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Re: C++ structure layout breakage


    This was an attempt to fix purge_addressof problems.  Along the way,
    it was decided that store_bit_field should abort if given an FP mode
    with no equivalent integer mode.  This is wrong.  FP modes are fine if
    we are inserting a value that is exactly the same size as the field we
    are inserting it into, and the field is aligned properly for the type.

Now it's coming back to me: I noticed this at the time and think I
actually pointed out that this could be made to work, but was trickier
than I cared to do and didn't think it was worth the trouble.

    The testcase has a structure with one long double field, and there is
    no 80-bit integral type.  If we don't allow this structure into a
    register, then we are accidentally changing the x86 ABI, and getting
    less efficient code too.

I knew the code would be less efficient, but didn't think that was worth
bothering with.  I hadn't realized the ABI implication.

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