[Bug c++/64077] New: dynamic_cast incorrectly rejected for private base

[Bug c++/64077] New: dynamic_cast incorrectly rejected for private base

[gcc at dixie dot net.nz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64077

            Bug ID: 64077
           Summary: dynamic_cast incorrectly rejected for private base
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc at dixie dot net.nz

I believe this is rejects-valid:

class Base { public: virtual ~Base () {} };
class Derived: virtual Base { public: virtual ~Derived() {} };
class D2: virtual public Base, public Derived { public: D2() {} ~D2() {} };

#include <cassert>
int main ()
{
        Derived *p = new D2;
        assert(dynamic_cast<Base *>(p)); // unexpected error: ‘Base’ is an
inaccessible base of ‘Derived’
}


The following lookup_base call should not issue errors.  Also it should do
access checks at global scope, not using friendship or access rights granted by
the local scope.

--- orig/gcc/cp/rtti.c     2014-06-13 08:47:08.000000000 +1200
+++ new/gcc/cp/rtti.c       2014-11-25 19:13:06.656252034 +1300
@@ -626,8 +626,8 @@ build_dynamic_cast_1 (tree type, tree ex
      convert statically.  */
   {
     tree binfo = lookup_base (TREE_TYPE (exprtype), TREE_TYPE (type),
-                             ba_check, NULL, complain);
-    if (binfo)
+                             ba_check | ba_ignore_scope, NULL, 0);
+    if (binfo && binfo != error_mark_node)
       return build_static_cast (type, expr, complain);
   }
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Subject: [Bug c/59332] Segmentation fault in inline_summary with LTO + attribute optimize
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idY332

--- Comment #7 from Dmitry Gorbachev <d.g.gorbachev at gmail dot com> ---
Recent GCC 5 accepts both "lto" and "no-lto". However, they work on a per-file
rather then on a per-function basis...

[Bug c++/64077] dynamic_cast incorrectly rejected for private base

[daniel.kruegler at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64077

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler@googlemail.
                   |                            |com

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to Andrew Dixie from comment #0)
> I believe this is rejects-valid:

I disagree with your interpretation. This was resolved a while ago by core
issue 665:

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#665

The essential wording that reflects this can be found in [expr.dynamic.cast]
p5:

"In both the pointer and reference cases, the program is ill-formed if cv2 has
greater cv-qualification than cv1 or if B is an inaccessible or ambiguous base
class of D."
>From gcc-bugs-return-468703-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Wed Nov 26 20:52:21 2014
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Subject: [Bug middle-end/64088] [5 Regression] ICE: in fold_abs_const, at fold-const.c:15550
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd088

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-11-26
                 CC|                            |mpolacek at gcc dot gnu.org
   Target Milestone|---                         |5.0
     Ever confirmed|0                           |1

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed.

[Bug c++/64077] dynamic_cast incorrectly rejected for private base

[gcc at dixie dot net.nz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64077

--- Comment #2 from Andrew Dixie <gcc at dixie dot net.nz> ---
(In reply to Daniel Krügler from comment #1)

Thanks for investigating and providing the reference.

I did not understand that upcasts were intended to override potential cross
casts, issue 665 makes this clear.

I agree the testcase is invalid.

In p5, is "inaccessible" meant to include friendship relationships granted by
the current scope or instead use the explicit public base rules spelt out in
p8?

The second part of the patch was implementing the latter, but I now also think
this is invalid.
>From gcc-bugs-return-468730-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Nov 27 08:35:27 2014
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--- Comment #2 from manfred.rudigier at omicron dot at ---
I've built 4.9.2 today and can also confirm that it is working with this
version, so it seems the bug has already been fixed in newer GCC versions.

[Bug c++/64077] dynamic_cast incorrectly rejected for private base

[gcc at dixie dot net.nz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64077

Andrew Dixie <gcc at dixie dot net.nz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #4 from Andrew Dixie <gcc at dixie dot net.nz> ---
(In reply to Daniel Krügler from comment #3)

Given the reference to core issue 665, I now think the wording and intent of
the standard is clear.

For completeness I've given an example below, but I'm happy this can be closed.

Thanks.


class base { virtual ~base() {} };
class derived : private base {
        friend bool t1(derived *);
};

bool t1(derived *x) {
        return dynamic_cast<base *>(x) != 0;
}

If the 'accessible' in p5 includes friendships relationships, then the
dynamic_cast should succeed.
If the 'accessible' in p5 requires a public base (like is required by p8), then
the dynamic cast should fail (or be ill-formed).
I think the wording of the standard clearly specifies succeed.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc833

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
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--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
The psABI

http://www.x86-64.org/svn/trunk/x86-64-ABI/

has been fixed.

[Bug c++/64077] dynamic_cast incorrectly rejected for private base

[daniel.kruegler at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64077

--- Comment #5 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to Andrew Dixie from comment #4)
> If the 'accessible' in p5 includes friendships relationships, then the
> dynamic_cast should succeed.

Yes, friendship relations need to be considered when accessibility is tested.

> If the 'accessible' in p5 requires a public base (like is required by p8),
> then the dynamic cast should fail (or be ill-formed).
> I think the wording of the standard clearly specifies succeed.

Yes.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc833

H.J. Lu <hjl.tools at gmail dot com> changed:

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

--- Comment #3 from H.J. Lu <hjl.tools at gmail dot com> ---
Fixed.