[llvm] [SelectionDAG] Add `STRICT_BF16_TO_FP` and `STRICT_FP_TO_BF16` (PR #80056)

[Matt Arsenault via llvm-commits]

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@@ -3271,8 +3278,14 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     Results.push_back(Op);
     break;
   }
+  case ISD::STRICT_FP_TO_BF16:
+    // When strict mode is enforced we can't do expansion because it
+    // does not honor the "strict" properties.
+    if (TLI.isStrictFPEnabled())
+      break;
+    LLVM_FALLTHROUGH;
   case ISD::FP_TO_BF16: {
-    SDValue Op = Node->getOperand(0);
+    SDValue Op = Node->getOperand(Node->getOpcode() == ISD::FP_TO_BF16 ? 0 : 1);
     if (Op.getValueType() != MVT::f32)
       Op = DAG.getNode(ISD::FP_ROUND, dl, MVT::f32, Op,
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arsenm wrote:

this needs to use STRICT_FP_ROUND in the strict case 

https://github.com/llvm/llvm-project/pull/80056