Let's reset m_last_used for each register that will be used
in an instruction before we start allocating any of them,
so that one of the earlier allocations doesn't spill a
register that we want in a later allocation. (We must still
also increment/reset m_last_used in R and RW, otherwise we
end up in trouble when emulating lmw/stmw since those access
more guest registers than there are available host registers.)
This should ensure that the asserts added earlier in this
pull request are never triggered.
JosJuice
d00430470b