commit 337dd5d35592d5a94454f705a910b60c832b8212
author Paul Berry <paulberry@google.com> Sat Sep 12 15:18:15 2020 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> Sat Sep 12 15:18:15 2020 +0000
tree ce27e4582fbb9ef01b6fb14b60edcb71fe04bd2f
parent dfc411cb90910835ae14a1d3abc99e539c42433d

Make flow analysis handle for-each loops more consistently with their desugaring.

Previously the flow analysis equations for a for-each loop `N` of the
form `for (var V in E) S` were approximately as follows:

- Let `before(E) = before(N)`
- Let `before(S) = conservativeJoin(after(E), assignedIn(N), capturedIn(N))`
- Let `after(N) = join(after(E), break(S))`

This CL changes the behavior to:

- Let `before(E) = before(N)`
- Let `before(S) = conservativeJoin(after(E), assignedIn(N), capturedIn(N))`
- Let `after(N) = join(before(S), break(S))`

(In other words, the result of the conservative join is carried
through to the state after the loop).  This isn't strictly necessary
for soundness, but it makes the behavior of a for-each loop more
consistent with its desugared equivalent.  In particular, it means
that if a variable is potentially assigned to or captured in the body
of the loop, then the effect of that potential assignment or capture
will be felt in the code that follows the loop, even if the potential
assignment or capture is not connected to the flow control path.

Change-Id: I7a70a8ae9f87bd40b6592992d8ee985a9aa87e80
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/162480
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>