[Ada] Implement pragma Short_Circuit_And_Or

[Arnaud Charlet <charlet at adacore dot com>]

This patch implements a new configuration pragma Short_Circuit_And_Or
that treats any AND on Standard.Boolean operands as AND THEN, and any
OR on Standard.Boolean operands as OR ELSE. This can be useful in the
context of certification tools requiring short circuited logical
operators.

The following program:

pragma Short_Circuit_And_Or;
function scandor (a, b : integer) return integer is
begin
   if a > 0 and b > 0 then
      return 23;
   elsif a > 23 or b > 23 then
      return 24;
   else
      return 43;
   end if;
end scandor;

compiled with -gnatG yields:

Source recreated from tree for scandor (body)

pragma short_circuit_and_or;

function scandor (a : integer; b : integer) return integer is
begin
   if a > 0 and then b > 0 then
      return 23;
   elsif a > 23 or else b > 23 then
      return 24;
   else
      return 43;
   end if;
end scandor;

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

2009-11-30  Robert Dewar  <dewar@adacore.com>

	* exp_ch4.adb (Expand_N_Op_And): Implement pragma Short_Circuit_And_Or
	(Expand_N_Op_Or): Implement pragma Short_Circuit_And_Or
	* opt.ads (Short_Circuit_And_Or): New flag
	* par-prag.adb: Add dummy entry for pragma Short_Circuit_And_Or
	* sem_prag.adb: Implement pragma Short_Circuit_And_Or
	* snames.ads-tmpl: Add entries for pragma Short_Circuit_And_Or

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