Andrew Trick dfc2d47f3b Redo the data flow part of AccessEnforcementOpts. ...

Directly implement the data flow. Eliminate the extraneous work.
Remove cubic behavior. Do a single iteration of the data flow state at
each program point only performing the necessary set operations. At
unidentified access, clear the sets for simplicity and efficiency.

This cleanup results in significant functional changes:

- Allowing scopes to merge even if they are enclosed.

- Handling unidentified access conservatively.

Note that most of the added lines of code are comments.

Somehow this cleanup incidentally fixes:
<rdar://problem/48514339> swift compiler hangs building project

(I expected the subsequent loop summary cleanup to fix that problem.)

2019-03-18 12:42:53 -07:00

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