Index: lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- lib/Transforms/IPO/PassManagerBuilder.cpp
+++ lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -168,11 +168,19 @@
   Extensions.push_back(std::make_pair(Ty, std::move(Fn)));
 }
 
+/// Avoid constructing the GlobalExtensions only to find out if it is empty
+static bool GlobalExtensionsNotEmpty() {
+  return GlobalExtensions.isConstructed() && !GlobalExtensions->empty();
+}
+
 void PassManagerBuilder::addExtensionsToPM(ExtensionPointTy ETy,
                                            legacy::PassManagerBase &PM) const {
-  for (unsigned i = 0, e = GlobalExtensions->size(); i != e; ++i)
-    if ((*GlobalExtensions)[i].first == ETy)
-      (*GlobalExtensions)[i].second(*this, PM);
+  if (GlobalExtensionsNotEmpty()) {
+    for (auto &Ext : *GlobalExtensions) {
+      if (Ext.first == ETy)
+        Ext.second(*this, PM);
+    }
+  }
   for (unsigned i = 0, e = Extensions.size(); i != e; ++i)
     if (Extensions[i].first == ETy)
       Extensions[i].second(*this, PM);
@@ -349,7 +357,7 @@
     // builds. The function merging pass is
     if (MergeFunctions)
       MPM.add(createMergeFunctionsPass());
-    else if (!GlobalExtensions->empty() || !Extensions.empty())
+    else if (GlobalExtensionsNotEmpty() || !Extensions.empty())
       MPM.add(createBarrierNoopPass());
 
     addExtensionsToPM(EP_EnabledOnOptLevel0, MPM);