IRCE has some overhead for runtime checks and in case number of iteration is small
the overhead can kill the benefit from optimizations.
This CL bases on BlockFrequencyInfo of pre-header and header to estimate the
number of loop iterations. If it is less than irce-min-estimated-iters we do not transform the loop.
Probably it is better to make more complex cost model but for simplicity it seems the be enough.
The usage of BFI is added only for new pass manager and tries to use it efficiently.
I think the name should hint that this is profile-based, e.g. "MinRuntimeLoopIterations" or so. We also might want to have another boolean flag to turn this check off, because some users of IRCE might not have a profile.