[Ada] finish implementation of local-raise-to-goto

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk

This patch completes the implementation of the local-raise-to-goto
transformation by generating appropriate warnings if the restriction
No_Exception_Propagation is active. Warnings are generates for implicit
and explicit raises of exceptions not covered by a local handler, and
for handlers that do not handle a local exception.

The following test program shows the warnings in action (text of
test program is appended below).

     1. pragma Restrictions (No_Exception_Propagation);
     2. procedure p (C : in out Natural) is
     3. begin
     4.    begin
     5.       C := C - 1;
     6.    exception
     7.       when Constraint_Error =>
     8.          null;
     9.       when Tasking_Error =>
              |
        >>> warning: pragma Restrictions (No_Exception_Propagation) in effect
        >>> warning: this handler can never be entered, and has been removed

    10.          null;
    11.    end;
    12.
    13.    begin
    14.       C := C - 1;
                     |
        >>> warning: pragma Restrictions (No_Exception_Propagation) in effect
        >>> warning: "Constraint_Error" may result in unhandled exception

    15.    end;
    16.
    17.    begin
    18.       raise Program_Error;
              |
        >>> warning: pragma Restrictions (No_Exception_Propagation) in effect
        >>> warning: execution may raise unhandled exception

    19.    end;
    20. end p;

pragma Restrictions (No_Exception_Propagation);
procedure p (C : in out Natural) is
begin
   begin
      C := C - 1;
   exception
      when Constraint_Error =>
         null;
      when Tasking_Error =>
         null;
   end;

   begin
      C := C - 1;
   end;

   begin
      raise Program_Error;
   end;
end p;

2007-06-06  Thomas Quinot  <quinot@adacore.com>
	    Olivier Hainque  <hainque@adacore.com>
	    Robert Dewar  <dewar@adacore.com>

	* a-except.ads, a-except.adb: (Rmsg_28): Fix description for E.4(18)
	check.
	(Raise_Current_Excep): Call Debug_Raise_Exception just before
	propagation starts, to let debuggers know about the event in a reliable
	fashion.
	(Local_Raise): Moved to System.Exceptions
	More convenient to have this as a separate unit

	* s-except.adb, s-except.ads: New files.

	* a-exextr.adb (Unhandled_Exception): Delete - replaced by
	Debug_Unhandled_Exception in System.Exceptions where it belongs
	together with a couple of other debug helpers.
	(Notify_Unhandled_Exception): Use Debug_Unhandled_Exception instead of
	the former Unhandled_Exception.

	* exp_ch11.ads, exp_ch11.adb: (Possible_Local_Raise): New procedure
	(Warn_No_Exception_Propagation): New procedure
	(Warn_If_No_Propagation): Rewritten for new warning generation
	(Expand_Exception_Handlers): New warning generation
	(Expand_N_Raise_xxx_Error): Rewritten for new warnings
	(Add_Exception_Label): Use Special_Exception_Package_Used for test
	instead of Most_Recent_Exception_Used (accomodates Exception_Traces)
	(Expand_Local_Exception_Handlers): Unconditionally add extra block wrap
	even if restriction is set (makes life easier in Check_Returns)
	(Expand_Local_Exception_Handlers): Follow renamed entity chain when
	checking exception identities.
	(Expand_Local_Exception_Handlers): Do not optimize when all others case
	(Expand_Local_Exception_Handlers): Set Exception_Junk flag on generated
	block for handler (used by Check_Returns)
	(Expand_Local_Exception_Handlers): Local_Raise now takes an address
	(Expand_N_Handled_Sequence_Of_Statements): Properly handle -gnatd.x to
	remove all exception handlers when optimizing local raise statements.
	(Find_Local_Handler): Use Get_Renamed_Entity
	(Expand_N_Handled_Sequence_Of_Statements): If the handled sequence is
	marked analyzed after expanding exception handlers, do not generate
	redundant cleanup actions, because they have been constructed already.

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