Index: test/SemaCXX/warn-unique-enum.cpp
===================================================================
--- test/SemaCXX/warn-unique-enum.cpp	(revision 0)
+++ test/SemaCXX/warn-unique-enum.cpp	(revision 0)
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 %s -fsyntax-only -verify -Wunique-enum
+enum A { A1 = 1, A2 = 1, A3 = 1 };  // expected-warning {{all elements of 'A' have value 1}}
+enum { B1 = 1, B2 = 1, B3 = 1 };  // expected-warning {{all elements of anonymous enum have value 1}}
+enum C { C1 = true, C2 = true}; // expected-warning {{all elements of 'C' have value 1}}
+enum D { D1 = 5, D2 = 5L, D3 = 5UL, D4 = 5LL, D5 = 5ULL };  // expected-warning {{all elements of 'D' have value 5}}
+
+// Don't warn on enums with less than 2 elements.
+enum E { E1 = 4 };
+enum F { F1 };
+enum G {};
+
+// Don't warn when integer literals do not initialize the elements.
+enum H { H1 = 4, H_MAX = H1, H_MIN = H1 };
+enum I { I1 = H1, I2 = 4 };
+enum J { J1 = 4, J2 = I2 };
+enum K { K1, K2, K3, K4 };
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td	(revision 156690)
+++ include/clang/Basic/DiagnosticSemaKinds.td	(working copy)
@@ -20,6 +20,10 @@
   "used in loop condition not modified in loop body">,
   InGroup<DiagGroup<"loop-analysis">>, DefaultIgnore;
 
+def warn_identical_enum_values : Warning<
+  "all elements of %select{anonymous enum|%1}0 have value %2">,
+  InGroup<DiagGroup<"unique-enum">>;
+
 // Constant expressions
 def err_expr_not_ice : Error<
   "expression is not an %select{integer|integral}0 constant expression">;
Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp	(revision 156690)
+++ lib/Sema/SemaDecl.cpp	(working copy)
@@ -10219,6 +10219,48 @@
   return New;
 }
 
+// Emits a warning if every element in the enum is the same value and if
+// every element is initialized with a integer or boolean literal.
+static void CheckForUniqueEnumValues(Sema &S, Decl **Elements,
+                                     unsigned NumElements, EnumDecl *Enum,
+                                     QualType EnumType) {
+  if (S.Diags.getDiagnosticLevel(diag::warn_identical_enum_values,
+                                 Enum->getLocation()) ==
+      DiagnosticsEngine::Ignored)
+    return;
+
+  if (NumElements < 2)
+    return;
+
+  llvm::APSInt FirstVal;
+
+  for (unsigned i = 0; i != NumElements; ++i) {
+    EnumConstantDecl *ECD = cast_or_null<EnumConstantDecl>(Elements[i]);
+    if (!ECD)
+      return;
+
+    Expr *InitExpr = ECD->getInitExpr();
+    if (!InitExpr)
+      return;
+    InitExpr = InitExpr->IgnoreImpCasts();
+    if (!isa<IntegerLiteral>(InitExpr) && !isa<CXXBoolLiteralExpr>(InitExpr))
+      return;
+
+    if (i == 0) {
+      FirstVal = ECD->getInitVal();
+      continue;
+    }
+
+    if (FirstVal != ECD->getInitVal())
+      return;
+  }
+
+  bool hasIdentifier = Enum->getIdentifier();
+  S.Diag(Enum->getLocation(), diag::warn_identical_enum_values)
+      << hasIdentifier << EnumType << FirstVal.toString(10)
+      << Enum->getSourceRange();
+}
+
 void Sema::ActOnEnumBody(SourceLocation EnumLoc, SourceLocation LBraceLoc,
                          SourceLocation RBraceLoc, Decl *EnumDeclX,
                          Decl **Elements, unsigned NumElements,
@@ -10442,6 +10484,7 @@
   if (InFunctionDeclarator)
     DeclsInPrototypeScope.push_back(Enum);
 
+  CheckForUniqueEnumValues(*this, Elements, NumElements, Enum, EnumType);
 }
 
 Decl *Sema::ActOnFileScopeAsmDecl(Expr *expr,