[PATCH] [MachineSink] Use the real post dominator tree

[Jiangning Liu]

Hi Jingyue,

I tried spec2000/int for cortex-a57, and got the following numbers, (negative is better),

164.gzip	-0.39%
175.vpr	0.91%
176.gcc	0.83%
181.mcf	0.78%
186.crafty	0.00%
197.parser	0.32%
252.eon	-0.73%
253.perlbmk	0.00%
254.gap	1.75%
255.vortex	-1.04%
256.bzip2	0.46%
300.twolf	1.12%

I think the result it's OK. All seem to be noises.

Thanks,
-Jiangning

http://reviews.llvm.org/D4814