swift234

Enable loop rotation and LICM

We want this to get tested.

O3:
Ackermann 8.0%
GlobalClass 30.8%
R17315246 -50.2%
Phonebook 7.4%

Ofast:
RC4 -9.7%

The R17315246 regression is because LLVM seems to unable to 'unswitch' the loop
that makes up this benchmark after rotation. The only explaination I have atm is
that after rotation the first exit is a cond_fail.

I looked at RC4's profile and did not see anything suspicious. I was chasing a
10% regression yesterday in phonebook (today it seems i see about 7%
improvement). So I am not sure how 'stable' wrt to cache effects our benchmarks
are (we are calling into runtimes and whatnot).

Swift SVN r20098