Both LTO and PGO require the use of clang so I think its easier to just
stick with clang for all builds, so PGO and LTO could in theory be used
without each other.
Lo and behold, we're finally catching up with Mozillas very own firefox
build in terms of speed.
PGO is an optimization technique in which in a first step we create a
build that supports instrumentation, meaning we can use it to create a
profile of how the browser behaved during usage. Then in a second pass
we create the final build that uses the acquired profiling data to
optimize the browser for the workload it actually received during
profiling.
The downside is that with PGO we now need to build Firefox twice, which
increases the build time from around 20 minutes to roughly 50 minutes.
In the Speedometer 2.0 benchmark multiple tests could see a
responsiveness improvemeant around 20-25%, which makes the increased
build time well worth it.
Sadly this benefit seems limited to x86_64-linux, builds on
aarch64-linux get stuck during profiling and I haven't found out why.
Finally, after a long time, we can say:
Closes: #76484
Supersedes: #129503
In #109133 @alyssais discovered that the drmSupport flag stopped
working. This is because Mozilla decided around Firefox 51
(mozbz#1289634) to swap the default values and our flag was asking for
the wrong thing all along.
Since this flag has now been enabled for multiple years, disabling it
would mean a regression for our users. Leaving it enabled should be
unproblematic since it only controls whether Firefox shows the EME nagbar,
that allows to enable Widevine CDM, when a site requests it. The choice is
therefore completely up to the enduser.
Disabling this nagbar is still possible at runtime by setting
`browser.eme.ui.enabled` to `false`. If Widevine CDM was inadvertently
enabled it can be disabled at `media.gmp-widevinecdm.enabled`.
Supersedes: #109133
This commit exposes that support for compilation without systemd,
controlled by the global systemdSupport argument. This argument is
understood by many other nixpkgs expressions and can be set globally
in ~/.config/nixpkgs/config.nix.
