Hi Andrew, On Wed, Mar 15, 2017 at 09:43:20PM +0000, Andrew Jenner wrote: > On 15/03/2017 14:26, Segher Boessenkool wrote: > >I do not think VLE can get in, not in its current shape at least. > > That's unfortunate. Disregarding the SPE splitting plan for a moment, > what do you think would need to be done to get it into shape? I had > thought we were almost there with the patches that I sent to you and > David off-list last year. > > > VLE > >is very unlike PowerPC in many ways so it comes at a very big cost to > >the port (maintenance and otherwise -- maintenance is what I care about > >most). > > I completely understand.
That answers your previous question, too. > >Since SPE and VLE only share the part of the rs6000 port that doesn't > >change at all (except for a bug fix once or twice a year), and everything > >else needs special cases all over the place, it seems to me it would be > >best for everyone if we split the rs6000 port in two, one for SPE and VLE > >and one for the rest. Both ports could then be very significantly > >simplified. > > > >I am assuming SPE and VLE do not support AltiVec or 64-bit PowerPC, > >please correct me if that is incorrect. Also, is "normal" floating > >point supported at all? > > My understanding is that SPE is only present in the e500v1, e500v2 and > e200z[3-7] cores, all of which are 32-bit only and do not have classic > floating-point units. SPE and Altivec cannot coexist as they have some > overlapping instruction encodings. The successor to e500v2 (e500mc) > reinstated classic floating-point and got rid of SPE. e500mc (like e5500, e6500) are just PowerPC (and they use the usual ABIs), so those should stay on the "rs6000 side". > >Do you (AdaCore and Mentor) think splitting the port is a good idea? > > It wouldn't have been my preference, but I can understand the appeal of > that plan for you. I'm surprised that the amount of shared code between > SPE and PowerPC is as little as you say, but you have much more > experience with the PowerPC port than I do, so I'll defer to your > expertise on that matter. > > Are you proposing to take on the task of actually splitting it yourself? > If so, that would make me a lot happier about it. Yes, I can do the mechanics. But I cannot do most of the testing. And this does not include any of the huge simplifications that can be done after the split: both ports will be very close to what we have now, immediately after the split. > >> -te200z0 > >> -te200z3 > >> -te200z4 > > > > These are VLE? > > Yes. > > > Do some of those also support PowerPC? > > All the e200 cores apart from e200z0 can execute 32-bit instructions as > well as VLE, though we'll always generate VLE code when targetting them > (otherwise they're fairly standard). Do any e200 support SPE, or classic FP? Segher
