Index: llvm/lib/Analysis/CFG.cpp
===================================================================
--- llvm/lib/Analysis/CFG.cpp
+++ llvm/lib/Analysis/CFG.cpp
@@ -254,8 +254,8 @@
   }
 
   if (DT) {
-    if (DT->isReachableFromEntry(A->getParent()) !=
-        DT->isReachableFromEntry(B->getParent()))
+    if (DT->isReachableFromEntry(A->getParent()) &&
+        !DT->isReachableFromEntry(B->getParent()))
       return false;
     if (!ExclusionSet || ExclusionSet->empty()) {
       if (A->getParent() == &A->getParent()->getParent()->getEntryBlock() &&
Index: llvm/unittests/Analysis/CFGTest.cpp
===================================================================
--- llvm/unittests/Analysis/CFGTest.cpp
+++ llvm/unittests/Analysis/CFGTest.cpp
@@ -491,3 +491,17 @@
                 "}");
   ExpectPath(true);
 }
+
+TEST_F(IsPotentiallyReachableTest, UnreachableToReachable) {
+  ParseAssembly("define void @test() {\n"
+                "entry:\n"
+                "  br label %exit\n"
+                "unreachableblock:\n"
+                "  %A = bitcast i8 undef to i8\n"
+                "  br label %exit\n"
+                "exit:\n"
+                "  %B = bitcast i8 undef to i8\n"
+                "  ret void\n"
+                "}");
+  ExpectPath(true);
+}