Fedora Looks To Build Firefox With Clang For Better Performance & Compilation Speed

Written by Michael Larabel in Fedora on 11 December 2018 at 06:16 AM EST. 26 Comments
Following the move by upstream Mozilla in switching their Linux builds of Firefox from being compiled by GCC to LLVM Clang, Fedora is planning the same transition of compilers in the name of compilation speed and resulting performance.

FESCo Ticket 2020 laid out the case, "Mozilla upstream switches from gcc to clang and we're going to follow upstream here due to clang performance, maintenance costs and compilation speed. Tom Stellard (clang maintainer) has asked me to file this ticket to comply with Fedora processes."

Fedora's Engineering and Steering Committee approved the plan during their Monday meeting to allow the official Fedora packages of Firefox to be built by Clang rather than GCC. As far as I know, the rest of the Fedora package set is compiled by the GNU Compiler Collection.

Firefox developers have increasingly been utilizing LLVM/Clang for faster compilation speed as well as the resulting binary performance, lower memory usage during the build process, etc. In response to the FESCO ticket, some have questioned why Firefox is allowed the compiler exception in Fedora, if Clang is better than GCC why don't they allow more packages to build with Clang, and also a belief GCC + LTO/PGO would be better than Clang. For at least now though, the Fedora package of Firefox is allowed to build with Clang.
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