dart2js: HGetLength may become fixed

dart2js: HGetLength may become fixed

We may not know initially that the input to HGetLength is fixed-length, but discover so later.
Most notably this happens with --trust-type-annotations, since the HTypeKnown for 'trusting' the type hides the underlying type, but it also happens as a consequence of local dataflow and other optimizations.


BUG=
R=efortuna@google.com

Committed: https://github.com/dart-lang/sdk/commit/50b6107eecc808f3227aee938c01f7ebd21a2d4b

[sra1, 2017-02-26 07:46:13]

sra@google.com changed reviewers:
+ sigmund@google.com

[sra1, 2017-02-27 18:43:24]

sra@google.com changed reviewers:
+ efortuna@google.com
- sigmund@google.com

[Emily Fortuna, 2017-02-27 18:45:37]

lgtm

[sra1, 2017-02-27 20:33:32]

Description was changed from

==========
dart2js: HGetLength may become fixed

We may not know initially that the input to HGetLength is fixed-length, but
discover so later.
Most notably this happens with --trust-type-annotations, since the HTypeKnown
for 'trusting' the type hides the underlying type, but it also happens as a
consequence of local dataflow and other optimizations.


BUG=
==========

to

==========
dart2js: HGetLength may become fixed

We may not know initially that the input to HGetLength is fixed-length, but
discover so later.
Most notably this happens with --trust-type-annotations, since the HTypeKnown
for 'trusting' the type hides the underlying type, but it also happens as a
consequence of local dataflow and other optimizations.


BUG=
R=efortuna@google.com

Committed:
https://github.com/dart-lang/sdk/commit/50b6107eecc808f3227aee938c01f7ebd21a2d4b
==========

[sra1, 2017-02-27 20:33:34]

Committed patchset #1 (id:1) manually as
50b6107eecc808f3227aee938c01f7ebd21a2d4b (presubmit successful).