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

[via llvm-commits]

================
@@ -6251,6 +6193,38 @@ bool SelectionDAG::isKnownNeverNaN(SDValue Op, const APInt &DemandedElts,
                                                Depth);
     }
 
+    // Try to infer NaN from known bits, but only for detecting signaling or
+    // nonsignaling NaNs
+    EVT VT = Op.getValueType();
+    if (!SNaN && VT.isFloatingPoint()) {
----------------
zGoldthorpe wrote:

If `SNaN` is `true`, then `isKnownNeverNaN` ignores quiet NaNs. I want it to be `false` so that `isKnownNeverNaN` considers *all* NaNs.

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