The old invalidation lattice was incorrect because changes to control flow could cause changes to the
call graph, so we've decided to change the way passes invalidate analysis. In the new scheme, the lattice
is replaced with a list of traits that passes preserve or invalidate. The current traits are Calls and Branches.
Now, passes report which traits they preserve, which is the opposite of the previous implementation where
passes needed to report what they invalidate.
Node: I tried to limit the changes in this commit to mechanical changes to ease the review. I will cleanup some
of the code in a following commit.
Swift SVN r26449
This ensures that if we have a bunch of passes in a row which modify the CFG, we
do not continually rebuild the post order, while at the same time preserving the
property of multiple passes which do not touch the CFG sharing the same post
order, reverse post order rather than recomputing them.
rdar://17654239
Swift SVN r19913
