Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -668,6 +668,12 @@
   let Documentation = [Undocumented];
 }
 
+def Flatten : InheritableAttr {
+  let Spellings = [GNU<"flatten">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [Undocumented];
+}
+
 def Format : InheritableAttr {
   let Spellings = [GCC<"format">];
   let Args = [IdentifierArgument<"Type">, IntArgument<"FormatIdx">,
Index: lib/CodeGen/CGCall.cpp
===================================================================
--- lib/CodeGen/CGCall.cpp
+++ lib/CodeGen/CGCall.cpp
@@ -1063,6 +1063,7 @@
 }
 
 void CodeGenModule::ConstructAttributeList(const CGFunctionInfo &FI,
+                                           const Decl *CallerDecl,
                                            const Decl *TargetDecl,
                                            AttributeListType &PAL,
                                            unsigned &CallingConv,
@@ -1075,6 +1076,11 @@
   if (FI.isNoReturn())
     FuncAttrs.addAttribute(llvm::Attribute::NoReturn);
 
+  if (CallerDecl) {
+    if (CallerDecl->hasAttr<FlattenAttr>())
+      FuncAttrs.addAttribute(llvm::Attribute::AlwaysInline);
+  }
+
   // FIXME: handle sseregparm someday...
   if (TargetDecl) {
     if (TargetDecl->hasAttr<ReturnsTwiceAttr>())
@@ -2913,7 +2919,7 @@
 
   unsigned CallingConv;
   CodeGen::AttributeListType AttributeList;
-  CGM.ConstructAttributeList(CallInfo, TargetDecl, AttributeList,
+  CGM.ConstructAttributeList(CallInfo, CurCodeDecl, TargetDecl, AttributeList,
                              CallingConv, true);
   llvm::AttributeSet Attrs = llvm::AttributeSet::get(getLLVMContext(),
                                                      AttributeList);
Index: lib/CodeGen/CodeGenModule.h
===================================================================
--- lib/CodeGen/CodeGenModule.h
+++ lib/CodeGen/CodeGenModule.h
@@ -906,12 +906,14 @@
   /// function type.
   ///
   /// \param Info - The function type information.
+  /// \param CallerDecl - The decl of the caller, if available
   /// \param TargetDecl - The decl these attributes are being constructed
   /// for. If supplied the attributes applied to this decl may contribute to the
   /// function attributes and calling convention.
   /// \param PAL [out] - On return, the attribute list to use.
   /// \param CallingConv [out] - On return, the LLVM calling convention to use.
   void ConstructAttributeList(const CGFunctionInfo &Info,
+                              const Decl *CallerDecl,
                               const Decl *TargetDecl,
                               AttributeListType &PAL,
                               unsigned &CallingConv,
Index: lib/CodeGen/CodeGenModule.cpp
===================================================================
--- lib/CodeGen/CodeGenModule.cpp
+++ lib/CodeGen/CodeGenModule.cpp
@@ -576,7 +576,7 @@
                                               llvm::Function *F) {
   unsigned CallingConv;
   AttributeListType AttributeList;
-  ConstructAttributeList(Info, D, AttributeList, CallingConv, false);
+  ConstructAttributeList(Info, 0, D, AttributeList, CallingConv, false);
   F->setAttributes(llvm::AttributeSet::get(getLLVMContext(), AttributeList));
   F->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
 }
Index: lib/CodeGen/MicrosoftCXXABI.cpp
===================================================================
--- lib/CodeGen/MicrosoftCXXABI.cpp
+++ lib/CodeGen/MicrosoftCXXABI.cpp
@@ -1113,7 +1113,7 @@
 
   unsigned CallingConv;
   CodeGen::AttributeListType AttributeList;
-  CGM.ConstructAttributeList(FnInfo, MD, AttributeList, CallingConv, true);
+  CGM.ConstructAttributeList(FnInfo, 0, MD, AttributeList, CallingConv, true);
   llvm::AttributeSet Attrs =
       llvm::AttributeSet::get(CGF.getLLVMContext(), AttributeList);
 
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -4140,6 +4140,9 @@
   case AttributeList::AT_OptimizeNone:
     handleOptimizeNoneAttr(S, D, Attr);
     break;
+  case AttributeList::AT_Flatten:
+    handleSimpleAttribute<FlattenAttr>(S, D, Attr);
+    break;
   case AttributeList::AT_Format:
     handleFormatAttr(S, D, Attr);
     break;
Index: test/CodeGen/flatten.c
===================================================================
--- /dev/null
+++ test/CodeGen/flatten.c
@@ -0,0 +1,10 @@
+// RUN: %clang -target x86_64-linux-gnu -S %s -emit-llvm -o - | FileCheck %s
+
+void f(void) {}
+
+__attribute__((flatten))
+// CHECK: define void @g()
+void g(void) {
+  // CHECK-NOT: call {{.*}} @f
+  f();
+}