alpha return address patch

[Richard Henderson]

> I believe it is safe to assume that builtin_return_address will never be
> used in a leaf function, because of the way that the old exception handling
> code works.

This may be true for the exception code, but it is not necessarily
true for any use of the function by user code.  Is it not, IMO, a
good idea to impose this restriction, since that it is pointlessly 
arbitrary -- the information is there to be had, we're just being
lazy about getting it.  It is completely inexcusable to just silently
generate bad code when it happens, as the MIPS port does.

I will investigate one of the other push/pop suggestions you make.


r~