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

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added a comment.

In https://reviews.llvm.org/D52997#1258717, @spatel wrote:

> So 2 options for moving forward:
>
> 1. Allow this transform as shown here because it is mostly just restoring the behavior of last week. Follow that up with a subtarget feature to prevent the transform (not ideal, but the alternative 'undo' is much harder).
> 2. Limit this transform to 'optsize' right now because it's a size win in all cases.


I'd vote for (1) for this patch - optsize + HasFastHorinzontalOp might be necessary depending on how soon we can agree on a scheduler model driven mechanism that re-expands HADD later on (per Andrea's suggestion - but hopefully we can discuss that at the devmtg)


https://reviews.llvm.org/D52997