ce08911515
Rationale:
(1) reset loop_info of block entries,
since recomputing on a modified graph
may encounter blocks that are no longer headers
(2) replaced O(n) linear scan over loop headers just
to test membership of the current block with
an O(1) test
(3) added some comments
https://github.com/dart-lang/sdk/issues/34473
Change-Id: I9e24a76bac9cf0225d8f1c996adfa6d82c175504
Reviewed-on: https://dart-review.googlesource.com/c/78703
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Aart Bik <ajcbik@google.com>