On Sun, 2020-03-01 at 01:06 +0900, Oleg Endo wrote: > On Sat, 2020-02-29 at 08:57 -0700, Jeff Law wrote: > > > It could open a can of worms. Off the top of my head, R0 is used to > > > hold the function return value, and R0:R1 to return structs with sizeof > > > > 4 bytes. So if DImode is allocated to R0, it implicitly uses R0:R1, > > > > > > AFAIR, doesn't it? Would that kind of thing cause troubles? > > > > It might. We might have to move a pair or even a quad if you have modes > > that > > cover r0-r3. It may not be feasible in practice. I was just thinking off > > the > > top of my head. > > > > Yeah, for instance 'double _Complex' will be returned in R0-R3 when > compiling for 'without FPU'. How about adding a target hook or look-up > table (default 1:1 mapping for other targets)? Would that be an > option? I think it's pretty deeply baked that we can iterate from the first register in a group to the last. Given we'd have to move quads, I suspect this isn't feasible in practice.
It really would have just been a workaround for some of the R0 issues anyway. I think at its core R0 on the SH probably needs to be treated more like a temporary rather than a general register. But that's probably a huge change, both in terms of just getting it working right and in terms of addressing the code quality regressions that would introduce. jeff
