[Bug c++/13118] New: Missed covariant return thunk

[Bug c++/13118] New: Missed covariant return thunk

[grigory at stl dot sarov dot ru]

For routine f6 of class c28 in the hirarchy listed below it is expected 5
covariant thunks to be emitted.
    covariant return thunk [nv:0] [v:0,-12] to c28::f6()
    covariant return thunk [nv:0] [v:0,-16] to c28::f6()
    covariant return thunk [v:0,-16] [v:0,-16] to c28::f6()
    covariant return thunk [v:0,-24] [v:0,-12] to c28::f6()
    covariant return thunk [v:0,-24] [v:0,-16] to c28::f6()

However G++ 3.4 compiler misses (does not generate) the last thunk from the
list. This seems to be a C++ ABI failure.

$ cat test.cpp
struct c0 {};
struct c1 : virtual c0 {
  virtual class ::c0* f6() {};
};

struct c5 {
    virtual void foo(){};
};

struct c10 : virtual c1 {
    virtual void foo(){};
};

struct c11 : virtual c10, c1 {
    int i;
    virtual c1* f6() {}
};

struct c18 : c5, virtual c1 {
    virtual void bar(){};
};

struct c28 : virtual c0, virtual c11 {
    virtual c18* f6() {};
} obj;

$ g++ -c test.cpp
$ nm test.o | grep "_ZTc.*c282f6"
00000006 W _ZTch0_v0_n12_N3c282f6Ev
00000036 W _ZTch0_v0_n16_N3c282f6Ev
00000056 W _ZTcv0_n16_v0_n16_N3c282f6Ev
00000026 W _ZTcv0_n24_v0_n12_N3c282f6Ev

There is no expected thunk "_ZTcv0_n24_v0_n12_N3c282f6Ev" generated.

-- 
           Summary: Missed covariant return thunk
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: grigory at stl dot sarov dot ru
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-redhat-linux
  GCC host triplet: i686-redhat-linux
GCC target triplet: i686-redhat-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118

[Bug c++/13118] [ABI] Missed covariant return thunk

[bangerth at dealii dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Missed covariant return     |[ABI] Missed covariant
                   |thunk                       |return thunk


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118

[Bug c++/13118] [ABI] Missed covariant return thunk

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-11-19 16:32 -------
Nathan, covariant return thunks are yours.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nathan at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118

[Bug c++/13118] [ABI] Missed covariant return thunk

[nathan at gcc dot gnu dot org]

------- Additional Comments From nathan at gcc dot gnu dot org  2003-11-21 09:16 -------
confirmed.
the c11-c28-c28 secondary vtable has two slots for f6. The first
was added by the c1-c1-c1 vtable and expects a c0 pointer return.
The second was added by the c11-c11-c11 vtable and expects
a c1 pointer return. (c0 is a virtual base of c1).
c11-c28-c28's first slot should point to the missing c0 in c18 adjusting
thunk (0,-24,0,-16). The second slot should point to the c1 in c18
adjusting thunk (0,-14,0,-12).

I'll try and attach a testcase that checks things at runtime.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P2                          |P1
   Target Milestone|---                         |3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118

[Bug c++/13118] [ABI] Missed covariant return thunk

[nathan at gcc dot gnu dot org]

------- Additional Comments From nathan at gcc dot gnu dot org  2003-11-21 09:33 -------
Created an attachment (id=5180)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=5180&action=view)
test case

this test case should succeed. on 3.4 it fails with exit code 1

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118

[Bug c++/13118] [ABI] Missed covariant return thunk

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-11-21 14:29 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2003-11-21 14:29:10
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118

[Bug c++/13118] [ABI] Missed covariant return thunk

[grigory at stl dot sarov dot ru]

------- Additional Comments From grigory at stl dot sarov dot ru  2003-11-22 14:46 -------
There is another example illustrating the same problem.

In the hierarchy listed below, c3 shares virtual table both with c2 and c1
bases. That is c3 v-table introduces 3 slots for covariant return type function
"foo". First and second slots contain pointer to adjustment thunks and third one
contains pointer to non-adjusting entry.
        [0] c1-in-c2-in-c3::foo, returning r1-in-r3
        [1] c2-in-c3::foo,       returning r2-in-r3
        [2] c3::foo,             returning r3-in-r3

However the actually generated vtable for c3 contains pointer to wrong thunk in
the first slot:
        [skip]
        16    c3::_ZTcv0_n12_v0_n12_N2c33fooEv
        20    c3::_ZTcv0_n12_v0_n12_N2c33fooEv
        24    c3::foo

Basing on thunk encoding "v0_n12_v0_n12_", contents of c3's and r3's virtual
tables we can say that "this" value will be incorrectly adjusted to c2-in-c3 and
the return value will be adjusted to r2 instead of r1 in the r3's hierarchy.
I.e. actually used thunk appears to be:
        c1-in-c2::foo, returning r1-in-r2

It looks like g++ 3.4 compiler just inherits this slot value from the vtable of
base class c2 introduced as complete object.
        Vtable for c2
        [skip]
        16    c2::_ZTcv0_n12_v0_n12_N2c23fooEv
        20    c2::foo


Class hierarchy
---------------

struct r1 {
    int j;
    virtual ~r1();
};

struct r2 : virtual r1 {
    int j;
    virtual ~r2();
};

struct r3 : virtual r2, virtual r1 {
    int i;
};

struct c1 {
    virtual r1& foo() {};
};

struct c2 : virtual c1 {
    virtual r2& foo() {};
};

struct c3 : c2 {
    virtual r3& foo() {};
};


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118

[Bug c++/13118] [ABI] Missed covariant return thunk

[nathan at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |nathan at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118

[Bug c++/13118] [ABI] Missed covariant return thunk

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2003-12-12 18:22 -------
Subject: Bug 13118

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	nathan@gcc.gnu.org	2003-12-12 18:22:24

Modified files:
	gcc/cp         : ChangeLog cp-tree.h class.c method.c 
	                 semantics.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/g++.dg/abi: covariant3.C 

Log message:
	cp:
	PR c++/13118
	* cp-tree.h (lang_decl_u): Add thunk_alias member.
	(THUNK_VIRTUAL_OFFSET): Must be a FUNCTION_DECL.
	(THUNK_ALIAS_P): Remove.
	(THUNK_ALIAS): Adjust.
	* class.c (update_vtable_entry_for_fn): Get the vbase within the
	overriding function's return type.
	(dump_thunk): Adjust THUNK_ALIAS printing.
	(build_vtbl_initializer): Adjust THUNK_ALIAS use.
	* method.c (make_thunk): Revert 12881 test change. Clear
	THUNK_ALIAS.
	(finish_thunk): Adjust THUNK_ALIAS setting.
	(use_thunk): Adjust THUNK_ALIAS use.
	* semantics.c (emit_associated_thunks): Likewise.
	testsuite:
	PR c++/13118
	* g++.dg/abi/covariant3.C: New.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&r1=1.3796&r2=1.3797
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/cp-tree.h.diff?cvsroot=gcc&r1=1.938&r2=1.939
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/class.c.diff?cvsroot=gcc&r1=1.585&r2=1.586
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/method.c.diff?cvsroot=gcc&r1=1.272&r2=1.273
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/semantics.c.diff?cvsroot=gcc&r1=1.374&r2=1.375
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.3249&r2=1.3250
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/abi/covariant3.C.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118

[Bug c++/13118] [ABI] Missed covariant return thunk

[nathan at gcc dot gnu dot org]

------- Additional Comments From nathan at gcc dot gnu dot org  2003-12-12 18:42 -------
2003-12-12  Nathan Sidwell  <nathan@codesourcery.com>

	PR c++/13118
	* cp-tree.h (lang_decl_u): Add thunk_alias member.
	(THUNK_VIRTUAL_OFFSET): Must be a FUNCTION_DECL.
	(THUNK_ALIAS_P): Remove.
	(THUNK_ALIAS): Adjust.
	* class.c (update_vtable_entry_for_fn): Get the vbase within the
	overriding function's return type.
	(dump_thunk): Adjust THUNK_ALIAS printing.
	(build_vtbl_initializer): Adjust THUNK_ALIAS use.
	* method.c (make_thunk): Revert 12881 test change. Clear
	THUNK_ALIAS.
	(finish_thunk): Adjust THUNK_ALIAS setting.
	(use_thunk): Adjust THUNK_ALIAS use.
	* semantics.c (emit_associated_thunks): Likewise.

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118