dart2js cps: Compute intercepted classes in optimize_interceptors.

dart2js cps: Compute intercepted classes in optimize_interceptors.

There was previously an optimization in type propagation that replaced
getInterceptor(x) with x, but this depends on the set of intercepted
classes (since null may or may not need interception).

That optimization is now handled at the use-site of the interceptor,
since each use knows if it needs null to be intercepted.

BUG=
R=kmillikin@google.com, sra@google.com

Committed: https://github.com/dart-lang/sdk/commit/11c7ad4d6f457882dc41bcf751c1b29b6dc90fe8

[asgerf, 2016-01-07 20:29:51]

Description was changed from

==========
dart2js cps: Compute intercepted classes in optimize_interceptors.

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

to

==========
dart2js cps: Compute intercepted classes in optimize_interceptors.

There was previously an optimization in type propagation that replaced
getInterceptor(x) with x, but this depends on the set of intercepted
classes (since null may or may not need interception).

That optimization is now handled at the use-site of the interceptor,
since each use knows if it needs null to be intercepted.

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

[asgerf, 2016-01-07 20:32:21]

asgerf@google.com changed reviewers:
+ kmillikin@google.com, sra@google.com

[Kevin Millikin (Google), 2016-01-08 01:13:29]

STV! (LGTM)

[sra1, 2016-01-08 03:24:05]

lgtm

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
File pkg/compiler/lib/src/cps_ir/optimize_interceptors.dart (right):

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
pkg/compiler/lib/src/cps_ir/optimize_interceptors.dart:108: bool
includeClass(ClassElement elem) {
perhaps change the name to indicate *why* it is included

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
File pkg/compiler/lib/src/cps_ir/optimizers.dart (right):

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
pkg/compiler/lib/src/cps_ir/optimizers.dart:58: final List<Selector>
selectorsOnNull = <Selector>[
Could this go in the World or somewhere?
It is wider scope than a single back-end.

Alternatively, it could be derived from the declaration of JSNull.

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
File pkg/compiler/lib/src/cps_ir/type_propagation.dart (right):

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
pkg/compiler/lib/src/cps_ir/type_propagation.dart:1867:
!canBeNonThrowingCallOnNull &&
Slightly nervous about  !can...
Usually something called can.../may... is imprecise, so its negation should not
be used.

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
File pkg/compiler/lib/src/js_backend/codegen/codegen.dart (right):

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
pkg/compiler/lib/src/js_backend/codegen/codegen.dart:866: // Default to all
intercepted classes if they have not been computed.
Does the lack of a recomputed result is mean something?
Or is it just to decouple passes?
Explain in comment.

[asgerf, 2016-01-08 17:17:49]

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
File pkg/compiler/lib/src/cps_ir/optimize_interceptors.dart (right):

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
pkg/compiler/lib/src/cps_ir/optimize_interceptors.dart:108: bool
includeClass(ClassElement elem) {
On 2016/01/08 03:24:04, sra1 wrote:
> perhaps change the name to indicate *why* it is included

Done.

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
File pkg/compiler/lib/src/cps_ir/optimizers.dart (right):

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
pkg/compiler/lib/src/cps_ir/optimizers.dart:58: final List<Selector>
selectorsOnNull = <Selector>[
On 2016/01/08 03:24:04, sra1 wrote:
> Could this go in the World or somewhere?
> It is wider scope than a single back-end.
> 
> Alternatively, it could be derived from the declaration of JSNull.

I don't have a strong opinion about where to put it, though I'm leaning towards
leaving it here. I prefer generalizing things as little as possible, as opposed
to generalizing as much as possible.

FWIW the list does not include noSuchMethod because it throws, so that's kind of
use-specific. If the list was put on World, it would be more natural for it to
include noSuchMethod, since the null class has that method.

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
File pkg/compiler/lib/src/cps_ir/type_propagation.dart (right):

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
pkg/compiler/lib/src/cps_ir/type_propagation.dart:1867:
!canBeNonThrowingCallOnNull &&
On 2016/01/08 03:24:04, sra1 wrote:
> Slightly nervous about  !can...
> Usually something called can.../may... is imprecise, so its negation should
not
> be used.

not may == must not

The negation of can/may is the only thing we can safely use to trigger an
optimization.

I admit the whole thing looks a bit confusing with the double negation ("non" in
the name). I cycled through a bunch of names but couldn't find anything better
than this.

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
File pkg/compiler/lib/src/js_backend/codegen/codegen.dart (right):

https://chromiumcodereview.appspot.com/1571433002/diff/80001/pkg/compiler/lib...
pkg/compiler/lib/src/js_backend/codegen/codegen.dart:866: // Default to all
intercepted classes if they have not been computed.
On 2016/01/08 03:24:04, sra1 wrote:
> Does the lack of a recomputed result is mean something?
> Or is it just to decouple passes?
> Explain in comment.

Just to decouple passes. Added comment.

[asgerf, 2016-01-08 18:06:12]

Description was changed from

==========
dart2js cps: Compute intercepted classes in optimize_interceptors.

There was previously an optimization in type propagation that replaced
getInterceptor(x) with x, but this depends on the set of intercepted
classes (since null may or may not need interception).

That optimization is now handled at the use-site of the interceptor,
since each use knows if it needs null to be intercepted.

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

to

==========
dart2js cps: Compute intercepted classes in optimize_interceptors.

There was previously an optimization in type propagation that replaced
getInterceptor(x) with x, but this depends on the set of intercepted
classes (since null may or may not need interception).

That optimization is now handled at the use-site of the interceptor,
since each use knows if it needs null to be intercepted.

BUG=
R=kmillikin@google.com, sra@google.com

Committed:
https://github.com/dart-lang/sdk/commit/11c7ad4d6f457882dc41bcf751c1b29b6dc90fe8
==========

[asgerf, 2016-01-08 18:06:14]

Committed patchset #6 (id:100001) manually as
11c7ad4d6f457882dc41bcf751c1b29b6dc90fe8 (presubmit successful).