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[Ada] Out parameters of a null-excluding access type in entries.

Message ID 20140729140233.GA4528@adacore.com
State New
Headers show

Commit Message

Arnaud Charlet July 29, 2014, 2:02 p.m. UTC 
If a procedure or entry has an formal out-parameter of a null-excluding access
type, there is no check applied to the actual before the call. This patch
removes a spurious access check on such parameters on entry calls.

Compiling and executing p.adb must yield;

    Procedure version did not raise exception
    Entry version did not raise exception

---
with Ada.Text_IO; use Ada.Text_IO;
procedure P is
   type Integer_Access is access all Integer;

   An_Integer : aliased Integer;

   procedure Procedure_Version (A : out not null Integer_Access) is
   begin
      A := An_Integer'Access;
   end Procedure_Version;

   protected Object is
      entry Entry_Version (A : out not null Integer_Access);
   end Object;

   protected body Object is
      entry Entry_Version (A : out not null Integer_Access) when True is
         Junk : integer := 0;
      begin
         A := An_Integer'Access;
      end Entry_Version;
   end Object;

   A : Integer_Access;
begin
   A := null;
   Procedure_Version (A);
   Put_Line ("Procedure version did not raise exception");

   A := null;
   Object.Entry_Version (A);
   Put_Line ("Entry version did not raise exception");
end;

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

2014-07-29  Ed Schonberg  <schonberg@adacore.com>

	* exp_ch5.adb (Expand_N_Assignment_Statement): If the target type
	is a null-excluding access type, do not generate a constraint
	check if Suppress_Assignment_Checks is set on assignment node.
	* exp_ch9.adb (Build_Simple_Entry_Call): If actual is an out
	parameter of a null-excluding access type, there is access check
	on entry, so set Suppress_Assignment_Checks on generated statement
	that assigns actual to parameter block.
	* sinfo.ads: Document additional use of Suppress_Assignment_Checks.

Comments

Duncan Sands July 30, 2014, 7:04 a.m. UTC | #1 
Hi Arnaud,

On 29/07/14 16:02, Arnaud Charlet wrote:
> If a procedure or entry has an formal out-parameter of a null-excluding access
> type, there is no check applied to the actual before the call. This patch
> removes a spurious access check on such parameters on entry calls.
>
> Compiling and executing p.adb must yield;
>
>      Procedure version did not raise exception
>      Entry version did not raise exception
>
> ---
> with Ada.Text_IO; use Ada.Text_IO;
> procedure P is
>     type Integer_Access is access all Integer;
>
>     An_Integer : aliased Integer;
>
>     procedure Procedure_Version (A : out not null Integer_Access) is
>     begin
>        A := An_Integer'Access;
>     end Procedure_Version;
>
>     protected Object is
>        entry Entry_Version (A : out not null Integer_Access);
>     end Object;
>
>     protected body Object is
>        entry Entry_Version (A : out not null Integer_Access) when True is
>           Junk : integer := 0;

this variable "Junk" seems useless.

>        begin
>           A := An_Integer'Access;
>        end Entry_Version;
>     end Object;
>
>     A : Integer_Access;
> begin
>     A := null;
>     Procedure_Version (A);
>     Put_Line ("Procedure version did not raise exception");
>
>     A := null;
>     Object.Entry_Version (A);
>     Put_Line ("Entry version did not raise exception");
> end;

Ciao, Duncan.
diff mbox

Patch

Index: exp_ch5.adb
===================================================================
--- exp_ch5.adb	(revision 213163)
+++ exp_ch5.adb	(working copy)
@@ -2001,6 +2001,7 @@ 
       if Is_Access_Type (Typ)
         and then Can_Never_Be_Null (Etype (Lhs))
         and then not Can_Never_Be_Null (Etype (Rhs))
+        and then not Suppress_Assignment_Checks (N)
       then
          Apply_Constraint_Check (Rhs, Etype (Lhs));
       end if;
Index: sinfo.ads
===================================================================
--- sinfo.ads	(revision 213194)
+++ sinfo.ads	(working copy)
@@ -2052,7 +2052,9 @@ 
    --    and range checks in cases where the generated code knows that the
    --    value being assigned is in range and satisfies any predicate. Also
    --    can be set in N_Object_Declaration nodes, to similarly suppress any
-   --    checks on the initializing value.
+   --    checks on the initializing value. In assignment statements it also
+   --    suppresses access checks in the generated code for out- and in-out
+   --    parameters in entry calls.
 
    --  Suppress_Loop_Warnings (Flag17-Sem)
    --    Used in N_Loop_Statement node to indicate that warnings within the
Index: exp_ch9.adb
===================================================================
--- exp_ch9.adb	(revision 213159)
+++ exp_ch9.adb	(working copy)
@@ -4755,7 +4755,8 @@ 
                   --  case of limited type. We cannot assign it unless the
                   --  Assignment_OK flag is set first. An out formal of an
                   --  access type must also be initialized from the actual,
-                  --  as stated in RM 6.4.1 (13).
+                  --  as stated in RM 6.4.1 (13), but no constraint is applied
+                  --  before the call.
 
                   if Ekind (Formal) /= E_Out_Parameter
                     or else Is_Access_Type (Etype (Formal))
@@ -4767,6 +4768,7 @@ 
                        Make_Assignment_Statement (Loc,
                          Name => N_Var,
                          Expression => Relocate_Node (Actual)));
+                     Set_Suppress_Assignment_Checks (Last (Stats));
                   end if;
 
                   Append (N_Node, Decls);