Revert "[Clang] Implement the 'counted_by' attribute" (#68603)

This reverts commit 9a954c6, which
causes clang crashes when compiling with `-fsanitize=bounds`. See

9a954c6#commitcomment-129529574
for details.

Author: alexfh

clang/docs/ReleaseNotes.rst

@@ -139,11 +139,6 @@ C Language Changes
 - ``structs``, ``unions``, and ``arrays`` that are const may now be used as
   constant expressions.  This change is more consistent with the behavior of
   GCC.
-- Clang now supports the C-only attribute ``counted_by``. When applied to a
-  struct's flexible array member, it points to the struct field that holds the
-  number of elements in the flexible array member. This information can improve
-  the results of the array bound sanitizer and the
-  ``__builtin_dynamic_object_size`` builtin.
 
 C23 Feature Support
 ^^^^^^^^^^^^^^^^^^^

clang/include/clang/AST/Decl.h

@@ -4302,30 +4302,6 @@ class RecordDecl : public TagDecl {
     return field_begin() == field_end();
   }
 
-  FieldDecl *getLastField() {
-    FieldDecl *FD = nullptr;
-    for (FieldDecl *Field : fields())
-      FD = Field;
-    return FD;
-  }
-  const FieldDecl *getLastField() const {
-    return const_cast<RecordDecl *>(this)->getLastField();
-  }
-
-  template <typename Functor>
-  const FieldDecl *findFieldIf(Functor &Pred) const {
-    for (const Decl *D : decls()) {
-      if (const auto *FD = dyn_cast<FieldDecl>(D); FD && Pred(FD))
-        return FD;
-
-      if (const auto *RD = dyn_cast<RecordDecl>(D))
-        if (const FieldDecl *FD = RD->findFieldIf(Pred))
-          return FD;
-    }
-
-    return nullptr;
-  }
-
   /// Note that the definition of this type is now complete.
   virtual void completeDefinition();
 

clang/include/clang/AST/DeclBase.h

@@ -18,7 +18,6 @@
 #include "clang/AST/DeclarationName.h"
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/LLVM.h"
-#include "clang/Basic/LangOptions.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/Specifiers.h"
 #include "llvm/ADT/ArrayRef.h"
@@ -478,15 +477,6 @@ class alignas(8) Decl {
   // Return true if this is a FileContext Decl.
   bool isFileContextDecl() const;
 
-  /// Whether it resembles a flexible array member. This is a static member
-  /// because we want to be able to call it with a nullptr. That allows us to
-  /// perform non-Decl specific checks based on the object's type and strict
-  /// flex array level.
-  static bool isFlexibleArrayMemberLike(
-      ASTContext &Context, const Decl *D, QualType Ty,
-      LangOptions::StrictFlexArraysLevelKind StrictFlexArraysLevel,
-      bool IgnoreTemplateOrMacroSubstitution);
-
   ASTContext &getASTContext() const LLVM_READONLY;
 
   /// Helper to get the language options from the ASTContext.

clang/include/clang/Basic/Attr.td

@@ -4246,21 +4246,3 @@ def AvailableOnlyInDefaultEvalMethod : InheritableAttr {
   let Subjects = SubjectList<[TypedefName], ErrorDiag>;
   let Documentation = [Undocumented];
 }
-
-def CountedBy : InheritableAttr {
-  let Spellings = [Clang<"counted_by">];
-  let Subjects = SubjectList<[Field]>;
-  let Args = [IdentifierArgument<"CountedByField">];
-  let Documentation = [CountedByDocs];
-  let LangOpts = [COnly];
-  // FIXME: This is ugly. Let using a DeclArgument would be nice, but a Decl
-  // isn't yet available due to the fact that we're still parsing the
-  // structure. Maybe that code could be changed sometime in the future.
-  code AdditionalMembers = [{
-    private:
-      SourceRange CountedByFieldLoc;
-    public:
-      SourceRange getCountedByFieldLoc() const { return CountedByFieldLoc; }
-      void setCountedByFieldLoc(SourceRange Loc) { CountedByFieldLoc = Loc; }
-  }];
-}

clang/include/clang/Basic/AttrDocs.td

@@ -7275,69 +7275,3 @@ relative ordering of values is important. For example:
 attribute, they default to the value ``65535``.
 }];
 }
-
-def CountedByDocs : Documentation {
-  let Category = DocCatField;
-  let Content = [{
-Clang supports the ``counted_by`` attribute on the flexible array member of a
-structure in C. The argument for the attribute is the name of a field member in
-the same structure holding the count of elements in the flexible array. This
-information can be used to improve the results of the array bound sanitizer and
-the ``__builtin_dynamic_object_size`` builtin.
-
-For example, the following code:
-
-.. code-block:: c
-
-  struct bar;
-
-  struct foo {
-    size_t count;
-    char other;
-    struct bar *array[] __attribute__((counted_by(count)));
-  };
-
-specifies that the flexible array member ``array`` has the number of elements
-allocated for it stored in ``count``. This establishes a relationship between
-``array`` and ``count``. Specifically, ``p->array`` must have at least
-``p->count`` number of elements available. It's the user's responsibility to
-ensure that this relationship is maintained through changes to the structure.
-
-In the following example, the allocated array erroneously has fewer elements
-than what's specified by ``p->count``. This would result in an out-of-bounds
-access not being detected.
-
-.. code-block:: c
-
-  #define SIZE_INCR 42
-
-  struct foo *p;
-
-  void foo_alloc(size_t count) {
-    p = malloc(MAX(sizeof(struct foo),
-                   offsetof(struct foo, array[0]) + count * sizeof(struct bar *)));
-    p->count = count + SIZE_INCR;
-  }
-
-The next example updates ``p->count``, breaking the relationship requirement
-that ``p->array`` must have at least ``p->count`` number of elements available:
-
-.. code-block:: c
-
-  #define SIZE_INCR 42
-
-  struct foo *p;
-
-  void foo_alloc(size_t count) {
-    p = malloc(MAX(sizeof(struct foo),
-                   offsetof(struct foo, array[0]) + count * sizeof(struct bar *)));
-    p->count = count;
-  }
-
-  void use_foo(int index) {
-    p->count += SIZE_INCR + 1; /* 'count' is now larger than the number of elements of 'array'. */
-    p->array[index] = 0;       /* the sanitizer can't properly check if this is an out-of-bounds access. */
-  }
-
-  }];
-}

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -6389,21 +6389,6 @@ def warn_superclass_variable_sized_type_not_at_end : Warning<
   "field %0 can overwrite instance variable %1 with variable sized type %2"
   " in superclass %3">, InGroup<ObjCFlexibleArray>;
 
-def err_counted_by_attr_not_on_flexible_array_member : Error<
-  "'counted_by' only applies to flexible array members">;
-def err_flexible_array_counted_by_attr_field_not_found : Error<
-  "field %0 in 'counted_by' not found">;
-def err_flexible_array_counted_by_attr_field_not_found_suggest : Error<
-  "field %0 in 'counted_by' not found; did you mean %1?">;
-def err_flexible_array_counted_by_attr_field_not_found_in_struct : Error<
-  "field %0 in 'counted_by' is not found in struct">;
-def err_flexible_array_counted_by_attr_refers_to_self : Error<
-  "field %0 in 'counted_by' cannot refer to the flexible array">;
-def err_flexible_array_counted_by_attr_field_not_integer : Error<
-  "field %0 in 'counted_by' is not a non-boolean integer type">;
-def note_flexible_array_counted_by_attr_field : Note<
-  "field %0 declared here">;
-
 let CategoryName = "ARC Semantic Issue" in {
 
 // ARC-mode diagnostics.

clang/include/clang/Sema/Sema.h

@@ -4795,8 +4795,6 @@ class Sema final {
   bool CheckAlwaysInlineAttr(const Stmt *OrigSt, const Stmt *CurSt,
                              const AttributeCommonInfo &A);
 
-  bool CheckCountedByAttr(Scope *Scope, const FieldDecl *FD);
-
   /// Adjust the calling convention of a method to be the ABI default if it
   /// wasn't specified explicitly.  This handles method types formed from
   /// function type typedefs and typename template arguments.

clang/lib/AST/ASTImporter.cpp

@@ -8978,10 +8978,6 @@ class AttrImporter {
 public:
   AttrImporter(ASTImporter &I) : Importer(I), NImporter(I) {}
 
-  // Useful for accessing the imported attribute.
-  template <typename T> T *castAttrAs() { return cast<T>(ToAttr); }
-  template <typename T> const T *castAttrAs() const { return cast<T>(ToAttr); }
-
   // Create an "importer" for an attribute parameter.
   // Result of the 'value()' of that object is to be passed to the function
   // 'importAttr', in the order that is expected by the attribute class.
@@ -9188,15 +9184,6 @@ Expected<Attr *> ASTImporter::Import(const Attr *FromAttr) {
                   From->args_size());
     break;
   }
-  case attr::CountedBy: {
-    AI.cloneAttr(FromAttr);
-    const auto *CBA = cast<CountedByAttr>(FromAttr);
-    Expected<SourceRange> SR = Import(CBA->getCountedByFieldLoc()).get();
-    if (!SR)
-      return SR.takeError();
-    AI.castAttrAs<CountedByAttr>()->setCountedByFieldLoc(SR.get());
-    break;
-  }
 
   default: {
     // The default branch works for attributes that have no arguments to import.

clang/lib/AST/DeclBase.cpp

@@ -29,6 +29,7 @@
 #include "clang/AST/Type.h"
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/LLVM.h"
+#include "clang/Basic/LangOptions.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/ObjCRuntime.h"
 #include "clang/Basic/PartialDiagnostic.h"
@@ -410,81 +411,6 @@ bool Decl::isFileContextDecl() const {
   return DC && DC->isFileContext();
 }
 
-bool Decl::isFlexibleArrayMemberLike(
-    ASTContext &Ctx, const Decl *D, QualType Ty,
-    LangOptions::StrictFlexArraysLevelKind StrictFlexArraysLevel,
-    bool IgnoreTemplateOrMacroSubstitution) {
-  // For compatibility with existing code, we treat arrays of length 0 or
-  // 1 as flexible array members.
-  const auto *CAT = Ctx.getAsConstantArrayType(Ty);
-  if (CAT) {
-    using FAMKind = LangOptions::StrictFlexArraysLevelKind;
-
-    llvm::APInt Size = CAT->getSize();
-    FAMKind StrictFlexArraysLevel =
-        Ctx.getLangOpts().getStrictFlexArraysLevel();
-
-    if (StrictFlexArraysLevel == FAMKind::IncompleteOnly)
-      return false;
-
-    // GCC extension, only allowed to represent a FAM.
-    if (Size.isZero())
-      return true;
-
-    if (StrictFlexArraysLevel == FAMKind::ZeroOrIncomplete && Size.uge(1))
-      return false;
-
-    if (StrictFlexArraysLevel == FAMKind::OneZeroOrIncomplete && Size.uge(2))
-      return false;
-  } else if (!Ctx.getAsIncompleteArrayType(Ty)) {
-    return false;
-  }
-
-  if (const auto *OID = dyn_cast_if_present<ObjCIvarDecl>(D))
-    return OID->getNextIvar() == nullptr;
-
-  const auto *FD = dyn_cast_if_present<FieldDecl>(D);
-  if (!FD)
-    return false;
-
-  if (CAT) {
-    // GCC treats an array memeber of a union as an FAM if the size is one or
-    // zero.
-    llvm::APInt Size = CAT->getSize();
-    if (FD->getParent()->isUnion() && (Size.isZero() || Size.isOne()))
-      return true;
-  }
-
-  // Don't consider sizes resulting from macro expansions or template argument
-  // substitution to form C89 tail-padded arrays.
-  if (IgnoreTemplateOrMacroSubstitution) {
-    TypeSourceInfo *TInfo = FD->getTypeSourceInfo();
-    while (TInfo) {
-      TypeLoc TL = TInfo->getTypeLoc();
-
-      // Look through typedefs.
-      if (TypedefTypeLoc TTL = TL.getAsAdjusted<TypedefTypeLoc>()) {
-        const TypedefNameDecl *TDL = TTL.getTypedefNameDecl();
-        TInfo = TDL->getTypeSourceInfo();
-        continue;
-      }
-
-      if (auto CTL = TL.getAs<ConstantArrayTypeLoc>()) {
-        const Expr *SizeExpr = dyn_cast<IntegerLiteral>(CTL.getSizeExpr());
-        if (!SizeExpr || SizeExpr->getExprLoc().isMacroID())
-          return false;
-      }
-
-      break;
-    }
-  }
-
-  // Test that the field is the last in the structure.
-  RecordDecl::field_iterator FI(
-      DeclContext::decl_iterator(const_cast<FieldDecl *>(FD)));
-  return ++FI == FD->getParent()->field_end();
-}
-
 TranslationUnitDecl *Decl::getTranslationUnitDecl() {
   if (auto *TUD = dyn_cast<TranslationUnitDecl>(this))
     return TUD;