[llvm] [VectorCombine] Fold Deinterleave/Interleave Pairs (PR #211022)

[Gaëtan Bossu via llvm-commits]

================

----------------
gbossu wrote:

Maybe add a test with a "diamond" pattern like
```
  %d = call { <vscale x 4 x i16>, <vscale x 4 x i16> } @llvm.vector.deinterleave2.nxv8i16(<vscale x 8 x i16> %v)
  %f0 = extractvalue { <vscale x 4 x i16>, <vscale x 4 x i16> } %d, 0
  %f1 = extractvalue { <vscale x 4 x i16>, <vscale x 4 x i16> } %d, 1
  %u = add <vscale x 4 x i16> %f0, %f0
  %r = call <vscale x 8 x i16> @llvm.vector.interleave2.nxv8i16(<vscale x 4 x i16> %u, <vscale x 4 x i16> %u)
```

https://github.com/llvm/llvm-project/pull/211022