[libcxx-commits] [libcxx] WIP - [libc++][debugging] P2546R5: Debugging support & P2810R4: `is_debugger_present` `is_replaceable` (PR #81447)

[Mark de Wever via libcxx-commits]

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@@ -0,0 +1,58 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_DEBUGGING
+#define _LIBCPP_DEBUGGING
+
+/*
+// all freestanding
+namespace std {
+  // [debugging.utility], utility
+  void breakpoint() noexcept;
+  void breakpoint_if_debugging() noexcept;
+  bool is_debugger_present() noexcept;
+}
+*/
+
+#include <__config>
+#include <version>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 26
+
+_LIBCPP_AVAILABILITY_DEBUGGING _LIBCPP_EXPORTED_FROM_ABI void __breakpoint() noexcept;
+
+_LIBCPP_AVAILABILITY_DEBUGGING _LIBCPP_HIDE_FROM_ABI inline void breakpoint() noexcept {
----------------
mordante wrote:

Based on 
```
4.1. Unconditional Breakpoint

The goal of the std::breakpoint function is to "break" or pause the running program when called. Having an unconditional, i.e. attempts to break even if the debugger is or is not actually monitoring the program allows for use in conditions where it is not possible to detect if a debugger is present.

Implementations are expected to optimize the code generated to be as minimal as possible for the platform. For example, on X86 it’s expected that this produces a single INT3 instruction. The goal in this expectation is to place the debugger as close as possible in the caller of breakpoint() to improve the debugging experience for users.
```
I think it would be good to mark this function `_LIBCPP_ALWAYS_INLINE` with a short comment.

Did you verify the generated assembly? Also for `-O0`?

https://github.com/llvm/llvm-project/pull/81447