[Clang][C++26] Remove the notion of replaceability.

cor3ntin · cor3ntin · commit fd1194ff9bcd · 2025-12-13T11:47:39.000+01:00
In Kona, WG21 decided to revert trivial relocation (P2786).

Given that the notion of replaceability that was introduced at
the same time does not appear to be used by clang 21 users,
and is less likely to come back, it is easier to fully
remove wholesale.

Subsequent patches will deal with relocation.
diff --git a/clang-tools-extra/clang-tidy/modernize/TypeTraitsCheck.cpp b/clang-tools-extra/clang-tidy/modernize/TypeTraitsCheck.cpp
@@ -83,7 +83,6 @@ static const llvm::StringSet<> ValueTraits = {
     "is_pointer_interconvertible_base_of",
     "is_polymorphic",
     "is_reference",
-    "is_replaceable",
     "is_rvalue_reference",
     "is_same",
     "is_scalar",
diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
@@ -2044,8 +2044,6 @@ The following type trait primitives are supported by Clang. Those traits marked
   is trivially relocatable, as defined by the C++26 standard [meta.unary.prop].
   Note that when relocating the caller code should ensure that if the object is polymorphic,
   the dynamic type is of the most derived type. Padding bytes should not be copied.
-* ``__builtin_is_replaceable`` (C++): Returns true if an object
-  is replaceable, as defined by the C++26 standard [meta.unary.prop].
 * ``__is_trivially_equality_comparable`` (Clang): Returns true if comparing two
   objects of the provided type is known to be equivalent to comparing their
   object representations. Note that types containing padding bytes are never
diff --git a/clang/include/clang/AST/ASTContext.h b/clang/include/clang/AST/ASTContext.h
@@ -666,7 +666,6 @@ class ASTContext : public RefCountedBase<ASTContext> {
 public:
   struct CXXRecordDeclRelocationInfo {
     unsigned IsRelocatable;
-    unsigned IsReplaceable;
   };
   std::optional<CXXRecordDeclRelocationInfo>
   getRelocationInfoForCXXRecord(const CXXRecordDecl *) const;
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
@@ -1952,14 +1952,6 @@ def TriviallyRelocatable : InheritableAttr {
   let Documentation = [InternalOnly];
 }
 
-def Replaceable : InheritableAttr {
-  let Spellings = [CustomKeyword<"replaceable_if_eligible">];
-  let SemaHandler = 0;
-  // Omitted from docs, since this is language syntax, not an attribute, as far
-  // as users are concerned.
-  let Documentation = [InternalOnly];
-}
-
 def MinSize : InheritableAttr {
   let Spellings = [Clang<"minsize">];
   let Subjects = SubjectList<[Function, ObjCMethod], ErrorDiag>;
diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -1077,23 +1077,24 @@ def ext_ms_abstract_keyword : ExtWarn<
   "'abstract' keyword is a Microsoft extension">,
   InGroup<MicrosoftAbstract>;
 
-def ext_relocatable_keyword : ExtWarn<
-  "'%select{trivially_relocatable_if_eligible|replaceable_if_eligible}0' "
-  "keyword is a C++2c extension">,
-  InGroup<CXX26>;
-def warn_relocatable_keyword  : Warning<
-  "'%select{trivially_relocatable|replaceable}0_if_eligible' "
-  "keyword is incompatible with standards before C++2c">,
-  DefaultIgnore, InGroup<CXXPre26Compat>;
+def ext_relocatable_keyword
+    : ExtWarn<
+          "'trivially_relocatable_if_eligible' keyword is a C++2c extension">,
+      InGroup<CXX26>;
+def warn_relocatable_keyword
+    : Warning<"'trivially_relocatable_if_eligible' keyword is incompatible "
+              "with standards before C++2c">,
+      DefaultIgnore,
+      InGroup<CXXPre26Compat>;
 
 def err_access_specifier_interface : Error<
   "interface types cannot specify '%select{private|protected}0' access">;
 
 def err_duplicate_class_virt_specifier : Error<
   "class already marked '%0'">;
 
-def err_duplicate_class_relocation_specifier : Error<
-  "class already marked '%select{trivially_relocatable_if_eligible|replaceable_if_eligible}0'">;
+def err_duplicate_class_relocation_specifier
+    : Error<"class already marked 'trivially_relocatable_if_eligible'">;
 
 def err_duplicate_virt_specifier : Error<
   "class member already marked '%0'">;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1770,7 +1770,6 @@ def err_user_defined_msg_constexpr : Error<
 def note_unsatisfied_trait
     : Note<"%0 is not %enum_select<TraitName>{"
            "%TriviallyRelocatable{trivially relocatable}|"
-           "%Replaceable{replaceable}|"
            "%TriviallyCopyable{trivially copyable}|"
            "%Empty{empty}|"
            "%StandardLayout{standard-layout}|"
@@ -1792,8 +1791,6 @@ def note_unsatisfied_trait_reason
            "class type}|"
            "%NTRBase{has a non-trivially-relocatable base %1}|"
            "%NTRField{has a non-trivially-relocatable member %1 of type %2}|"
-           "%NonReplaceableBase{has a non-replaceable base %1}|"
-           "%NonReplaceableField{has a non-replaceable member %1 of type %2}|"
            "%NTCBase{has a non-trivially-copyable base %1}|"
            "%NTCField{has a non-trivially-copyable member %1 of type %2}|"
            "%NonEmptyMember{has a non-static data member %1 of type %2}|"
diff --git a/clang/include/clang/Basic/TokenKinds.def b/clang/include/clang/Basic/TokenKinds.def
@@ -564,7 +564,6 @@ TYPE_TRAIT_2(/*EmptySpellingName*/, IsDeducible, KEYCXX)
 TYPE_TRAIT_1(__builtin_is_cpp_trivially_relocatable, IsCppTriviallyRelocatable, KEYCXX)
 TYPE_TRAIT_1(__is_trivially_relocatable, IsTriviallyRelocatable, KEYCXX)
 TYPE_TRAIT_1(__is_bitwise_cloneable, IsBitwiseCloneable, KEYALL)
-TYPE_TRAIT_1(__builtin_is_replaceable, IsReplaceable, KEYCXX)
 TYPE_TRAIT_1(__builtin_structured_binding_size, StructuredBindingSize, KEYCXX)
 
 
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
@@ -2835,7 +2835,6 @@ class Parser : public CodeCompletionHandler {
   mutable IdentifierInfo *Ident_GNU_final;
   mutable IdentifierInfo *Ident_override;
   mutable IdentifierInfo *Ident_trivially_relocatable_if_eligible;
-  mutable IdentifierInfo *Ident_replaceable_if_eligible;
 
   /// Representation of a class that has been parsed, including
   /// any member function declarations or definitions that need to be
@@ -3129,7 +3128,7 @@ class Parser : public CodeCompletionHandler {
 
   /// isClassCompatibleKeyword - Determine whether the next token is a C++11
   /// 'final', a C++26 'trivially_relocatable_if_eligible',
-  /// 'replaceable_if_eligible', or Microsoft 'sealed' or 'abstract' contextual
+  /// or Microsoft 'sealed' or 'abstract' contextual
   /// keyword.
   bool isClassCompatibleKeyword() const;
 
@@ -3603,12 +3602,8 @@ class Parser : public CodeCompletionHandler {
   bool isCXX2CTriviallyRelocatableKeyword() const;
   void ParseCXX2CTriviallyRelocatableSpecifier(SourceLocation &TRS);
 
-  bool isCXX2CReplaceableKeyword(Token Tok) const;
-  bool isCXX2CReplaceableKeyword() const;
-  void ParseCXX2CReplaceableSpecifier(SourceLocation &MRS);
-
   /// 'final', a C++26 'trivially_relocatable_if_eligible',
-  /// 'replaceable_if_eligible', or Microsoft 'sealed' or 'abstract' contextual
+  /// or Microsoft 'sealed' or 'abstract' contextual
   /// keyword.
   bool isClassCompatibleKeyword(Token Tok) const;
 
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
@@ -4366,7 +4366,6 @@ class Sema final : public SemaBase {
                                        bool IsFinalSpelledSealed,
                                        bool IsAbstract,
                                        SourceLocation TriviallyRelocatable,
-                                       SourceLocation Replaceable,
                                        SourceLocation LBraceLoc);
 
   /// ActOnTagFinishDefinition - Invoked once we have finished parsing
@@ -4375,7 +4374,7 @@ class Sema final : public SemaBase {
                                 SourceRange BraceRange);
 
   ASTContext::CXXRecordDeclRelocationInfo
-  CheckCXX2CRelocatableAndReplaceable(const clang::CXXRecordDecl *D);
+  CheckCXX2CRelocatable(const clang::CXXRecordDecl *D);
 
   void ActOnTagFinishSkippedDefinition(SkippedDefinitionContext Context);
 
@@ -8733,12 +8732,6 @@ class Sema final : public SemaBase {
   bool IsCXXTriviallyRelocatableType(QualType T);
   bool IsCXXTriviallyRelocatableType(const CXXRecordDecl &RD);
 
-  //// Determines if a type is replaceable
-  /// according to the C++26 rules.
-  // FIXME: This is in Sema because it requires
-  // overload resolution, can we move to ASTContext?
-  bool IsCXXReplaceableType(QualType T);
-
   /// Check the operands of ?: under C++ semantics.
   ///
   /// See C++ [expr.cond]. Note that LHS is never null, even for the GNU x ?: y
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -2498,40 +2498,13 @@ void Parser::ParseCXX2CTriviallyRelocatableSpecifier(SourceLocation &TRS) {
 
   Diag(Tok.getLocation(), getLangOpts().CPlusPlus26
                               ? diag::warn_relocatable_keyword
-                              : diag::ext_relocatable_keyword)
-      << /*relocatable*/ 0;
+                              : diag::ext_relocatable_keyword);
 
   TRS = ConsumeToken();
 }
 
-bool Parser::isCXX2CReplaceableKeyword(Token Tok) const {
-  if (!getLangOpts().CPlusPlus || Tok.isNot(tok::identifier))
-    return false;
-  if (!Ident_replaceable_if_eligible)
-    Ident_replaceable_if_eligible =
-        &PP.getIdentifierTable().get("replaceable_if_eligible");
-  IdentifierInfo *II = Tok.getIdentifierInfo();
-  return II == Ident_replaceable_if_eligible;
-}
-
-bool Parser::isCXX2CReplaceableKeyword() const {
-  return isCXX2CReplaceableKeyword(Tok);
-}
-
-void Parser::ParseCXX2CReplaceableSpecifier(SourceLocation &MRS) {
-  assert(isCXX2CReplaceableKeyword() &&
-         "expected a replaceable_if_eligible specifier");
-
-  Diag(Tok.getLocation(), getLangOpts().CPlusPlus26
-                              ? diag::warn_relocatable_keyword
-                              : diag::ext_relocatable_keyword)
-      << /*replaceable*/ 1;
-
-  MRS = ConsumeToken();
-}
-
 bool Parser::isClassCompatibleKeyword(Token Tok) const {
-  if (isCXX2CTriviallyRelocatableKeyword(Tok) || isCXX2CReplaceableKeyword(Tok))
+  if (isCXX2CTriviallyRelocatableKeyword(Tok))
     return true;
   VirtSpecifiers::Specifier Specifier = isCXX11VirtSpecifier(Tok);
   return Specifier == VirtSpecifiers::VS_Final ||
@@ -3587,7 +3560,6 @@ void Parser::ParseCXXMemberSpecification(SourceLocation RecordLoc,
   bool IsFinalSpelledSealed = false;
   bool IsAbstract = false;
   SourceLocation TriviallyRelocatable;
-  SourceLocation Replaceable;
 
   // Parse the optional 'final' keyword.
   if (getLangOpts().CPlusPlus && Tok.is(tok::identifier)) {
@@ -3599,23 +3571,12 @@ void Parser::ParseCXXMemberSpecification(SourceLocation RecordLoc,
             auto Skipped = Tok;
             ConsumeToken();
             Diag(Skipped, diag::err_duplicate_class_relocation_specifier)
-                << /*trivial_relocatable*/ 0 << TriviallyRelocatable;
+                << TriviallyRelocatable;
           } else {
             ParseCXX2CTriviallyRelocatableSpecifier(TriviallyRelocatable);
           }
           continue;
         }
-        if (isCXX2CReplaceableKeyword(Tok)) {
-          if (Replaceable.isValid()) {
-            auto Skipped = Tok;
-            ConsumeToken();
-            Diag(Skipped, diag::err_duplicate_class_relocation_specifier)
-                << /*replaceable*/ 1 << Replaceable;
-          } else {
-            ParseCXX2CReplaceableSpecifier(Replaceable);
-          }
-          continue;
-        }
         break;
       }
       if (isCXX11FinalKeyword()) {
@@ -3654,7 +3615,7 @@ void Parser::ParseCXXMemberSpecification(SourceLocation RecordLoc,
         Diag(FinalLoc, diag::ext_warn_gnu_final);
     }
     assert((FinalLoc.isValid() || AbstractLoc.isValid() ||
-            TriviallyRelocatable.isValid() || Replaceable.isValid()) &&
+            TriviallyRelocatable.isValid()) &&
            "not a class definition");
 
     // Parse any C++11 attributes after 'final' keyword.
@@ -3729,7 +3690,7 @@ void Parser::ParseCXXMemberSpecification(SourceLocation RecordLoc,
   if (TagDecl)
     Actions.ActOnStartCXXMemberDeclarations(
         getCurScope(), TagDecl, FinalLoc, IsFinalSpelledSealed, IsAbstract,
-        TriviallyRelocatable, Replaceable, T.getOpenLocation());
+        TriviallyRelocatable, T.getOpenLocation());
 
   // C++ 11p3: Members of a class defined with the keyword class are private
   // by default. Members of a class defined with the keywords struct or union
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
@@ -515,7 +515,6 @@ void Parser::Initialize() {
   Ident_abstract = nullptr;
   Ident_override = nullptr;
   Ident_trivially_relocatable_if_eligible = nullptr;
-  Ident_replaceable_if_eligible = nullptr;
   Ident_GNU_final = nullptr;
   Ident_import = nullptr;
   Ident_module = nullptr;
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
@@ -18794,10 +18794,12 @@ bool Sema::ActOnDuplicateDefinition(Scope *S, Decl *Prev,
   return true;
 }
 
-void Sema::ActOnStartCXXMemberDeclarations(
-    Scope *S, Decl *TagD, SourceLocation FinalLoc, bool IsFinalSpelledSealed,
-    bool IsAbstract, SourceLocation TriviallyRelocatable,
-    SourceLocation Replaceable, SourceLocation LBraceLoc) {
+void Sema::ActOnStartCXXMemberDeclarations(Scope *S, Decl *TagD,
+                                           SourceLocation FinalLoc,
+                                           bool IsFinalSpelledSealed,
+                                           bool IsAbstract,
+                                           SourceLocation TriviallyRelocatable,
+                                           SourceLocation LBraceLoc) {
   AdjustDeclIfTemplate(TagD);
   CXXRecordDecl *Record = cast<CXXRecordDecl>(TagD);
 
@@ -18820,9 +18822,6 @@ void Sema::ActOnStartCXXMemberDeclarations(
     Record->addAttr(
         TriviallyRelocatableAttr::Create(Context, TriviallyRelocatable));
 
-  if (Replaceable.isValid())
-    Record->addAttr(ReplaceableAttr::Create(Context, Replaceable));
-
   // C++ [class]p2:
   //   [...] The class-name is also inserted into the scope of the
   //   class itself; this is known as the injected-class-name. For
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
diff --git a/clang/test/Parser/cxx2c-trivially-relocatable.cpp b/clang/test/Parser/cxx2c-trivially-relocatable.cpp
diff --git a/clang/test/SemaCXX/cxx2c-trivially-relocatable.cpp b/clang/test/SemaCXX/cxx2c-trivially-relocatable.cpp
diff --git a/clang/test/SemaCXX/ptrauth-type-traits.cpp b/clang/test/SemaCXX/ptrauth-type-traits.cpp
diff --git a/clang/test/SemaCXX/type-traits-unsatisfied-diags-std.cpp b/clang/test/SemaCXX/type-traits-unsatisfied-diags-std.cpp
diff --git a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
