Remove leaf operations which have no side-effects

[mhevery]

There are a lot of statements in code which only make sense if there is a next item following. If it is a leaf they should be removed.

Example:

    var change_interpolate1 = false; // NOT NEEDED


    if (change_componentName0) {
      currentProto = _protos[1];
      interpolate1 = "" "${componentName0 == null ? "" : componentName0}" "";
      if (!_gen.looseIdentical(interpolate1, _interpolate1)) {
        change_interpolate1 = true;  // NOT NEEDED
        if (throwOnChange) {
          _gen.ChangeDetectionUtil.throwOnChange(_protos[1],
              _gen.ChangeDetectionUtil.simpleChange(
                  _interpolate1, interpolate1));
        }

        _dispatcher.notifyOnBinding(currentProto.bindingRecord, _interpolate1 = interpolate1);

        _interpolate1 = interpolate1;
      }
    } else {  // NOT NEEDED
      interpolate1 = _interpolate1; // NOT NEEDED
    }

Notice the else and assignment at the end. This is only needed if there would be a next item dereferencing it..

should be:

    if (change_componentName0) {
      currentProto = _protos[1];
      interpolate1 = "" "${componentName0 == null ? "" : componentName0}" "";
      if (!_gen.looseIdentical(interpolate1, _interpolate1)) {
        if (throwOnChange) {
          _gen.ChangeDetectionUtil.throwOnChange(_protos[1],
              _gen.ChangeDetectionUtil.simpleChange(
                  _interpolate1, interpolate1));
        }

        _dispatcher.notifyOnBinding(currentProto.bindingRecord, _interpolate1 = interpolate1);

        _interpolate1 = interpolate1;
      }
    }

This requires some form of detecting leaves and stripping out the vars which are used of chaining.

[kegluneq]

@jakemac53 please evaluate and determine if this gives any benefit after dart2js compilation.

[jakemac53]

Definitely the change_* booleans get filtered out by dart2js if the value is never used.

[jakemac53]

@yjbanov is this still relevant based on the changes coming?

[vsavkin]

Sorry, I fixed it in #3361 by accident. I am reassigning this to myself.

[vsavkin]

Closed via c1ee9435330ba1e24eea25fcdeacd81b8bf4f0fbhttps://github.com/angular/angular/commit/c1ee9435330ba1e24eea25fcdeacd81b8bf4f0fb

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