`longString[1]` is loop-independent and can hence be hoisted out of the
loop. `longString[i]` actually has to be loaded from memory in each
iteration.
(I haven't spent the time to check whether that's really what's happening.
Using `--print-opt-code`, or `--trace-turbo` and Turbolizer, you can check
on your own.)
On Thu, Mar 23, 2023 at 2:45 PM Jeong HyunJun <rollrat.softw...@gmail.com>
wrote:
> hello, I've seen a performance difference depending on whether or not a
> variable is used in the loop.
>
> let longString = '';
>
> for (let i=0;i<10000000;i++) {
> longString += `${i}`;
> }
>
> console.log(longString.length);
>
> let cnt = 0;
> const st = Date.now();
>
> for (let i=0;i<longString.length - 1;i++) {
> if (longString[1] === longString[0]) {
> /// if (longString[i] === longString[0]) {
> cnt ++;
> }
> }
>
> console.log(Date.now() - st, cnt);
>
> It is twice as slow with longString[i] than with longString[1].
> What optimizations are causing these results?
> It doesn't seem to have anything to do with ConsString flattening.
>
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