[Bug ada/19220] New: Return-by-reference type wrongly considered return-by-copy (regression)

[baldrick at free dot fr]

gcc from current CVS, and also at the pre-ssa tag, both generate wrong code 
for the following example (a version of the Rosen trick).  The basic problem 
seems to be that A_Type is returned by copy even though it is a 
return-by-reference type (it has a component, R, which is a return-by-reference 
type; R is a return-by-reference type because the full view is limited 
private).  GNAT 3.15p produces the following correct result: 
 
./x 
Mechanism: 2 
 
 0 
 1 
 
 1 
 2 
 
Recent versions of gcc produce the following wrong result: 
 
./x 
Mechanism: 1 
 
 0 
 0 
 
 1 
 1 
 
---chop here--- 
 
package B is 
 
   type A_Type is limited private; 
 
   function Get_The_A return A_Type; 
 
   procedure Increment (An_A : A_Type); 
 
   procedure Print (An_A : A_Type); 
 
private 
 
   type R_Type (An_A : access A_Type) is limited null record; 
 
   type A_Type is record 
      R : R_Type (A_Type'Access); 
      I : Integer := 0; 
   end record; 
 
end; 
 
with Ada.Text_IO; use Ada.Text_IO; 
 
package body B is 
 
   The_A : A_Type; 
 
   function Get_The_A return A_Type is 
   begin 
      return The_A; 
   end; 
 
   procedure Increment (An_A : A_Type) is 
   begin 
      An_A.R.An_A.I := An_A.R.An_A.I + 1; 
   end; 
 
   procedure Print (An_A : A_Type) is 
   begin 
      Put_Line (An_A.I'Img); 
   end; 
 
end; 
 
with Ada.Text_IO; use Ada.Text_IO; 
with B; use B; 
 
procedure X is 
 
   procedure Look is 
      The_A_Reference : A_Type renames Get_The_A; 
   begin 
      Print (The_A_Reference); 
      Increment (The_A_Reference); 
      Print (The_A_Reference); 
   end; 
 
begin 
   Put_Line ("Mechanism:" & Integer'Image (Get_The_A'Mechanism_Code)); 
   New_Line; 
   Look; 
   New_Line; 
   Look; 
end;

-- 
           Summary: Return-by-reference type wrongly considered return-by-
                    copy (regression)
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ada
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: baldrick at free dot fr
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19220