diff --git a/clang/include/clang/Basic/DiagnosticCommonKinds.td b/clang/include/clang/Basic/DiagnosticCommonKinds.td
--- a/clang/include/clang/Basic/DiagnosticCommonKinds.td
+++ b/clang/include/clang/Basic/DiagnosticCommonKinds.td
@@ -169,6 +169,11 @@
 
 def err_duplicate_declspec : Error<"%sub{duplicate_declspec}0">;
 
+def warn_redundant_weaker_declspec_constexpr : Warning<
+  "'%0' declaration specifier is redundant due to the presence "
+  "of stricter '%sub{select_constexpr_spec_kind}1' declaration specifier">,
+  InGroup<RedundantDeclSpecifier>;
+
 def err_friend_decl_spec : Error<"'%0' is invalid in friend declarations">;
 
 def err_invalid_member_in_interface : Error<
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -641,6 +641,7 @@
                                      TautologicalObjCBoolCompare]>;
 def HeaderHygiene : DiagGroup<"header-hygiene">;
 def DuplicateDeclSpecifier : DiagGroup<"duplicate-decl-specifier">;
+def RedundantDeclSpecifier : DiagGroup<"redundant-decl-specifier">;
 def CompareDistinctPointerType : DiagGroup<"compare-distinct-pointer-types">;
 def GNUUnionCast : DiagGroup<"gnu-union-cast">;
 def GNUVariableSizedTypeNotAtEnd : DiagGroup<"gnu-variable-sized-type-not-at-end">;
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -2707,6 +2707,7 @@
 
   static bool adjustContextForLocalExternDecl(DeclContext *&DC);
   void DiagnoseFunctionSpecifiers(const DeclSpec &DS);
+  void DiagnoseRedundantSpecifiers(QualType T, const DeclSpec &DS);
   NamedDecl *getShadowedDeclaration(const TypedefNameDecl *D,
                                     const LookupResult &R);
   NamedDecl *getShadowedDeclaration(const VarDecl *D, const LookupResult &R);
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -6209,6 +6209,20 @@
          diag::err_noreturn_non_function);
 }
 
+/// Diagnose specifiers on a declaration of an identifier that
+/// are redundant due to the presence of stricter specifiers
+void Sema::DiagnoseRedundantSpecifiers(QualType T, const DeclSpec &DS) {
+  if (T->isFunctionType()) {
+    // [dcl.constexpr]p1: A function declared with the constexpr or consteval
+    // specifier is implicitly an inline function
+    if (DS.hasConstexprSpecifier() && DS.isInlineSpecified()) {
+      Diag(DS.getInlineSpecLoc(),
+           diag::warn_redundant_weaker_declspec_constexpr)
+          << "inline" << static_cast<int>(DS.getConstexprSpecifier());
+    }
+  }
+}
+
 NamedDecl*
 Sema::ActOnTypedefDeclarator(Scope* S, Declarator& D, DeclContext* DC,
                              TypeSourceInfo *TInfo, LookupResult &Previous) {
@@ -9046,6 +9060,8 @@
   if (R.getCanonicalType()->castAs<FunctionType>()->getCmseNSCallAttr())
     Diag(D.getIdentifierLoc(), diag::err_function_decl_cmse_ns_call);
 
+  DiagnoseRedundantSpecifiers(R, D.getDeclSpec());
+
   SmallVector<TemplateParameterList *, 4> TemplateParamLists;
   for (TemplateParameterList *TPL : TemplateParamListsRef)
     TemplateParamLists.push_back(TPL);
diff --git a/clang/test/Parser/cxx0x-decl.cpp b/clang/test/Parser/cxx0x-decl.cpp
--- a/clang/test/Parser/cxx0x-decl.cpp
+++ b/clang/test/Parser/cxx0x-decl.cpp
@@ -172,6 +172,15 @@
   consteval constinit int huh(); // expected-error {{cannot combine with previous 'consteval'}}
 }
 
+namespace RedundantSpecifier {
+  consteval inline int f1(); // expected-warning {{'inline' declaration specifier is redundant due to the presence of stricter 'consteval' declaration specifier}}
+  inline constexpr int f2(); // expected-warning {{'inline' declaration specifier is redundant due to the presence of stricter 'constexpr' declaration specifier}}
+  inline constexpr inline int f3(); // expected-warning {{'inline' declaration specifier is redundant due to the presence of stricter 'constexpr' declaration specifier}} \
+                                    // expected-warning {{duplicate 'inline' declaration specifier}}
+  template<typename T> inline consteval int f4(T t); // expected-warning {{'inline' declaration specifier is redundant due to the presence of stricter 'consteval' declaration specifier}}
+  inline constexpr int i1 = 0;
+}
+
 namespace ColonColonDecltype {
   struct S { struct T {}; };
   ::decltype(S())::T invalid; // expected-error {{expected unqualified-id}}