1963672 - Optimize and tidy up some LSafepoint methods

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, task)

Description

[Jan de Mooij [:jandem]]

addBoxedValue has quadratic behavior for no good reason.

See bug 1938512 comment 11 where this showed up in a profile from Mayank.

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Bug 1963672 part 1 - Remove hasValueSlot check from LSafepoint::addBoxedValue. r?iain!

This avoids quadratic behavior that showed up in a profile. It's also consistent
with what we do in addGcPointer, addSlotsOrElementsPointer, etc.

(Furthermore, all jit-tests passed when turning this check into an assertion and
this vector is converted to a BitSet of slots when we encode the safepoint.)

This likely was based on the nunbox code for 32-bit platforms where we need a
lookup because we have separate type and payload halves, but that doesn't apply
to 64-bit.

Comment 2

[Jan de Mooij [:jandem]]

Attachment: Bug 1963672 part 2 - Inline addRegister methods into their callers. r?iain!

This also avoids some redundant assertInvariants calls.

Also turn some alloc.isGeneralReg() checks into assertions because GC things
can't be in float registers.

Comment 3

[Jan de Mooij [:jandem]]

Attachment: Bug 1963672 part 3 - Optimize nunbox handling in safepoints. r?iain!

Nunbox handling for 32-bit platforms also had quadratic behavior and has gotten
pretty complicated over the years.

This patch rewrites it with a simpler approach: we now add the separate type and
payload parts to a vector initially (similar to the other things stored in safepoints)
without trying to combine them. Then at the end we sort the entries and process them
all at once.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/360898bc3638
part 1 - Remove hasValueSlot check from LSafepoint::addBoxedValue. r=iain
https://hg.mozilla.org/integration/autoland/rev/80fb19bd626e
part 2 - Inline addRegister methods into their callers. r=iain
https://hg.mozilla.org/integration/autoland/rev/f479a53a3df5
part 3 - Optimize nunbox handling in safepoints. r=iain

Comment 5

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/360898bc3638
https://hg.mozilla.org/mozilla-central/rev/80fb19bd626e
https://hg.mozilla.org/mozilla-central/rev/f479a53a3df5

Comment 6

[Mayank Bansal]

Profile with latest Nightly which hopefully has the patches from this bug: https://share.firefox.dev/4kcSHlf
(Looks to me like the Lsnapshot stuff is mostly gone)