[Ada] Remove out-of-range warning in unreachable code

This patch removes a warning in examples like this:

    if cond then
       return; -- or other jump
    end if;
    X := ...; -- where the value is out of range

where cond is known at compile time. It could, for example, be a generic
formal parameter that is known to be True in some instances.

As a side effect, this patch adds new warnings about unreachable code.

gcc/ada/

	* gnatls.adb (Output_License_Information): Remove pragma
	No_Return; call sites deal with Exit_Program.
	* libgnat/g-socthi.adb (C_Connect): Suppress warning about
	unreachable code.
	* sem_ch5.adb (Check_Unreachable_Code): Special-case if
	statements with static conditions.  If we remove unreachable
	code (including the return statement) from a function, add
	"raise Program_Error", so we won't warn about missing returns.
	Remove Original_Node in test for N_Raise_Statement; it's not
	needed.  Remove test for CodePeer_Mode; if Operating_Mode =
	Generate_Code, then CodePeer_Mode can't be True.  Misc cleanup.
	Do not reuse Nxt variable for unrelated purpose (the usage in
	the Kill_Dead_Code loop is entirely local to the loop).
	* sem_ch6.adb: Add check for Is_Transfer. Misc cleanup.
	* sem_prag.adb: Minor.
	* sem_res.adb: Minor.
	* sem_util.adb: Minor cleanup.
	(Is_Trivial_Boolean): Move to nonnested place, so it can be
	called from elsewhere.
	(Is_Static_Constant_Boolean): New function.
	* sem_util.ads (Is_Trivial_Boolean): Export.
	(Is_Static_Constant_Boolean): New function.

1 files changed, 29 insertions, 27 deletions

diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb
index 9cff0f7..cfbf010 100644
--- a/gcc/ada/sem_util.adb
+++ b/gcc/ada/sem_util.adb
@@ -4868,9 +4868,6 @@ package body Sem_Util is
       --  and post-state. Prag is a [refined] postcondition or a contract-cases
       --  pragma. Result_Seen is set when the pragma mentions attribute 'Result
 
-      function Is_Trivial_Boolean (N : Node_Id) return Boolean;
-      --  Determine whether source node N denotes "True" or "False"
-
       -------------------------------------------
       -- Check_Result_And_Post_State_In_Pragma --
       -------------------------------------------
@@ -5243,20 +5240,6 @@ package body Sem_Util is
          end if;
       end Check_Result_And_Post_State_In_Pragma;
 
-      ------------------------
-      -- Is_Trivial_Boolean --
-      ------------------------
-
-      function Is_Trivial_Boolean (N : Node_Id) return Boolean is
-      begin
-         return
-           Comes_From_Source (N)
-             and then Is_Entity_Name (N)
-             and then (Entity (N) = Standard_True
-                         or else
-                       Entity (N) = Standard_False);
-      end Is_Trivial_Boolean;
-
       --  Local variables
 
       Items        : constant Node_Id := Contract (Subp_Id);
@@ -21501,19 +21484,15 @@ package body Sem_Util is
       Kind : constant Node_Kind := Nkind (N);
 
    begin
-      if Kind = N_Simple_Return_Statement
-           or else
-         Kind = N_Extended_Return_Statement
-           or else
-         Kind = N_Goto_Statement
-           or else
-         Kind = N_Raise_Statement
-           or else
-         Kind = N_Requeue_Statement
+      if Kind in N_Simple_Return_Statement
+               | N_Extended_Return_Statement
+               | N_Goto_Statement
+               | N_Raise_Statement
+               | N_Requeue_Statement
       then
          return True;
 
-      elsif (Kind = N_Exit_Statement or else Kind in N_Raise_xxx_Error)
+      elsif Kind in N_Exit_Statement | N_Raise_xxx_Error
         and then No (Condition (N))
       then
          return True;
@@ -21542,6 +21521,29 @@ package body Sem_Util is
       return No (U) or else U = Uint_1;
    end Is_True;
 
+   ------------------------
+   -- Is_Trivial_Boolean --
+   ------------------------
+
+   function Is_Trivial_Boolean (N : Node_Id) return Boolean is
+   begin
+      return Comes_From_Source (N)
+        and then Nkind (N) in N_Identifier | N_Expanded_Name
+        and then Entity (N) in Standard_True | Standard_False;
+   end Is_Trivial_Boolean;
+
+   -----------------------------
+   -- Is_Static_Constant_Name --
+   -----------------------------
+
+   function Is_Static_Constant_Name (N : Node_Id) return Boolean is
+   begin
+      return Comes_From_Source (N)
+        and then Is_Static_Expression (N)
+        and then Nkind (N) in N_Identifier | N_Expanded_Name
+        and then Ekind (Entity (N)) = E_Constant;
+   end Is_Static_Constant_Name;
+
    --------------------------------------
    -- Is_Unchecked_Conversion_Instance --
    --------------------------------------