1769677 - Using a WITH statement on Firefox takes more time than on Chrome

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, enhancement)

Description

[xuelanxu]

Steps to reproduce:

function main() {
    const v48 = [1000.0];
    with (v48) {
    }
    for (let v87 = 0; v87 < 1000; v87++) {
        for (let v93 = 0; v93 < 1000; v93++) {
        }
    }
}
let t = performance.now();
main();
console.log(performance.now() - t)

Actual results:

Firefox(100.0.1): 44 milliseconds

Chrome(101.0.4951.67): 1.1 milliseconds

Expected results:

Times in the same ballpark.

Comment 1

[Jan de Mooij [:jandem]]

Using with is not recommended, see the warning on MDN. Also, with statements are not allowed in strict-mode ("use strict"). SM doesn't really try hard to optimize functions containing with because of this.

Comment 2

[Nicolas B. Pierron [:nbp]]

To be clearer, SpiderMonkey currently uses with all over its test suite to explicitly prevent code from being optimized.

Comment 3

[Nicolas B. Pierron [:nbp]]

Unless there is a compelling use case which is getting spread across the web, I will flag this issue as WONTFIX.

Comment 4

[Nicolas B. Pierron [:nbp]]

Looking at a JS code sample from the top 50 websites taken in 2019, the with keyword appears 160 times over 379016763 characters.