1684914 - Don't attempt to use thin LTO with gcc

Status: RESOLVED FIXED

(Firefox Build System :: General, defect)

Description

[Mitchell Hentges [:mhentges] 🦀]

-flto=thin doesn't work with GCC 10+ (though It didn't work on GCC <10 either, but GCC would just ignore the thin part).

This is forcing GCC users to provide --enable-lto=full in their mozconfigs.

Comment 1

[Connor Sheehan [:sheehan]]

Attachment: Bug 1684914: stop passing `-flto=thin` to gcc since it doesn't actually work r?#build

This is essentially just a backout of D84773. Passing -flto=thin worked
previously but the value passed was just ignored and full lto was performed.
On newer versions of gcc passing an unknown value causes failure. So just
revert to the old behaviour.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/129bc6a92cbb
stop passing `-flto=thin` to gcc since it doesn't actually work r=glandium,mhentges

Comment 3

[Alexandru Michis [:malexandru]]

https://hg.mozilla.org/mozilla-central/rev/129bc6a92cbb

Comment 4

[tt_1]

can this possibly be uplifted to beta-85, or is it too late for that?

Comment 5

[Connor Sheehan [:sheehan]]

Comment on attachment 9195724 [details]
Bug 1684914: stop passing -flto=thin to gcc since it doesn't actually work r?#build

Beta/Release Uplift Approval Request

• User impact if declined: Downstream consumers attempting to build with thin LTO and gcc will hit failures during the build. gcc only supports full LTO.
• Is this code covered by automated tests?: Yes
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Only impacts building Firefox using gcc and requesting thin LTO
• String changes made/needed:

Comment 6

[Ryan VanderMeulen [:RyanVM]]

Comment on attachment 9195724 [details]
Bug 1684914: stop passing -flto=thin to gcc since it doesn't actually work r?#build

Approved for 85.0rc1.

Comment 7

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/releases/mozilla-beta/rev/38febe1e15c4