[PATCH] D52997: [x86] allow single source horizontal op matching (PR39195)

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In https://reviews.llvm.org/D52997#1259162, @dyung wrote:

> In https://reviews.llvm.org/D52997#1258717, @spatel wrote:
>
> > In https://reviews.llvm.org/D52997#1258666, @andreadb wrote:
> >
> > > I don't see it as a big problem if we start "regressing" this particular case on Jaguar.
> >
> >
> > Ok - that's not the impression I got reading PR39195. @dyung - how important is this pattern?
>
>
> I will defer to Andrea's expertise in this area. I was under the impression that generating the horizontal add/sub instructions was preferred for these cases (especially for btver2), but if that is not the case, I can update our test to not expect it to be generated.


Thanks. I think we're all in agreement: we have 2 wrongs making it right (less h-ops) for most CPUs (but not Jaguar) currently. This patch will remove 1 of those wrongs, but there's little regression potential because it's just restoring what happened before (h-ops are unusually good for Jaguar). I should have the follow-up patch to try to make every CPU happy posted soon after this is committed.


https://reviews.llvm.org/D52997