Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -1716,6 +1716,12 @@
   let Documentation = [PcsDocs];
 }
 
+def WriteOnlyFunc : InheritableAttr {
+  let Spellings = [Clang<"write_only_func">];
+  let Subjects = SubjectList<[Function], ErrorDiag>;
+  let Documentation = [WriteOnlyFuncDocs];
+}
+
 def Pure : InheritableAttr {
   let Spellings = [GCC<"pure">];
   let Documentation = [Undocumented];
Index: include/clang/Basic/AttrDocs.td
===================================================================
--- include/clang/Basic/AttrDocs.td
+++ include/clang/Basic/AttrDocs.td
@@ -3324,3 +3324,21 @@
 corresponding line within the inlined callee.
   }];
 }
+
+def WriteOnlyFuncDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+The ``write_only_func`` attribute can be applied to a function to indicate
+that the function may write to, but does not read from, memory.  A write-only
+function always writes the same value to the same memory location when called
+with the same set of arguments and global state.  
+
+When the ``write_only_func`` attribute is applied, function calls may be
+hoisted or eliminated when memory analysis determines it to be safe. When
+applied to a virtual function, the overridden functions are expected to
+adhere to be write-only functions.
+
+Mis-applying this attribute may lead to a memory location containing an
+incorrect value.
+  }];
+}
Index: lib/CodeGen/CGCall.cpp
===================================================================
--- lib/CodeGen/CGCall.cpp
+++ lib/CodeGen/CGCall.cpp
@@ -1841,6 +1841,9 @@
         FuncAttrs.addAttribute(llvm::Attribute::NoReturn);
     }
 
+    if (TargetDecl->hasAttr<WriteOnlyFuncAttr>())
+      FuncAttrs.addAttribute(llvm::Attribute::WriteOnly);
+
     // 'const', 'pure' and 'noalias' attributed functions are also nounwind.
     if (TargetDecl->hasAttr<ConstAttr>()) {
       FuncAttrs.addAttribute(llvm::Attribute::ReadNone);
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -6206,6 +6206,9 @@
   case AttributeList::AT_Sentinel:
     handleSentinelAttr(S, D, AL);
     break;
+  case AttributeList::AT_WriteOnlyFunc:
+    handleSimpleAttribute<WriteOnlyFuncAttr>(S, D, AL);
+    break;
   case AttributeList::AT_Const:
     handleSimpleAttribute<ConstAttr>(S, D, AL);
     break;
Index: test/CodeGen/function-attributes.c
===================================================================
--- test/CodeGen/function-attributes.c
+++ test/CodeGen/function-attributes.c
@@ -109,11 +109,24 @@
   _setjmp(0);
 }
 
+// CHECK-LABEL: define void @f22()
+// CHECK: [[WO:#[0-9]+]]
+// CHECK: {
+// CHECK: call void @f21()
+// CHECK: [[WO_CALL:#[0-9]+]]
+// CHECK: ret void
+__attribute__ ((write_only_func)) void f21(void);
+__attribute__ ((write_only_func)) void f22(void) {
+  f21();
+}
+
 // CHECK: attributes [[NUW]] = { nounwind optsize{{.*}} }
 // CHECK: attributes [[AI]] = { alwaysinline nounwind optsize{{.*}} }
 // CHECK: attributes [[NUW_OS_RN]] = { nounwind optsize readnone{{.*}} }
 // CHECK: attributes [[SR]] = { nounwind optsize{{.*}} "stackrealign"{{.*}} }
 // CHECK: attributes [[RT]] = { nounwind optsize returns_twice{{.*}} }
+// CHECK: attributes [[WO]] = { nounwind optsize writeonly{{.*}} }
 // CHECK: attributes [[NR]] = { noreturn optsize }
 // CHECK: attributes [[NUW_RN]] = { nounwind optsize readnone }
 // CHECK: attributes [[RT_CALL]] = { optsize returns_twice }
+// CHECK: attributes [[WO_CALL]] = { optsize writeonly }
Index: test/Misc/pragma-attribute-supported-attributes-list.test
===================================================================
--- test/Misc/pragma-attribute-supported-attributes-list.test
+++ test/Misc/pragma-attribute-supported-attributes-list.test
@@ -2,7 +2,7 @@
 
 // The number of supported attributes should never go down!
 
-// CHECK: #pragma clang attribute supports 69 attributes:
+// CHECK: #pragma clang attribute supports 70 attributes:
 // CHECK-NEXT: AMDGPUFlatWorkGroupSize (SubjectMatchRule_function)
 // CHECK-NEXT: AMDGPUNumSGPR (SubjectMatchRule_function)
 // CHECK-NEXT: AMDGPUNumVGPR (SubjectMatchRule_function)
@@ -70,5 +70,6 @@
 // CHECK-NEXT: TestTypestate (SubjectMatchRule_function_is_member)
 // CHECK-NEXT: TrivialABI (SubjectMatchRule_record)
 // CHECK-NEXT: WarnUnusedResult (SubjectMatchRule_objc_method, SubjectMatchRule_enum, SubjectMatchRule_record, SubjectMatchRule_hasType_functionType)
+// CHECK-NEXT: WriteOnlyFunc (SubjectMatchRule_function)
 // CHECK-NEXT: XRayInstrument (SubjectMatchRule_function, SubjectMatchRule_objc_method)
 // CHECK-NEXT: XRayLogArgs (SubjectMatchRule_function, SubjectMatchRule_objc_method)