Fortunately gcc 4.3 will have also faster compilation speed than 4.2 even with the df infrastructure (which may be, and I hope, helps to improve the code finally). That is because some work was done to speed up tree-SSA infrastructure (and Paolo Bonizini's frwprop) to improve the compilation speed.
Just something to point out: despite fwprop being often associated with me (in bug reports too ;-) it was the joint work of me and Steven Bosscher. His name is at them top of the fwprop.c file for a reason, as his work, and SuSE/Novell's infrastructure, were invaluable.
Paolo
