[Bug c++/32992] New: Incorrect code generated for anonymous union

[Bug c++/32992] New: Incorrect code generated for anonymous union

[scovich at gmail dot com]

Compiling and running the code below produces the following output:
    $ g++ -Wall -DT=long -g3 union-bug.C && ./a.out
    &array=   0x7fff11782ef0
    &a=       0x7fff11782f20
    B={1,3,5}
    A={-1719443200,4196007,-1719451616}

A and B should contain the same values, but A contains garbage instead because
the two members of the union do not reside at the same address.

Changing T 'int' produces the expected output:
    $ g++ -Wall -DT=int -g3 union-bug.C && ./a.out
    &array=   0x7fff1fbf6370
    &a=       0x7fff1fbf6370
    B={1,3,5}
    A={1,3,5}

'char' and 'short' also work correctly; '__m128i' (SSE register) breaks. 

This bug affects both gcc-4.1.2 and gcc-4.3

// union-bug.C
#include <cstdio>
struct A {
  T _a;
  T _b;
  T _c;
};
struct B {
  T _array[3];
  operator A() {
    union {
      T array[3];
      A a;
    };
    printf("&array=   %p\n&a=       %p\n", &array, &a);
    for(int i=0; i < 3; i++)
      array[i] = _array[i];
    return a;
  }
};
int main() {
  B b = {{1,3,5}};
  A a = b;
  printf("B={%d,%d,%d}\n", (int) b._array[0], (int) b._array[1], (int)
b._array[2]);
  printf("A={%d,%d,%d}\n", (int) a._a, (int) a._b, (int) a._c);
  return 0;
}


-- 
           Summary: Incorrect code generated for anonymous union
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: scovich at gmail dot com
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32992

[Bug c++/32992] Incorrect code generated for anonymous union and return

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-08-06 05:07 -------
This is a front-end bug.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
 GCC target triplet|x86_64-linux-gnu            |
           Keywords|                            |wrong-code
            Summary|Incorrect code generated for|Incorrect code generated for
                   |anonymous union             |anonymous union and return


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32992

[Bug c++/32992] [4.1/4.2/4.3 Regression] Incorrect code generated for anonymous union and return

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-08-10 00:51 -------
This is most likely caused by:
2005-09-09  Richard Henderson  <rth@redhat.com>

        PR debug/20998
        * cp-tree.def (ALIAS_DECL): Remove.
        * cp-lang.c (cp_init_ts): Remove support for it.
        * error.c (dump_decl): Likewise.
        * name-lookup.c (pushdecl): Likewise.
        * semantics.c (finish_id_expression): Likewise.
        * decl2.c (build_anon_union_vars): Use a VAR_DECL with
        DECL_VALUE_EXPR instead.


Confirmed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
      Known to fail|                            |4.1.0 4.2.0 4.3.0
      Known to work|                            |4.0.0 3.4.0 3.3.3
   Last reconfirmed|0000-00-00 00:00:00         |2007-08-10 00:51:02
               date|                            |
            Summary|Incorrect code generated for|[4.1/4.2/4.3 Regression]
                   |anonymous union and return  |Incorrect code generated for
                   |                            |anonymous union and return
   Target Milestone|---                         |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32992

[Bug c++/32992] [4.1/4.2/4.3 Regression] Incorrect code generated for anonymous union and return

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-08-10 00:51:02         |2007-08-13 16:03:38
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32992

[Bug c++/32992] [4.1/4.2/4.3 Regression] Incorrect code generated for anonymous union and return

[jakub at gcc dot gnu dot org]

------- Comment #3 from jakub at gcc dot gnu dot org  2007-08-15 12:08 -------
Subject: Bug 32992

Author: jakub
Date: Wed Aug 15 12:08:42 2007
New Revision: 127510

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=127510
Log:
        PR c++/32992
        * typeck.c (check_return_expr): Don't NRV optimize vars in
        anonymous unions.
        * decl.c (finish_function): Comment fix.

        * g++.dg/opt/nrv14.C: New test.

Added:
    trunk/gcc/testsuite/g++.dg/opt/nrv14.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl.c
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32992

[Bug c++/32992] [4.1/4.2/4.3 Regression] Incorrect code generated for anonymous union and return

[jakub at gcc dot gnu dot org]

------- Comment #4 from jakub at gcc dot gnu dot org  2007-08-20 08:11 -------
Subject: Bug 32992

Author: jakub
Date: Mon Aug 20 08:10:54 2007
New Revision: 127640

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=127640
Log:
        PR c++/32992
        * typeck.c (check_return_expr): Don't NRV optimize vars in
        anonymous unions.
        * decl.c (finish_function): Comment fix.

        * g++.dg/opt/nrv14.C: New test.

Added:
    branches/gcc-4_2-branch/gcc/testsuite/g++.dg/opt/nrv14.C
Modified:
    branches/gcc-4_2-branch/gcc/cp/ChangeLog
    branches/gcc-4_2-branch/gcc/cp/decl.c
    branches/gcc-4_2-branch/gcc/cp/typeck.c
    branches/gcc-4_2-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32992

[Bug c++/32992] [4.1/4.2/4.3 Regression] Incorrect code generated for anonymous union and return

[jakub at gcc dot gnu dot org]

------- Comment #5 from jakub at gcc dot gnu dot org  2007-08-20 08:17 -------
Subject: Bug 32992

Author: jakub
Date: Mon Aug 20 08:17:21 2007
New Revision: 127641

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=127641
Log:
        PR c++/32992
        * typeck.c (check_return_expr): Don't NRV optimize vars in
        anonymous unions.
        * decl.c (finish_function): Comment fix.

        * g++.dg/opt/nrv14.C: New test.

Added:
    branches/gcc-4_1-branch/gcc/testsuite/g++.dg/opt/nrv14.C
Modified:
    branches/gcc-4_1-branch/gcc/cp/ChangeLog
    branches/gcc-4_1-branch/gcc/cp/decl.c
    branches/gcc-4_1-branch/gcc/cp/typeck.c
    branches/gcc-4_1-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32992

[Bug c++/32992] [4.1/4.2/4.3 Regression] Incorrect code generated for anonymous union and return

[jakub at gcc dot gnu dot org]

------- Comment #6 from jakub at gcc dot gnu dot org  2007-08-20 08:19 -------
Fixed.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32992