We can easily register allocate the entire extended basic block
(in this case, the set of blocks connected by fallthru), simply
by not discarding the register state at the branch.
This does not help blocks starting with a label, as they are
reached via a taken branch, and that would require saving the
complete register state at the branch.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
b4cb76e620