Arch Linux Looking To Employ LTO By Default, Possibly Raise x86-64 Requirements
Following openSUSE Tumbleweed using LTO by default, Fedora 33 doing it too, and Ubuntu 21.04 set to ship with LTO'ed packages, Arch Linux is finally looking at enabling link-time optimizations by default for their package builds.
Turning on link-time optimizations (LTO) often enhances the performance of the resulting binary thanks to the added optimizations that can be done at link-time on the entire binary. LTO can also provide some size benefits and other enhancements but at the cost of slower compilation times and increased memory usage. LTO though is normally working quite well these days on both the GCC and LLVM Clang compilers.
There is this change looking at enabling LTO by default for Arch and is currently under discussion. One of the concerns raised is indeed over the higher RAM usage but hopefully Arch will move forward and shifting to it by default.
Another notable change being considered at the same time for Arch is using the x86-64-v2 microarchitecture level. This would make Arch Linux faster by allowing to assume some CPU instruction set extensions by default while still running on most x86-64 Intel/AMD hardware from over one decade. This is the same as RHEL9 set to require x86-64-v2 instead of vanilla x86-64.
The x86-64-v2 baseline basically means Intel Nehalem CPUs or newer. Only the very oldest and original x86-64 CPUs would suffer as a result if wanting to run newer Arch Linux builds. This change though is receiving some criticism that x86-64-v2 requiring SSE4.1/SSE4.2 rules out some processors still in use by Arch users.
Instead some are suggesting making use of Glibc-HWCAPS in offering optimized library builds for the various x86-64 feature micro-architecture levels without raising the baseline requirement to run Arch. In either case, we are happy to see Arch Linux developers working on this and will hopefully join more Linux distributions looking at HWCAPS / optimized packages for today's processors. So hopefully some form of this will happen plus LTO'ing by default to making for some nice stock performance gains on Arch this year.