[RFC PATCH for 9] rs6000: Ordered comparisons (PR56864)

[Segher Boessenkool]

Hi again,

On Tue, Mar 27, 2018 at 07:59:30PM +0200, Uros Bizjak wrote:
> > (the two compares were combined, by fwprop1) but without the flag we get
> >
> >         fcmpo 5,1,2
> >         li 3,-1
> >         bltlr 5
> >         mfcr 3,4
> >         rlwinm 3,3,22,1
> >         fcmpo 7,1,2
> >         blr
> >
> > (it's still combined, but the redundant compare isn't deleted).
> 
> Yes, I think this case will be fixed by wrapping the compare inside UNSPEC.

I don't think that will work, but I haven't tried it yet.  Will do.

> > Are ordered compares faster than unordered on x86?  Strange stuff.
> 
> Not faster, but on x87 unordered compares operate only with registers,
> while some (legacy) ordered can also use memory operands.

Ah ok.  Nasty.  Maybe you should only do ordered by default for the legacy
compares then?


Segher