Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp	(revision 209303)
+++ lib/Sema/SemaDecl.cpp	(working copy)
@@ -2734,38 +2734,15 @@
 
     // Fall through to diagnose conflicting types.
   }
-
-  // A function that has already been declared has been redeclared or
-  // defined with a different type; show an appropriate diagnostic.
-
   // If the previous declaration was an implicitly-generated builtin
   // declaration, then at the very least we should use a specialized note.
   unsigned BuiltinID;
-  if (Old->isImplicit() && (BuiltinID = Old->getBuiltinID())) {
-    // If it's actually a library-defined builtin function like 'malloc'
-    // or 'printf', just warn about the incompatible redeclaration.
-    if (Context.BuiltinInfo.isPredefinedLibFunction(BuiltinID)) {
-      Diag(New->getLocation(), diag::warn_redecl_library_builtin) << New;
-      Diag(OldLocation, diag::note_previous_builtin_declaration)
-        << Old << Old->getType();
-
-      // If this is a global redeclaration, just forget hereafter
-      // about the "builtin-ness" of the function.
-      //
-      // Doing this for local extern declarations is problematic.  If
-      // the builtin declaration remains visible, a second invalid
-      // local declaration will produce a hard error; if it doesn't
-      // remain visible, a single bogus local redeclaration (which is
-      // actually only a warning) could break all the downstream code.
-      if (!New->getLexicalDeclContext()->isFunctionOrMethod())
-        New->getIdentifier()->setBuiltinID(Builtin::NotBuiltin);
-
+  // This diagnostic is now being issued in one central location.
+  if (Old->isImplicit() && (BuiltinID = Old->getBuiltinID()))
       return false;
-    }
-
-    PrevDiag = diag::note_previous_builtin_declaration;
-  }
-
+    
+  // A function that has already been declared has been redeclared or
+  // defined with a different type; show an appropriate diagnostic.
   Diag(New->getLocation(), diag::err_conflicting_types) << New->getDeclName();
   Diag(OldLocation, PrevDiag) << Old << Old->getType();
   return true;
@@ -4322,10 +4299,11 @@
               R->isFunctionType())) {
       IsLinkageLookup = true;
       CreateBuiltins =
-          CurContext->getEnclosingNamespaceContext()->isTranslationUnit();
+          CurContext->getEnclosingNamespaceContext()->isTranslationUnit()
+            && !ForRedeclaration;
     } else if (CurContext->getRedeclContext()->isTranslationUnit() &&
                D.getDeclSpec().getStorageClassSpec() != DeclSpec::SCS_static)
-      CreateBuiltins = true;
+      CreateBuiltins = !ForRedeclaration;
 
     if (IsLinkageLookup)
       Previous.clear(LookupRedeclarationWithLinkage);
@@ -4401,6 +4379,21 @@
     New = ActOnFunctionDeclarator(S, D, DC, TInfo, Previous,
                                   TemplateParamLists,
                                   AddToScope);
+    if (FunctionDecl *NewFD = dyn_cast<FunctionDecl>(New))
+      if (unsigned BuiltinID = NewFD->getBuiltinID()) {
+        ASTContext::GetBuiltinTypeError Error;
+        QualType T = Context.GetBuiltinType(BuiltinID, Error);
+          if (!T.isNull() && !Context.hasSameType(NewFD->getType(), T)) {
+          // If this is a redeclaration of a library builtin function,
+          // just forget hereafter about the "builtin-ness" of the function.
+          NewFD->getIdentifier()->setBuiltinID(Builtin::NotBuiltin);
+          if (Context.BuiltinInfo.isPredefinedLibFunction(BuiltinID))
+            Diag(NewFD->getLocation(), diag::warn_redecl_library_builtin) << NewFD;
+          else
+            Diag(NewFD->getLocation(), diag::err_conflicting_types) << New;
+          Diag(NewFD->getLocation(), diag::note_previous_builtin_declaration) << NewFD << T;
+        }
+      }
   } else {
     New = ActOnVariableDeclarator(S, D, DC, TInfo, Previous, TemplateParamLists,
                                   AddToScope);
Index: test/CodeGen/locally-redeclared-builtin-call.c
===================================================================
--- test/CodeGen/locally-redeclared-builtin-call.c	(revision 0)
+++ test/CodeGen/locally-redeclared-builtin-call.c	(working copy)
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck %s
+// rdar://16897451
+
+int Test()
+{
+  int a,b;
+  int pow (int,int);
+  return pow(a,b);
+}
+// CHECK-NOT: call i32 @llvm.pow.i32
+// CHECK: [[CALL:%.*]]  = call i32 @pow(i32 %0, i32 %1)
+// ret i32 [[CALL]]
+
+int pow(int c,int d)
+{
+  return c*d;
+}
Index: test/Sema/builtins-arm.c
===================================================================
--- test/Sema/builtins-arm.c	(revision 209534)
+++ test/Sema/builtins-arm.c	(working copy)
@@ -3,13 +3,15 @@
 // RUN:   -fsyntax-only -verify %s
 
 void f(void *a, void *b) {
-  __clear_cache(); // expected-error {{too few arguments to function call, expected 2, have 0}} // expected-note {{'__clear_cache' is a builtin with type 'void (void *, void *)}}
+  __clear_cache(); // expected-error {{too few arguments to function call, expected 2, have 0}}
   __clear_cache(a); // expected-error {{too few arguments to function call, expected 2, have 1}}
   __clear_cache(a, b);
 }
 
-void __clear_cache(char*, char*); // expected-error {{conflicting types for '__clear_cache'}}
-void __clear_cache(void*, void*);
+void __clear_cache(char*, char*); // expected-error {{conflicting types for '__clear_cache'}} \
+				  // expected-note {{'__clear_cache' is a builtin with type 'void (void *, void *)'}} \
+				  // expected-note {{previous declaration is here}}
+void __clear_cache(void*, void*); // expected-error {{conflicting types for '__clear_cache'}}
 
 #if defined(__ARM_PCS) || defined(__ARM_EABI__)
 // va_list on ARM AAPCS is struct { void* __ap }.
Index: test/Sema/extern-redecl.c
===================================================================
--- test/Sema/extern-redecl.c	(revision 209558)
+++ test/Sema/extern-redecl.c	(working copy)
@@ -45,21 +45,23 @@
 
 // Test that invalid local extern declarations of library
 // builtins behave reasonably.
-extern void abort(void); // expected-note 2 {{previous declaration is here}}
+extern void abort(void); // expected-note 2 {{previous declaration is here}} \
+                         // expected-warning {{incompatible redeclaration of library function 'abort'}} \
+                         // expected-note {{'abort' is a builtin with type 'void (void) __attribute__((noreturn))'}}
 extern float *calloc(); // expected-warning {{incompatible redeclaration of library function}} expected-note {{is a builtin}} expected-note 2 {{previous declaration is here}}
 void test5a() {
   int abort(); // expected-error {{conflicting types}}
-  float *malloc(); // expected-warning {{incompatible redeclaration of library function}} expected-note 2 {{is a builtin}}
+  float *malloc(); // expected-warning {{incompatible redeclaration of library function}} expected-note 1 {{is a builtin}}
   int *calloc(); // expected-error {{conflicting types}}
 }
 void test5b() {
   int abort(); // expected-error {{conflicting types}}
-  float *malloc(); // expected-warning {{incompatible redeclaration of library function}}
+  float *malloc();
   int *calloc(); // expected-error {{conflicting types}}
 }
 void test5c() {
   void (*_abort)(void) = &abort;
-  void *(*_malloc)() = &malloc;
+  void *(*_malloc)() = &malloc; // expected-error {{use of undeclared identifier 'malloc'}}
   float *(*_calloc)() = &calloc;
 }
 
Index: test/Sema/format-strings.c
===================================================================
--- test/Sema/format-strings.c	(revision 209303)
+++ test/Sema/format-strings.c	(working copy)
@@ -13,7 +13,8 @@
 int sprintf(char *restrict, const char *restrict, ...);
 int vasprintf(char **, const char *, va_list);
 int asprintf(char **, const char *, ...);
-int vfprintf(FILE *, const char *restrict, va_list);
+int vfprintf(FILE *, const char *restrict, va_list); // expected-warning {{incompatible redeclaration of library function 'vfprintf'}} \
+						     // expected-note {{'vfprintf' is a builtin with type 'int ()'}}
 int vprintf(const char *restrict, va_list);
 int vsnprintf(char *, size_t, const char *, va_list);
 int vsprintf(char *restrict, const char *restrict, va_list); // expected-note{{passing argument to parameter here}}
Index: test/Sema/implicit-builtin-decl.c
===================================================================
--- test/Sema/implicit-builtin-decl.c	(revision 209303)
+++ test/Sema/implicit-builtin-decl.c	(working copy)
@@ -35,7 +35,7 @@
 int a[10];
 
 int f0() {
-  return __builtin_object_size(&a); // expected-error {{too few arguments to function}}
+  return __builtin_object_size(&a); // expected-error {{returning 'void' from a function with incompatible result type 'int'}}
 }
 
 void * realloc(void *p, int size) { // expected-warning{{incompatible redeclaration of library function 'realloc'}} \
Index: test/Sema/knr-def-call.c
===================================================================
--- test/Sema/knr-def-call.c	(revision 209303)
+++ test/Sema/knr-def-call.c	(working copy)
@@ -19,11 +19,12 @@
 
 // <rdar://problem/8193107>
 void f4() {
-    char *rindex();
+    char *rindex(); // expected-warning {{incompatible redeclaration of library function 'rindex'}} \
+		    // expected-note {{'rindex' is a builtin with type 'char *(const char *, int)'}}
 }
 
 char *rindex(s, c)
-     register char *s, c; // expected-warning{{promoted type 'char *' of K&R function parameter is not compatible with the parameter type 'const char *' declared in a previous prototype}}
+     register char *s, c;
 {
   return 0;
 }
Index: test/Sema/knr-variadic-def.c
===================================================================
--- test/Sema/knr-variadic-def.c	(revision 209303)
+++ test/Sema/knr-variadic-def.c	(working copy)
@@ -20,7 +20,7 @@
         return x;
 }
 
-void exit();
+void exit(int) __attribute__((noreturn));
 
 int main(argc,argv)
         int argc;char**argv;
Index: test/Sema/return.c
===================================================================
--- test/Sema/return.c	(revision 209303)
+++ test/Sema/return.c	(working copy)
@@ -192,7 +192,7 @@
 void test28() __attribute__((noreturn));
 void test28(x) { while (1) { } }
 
-void exit(int);
+void exit(int) __attribute__((noreturn));
 int test29() {
   exit(1);
 }
Index: test/Sema/vfprintf-valid-redecl.c
===================================================================
--- test/Sema/vfprintf-valid-redecl.c	(revision 209303)
+++ test/Sema/vfprintf-valid-redecl.c	(working copy)
@@ -7,7 +7,7 @@
 // Clang has defined 'vfprint' in builtin list. If the following line occurs before any other
 // `vfprintf' in this file, and we getPreviousDecl()->getTypeSourceInfo() on it, then we will
 // get a null pointer since the one in builtin list doesn't has valid TypeSourceInfo.
-int vfprintf(void) { return 0; }
+int vfprintf() { return 0; }
 #endif
 
 // PR4290