> On the other hand, even RVA23 is quite poor at signed overflow checking.

On the other hand it avoids integer flags which is nice. I doubt it makes a measurable performance impact either way on modern OoO CPUs. There's going to be no data dependence on the extra instructions needed to calculate overflow except for the branch, which will be predicted not-taken, so the other instructions after it will basically always run speculatively in parallel with the overflow-checking instructions.

It's nice for a C simulator to avoid condition codes. It's not so nice if you want consistent overflow checks (e.g., for automatically overflowing from fixnums to bignums).

Even with XNOR (which isn't even part of RVA23, if I recall correctly), the sequence for doing an overflow check is quite messy. On AArch64 and x86-64, it's just the operation followed by a conditional jump: https://godbolt.org/z/968Eb1dh1