diff --git a/include/llvm/InitializePasses.h b/include/llvm/InitializePasses.h
index 263b84a08eb..3fda779ae90 100644
--- a/include/llvm/InitializePasses.h
+++ b/include/llvm/InitializePasses.h
@@ -66,6 +66,7 @@ void initializeAliasDebuggerPass(PassRegistry&);
 void initializeAliasSetPrinterPass(PassRegistry&);
 void initializeAlwaysInlinerPass(PassRegistry&);
 void initializeArgPromotionPass(PassRegistry&);
+void initializeBarrierNoopPass(PassRegistry&);
 void initializeBasicAliasAnalysisPass(PassRegistry&);
 void initializeBasicCallGraphPass(PassRegistry&);
 void initializeBlockExtractorPassPass(PassRegistry&);
diff --git a/include/llvm/Transforms/IPO.h b/include/llvm/Transforms/IPO.h
index 962cb63758d..08d3bbd941d 100644
--- a/include/llvm/Transforms/IPO.h
+++ b/include/llvm/Transforms/IPO.h
@@ -198,6 +198,11 @@ ModulePass *createPartialInliningPass();
 //
 ModulePass *createMetaRenamerPass();
 
+//===----------------------------------------------------------------------===//
+/// createBarrierNoopPass - This pass is purely a module pass barrier in a pass
+/// manager.
+ModulePass *createBarrierNoopPass();
+
 } // End llvm namespace
 
 #endif
diff --git a/lib/Transforms/IPO/BarrierNoopPass.cpp b/lib/Transforms/IPO/BarrierNoopPass.cpp
new file mode 100644
index 00000000000..2e32240621f
--- /dev/null
+++ b/lib/Transforms/IPO/BarrierNoopPass.cpp
@@ -0,0 +1,47 @@
+//===- BarrierNoopPass.cpp - A barrier pass for the pass manager ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// NOTE: DO NOT USE THIS IF AVOIDABLE
+//
+// This pass is a nonce pass intended to allow manipulation of the implicitly
+// nesting pass manager. For example, it can be used to cause a CGSCC pass
+// manager to be closed prior to running a new collection of function passes.
+//
+// FIXME: This is a huge HACK. This should be removed when the pass manager's
+// nesting is made explicit instead of implicit.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Pass.h"
+#include "llvm/Transforms/IPO.h"
+using namespace llvm;
+
+namespace {
+/// \brief A nonce module pass used to place a barrier in a pass manager.
+///
+/// There is no mechanism for ending a CGSCC pass manager once one is started.
+/// This prevents extension points from having clear deterministic ordering
+/// when they are phrased as non-module passes.
+class BarrierNoop : public ModulePass {
+public:
+  static char ID; // Pass identification.
+
+  BarrierNoop() : ModulePass(ID) {
+    initializeBarrierNoopPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnModule(Module &M) { return false; }
+};
+}
+
+ModulePass *llvm::createBarrierNoopPass() { return new BarrierNoop(); }
+
+char BarrierNoop::ID = 0;
+INITIALIZE_PASS(BarrierNoop, "barrier", "A No-Op Barrier Pass",
+                false, false)
diff --git a/lib/Transforms/IPO/CMakeLists.txt b/lib/Transforms/IPO/CMakeLists.txt
index 3f6b1de614d..90c1c33e6dc 100644
--- a/lib/Transforms/IPO/CMakeLists.txt
+++ b/lib/Transforms/IPO/CMakeLists.txt
@@ -1,5 +1,6 @@
 add_llvm_library(LLVMipo
   ArgumentPromotion.cpp
+  BarrierNoopPass.cpp
   ConstantMerge.cpp
   DeadArgumentElimination.cpp
   ExtractGV.cpp
diff --git a/lib/Transforms/IPO/PassManagerBuilder.cpp b/lib/Transforms/IPO/PassManagerBuilder.cpp
index 97698caa516..1d8f1e531a0 100644
--- a/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -119,6 +119,14 @@ void PassManagerBuilder::populateModulePassManager(PassManagerBase &MPM) {
       MPM.add(Inliner);
       Inliner = 0;
     }
+
+    // FIXME: This is a HACK! The inliner pass above implicitly creates a CGSCC
+    // pass manager, but we don't want to add extensions into that pass manager.
+    // To prevent this we must insert a no-op module pass to reset the pass
+    // manager to get the same behavior as EP_OptimizerLast in non-O0 builds.
+    if (!GlobalExtensions->empty() || !Extensions.empty())
+      MPM.add(createBarrierNoopPass());
+
     addExtensionsToPM(EP_EnabledOnOptLevel0, MPM);
     return;
   }