[llvm] [RISCV] Lower SEW<=32 vector_deinterleave(2) via vunzip2{a, b} (PR #136463)

[Luke Lau via llvm-commits]

================
@@ -4569,36 +4569,48 @@ static SDValue lowerScalarInsert(SDValue Scalar, SDValue VL, MVT VT,
                      VL);
 }
 
-// Can this shuffle be performed on exactly one (possibly larger) input?
-static SDValue getSingleShuffleSrc(MVT VT, SDValue V1, SDValue V2) {
-
-  if (V2.isUndef())
-    return V1;
-
+/// If concat_vector(V1,V2) could be folded away to some existing
+/// vector source, return it.  Note that the source may be larger
+/// than the requested concat_vector (i.e. a extract_subvector
+/// might be required.)
+static SDValue FoldConcatVector(SDValue V1, SDValue V2) {
+  EVT VT = V1.getValueType();
+  assert(VT == V1.getValueType() && "precondition");
   // Both input must be extracts.
   if (V1.getOpcode() != ISD::EXTRACT_SUBVECTOR ||
       V2.getOpcode() != ISD::EXTRACT_SUBVECTOR)
     return SDValue();
 
   // Extracting from the same source.
   SDValue Src = V1.getOperand(0);
-  if (Src != V2.getOperand(0))
-    return SDValue();
-
-  // Src needs to have twice the number of elements.
-  unsigned NumElts = VT.getVectorNumElements();
-  if (!Src.getValueType().isFixedLengthVector() ||
-      Src.getValueType().getVectorNumElements() != (NumElts * 2))
+  if (Src != V2.getOperand(0) ||
+      VT.isScalableVector() != Src.getValueType().isScalableVector())
     return SDValue();
 
   // The extracts must extract the two halves of the source.
   if (V1.getConstantOperandVal(1) != 0 ||
-      V2.getConstantOperandVal(1) != NumElts)
+      V2.getConstantOperandVal(1) != VT.getVectorMinNumElements())
     return SDValue();
 
   return Src;
 }
 
+// Can this shuffle be performed on exactly one (possibly larger) input?
+static SDValue getSingleShuffleSrc(MVT VT, SDValue V1, SDValue V2) {
+
+  if (V2.isUndef())
+    return V1;
+
+  unsigned NumElts = VT.getVectorNumElements();
+  // Src needs to have twice the number of elements.
+  // TODO: Update shuffle lowering to add the extract subvector
+  if (SDValue Src = FoldConcatVector(V1, V2);
+      Src && Src.getValueType().getVectorNumElements() == (NumElts * 2))
----------------
lukel97 wrote:

Do we need to add back the isFixedLengthVector() check here?

https://github.com/llvm/llvm-project/pull/136463