Actually add Jeff this time...
> -----Original Message----- > From: Matthew Fortune > Sent: 07 April 2014 09:07 > To: 'Richard Sandiford' > Cc: gcc@gcc.gnu.org > Subject: RE: HARD_REGNO_CALL_PART_CLOBBERED and regs_invalidated_by_call > > Richard Sandiford <rdsandif...@googlemail.com> writes: > > Matthew Fortune <matthew.fort...@imgtec.com> writes: > > > Richard Sandiford <rdsandif...@googlemail.com> writes: > > >> Matthew Fortune <matthew.fort...@imgtec.com> writes: > > >> Maybe some RA heuristics will need tweaking to reflect the extra > > cost > > >> of these registers, but I imagine that's true either way. > > > > > > Perhaps. I am currently thinking/hoping that simply having them > > marked > > > as call clobbered will be enough. > > > > FWIW, I have some patches queued for stage 1 that tell the target- > > independent code which registers are saved by the current function. > > This makes things like interrupt functions less magical. > > Maybe it would help with exposing the "call-clobbered and call-saved" > > thing to RA. > > That could be useful if existing costs don't lead to the correct > registers being targeted first. > > > > In terms of the HARD_REGNO_CALL_PART_CLOBBERED macro. I would say > > that > > > it is poorly named as it gives no indication to GCC internals as to > > > which part of the register is clobbered and which is not. > > > > I don't think it was really supposed to matter. (Not that I'm > > defending the name. :-)) > > > > > When this macro > > > returns true GCC simply takes that to mean the whole register is > > > clobbered. I'd say that then makes my usage legitimate. If I had > > > time and will power I'd remove the 'PART' from this macro and switch > > > over to having it as the primary source of call-clobbered > > > information in GCC doing away with call_used_regs etc. Having the > > > mode information > > is > > > quite valuable as we are seeing with SIMD ISA extensions that use > > this macro. > > > Supporting two sources of call-clobbered data is probably what lead > > us > > > to the current situation of broken optimisation passes. > > > > Definitely agree with the last part. But I think it'd be better to > > fix it the other way: get rid of the existing > > HARD_REGNO_CALL_PART_CLOBBERED uses in the generic code and replace > > things like call_used_regs with mode-indexed HARD_REG_SETs of the > > call- clobbered registers. You could then add a cleaner target > > interface that says whether a given register is call-clobbered in a > given mode. > > The default could use the existing HARD_REGNO_CALL_PART_CLOBBERED, > > CALL_USED_REGISTERS and CALL_REALLY_USED_REGISTERS (another horrible > > part of the interface). > > Indeed and this could potentially capture information on which part of a > register is clobbered though it is difficult to imagine what to then do > with such information! > > > Doing it that way wouldn't involve any changes to port-specific code > > other than MIPS. Other ports could use the default implementation and > > switch to the new interface later. > > > > I realise that might be more work than you were planning on, but if > > you're having to change existing passes anyway then we might as well > > fix it in a way that reduces the number of places that need to check > > two things instead of one. > > I have an urgent need to get all this working so it may simply have to > Include whatever changes are necessary. > > > All IMO of course. I don't maintain this part of GCC. > > It's not clear who would be best to talk to about this. I've added Jeff > as he appears to be listed against some mostly relevant areas in the > maintainers file. If you could point me towards anyone more suitable > that would be good. > > Regards, > Matthew
