Mill Computing, Inc. Forums The Mill Architecture Benchmarks Reply To: Benchmarks

Ivan Godard
Post count: 689

Code size varies by member. Because we mechanically create a custom entropy-optimal encoding for each member, the bitsize depends both on how many ops are supported in a slot, and the number of bits needed to express architectural constants such as a belt position number. Thus the opcodes on a Tin do not have to be able to represent floating-point ops because those are software (and hence function calls in the binary) on a Tin.

In addition, the encoding does not let us provide all the entropy needed by some ops in a single slot. Those are encoded as a “gang”, using two slots. The bitwise entropy for the op is really that of two slots, which makes valid op sizes a bit complicated to figure. Also, we haven’t tuned for space yet. Those gangs in particular may be able to encode better if we move some of the fields into the second slot, even if we can fit them into the first.

Finally, for inter-ISA comparisons, there’s the differences between machines in number of ops to represent a single semantic notion, such as a function call. A small op size doesn’t save much if it takes a dozen ops to do the job that one does with a longer op. X86 compared with RISC encodingd suffers from the same apples-to-oranges problem.

That said, for whole-program size when built for space we seem to be marginally more compact than x86 for all members, and significantly more compact than the 64-bit RISC machines. We seem close to the sizes of 16-bit encodings, worse on the larger members.

However, take this with a grain of salt: we haven’t paid much attention to size, neither measurement not improvement.