1342068 - Make it easier to optimize functions whose return value isn't used

Status: NEW

(Core :: JavaScript Engine: JIT, defect, P3)

Description

[Till Schneidereit [:till]]

Some functions that return values are frequently called for their side effects, with the return value getting ignored. A prominent example of this is Array.prototype.splice. We do optimize that in ion, using quite a bit of boilerplate.

It'd be very nice to be able to do this for more functions, such as Promise.prototype.then and Promise.prototype.catch, without requiring the duplication of all that boilerplate.

Comment 1

[Hannes Verschore [:h4writer]]

Wondering about this a little bit more.

I think we might be able to add some optimization pass that checks if a MCall has no uses and replaces the called native function with a similar (same signature) function that doesn't return a value (or undefined/magic placeholder). Instead of adding a new MIR-node. (Note that the MIR-node might be more optimized, since it also specializes the input values.)

@jandem: right?

Comment 2

[Jan de Mooij [:jandem]]

arai is fixing this in bug 1344477 by adding a separate bytecode op. I agree an Ion optimization pass could probably also work.

Comment 3

[Sylvestre Ledru [:Sylvestre]]

Moving to p3 because no activity for at least 1 year(s).
See https://github.com/mozilla/bug-handling/blob/master/policy/triage-bugzilla.md#how-do-you-triage for more information