VM: Fix bug in type propagation at conditionals.

VM: Fix bug in type propagation at conditionals.

Propagating type/cid at conditional branches is not possible because
it may cause invalid code motion.

For this to be safe we need to explicitly represent the dependency
between checks eliminated in a branch and the condition that constrains the type/cid.

BUG=
R=vegorov@google.com

Committed: https://github.com/dart-lang/sdk/commit/dff13bef8de104d33b04820136da2d80f3c835d7

[Florian Schneider, 2015-12-03 20:03:12]

fschneider@google.com changed reviewers:
+ vegorov@google.com

[Vyacheslav Egorov (Google), 2015-12-03 20:07:07]

lgtm

[Florian Schneider, 2015-12-03 20:14:39]

Description was changed from

==========
VM: Fix bug in type propagation at conditionals.

Propagating type/cid at conditional branches is not possible because
it may cause invalid code motion.

For this to be safe we need to explicitly represent the dependency
between checks eliminated in a branch and the condition that constrains the
type/cid.

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

to

==========
VM: Fix bug in type propagation at conditionals.

Propagating type/cid at conditional branches is not possible because
it may cause invalid code motion.

For this to be safe we need to explicitly represent the dependency
between checks eliminated in a branch and the condition that constrains the
type/cid.

BUG=
R=vegorov@google.com

Committed:
https://github.com/dart-lang/sdk/commit/dff13bef8de104d33b04820136da2d80f3c835d7
==========

[Florian Schneider, 2015-12-03 20:14:40]

Committed patchset #2 (id:20001) manually as
dff13bef8de104d33b04820136da2d80f3c835d7 (presubmit successful).