[clang] [Clang] Add __builtin_get_counted_by builtin (PR #102549)

[via cfe-commits]

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@@ -222,6 +222,49 @@ bool Expr::isFlexibleArrayMemberLike(
                                          IgnoreTemplateOrMacroSubstitution);
 }
 
+namespace {
+
+/// MemberExprVisitor - Find the MemberExpr through all of the casts, array
+/// subscripts, and unary ops. This intentionally avoids all of them because
+/// we're interested only in the MemberExpr to check if it's a flexible array
+/// member.
+class MemberExprVisitor
+    : public ConstStmtVisitor<MemberExprVisitor, const Expr *> {
+public:
+  //===--------------------------------------------------------------------===//
+  //                            Visitor Methods
+  //===--------------------------------------------------------------------===//
+
+  const Expr *Visit(const Expr *E) {
+    return ConstStmtVisitor<MemberExprVisitor, const Expr *>::Visit(E);
+  }
+  const Expr *VisitStmt(const Stmt *S) { return nullptr; }
+
+  const Expr *VisitMemberExpr(const MemberExpr *E) { return E; }
+
+  const Expr *VisitArraySubscriptExpr(const ArraySubscriptExpr *E) {
+    return Visit(E->getBase());
+  }
+  const Expr *VisitCastExpr(const CastExpr *E) {
+    return Visit(E->getSubExpr());
+  }
+  const Expr *VisitParenExpr(const ParenExpr *E) {
+    return Visit(E->getSubExpr());
+  }
+  const Expr *VisitUnaryAddrOf(const UnaryOperator *E) {
+    return Visit(E->getSubExpr());
+  }
+  const Expr *VisitUnaryDeref(const UnaryOperator *E) {
+    return Visit(E->getSubExpr());
+  }
----------------
Sirraide wrote:

> Wouldn’t it be enough to just accept a (possibly parenthesised) `MemberExpr`?

I just saw that you also have `&foo.x[0]` as a test case, but given that this is a new builtin that no compiler supports (yet), is it too much to ask for to require people to just write `foo.x` (or maybe e.g. `(foo.x)` because macro shenanigans)? ;Þ

https://github.com/llvm/llvm-project/pull/102549