Bug 240162 – [Flatpak SDK] Update mold to version 1.2.1

• Component: Tools / Tests
• Status: RESOLVED FIXED

[Adrian Perez]

Version 1.2.1 was released a few days ago, with many improvements for LTO
support (and Clang's ThinLTO):

  https://github.com/rui314/mold/releases/tag/v1.2.1

Now --gdb-index is properly supported, and reading the release notes I've
learnt that one needs to pass -ggnu-pubnames to the compiler for the option
to actually do something (which we are not currently doing, follow-up patch
later on).

[Adrian Perez]

Here there's some numbers for my build machine, making an initial
RelWithDebInfo build, removing bin/* and lib/*.so* from the build
directory and then measuring how much it takes for the build to
complete, in order to (mostly) measure link time:

Mold				LLD			
usr	sys	wall		usr	sys	wall	
							
45,94	1,64	48,77		56,86	79,31	46,27	
42,32	1,19	44,48		60,09	77,43	49,78	
45,69	1,33	48,19		56,30	74,35	46,04	
42,19	1,29	44,65		60,19	78,22	49,77	
45,54	1,73	48,52		56,56	79,41	46,33	
							
44,03	1,36	46,52		58,36	77,33	47,96	avg
							
				1,33x	56,75x	1,03x	diff

Something very interesting to note is that the wall time for both
linkers is quite similar, but LLD is taking considerably more user
and system time than Mold. Neither manage to bring CPU usage up
to 100% across all 64 cores in my build machine, which means the
bottleneck here is disk access.

On machines with higher I/O thoroughput (better bus, better drives,
RAID-0 arrangement, etc.), the faster the disk access gets, the
faster using Mold will be.

[Adrian Perez]

Pull request: https://github.com/WebKit/WebKit/pull/542

[EWS]

Committed r293887 (250345@main): <https://commits.webkit.org/250345@main>

Reviewed commits have been landed. Closing PR #542 and removing active labels.

[Radar WebKit Bug Importer]

<rdar://problem/92859456>