[Ada] Optimization of anonymous access-to-controlled types

[Arnaud Charlet <charlet at adacore dot com>]

This patch modifies the creation of finalization masters for anonymous access-
to-controlled types. Prior to this change, each compilation unit utilized a
single heterogeneous finalization master to service all allocations where the
associated type is anonymous access-to-controlled. This patch removes the use
of the single heterogeneous finalization master and instead introduces multiple
homogenous finalization masters. This leads to increase in performance because
allocation no longer needs to maintain a mapping between allocated object and
corresponding Finalize_Address primitive in a runtime hash data structure. As
a result, anonymous access-to-controlled types are on par with named access-to-
controlled types.

------------
-- Source --
------------

--  types.ads

with Ada.Finalization; use Ada.Finalization;

package Types is
   type Ctrl is new Controlled with record
      Id : Natural;
   end record;

   --  Anonymous types

   type Anon_Discr (Discr : access Ctrl) is null record;

   type Anon_Comps is record
      Comp_1 : access Ctrl;
      Comp_2 : access Ctrl;
   end record;

   type Anon_Array is array (1 .. 5) of access Ctrl;

   --  Named types

   type Ctrl_Ptr is access all Ctrl;

   type Named_Discr (Discr : Ctrl_Ptr) is null record;

   type Named_Discr_Ptr is access all Named_Discr;

   type Named_Comps is record
      Comp_1 : Ctrl_Ptr;
      Comp_2 : Ctrl_Ptr;
   end record;
end Types;

--  performance.adb

with Ada.Calendar;     use Ada.Calendar;
with Ada.Finalization; use Ada.Finalization;
with Ada.Text_IO;      use Ada.Text_IO;
with Types;            use Types;

procedure Performance is
   Percentage     : constant := 0.3;     --  30%
   Max_Iterations : constant := 50_000;

   Diff_A  : Duration;
   Diff_N  : Duration;
   Factor  : Duration;
   Start_A : Time;
   Start_N : Time;

begin
   Start_A := Clock;

   for Iteration in 1 .. Max_Iterations loop
      declare
         Anon_Discr_Obj : access Anon_Discr :=
                            new Anon_Discr'(Discr =>
                              new Ctrl'(Controlled with Id => 1));
         Anon_Comps_Obj : constant Anon_Comps :=
                            (Comp_1 => new Ctrl'(Controlled with Id => 2),
                             Comp_2 => new Ctrl'(Controlled with Id => 3));
      begin null; end;
   end loop;

   Diff_A  := Clock - Start_A;
   Start_N := Clock;

   for Iteration in 1 .. Max_Iterations loop
      declare
         Named_Discr_Obj : Named_Discr_Ptr :=
                             new Named_Discr'(Discr =>
                               new Ctrl'(Controlled with Id => 4));
         Named_Comps_Obj : constant Named_Comps :=
                             (Comp_1 => new Ctrl'(Controlled with Id => 5),
                              Comp_2 => new Ctrl'(Controlled with Id => 6));
      begin null; end;
   end loop;

   Diff_N := Clock - Start_N;
   Factor := Diff_N * Percentage;

   if Diff_N - Factor < Diff_A and then Diff_A < Diff_N + Factor then
      Put_Line ("Anonymous vs Named within expected percentage");
   else
      Put_Line ("ERROR");
   end if;
end Performance;

----------------------------
-- Compilation and output --
----------------------------

$ gnatmake -q performance.adb
$ ./performance
Anonymous vs Named within expected percentage

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

2016-05-02  Hristian Kirtchev  <kirtchev@adacore.com>

	* einfo.adb Anonymous_Master now uses Node35.
	(Anonymous_Master): Update the assertion and node reference.
	(Set_Anonymous_Master): Update the assertion and node reference.
	(Write_Field35_Name): Add output for Anonymous_Master.
	(Write_Field36_Name): The output is now undefined.
	* einfo.ads Update the node and description of attribute
	Anonymous_Master. Remove prior occurrences in entities as this
	is now a type attribute.
	* exp_ch3.adb (Expand_Freeze_Array_Type): Remove local variable
	Ins_Node. Anonymous access- to-controlled component types no
	longer need finalization masters. The master is now built when
	a related allocator is expanded.
	(Expand_Freeze_Record_Type): Remove local variable Has_AACC. Do not
	detect whether the record type has at least one component of anonymous
	access-to- controlled type. These types no longer need finalization
	masters. The master is now built when a related allocator is expanded.
	* exp_ch4.adb Remove with and use clauses for Lib and Sem_Ch8.
	(Current_Anonymous_Master): Removed.
	(Expand_N_Allocator): Call Build_Anonymous_Master to create a
	finalization master for an anonymous access-to-controlled type.
	* exp_ch6.adb (Add_Finalization_Master_Actual_To_Build_In_Place_Call):
	Call routine Build_Anonymous_Master to create a finalization master
	for an anonymous access-to-controlled type.
	* exp_ch7.adb (Allows_Finalization_Master): New routine.
	(Build_Anonymous_Master): New routine.
	(Build_Finalization_Master): Remove formal parameter
	For_Anonymous. Use Allows_Finalization_Master to determine whether
	circumstances warrant a finalization master. This routine no
	longer creates masters for anonymous access-to-controlled types.
	(In_Deallocation_Instance): Removed.
	* exp_ch7.ads (Build_Anonymous_Master): New routine.
	(Build_Finalization_Master): Remove formal parameter For_Anonymous
	and update the comment on usage.
	* sem_util.adb (Get_Qualified_Name): New routines.
	(Output_Name): Reimplemented.
	(Output_Scope): Removed.
	* sem_util.ads (Get_Qualified_Name): New routines.

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