This patch recognizes additional object declarations whose defining
identifier is known statically to be valid. This allows additional
optimizations to be performed by the front-end.

Executing:

   gcc -c -gnatDG p.ads

On the following sources:

----
with G;
With Q;

package P is

  Val : constant Positive := Q.Config_Value ("Size");

  package My_G is new G (Val);

end P;
----
generic

  Num : Natural := 0;

package G is

  Multi : constant Boolean := Num > 0;

  type Info is array (True .. Multi) of Integer;

  type Arr is array (Natural range <>) of Boolean;

  type Rec (D : Natural) is record
    C : character;
    I : Info;
    E : Arr (0 .. D);
  end record;

end G;
----
package Q is

  function Config_Value (S : String) return Integer;

end Q;
----

Must yield (note that variable Multi has been statically optimized to
true):

----
with g;
with q;
p_E : short_integer := 0;

package p is
   p__R2s : constant integer := q.q__config_value ("Size");
   [constraint_error when
     not (p__R2s >= 1)
     "range check failed"]
   p__val : constant positive := p__R2s;

   package p__my_g is
      p__my_g__num : constant natural := p__val;
      package p__my_g__g renames p__my_g;
      package p__my_g__gGH renames p__my_g__g;
      p__my_g__multi : constant boolean := true;
      type p__my_g__info is array (true .. p__my_g__multi) of integer;
      type p__my_g__arr is array (0 .. 16#7FFF_FFFF# range <>) of
        boolean;
      type p__my_g__rec (d : natural) is record
         c : character;
         i : p__my_g__info;
         e : p__my_g__arr (0 .. d);
      end record;
      [type p__my_g__TinfoB is array (true .. p__my_g__multi range <>) of
        integer]
      freeze p__my_g__TinfoB [
         procedure p__my_g__TinfoBIP (_init : in out p__my_g__TinfoB) is
         begin
            null;
            return;
         end p__my_g__TinfoBIP;
      ]
      freeze p__my_g__info []
      freeze p__my_g__arr [
         procedure p__my_g__arrIP (_init : in out p__my_g__arr) is
         begin
            null;
            return;
         end p__my_g__arrIP;
      ]
      freeze p__my_g__rec [
         procedure p__my_g__recIP (_init : in out p__my_g__rec; d :
           natural) is
         begin
            _init.d := d;
            null;
            return;
         end p__my_g__recIP;
      ]
   end p__my_g;

   package my_g is new g (p__val);
end p;

freeze_generic info
[subtype TinfoD1 is boolean range true .. multi]
freeze_generic TinfoD1
[type TinfoB is array (true .. multi range <>) of integer]
freeze_generic TinfoB
freeze_generic arr
freeze_generic rec
----

2018-11-14  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch3.adb (Analyze_Object_Declaration): Use the
	Actual_Subtype to preserve information about a constant
	initialized with a non-static entity that is known to be valid,
	when the type of the entity has a narrower range than that of
	the nominal subtype of the constant.
	* checks.adb (Determine_Range): If the expression is a constant
	entity that is known-valid and has a defined Actual_Subtype, use
	it to determine the actual bounds of the value, to enable
	additional optimizations.

From-SVN: r266123