[PATCH] D139691: [PowerPC] add a peephole to remove redundant swap instructions after vector splats on P8

[Ting Wang via Phabricator via llvm-commits]

tingwang added inline comments.


================
Comment at: llvm/lib/Target/PowerPC/PPCMIPeephole.cpp:647
           LLVM_DEBUG(MI.dump());
+        } else if (Immed == 2 &&
+                   (DefOpc == PPC::VSPLTB || DefOpc == PPC::VSPLTH ||
----------------
shchenz wrote:
> tingwang wrote:
> > shchenz wrote:
> > > Can this branch be merged to the above one at line 627? Splat a double word and the double word is a splat of a small unit should also can be removed?
> > Sure, I can do the merge to reuse logic. 
> > 
> > Are you referring to instructions like xxspltib? I think those are introduced in v3.0, and they will not appear on P8, so I did not include those.
> Oh, I meant the `XXPERMDI` instruction can be removed like the above branch(at like 627) does. Not referring to any other instructions.
IMHO, we saw these additional swaps on P8 because of stores, and that's why only saw Immed == 2. I'm not sure of any origin that can produce splat (i.e. Immed == 0 || Immed == 3 like 627) and reach peephole. If there is any such origin, it maybe more interesting to fix in the origin. To me, it is a little bit  confused why need to handle splat here?


Repository:
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  https://reviews.llvm.org/D139691/new/

https://reviews.llvm.org/D139691