VM-codegen: Restrict widening class ranges in method dispatch

VM-codegen: Restrict widening class ranges in method dispatch

We widen the range of class-ids that we dispatch to if the
neighbouring classes dispatch to the same methods.  With this
change we don't widen the range to encompass abstract classes
unless we also catch more concrete classes in that way.

This improves the Megamorhphic benchmark suite scores by about
10% on average.

This is split off from https://codereview.chromium.org/2955073005/

R=vegorov@google.com
BUG=

Committed: https://github.com/dart-lang/sdk/commit/1ef0ec401a1498ea2ce4b03a44d1a418f9283c79

[Vyacheslav Egorov (Google), 2017-06-30 16:53:21]

lgtm

https://codereview.chromium.org/2962333002/diff/1/runtime/vm/flow_graph_compi...
File runtime/vm/flow_graph_compiler.h (right):

https://codereview.chromium.org/2962333002/diff/1/runtime/vm/flow_graph_compi...
runtime/vm/flow_graph_compiler.h:612: bool* class_is_abstract_return = NULL);
maybe just class_is_abstract?

[erikcorry, 2017-07-03 07:27:13]

Description was changed from

==========
VM-codegen: Restrict widening class ranges in method dispatch

We widen the range of class-ids that we dispatch to if the
neighbouring classes dispatch to the same methods.  With this
change we don't widen the range to encompass abstract classes
unless we also catch more concrete classes in that way.

This improves the Megamorhphic benchmark suite scores by about
10% on average.

This is split off from https://codereview.chromium.org/2955073005/

R=vegorov@google.com
BUG=
==========

to

==========
VM-codegen: Restrict widening class ranges in method dispatch

We widen the range of class-ids that we dispatch to if the
neighbouring classes dispatch to the same methods.  With this
change we don't widen the range to encompass abstract classes
unless we also catch more concrete classes in that way.

This improves the Megamorhphic benchmark suite scores by about
10% on average.

This is split off from https://codereview.chromium.org/2955073005/

R=vegorov@google.com
BUG=

Committed:
https://github.com/dart-lang/sdk/commit/1ef0ec401a1498ea2ce4b03a44d1a418f9283c79
==========

[erikcorry, 2017-07-03 07:27:15]

Committed patchset #1 (id:1) manually as
1ef0ec401a1498ea2ce4b03a44d1a418f9283c79 (presubmit successful).