Reland "VM: Handle null-comparisons in the flow graph type propagation"

Reland "VM: Handle null-comparisons in the flow graph type propagation"

This reverts commit ee452a8600f393d892fa482e60bac2af27bff0ae.

Original CL: https://codereview.chromium.org/2772143002/

Additional bug fix: Correctly replace ToCid with ToNullableCid in
RedefinitionInstr::ComputeType.

R=rmacnak@google.com

Committed: https://github.com/dart-lang/sdk/commit/80b43ff15cfa3e042e21d9d95eca695443c140b1

[Florian Schneider, 2017-03-31 20:54:20]

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

[Florian Schneider, 2017-03-31 20:54:21]

Ptal.

I fixed the bug I introduced when addressing previous comments (use
ToNullableCid consistently)

https://codereview.chromium.org/2789943002/diff/1/runtime/vm/flow_graph_type_...
File runtime/vm/flow_graph_type_propagator.cc (right):

https://codereview.chromium.org/2789943002/diff/1/runtime/vm/flow_graph_type_...
runtime/vm/flow_graph_type_propagator.cc:797: value()->Type()->ToNullableCid());
Used ToNullableCid here: Otherwise the type of the redefinition would
incorrectly become less precise than the incoming type which can lead to an
infinite loop in type propagation.

https://codereview.chromium.org/2789943002/diff/1/runtime/vm/flow_graph_type_...
runtime/vm/flow_graph_type_propagator.cc:801:
constrained_type_->ToNullableCid());
Same here.

[rmacnak, 2017-03-31 22:28:58]

lgtm

https://codereview.chromium.org/2789943002/diff/1/runtime/vm/intrinsifier.cc
File runtime/vm/intrinsifier.cc (right):

https://codereview.chromium.org/2789943002/diff/1/runtime/vm/intrinsifier.cc#...
runtime/vm/intrinsifier.cc:291: empty_env_(new Environment(0,
Maybe fall_through_env_ ?

[Florian Schneider, 2017-03-31 22:39:09]

Description was changed from

==========
Reland "VM: Handle null-comparisons in the flow graph type propagation"

This reverts commit ee452a8600f393d892fa482e60bac2af27bff0ae.

Original CL: https://codereview.chromium.org/2772143002/

Additional bug fix: Correctly replace ToCid with ToNullableCid in
RedefinitionInstr::ComputeType.
==========

to

==========
Reland "VM: Handle null-comparisons in the flow graph type propagation"

This reverts commit ee452a8600f393d892fa482e60bac2af27bff0ae.

Original CL: https://codereview.chromium.org/2772143002/

Additional bug fix: Correctly replace ToCid with ToNullableCid in
RedefinitionInstr::ComputeType.

R=rmacnak@google.com

Committed:
https://github.com/dart-lang/sdk/commit/80b43ff15cfa3e042e21d9d95eca695443c140b1
==========

[Florian Schneider, 2017-03-31 22:39:11]

Committed patchset #2 (id:20001) manually as
80b43ff15cfa3e042e21d9d95eca695443c140b1 (presubmit successful).