[clang-tools-extra] [clang-tidy] Add `bugprone-pointer-arithmetic-on-polymorphic-object` check (PR #91951)

[Julian Schmidt via cfe-commits]

================
@@ -0,0 +1,49 @@
+//===--- VirtualArithmeticCheck.cpp - clang-tidy---------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "VirtualArithmeticCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+void VirtualArithmeticCheck::registerMatchers(MatchFinder *Finder) {
+  const auto PointerExprWithVirtualMethod =
+      expr(hasType(pointerType(pointee(hasDeclaration(
+               cxxRecordDecl(hasMethod(isVirtualAsWritten())))))))
+          .bind("pointer");
+
+  const auto ArraySubscript =
+      arraySubscriptExpr(hasBase(PointerExprWithVirtualMethod));
+
+  const auto BinaryOperators =
+      binaryOperator(hasAnyOperatorName("+", "-", "+=", "-="),
+                     hasEitherOperand(PointerExprWithVirtualMethod));
+
+  const auto UnaryOperators =
+      unaryOperator(hasAnyOperatorName("++", "--"),
+                    hasUnaryOperand(PointerExprWithVirtualMethod));
+
+  Finder->addMatcher(
+      expr(anyOf(ArraySubscript, BinaryOperators, UnaryOperators)), this);
----------------
5chmidti wrote:

> with the amount of final classes in my test projects, it might even be slower in practice...

Hm, good point.

I ran this check with `time run-clang-tidy -clang-tidy-binary ./bin/clang-tidy -checks="-*,*polymorphic*" CodeGen` and couldn't measure any real difference when swapping around any of the matchers inside the `cxxRecordDecl` around. So maybe this isn't needed. I was originally about to suggest moving `isAbstract` before `hasMethod`, but that didn't matter either, at least in llvm. If you measure a noticeable difference in another project, then you can probably adjust the order of the matchers.

https://github.com/llvm/llvm-project/pull/91951