[Reg 6.5 -> 6.6] Qml: Compiler generates wrong code for Array.prototype.join invocation

qml: foo1: 
qml: foo2: A+B
qml: foo3: A+B

import QtQuick

Window {
  width: 640
  height: 480
  visible: true
  title: qsTr("Hello World")

  // compiled: fail
  function foo1() : string
  {
    var s = [];
    s.push("A")
    s.push("B")
    return s.join("+");
  }

  // not compiled: "toString" seems to disable the compiler
  function foo2() : string
  {
    var s = [];
    s.push("A")
    s.push("B")
    return s.join("+").toString();
  }

  // not compiled: no return type annotation
  function foo3()
  {
    var s = [];
    s.push("A")
    s.push("B")
    return s.join("+");
  }

  Component.onCompleted: {
    console.log("foo1:", foo1());
    console.log("foo2:", foo2());
    console.log("foo3:", foo3());
  }
}