Bad news first. The drop in speed between the Zeros in IcedTea6 1.3 and 1.4 doesn’t seem to come from Zero itself. I did a build of IcedTea6 1.4 with everything in
ports/hotspot/src/*cpu reverted to 1.3, and the speed loss remained. It must be something to do with the newer HotSpot, or some other patch that got added or changed. I don’t really want to spend any more time on this than I have, so we’ll just have to live with it.
I’ve not come to any conclusions as to the difference in speed between the native-layer C++ interpreter and Zero either. It’s not the unaligned access stuff I mentioned: I ran some benchmarks, but the results were ambiguous. It may be libffi, but again, I don’t want to spend more time on this…
The good news is that I’ve been checking the Zero sources for SCA cover, emailing various people, and there’s only one tiny easily-removable bit I’m unsure about. I spent the morning preparing and submitting the first of the patches that will be required, the core build patch, which will hopefully be well received.