[llvm] SelectionDAG: Use qNaN constant if FCANONICALIZE not LegalOrCustom (PR #104564)

[Matt Arsenault via llvm-commits]

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@@ -8622,8 +8622,16 @@ SDValue TargetLowering::expandFMINIMUMNUM_FMAXIMUMNUM(SDNode *Node,
   // If MinMax is NaN, let's quiet it.
   if (!Flags.hasNoNaNs() && !DAG.isKnownNeverNaN(LHS) &&
       !DAG.isKnownNeverNaN(RHS)) {
-    SDValue MinMaxQuiet =
-        DAG.getNode(ISD::FCANONICALIZE, DL, VT, MinMax, Flags);
+    SDValue MinMaxQuiet;
+    if (isOperationLegalOrCustom(ISD::FCANONICALIZE, VT)) {
+      MinMaxQuiet = DAG.getNode(ISD::FCANONICALIZE, DL, VT, MinMax, Flags);
+    } else {
+      // MIPS pre-R5 and HPPA use different encoding of qNaN and sNaN.
+      // ISD::FCANONICALIZE is supported by MIPS.
+      // HPPA is not supported by LLVM yet.
+      MinMaxQuiet =
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arsenm wrote:

A make_quiet would need to be is_signaling(x) ? qnan : x. Or preferably is_signaling(x) ? make_quiet(x) : x. But really should just use the canonicalize, and not workaround it not being implemented here 

https://github.com/llvm/llvm-project/pull/104564