diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -5185,8 +5185,9 @@
   }
 }
 
-/// Turn a switch with two reachable destinations into an integer range
-/// comparison and branch.
+/// Turn a switch into an integer range comparison and branch.
+/// Switches with more than 2 destinations are ignored.
+/// Switches with 1 destation are also ignored.
 bool SimplifyCFGOpt::TurnSwitchRangeIntoICmp(SwitchInst *SI,
                                              IRBuilder<> &Builder) {
   assert(SI->getNumCases() > 1 && "Degenerate switch?");
@@ -5218,6 +5219,10 @@
     }
     return false; // More than two destinations.
   }
+  // All destinations are the same and the default is undef
+  if (!DestB) {
+    return false;
+  }
 
   assert(DestA && DestB &&
          "Single-destination switch should have been folded.");
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-default-undef.ll b/llvm/test/Transforms/SimplifyCFG/switch-default-undef.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/switch-default-undef.ll
@@ -0,0 +1,45 @@
+; RUN: opt -passes=simplifycfg"<switch-range-to-icmp>" -S %s | FileCheck %s
+
+; CHECK: define void @0(i8 %sw, i32* %p0) {
+; CHECK: group2:
+; CHECK: call void @bar(i32* %p0)
+; CHECK: ret void
+; CHECK: }
+define void @0(i8 %sw, i32* %p0) {
+  switch i8 %sw, label %group3 [
+    i8 0, label %group1
+    i8 1, label %group1
+    i8 2, label %group1
+    i8 3, label %group1
+    i8 11, label %group1
+    i8 12, label %group1
+    i8 13, label %group1
+    i8 7, label %group1
+    i8 17, label %group1
+    i8 14, label %group1
+    i8 15, label %group1
+    i8 4, label %group2
+    i8 5, label %group2
+    i8 6, label %group2
+    i8 8, label %group2
+    i8 9, label %group2
+    i8 10, label %group2
+  ]
+
+group1:
+  br label %exit
+
+group2:
+  br label %exit
+
+group3:
+  br label %exit
+
+exit:
+  %phi = phi i32* [ null, %group3 ], [ %p0, %group2 ], [ null, %group1 ]
+  call void @bar(i32* %phi)
+  ret void
+}
+
+; CHECK: declare void @bar(i32* nonnull dereferenceable(4))
+declare void @bar(i32* nonnull dereferenceable(4))
\ No newline at end of file