rebuild dominance tree during CFG cleanup
Currently, the dominance tree is build once, just before the
SSA conversion.
However, changes in the CFG potentially changes the dominance
relationships.
So, rebuild the dominance tree after changes to the CFG.
Note: This doesn't seems to significantly affect the performance
(at least when used on the kernel):
before after
real 4m15.854s real 4m16.95&s
user 71m11.390s user 71m29.180s
sys 28m45.222s sys 28m46.145s
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>