[Ada] Secondary stack leaks during object initialization

[Ada] Secondary stack leaks during object initialization

This patch modifies the transient scope mechanism to prevent secondary stack
leaks during object initialization. The modifications are as follows:

1) Prior to this change, the secondary stack was never managed within type
initialization procedures, for reasons unknown. It is speculated that the
controlled type model used at that time may have influenced this decision.
The secondary stack is now managed within type initialization procedures
in order to recover the memory once individual components or whole objects
are initialized.

2) A transient scope now delegates the secondary stack management to an
enclosing scope if there is no suitable context to wrap. This ensures that
the requirement to manage the secondary stack is not lost when the scope was
established for that purpose in mind.

3) A previous mechanism which examined the definition of a type (recursively)
to determine whether the type will involve the secondary stack was removed
because a) the mechanism could not detect this need with certainty, and b) the
trigger for secondary stack usage is now moved to the resolution of function
calls, which is always accurate.

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

--  types.ads

with Ada.Finalization; use Ada.Finalization;

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

   procedure Initialize (Obj : in out Ctrl);

   function Make_Ctrl return Ctrl;
   function Make_Ctrl_From (Obj : Ctrl) return Ctrl;

   type Constr is array (1 .. 3) of Ctrl;
   type Unconstr is array (Integer range <>) of Ctrl;

   function Make_Constr return Constr;
   function Make_Unconstr (Low : Integer; High : Integer) return Unconstr;

   type Rec_1 is new Controlled with record
      Comp : Ctrl := Make_Ctrl;
   end record;

   type Rec_2 is new Controlled with record
      Comp : Ctrl := Make_Ctrl_From (Make_Ctrl);
   end record;

   type Rec_3 is new Controlled with record
      Comp : Constr := Make_Constr;
   end record;

   type Rec_4 is new Controlled with record
      Comp : Unconstr (1 .. 3) := Make_Unconstr (1, 3);
   end record;

   type Rec_5 is record
      Comp : Integer := 1 + Make_Ctrl.Id;
   end record;

   type Rec_6 is record
      Comp : Boolean := (for all X in 1 .. Make_Ctrl.Id =>
                           X = Make_Ctrl.Id);
   end record;
end Types;

--  types.adb

package body Types is
   Id_Gen : Integer := 0;

   procedure Initialize (Obj : in out Ctrl) is
   begin
      Id_Gen := Id_Gen + 1;
      Obj.Id := Id_Gen;
   end Initialize;

   function Make_Constr return Constr is
      Result : constant Constr := (others => Make_Ctrl);
   begin
      return Result;
   end Make_Constr;

   function Make_Ctrl return Ctrl is
      Result : Ctrl;
   begin
      return Result;
   end Make_Ctrl;

   function Make_Ctrl_From (Obj : Ctrl) return Ctrl is
      Result : Ctrl;
   begin
      Result.Id := Obj.Id;
      return Result;
   end Make_Ctrl_From;

   function Make_Unconstr (Low : Integer; High : Integer) return Unconstr is
      Result : constant Unconstr (Low .. High) := (others => Make_Ctrl);
   begin
      return Result;
   end Make_Unconstr;
end Types;

--  maker.ads

generic
   type Obj_Typ is private;
procedure Maker (Count : Positive);

--  maker.adb

procedure Maker (Count : Positive) is
   procedure Create is
      Obj : Obj_Typ;
      pragma Warnings (Off, Obj);
   begin null; end Create;

begin
   for Iter in 1 .. Count loop
      Create;
   end loop;
end Maker;

--  leaks.adb

with Maker;
with Types; use Types;

with Maker;
with Types; use Types;

procedure Leaks is
   procedure Make_1 is new Maker (Rec_1);
   procedure Make_2 is new Maker (Rec_2);
   procedure Make_3 is new Maker (Rec_3);
   procedure Make_4 is new Maker (Rec_4);
   procedure Make_5 is new Maker (Rec_5);
   procedure Make_6 is new Maker (Rec_6);

begin
   Make_1 (5_000);
   Make_2 (5_000);
   Make_3 (5_000);
   Make_4 (5_000);
   Make_5 (5_000);
   Make_6 (5_000);
end Leaks;

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

$ gnatmake -q leaks.adb
$ valgrind ./leaks > leaks.txt 2>&1
$ grep -c "still reachable" leaks.txt
0

2018-01-11  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* exp_aggr.adb (Convert_Aggr_In_Object_Decl): Update the call to
	Establish_Transient_Scope.
	(Convert_To_Assignments): Update the call to Establish_Transient_Scope.
	(Expand_Array_Aggregate): Update the call to Establish_Transient_Scope.
	* exp_ch6.adb (Expand_Call_Helper): Update the call to
	Establish_Transient_Scope.
	(Make_Build_In_Place_Call_In_Object_Declaration): Update the call to
	Establish_Transient_Scope.
	* exp_ch7.adb (Establish_Transient_Scope): Restructured. Delegate the
	management of the secondary stack to an enclosing scope if there is no
	suitable construct to wrap, and the transient scope was intended to
	manage the secondary stack.
	(Find_Node_To_Be_Wrapped): Restructured. A case_statement_alternative
	is a valid boundary for a transient expression which comes from the
	statements of the alternative, otherwise alternatives cannot be
	wrapped. Assignments of controlled objects which have controlled
	actions suppressed now stop the traversal as there is no point in
	looking for an enclosing construct. Add several N_xxx_Body choices to
	the termination conditions for completeness.
	* exp_ch7.ads (Establish_Transient_Scope): Update the parameter profile
	and the associated comment on usage.
	* exp_smem.adb (Add_Shared_Var_Lock_Procs): Update the call to
	Establish_Transient_Scope.
	(Add_Write_After): Update the call to Establish_Transient_Scope.
	* sem_res.adb (Check_Initialization_Call): Removed.
	(Resolve_Actuals): Account for additional cases where finalization
	actions are required by utilizing predicate Needs_Finalization rather
	than Is_Controlled.
	(Resolve_Call): Type initialization procedures can now utilize
	transient scopes to manage the secondary stack, thus preventing leaks
	during initialization.  Remove the previous kludgy algorithm which
	attempts to manage the secondary stack at the object creation site.

From-SVN: r256513