> Sorry for missing the truncation patterns, I should have grepped > more than m32c.md. They look a lot like normal moves though. Is > truncation really not a noop, or are the patterns there to work > around something (probably this :-))?
Not sure which pattern you're talking about, but in general, the m32c's registers are either 16-bit or 24-bit. You can move a pair of 16-bit registers into a 24-bit register and it truncates as part of the move, likewise from 32-bit memory to 24-bit reg. Note that moves to other 32-bit destinations do *not* truncate, nor can 24-bit registers hold 32-bit values (duh). The 24-bit registers may also hold a 16-bit value. If you move a 16-bit value into a 24-bit register, it zero_extends.
