detail: https://twitter.com/yosuke_furukawa/status/1204549961267867649

TestCode1.js

const f = () => {
    const arr = new Array();
    for (let i = 0; i < 1000000; i++) {
        arr.push((Math.random() * 100) | 0);
    }

    let sum = 0;
    for (let i = 0; i < arr.length; i++) {
        const value = arr[i];
        sum += value;
    }
}

for (let i = 0; i < 9999; i++) f();

// $ time out/x64.release/d8 --print-opt-code --code-comments TestCode1.js > tc1.code
// out/x64.release/d8 --print-opt-code --code-comments TestCode1.js > tc1.code  184.06s user 36.83s system 105% cpu 3:30.02 total

TestCode2.js

const f = () => {
    const arr = new Array();
    for (let i = 0; i < 1000000; i++) {
        arr.push((Math.random() * 100) | 0);
    }

    let sum = 0;
    for (let i = 0; i < 1000000; i++) {
        const value = arr[i];
        sum += value;
    }
}

for (let i = 0; i < 9999; i++) f();

// $ time out/x64.release/d8 --print-opt-code --code-comments TestCode2.js > tc2.code
// out/x64.release/d8 --print-opt-code --code-comments TestCode2.js > tc2.code  184.69s user 36.32s system 105% cpu 3:30.13 total