c++/10179: alignment attributes are not inherited correctly with empty classes

c++/10179: alignment attributes are not inherited correctly with empty classes

[jamagallon]

>Number:         10179
>Category:       c++
>Synopsis:       alignment attributes are not inherited correctly with empty classes
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Mar 21 11:46:01 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     jamagallon@able.es
>Release:        gcc-3.2.2
>Organization:
>Environment:
Linux Mandrake 9.1
>Description:
__attribute__((__aligned__(16))) is applied to an empty base class, used just to propagate that and new/delete operators, not defined in the example (do you remember SSE...).
If derived class T is smaller than the alignment, it is obeyed so arrays of T give aligned alements. If size of T is bigger that alignment, elements in T[] are unaligned. If base is not empty, it works ok. Is this expected behaviour ?
>How-To-Repeat:
#include <iostream>

using namespace std;
#define __class class __attribute__((__aligned__(16)))

__class A
{
public:
    void id() { cout << this << endl; };
};

class T : public A
{
public:
//    with 3 floats, sizeof(T)==16
//    with 5 floats, sizeof(T)==20
      float   f[5];
};

int main()
{
    A a;
    cout << "sizeof(A) = " << sizeof(A) << endl;
    cout << &a << endl;
    A aa[2];
    cout << "sizeof(A[2]) = " << sizeof(aa) << endl;
    cout << &aa[0] << endl;
    cout << &aa[1] << endl;

    T t;
    cout << "sizeof(T) = " << sizeof(T) << endl;
    cout << &t << endl;
    T tt[2];
    cout << "sizeof(T[2]) = " << sizeof(tt) << endl;
    cout << &tt[0] << endl;
    cout << &tt[1] << endl;

    return 0;
}
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: