anchor.diff:  class Float64x2 {
     @patch
     @pragma("vm:prefer-inline")
  -  factory Float64x2(double x, double y) => _Float64x2FromDoubles(x, y);
  +  factory Float64x2(double x, double y) {
  +    _throwIfNull(x, 'x');
  +    _throwIfNull(y, 'y');
  +    return _Float64x2FromDoubles(x, y);
  +  }
   
     @pragma("vm:exact-result-type", _Float64x2)
     static _Float64x2 _Float64x2FromDoubles(double x, double y)
  
positive.code:   bool get flagZ native "Int32x4_getFlagZ";
    @pragma("vm:exact-result-type", bool)
    bool get flagW native "Int32x4_getFlagW";
    @pragma("vm:exact-result-type", _Int32x4)
    Int32x4 withFlagX(bool x) native "Int32x4_setFlagX";
    @pragma("vm:exact-result-type", _Int32x4)
    Int32x4 withFlagY(bool y) native "Int32x4_setFlagY";
    @pragma("vm:exact-result-type", _Int32x4)
    Int32x4 withFlagZ(bool z) native "Int32x4_setFlagZ";
    @pragma("vm:exact-result-type", _Int32x4)
    Int32x4 withFlagW(bool w) native "Int32x4_setFlagW";
    @pragma("vm:exact-result-type", _Float32x4)
    Float32x4 select(Float32x4 trueValue, Float32x4 falseValue)
        native "Int32x4_select";
  
negative.code: class Int32x4 {
    @patch
    @pragma("vm:prefer-inline")
    factory Int32x4(int x, int y, int z, int w) {
      _throwIfNull(x, 'x');
      _throwIfNull(y, 'y');
      _throwIfNull(z, 'z');
      _throwIfNull(w, 'w');
      return _Int32x4FromInts(x, y, z, w);
    }
  
    @pragma("vm:exact-result-type", _Int32x4)
    static _Int32x4 _Int32x4FromInts(int x, int y, int z, int w)
  