[evincarofautumn]

I develop a compiler for ActionScript 3. Though it’s not a great language, it does have a few distinct advantages over its cousin JavaScript. First, type annotations. Obviously the more knowledge you have about the structure of the program, the better you can help it run well. Having a class model instead of a prototype model also helps—much as I like working with prototypes—because you can easily eliminate late binding (“hash lookups”) and allocations, two of the performance killers mentioned in the slides. The operative word there is easily. You can analyse and JIT all you want, but you cannot feasibly solve at runtime the fundamental constraints imposed by the language.

Say a compiler author needs twice as much effort and cleverness to make programs in language X run fast than for language Y. That means that—all other things being equal—implementations of X will be twice as slow as Y for the same basic quality of implementation.