RFA: improvement to if-conversion

[Joern RENNECKE]

I've finally found some time to finish the iinitial coding for 
if-conversion / cross-jump merge.

 > > I think full register liveness information would be harder to keep
 > > up-to-date as if conversion progresses.
 >
 > I think that global_live_at_start/end are kept up-to-date.  Leastwise,
 > I'd be interested to know how badly they're off.  We re-run life info
 > at the end, but that's to get death notes inserted properly.

It turns out that it's actually much worse.  We don't have any life info 
in the first
if-conversion pass at all.  A lot of loop optimizations only make sense 
after
if-conversion has been properly performed, so I don't think only relying 
on the
second if-conversion pass is much good.  I suppose that means that I'll 
have to
run flow before if-conversion then.



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