Multiple-comparison optimization suggestion

[stevemessick]

[user feedback]

Dart2Js generates the following code for me:

removeEntity$1: [function(entity) {
      var t1 = J.getInterceptor(entity);
      if (typeof entity === "object" && entity !== null && !!t1.$isAmbientLightEntity)
        C.JSArray_methods.remove$1(this._ambientLights, entity);
      if (typeof entity === "object" && entity !== null && !!t1.$isDirectionalLightEntity)
        C.JSArray_methods.remove$1(this._directionalLights, entity);
      if (typeof entity === "object" && entity !== null && !!t1.$isPointLightEntity)
        C.JSArray_methods.remove$1(this._pointLights, entity);
      if (typeof entity === "object" && entity !== null && !!t1.$isSpotLightEntity)
        C.JSArray_methods.remove$1(this._spotLights, entity);
      E.RendererComponent.prototype.removeEntity$1.call(this, entity);
    }, "call$1", "get$removeEntity", 2, 0, null, 676],

based on:

  void removeEntity(Entity entity) {
    if (entity is AmbientLightEntity) {
      _ambientLights.remove(entity);
    }

    if (entity is DirectionalLightEntity) {
      _directionalLights.remove(entity);
    }

    if (entity is PointLightEntity) {
      _pointLights.remove(entity);
    }

    if (entity is SpotLightEntity) {
      _spotLights.remove(entity);
    }

    super.removeEntity(entity);
  }

Dart2Js should notice that it is checking the same thing multiple times (entity == null) and move it into an outer if statement.
////////////////////////////////////////////////////////////////////////////////////
Editor: 1.2.0.dev_02_04 (2014-01-31)
OS: Windows 8 - amd64 (6.2)
JVM: 1.7.0_21

projects: 1

open dart files: 0

auto-run pub: true
localhost resolves to: 127.0.0.1
mem max/total/free: 1778 / 784 / 113 MB
thread count: 29
index: 559247 relationships in 108843 keys in 15293 sources

SDK installed: true
Dartium installed: true

[floitschG]

Added Optimization label.

[rakudrama]

True. We don't have an optimization for

if (a && b) ...
if (a && c) ...

--->
if (a) {
  if (b) ...
  if (c) ...
}

In fact we have no optimizations the change the shape of the SSA graph.

In this case we could make a different improvement. The canned check

  typeof entity === "object" && entity !== null && !!t1.$isXXX

could be replaced by

  t1.$isXXX

since it is reading from an interceptor.

There are some cases where we don't use the interceptor.
To enable the control flow optimization, we would have to introduce the null/primitive dereference check as a separate instruction.

[rakudrama]

This reduces the code size by always using the interceptor https://codereview.chromium.org/188433002/

[floitschG]

Removed the owner.