Canonicalize BackendImpact

Canonicalize BackendImpact

BUG=
R=sigurdm@google.com

Committed: https://github.com/dart-lang/sdk/commit/686faebf707c8e92db41b0d766ffcedd83d168d8

[Johnni Winther, 2015-11-09 17:16:34]

johnniwinther@google.com changed reviewers:
+ sigurdm@google.com

[Johnni Winther, 2015-11-09 17:16:34]

This prepares for using impact strategies to only computing and applying each
backend impact once if dependency tracking is not needed.

[sigurdm, 2015-11-10 08:07:07]

LGTM

https://codereview.chromium.org/1431983003/diff/1/pkg/compiler/lib/src/js_bac...
File pkg/compiler/lib/src/js_backend/backend_impact.dart (right):

https://codereview.chromium.org/1431983003/diff/1/pkg/compiler/lib/src/js_bac...
pkg/compiler/lib/src/js_backend/backend_impact.dart:52: _getRuntimeTypeArgument
= new BackendImpact(
These could be done with ?= null-aware assignment. Not sure its better though.

[Johnni Winther, 2015-11-10 10:25:21]

Committed patchset #1 (id:1) manually as
686faebf707c8e92db41b0d766ffcedd83d168d8 (presubmit successful).

[Johnni Winther, 2015-11-10 10:26:37]

https://codereview.chromium.org/1431983003/diff/1/pkg/compiler/lib/src/js_bac...
File pkg/compiler/lib/src/js_backend/backend_impact.dart (right):

https://codereview.chromium.org/1431983003/diff/1/pkg/compiler/lib/src/js_bac...
pkg/compiler/lib/src/js_backend/backend_impact.dart:52: _getRuntimeTypeArgument
= new BackendImpact(
On 2015/11/10 08:07:07, sigurdm wrote:
> These could be done with ?= null-aware assignment. Not sure its better though.

It looks strange:

  return _getRuntimeTypeArgument ?= new Backend(...)

Maybe me (and my editor) just need to get used to it. Not in this CL though.

[sigurdm, 2015-11-10 12:11:07]

https://codereview.chromium.org/1431983003/diff/1/pkg/compiler/lib/src/js_bac...
File pkg/compiler/lib/src/js_backend/backend_impact.dart (right):

https://codereview.chromium.org/1431983003/diff/1/pkg/compiler/lib/src/js_bac...
pkg/compiler/lib/src/js_backend/backend_impact.dart:52: _getRuntimeTypeArgument
= new BackendImpact(
On 2015/11/10 10:26:37, Johnni Winther wrote:
> On 2015/11/10 08:07:07, sigurdm wrote:
> > These could be done with ?= null-aware assignment. Not sure its better
though.
> 
> It looks strange:
> 
>   return _getRuntimeTypeArgument ?= new Backend(...)
> 
> Maybe me (and my editor) just need to get used to it. Not in this CL though.

I thought about two lines:
_getRuntimeTypeArgument ?= new Backend(...)
return _getRuntimeTypeArgument;