[Ada] Crash on 'Img attribute

This patch fixes and issue whereby applying 'Img to a constant
enumerated character type would result in a compiler crash when
assertions are enabled and infinite recursion when they are not.

2019-07-09  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* sem_eval.adb (Expr_Value_E): Add conditional to correctly
	handle constant enumerated character types.

gcc/testsuite/

	* gnat.dg/image1.adb: New testcase.

From-SVN: r273292

gcc/ada/ChangeLog

+2019-07-09  Justin Squirek  <squirek@adacore.com>
+
+	* sem_eval.adb (Expr_Value_E): Add conditional to correctly
+	handle constant enumerated character types.
+
 2019-07-09  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* libgnarl/s-osinte__mingw.ads (CRITICAL_SECTION): Use proper

gcc/ada/sem_eval.adb

@@ -4281,8 +4281,16 @@ package body Sem_Eval is
          return Ent;
       else
          pragma Assert (Ekind (Ent) = E_Constant);
+
+         --  We may be dealing with a enumerated character type constant, so
+         --  handle that case here.
+
+         if Nkind (Constant_Value (Ent)) = N_Character_Literal then
+            return Ent;
+         else
             return Expr_Value_E (Constant_Value (Ent));
          end if;
+      end if;
    end Expr_Value_E;
 
    ------------------

gcc/testsuite/ChangeLog

+2019-07-09  Justin Squirek  <squirek@adacore.com>
+
+	* gnat.dg/image1.adb: New testcase.
+
 2019-07-09  Javier Miranda  <miranda@adacore.com>
 
 	* gnat.dg/rep_clause8.adb: New testcase.

gcc/testsuite/gnat.dg/image1.adb

+--  { dg-do run }
+
+with Ada.Text_IO; use Ada.Text_IO;
+with Ada.Characters.Latin_1;
+
+procedure Image1 is
+   Str : String := Ada.Characters.Latin_1.LF'Img;
+begin
+   if Str /= "LF" then
+      raise Program_Error;
+   end if;
+end Image1;