On 08/31/2018 09:41 AM, Matthew Malcomson wrote: > Hi there, > > I'm looking into whether it's possible to require even numbered > registers on > modes that need more than one hard-register to represent them. But only in > some cases. > > The problem is the one mentioned explicitly here > https://gcc.gnu.org/onlinedocs/gccint/Register-Classes.html about > enforcing a > requirement for a register pair to start with an even-numbered register. > I can't use TARGET_HARD_REGNO_MODE_OK as suggested in that document > because I'd > like to allow register pairs starting with odd-numbered registers in > general, > but not in some specific cases. > > From a comment in gcc/config/sparc/constraints.md above the constraint > "U" it > looks like there isn't a way to define such a constraint when using LRA, > and I > haven't found any hook that could do so but I'm hoping there's something > I'm > missing. > > The best thing I can think of is to define a bunch of classes ZERO_ONE, > TWO_THREE, FOUR_FIVE, ..., define a constraint on each of those classes, > then > use all the constraints as one alternative in my pattern. > > Is there a better method? > > Is there some small change that could enable a nicer method? It would help to know more about when you want to allow odd registers.
I'd be surprised if creating a class, but still rejecting in HARD_REGNO_MODE_OK worked... Jeff
