1 files changed, 19 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 879015b..af82276 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4439,6 +4439,25 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
 
     break;
   }
+  case Instruction::FAdd:
+  case Instruction::FSub: {
+    KnownFPClass KnownLHS, KnownRHS;
+    computeKnownFPClass(Op->getOperand(1), DemandedElts, fcNan | fcInf,
+                        KnownRHS, Depth + 1, Q, TLI);
+    if (KnownRHS.isKnownNeverNaN()) {
+      // RHS is canonically cheaper to compute. Skip inspecting the LHS if
+      // there's no point.
+      computeKnownFPClass(Op->getOperand(0), DemandedElts, fcNan | fcInf,
+                          KnownLHS, Depth + 1, Q, TLI);
+      // Adding positive and negative infinity produces NaN.
+      // TODO: Check sign of infinities.
+      if (KnownLHS.isKnownNeverNaN() &&
+          (KnownLHS.isKnownNeverInfinity() || KnownRHS.isKnownNeverInfinity()))
+        Known.knownNot(fcNan);
+    }
+
+    break;
+  }
   case Instruction::SIToFP:
   case Instruction::UIToFP: {
     // Cannot produce nan