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

[Benjamin Maxwell via llvm-commits]

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MacDue wrote:

I think it'd be good to try to preserve debug info and the general block layout by taking the location/debug info from the first narrow instruction. Currently, this transform drops all debug info and sinks all operations to the same block as the interleave. 
```suggestion
    Builder.SetInsertPoint(NarrowInst);
    Builder.SetCurrentDebugLocation(NarrowInst->getDebugLoc());
```

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