[llvm] Fixes simple issue found static analyzer (PR #169958)

[Matt Arsenault via llvm-commits]

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@@ -1373,7 +1373,7 @@ void GISelValueTracking::computeKnownFPClass(Register R,
           (KnownLHS.isKnownNeverInfinity() || KnownRHS.isKnownNeverInfinity()))
         Known.knownNot(fcNan);
 
-      if (Opcode == Instruction::FAdd) {
+      if (Opcode == TargetOpcode::G_FADD) {
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arsenm wrote:

Clearly there is missing test coverage 

https://github.com/llvm/llvm-project/pull/169958