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Accessing elements after the end of the arguments array triggers deoptimization of the entire function on v8, so avoid doing so. Also tweak all the checks into the same standard form for consistency.
Add a bogus assignment to a function prototype, which appears to be the magic hint to treat function assignments as constant (until proven otherwise). Also get rid of the after-the-fact mutation of the ES object by making IsPromise an ordinary function. (We could also call `Object.freeze(ES)` but it doesn't actually improve performance further.)
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how does this impact other engines? v8-specific optimizations have hurt other engines' performance in the past, with bluebird for example.
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I can't imagine it would hurt performance, since it's just a throwaway assignment. I'll try to double-check, but I don't know of any equivalent low-level IR tools on the firefox side. (jsperf can be highly misleading.)
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I've cherry-picked in one of these commits - a rebase should result in only the one commit left on top |
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Be careful about how
argumentsis accessed, and ensure that theES.*helpers are treated as constant functions which can be inlined.