mingw-qt5-qtwebkit FTBFS: C++ struct size question

[Sandro Mani <manisandro@xxxxxxxxx>]

Hi

I've spent some time debugging mingw-qt5-qtwebkit being FTBFS since the 
last mass rebuild, and I've narrowed it down to this:

struct Foo {
    unsigned u1 : 5;
    unsigned u2 : 5;
    unsigned u3 : 3;
    unsigned u4 : 3;
    unsigned u5 : 4;
    unsigned u6 : 2;
    unsigned u7 : 3;
    unsigned u8 : 2;
    unsigned u9 : 1;

    unsigned u10 : 3;
    // 31 bits
    unsigned u11 : 2;
    unsigned u12 : 2;
    unsigned u13 : 2;

    unsigned u14 : 6;
    unsigned u15 : 7;
    unsigned u16 : 1;
    unsigned u17 : 1;
    unsigned u18 : 1;
    unsigned u19 : 1;
    unsigned u20 : 1;

    bool bar() const { return false; }
private:
    unsigned u21 : 1;
    unsigned u22 : 1;
    unsigned u23 : 1;
    unsigned u24 : 1;
    // 59 bits
};

COMPILE_ASSERT((sizeof(Foo) <= 8), Foo_does_not_grow);

The COMPILE_ASSERT fails, since apparently sizeof(Foo) = 12. But without 
the bool bar() member function, sizeof(Foo) = 8, which is what I would 
expect regardless of the presence of (non-virtual) member functions - as 
far as my C/C++ knowledge goes, non-virtual functions should not take up 
any space. Am I missing something, or is this a compiler issue?

(Coincidentally, the failed build used mingw-gcc-8.1.0 which landed 
before the mass rebuild, but previous (successful) builds were performed 
with mingw-gcc-7.3.0).

Thanks
Sandro
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