[gentoo-user] Firefox 64 binaries - LLVM6+PGO+LTO now used, faster than GCC6.4+PGO

[gentoo-user] Firefox 64 binaries - LLVM6+PGO+LTO now used, faster than GCC6.4+PGO

[Adam Carter]

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https://www.phoronix.com/scan.php?page=news_item&px=Firefox-Clang-LTO-All-Platforms

"Firefox nightly builds are now built with the LLVM Clang compiler on all
major platforms and the Linux build in particular is also now utilizing PGO
optimizations too. Faster Firefox is coming thanks to this compiler work.

All of Mozilla's tier-one platforms are now building the newest Firefox
browser code under the Clang compiler and having LTO (Link Time
Optimizations <https://www.phoronix.com/vr.php?view=17785>) enabled. That
includes Linux, Mac, Android, Windows across ARM / AArch64 / x86 relying
upon this open-source compiler. For now only the Linux builds also have PGO
(Profile Guided Optimizations <https://www.phoronix.com/vr.php?view=26589>)
enabled.

With the compiler re-tooling on Linux they are seeing about 5% better
performance and upwards of 18% in select tests compared to their previous
GCC (6.4-based) compiler with PGO. The current Clang stack they are using
is based on LLVM6 while when they transition to the upcoming LLVM/Clang 7.0
they expect 2~5% better performance on top of that.

Mozilla developers did try GCC LTO as well as switching to the newest GCC8
release, but ran into problems. These new release binaries should go into
effect for the Firefox 64 release."

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