Incorrect bitfield aliasing with Tree SSA

[Eric Botcazou]

> I'm completely unsurprised this is broken at the tree level given how
> it is implemented

Nice tautology. :-)  You have resisted implementing anything at the tree level 
to fix the problem and now you're complaining there is a problem...

Let's try and devise something plausible at the tree level.  If we eventually 
fail, we could indeed consider disabling the optimization at the RTL level.

-- 
Eric Botcazou