[llvm] [GlobalISel]: G_UNMERGE_VALUES for vectors with different element sizes (PR #133335)

[Robert Imschweiler via llvm-commits]

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@@ -1510,11 +1510,11 @@ void MachineVerifier::verifyPreISelGenericInstruction(const MachineInstr *MI) {
 
     LLT SrcTy = MRI->getType(MI->getOperand(NumDsts).getReg());
     if (DstTy.isVector()) {
-      // This case is the converse of G_CONCAT_VECTORS.
-      if (!SrcTy.isVector() ||
-          (SrcTy.getScalarType() != DstTy.getScalarType() &&
-           !SrcTy.isPointerVector()) ||
-          SrcTy.isScalableVector() != DstTy.isScalableVector() ||
+      // This case is the converse of G_CONCAT_VECTORS, but relaxed since
+      // G_UNMERGE_VALUES can handle src and dst vectors with different
+      // element sizes:
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ro-i wrote:

Hm, so I could do this in `LegalizationArtifactCombiner::ArtifactValueFinder::tryCombineMergeLike`.
But wouldn't that *add* complexity in other code, such as the `tryCombineMergeLike`? Because I think this method is currently relying on unmerge to do the right thing:

https://github.com/llvm/llvm-project/blob/c13c04fdfe9b312160310eeeee785867627ffe2f/llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h#L998-L1021

https://github.com/llvm/llvm-project/pull/133335