https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66583
Bug ID: 66583
Summary: incorrect implicitly-defined move constructor for
class with anonymous union and NSDMI
Product: gcc
Version: 5.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jens.maurer at gmx dot net
Target Milestone: ---
The following code wrongly prints 0 instead of the correct 1:
$ g++ -std=c++11 union.cc
$ ./a.out
0
(reproducible with both 4.9.2 and 5.1.0)
#include <algorithm>
#include <iostream>
struct A {
A() { };
A(const A&) { }
};
struct B {
union {
int m_1 = 0;
int m_2;
};
A dummy;
};
int main()
{
B b;
b.m_1 = 1;
B c(std::move(b));
std::cout << c.m_1 << std::endl;
}
The assembly code for B::B(B&&) when compiling unoptimized has this (x86-64):
movl (%rdx), %edx
movl %edx, (%rax)
Until here, we correctly copy the object representation of the anonymous union
(12.8p16).
movq -8(%rbp), %rax
movl $0, (%rax)
And then we seem to evaluate the non-static data member initializer for m_1,
which is (obviously) wrong.
