On Thu, Nov 19, 2020 at 03:30:37PM -0700, Jeff Law wrote: > > No, the vast majority of people will *not* (consciously) use them, > > because the target defaults will set things to useful values. > > > > The compiler could use saner "generic" defaults perhaps, but those will > > still not be satisfactory for anyone (except when they aren't generic in > > fact but instead tuned for one arch ;-) ) -- unrolling is just too > > important for performance. > Then fix the heuristics, don't add new PARAMS :-)
I just said that cannot work? > It didn't even occur to me until now that you may be pushing to have the > ppc backend have different values for the PARAMS. I would strongly > discourage that. It's been a huge headache in the s390 backend already. It also makes a huge performance difference. That the generic parts of GCC are only tuned for x86 (or not well tuned for anything?) is a huge roadblock for us. I am not saying we should have six hundred different tunings. But we need a few (and we already *have* a few, not params but generic flags, just like many other targets fwiw). We *do* have a few custom param settings already, just like aarch64, ia64, and sh, actually. > >> In my mind fixing things so they work with no magic arguments is best. > >> PARAMS are the worst solution. A -f flag with no arguments is somewhere > >> in between. Others may clearly have different opinions here. > > There is no big difference between params and flags here, IMO -- it has > > to be a -f with a value as well, for good results. > Which is a signal that we have a deeper problem. -f with a value is no > different than a param. Yes exactly. > > Since we have (almost) all such tunings in --param already, I'd say this > > one belongs there as well? > I'm not convinced at this point. Why not? We have way many params, yes. But the first step to counteract that would be to deprecate and get rid of many existing ones, not to block having new ones which can be useful (while many of the existing ones are not). Or, we could accept that it is not really a problem at all. You seem to have a strong opinion that it *is*, but I don't understand that; maybe you can explain a bit more? Thanks, Segher
