[Bug c++/15580] New: wrong code generation in c++ assignment operator

["gcc-bugzilla at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

`this' calculated incorrectly for the assignment operator of the virtual base.

Environment:
gcc 3.3.x

How-To-Repeat:

[8<---test.cc---]
struct A { int a; };
struct B : virtual A { };
struct C : virtual A { };
struct D : B, C { };

int
main()
{
    D d;
    d = d;
    d.a = 5;
}
[--->8]

g++ test.cc
./a.out

no optimization should be used, otherwise `d.a' reference will be cached
from assignment operation. in any doubt this is an optimizer error here
is a modified version of the same test.cc which will crash in any of -Oxx
switches:
[...]

void test(D d);

int
main()
{
    D d;
    d = d;
    test(d);
}

void test(D d)
{
}

>Workaround:
downgrade to 3.2.x
------- Additional Comments From unicorn at re dot com dot ua  2004-05-21 23:45 -------
Fix:
downgrade to 3.2.x
- or -
here is a patch for gcc version 3.3.3 [FreeBSD] 20031106:

Index: method.c
===================================================================
RCS file: /home/ncvs/src/contrib/gcc/cp/method.c,v
retrieving revision 1.1.1.10
diff -u -r1.1.1.10 method.c
--- method.c    22 Aug 2003 02:56:03 -0000      1.1.1.10
+++ method.c    21 May 2004 04:52:33 -0000
@@ -665,15 +665,17 @@
       for (i = 0; i < CLASSTYPE_N_BASECLASSES (current_class_type); ++i)
        {
          tree binfo;
+         tree dst;
          tree converted_parm;
 
          binfo = BINFO_BASETYPE (TYPE_BINFO (current_class_type), i);
          /* We must convert PARM directly to the base class
             explicitly since the base class may be ambiguous.  */
          converted_parm = build_base_path (PLUS_EXPR, parm, binfo, 1);
+         dst = build_base_path (PLUS_EXPR, current_class_ref, binfo, 1);
          /* Call the base class assignment operator.  */
          finish_expr_stmt 
-           (build_special_member_call (current_class_ref, 
+           (build_special_member_call (dst, 
                                        ansi_assopname (NOP_EXPR),
                                        build_tree_list (NULL_TREE, 
                                                         converted_parm),

-- 
           Summary: wrong code generation in c++ assignment operator
           Product: gcc
           Version: 3.3
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: unicorn at re dot com dot ua
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15580