[tachyonbeam]

Indeed, static analysis is generally rather costly. It's usually a fixed-point computation that iterates over the code multiple times. You generally need to allocate many objects to keep track of facts the analysis produces about different instructions, which need to be propagated around. Running a general-purpose static analysis on this test program would probably be more expensive than what I'm already doing.

In the case of my minimalist test program, it's easy to say "well, ha! that's obviously not an accessor!", but in the general case, it's much harder. Consider, for example, that there could be load() or eval() statements in the code. That means invisible code you haven't seen yet, and can't analyze. Then consider a much more trivial case where you find this somewhere in the code:

function foo(o) { delete o.a; }

Now, you know that "o" is very unlikely to be the global object... But can you prove that with absolute certainty? It's possible you can't, so then you must assume that maybe the global variable "a" doesn't exist, and accesses to it might throw an exception.

TL;DR: compiler design is no easy task.