Mangler performance - some improvement

[boopathi]

This gives a ~=200ms of mangler perf.

1. If NOT shouldConsiderSource, don't traverse Identifier & Literals for charset considerations
2. Don't recalculate hasBinding
3. loops

Most time was spent getting and verifying scope's bindings.

The following difference is between scope.hasBinding(next) and bindings.hop(next)

run-mangle                 740.549  1        740.549       
scopable-loop              547.912  2222     0.247         
run-collect                370.834  1        370.834       
next-identifier            222.018  3693     0.060         
get-all-bindings           171.469  2222     0.077         
Collect-Identifier         65.521   19176    0.003         
compute-oldname            54.560   64879    0.001         
scopable-rename            49.586   3693     0.013         
rename                     42.556   3693     0.012         

and now after this

run-mangle                 558.121  1        558.121       
scopable-loop              378.939  2222     0.171         
run-collect                369.423  1        369.423       
get-all-bindings           180.804  2222     0.081         
compute-oldname            53.859   64879    0.001         
scopable-rename            53.098   3693     0.014         
rename                     47.032   3693     0.013         
Collect-Identifier         44.661   19176    0.002         
next-identifier            39.646   3693     0.011         

[kangax]

Idea: collect global references upfront and check manually instead of calling hasGlobal for each

[boopathi]

each scope maintains its global references when the scope is created only (I think), and we visit scopes only once - and we transform in place. So my gut feel is that it's not possible to do better that that.

[kangax]

Wait, all scopes end up in the global... why do they need to store references?

[boopathi]

I'm not sure. scope is created (globals calculated from bindings) -> visitor applied is what I thought. I'll check though.

[boopathi]

Also, from the timing values, the next-identifier is just 39ms (0.011 ms per call) - this includes -

let next;
            do {
              next = getNext();
            } while (
              !t.isValidIdentifier(next)
              || hop.call(bindings, next)
              || scope.hasGlobal(next)
              || scope.hasReference(next)
            );

So this is not something we need to worry about ...