1 files changed, 75 insertions, 0 deletions
diff --git a/include/clang/AST/ASTImporterLookupTable.h b/include/clang/AST/ASTImporterLookupTable.h
new file mode 100644
index 0000000000..14cafe817d
--- /dev/null
+++ b/include/clang/AST/ASTImporterLookupTable.h
@@ -0,0 +1,75 @@
+//===- ASTImporterLookupTable.h - ASTImporter specific lookup--*- C++ -*---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the ASTImporterLookupTable class which implements a
+//  lookup procedure for the import mechanism.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_ASTIMPORTERLOOKUPTABLE_H
+#define LLVM_CLANG_AST_ASTIMPORTERLOOKUPTABLE_H
+
+#include "clang/AST/DeclBase.h" // lookup_result
+#include "clang/AST/DeclarationName.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SetVector.h"
+
+namespace clang {
+
+class ASTContext;
+class NamedDecl;
+class DeclContext;
+
+// There are certain cases when normal C/C++ lookup (localUncachedLookup)
+// does not find AST nodes. E.g.:
+// Example 1:
+//   template <class T>
+//   struct X {
+//     friend void foo(); // this is never found in the DC of the TU.
+//   };
+// Example 2:
+//   // The fwd decl to Foo is not found in the lookupPtr of the DC of the
+//   // translation unit decl.
+//   // Here we could find the node by doing a traverse throught the list of
+//   // the Decls in the DC, but that would not scale.
+//   struct A { struct Foo *p; };
+// This is a severe problem because the importer decides if it has to create a
+// new Decl or not based on the lookup results.
+// To overcome these cases we need an importer specific lookup table which
+// holds every node and we are not interested in any C/C++ specific visibility
+// considerations. Simply, we must know if there is an existing Decl in a
+// given DC. Once we found it then we can handle any visibility related tasks.
+class ASTImporterLookupTable {
+
+  // We store a list of declarations for each name.
+  // And we collect these lists for each DeclContext.
+  // We could have a flat map with (DeclContext, Name) tuple as key, but a two
+  // level map seems easier to handle.
+  using DeclList = llvm::SmallSetVector<NamedDecl *, 2>;
+  using NameMap = llvm::SmallDenseMap<DeclarationName, DeclList, 4>;
+  using DCMap = llvm::DenseMap<DeclContext *, NameMap>;
+
+  void add(DeclContext *DC, NamedDecl *ND);
+  void remove(DeclContext *DC, NamedDecl *ND);
+
+  DCMap LookupTable;
+
+public:
+  ASTImporterLookupTable(TranslationUnitDecl &TU);
+  void add(NamedDecl *ND);
+  void remove(NamedDecl *ND);
+  using LookupResult = DeclList;
+  LookupResult lookup(DeclContext *DC, DeclarationName Name) const;
+  void dump(DeclContext *DC) const;
+  void dump() const;
+};
+
+} // namespace clang
+
+#endif // LLVM_CLANG_AST_ASTIMPORTERLOOKUPTABLE_H