Index: lib/Sema/SemaTemplateInstantiateDecl.cpp
===================================================================
--- lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -2176,6 +2176,24 @@
     Owner->addDecl(Method);
   }
 
+  // facebook begin T10336705
+  // PR17480: Honor the used attribute to instantiate member function
+  // definitions
+  if (Method->hasAttr<UsedAttr>()) {
+    if (auto *A = dyn_cast<CXXRecordDecl>(Owner)) {
+      SourceLocation Loc;
+      if (MemberSpecializationInfo *MSInfo = A->getMemberSpecializationInfo()) {
+        Loc = MSInfo->getPointOfInstantiation();
+      } else if (ClassTemplateSpecializationDecl *Spec =
+                     dyn_cast<ClassTemplateSpecializationDecl>(A)) {
+        Loc = Spec->getPointOfInstantiation();
+      }
+
+      SemaRef.MarkFunctionReferenced(Loc, Method, /*MightBeOdrUse=*/true);
+    }
+  }
+  // end facebook
+
   return Method;
 }
 
Index: test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp
===================================================================
--- /dev/null
+++ test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -O0 -o - %s \
+// RUN:  | FileCheck %s
+
+#define USED __attribute__((used))
+
+namespace InstantiateUsedMemberDefinition {
+  template <typename T> struct S {
+    int USED f() {
+      return 0;
+    }
+  };
+
+  void test() {
+    // Check that InstantiateUsedMemberDefinition::S<int>::f() is defined
+    // as a result of the S class template implicit instantiation
+    // CHECK-DAG: define linkonce_odr i32 @_ZN31InstantiateUsedMemberDefinition1SIiE1fEv
+    S<int> inst;
+  }
+}