Segher Boessenkool <seg...@kernel.crashing.org> writes: > Hi! > > On Thu, May 28, 2020 at 04:22:16PM +0200, Richard Biener wrote: >> For GIMPLE level transforms I don't think targets have more knowledge >> than the middle-end. > > Yes, certainly. > >> In fact GIMPLE complete unrolling is about >> secondary effects, removing redundancies and abstraction. So IMHO >> the correct approach is to look at individual cases and try to improve >> the generic code > > Yep. > >> rather than try to get better benchmark results >> on a per-target manner by magical parameter tuning. > > I'm no fan of that for target-specific code either. It's fine to be led > by benchmarks, but usually a better justification is needed.
Thanks all, Agree, we'd better tune it in generic code. Jiufu > >> For what the RTL unroller does it indeed depends very heavily on >> the target whether sth is beneficial or not. > > Yes :-( And this means it will need to remain late in the pass > pipeline, or at least the decision needs to use target information > (just like what ivopts does). > >> So I'd like to see specific cases where you think cunroll should >> do "better" on powerpc only but not elsewhere. > > It is probably not a good idea in general to unroll 14 times, yes :-) > > > Segher
