Re: Caching last used table index

[云风 Cloud Wu <cloudwu@...>]

Soni "They/Them" L. <fakedme@gmail.com> 于2019年5月5日周日 上午11:05写道：
>
> I often write code like:
>
> local foo = t.foo
> if not foo then foo = whatever t.foo = foo end
> -- use foo here
>
> but ideally I'd like to write it like:
>
> if not t.foo then t.foo = whatever end
> local foo = t.foo
>
> and still have the same performance (or better).
>
> does lua do any optimizations related to this?
>

I have had tried to do this optimization many years ago (2012), See
the attachment for the patch, it's based on lua 5.2.1 .

I cached the last index of table hash part in Proto struct , so that
it can use it directly on next access ( for OP_GETTABUP, OP_GETTABLE,
OP_SELF) .

But I haven't seen the better performance. I guess lua's hash table is
good enough for short string keys, > 70% short string keys are on the
main index according to my experience.


-- 
http://blog.codingnow.com

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