Index: llvm/lib/Transforms/Utils/UnifyFunctionExitNodes.cpp
===================================================================
--- llvm/lib/Transforms/Utils/UnifyFunctionExitNodes.cpp
+++ llvm/lib/Transforms/Utils/UnifyFunctionExitNodes.cpp
@@ -54,6 +54,7 @@
   //
   std::vector<BasicBlock*> ReturningBlocks;
   std::vector<BasicBlock*> UnreachableBlocks;
+  bool Changed = false;
   for (BasicBlock &I : F)
     if (isa<ReturnInst>(I.getTerminator()))
       ReturningBlocks.push_back(&I);
@@ -74,15 +75,16 @@
       BB->getInstList().pop_back();  // Remove the unreachable inst.
       BranchInst::Create(UnreachableBlock, BB);
     }
+    Changed = true;
   }
 
   // Now handle return blocks.
   if (ReturningBlocks.empty()) {
     ReturnBlock = nullptr;
-    return false;                          // No blocks return
+    return Changed;                        // No blocks return
   } else if (ReturningBlocks.size() == 1) {
     ReturnBlock = ReturningBlocks.front(); // Already has a single return block
-    return false;
+    return Changed;
   }
 
   // Otherwise, we need to insert a new basic block into the function, add a PHI
Index: llvm/test/Transforms/UnifyFunctionExitNodes/unreachable-blocks-status.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/UnifyFunctionExitNodes/unreachable-blocks-status.ll
@@ -0,0 +1,67 @@
+; RUN: opt -mergereturn -S < %s | FileCheck %s
+
+; The pass did previously not report the correct Modified status in the case
+; where a function had at most one return block, and an unified unreachable
+; block was created. This was caught by the pass return status check that is
+; hidden under EXPENSIVE_CHECKS.
+
+; CHECK: for.foo.body2:
+; CHECK-NEXT: br label %UnifiedUnreachableBlock
+
+; CHECK: for.foo.end:
+; CHECK-NEXT: br label %UnifiedUnreachableBlock
+
+; CHECK: UnifiedUnreachableBlock:
+; CHECK-NEXT: unreachable
+
+define i32 @foo() {
+entry:
+  br label %for.foo.cond
+
+for.foo.cond:                                         ; preds = %entry
+  br i1 false, label %for.foo.body, label %for.foo.end3
+
+for.foo.body:                                         ; preds = %for.foo.cond
+  br label %for.foo.cond1
+
+for.foo.cond1:                                        ; preds = %for.foo.body
+  br i1 false, label %for.foo.body2, label %for.foo.end
+
+for.foo.body2:                                        ; preds = %for.foo.cond1
+  unreachable
+
+for.foo.end:                                          ; preds = %for.foo.cond1
+  unreachable
+
+for.foo.end3:                                         ; preds = %for.foo.cond
+  ret i32 undef
+}
+
+; CHECK: for.bar.body2:
+; CHECK-NEXT: br label %UnifiedUnreachableBlock
+
+; CHECK: for.bar.end:
+; CHECK-NEXT: br label %UnifiedUnreachableBlock
+
+; CHECK: UnifiedUnreachableBlock:
+; CHECK-NEXT: unreachable
+
+define void @bar() {
+entry:
+  br label %for.bar.cond
+
+for.bar.cond:                                         ; preds = %entry
+  br i1 false, label %for.bar.body, label %for.bar.end
+
+for.bar.body:                                         ; preds = %for.bar.cond
+  br label %for.bar.cond1
+
+for.bar.cond1:                                        ; preds = %for.bar.body
+  br i1 false, label %for.bar.body2, label %for.bar.end
+
+for.bar.body2:                                        ; preds = %for.bar.cond1
+  unreachable
+
+for.bar.end:                                          ; preds = %for.bar.cond1
+  unreachable
+}