Adds support for situations when block don't become dead after the
folding, but stop being a part of the current loop. In this case, we
should do proper upates to Loop Info to keep it consistent.
Still WIP, some bug with subloops.
Just setting "Plan changes" to not confuse reviewers too much with amount of patches in progress.
Rebased, ready for review since underlying patches are now merged.
I plan to hold it off before current implementation is enabled and works without issues for some time.