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> won't work if num is negative I remember reading (although I can't find it now) a great analysis of all the optimizations that Javascript compilers _can't_ d

> won't work if num is negative I remember reading (although I can't find it now) a great analysis of all the optimizations that Javascript compilers _can't_ do because of the existence of the "eval" instruction.

astrange 10mo ago
A JIT can do any optimization it wants, as long as it can deoptimize if it turns out it was wrong.
- adrianN 10mo ago
  You also want to prove that the „optimization“ doesn’t make things slower.
  - astrange 10mo ago
    I don't think anyone actually bothers to do that tbh.
LoganDark 10mo ago
Could this perhaps be it? https://janvitek.org/pubs/ecoop11.pdf https://janvitek.org/pubs/ecoop11.pdf
cibyr 10mo ago
The extra fun thing about this is that eval has different semantics if it's assigned to a different name, in order to allow JavaScript implementations to apply extra optimizations to code that doesn't call a function literally named "eval": https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval#direct_and_indirect_eval https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... Andy Wingo (of course!) has a good explanation of this: https://wingolog.org/archives/2012/01/12/javascript-eval-considered-crazy https://wingolog.org/archives/2012/01/12/javascript-eval-con...