Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -14197,16 +14197,22 @@
                                       SourceLocation PragmaLoc,
                                       SourceLocation NameLoc,
                                       SourceLocation AliasNameLoc) {
-  Decl *PrevDecl = LookupSingleName(TUScope, Name, NameLoc,
-                                    LookupOrdinaryName);
-  AsmLabelAttr *Attr = ::new (Context) AsmLabelAttr(AliasNameLoc, Context,
-                                                    AliasName->getName(), 0);
-
-  if (PrevDecl) 
-    PrevDecl->addAttr(Attr);
-  else 
+  NamedDecl *PrevDecl = LookupSingleName(TUScope, Name, NameLoc,
+                                         LookupOrdinaryName);
+  // If a declaration that:
+  // 1) declares a function or a variable
+  // 2) has external linkage
+  // already exists, add a label attribute to it.
+  if (PrevDecl &&
+      (isa<FunctionDecl>(PrevDecl) || isa<VarDecl>(PrevDecl)) &&
+      PrevDecl->hasExternalFormalLinkage())
+    PrevDecl->addAttr(AsmLabelAttr::CreateImplicit(
+        Context, AliasName->getName(), AliasNameLoc));
+  // Otherwise, add a label atttibute to ExtnameUndeclaredIdentifiers.
+  else
     (void)ExtnameUndeclaredIdentifiers.insert(
-      std::pair<IdentifierInfo*,AsmLabelAttr*>(Name, Attr));
+      std::make_pair(Name, AsmLabelAttr::CreateImplicit(
+          Context, AliasName->getName(), AliasNameLoc)));
 }
 
 void Sema::ActOnPragmaWeakID(IdentifierInfo* Name,
Index: test/CodeGen/redefine_extname.c
===================================================================
--- test/CodeGen/redefine_extname.c
+++ test/CodeGen/redefine_extname.c
@@ -3,6 +3,12 @@
 #pragma redefine_extname fake real
 #pragma redefine_extname name alias
 
+struct statvfs64 {
+  int f;
+};
+#pragma redefine_extname statvfs64 statvfs
+int statvfs64(struct statvfs64 *);
+
 extern int fake(void);
 
 int name;
@@ -13,3 +19,12 @@
 // CHECK:   call i32 @real()
 // Check that this also works with variables names
 // CHECK:   load i32, i32* @alias
+
+void foo() {
+  struct statvfs64 st;
+  statvfs64(&st);
+// Check that even if there is a structure with redefined name before the
+// pragma, subsequent function name redefined properly. PR5172, Comment 11.
+// CHECK:  call i32 @statvfs(%struct.statvfs64* %st)
+}
+