[llvm] [Mips] Fix wrong qNaN encoding when -mnan=legacy (PR #153777)

[Simon Pilgrim via llvm-commits]

================
@@ -8773,8 +8778,7 @@ SDValue TargetLowering::expandFMINIMUM_FMAXIMUM(SDNode *N,
   // Propagate any NaN of both operands
   if (!N->getFlags().hasNoNaNs() &&
       (!DAG.isKnownNeverNaN(RHS) || !DAG.isKnownNeverNaN(LHS))) {
-    ConstantFP *FPNaN = ConstantFP::get(*DAG.getContext(),
-                                        APFloat::getNaN(VT.getFltSemantics()));
+    ConstantFP *FPNaN = ConstantFP::get(*DAG.getContext(), TLI.getNaNValue(VT));
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RKSimon wrote:

```
ConstantFP *FPNaN = ConstantFP::get(*DAG.getContext(), getNaNValue(VT));
```

https://github.com/llvm/llvm-project/pull/153777