JDK-8038396 deoptimizes access to scoped variables that start out as undefined too much.
E.g.

var x = foo()
var a = 3;
a++; // becomes double instead of optimistic int

function foo() { return null };

The reason is that the first deoptimizing recompilation happens when "foo()" is invoked and the return value doesn't fit in an int. At this time, "a" is not yet initialized, so naively observing Undefined value turns its subsequent accessor into Object one. The fix is to avoid inferring expression types for undefined scoped variables (those for which Property.getCurrentType() == null), instead of presuming Object.