[mananaysiempre]

Unfortunately, PGO done the default way is antithetical to reproducible builds. You can avoid that by putting the profiling data in your VCS, but then you suffer of all the consequences of a version-controlled binary blob, one heavily dependent on other files at that.

Perhaps it should be possible use profiling data to keep human-managed {un,}likely or {hot,cold} annotations up to date? How valuable are PGO’s frequencies compared to these discrete-valued labels? (I know GCC allows you to specify frequencies in the source, but that sounds less than convenient.)