3 files changed, 24 insertions, 1 deletions
diff --git a/lib/CodeGen/CGCall.cpp b/lib/CodeGen/CGCall.cpp
index eb0dcf3bef..f52abef330 100644
--- a/lib/CodeGen/CGCall.cpp
+++ b/lib/CodeGen/CGCall.cpp
@@ -740,6 +740,9 @@ void CodeGenModule::ConstructAttributeList(const CGFunctionInfo &FI,
     if (TargetDecl->hasAttr<NoReturnAttr>())
       FuncAttrs |= llvm::Attribute::NoReturn;
 
+    if (TargetDecl->hasAttr<ReturnsTwiceAttr>())
+      FuncAttrs |= llvm::Attribute::ReturnsTwice;
+
     // 'const' and 'pure' attribute functions are also nounwind.
     if (TargetDecl->hasAttr<ConstAttr>()) {
       FuncAttrs |= llvm::Attribute::ReadNone;
diff --git a/lib/Sema/AttributeList.cpp b/lib/Sema/AttributeList.cpp
index 9d366ad255..13a0edec28 100644
--- a/lib/Sema/AttributeList.cpp
+++ b/lib/Sema/AttributeList.cpp
@@ -159,7 +159,7 @@ AttributeList::Kind AttributeList::getKind(const IdentifierInfo *Name) {
     .Case("address_space", AT_address_space)
     .Case("opencl_image_access", AT_opencl_image_access)
     .Case("always_inline", AT_always_inline)
-    .Case("returns_twice", IgnoredAttribute)
+    .Case("returns_twice", AT_returns_twice)
     .Case("vec_type_hint", IgnoredAttribute)
     .Case("objc_exception", AT_objc_exception)
     .Case("objc_method_family", AT_objc_method_family)
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index d9e4df058d..79afbe538d 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -1427,6 +1427,23 @@ static void handleUnusedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   D->addAttr(::new (S.Context) UnusedAttr(Attr.getRange(), S.Context));
 }
 
+static void handleReturnsTwiceAttr(Sema &S, Decl *D,
+                                   const AttributeList &Attr) {
+  // check the attribute arguments.
+  if (Attr.hasParameterOrArguments()) {
+    S.Diag(Attr.getLoc(), diag::err_attribute_wrong_number_arguments) << 0;
+    return;
+  }
+
+  if (!isa<FunctionDecl>(D)) {
+    S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
+      << Attr.getName() << ExpectedFunction;
+    return;
+  }
+
+  D->addAttr(::new (S.Context) ReturnsTwiceAttr(Attr.getRange(), S.Context));
+}
+
 static void handleUsedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   // check the attribute arguments.
   if (Attr.hasParameterOrArguments()) {
@@ -3567,6 +3584,9 @@ static void ProcessInheritableDeclAttr(Sema &S, Scope *scope, Decl *D,
     handleArcWeakrefUnavailableAttr (S, D, Attr); 
     break;
   case AttributeList::AT_unused:      handleUnusedAttr      (S, D, Attr); break;
+  case AttributeList::AT_returns_twice:
+    handleReturnsTwiceAttr(S, D, Attr);
+    break;
   case AttributeList::AT_used:        handleUsedAttr        (S, D, Attr); break;
   case AttributeList::AT_visibility:  handleVisibilityAttr  (S, D, Attr); break;
   case AttributeList::AT_warn_unused_result: handleWarnUnusedResult(S, D, Attr);