[Ada] Implement new Expression_With_Actions node

[Arnaud Charlet <charlet at adacore dot com>]

This patch is the front end work for implementing a new node type
Expression_With_Actions. This is currently used if the debug flag
-gnatd.X is set and a short circuit form has right hand operand
actions. The sprint syntax is do action; action ... in expression end.
This test program:

procedure ExprActions (A, B, C : Natural; M, N : String) is
begin
   if (A = 23 and then M (1 .. A) = N (1 .. B))
     or else M (A .. B) = M (B .. C)
   then
      null;
   end if;
end ExprActions;

Now generates the following -gnatG output if -gnatd.X is set:

Source recreated from tree for Expractions (body)


procedure expractions (a : natural; b : natural; c : natural; m :
  string; n : string) is
   subtype expractions__S2b is string (n'first(1) .. n'last(1));
   subtype expractions__S1b is string (m'first(1) .. m'last(1));
begin
   if (a = 23 and then
      do
         [constraint_error when
           a >= 1 and then (1 < m'first(1) or else integer(a) > m'last(
             1))
           "range check failed"]
         reference expractions__T4b[constraint_error when
           b >= 1 and then (1 < n'first(1) or else integer(b) > n'last(
             1))
           "range check failed"]
         reference expractions__T6b
      in m (1 .. a) = n (1 .. b) end
   ) or else
      do
         [constraint_error when
           b >= a and then (integer(a) < m'first(1) or else integer(b) >
             m'last(1))
           "range check failed"]
         reference expractions__T8b[constraint_error when
           c >= b and then (integer(b) < m'first(1) or else integer(c) >
             m'last(1))
           "range check failed"]
         reference expractions__T10b
      in m (a .. b) = m (b .. c) end
    then
      null;
   end if;
   return;
end expractions;

This patch does not include the required gigi adjustments to process
this new node (which is why it is under a debug flag for now), so with
only this patch, the above test compiled with -gnatd.X will blowup
in gigi. Eric will commit the corresponding support for
N_Expression_With_Actions in gigi later.

The motivation behind this is to avoid the problem with the old style
expansion of short circuit forms with right operand actions. The old
style introduced a boolean temporary which caused problems with
coverage analysis.

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

2010-06-17  Robert Dewar  <dewar@adacore.com>

	* debug.adb: New debug flag -gnatd.X to use Expression_With_Actions
	node when expanding short circuit form with actions present for right
	opnd.
	* exp_ch4.adb: Minor reformatting
	(Expand_Short_Circuit_Operator): Use new Expression_With_Actions node if
	right opeand has actions present, and debug flag -gnatd.X is set.
	* exp_util.adb (Insert_Actions): Handle case of Expression_With_Actions
	node.
	* nlists.adb (Prepend_List): New procedure
	(Prepend_List_To): New procedure
	* nlists.ads (Prepend_List): New procedure
	(Prepend_List_To): New procedure
	* sem.adb: Add processing for Expression_With_Actions
	* sem_ch4.adb (Analyze_Expression_With_Actions): New procedure
	* sem_ch4.ads (Analyze_Expression_With_Actions): New procedure
	* sem_res.adb: Add processing for Expression_With_Actions.
	* sem_scil.adb: Add processing for Expression_With_Actions
	* sinfo.ads, sinfo.adb (N_Expression_With_Actions): New node.
	* sprint.ads, sprint.adb: Add processing for Expression_With_Actions

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