"Unsupported physical register copy" when copying between MOSReg1Class about llvm-mos

[mysterymath]

Ah, interesting about using the high bit re LSR and BIT.

No real strategy, making it up as I go along. At the moment, the mechanism for copying values into and out of $alsb is pretty undefined at the moment, and I don't even think what's there is internally consistent. It's more consistent than it used to be at least; this is something I'm still actively hashing out.

It's very unlikely on the outset that PHP/PLA will be a good sequence for extracting values out of P to be stored elsewhere; it takes 2 bytes and 7 cycles before starting to extract the part of P we need, while a branch to a pair of immediate loads takes 6 bytes and 4 or 5 cycles for the whole thing, and that's the worst case for extracting flag to value. For value to flag, we can get a LSB or MSB into C via ASL and LSR, and V from a MSB via LSR,BIT, etc.

[mysterymath]

All possible physreg copies have now been implemented in terms of other types of copies, CMP, or a SelectImm diamond pseudo. Lowering for the SelectImm pseudo isn't yet implemented.