[PATCH] D86458: GlobalISel: Artifact combine unmerge of unmerge

Mon Aug 31 16:14:53 PDT 2020

aemerson accepted this revision.
aemerson added inline comments.
This revision is now accepted and ready to land.

================
Comment at: llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h:548
+      // of an unmerge, this would involve the creation of an equivalent unmerge
+      // to copy back to the original result registers.
+      LegalizeActionStep ActionStep = LI.getAction(
----------------
arsenm wrote:
> aemerson wrote:
> > I'm not sure what point this comment block is trying to get across? What do you mean "equivalent unmerge to copy back..."
> > 
> > ```// %0:_(<4 x s16>) = G_FOO
> > // %1:_(<2 x s16>), %2:_(<2 x s16>) = G_UNMERGE_VALUES %0
> > // %3:_(s16), %4:_(s16) = G_UNMERGE_VALUES %1
> > //
> > // %3:_(s16), %4:_(s16), %5:_(s16), %6:_(s16) = G_UNMERGE_VALUES %0
> > ```
> > For this case, the new unmerge is what this comment is referring to?
> If you were to try to implement FewerElements for a G_UNMERGE_VALUES, you would end up producing the same G_UNMERGE_VALUES. This isn't produced here
Ok got it.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D86458/new/

https://reviews.llvm.org/D86458