VM-codegen: For polymorphic methods don't expand Cids at call sites

VM-codegen: For polymorphic methods don't expand Cids at call sites

When dispatching polymorphic calls we try to recognize the case where
adjacent classes have the same method, so that we can group the classes
in the dispatch.  That fails for polymorphic methods, which are pretending to
be the same method, but actually do a class test on the receiver internally. In
this case, we should not expand the classes, because it messes up some other
inlining optimizations.

R=vegorov@google.com
BUG=https://github.com/dart-lang/sdk/issues/29892

Committed: https://github.com/dart-lang/sdk/commit/b683e47c1ad83ba8bb73a4978d32508d63662649

[Vyacheslav Egorov (Google), 2017-06-23 16:09:46]

LGTM with a comment addressed. 

I believe that we need a scalable strategy for handling this:

- we need tests for this logic, either in the form of benchmarks or compiler
unit tests (or both); 
- we need an idea of how to handle certain cases better, I think if you create
view with different types of storage then you performance goes completely down
the drain due to polymorphism - so we need a strategy for handling that in a
more scalable manner. 

We at the very least need tracking bugs for this.

https://codereview.chromium.org/2956653002/diff/1/runtime/vm/intermediate_lan...
File runtime/vm/intermediate_language.cc (right):

https://codereview.chromium.org/2956653002/diff/1/runtime/vm/intermediate_lan...
runtime/vm/intermediate_language.cc:2978: targets.MergeIntoRanges();
This will merge stuff together if you have two polymorphic targets that have
adjacent receiver cids.

I think you need to guard in the same way there.

[erikcorry, 2017-06-23 17:10:23]

https://codereview.chromium.org/2956653002/diff/1/runtime/vm/intermediate_lan...
File runtime/vm/intermediate_language.cc (right):

https://codereview.chromium.org/2956653002/diff/1/runtime/vm/intermediate_lan...
runtime/vm/intermediate_language.cc:2978: targets.MergeIntoRanges();
On 2017/06/23 16:09:46, Vyacheslav Egorov (Google) wrote:
> This will merge stuff together if you have two polymorphic targets that have
> adjacent receiver cids.
> 
> I think you need to guard in the same way there. 

Done.

[erikcorry, 2017-06-24 11:37:07]

Description was changed from

==========
VM-codegen: For polymorphic methods don't expand Cids at call sites

When dispatching polymorphic calls we try to recognize the case where
adjacent classes have the same method, so that we can group the classes
in the dispatch.  That fails for polymorphic methods, which are pretending to
be the same method, but actually do a class test on the receiver internally. In
this case, we should not expand the classes, because it messes up some other
inlining optimizations.

R=vegorov@google.com
BUG=https://github.com/dart-lang/sdk/issues/29892
==========

to

==========
VM-codegen: For polymorphic methods don't expand Cids at call sites

When dispatching polymorphic calls we try to recognize the case where
adjacent classes have the same method, so that we can group the classes
in the dispatch.  That fails for polymorphic methods, which are pretending to
be the same method, but actually do a class test on the receiver internally. In
this case, we should not expand the classes, because it messes up some other
inlining optimizations.

R=vegorov@google.com
BUG=https://github.com/dart-lang/sdk/issues/29892

Committed:
https://github.com/dart-lang/sdk/commit/b683e47c1ad83ba8bb73a4978d32508d63662649
==========

[erikcorry, 2017-06-24 11:37:09]

Committed patchset #2 (id:20001) manually as
b683e47c1ad83ba8bb73a4978d32508d63662649 (presubmit successful).