[libc++] Implement P0627R6 (Function to mark unreachable code)

Reviewed By: ldionne, Quuxplusone, #libc Spies: arichardson, mstorsjo, libcxx-commits, mgorny Differential Revision: https://reviews.llvm.org/D119152
llvm · Feb 14, 2022 · 2a8f9a5 · 2a8f9a5
1 parent b305de1
commit 2a8f9a5
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Showing 28 changed files with 152 additions and 76 deletions.
diff --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
@@ -350,6 +350,6 @@ Status
     ------------------------------------------------- -----------------
     ``__cpp_lib_to_underlying``                       ``202102L``
     ------------------------------------------------- -----------------
-    ``__cpp_lib_unreachable``                         *unimplemented*
+    ``__cpp_lib_unreachable``                         ``202202L``
     ================================================= =================
 
diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
@@ -38,6 +38,8 @@ What's New in Libc++ 15.0.0?
 New Features
 ------------
 
+ - Implemented P0627R6 (Function to mark unreachable code)
+
 API Changes
 -----------
 

diff --git a/libcxx/docs/Status/Cxx2bPapers.csv b/libcxx/docs/Status/Cxx2bPapers.csv
@@ -40,7 +40,7 @@
 "","","","","",""
 "`P0323R12 <https://wg21.link/P0323R12>`__","LWG","``std::expected``","February 2022","",""
 "`P0533R9 <https://wg21.link/P0533R9>`__","LWG","``constexpr`` for ``<cmath>`` and ``<cstdlib>``","February 2022","",""
-"`P0627R6 <https://wg21.link/P0627R6>`__","LWG","Function to mark unreachable code","February 2022","",""
+"`P0627R6 <https://wg21.link/P0627R6>`__","LWG","Function to mark unreachable code","February 2022","|Complete|","15.0"
 "`P1206R7 <https://wg21.link/P1206R7>`__","LWG","``ranges::to``: A function to convert any range to a container","February 2022","",""
 "`P1413R3 <https://wg21.link/P1413R3>`__","LWG","Deprecate ``std::aligned_storage`` and ``std::aligned_union``","February 2022","",""
 "`P2255R3 <https://wg21.link/P2255R3>`__","LWG","A type trait to detect reference binding to temporary","February 2022","",""

diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
@@ -401,6 +401,7 @@ set(files
   __utility/swap.h
   __utility/to_underlying.h
   __utility/transaction.h
+  __utility/unreachable.h
   __variant/monostate.h
   algorithm
   any

diff --git a/libcxx/include/__filesystem/directory_entry.h b/libcxx/include/__filesystem/directory_entry.h
@@ -20,6 +20,7 @@
 #include <__filesystem/operations.h>
 #include <__filesystem/path.h>
 #include <__filesystem/perms.h>
+#include <__utility/unreachable.h>
 #include <chrono>
 #include <cstdint>
 #include <cstdlib>
@@ -362,7 +363,7 @@ class directory_entry {
         __ec->clear();
       return __data_.__type_;
     }
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
   }
 
   _LIBCPP_INLINE_VISIBILITY
@@ -383,7 +384,7 @@ class directory_entry {
       return __data_.__type_;
     }
     }
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
   }
 
   _LIBCPP_INLINE_VISIBILITY
@@ -398,7 +399,7 @@ class directory_entry {
     case _RefreshSymlink:
       return file_status(__get_ft(__ec), __data_.__non_sym_perms_);
     }
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
   }
 
   _LIBCPP_INLINE_VISIBILITY
@@ -414,7 +415,7 @@ class directory_entry {
     case _RefreshSymlinkUnresolved:
       return file_status(__get_sym_ft(__ec), __data_.__sym_perms_);
     }
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
   }
 
   _LIBCPP_INLINE_VISIBILITY
@@ -439,7 +440,7 @@ class directory_entry {
       return __data_.__size_;
     }
     }
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
   }
 
   _LIBCPP_INLINE_VISIBILITY
@@ -458,7 +459,7 @@ class directory_entry {
       return __data_.__nlink_;
     }
     }
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
   }
 
   _LIBCPP_INLINE_VISIBILITY
@@ -481,7 +482,7 @@ class directory_entry {
       return __data_.__write_time_;
     }
     }
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
   }
 
 private:

diff --git a/libcxx/include/__format/format_arg.h b/libcxx/include/__format/format_arg.h
@@ -16,6 +16,7 @@
 #include <__format/format_fwd.h>
 #include <__format/format_parse_context.h>
 #include <__memory/addressof.h>
+#include <__utility/unreachable.h>
 #include <__variant/monostate.h>
 #include <string>
 #include <string_view>
@@ -77,7 +78,7 @@ visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
 #ifndef _LIBCPP_HAS_NO_INT128
     return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__i128);
 #else
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
 #endif
   case __format::__arg_t::__unsigned:
     return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__unsigned);
@@ -88,7 +89,7 @@ visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
 #ifndef _LIBCPP_HAS_NO_INT128
     return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__u128);
 #else
-   _LIBCPP_UNREACHABLE();
+   __libcpp_unreachable();
 #endif
   case __format::__arg_t::__float:
     return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__float);
@@ -106,7 +107,7 @@ visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
   case __format::__arg_t::__handle:
     return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__handle);
   }
-  _LIBCPP_UNREACHABLE();
+  __libcpp_unreachable();
 }
 
 template <class _Context>

diff --git a/libcxx/include/__format/formatter.h b/libcxx/include/__format/formatter.h
@@ -18,6 +18,7 @@
 #include <__format/format_fwd.h>
 #include <__format/format_string.h>
 #include <__format/parser_std_format_spec.h>
+#include <__utility/unreachable.h>
 #include <string_view>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -116,7 +117,7 @@ __padding_size(size_t __size, size_t __width,
   size_t __fill = __width - __size;
   switch (__align) {
   case __format_spec::_Flags::_Alignment::__default:
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
 
   case __format_spec::_Flags::_Alignment::__left:
     return {0, __fill};
@@ -132,7 +133,7 @@ __padding_size(size_t __size, size_t __width,
   case __format_spec::_Flags::_Alignment::__right:
     return {__fill, 0};
   }
-  _LIBCPP_UNREACHABLE();
+  __libcpp_unreachable();
 }
 
 /**

diff --git a/libcxx/include/__format/formatter_floating_point.h b/libcxx/include/__format/formatter_floating_point.h
@@ -27,6 +27,7 @@
 #include <__format/formatter_integral.h>
 #include <__format/parser_std_format_spec.h>
 #include <__utility/move.h>
+#include <__utility/unreachable.h>
 #include <charconv>
 #include <cmath>
 
@@ -689,7 +690,7 @@ class _LIBCPP_TEMPLATE_VIS __formatter_floating_point : public __parser_floating
 
     default:
       _LIBCPP_ASSERT(false, "The parser should have validated the type");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
   }
 };

diff --git a/libcxx/include/__format/formatter_integral.h b/libcxx/include/__format/formatter_integral.h
@@ -19,6 +19,7 @@
 #include <__format/format_fwd.h>
 #include <__format/formatter.h>
 #include <__format/parser_std_format_spec.h>
+#include <__utility/unreachable.h>
 #include <array>
 #include <charconv>
 #include <concepts>
@@ -176,7 +177,7 @@ __determine_grouping(ptrdiff_t __size, const string& __grouping) {
     }
   }
 
-  _LIBCPP_UNREACHABLE();
+  __libcpp_unreachable();
 }
 
 template <class _Parser>
@@ -292,7 +293,7 @@ class _LIBCPP_TEMPLATE_VIS __formatter_integral : public _Parser {
     }
     default:
       _LIBCPP_ASSERT(false, "The parser should have validated the type");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
   }
 

diff --git a/libcxx/include/__iterator/advance.h b/libcxx/include/__iterator/advance.h
@@ -16,6 +16,7 @@
 #include <__iterator/incrementable_traits.h>
 #include <__iterator/iterator_traits.h>
 #include <__utility/move.h>
+#include <__utility/unreachable.h>
 #include <concepts>
 #include <cstdlib>
 #include <limits>
@@ -181,7 +182,7 @@ struct __fn {
       return __n;
     }
 
-    _LIBCPP_UNREACHABLE();
+    __libcpp_unreachable();
   }
 };
 

diff --git a/libcxx/include/__utility/unreachable.h b/libcxx/include/__utility/unreachable.h
@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___UTILITY_UNREACHABLE_H
+#define _LIBCPP___UTILITY_UNREACHABLE_H
+
+#include <__config>
+#include <cstdlib>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+_LIBCPP_NORETURN _LIBCPP_HIDE_FROM_ABI inline void __libcpp_unreachable()
+{
+#if __has_builtin(__builtin_unreachable)
+  __builtin_unreachable();
+#else
+  std::abort();
+#endif
+}
+
+#if _LIBCPP_STD_VER > 20
+
+[[noreturn]] _LIBCPP_HIDE_FROM_ABI inline void unreachable() { __libcpp_unreachable(); }
+
+#endif // _LIBCPP_STD_VER > 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif
diff --git a/libcxx/include/array b/libcxx/include/array
@@ -111,8 +111,8 @@ template <size_t I, class T, size_t N> const T&& get(const array<T, N>&&) noexce
 #include <__config>
 #include <__debug>
 #include <__tuple>
+#include <__utility/unreachable.h>
 #include <algorithm>
-#include <cstdlib> // for _LIBCPP_UNREACHABLE
 #include <iterator>
 #include <stdexcept>
 #include <type_traits>
@@ -309,54 +309,54 @@ struct _LIBCPP_TEMPLATE_VIS array<_Tp, 0>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
     reference operator[](size_type) _NOEXCEPT {
       _LIBCPP_ASSERT(false, "cannot call array<T, 0>::operator[] on a zero-sized array");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     const_reference operator[](size_type) const _NOEXCEPT {
       _LIBCPP_ASSERT(false, "cannot call array<T, 0>::operator[] on a zero-sized array");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
     reference at(size_type) {
       __throw_out_of_range("array<T, 0>::at");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     const_reference at(size_type) const {
       __throw_out_of_range("array<T, 0>::at");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
     reference front() _NOEXCEPT {
       _LIBCPP_ASSERT(false, "cannot call array<T, 0>::front() on a zero-sized array");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     const_reference front() const _NOEXCEPT {
       _LIBCPP_ASSERT(false, "cannot call array<T, 0>::front() on a zero-sized array");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
     reference back() _NOEXCEPT {
       _LIBCPP_ASSERT(false, "cannot call array<T, 0>::back() on a zero-sized array");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     const_reference back() const _NOEXCEPT {
       _LIBCPP_ASSERT(false, "cannot call array<T, 0>::back() on a zero-sized array");
-      _LIBCPP_UNREACHABLE();
+      __libcpp_unreachable();
     }
 };
 
 
-#if _LIBCPP_STD_VER >= 17
+#if _LIBCPP_STD_VER > 14
 template<class _Tp, class... _Args,
          class = enable_if_t<__all<_IsSame<_Tp, _Args>::value...>::value>
          >

diff --git a/libcxx/include/charconv b/libcxx/include/charconv
@@ -83,16 +83,16 @@ namespace std {
 #include <__charconv/from_chars_result.h>
 #include <__charconv/to_chars_result.h>
 #include <__config>
+#include <__debug>
 #include <__errc>
+#include <__utility/unreachable.h>
 #include <cmath> // for log2f
 #include <cstdint>
-#include <cstdlib> // for _LIBCPP_UNREACHABLE
+#include <cstdlib>
 #include <cstring>
 #include <limits>
 #include <type_traits>
 
-#include <__debug>
-
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
@@ -341,7 +341,7 @@ _LIBCPP_AVAILABILITY_TO_CHARS _LIBCPP_INLINE_VISIBILITY int __to_chars_integral_
     __r += 4;
   }
 
-  _LIBCPP_UNREACHABLE();
+  __libcpp_unreachable();
 }
 
 template <typename _Tp>

diff --git a/libcxx/include/cstdlib b/libcxx/include/cstdlib
@@ -88,12 +88,6 @@ void *aligned_alloc(size_t alignment, size_t size);                       // C11
 #  pragma GCC system_header
 #endif
 
-#ifdef __GNUC__
-#define _LIBCPP_UNREACHABLE() __builtin_unreachable()
-#else
-#define _LIBCPP_UNREACHABLE() _VSTD::abort()
-#endif
-
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 using ::size_t _LIBCPP_USING_IF_EXISTS;

diff --git a/libcxx/include/fstream b/libcxx/include/fstream
@@ -183,6 +183,7 @@ typedef basic_fstream<wchar_t> wfstream;
 #include <__config>
 #include <__debug>
 #include <__locale>
+#include <__utility/unreachable.h>
 #include <cstdio>
 #include <cstdlib>
 #include <istream>
@@ -538,7 +539,7 @@ const char* basic_filebuf<_CharT, _Traits>::__make_mdstring(
   default:
     return nullptr;
   }
-  _LIBCPP_UNREACHABLE();
+  __libcpp_unreachable();
 }
 
 template <class _CharT, class _Traits>