Add support for importing and exporting Registry objects on Windows

On Windows, the DLL containing the registry will get its own global head
and tail variables, so the entries registered in the DLL will be
invisible to the consumer.

In order to solve this, we need to export a getter function from the
plugin DLL per registry and copy over the data inside it.  This patch
adds support for this.  This will be used to support clang plugins on
Windows.

llvm-svn: 260261

include/llvm/Support/Registry.h

@@ -14,9 +14,10 @@
 #ifndef LLVM_SUPPORT_REGISTRY_H
 #define LLVM_SUPPORT_REGISTRY_H
 
-#include "llvm/ADT/iterator_range.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/DynamicLibrary.h"
 #include <memory>
 
 namespace llvm {
@@ -59,20 +60,23 @@ namespace llvm {
     ///
     class node {
       friend class iterator;
+      friend Registry<T>;
 
       node *Next;
       const entry& Val;
 
     public:
-      node(const entry& V) : Next(nullptr), Val(V) {
-        if (Tail)
-          Tail->Next = this;
-        else
-          Head = this;
-        Tail = this;
-      }
+      node(const entry &V) : Next(nullptr), Val(V) {}
     };
 
+    static void add_node(node *N) {
+      if (Tail)
+        Tail->Next = N;
+      else
+        Head = N;
+      Tail = N;
+    }
+
     /// Iterators for registry entries.
     ///
     class iterator {
@@ -112,8 +116,41 @@ namespace llvm {
 
     public:
       Add(const char *Name, const char *Desc)
-        : Entry(Name, Desc, CtorFn), Node(Entry) {}
+          : Entry(Name, Desc, CtorFn), Node(Entry) {
+        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 =
+          reinterpret_cast<GetRegistry>(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;
+    }
   };
 
   
@@ -126,4 +163,18 @@ namespace llvm {
   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();                                   \
+  }                                                                            \
+  }
+#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