[Bug lto/115432] Building a program with -flto generates wrong code (missing the call to a function) unless -fno-strict-aliasing

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115432

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
struct file_output_stream
{

    union
    {
        void *voidp;
        int fd;
    } data;

    const output_stream_vtbl* vtbl;
};

struct output_stream
{
    void* data;
    const output_stream_vtbl* vtbl;
};

those are two unrelated types.  Doing

 ((file_output_stream *)p)->vtbl = x;
 ... = ((output_stream *)p)->vtbl;

is invoking undefined behavior (unless -fno-strict-aliasing).