Thanks for the reply but I'm not sure what you mean. Are you saying you want to add an i32 to a u64? Or am I completely misunderstanding? I'm not sure why unsigned-unsigned or signed-signed instructions would be hard. Idk about mixed sign operations, but when do they ever occur without first casting one to the other?

I mean you will do overflow checks on the following. I’ll use the “s” and “u” prefixes to mean signed and unsigned. Unsigned matters less than signed.

sadd32, sadd64, uadd32, uadd64, ssub32, ssub64, usub32, usub64, smul32, smul64, umul32, umul64

Ah, I get you now. Yes, this looks like a weak point, and I totally get why it'd screw with Javascript optimizations.

I don't think it's a fusion problem; even if you did fuse these sequences, they'd still be bad, since they'd be writing lots of extra registers.

Yeah exactly!

And worth noting that these are just the ones where you usually have good sequences on other cpus, but even then (like signed mul) they’re not perfect. Lots of room for improvement. It’s just that risc-v didn’t seize the opportunity.