dart2js: consider canonicalization of tear-off closures

[rakudrama]

The 'tear-off' closure that binds 'this' is slow to create and slow to apply. The following change fixes both issues:

Test.prototype.get$tearOff = function() {
  return Test.prototype.tearOff.bind(this);
}
Test.prototype.get$tearOff = function() {
  // Caching on object (canonicalizing) make second creation fast.
  if (this.get$tearOff$$) return this.get$tearOff$$;
  var $this = this;
  var f = Test.prototype.tearOff.bind(this); // (Is f ever called directly?)
  f.call$0 = function() { $this.tearOff(); }; // Makes calls fast call
  this.get$tearOff$$ = f;
  return f;
}

This needs to be validated for other browsers, and it should also be validated that single-use tear-offs are not too expensive with all this extra code.
The idea needs to be worked through for named optional arguments and type checking.

See also Issue #551.

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Attachments:
bug1o2.dart (774 Bytes)
bug1o3.dart (759 Bytes)

[jmesserly]

Removed Type-Defect label.
Added Type-Enhancement label.

[anders-sandholm]

Removed Area-Frog label.
Added Area-Dart2JS, FromAreaFrog labels.

[kasperl]

This might make sense for dart2js.

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Removed FromAreaFrog label.
Changed the title to: "Consider canonicalization of tear-off closures".

[kasperl]

Added this to the Later milestone.

[kasperl]

Removed this from the Later milestone.

[kasperl]

Added this to the Later milestone.

[kasperl]

Added TriageForM5 label.

[kasperl]

Removed TriageForM5 label.
Changed the title to: "dart2js: consider canonicalization of tear-off closures".

[kasperl]

Removed this from the Later milestone.
Added Oldschool-Milestone-Later label.

[kasperl]

Removed Oldschool-Milestone-Later label.

[floitschG]

I think we decided not to canonicalize tear-off closures.
(Note that the proposed approach would also change the hidden class of the object).

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Added NotPlanned label.