[alex-g]

The Mill certainly raises a lot of interesting code generation and optimization issues. I'm sure there's plenty of scope for figuring out good optimization strategies, as a lot seems to depend on the ability of the compiler to make good choices about instruction scheduling and belt slot allocation. Sure, that's the case for traditional architectures as well, but there's more prior art there too. There may also be ingenious algorithms which work better on the Mill architecture specifically. I'd love to know if there's any theory on the hardness of allocating positions on the belt, compared to traditional register allocation.

[willvarfar]

Actually, as its co-designed by a compiler writer (read the bio we paste with the talks:

> Ivan Godard has designed, implemented or led the teams for 11 compilers for a variety of languages and targets, an operating system, an object-oriented database, and four instruction set architectures. He participated in the revision of Algol68 and is mentioned in its Report, was on the Green team that won the Ada language competition, designed the Mary family of system implementation languages, and was founding editor of the Machine Oriented Languages Bulletin. He is a Member Emeritus of IFIPS Working Group 2.4 (Implementation languages) and was a member of the committee that produced the IEEE and ISO floating-point standard 754-2011.

), its actually designed to be easy to write a compiler for. It's he polar opposite of the "sufficiently smart compiler syndrome" :)

I keep suggesting we do a "sufficiently dumb compiler syndrome" talk, but it'd contain nothing novel; the art is well established by all the VLIW machines that have come before.

[igodard]

It's actually rather easy to allocate belt positions, because the belt is a FIFO and allocates them itself :-)

However, the scheduler must track lifetimes and make sure that nothing still live falls off the end. This is also (not quite so) easy to do, because the scheduler knows exactly what is the belt behavior of each operation it schedules (the Mill is exposed-pipeline), so it is sufficient to symbolically execute a candidate schedule to know if it is feasible.

If not, the scheduler inserts a spill/fill pair at appropriate places and reschedules. This is guaranteed to terminate, and in practice usually is immediately feasible and rarely takes more than one iteration.

The operation scheduling itself is the standard time-reversed tableau scheduler used in VLIWs, probably 40 years old at this point.