1 files changed, 12 insertions, 2 deletions
diff --git a/include/clang/Basic/Module.h b/include/clang/Basic/Module.h
index 31c5c7ec9ca8..8fcb0e8b056a 100644
--- a/include/clang/Basic/Module.h
+++ b/include/clang/Basic/Module.h
@@ -42,7 +42,17 @@ class IdentifierInfo;
   
 /// \brief Describes the name of a module.
 typedef SmallVector<std::pair<std::string, SourceLocation>, 2> ModuleId;
-  
+
+/// The signature of a module, which is a hash of the AST content.
+struct ASTFileSignature : std::array<uint32_t, 5> {
+  ASTFileSignature(std::array<uint32_t, 5> S = {{0}})
+      : std::array<uint32_t, 5>(std::move(S)) {}
+
+  explicit operator bool() const {
+    return *this != std::array<uint32_t, 5>({{0}});
+  }
+};
+
 /// \brief Describes a module or submodule.
 class Module {
 public:
@@ -65,7 +75,7 @@ public:
   llvm::PointerUnion<const DirectoryEntry *, const FileEntry *> Umbrella;
 
   /// \brief The module signature.
-  uint64_t Signature;
+  ASTFileSignature Signature;
 
   /// \brief The name of the umbrella entry, as written in the module map.
   std::string UmbrellaAsWritten;