[llvm] [SelectionDAG] Use `KnownBits` to determine if an operand may be NaN. (PR #188606)

[via llvm-commits]

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@@ -6112,6 +6112,16 @@ KnownFPClass SelectionDAG::computeKnownFPClass(SDValue Op,
     }
     break;
   }
+  case ISD::BITCAST: {
+    // Try to infer NaN from known bits, but only for detecting signaling or
+    // nonsignaling NaNs
+    EVT VT = Op.getValueType();
+    if (VT.isFloatingPoint()) {
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zGoldthorpe wrote:

It seems such an assertion would throw on a handful of test cases.

https://github.com/llvm/llvm-project/pull/188606