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

[Matt Arsenault via llvm-commits]

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@@ -1255,6 +1255,20 @@ static SDValue performSignExtendCombine(SDNode *N, SelectionDAG &DAG,
   return SDValue();
 }
 
+APFloat MipsTargetLowering::getNaNValue(EVT VT) const {
+  if (!Subtarget.isNaN2008()) {
+    if (&VT.getFltSemantics() == &APFloat::IEEEsingle()) {
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arsenm wrote:

Avoid repeated getFltSemantics calls. Plus this should be rewritten generically to not depend on the exact format, but derived from the format properties 

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