A modern optimization pipeline.
The Go folks have adopted some of the same ideas (minimal optimization and no nested include files), and they build on the experience of the Plan 9 compiler to better divide the work between the "compiler" and "linker", so we gain more from parallel make.
The build speed doesn't matter much if you don't like the runtime speed.
Do you have any sources on this? Can you perhaps link me to something that explains the differences between the ARM and the P2 that lead to such a difference in performance despite the clock speeds?
I did this partly because plan9 had published some source code and times on a system with exactly the same hardware as mine - AMD k6/350.
I suspect the plan9 compiler hasn't had nearly as many changes since then so the gap would be much wider.
I acknowledge compile time is important also - and this is where the plan9/golang people have made a reasonable trade-off.