Reapply r276973 "Adjust Registry interface to not require plugins to export a registry"

This differs from the previous version by being more careful about template
instantiation/specialization in order to prevent errors when building with
clang -Werror. Specifically:
 * begin is not defined in the template and is instead instantiated when Head
   is. I think the warning when we don't do that is wrong (PR28815) but for now
   at least do it this way to avoid the warning.
 * Instead of performing template specializations in LLVM_INSTANTIATE_REGISTRY
   instead provide a template definition then do explicit instantiation. No
   compiler I've tried has problems with doing it the other way, but strictly
   speaking it's not permitted by the C++ standard so better safe than sorry.

Original commit message:

Currently the Registry class contains the vestiges of a previous attempt to
allow plugins to be used on Windows without using BUILD_SHARED_LIBS, where a
plugin would have its own copy of a registry and export it to be imported by
the tool that's loading the plugin. This only works if the plugin is entirely
self-contained with the only interface between the plugin and tool being the
registry, and in particular this conflicts with how IR pass plugins work.

This patch changes things so that instead the add_node function of the registry
is exported by the tool and then imported by the plugin, which solves this
problem and also means that instead of every plugin having to export every
registry they use instead LLVM only has to export the add_node functions. This
allows plugins that use a registry to work on Windows if
LLVM_EXPORT_SYMBOLS_FOR_PLUGINS is used.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277806 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/Registry.h

@@ -44,6 +44,7 @@ namespace llvm {
   template <typename T>
   class Registry {
   public:
+    typedef T type;
     typedef SimpleRegistryEntry<T> entry;
 
     class node;
@@ -69,13 +70,14 @@ namespace llvm {
       node(const entry &V) : Next(nullptr), Val(V) {}
     };
 
-    static void add_node(node *N) {
-      if (Tail)
-        Tail->Next = N;
-      else
-        Head = N;
-      Tail = N;
-    }
+    /// Add a node to the Registry: this is the interface between the plugin and
+    /// the executable.
+    ///
+    /// This function is exported by the executable and called by the plugin to
+    /// add a node to the executable's registry. Therefore it's not defined here
+    /// to avoid it being instantiated in the plugin and is instead defined in
+    /// the executable (see LLVM_INSTANTIATE_REGISTRY below).
+    static void add_node(node *N);
 
     /// Iterators for registry entries.
     ///
@@ -92,7 +94,9 @@ namespace llvm {
       const entry *operator->() const { return &Cur->Val; }
     };
 
-    static iterator begin() { return iterator(Head); }
+    // begin is not defined here in order to avoid usage of an undefined static
+    // data member, instead it's instantiated by LLVM_INSTANTIATE_REGISTRY.
+    static iterator begin();
     static iterator end()   { return iterator(nullptr); }
 
     static iterator_range<iterator> entries() {
@@ -120,61 +124,37 @@ namespace llvm {
         add_node(&Node);
       }
     };
-
-    /// A dynamic import facility.  This is used on Windows to
-    /// import the entries added in the plugin.
-    static void import(sys::DynamicLibrary &DL, const char *RegistryName) {
-      typedef void *(*GetRegistry)();
-      std::string Name("LLVMGetRegistry_");
-      Name.append(RegistryName);
-      GetRegistry Getter =
-          (GetRegistry)(intptr_t)DL.getAddressOfSymbol(Name.c_str());
-      if (Getter) {
-        // Call the getter function in order to get the full copy of the
-        // registry defined in the plugin DLL, and copy them over to the
-        // current Registry.
-        typedef std::pair<const node *, const node *> Info;
-        Info *I = static_cast<Info *>(Getter());
-        iterator begin(I->first);
-        iterator end(I->second);
-        for (++end; begin != end; ++begin) {
-          // This Node object needs to remain alive for the
-          // duration of the program.
-          add_node(new node(*begin));
-        }
-      }
-    }
-
-    /// Retrieve the data to be passed across DLL boundaries when
-    /// importing registries from another DLL on Windows.
-    static void *exportRegistry() {
-      static std::pair<const node *, const node *> Info(Head, Tail);
-      return &Info;
-    }
   };
-
-  
-  // Since these are defined in a header file, plugins must be sure to export
-  // these symbols.
-  template <typename T>
-  typename Registry<T>::node *Registry<T>::Head;
-
-  template <typename T>
-  typename Registry<T>::node *Registry<T>::Tail;
 } // end namespace llvm
 
-#ifdef LLVM_ON_WIN32
-#define LLVM_EXPORT_REGISTRY(REGISTRY_CLASS)                                   \
-  extern "C" {                                                                 \
-  __declspec(dllexport) void *__cdecl LLVMGetRegistry_##REGISTRY_CLASS() {     \
-    return REGISTRY_CLASS::exportRegistry();                                   \
-  }                                                                            \
+/// Instantiate a registry class.
+///
+/// This provides template definitions of add_node, begin, and the Head and Tail
+/// pointers, then explicitly instantiates them. We could explicitly specialize
+/// them, instead of the two-step process of define then instantiate, but
+/// strictly speaking that's not allowed by the C++ standard (we would need to
+/// have explicit specialization declarations in all translation units where the
+/// specialization is used) so we don't.
+#define LLVM_INSTANTIATE_REGISTRY(REGISTRY_CLASS) \
+  namespace llvm { \
+  template<typename T> typename Registry<T>::node *Registry<T>::Head = nullptr;\
+  template<typename T> typename Registry<T>::node *Registry<T>::Tail = nullptr;\
+  template<typename T> \
+  void Registry<T>::add_node(typename Registry<T>::node *N) { \
+    if (Tail) \
+      Tail->Next = N; \
+    else \
+      Head = N; \
+    Tail = N; \
+  } \
+  template<typename T> typename Registry<T>::iterator Registry<T>::begin() { \
+    return iterator(Head); \
+  } \
+  template REGISTRY_CLASS::node *Registry<REGISTRY_CLASS::type>::Head; \
+  template REGISTRY_CLASS::node *Registry<REGISTRY_CLASS::type>::Tail; \
+  template
+  void Registry<REGISTRY_CLASS::type>::add_node(REGISTRY_CLASS::node*); \
+  template REGISTRY_CLASS::iterator Registry<REGISTRY_CLASS::type>::begin(); \
   }
-#define LLVM_IMPORT_REGISTRY(REGISTRY_CLASS, DL)                               \
-  REGISTRY_CLASS::import(DL, #REGISTRY_CLASS)
-#else
-#define LLVM_EXPORT_REGISTRY(REGISTRY_CLASS)
-#define LLVM_IMPORT_REGISTRY(REGISTRY_CLASS, DL)
-#endif
 
 #endif // LLVM_SUPPORT_REGISTRY_H

lib/CodeGen/GCMetadataPrinter.cpp

@@ -14,6 +14,8 @@
 #include "llvm/CodeGen/GCMetadataPrinter.h"
 using namespace llvm;
 
+LLVM_INSTANTIATE_REGISTRY(GCMetadataPrinterRegistry)
+
 GCMetadataPrinter::GCMetadataPrinter() {}
 
 GCMetadataPrinter::~GCMetadataPrinter() {}

lib/CodeGen/GCStrategy.cpp

@@ -16,6 +16,8 @@
 
 using namespace llvm;
 
+LLVM_INSTANTIATE_REGISTRY(GCRegistry)
+
 GCStrategy::GCStrategy()
     : UseStatepoints(false), NeededSafePoints(0), CustomReadBarriers(false),
       CustomWriteBarriers(false), CustomRoots(false), InitRoots(true),