[clang] [Clang][counted_by] Refactor __builtin_dynamic_object_size on FAMs (PR #122198)

[Bill Wendling via cfe-commits]

================
@@ -1060,236 +1061,358 @@ CodeGenFunction::evaluateOrEmitBuiltinObjectSize(const Expr *E, unsigned Type,
   return ConstantInt::get(ResType, ObjectSize, /*isSigned=*/true);
 }
 
-const FieldDecl *CodeGenFunction::FindFlexibleArrayMemberFieldAndOffset(
-    ASTContext &Ctx, const RecordDecl *RD, const FieldDecl *FAMDecl,
-    uint64_t &Offset) {
+namespace {
+
+/// StructFieldAccess is a simple visitor class to grab the first MemberExpr
+/// from an Expr. It records any ArraySubscriptExpr we meet along the way.
+class StructFieldAccess
+    : public ConstStmtVisitor<StructFieldAccess, const MemberExpr *> {
+  bool AddrOfSeen = false;
+
+public:
+  const ArraySubscriptExpr *ASE = nullptr;
+
+  const MemberExpr *VisitMemberExpr(const MemberExpr *E) {
+    if (AddrOfSeen && E->getType()->isArrayType())
+      // Avoid forms like '&ptr->array'.
+      return nullptr;
+    return E;
+  }
+
+  const MemberExpr *VisitArraySubscriptExpr(const ArraySubscriptExpr *E) {
+    AddrOfSeen = false; // '&ptr->array[idx]' is okay.
+    ASE = E;
+    return Visit(E->getBase());
+  }
+  const MemberExpr *VisitCastExpr(const CastExpr *E) {
+    return Visit(E->getSubExpr());
----------------
bwendling wrote:

Okay, so what do I do with an lvalue-to-rvalue cast when I encounter it?

As I explained in the comment, I'm using the already emitted `Expr` to calculate the offset to the 'count' object. To get that, all I need is the `MemberExpr` of the flexible array member.

https://github.com/llvm/llvm-project/pull/122198