Not assembly, but one of the side benefits of Go’s infamously verbose error handling is that code coverage generally tells you when you’ve never tested error cases. It gives a more fine-grained picture than languages using exception handling (unless you try/catch at a similarly fine-grained level).

OK, sure. That could be fixed at the code coverage level - you're looking for something along the lines of store the select mask (as opposed to the bit branched on).

Could report it in similar fashion to the mcdc coverage, would look a bit like check each bit in the word is set or clear on some execution. Probably a reasonable extension to implement.