Index: lib/Transforms/Utils/Local.cpp
===================================================================
--- lib/Transforms/Utils/Local.cpp
+++ lib/Transforms/Utils/Local.cpp
@@ -2233,6 +2233,7 @@
     BB->dropAllReferences();
   }
 
+  bool Deleted = false;
   for (Function::iterator I = ++F.begin(); I != F.end();) {
     auto *BB = &*I;
     if (Reachable.count(BB)) {
@@ -2240,6 +2241,10 @@
       continue;
     }
     if (DDT) {
+      if (DDT->pendingDeletedBB(BB)) // BB has already been deleted.
+        --NumRemoved;
+      else
+        Deleted = true;
       DDT->deleteBB(BB); // deferred deletion of BB.
       ++I;
     } else {
@@ -2249,6 +2254,8 @@
 
   if (DDT)
     DDT->applyUpdates(Updates);
+  if (DDT && !Deleted)
+    return false;
   return true;
 }
 
Index: unittests/Transforms/Utils/Local.cpp
===================================================================
--- unittests/Transforms/Utils/Local.cpp
+++ unittests/Transforms/Utils/Local.cpp
@@ -618,3 +618,26 @@
   verifyModule(*M, &errs(), &BrokenDebugInfo);
   ASSERT_FALSE(BrokenDebugInfo);
 }
+
+TEST(Local, RemoveUnreachableBlocks) {
+  LLVMContext C;
+
+  std::unique_ptr<Module> M = parseIR(C,
+                                      R"(
+      define void @f() {
+      entry:
+        br label %entry
+      bb0:
+        ret void
+      }
+        )");
+
+  auto callRemoveUnreachableBlocks = [&](Function &F, DominatorTree *DT) {
+    DeferredDominance DDT(*DT);
+    EXPECT_TRUE(removeUnreachableBlocks(F, nullptr, &DDT));
+    EXPECT_FALSE(removeUnreachableBlocks(F, nullptr, &DDT));
+    EXPECT_TRUE(DDT.flush().verify());
+  };
+
+  runWithDomTree(*M, "f", callRemoveUnreachableBlocks);
+}