1697215 - Update to clang 12.0.0

Status: RESOLVED FIXED

(Firefox Build System :: Toolchains, task)

Description

[(Away)]

At the time that I am filing this, this is only a placeholder/planning-ahead bug.

We should not proceed for shippable builds until:

• clang 12.0.0 reaches the official release tag
• Rust gets LLVM 12 (https://github.com/rust-lang/rust/pull/81451). The PGO format changed between 11 and 12, and builds will have poor optimization if we mix versions in xLTO. The above PR has landed on Rust nightly 1.52. We should figure out how long we want that to ride the trains -- one possibility to use 1.52 beta on our nightly, and pick up the final during our beta.

Comment 1

[(Away)]

Attachment: [PLACEHOLDER] Update to clang 12.0.0 final

Comment 2

[(Away)]

Attachment: Move builds to clang-12 toolchains

Comment 3

[(Away)]

Attachment: [DONT LAND] Disable value profiling in Rust PGO

Comment 4

[Andi [:andi]]

Attachment: Bug 1697215 - Update to clang 12.0.0.

Comment 5

[Andi [:andi]]

Attachment: Bug 1697215 - Move builds to clang-12 toolchains.

Credit goes to dmajor since he's the one who started work on this.

Depends on D113325

Comment 6

[Andi [:andi]]

Attachment: Bug 1697215 - Disable value profiling in Rust PGO until we move to to rust 1.52.

Credit goes to dmajor.
Rust gets LLVM 12 - https://github.com/rust-lang/rust/pull/81451.
The PGO format changed between 11 and 12, and builds will have poor optimization if we mix versions in xLTO.
The above PR has landed on Rust nightly 1.52.
Until we move to 1.52 nightly we should have this landed.

In the meantime, for unblocking try builds, we can disable value-PGO in Rust.

Depends on D113326

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/bd89c077a1e4
Disable value profiling in Rust PGO until we move to to rust 1.52. r=firefox-build-system-reviewers,glandium
https://hg.mozilla.org/integration/autoland/rev/5ea8b144080f
Update to clang 12.0.0. r=firefox-build-system-reviewers,mhentges
https://hg.mozilla.org/integration/autoland/rev/27f3a6f6ac87
Move builds to clang-12 toolchains. r=firefox-build-system-reviewers,mhentges

Comment 8

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/bd89c077a1e4
https://hg.mozilla.org/mozilla-central/rev/5ea8b144080f
https://hg.mozilla.org/mozilla-central/rev/27f3a6f6ac87

Comment 9

[Ed Lee :Mardak]

I think the perf-alert from bug 1707141 comment 21 should have been attributed to this bug.

== Change summary for alert #29965 (as of Wed, 05 May 2021 04:16:02 GMT) ==

Improvements:

Ratio	Suite	Test	Platform	Options	Absolute values (old vs new)
18%	amazon-search	fnbpaint	android-hw-g5-7-0-arm7-api-16-shippable	warm	905.79 -> 740.12
18%	amazon-search	fcp	android-hw-g5-7-0-arm7-api-16-shippable	warm	875.77 -> 722.00
16%	bbc	SpeedIndex	android-hw-p2-8-0-android-aarch64-shippable-qr	warm webrender	599.67 -> 503.08
16%	amazon-search	FirstVisualChange	android-hw-g5-7-0-arm7-api-16-shippable	warm	1,149.33 -> 965.08
14%	amazon-search	FirstVisualChange	android-hw-p2-8-0-android-aarch64-shippable-qr	warm webrender	496.04 -> 424.75
...	...	...	...	...	...
8%	booking	PerceptualSpeedIndex	android-hw-g5-7-0-arm7-api-16-shippable-qr	warm webrender	2,515.88 -> 2,314.83

For up to date results, see: https://treeherder.mozilla.org/perfherder/alerts?id=29965

Comment 10

[Arthur K. (he/him)]

With Clang 12.0.1 having been released the other day, are there plans to migrate after FF91?

Comment 11

[Mitchell Hentges [:mhentges] 🦀]

I have good news for you :)