dart2js better code for "is type" check

[DartBot]

This issue was originally filed by @bp74

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What steps will reproduce the problem?

I tried to optimize the dart2js output for a hot function in my code. The generated code get's a lot better if i add a type check. But the code for the type check itself is not optimal. The code below shows the code of a simple type check for class "foo":

var x = [new foo()];
void main() {
 if (x[0] is! foo) print("is not foo");
}

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$.main = function() {
  var t1 = $.$index$as($.get$x(), 0);
  if (typeof t1 !== "object" || t1 === null || !$.getInterceptor(t1).$isfoo)
    $.Primitives_printString("is not foo");
};
    
$.getInterceptor = function(receiver) {
  if (typeof receiver == "number") {
    if (Math.floor(receiver) == receiver) return $.JSInt.prototype;
    return $.JSDouble.prototype;
  }
  if (typeof receiver == "string") return $.JSString.prototype;
  if (receiver == null) return $.JSNull.prototype;
  if (typeof receiver == "function") return $.JSFunction.prototype;
  if (typeof receiver == "boolean") return $.JSBool.prototype;
  if (receiver.constructor == Array) return $.JSArray.prototype;
  if (typeof receiver != "object") return receiver;
  if (receiver instanceof $.Object) return receiver;
  if (Object.getPrototypeOf(receiver) === Object.prototype) return $.Interceptor.prototype;
  return $.getNativeInterceptor(receiver);
};

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What is the expected output? What do you see instead?

if (typeof t1 !== "object" || t1 === null || !$.getInterceptor(t1).$isfoo)

Is the call to getInterceptor really needed? Most of the if-checks in getInterceptor will fail because it is guaranteed that "typeof receiver" is an object and receiver is surely not null. Do i need an interceptor at all, would it be okay to just check "t1.$isFoo" ?

What version of the product are you using? On what operating system?

Dart Editor version 0.1.2_r21625
Dart SDK version 0.1.2.0_r21623

Please provide any additional information below.

[sethladd]

Added Area-Dart2JS, C3, Triaged labels.

[kasperl]

Added this to the Later milestone.

[rakudrama]

In the general case the getInterceptor call is needed when there may be DOM objects floating around. For example, a DOM Storage object in JavaScript materializes the keys and values as properties. So it is possible for the Storage object to "accidentally" be truthy for "t1.$isfoo" following a statement like

  window.localStorage['$isfoo'] = '1'

dart2js should definitely be generating a faster, specialized version of getInterceptor.
Before we can do this, we should make the getInterceptor call explicit in the SSA graph (Issue #9732)

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Marked this as being blocked by #9732.

[kasperl]

Added TriageForM5 label.

[kasperl]

Removed TriageForM5 label.

[DartBot]

This comment was originally written by ngeoffray@google.com

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The getInterceptor call gets removed now, so I'll assume this bug as staled.

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Added AssumedStale label.