[clang] [clang][SYCL] Diagnose reference kernel parameters (PR #192957)

[Tom Honermann via cfe-commits]

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@@ -0,0 +1,105 @@
+//===---------- SubobjectVisitor.h - Subobject Visitor ----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the SubobjectVisitor interface, which recursively
+//  traverses subobjects within a type.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_SUBOBJECTVISITOR_H
+#define LLVM_CLANG_AST_SUBOBJECTVISITOR_H
+
+#include "clang/AST/Type.h"
+
+namespace clang {
+
+/// Given a type, subobject visitors visit all subobjects of the type in depth
+/// first order. Both pre-order and post-order visitation are performed so that
+/// derived classes can maintain an access path to the visited elements.
+/// Subobjects include all base classes and non-static data members, including
+/// those that are not subobjects according to the C++standard like data
+/// members with a reference type. Virtual base classes are visited each time
+/// they appear in a class hierarchy despite there being only one actual
+/// subobject present in an object of a most derived type. Array elements are
+/// not individually visited; only their containing array is.
+template <template <typename> class Ptr, typename Derived>
+class SubobjectVisitorBase {
+  ASTContext &Ctx;
+  template <typename Class> using ptr_t = typename Ptr<Class>::type;
+
+public:
+  SubobjectVisitorBase(ASTContext &Ctx) : Ctx(Ctx) {}
+
+  /// Return a reference to the derived class.
+  Derived &getDerived() { return *static_cast<Derived *>(this); }
+
+  void visit(QualType QT) {
+    // If the type is an array, visit its element type. Separate traversal of
+    // arrays is not needed because the array will be encountered as a
+    // FieldDecl.
+
+    if (QT->isArrayType()) {
+      QualType ElTy =
+          cast<ConstantArrayType>(Ctx.getAsArrayType(QT))->getElementType();
+      getDerived().visit(ElTy);
+      return;
+    }
+
+    if (ptr_t<RecordDecl> RD = QT->getAsRecordDecl()) {
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tahonermann wrote:

> Should there be an assert that this isn't used on dependent types?

I guess visitation of dependent types could be reasonable, but without a motivating use case, I don't think it is worth adding support for now. I think adding `assert(!QT->isDependentType());` to `visit(QualType)` would make sense.

https://github.com/llvm/llvm-project/pull/192957