Fedora's Firefox To Stick With GCC Over Clang, Beefed Up By LTO/PGO Optimizations

Last month Fedora developers were planning on building their Firefox package with Clang rather than GCC to follow the move by upstream Mozilla in transitioning their production builds from being built under GCC to LLVM Clang. But now Fedora has reversed course and will continue building with GCC though now benefiting also from PGO and LTO optimizations.

After announcing their plans to move over to Clang-built Firefox builds for Fedora (and receiving the necessary permission from the FESCo committee), they are sticking to the GNU Compiler Collection after all. GCC developers from both Red Hat and SUSE stepped up and found and fixed some bugs that improved the Firefox build. Additionally, arguments against Clang were raised on the basis of missing features and security.

As a result, Firefox for Fedora is continuing to be built with GCC. But thanks to the latest fixes, the Firefox package will be built using Link Time Optimizations (LTO) and Profile Guided Optimizations (PGO) for enhancing the performance. There are currently updates pending for Fedora 28 and Fedora 29 that offer up these optimized Firefox builds and will soon be rolling down as stable release updates.

More details in this blog post by Fedora Firefox packager Martin Stransky. This should be fun for a benchmarking comparison against the official Mozilla Clang-built Firefox Linux binaries once time allows.