================
@@ -859,53 +859,60 @@ CodeGenFunction::emitBuiltinObjectSize(const Expr *E,
unsigned Type,
}
if (IsDynamic) {
- LangOptions::StrictFlexArraysLevelKind StrictFlexArraysLevel =
- getLangOpts().getStrictFlexArraysLevel();
- const Expr *Base = E->IgnoreParenImpCasts();
-
- if (FieldDecl *FD = FindCountedByField(Base, StrictFlexArraysLevel)) {
- const auto *ME = dyn_cast<MemberExpr>(Base);
- llvm::Value *ObjectSize = nullptr;
-
- if (!ME) {
- const auto *DRE = dyn_cast<DeclRefExpr>(Base);
- ValueDecl *VD = nullptr;
-
- ObjectSize = ConstantInt::get(
- ResType,
- getContext().getTypeSize(DRE->getType()->getPointeeType()) / 8,
- true);
-
- if (auto *RD = DRE->getType()->getPointeeType()->getAsRecordDecl())
- VD = RD->getLastField();
-
- Expr *ICE = ImplicitCastExpr::Create(
- getContext(), DRE->getType(), CK_LValueToRValue,
- const_cast<Expr *>(cast<Expr>(DRE)), nullptr, VK_PRValue,
- FPOptionsOverride());
- ME = MemberExpr::CreateImplicit(getContext(), ICE, true, VD,
- VD->getType(), VK_LValue, OK_Ordinary);
- }
-
- // At this point, we know that \p ME is a flexible array member.
- const auto *ArrayTy = getContext().getAsArrayType(ME->getType());
+ // The code generated here calculates the size of a struct with a flexible
+ // array member that uses the counted_by attribute. There are two instances
+ // we handle:
+ //
+ // struct s {
+ // unsigned long flags;
+ // int count;
+ // int array[] __attribute__((counted_by(count)));
+ // }
+ //
+ // 1) bdos of the flexible array itself:
+ //
+ // __builtin_dynamic_object_size(p->array, 1) ==
+ // p->count * sizeof(*p->array)
+ //
+ // 2) bdos of the whole struct, including the flexible array:
+ //
+ // __builtin_dynamic_object_size(p, 1) ==
+ // sizeof(*p) + p->count * sizeof(*p->array)
----------------
rapidsna wrote:
> __builtin_dynamic_object_size only adds the full struct size to the
> calculation when the full struct pointer is specified:
> __builtin_dynamic_object_size(p, 1) == 23. __builtin_dynamic_object_size only
> adds the full struct size to the calculation when the full struct pointer is
> specified: __builtin_dynamic_object_size(p, 1) == 23. When it's specified on
> the fam itself (__builtin_dynamic_object_size(*p->array, 1)) it returns only
> the size of the fam (7 in this example). This seems entirely reasonable to me
> and fits the definition of __builtin_dynamic_object_size:
I know, but the question is why "the full struct size" should include the part
of `&s->fam[13]`? It's not even conformed to how the statically initialized
struct size is determined in C (like @apple-fcloutier 's example also
indicates).
https://github.com/llvm/llvm-project/pull/70606
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