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

[Shilei Tian via llvm-commits]

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@@ -3248,12 +3249,18 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
       Results.push_back(Tmp1);
     break;
   }
+  case ISD::STRICT_BF16_TO_FP:
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shiltian wrote:

This is more like a "fallback" to the non-strict variant when the strict FP is not enforced, which is the purpose of the check below. We have something similar in this big `switch`, such as `case ISD::STRICT_FP_EXTEND`.

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