[PATCH] D107597: [DAG] Fold concat_vectors(concat_vectors(x,y),concat_vectors(a,b)) -> concat_vectors(x,y,a,b)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:19863-19864
+// Attempt to merge nested concat_vectors/undefs.
+// Fold concat_vectors(concat_vectors(x,y,z,w),u,u,concat_vectors(a,b,c,d))
+//  --> concat_vectors(x,y,z,w,u,u,u,u,u,u,u,u,a,b,c,d)
+static SDValue combineConcatVectorOfConcatVectors(SDNode *N,
----------------
Does `concat_vectors` pad with undef?
Or should this be
```
//  --> concat_vectors(x,y,z,w,u,u,a,b,c,d)

```


Repository:
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https://reviews.llvm.org/D107597