Index: llvm/include/llvm/Transforms/IPO/PassManagerBuilder.h
===================================================================
--- llvm/include/llvm/Transforms/IPO/PassManagerBuilder.h
+++ llvm/include/llvm/Transforms/IPO/PassManagerBuilder.h
@@ -62,6 +62,8 @@
   typedef std::function<void(const PassManagerBuilder &Builder,
                              legacy::PassManagerBase &PM)>
       ExtensionFn;
+  typedef int GlobalExtensionID;
+
   enum ExtensionPointTy {
     /// EP_EarlyAsPossible - This extension point allows adding passes before
     /// any other transformations, allowing them to see the code as it is coming
@@ -193,7 +195,17 @@
   /// Adds an extension that will be used by all PassManagerBuilder instances.
   /// This is intended to be used by plugins, to register a set of
   /// optimisations to run automatically.
-  static void addGlobalExtension(ExtensionPointTy Ty, ExtensionFn Fn);
+  ///
+  /// \returns A global extension identifier that can be used to remove the
+  /// extension.
+  static GlobalExtensionID addGlobalExtension(ExtensionPointTy Ty,
+                                              ExtensionFn Fn);
+  /// Removes an extension that was previously added using addGlobalExtension.
+  /// This is also intended to be used by plugins, to remove any extension that
+  /// was previously registered before being unloaded.
+  ///
+  /// \param ExtensionID Identifier of the extension to be removed.
+  static void removeGlobalExtension(GlobalExtensionID ExtensionID);
   void addExtension(ExtensionPointTy Ty, ExtensionFn Fn);
 
 private:
@@ -222,10 +234,20 @@
 /// used by optimizer plugins to allow all front ends to transparently use
 /// them.  Create a static instance of this class in your plugin, providing a
 /// private function that the PassManagerBuilder can use to add your passes.
-struct RegisterStandardPasses {
+class RegisterStandardPasses {
+  PassManagerBuilder::GlobalExtensionID ExtensionID;
+
+public:
   RegisterStandardPasses(PassManagerBuilder::ExtensionPointTy Ty,
                          PassManagerBuilder::ExtensionFn Fn) {
-    PassManagerBuilder::addGlobalExtension(Ty, std::move(Fn));
+    ExtensionID = PassManagerBuilder::addGlobalExtension(Ty, std::move(Fn));
+  }
+
+  ~RegisterStandardPasses() {
+    // If the collection holding the global extensions is destroyed after the
+    // plugin is unloaded, the extension has to be removed here. Indeed, the
+    // destructor of the ExtensionFn may reference code in the plugin.
+    PassManagerBuilder::removeGlobalExtension(ExtensionID);
   }
 };
 
Index: llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -13,6 +13,7 @@
 
 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
 #include "llvm-c/Transforms/PassManagerBuilder.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Analysis/BasicAliasAnalysis.h"
 #include "llvm/Analysis/CFLAndersAliasAnalysis.h"
@@ -183,8 +184,13 @@
 }
 
 /// Set of global extensions, automatically added as part of the standard set.
-static ManagedStatic<SmallVector<std::pair<PassManagerBuilder::ExtensionPointTy,
-   PassManagerBuilder::ExtensionFn>, 8> > GlobalExtensions;
+static ManagedStatic<
+    SmallVector<std::tuple<PassManagerBuilder::ExtensionPointTy,
+                           PassManagerBuilder::ExtensionFn,
+                           PassManagerBuilder::GlobalExtensionID>,
+                8>>
+    GlobalExtensions;
+static PassManagerBuilder::GlobalExtensionID GlobalExtensionsCounter;
 
 /// Check if GlobalExtensions is constructed and not empty.
 /// Since GlobalExtensions is a managed static, calling 'empty()' will trigger
@@ -193,10 +199,29 @@
   return GlobalExtensions.isConstructed() && !GlobalExtensions->empty();
 }
 
-void PassManagerBuilder::addGlobalExtension(
-    PassManagerBuilder::ExtensionPointTy Ty,
-    PassManagerBuilder::ExtensionFn Fn) {
-  GlobalExtensions->push_back(std::make_pair(Ty, std::move(Fn)));
+PassManagerBuilder::GlobalExtensionID
+PassManagerBuilder::addGlobalExtension(PassManagerBuilder::ExtensionPointTy Ty,
+                                       PassManagerBuilder::ExtensionFn Fn) {
+  auto ExtensionID = GlobalExtensionsCounter++;
+  GlobalExtensions->push_back(std::make_tuple(Ty, std::move(Fn), ExtensionID));
+  return ExtensionID;
+}
+
+void PassManagerBuilder::removeGlobalExtension(
+    PassManagerBuilder::GlobalExtensionID ExtensionID) {
+  // RegisterStandardPasses may try to call this function after GlobalExtensions
+  // has already been destroyed; doing so should not generate an error.
+  if (!GlobalExtensions.isConstructed())
+    return;
+
+  auto GlobalExtension =
+      llvm::find_if(*GlobalExtensions, [ExtensionID](const auto &elem) {
+        return std::get<2>(elem) == ExtensionID;
+      });
+  assert(GlobalExtension != GlobalExtensions->end() &&
+         "The extension ID to be removed should always be valid.");
+
+  GlobalExtensions->erase(GlobalExtension);
 }
 
 void PassManagerBuilder::addExtension(ExtensionPointTy Ty, ExtensionFn Fn) {
@@ -207,8 +232,8 @@
                                            legacy::PassManagerBase &PM) const {
   if (GlobalExtensionsNotEmpty()) {
     for (auto &Ext : *GlobalExtensions) {
-      if (Ext.first == ETy)
-        Ext.second(*this, PM);
+      if (std::get<0>(Ext) == ETy)
+        std::get<1>(Ext)(*this, PM);
     }
   }
   for (unsigned i = 0, e = Extensions.size(); i != e; ++i)