[clang] Add scoped enum support to `StreamingDiagnostic` (#138089)

This patch adds templated `operator<<` for diagnostics that pass scoped
enums, saving people from `llvm::to_underlying()` clutter on the side of
emitting the diagnostic. This eliminates 80 out of 220 usages of
`llvm::to_underlying()` in Clang.

I also backported `std::is_scoped_enum_v` from C++23.

17 files changed, 78 insertions, 106 deletions

diff --git a/clang/lib/Sema/SemaAccess.cpp b/clang/lib/Sema/SemaAccess.cpp
index b77cbdb..890df09 100644
--- a/clang/lib/Sema/SemaAccess.cpp
+++ b/clang/lib/Sema/SemaAccess.cpp
@@ -1670,24 +1670,21 @@ Sema::AccessResult Sema::CheckConstructorAccess(SourceLocation UseLoc,
   case InitializedEntity::EK_Base:
     PD = PDiag(diag::err_access_base_ctor);
     PD << Entity.isInheritedVirtualBase()
-       << Entity.getBaseSpecifier()->getType()
-       << llvm::to_underlying(getSpecialMember(Constructor));
+       << Entity.getBaseSpecifier()->getType() << getSpecialMember(Constructor);
     break;
 
   case InitializedEntity::EK_Member:
   case InitializedEntity::EK_ParenAggInitMember: {
     const FieldDecl *Field = cast<FieldDecl>(Entity.getDecl());
     PD = PDiag(diag::err_access_field_ctor);
-    PD << Field->getType()
-       << llvm::to_underlying(getSpecialMember(Constructor));
+    PD << Field->getType() << getSpecialMember(Constructor);
     break;
   }
 
   case InitializedEntity::EK_LambdaCapture: {
     StringRef VarName = Entity.getCapturedVarName();
     PD = PDiag(diag::err_access_lambda_capture);
-    PD << VarName << Entity.getType()
-       << llvm::to_underlying(getSpecialMember(Constructor));
+    PD << VarName << Entity.getType() << getSpecialMember(Constructor);
     break;
   }
 
diff --git a/clang/lib/Sema/SemaCUDA.cpp b/clang/lib/Sema/SemaCUDA.cpp
index 0a8c24f..4559506 100644
--- a/clang/lib/Sema/SemaCUDA.cpp
+++ b/clang/lib/Sema/SemaCUDA.cpp
@@ -450,8 +450,7 @@ bool SemaCUDA::inferTargetForImplicitSpecialMember(CXXRecordDecl *ClassDecl,
         if (Diagnose) {
           Diag(ClassDecl->getLocation(),
                diag::note_implicit_member_target_infer_collision)
-              << (unsigned)CSM << llvm::to_underlying(*InferredTarget)
-              << llvm::to_underlying(BaseMethodTarget);
+              << (unsigned)CSM << *InferredTarget << BaseMethodTarget;
         }
         MemberDecl->addAttr(
             CUDAInvalidTargetAttr::CreateImplicit(getASTContext()));
@@ -496,8 +495,7 @@ bool SemaCUDA::inferTargetForImplicitSpecialMember(CXXRecordDecl *ClassDecl,
         if (Diagnose) {
           Diag(ClassDecl->getLocation(),
                diag::note_implicit_member_target_infer_collision)
-              << (unsigned)CSM << llvm::to_underlying(*InferredTarget)
-              << llvm::to_underlying(FieldMethodTarget);
+              << (unsigned)CSM << *InferredTarget << FieldMethodTarget;
         }
         MemberDecl->addAttr(
             CUDAInvalidTargetAttr::CreateImplicit(getASTContext()));
@@ -713,7 +711,7 @@ void SemaCUDA::checkAllowedInitializer(VarDecl *VD) {
       if (InitFnTarget != CUDAFunctionTarget::Host &&
           InitFnTarget != CUDAFunctionTarget::HostDevice) {
         Diag(VD->getLocation(), diag::err_ref_bad_target_global_initializer)
-            << llvm::to_underlying(InitFnTarget) << InitFn;
+            << InitFnTarget << InitFn;
         Diag(InitFn->getLocation(), diag::note_previous_decl) << InitFn;
         VD->setInvalidDecl();
       }
@@ -952,8 +950,8 @@ bool SemaCUDA::CheckCall(SourceLocation Loc, FunctionDecl *Callee) {
 
   SemaDiagnosticBuilder(DiagKind, Loc, diag::err_ref_bad_target, Caller,
                         SemaRef)
-      << llvm::to_underlying(IdentifyTarget(Callee)) << /*function*/ 0 << Callee
-      << llvm::to_underlying(IdentifyTarget(Caller));
+      << IdentifyTarget(Callee) << /*function*/ 0 << Callee
+      << IdentifyTarget(Caller);
   if (!Callee->getBuiltinID())
     SemaDiagnosticBuilder(DiagKind, Callee->getLocation(),
                           diag::note_previous_decl, Caller, SemaRef)
@@ -1049,8 +1047,7 @@ void SemaCUDA::checkTargetOverload(FunctionDecl *NewFD,
           (NewTarget == CUDAFunctionTarget::Global) ||
           (OldTarget == CUDAFunctionTarget::Global)) {
         Diag(NewFD->getLocation(), diag::err_cuda_ovl_target)
-            << llvm::to_underlying(NewTarget) << NewFD->getDeclName()
-            << llvm::to_underlying(OldTarget) << OldFD;
+            << NewTarget << NewFD->getDeclName() << OldTarget << OldFD;
         Diag(OldFD->getLocation(), diag::note_previous_declaration);
         NewFD->setInvalidDecl();
         break;
@@ -1060,7 +1057,7 @@ void SemaCUDA::checkTargetOverload(FunctionDecl *NewFD,
           (NewTarget == CUDAFunctionTarget::Device &&
            OldTarget == CUDAFunctionTarget::Host)) {
         Diag(NewFD->getLocation(), diag::warn_offload_incompatible_redeclare)
-            << llvm::to_underlying(NewTarget) << llvm::to_underlying(OldTarget);
+            << NewTarget << OldTarget;
         Diag(OldFD->getLocation(), diag::note_previous_declaration);
       }
     }
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 2d64889..92ec2fe 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -8339,8 +8339,7 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
       } else {
         EmitFormatDiagnostic(
             S.PDiag(diag::warn_non_pod_vararg_with_format_string)
-                << S.getLangOpts().CPlusPlus11 << ExprTy
-                << llvm::to_underlying(CallType)
+                << S.getLangOpts().CPlusPlus11 << ExprTy << CallType
                 << AT.getRepresentativeTypeName(S.Context) << CSR
                 << E->getSourceRange(),
             E->getBeginLoc(), /*IsStringLocation*/ false, CSR);
@@ -8354,8 +8353,7 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
       else if (ExprTy->isObjCObjectType())
         EmitFormatDiagnostic(
             S.PDiag(diag::err_cannot_pass_objc_interface_to_vararg_format)
-                << S.getLangOpts().CPlusPlus11 << ExprTy
-                << llvm::to_underlying(CallType)
+                << S.getLangOpts().CPlusPlus11 << ExprTy << CallType
                 << AT.getRepresentativeTypeName(S.Context) << CSR
                 << E->getSourceRange(),
             E->getBeginLoc(), /*IsStringLocation*/ false, CSR);
@@ -8363,7 +8361,7 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
         // FIXME: If this is an initializer list, suggest removing the braces
         // or inserting a cast to the target type.
         S.Diag(E->getBeginLoc(), diag::err_cannot_pass_to_vararg_format)
-            << isa<InitListExpr>(E) << ExprTy << llvm::to_underlying(CallType)
+            << isa<InitListExpr>(E) << ExprTy << CallType
             << AT.getRepresentativeTypeName(S.Context) << E->getSourceRange();
       break;
     }
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 517b3067..a3285e8 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -4034,13 +4034,13 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, NamedDecl *&OldD, Scope *S,
         } else {
           Diag(NewMethod->getLocation(),
                diag::err_definition_of_implicitly_declared_member)
-              << New << llvm::to_underlying(getSpecialMember(OldMethod));
+              << New << getSpecialMember(OldMethod);
           return true;
         }
       } else if (OldMethod->getFirstDecl()->isExplicitlyDefaulted() && !isFriend) {
         Diag(NewMethod->getLocation(),
              diag::err_definition_of_explicitly_defaulted_member)
-            << llvm::to_underlying(getSpecialMember(OldMethod));
+            << getSpecialMember(OldMethod);
         return true;
       }
     }
@@ -5249,7 +5249,7 @@ Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
   if (DS.isModulePrivateSpecified() &&
       Tag && Tag->getDeclContext()->isFunctionOrMethod())
     Diag(DS.getModulePrivateSpecLoc(), diag::err_module_private_local_class)
-        << llvm::to_underlying(Tag->getTagKind())
+        << Tag->getTagKind()
         << FixItHint::CreateRemoval(DS.getModulePrivateSpecLoc());
 
   ActOnDocumentableDecl(TagD);
@@ -7722,15 +7722,14 @@ NamedDecl *Sema::ActOnVariableDeclarator(
             // data members.
             Diag(D.getIdentifierLoc(),
                  diag::err_static_data_member_not_allowed_in_local_class)
-                << Name << RD->getDeclName()
-                << llvm::to_underlying(RD->getTagKind());
+                << Name << RD->getDeclName() << RD->getTagKind();
           } else if (AnonStruct) {
             // C++ [class.static.data]p4: Unnamed classes and classes contained
             // directly or indirectly within unnamed classes shall not contain
             // static data members.
             Diag(D.getIdentifierLoc(),
                  diag::err_static_data_member_not_allowed_in_anon_struct)
-                << Name << llvm::to_underlying(AnonStruct->getTagKind());
+                << Name << AnonStruct->getTagKind();
             Invalid = true;
           } else if (RD->isUnion()) {
             // C++98 [class.union]p1: If a union contains a static data member,
@@ -17661,7 +17660,7 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
 
       // A tag 'foo::bar' must already exist.
       Diag(NameLoc, diag::err_not_tag_in_scope)
-          << llvm::to_underlying(Kind) << Name << DC << SS.getRange();
+          << Kind << Name << DC << SS.getRange();
       Name = nullptr;
       Invalid = true;
       goto CreateNewDecl;
@@ -18119,7 +18118,7 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
           !Previous.isForRedeclaration()) {
         NonTagKind NTK = getNonTagTypeDeclKind(PrevDecl, Kind);
         Diag(NameLoc, diag::err_tag_reference_non_tag)
-            << PrevDecl << NTK << llvm::to_underlying(Kind);
+            << PrevDecl << NTK << Kind;
         Diag(PrevDecl->getLocation(), diag::note_declared_at);
         Invalid = true;
 
@@ -19018,8 +19017,7 @@ bool Sema::CheckNontrivialField(FieldDecl *FD) {
             getLangOpts().CPlusPlus11
                 ? diag::warn_cxx98_compat_nontrivial_union_or_anon_struct_member
                 : diag::err_illegal_union_or_anon_struct_member)
-            << FD->getParent()->isUnion() << FD->getDeclName()
-            << llvm::to_underlying(member);
+            << FD->getParent()->isUnion() << FD->getDeclName() << member;
         DiagnoseNontrivial(RDecl, member);
         return !getLangOpts().CPlusPlus11;
       }
@@ -19359,8 +19357,7 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
         unsigned DiagID = 0;
         if (!Record->isUnion() && !IsLastField) {
           Diag(FD->getLocation(), diag::err_flexible_array_not_at_end)
-              << FD->getDeclName() << FD->getType()
-              << llvm::to_underlying(Record->getTagKind());
+              << FD->getDeclName() << FD->getType() << Record->getTagKind();
           Diag((*(i + 1))->getLocation(), diag::note_next_field_declaration);
           FD->setInvalidDecl();
           EnclosingDecl->setInvalidDecl();
@@ -19376,7 +19373,7 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
 
         if (DiagID)
           Diag(FD->getLocation(), DiagID)
-              << FD->getDeclName() << llvm::to_underlying(Record->getTagKind());
+              << FD->getDeclName() << Record->getTagKind();
         // While the layout of types that contain virtual bases is not specified
         // by the C++ standard, both the Itanium and Microsoft C++ ABIs place
         // virtual bases after the derived members.  This would make a flexible
@@ -19384,10 +19381,10 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
         // of the type.
         if (CXXRecord && CXXRecord->getNumVBases() != 0)
           Diag(FD->getLocation(), diag::err_flexible_array_virtual_base)
-              << FD->getDeclName() << llvm::to_underlying(Record->getTagKind());
+              << FD->getDeclName() << Record->getTagKind();
         if (!getLangOpts().C99)
           Diag(FD->getLocation(), diag::ext_c99_flexible_array_member)
-              << FD->getDeclName() << llvm::to_underlying(Record->getTagKind());
+              << FD->getDeclName() << Record->getTagKind();
 
         // If the element type has a non-trivial destructor, we would not
         // implicitly destroy the elements, so disallow it for now.
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index ab66ae8..9d6a1c7 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -5058,7 +5058,7 @@ static void handleSharedAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   }
   if (S.getLangOpts().CUDA && VD->hasLocalStorage() &&
       S.CUDA().DiagIfHostCode(AL.getLoc(), diag::err_cuda_host_shared)
-          << llvm::to_underlying(S.CUDA().CurrentTarget()))
+          << S.CUDA().CurrentTarget())
     return;
   D->addAttr(::new (S.Context) CUDASharedAttr(S.Context, AL));
 }
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 645a088..a7e6868 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -647,7 +647,7 @@ bool Sema::MergeCXXFunctionDecl(FunctionDecl *New, FunctionDecl *Old,
       ParmVarDecl *NewParam = New->getParamDecl(New->getMinRequiredArguments());
       assert(NewParam->hasDefaultArg());
       Diag(NewParam->getLocation(), diag::err_default_arg_makes_ctor_special)
-          << NewParam->getDefaultArgRange() << llvm::to_underlying(NewSM);
+          << NewParam->getDefaultArgRange() << NewSM;
       Diag(Old->getLocation(), diag::note_previous_declaration);
     }
   }
@@ -6978,7 +6978,7 @@ void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
           (F->getType().isConstQualified() && F->getType()->isScalarType())) {
         if (!Complained) {
           Diag(Record->getLocation(), diag::warn_no_constructor_for_refconst)
-              << llvm::to_underlying(Record->getTagKind()) << Record;
+              << Record->getTagKind() << Record;
           Complained = true;
         }
 
@@ -7774,14 +7774,14 @@ bool Sema::CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
     // default argument is classified as a default constructor, and assignment
     // operations and destructors can't have default arguments.
     Diag(MD->getLocation(), diag::err_defaulted_special_member_params)
-        << llvm::to_underlying(CSM) << MD->getSourceRange();
+        << CSM << MD->getSourceRange();
     HadError = true;
   } else if (MD->isVariadic()) {
     if (DeleteOnTypeMismatch)
       ShouldDeleteForTypeMismatch = true;
     else {
       Diag(MD->getLocation(), diag::err_defaulted_special_member_variadic)
-          << llvm::to_underlying(CSM) << MD->getSourceRange();
+          << CSM << MD->getSourceRange();
       HadError = true;
     }
   }
@@ -7868,7 +7868,7 @@ bool Sema::CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
       else {
         Diag(MD->getLocation(),
              diag::err_defaulted_special_member_volatile_param)
-            << llvm::to_underlying(CSM);
+            << CSM;
         HadError = true;
       }
     }
@@ -7929,12 +7929,12 @@ bool Sema::CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
         if (!MD->isConsteval() && RD->getNumVBases()) {
           Diag(MD->getBeginLoc(),
                diag::err_incorrect_defaulted_constexpr_with_vb)
-              << llvm::to_underlying(CSM);
+              << CSM;
           for (const auto &I : RD->vbases())
             Diag(I.getBeginLoc(), diag::note_constexpr_virtual_base_here);
         } else {
           Diag(MD->getBeginLoc(), diag::err_incorrect_defaulted_constexpr)
-              << llvm::to_underlying(CSM) << MD->isConsteval();
+              << CSM << MD->isConsteval();
         }
         HadError = true;
         // FIXME: Explain why the special member can't be constexpr.
@@ -7967,11 +7967,9 @@ bool Sema::CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
     if (First) {
       SetDeclDeleted(MD, MD->getLocation());
       if (!inTemplateInstantiation() && !HadError) {
-        Diag(MD->getLocation(), diag::warn_defaulted_method_deleted)
-            << llvm::to_underlying(CSM);
+        Diag(MD->getLocation(), diag::warn_defaulted_method_deleted) << CSM;
         if (ShouldDeleteForTypeMismatch) {
-          Diag(MD->getLocation(), diag::note_deleted_type_mismatch)
-              << llvm::to_underlying(CSM);
+          Diag(MD->getLocation(), diag::note_deleted_type_mismatch) << CSM;
         } else if (ShouldDeleteSpecialMember(MD, CSM, nullptr,
                                              /*Diagnose*/ true) &&
                    DefaultLoc.isValid()) {
@@ -7982,14 +7980,13 @@ bool Sema::CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
       if (ShouldDeleteForTypeMismatch && !HadError) {
         Diag(MD->getLocation(),
              diag::warn_cxx17_compat_defaulted_method_type_mismatch)
-            << llvm::to_underlying(CSM);
+            << CSM;
       }
     } else {
       // C++11 [dcl.fct.def.default]p4:
       //   [For a] user-provided explicitly-defaulted function [...] if such a
       //   function is implicitly defined as deleted, the program is ill-formed.
-      Diag(MD->getLocation(), diag::err_out_of_line_default_deletes)
-          << llvm::to_underlying(CSM);
+      Diag(MD->getLocation(), diag::err_out_of_line_default_deletes) << CSM;
       assert(!ShouldDeleteForTypeMismatch && "deleted non-first decl");
       ShouldDeleteSpecialMember(MD, CSM, nullptr, /*Diagnose*/true);
       HadError = true;
@@ -9555,16 +9552,15 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
     if (Field) {
       S.Diag(Field->getLocation(),
              diag::note_deleted_special_member_class_subobject)
-          << llvm::to_underlying(getEffectiveCSM()) << MD->getParent()
-          << /*IsField*/ true << Field << DiagKind << IsDtorCallInCtor
-          << /*IsObjCPtr*/ false;
+          << getEffectiveCSM() << MD->getParent() << /*IsField*/ true << Field
+          << DiagKind << IsDtorCallInCtor << /*IsObjCPtr*/ false;
     } else {
       CXXBaseSpecifier *Base = cast<CXXBaseSpecifier *>(Subobj);
       S.Diag(Base->getBeginLoc(),
              diag::note_deleted_special_member_class_subobject)
-          << llvm::to_underlying(getEffectiveCSM()) << MD->getParent()
-          << /*IsField*/ false << Base->getType() << DiagKind
-          << IsDtorCallInCtor << /*IsObjCPtr*/ false;
+          << getEffectiveCSM() << MD->getParent() << /*IsField*/ false
+          << Base->getType() << DiagKind << IsDtorCallInCtor
+          << /*IsObjCPtr*/ false;
     }
 
     if (DiagKind == 1)
@@ -9633,9 +9629,8 @@ bool SpecialMemberDeletionInfo::shouldDeleteForVariantObjCPtrMember(
   if (Diagnose) {
     auto *ParentClass = cast<CXXRecordDecl>(FD->getParent());
     S.Diag(FD->getLocation(), diag::note_deleted_special_member_class_subobject)
-        << llvm::to_underlying(getEffectiveCSM()) << ParentClass
-        << /*IsField*/ true << FD << 4 << /*IsDtorCallInCtor*/ false
-        << /*IsObjCPtr*/ true;
+        << getEffectiveCSM() << ParentClass << /*IsField*/ true << FD << 4
+        << /*IsDtorCallInCtor*/ false << /*IsObjCPtr*/ true;
   }
 
   return true;
@@ -9658,8 +9653,8 @@ bool SpecialMemberDeletionInfo::shouldDeleteForVariantPtrAuthMember(
   if (Diagnose) {
     auto *ParentClass = cast<CXXRecordDecl>(FD->getParent());
     S.Diag(FD->getLocation(), diag::note_deleted_special_member_class_subobject)
-        << llvm::to_underlying(getEffectiveCSM()) << ParentClass
-        << /*IsField*/ true << FD << 4 << /*IsDtorCallInCtor*/ false << 2;
+        << getEffectiveCSM() << ParentClass << /*IsField*/ true << FD << 4
+        << /*IsDtorCallInCtor*/ false << 2;
   }
 
   return true;
@@ -9684,9 +9679,9 @@ bool SpecialMemberDeletionInfo::shouldDeleteForBase(CXXBaseSpecifier *Base) {
     if (BaseCtor->isDeleted() && Diagnose) {
       S.Diag(Base->getBeginLoc(),
              diag::note_deleted_special_member_class_subobject)
-          << llvm::to_underlying(getEffectiveCSM()) << MD->getParent()
-          << /*IsField*/ false << Base->getType() << /*Deleted*/ 1
-          << /*IsDtorCallInCtor*/ false << /*IsObjCPtr*/ false;
+          << getEffectiveCSM() << MD->getParent() << /*IsField*/ false
+          << Base->getType() << /*Deleted*/ 1 << /*IsDtorCallInCtor*/ false
+          << /*IsObjCPtr*/ false;
       S.NoteDeletedFunction(BaseCtor);
     }
     return BaseCtor->isDeleted();
@@ -10182,21 +10177,20 @@ static bool checkTrivialSubobjectCall(Sema &S, SourceLocation SubobjLoc,
         S.Diag(CD->getLocation(), diag::note_user_declared_ctor);
     } else if (!Selected)
       S.Diag(SubobjLoc, diag::note_nontrivial_no_copy)
-          << Kind << SubType.getUnqualifiedType() << llvm::to_underlying(CSM)
-          << SubType;
+          << Kind << SubType.getUnqualifiedType() << CSM << SubType;
     else if (Selected->isUserProvided()) {
       if (Kind == TSK_CompleteObject)
         S.Diag(Selected->getLocation(), diag::note_nontrivial_user_provided)
-            << Kind << SubType.getUnqualifiedType() << llvm::to_underlying(CSM);
+            << Kind << SubType.getUnqualifiedType() << CSM;
       else {
         S.Diag(SubobjLoc, diag::note_nontrivial_user_provided)
-            << Kind << SubType.getUnqualifiedType() << llvm::to_underlying(CSM);
+            << Kind << SubType.getUnqualifiedType() << CSM;
         S.Diag(Selected->getLocation(), diag::note_declared_at);
       }
     } else {
       if (Kind != TSK_CompleteObject)
         S.Diag(SubobjLoc, diag::note_nontrivial_subobject)
-            << Kind << SubType.getUnqualifiedType() << llvm::to_underlying(CSM);
+            << Kind << SubType.getUnqualifiedType() << CSM;
 
       // Explain why the defaulted or deleted special member isn't trivial.
       S.SpecialMemberIsTrivial(Selected, CSM, Sema::TAH_IgnoreTrivialABI,
@@ -11471,7 +11465,7 @@ Decl *Sema::ActOnConversionDeclarator(CXXConversionDecl *Conversion) {
     if (ConvType->isUndeducedAutoType()) {
       Diag(Conversion->getTypeSpecStartLoc(), diag::err_auto_not_allowed)
           << getReturnTypeLoc(Conversion).getSourceRange()
-          << llvm::to_underlying(ConvType->castAs<AutoType>()->getKeyword())
+          << ConvType->castAs<AutoType>()->getKeyword()
           << /* in declaration of conversion function template= */ 24;
     }
 
diff --git a/clang/lib/Sema/SemaDeclObjC.cpp b/clang/lib/Sema/SemaDeclObjC.cpp
index 0a14ce2..501d441 100644
--- a/clang/lib/Sema/SemaDeclObjC.cpp
+++ b/clang/lib/Sema/SemaDeclObjC.cpp
@@ -3890,7 +3890,7 @@ static void DiagnoseVariableSizedIvars(Sema &S, ObjCContainerDecl *OCD) {
     if (IvarTy->isIncompleteArrayType()) {
       S.Diag(ivar->getLocation(), diag::err_flexible_array_not_at_end)
           << ivar->getDeclName() << IvarTy
-          << llvm::to_underlying(TagTypeKind::Class); // Use "class" for Obj-C.
+          << TagTypeKind::Class; // Use "class" for Obj-C.
       IsInvalidIvar = true;
     } else if (const RecordType *RecordTy = IvarTy->getAs<RecordType>()) {
       if (RecordTy->getDecl()->hasFlexibleArrayMember()) {
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index b1cdf37..b686707 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -1022,8 +1022,7 @@ void Sema::checkVariadicArgument(const Expr *E, VariadicCallType CT) {
   case VAK_ValidInCXX11:
     DiagRuntimeBehavior(
         E->getBeginLoc(), nullptr,
-        PDiag(diag::warn_cxx98_compat_pass_non_pod_arg_to_vararg)
-            << Ty << llvm::to_underlying(CT));
+        PDiag(diag::warn_cxx98_compat_pass_non_pod_arg_to_vararg) << Ty << CT);
     [[fallthrough]];
   case VAK_Valid:
     if (Ty->isRecordType()) {
@@ -1031,8 +1030,7 @@ void Sema::checkVariadicArgument(const Expr *E, VariadicCallType CT) {
       // 'c_str' member function, the user probably meant to call that.
       DiagRuntimeBehavior(E->getBeginLoc(), nullptr,
                           PDiag(diag::warn_pass_class_arg_to_vararg)
-                              << Ty << llvm::to_underlying(CT)
-                              << hasCStrMethod(E) << ".c_str()");
+                              << Ty << CT << hasCStrMethod(E) << ".c_str()");
     }
     break;
 
@@ -1040,22 +1038,21 @@ void Sema::checkVariadicArgument(const Expr *E, VariadicCallType CT) {
   case VAK_MSVCUndefined:
     DiagRuntimeBehavior(E->getBeginLoc(), nullptr,
                         PDiag(diag::warn_cannot_pass_non_pod_arg_to_vararg)
-                            << getLangOpts().CPlusPlus11 << Ty
-                            << llvm::to_underlying(CT));
+                            << getLangOpts().CPlusPlus11 << Ty << CT);
     break;
 
   case VAK_Invalid:
     if (Ty.isDestructedType() == QualType::DK_nontrivial_c_struct)
       Diag(E->getBeginLoc(),
            diag::err_cannot_pass_non_trivial_c_struct_to_vararg)
-          << Ty << llvm::to_underlying(CT);
+          << Ty << CT;
     else if (Ty->isObjCObjectType())
       DiagRuntimeBehavior(E->getBeginLoc(), nullptr,
                           PDiag(diag::err_cannot_pass_objc_interface_to_vararg)
-                              << Ty << llvm::to_underlying(CT));
+                              << Ty << CT);
     else
       Diag(E->getBeginLoc(), diag::err_cannot_pass_to_vararg)
-          << isa<InitListExpr>(E) << Ty << llvm::to_underlying(CT);
+          << isa<InitListExpr>(E) << Ty << CT;
     break;
   }
 }
@@ -18557,8 +18554,7 @@ MarkVarDeclODRUsed(ValueDecl *V, SourceLocation Loc, Sema &SemaRef,
       // through shadow variables therefore it is not diagnosed.
       if (SemaRef.LangOpts.CUDAIsDevice && !SemaRef.LangOpts.HIPStdPar) {
         SemaRef.targetDiag(Loc, diag::err_ref_bad_target)
-            << /*host*/ 2 << /*variable*/ 1 << Var
-            << llvm::to_underlying(UserTarget);
+            << /*host*/ 2 << /*variable*/ 1 << Var << UserTarget;
         SemaRef.targetDiag(Var->getLocation(),
                            Var->getType().isConstQualified()
                                ? diag::note_cuda_const_var_unpromoted
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 727eefa..09edc34 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -865,7 +865,7 @@ ExprResult Sema::BuildCXXThrow(SourceLocation OpLoc, Expr *Ex,
   // Exceptions aren't allowed in CUDA device code.
   if (getLangOpts().CUDA)
     CUDA().DiagIfDeviceCode(OpLoc, diag::err_cuda_device_exceptions)
-        << "throw" << llvm::to_underlying(CUDA().CurrentTarget());
+        << "throw" << CUDA().CurrentTarget();
 
   if (getCurScope() && getCurScope()->isOpenMPSimdDirectiveScope())
     Diag(OpLoc, diag::err_omp_simd_region_cannot_use_stmt) << "throw";
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 6900ccb..3737962 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -9233,8 +9233,7 @@ bool InitializationSequence::Diagnose(Sema &S,
         // implicit.
         if (S.isImplicitlyDeleted(Best->Function))
           S.Diag(Kind.getLocation(), diag::err_ovl_deleted_special_init)
-              << llvm::to_underlying(
-                     S.getSpecialMember(cast<CXXMethodDecl>(Best->Function)))
+              << S.getSpecialMember(cast<CXXMethodDecl>(Best->Function))
               << DestType << ArgsRange;
         else {
           StringLiteral *Msg = Best->Function->getDeletedMessage();
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index b8c2356..7efd92b 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -12355,7 +12355,7 @@ static void DiagnoseBadTarget(Sema &S, OverloadCandidate *Cand) {
   S.Diag(Callee->getLocation(), diag::note_ovl_candidate_bad_target)
       << (unsigned)FnKindPair.first << (unsigned)ocs_non_template
       << FnDesc /* Ignored */
-      << llvm::to_underlying(CalleeTarget) << llvm::to_underlying(CallerTarget);
+      << CalleeTarget << CallerTarget;
 
   // This could be an implicit constructor for which we could not infer the
   // target due to a collsion. Diagnose that case.
@@ -15528,8 +15528,7 @@ ExprResult Sema::CreateOverloadedBinOp(SourceLocation OpLoc,
         DefaultedFunctionKind DFK = getDefaultedFunctionKind(DeletedFD);
         if (DFK.isSpecialMember()) {
           Diag(OpLoc, diag::err_ovl_deleted_special_oper)
-              << Args[0]->getType()
-              << llvm::to_underlying(DFK.asSpecialMember());
+              << Args[0]->getType() << DFK.asSpecialMember();
         } else {
           assert(DFK.isComparison());
           Diag(OpLoc, diag::err_ovl_deleted_comparison)
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index e207251..9f517b2 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -4318,7 +4318,7 @@ StmtResult Sema::ActOnCXXTryBlock(SourceLocation TryLoc, Stmt *TryBlock,
   // Exceptions aren't allowed in CUDA device code.
   if (getLangOpts().CUDA)
     CUDA().DiagIfDeviceCode(TryLoc, diag::err_cuda_device_exceptions)
-        << "try" << llvm::to_underlying(CUDA().CurrentTarget());
+        << "try" << CUDA().CurrentTarget();
 
   if (getCurScope() && getCurScope()->isOpenMPSimdDirectiveScope())
     Diag(TryLoc, diag::err_omp_simd_region_cannot_use_stmt) << "try";
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 633ce2b..6a258ca 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -3911,7 +3911,7 @@ TypeResult Sema::ActOnTagTemplateIdType(TagUseKind TUK,
     //   resolves to an alias template specialization, the
     //   elaborated-type-specifier is ill-formed.
     Diag(TemplateLoc, diag::err_tag_reference_non_tag)
-        << TAT << NTK_TypeAliasTemplate << llvm::to_underlying(TagKind);
+        << TAT << NTK_TypeAliasTemplate << TagKind;
     Diag(TAT->getLocation(), diag::note_declared_at);
   }
 
@@ -9779,8 +9779,7 @@ DeclResult Sema::ActOnExplicitInstantiation(
 
   if (!ClassTemplate) {
     NonTagKind NTK = getNonTagTypeDeclKind(TD, Kind);
-    Diag(TemplateNameLoc, diag::err_tag_reference_non_tag)
-        << TD << NTK << llvm::to_underlying(Kind);
+    Diag(TemplateNameLoc, diag::err_tag_reference_non_tag) << TD << NTK << Kind;
     Diag(TD->getLocation(), diag::note_previous_use);
     return true;
   }
@@ -10643,8 +10642,7 @@ TypeResult Sema::ActOnDependentTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
 
   if (TUK == TagUseKind::Declaration || TUK == TagUseKind::Definition) {
     Diag(NameLoc, diag::err_dependent_tag_decl)
-        << (TUK == TagUseKind::Definition) << llvm::to_underlying(Kind)
-        << SS.getRange();
+        << (TUK == TagUseKind::Definition) << Kind << SS.getRange();
     return true;
   }
 
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 0e81804..390ff3e 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1124,7 +1124,7 @@ void Sema::PrintInstantiationStack(InstantiationContextDiagFuncRef DiagFunc) {
       DiagFunc(Active->PointOfInstantiation,
                PDiag(diag::note_in_declaration_of_implicit_special_member)
                    << cast<CXXRecordDecl>(Active->Entity)
-                   << llvm::to_underlying(Active->SpecialMember));
+                   << Active->SpecialMember);
       break;
 
     case CodeSynthesisContext::DeclaringImplicitEqualityComparison:
@@ -1143,8 +1143,7 @@ void Sema::PrintInstantiationStack(InstantiationContextDiagFuncRef DiagFunc) {
         auto *MD = cast<CXXMethodDecl>(FD);
         DiagFunc(Active->PointOfInstantiation,
                  PDiag(diag::note_member_synthesized_at)
-                     << MD->isExplicitlyDefaulted()
-                     << llvm::to_underlying(DFK.asSpecialMember())
+                     << MD->isExplicitlyDefaulted() << DFK.asSpecialMember()
                      << Context.getTagDeclType(MD->getParent()));
       } else if (DFK.isComparison()) {
         QualType RecordType = FD->getParamDecl(0)
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 76c055d..08b3a42 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -2211,8 +2211,8 @@ Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
 
     if (!PrevClassTemplate && QualifierLoc) {
       SemaRef.Diag(Pattern->getLocation(), diag::err_not_tag_in_scope)
-          << llvm::to_underlying(D->getTemplatedDecl()->getTagKind())
-          << Pattern->getDeclName() << DC << QualifierLoc.getSourceRange();
+          << D->getTemplatedDecl()->getTagKind() << Pattern->getDeclName() << DC
+          << QualifierLoc.getSourceRange();
       return nullptr;
     }
   }
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 6e7ee8b..444b8d9 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -2298,7 +2298,7 @@ QualType Sema::BuildArrayType(QualType T, ArraySizeModifier ASM,
       (ASM != ArraySizeModifier::Normal || Quals != 0)) {
     Diag(Loc, getLangOpts().CPlusPlus ? diag::err_c99_array_usage_cxx
                                       : diag::ext_c99_array_usage)
-        << llvm::to_underlying(ASM);
+        << ASM;
   }
 
   // OpenCL v2.0 s6.12.5 - Arrays of blocks are not supported.
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index b6af919..3bcbe0f 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -1223,14 +1223,13 @@ public:
         NamedDecl *SomeDecl = Result.getRepresentativeDecl();
         Sema::NonTagKind NTK = SemaRef.getNonTagTypeDeclKind(SomeDecl, Kind);
         SemaRef.Diag(IdLoc, diag::err_tag_reference_non_tag)
-            << SomeDecl << NTK << llvm::to_underlying(Kind);
+            << SomeDecl << NTK << Kind;
         SemaRef.Diag(SomeDecl->getLocation(), diag::note_declared_at);
         break;
       }
         default:
           SemaRef.Diag(IdLoc, diag::err_not_tag_in_scope)
-              << llvm::to_underlying(Kind) << Id << DC
-              << QualifierLoc.getSourceRange();
+              << Kind << Id << DC << QualifierLoc.getSourceRange();
           break;
       }
       return QualType();
@@ -7510,8 +7509,7 @@ TreeTransform<Derived>::TransformElaboratedType(TypeLocBuilder &TLB,
         SemaRef.Diag(TL.getNamedTypeLoc().getBeginLoc(),
                      diag::err_tag_reference_non_tag)
             << TAT << Sema::NTK_TypeAliasTemplate
-            << llvm::to_underlying(
-                   ElaboratedType::getTagTypeKindForKeyword(T->getKeyword()));
+            << ElaboratedType::getTagTypeKindForKeyword(T->getKeyword());
         SemaRef.Diag(TAT->getLocation(), diag::note_declared_at);
       }
     }