sorry, longString[i] is faster than longString[1]
i checked with `--print-opt-code`, but it was too hard to see the difference
2023년 3월 23일 목요일 오후 11시 11분 44초 UTC+9에 Jakob Kummerow님이 작성:
> `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....@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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