Fedora Firefox – GCC/CLANG dilemma

After reading Mike’s blog post about official Mozilla Firefox switch to LLVM Clang, I was wondering if we should also use that setup for official Fedora Firefox binaries.

The numbers look strong but as Honza Hubicka mentioned, Mozilla uses pretty ancient GCC6 to create binaries and it’s not very fair to compare it with up-to date LLVM Clang 6.

Also if I’m reading the mozilla bug correctly the PGO/LTO is not yet enabled for Linux, only plain optimized builds are used for now…which means the transition at Mozilla is not so far than I expected.

I also went through some Poronix tests which indicates there’s no black and white situation there although Mike claimed that LLVM Clang is generally better that GCC. But it’s possible that Firefox codebase somehow fits better LLVM Clang than GCC.

After some consideration I think we’ll stay with GCC for now and I’m going compare Fedora GCC 8 builds with the Mozilla  LLVM Clang ones when there are available. Both builds can’t use -march=native so It may be an equal comparsion. Also Fedora should enable the PGO+LTO GCC setup to get the best from GCC.

[Update] I was wrong and PGO+LTO should be enabled also for Linux builds now. The numbers looks very well and I wonder if we can match them with GCC8! 🙂