[nicois]

It would be interesting to know how effective Profile Guided Optimisation is here.

[benhoyt]

Unfortunately it doesn't seem to help at all, I think mainly because (at present) Go's PGO basically inlines hot functions, and the important code here is all in one big function.

[neonsunset]

It is only mildly effective because how anemic Go compiler is. And even then it's extremely limited. If you want to see actual good implementations - look into what OpenJDK HotSpot and .NET JIT compilers do with runtime profiling and recompilation (.NET calls it Dynamic PGO).