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

[Tom Honermann via cfe-commits]

================
@@ -0,0 +1,98 @@
+//===---------- 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 {
+
+template <template <typename> class Ptr, typename Derived>
+class SubobjectVisitorBase {
+  ASTContext &Ctx;
+  template <typename Class> using ptr_t = typename Ptr<Class>::type;
+  template <typename Class>
+  using non_ptr_t = typename std::remove_pointer<ptr_t<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()) {
+      getDerived().traverseRecord(RD);
+      return;
+    }
+  }
+
+  void traverseRecord(ptr_t<RecordDecl> RD) {
+    if (ptr_t<CXXRecordDecl> CRD = dyn_cast<CXXRecordDecl>(RD)) {
+      for (non_ptr_t<CXXBaseSpecifier &> BS : CRD->bases()) {
+        if (getDerived().visitBaseSpecifierPre(&BS))
+          getDerived().visit(BS.getType());
+        getDerived().visitBaseSpecifierPost(&BS);
----------------
tahonermann wrote:

Yes, it is unusual for a reference to be provided here and the use of `auto` goes against the LLVM coding standards. The deduction for `const` justifies the deviation though. Thanks for making the change.

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