[Bug middle-end/44164] [4.5 Regression] Aliasing bug triggered by Boost.Bind/Boost.Function

[pdimov at gmail dot com]

------- Comment #7 from pdimov at gmail dot com  2010-05-17 19:10 -------
(In reply to comment #6)
> Basically the middle-end sees this the same as
>   int i = 1, j;
>   float *p = new (&i) float(0.0);
>   j = i;
>   return *reinterpret_cast<float *>(&j);
> and you expect to return 0.0.

The int/float example does violate the aliasing rules, but I don't think that
it properly describes what's happening.

I see it more like a combination of the following two examples:

#include <iostream>

struct X
{
    char data[ sizeof( float ) ];
};

int main()
{
    X x1;
    new( &x1.data ) float( 3.14f );

    X x2 = x1;

    std::cout << *(float const*)&x2.data << std::endl;
}

and

#include <iostream>

union Y
{
    int i;
    float f;
};

int main()
{
    Y y1;
    y1.f = 3.14f;

    Y y2 = y1;

    std::cout << y2.f << std::endl;
}

I don't think either of them violates the standard.


-- 

pdimov at gmail dot com changed:

           What    |Removed                     |Added
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                 CC|                            |pdimov at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164