On Tue, Mar 31, 2020 at 03:44:51PM -0700, Richard Henderson wrote: > If we add more CC modes, does that mean that we have to improve SELECT_CC_MODE > to match those patterns? Or do we add new CC modes just so that combine's use > of SELECT_CC_MODE *cannot* match them?
Adding new CC modes isn't helpful if nothing ever generates them. To have combine decide to use a different CC mode for a combined insn, you need SELECT_CC_MODE. The result of a combination is always valid (as RTL) with the original CC mode, but such an insn might not exist, and perhaps it does exist with some weaker CC mode (or more general CC mode, in some cases). Segher
