Index: include/llvm/IR/Instructions.h
===================================================================
--- include/llvm/IR/Instructions.h
+++ include/llvm/IR/Instructions.h
@@ -3529,6 +3529,7 @@
 public:
   // -2
   static const unsigned DefaultPseudoIndex = static_cast<unsigned>(~0L-1);
+  bool Widened = false;
 
   template <typename CaseHandleT> class CaseIteratorImpl;
 
Index: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -279,11 +279,12 @@
     const Value *SValue;
     MachineBasicBlock *HeaderBB;
     bool Emitted;
+    bool OmitRangeCheck;
 
     JumpTableHeader(APInt F, APInt L, const Value *SV, MachineBasicBlock *H,
-                    bool E = false)
+                    bool E = false, bool O = false)
         : First(std::move(F)), Last(std::move(L)), SValue(SV), HeaderBB(H),
-          Emitted(E) {}
+          Emitted(E), OmitRangeCheck(O) {}
   };
   using JumpTableBlock = std::pair<JumpTableHeader, JumpTable>;
 
Index: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2178,24 +2178,30 @@
                                     JumpTableReg, SwitchOp);
   JT.Reg = JumpTableReg;
 
-  // Emit the range check for the jump table, and branch to the default block
-  // for the switch statement if the value being switched on exceeds the largest
-  // case in the switch.
-  SDValue CMP = DAG.getSetCC(
-      dl, TLI.getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(),
-                                 Sub.getValueType()),
-      Sub, DAG.getConstant(JTH.Last - JTH.First, dl, VT), ISD::SETUGT);
-
-  SDValue BrCond = DAG.getNode(ISD::BRCOND, dl,
-                               MVT::Other, CopyTo, CMP,
-                               DAG.getBasicBlock(JT.Default));
-
-  // Avoid emitting unnecessary branches to the next block.
-  if (JT.MBB != NextBlock(SwitchBB))
-    BrCond = DAG.getNode(ISD::BR, dl, MVT::Other, BrCond,
-                         DAG.getBasicBlock(JT.MBB));
-
-  DAG.setRoot(BrCond);
+  if (!JTH.OmitRangeCheck) {
+    // Emit the range check for the jump table, and branch to the default block
+    // for the switch statement if the value being switched on exceeds the
+    // largest case in the switch.
+    SDValue CMP = DAG.getSetCC(
+        dl, TLI.getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(),
+                                   Sub.getValueType()),
+        Sub, DAG.getConstant(JTH.Last - JTH.First, dl, VT), ISD::SETUGT);
+
+    SDValue BrCond = DAG.getNode(ISD::BRCOND, dl,
+                                 MVT::Other, CopyTo, CMP,
+                                 DAG.getBasicBlock(JT.Default));
+
+    // Avoid emitting unnecessary branches to the next block.
+    if (JT.MBB != NextBlock(SwitchBB))
+      BrCond = DAG.getNode(ISD::BR, dl, MVT::Other, BrCond,
+                           DAG.getBasicBlock(JT.MBB));
+
+    DAG.setRoot(BrCond);
+  } else {
+    SDValue BrCond = DAG.getNode(ISD::BR, dl, MVT::Other, CopyTo,
+                                 DAG.getBasicBlock(JT.MBB));
+    DAG.setRoot(BrCond);
+  }
 }
 
 /// Create a LOAD_STACK_GUARD node, and let it carry the target specific global
@@ -9465,10 +9471,13 @@
                      ->createJumpTableIndex(Table);
 
   // Set up the jump table info.
+  bool UnreachableDefault =
+              isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
+  bool OmitRangeCheck = UnreachableDefault  &&  SI->Widened  &&  SI->getNumCases() > 0;
   JumpTable JT(-1U, JTI, JumpTableMBB, nullptr);
   JumpTableHeader JTH(Clusters[First].Low->getValue(),
                       Clusters[Last].High->getValue(), SI->getCondition(),
-                      nullptr, false);
+                      nullptr, false, OmitRangeCheck);
   JTCases.emplace_back(std::move(JTH), std::move(JT));
 
   JTCluster = CaseCluster::jumpTable(Clusters[First].Low, Clusters[Last].High,
@@ -10205,6 +10214,7 @@
     const SwitchInst &SI, CaseClusterVector &Clusters,
     BranchProbability &PeeledCaseProb) {
   MachineBasicBlock *SwitchMBB = FuncInfo.MBB;
+
   // Don't perform if there is only one cluster or optimizing for size.
   if (SwitchPeelThreshold > 100 || !FuncInfo.BPI || Clusters.size() < 2 ||
       TM.getOptLevel() == CodeGenOpt::None ||
@@ -10257,6 +10267,7 @@
   // Extract cases from the switch.
   BranchProbabilityInfo *BPI = FuncInfo.BPI;
   CaseClusterVector Clusters;
+
   Clusters.reserve(SI.getNumCases());
   for (auto I : SI.cases()) {
     MachineBasicBlock *Succ = FuncInfo.MBBMap[I.getCaseSuccessor()];
@@ -10274,38 +10285,6 @@
   // if there are many clusters.
   sortAndRangeify(Clusters);
 
-  if (TM.getOptLevel() != CodeGenOpt::None) {
-    // Replace an unreachable default with the most popular destination.
-    // FIXME: Exploit unreachable default more aggressively.
-    bool UnreachableDefault =
-        isa<UnreachableInst>(SI.getDefaultDest()->getFirstNonPHIOrDbg());
-    if (UnreachableDefault && !Clusters.empty()) {
-      DenseMap<const BasicBlock *, unsigned> Popularity;
-      unsigned MaxPop = 0;
-      const BasicBlock *MaxBB = nullptr;
-      for (auto I : SI.cases()) {
-        const BasicBlock *BB = I.getCaseSuccessor();
-        if (++Popularity[BB] > MaxPop) {
-          MaxPop = Popularity[BB];
-          MaxBB = BB;
-        }
-      }
-      // Set new default.
-      assert(MaxPop > 0 && MaxBB);
-      DefaultMBB = FuncInfo.MBBMap[MaxBB];
-
-      // Remove cases that were pointing to the destination that is now the
-      // default.
-      CaseClusterVector New;
-      New.reserve(Clusters.size());
-      for (CaseCluster &CC : Clusters) {
-        if (CC.MBB != DefaultMBB)
-          New.push_back(CC);
-      }
-      Clusters = std::move(New);
-    }
-  }
-
   // The branch probablity of the peeled case.
   BranchProbability PeeledCaseProb = BranchProbability::getZero();
   MachineBasicBlock *PeeledSwitchMBB =