diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 2ce3274..611cf10 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -19,6 +19,7 @@
 #include "llvm/CodeGen/GlobalISel/LostDebugLocObserver.h"
 #include "llvm/CodeGen/GlobalISel/MIPatternMatch.h"
 #include "llvm/CodeGen/GlobalISel/Utils.h"
+#include "llvm/CodeGen/LowLevelType.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/TargetFrameLowering.h"
 #include "llvm/CodeGen/TargetInstrInfo.h"
@@ -3486,6 +3487,8 @@
   case G_ROTL:
   case G_ROTR:
     return lowerRotate(MI);
+  case G_ISNAN:
+    return lowerIsNaN(MI);
   }
 }
 
@@ -7355,3 +7358,34 @@
   MI.eraseFromParent();
   return Legalized;
 }
+
+LegalizerHelper::LegalizeResult LegalizerHelper::lowerIsNaN(MachineInstr &MI) {
+  Register Dst = MI.getOperand(0).getReg();
+  Register Src = MI.getOperand(1).getReg();
+  LLT SrcTy = MRI.getType(Src);
+  if (MI.getFlags() & MachineInstr::NoFPExcept) {
+    // Lower to an unordered comparison.
+    auto Zero = MIRBuilder.buildFConstant(SrcTy, 0.0);
+    MIRBuilder.buildFCmp(CmpInst::Predicate::FCMP_UNO, Dst, Src, Zero);
+    MI.eraseFromParent();
+    return Legalized;
+  }
+
+  // Use integer operations to avoid traps if the argument is SNaN.
+
+  // NaN has all exp bits set and a non zero significand. Therefore:
+  // isnan(V) == exp mask < abs(V)
+  auto FPToSI = MIRBuilder.buildFPTOSI(SrcTy, Src);
+  auto Mask = APInt::getSignedMaxValue(SrcTy.getScalarSizeInBits());
+  auto MaskCst = MIRBuilder.buildConstant(SrcTy, Mask);
+  auto AbsV = MIRBuilder.buildAnd(SrcTy, FPToSI, MaskCst);
+  auto *FloatTy = getFloatTypeForLLT(MI.getMF()->getFunction().getContext(),
+                                     SrcTy.getScalarType());
+  if (!FloatTy)
+    return UnableToLegalize;
+  auto ExpMask = APFloat::getInf(FloatTy->getFltSemantics()).bitcastToAPInt();
+  auto ExpMaskCst = MIRBuilder.buildConstant(SrcTy, ExpMask);
+  MIRBuilder.buildICmp(CmpInst::Predicate::ICMP_SLT, Dst, ExpMaskCst, AbsV);
+  MI.eraseFromParent();
+  return Legalized;
+}