Implement fast symbol lookup in the interpreter

[laurentlb]

We talked about speeding up the interpreter by avoiding hash maps for variable lookup. We should be able to assign statically an integer to each variable.

Unfortunately, we can't do this safely right now because of a bug in the interpreter (#5637). In some cases, the name resolution is not static. Once the bug is fixed, that should be feasible.

cc @ttsugriy

[meisterT]

I assume @alandonovan's work makes this obsolete?

[laurentlb]

I'd say it's part of Alan's work. You first need the static resolution before you can generate (decent) bytecode.

[alandonovan]

What Laurent said. The following changes are necessary first:

• decouple thread from module (CL 309983907, in review)
• add loadBindsGlobally option to resolver (will port go.starlark.net resolver)
• make the prelude behave like a load statement (no shared syntax trees => recordScope always on) (CL 309105613, in progress)
• use arrays for local variables (the actual optimization; it is trivial)

[brandjon]

Alan implemented this some time ago.