[rfc] Frame based register cache / frame->unwind

[Andrew Cagney]

> Performance is hard to quantify(1) but looks positive.  Using a native 
>> GDB (not typical for me :-) it appears that each frame is ~2% slower to 
>> create (``(gdb) up'').  Once created, the frame is ~20-25% faster 
>> (``(gdb) info registers'').
> 
> 
> You might want to try timing the testsuite with and without this patch
> (using /usr/bin/time et al., to get real/user/sys times) and see what
> changes.  It'll probably be negligible, but you never know.

Good point.  Negligible.  Given the differences were to the order of 
~0.01s when native I'm not suprised.  Against a remote target is next.


Andrew