dart2js cps: Bugfix in assignment propagation into branch conditions.

dart2js cps: Bugfix in assignment propagation into branch conditions.

Assignment propagation traverses the tree backwards, and should therefore
visit the branch condition of an 'if' after its two branches.

It happened to work (in the sense of not breaking the code) but
only for very subtle reasons.

This fixes an optimization bug that prevented assignments from
propagating to their first use when the first use was in a branch
condition.

BUG=
R=karlklose@google.com

Committed: https://github.com/dart-lang/sdk/commit/5a20c361b938fceb33f2cdd9460f8f32c4edf0f4

[asgerf, 2015-07-09 11:19:01]

asgerf@google.com changed reviewers:
+ karlklose@google.com

[asgerf, 2015-07-09 11:19:02]

https://codereview.chromium.org/1226353003/diff/1/pkg/compiler/lib/src/tree_i...
File pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart (left):

https://codereview.chromium.org/1226353003/diff/1/pkg/compiler/lib/src/tree_i...
pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart:593: // be
handled well.
This comment was just outdated. It's not really related to the change.

[karlklose, 2015-07-09 12:56:12]

LGTM!

[asgerf, 2015-07-09 15:05:00]

Committed patchset #1 (id:1) manually as
5a20c361b938fceb33f2cdd9460f8f32c4edf0f4 (presubmit successful).