/testsuite/gnat.dg/warn26.adb

+--  { dg-do compile }
+
+procedure Warn26 is
+
+   Monitor_Period_Min : constant := 5;
+   Monitor_Period_Max : constant := 30;
+
+   type Monitor_Period is range Monitor_Period_Min .. Monitor_Period_Max;
+
+   subtype Period_T is Positive range 5 .. 30;
+
+   function Id (X : Period_T) return Period_T is (X);
+   Input_Period : Period_T := Id (20);
+begin
+   if Input_Period in
+      Integer (Monitor_Period'First) .. Integer ( Monitor_Period'Last)
+   then
+      null;
+   end if;
+end Warn26;