1983130 - Optimize comparisons with object-or-null values better

Status: NEW

(Core :: JavaScript Engine: JIT, task, P2)

Description

[Jan de Mooij [:jandem]]

One of the hottest functions in JetStream3's raytrace tests with both private and public class fields has a !== operation where we use a BinaryBoolCache IC in Ion.

The LHS is always an object but the RHS is an object or null. This is likely quite common and we should find a way to optimize this without using an IC in Ion.

Below is a micro-benchmark for this (if I change the null value in the array to {} we're almost 2x faster with --spectre-mitigations=off).

function f() {
    var arr = [{}, null];
    var res = 0;
    var t = Date.now();
    for (var i = 0; i < 100_000_000; i++) {
        res += arr[0] !== arr[i & 1];
    }
    print(Date.now() - t);
    return res;
}
f();

Comment 1

[Jan de Mooij [:jandem]]

A related case shows up in prettier-wtb. Their traversal code uses a marker object (from the non-minified version):

const traverseDocOnExitStackMarker = {};

And then inside a function:

    const doc = docsStack.pop();
    if (doc === traverseDocOnExitStackMarker) {

We use an IC for the comparison in Ion (I think the values can be strings?) but the RHS is always going to be an object.