Comments on Meeting Notes

Jeff Walden jwalden+es at MIT.EDU
Thu Dec 6 21:50:34 PST 2012

On 12/04/2012 03:57 PM, Brendan Eich wrote:
> Allen Wirfs-Brock wrote:
>> The timing of copying is only an issue if the function actually assigns to a formal parameter.  Such assignments should be pretty easy to (conservatively) statically check for.
> I'm telling you what engines do. Not what they might do. I did assignment analysis in SpiderMonkey for Firefox 3.6, it was helpful in its day. I think a bunch has been ripped out because modern JITs don't need it.
> [...]the point I made, cited above: " engines don't do it currently and feel little pressure to do so. Chicken and egg."

SpiderMonkey's implementation of the arguments object functions exactly as described here for functions with strict mode code -- actually for all functions, I think.  Regarding the strict mode semantics specifically, it was fairly easy to make those optimizations when I was implementing the various strict mode arguments semantics, so I did them.  There hasn't been a time where SpiderMonkey's had strict mode arguments semantics, without these optimizations.


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