1801851 - Use ValueUsage::IgnoreValue in short-circuit and void expressions

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P1)

Description

[André Bargull [:anba]]

This allows to use JSOp::CallIgnoresRv for code like c && f(), which is common in minified code.

Comment 1

[André Bargull [:anba]]

Attachment: Bug 1801851 - Part 1: Pass ValueUsage to short-circuit expressions. r=arai!

Pass ValueUsage to the last expression in a short-circuit expression sequence
to allow emitting CallIgnoresRv in minified code.

Minifiers often rewrite this code:

if (c) f();

Into the equivalent expression:

c && f();

The last expression's value is never used, so we can optimise it to use
JSOp::CallIgnoresRv instead of JSOp::Call.

Comment 2

[André Bargull [:anba]]

Attachment: Bug 1801851 - Part 2: Remove unnecessary ValueUsage default parameters. r=arai!

All callers are explicitly passing a ValueUsage argument, so we don't need
the default parameter anymore.

Depends on D162714

Comment 3

[André Bargull [:anba]]

Attachment: Bug 1801851 - Part 3: Use IgnoreValue for void expressions. r=arai!

void expressions don't use their value, so we can trivially use IgnoreValue.

Depends on D162715

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/cc76bba0db29
Part 1: Pass ValueUsage to short-circuit expressions. r=arai
https://hg.mozilla.org/integration/autoland/rev/b0321dddbda0
Part 2: Remove unnecessary ValueUsage default parameters. r=arai
https://hg.mozilla.org/integration/autoland/rev/240da2ef1c8f
Part 3: Use IgnoreValue for void expressions. r=arai

Comment 5

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/cc76bba0db29
https://hg.mozilla.org/mozilla-central/rev/b0321dddbda0
https://hg.mozilla.org/mozilla-central/rev/240da2ef1c8f