[llvm] [LLVM][CodeGen] Add lowering for scalable vector bfloat operations. (PR #109803)

[Graham Hunter via llvm-commits]

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@@ -11917,3 +11923,38 @@ bool TargetLowering::LegalizeSetCCCondCode(SelectionDAG &DAG, EVT VT,
   }
   return false;
 }
+
+SDValue TargetLowering::expandVectorNaryOpBySplitting(SDNode *Node,
+                                                      SelectionDAG &DAG) const {
+  EVT VT = Node->getValueType(0);
+  // Despite its documentation, GetSplitDestVTs will assert if VT cannot be
+  // split into two equal parts.
+  if (!VT.isVector() || !VT.getVectorElementCount().isKnownMultipleOf(2))
+    return SDValue();
+
+  EVT LoVT, HiVT;
+  std::tie(LoVT, HiVT) = DAG.GetSplitDestVTs(VT);
+
+  // Restrict expansion to cases where both parts can be concatenated.
+  if (LoVT != HiVT || !isTypeLegal(LoVT))
+    return SDValue();
+
+  SDLoc DL(Node);
+  unsigned Opcode = Node->getOpcode();
+
+  // Don't expand if the result is likely to be unrolled anyway.
+  if (!isOperationLegalOrCustomOrPromote(Opcode, LoVT))
+    return SDValue();
+
+  SmallVector<SDValue, 4> LoOps, HiOps;
+  for (const SDValue &V : Node->op_values()) {
+    SDValue Lo, Hi;
+    std::tie(Lo, Hi) = DAG.SplitVector(V, DL, LoVT, HiVT);
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huntergr-arm wrote:

Same structured binding style can be applied here.

https://github.com/llvm/llvm-project/pull/109803