[Bug target/86677] popcount builtin detection is breaking some kernel build

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86677

--- Comment #11 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Wilco from comment #10)
> (In reply to Martin Liška from comment #9)
> > Taking look at
> > ../drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c file:
> > 
> > The __builtin_popcount is generated from:
> > 
> > static int brcmf_setup_wiphybands(struct brcmf_cfg80211_info *cfg)
> > {
> > ...
> >  } else {
> >   for (nchain = 0; rxchain; nchain++)
> >    rxchain = rxchain & (rxchain - 1);
> >  }
> > ...
> > }
> > 
> > It started from r262486. I would that in this situation it's maybe
> > unexpected that a popcount call will be eventually generated. So I'm for an
> > option what will disable the pattern recognition.
> 
> I'd say this is exactly a case where using a faster popcount instruction
> helps - if available of course. 

Yes, but as seen in PR87528, using a libgcc can slow down a SPEC benchmark. But
it's related to generic tuning.

> 
> Is there any reason -fno-builtin-popcount can't also block automatic
> generation of popcount?

Do we really have such option?