1808744 - Improve JIT codegen for GC barriers a bit

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, task)

Description

[Jan de Mooij [:jandem]]

For example, to test if a Value is a nursery cell, we can combine the unboxing with the chunk mask on 64-bit platforms.

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Bug 1808744 part 1 - Combine Value unboxing mask with ChunkMask for Value barriers in JIT code. r?jonco!

This gets rid of an extra or-instruction on 64-bit platforms and simplifies
loading the store buffer.

Comment 2

[Jan de Mooij [:jandem]]

Attachment: Bug 1808744 part 2 - Remove ChunkStoreBufferOffsetFromLastByte. r?jonco!

We can use andPtr with a 32-bit value because it's sign-extended. We already rely
on this in other places where we do similar masking.

On ARM64, use 3-operand And to avoid an extra register move.

Depends on D166137

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5112c2428646
part 1 - Combine Value unboxing mask with ChunkMask for Value barriers in JIT code. r=jonco
https://hg.mozilla.org/integration/autoland/rev/891c7d2112df
part 2 - Remove ChunkStoreBufferOffsetFromLastByte. r=jonco

Comment 4

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/5112c2428646
https://hg.mozilla.org/mozilla-central/rev/891c7d2112df

Comment 5

[Andra Esanu (needinfo me)]

(In reply to Pulsebot from comment #3)

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5112c2428646
part 1 - Combine Value unboxing mask with ChunkMask for Value barriers in
JIT code. r=jonco
https://hg.mozilla.org/integration/autoland/rev/891c7d2112df
part 2 - Remove ChunkStoreBufferOffsetFromLastByte. r=jonco

== Change summary for alert #36720 (as of Thu, 12 Jan 2023 05:46:24 GMT) ==

Improvements:

Ratio	Test	Platform	Options	Absolute values (old vs new)	Performance Profiles
12%	assorted-dom	windows10-64-shippable-qr	fission webrender	18.88 -> 16.58	Before/After
12%	assorted-dom	windows10-64-shippable-qr	fission webrender	18.76 -> 16.60	Before/After

For up to date results, see: https://treeherder.mozilla.org/perfherder/alerts?id=36720