http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57319
Bug ID: 57319
Summary: [4.8/4.9] Regression: bogus "defaulted move assignment
for ... calls a non-trivial move assignment operator
for virtual base ..."
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ppluzhnikov at google dot com
Google reference: b/9004260
Test case:
class A { };
class B: virtual A { };
class C: virtual B { };
class D: C
{
void operator= (D &);
};
Using current trunk (@r199023):
g++ -c t.ii -std=c++11
t.ii:3:7: warning: defaulted move assignment for ‘C’ calls a non-trivial move
assignment operator for virtual base ‘B’ [-Wvirtual-move-assign]
class C: virtual B { };
^
Richard Smith writes:
The problem is that a defaulted move assignment for a class with two
inheritance paths to a virtual base may move-assign that virtual base
multiple times (and thus may lose state).
However, this particular case *isn't* the problematic case, because
(a) this sample code should not trigger the definition of C's move
assignment operator, and
(b) there is only one inheritance path from C to B, so it won't be
move-assigned multiple times, and
(c) the issue isn't with *non-trivial* move assignments, it's with
*user-provided* move-assignments (for the virtual base or any of its
subobjects), which B does not have.
=> This is a false positive.
