[NFC][libc++] Recognize int128 as an ABI affecting property

[daltenty]

Summary

Whether we have __int128 support in the compiler affects the resulting
library ABI, but there are a few places where we currently don't
reflect this.

Firstly, __config dynamically detects _LIBCPP_HAS_NO_INT128 in the
public headers. This could generate inconsistent results with how the
library was built, if the user uses a compiler with __int128 support
while the library was build without. This change moves
_LIBCPP_HAS_NO_INT128 to __config_site and introduces an option
LIBCXX_USE_INT128 that allows toggling __int128 usage even if it is
available in the build compiler.

Secondly, we add LIBCXX_USE_INT128 to the abi affecting properties for
abilists and update the extension of the existing lists. This will allow
us to generate consistent abis lists on platforms where some compilers
may support __int128 and others don't (e.g. AIX).

[daltenty]

Gentle ping

[ldionne]

I trust that you're right when you say it affects the ABI, but do you have an example (I'm sure there's many, I just can't think of one right now).

Also, can you please rebase and re-upload to poke the CI? I have a few comments but I think this makes sense.

libcxx/CMakeLists.txt

330

I don't think we should allow this to be set explicitly during CMake configuration. If it's an ABI affecting property of the compiler, I believe we should just detect it and set/unset it unconditionally.

I can't imagine building libc++ with one compiler and using it with a compiler so different that it would differ in whether it supports int128. For example, compiling libc++ with a version of Clang and using the headers with a different version of Clang clearly works, however I wouldn't dare ship a library compiled with e.g. GCC to my users. Not saying it won't work, but it seems like living on the edge -- enough that I don't think it's worth supporting. WDYT?

[daltenty]

I trust that you're right when you say it affects the ABI, but do you have an example (I'm sure there's many, I just can't think of one right now).

The problem seems to arise primarily with the implementation of std::chrono::file_clock.

Build with compiler without int128 support:

_ZNSt3__14__fs10filesystem17__last_write_timeERKNS1_4pathENS_6chrono10time_pointINS1_16_FilesystemClockENS5_8durationIxNS_5ratioILl1ELl1000000000EEEEEEEPNS_10error_codeE
std::__1::__fs::filesystem::__last_write_time(std::__1::__fs::filesystem::path const&, std::__1::chrono::time_point<std::__1::__fs::filesystem::_FilesystemClock, std::__1::chrono::duration<long long, std::__1::ratio<1l, 1000000000l> > >, std::__1::error_code*)

Build with int128 support:

_ZNSt3__14__fs10filesystem17__last_write_timeERKNS1_4pathENS_6chrono10time_pointINS1_16_FilesystemClockENS5_8durationInNS_5ratioILl1ELl1000000000EEEEEEEPNS_10error_codeE
std::__1::__fs::filesystem::__last_write_time(std::__1::__fs::filesystem::path const&, std::__1::chrono::time_point<std::__1::__fs::filesystem::_FilesystemClock, std::__1::chrono::duration<__int128, std::__1::ratio<1l, 1000000000l> > >, std::__1::error_code*)

libcxx/CMakeLists.txt

330

The only problem I see with taking the our direction from the build compiler is it doesn't even require something as esoteric as the example of mixing compilers you mentioned. If a compiler transitions in support for the type in a new release, you'd have no way to easily move up the build compiler while still selecting compatibility with the existing ABI.

For example, on AIX clang's support for __int128 only recently landed in https://reviews.llvm.org/D111078 for 64-bit, so clang-13 (and thus Open XL 17.1) don't support it, but clang-14 will.

That said, since the interfaces involving __int128 are relatively new and limited to C++ 20 we might still have some wiggle room about which ABI to choose on AIX, but it still seems better to give the configuration choice in case we aren't the only ones with this problem going forward.

[daltenty]

Rebase to trigger CI

[daltenty]

Rename remaining ABI lists

[ldionne]

libcxx/CMakeLists.txt

330

Okay, I guess this makes sense. Could you also update the AIX.cmake cache accordingly? And also we should be running the check-cxx-abilist target on AIX (I assume we aren't right now). I think this patch would make more sense if we did.

[ldionne]

Is there still interest in shipping this patch? If so, let's rebase it, otherwise let's abandon it to clear the Phabricator queue.

libcxx/CMakeLists.txt

if (MSVC)
   message(STATUS "Configuring for MSVC")
 else()
   set(LIBCXX_TARGETING_MSVC OFF)
 endif()
 
 #===============================================================================
 # Setup CMake Options
 #===============================================================================
+include(CheckCXXSymbolExists)
 include(CMakeDependentOption)
 include(HandleCompilerRT)
 
 # Basic options ---------------------------------------------------------------
 option(LIBCXX_ENABLE_ASSERTIONS "Enable assertions independent of build mode." OFF)
 option(LIBCXX_ENABLE_SHARED "Build libc++ as a shared library." ON)
 option(LIBCXX_ENABLE_STATIC "Build libc++ as a static library." ON)
 option(LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY "Build libc++experimental.a" ON)
if (XCODE OR MSVC_IDE)
   set(LIBCXX_CONFIGURE_IDE_DEFAULT ON)
 endif()
 option(LIBCXX_CONFIGURE_IDE "Configure libcxx for use within an IDE"
       ${LIBCXX_CONFIGURE_IDE_DEFAULT})
 
 option(LIBCXX_HERMETIC_STATIC_LIBRARY
   "Do not export any symbols from the static library." OFF)
 
+check_cxx_symbol_exists(__SIZEOF_INT128__ "" LIBCXX_HAVE_INT128)
+cmake_dependent_option(LIBCXX_USE_INT128   "Use __int128 in the library" ON
+"LIBCXX_HAVE_INT128" OFF)
+
 #===============================================================================
 # Check option configurations
 #===============================================================================
 
 # Ensure LIBCXX_ENABLE_MONOTONIC_CLOCK is set to ON only when
 # LIBCXX_ENABLE_THREADS is on.
 if(LIBCXX_ENABLE_THREADS AND NOT LIBCXX_ENABLE_MONOTONIC_CLOCK)
   message(FATAL_ERROR "LIBCXX_ENABLE_MONOTONIC_CLOCK can only be set to OFF"

 config_define_if_not(LIBCXX_ENABLE_LOCALIZATION _LIBCPP_HAS_NO_LOCALIZATION)
 config_define_if_not(LIBCXX_ENABLE_UNICODE _LIBCPP_HAS_NO_UNICODE)
 config_define_if_not(LIBCXX_ENABLE_WIDE_CHARACTERS _LIBCPP_HAS_NO_WIDE_CHARACTERS)
 config_define_if_not(LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS)
 # Incomplete features get their own specific disabling flags. This makes it
 # easier to grep for target specific flags once the feature is complete.
 config_define_if_not(LIBCXX_ENABLE_INCOMPLETE_FEATURES _LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
 config_define_if_not(LIBCXX_ENABLE_INCOMPLETE_FEATURES _LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+config_define_if_not(LIBCXX_USE_INT128 _LIBCPP_HAS_NO_INT128)
 
 if (LIBCXX_ABI_DEFINES)
   set(abi_defines)
   foreach (abi_define ${LIBCXX_ABI_DEFINES})
     if (NOT abi_define MATCHES "^_LIBCPP_ABI_")
       message(SEND_ERROR "Invalid ABI macro ${abi_define} in LIBCXX_ABI_DEFINES")
     endif()
     list(APPEND abi_defines "#define ${abi_define}")

libcxx/include/__config

 #  define _NOEXCEPT_(x)
 #endif
 
 #ifdef _LIBCPP_HAS_NO_UNICODE_CHARS
 typedef unsigned short char16_t;
 typedef unsigned int   char32_t;
 #endif
 
-#ifndef __SIZEOF_INT128__
-#define _LIBCPP_HAS_NO_INT128
-#endif
-
 #ifdef _LIBCPP_CXX03_LANG
 # define static_assert(...) _Static_assert(__VA_ARGS__)
 # define decltype(...) __decltype(__VA_ARGS__)
 #endif // _LIBCPP_CXX03_LANG
 
 #ifdef _LIBCPP_CXX03_LANG
 #  define _LIBCPP_CONSTEXPR
 #else

libcxx/include/__config_site.in

 #cmakedefine _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION @_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION@
 #cmakedefine _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
 #cmakedefine _LIBCPP_HAS_PARALLEL_ALGORITHMS
 #cmakedefine _LIBCPP_HAS_NO_RANDOM_DEVICE
 #cmakedefine _LIBCPP_HAS_NO_LOCALIZATION
 #cmakedefine _LIBCPP_HAS_NO_WIDE_CHARACTERS
 #cmakedefine _LIBCPP_HAS_NO_INCOMPLETE_FORMAT
 #cmakedefine _LIBCPP_HAS_NO_INCOMPLETE_RANGES
+#cmakedefine _LIBCPP_HAS_NO_INT128
 
 // __USE_MINGW_ANSI_STDIO gets redefined on MinGW
 #ifdef __clang__
 #  pragma clang diagnostic push
 #  pragma clang diagnostic ignored "-Wmacro-redefined"
 #endif
 
 @_LIBCPP_ABI_DEFINES@
 @_LIBCPP_EXTRA_SITE_DEFINES@
 
 #ifdef __clang__
 #  pragma clang diagnostic pop
 #endif
 
 #endif // _LIBCPP_CONFIG_SITE

libcxx/lib/abi/CMakeLists.txt

 
 # This function generates a "unique" identifier based on various properties
 # given as arguments. The idea is to encode all ABI-affecting properties
 # in that identifier, so that we can store ABI information and associate it
 # to a specific ABI configuration.
 #
 # Right now, this is done by using the ABI identifier as the filename containing
 # the list of symbols exported by libc++ for that configuration, however we could
 # make it more sophisticated if the number of ABI-affecting parameters grew.
-function(cxx_abi_list_identifier result triple abi_library abi_version unstable exceptions new_delete_in_libcxx debug_mode_enabled allow_incomplete)
+function(cxx_abi_list_identifier result triple abi_library abi_version unstable exceptions new_delete_in_libcxx debug_mode_enabled allow_incomplete using_int128)
   set(abi_properties)
 
   if ("${triple}" MATCHES "darwin")
     # Ignore the major, minor, and patchlevel versions of darwin targets.
     string(REGEX REPLACE "darwin[0-9]+\\.[0-9]+\\.[0-9]+" "darwin" triple "${triple}")
   elseif("${triple}" MATCHES "freebsd")
     # Ignore the major and minor versions of freebsd targets.
     string(REGEX REPLACE "freebsd[0-9]+\\.[0-9]+" "freebsd" triple "${triple}")
function(cxx_abi_list_identifier result triple abi_library abi_version unstable exceptions new_delete_in_libcxx debug_mode_enabled allow_incomplete using_int128)
   else()
     list(APPEND abi_properties "nodebug")
   endif()
   if (${allow_incomplete})
     list(APPEND abi_properties "incomplete")
   else()
     list(APPEND abi_properties "noincomplete")
   endif()
+  if (${using_int128})
+    list(APPEND abi_properties "int128")
+  else()
+    list(APPEND abi_properties "no_int128")
+  endif()
 
   list(JOIN abi_properties "." tmp)
   set(${result} "${tmp}" PARENT_SCOPE)
 endfunction()
 
 if (CMAKE_CXX_COMPILER_TARGET)
   set(triple "${CMAKE_CXX_COMPILER_TARGET}")
 else()
   set(triple "${LLVM_DEFAULT_TARGET_TRIPLE}")
 endif()
 cxx_abi_list_identifier(abi_list_identifier
   "${triple}"
   "${LIBCXX_CXX_ABI_LIBNAME}"
   "${LIBCXX_ABI_VERSION}"
   "${LIBCXX_ABI_UNSTABLE}"
   "${LIBCXX_ENABLE_EXCEPTIONS}"
   "${LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS}"
   "${LIBCXX_ENABLE_DEBUG_MODE_SUPPORT}"
   "${LIBCXX_ENABLE_INCOMPLETE_FEATURES}"
+  "${LIBCXX_USE_INT128}"
 )
 
 if (TARGET cxx_shared)
   set(abi_list_file "${CMAKE_CURRENT_SOURCE_DIR}/${abi_list_identifier}.abilist")
 
   if (EXISTS "${abi_list_file}")
     add_custom_target(check-cxx-abilist
       "${Python3_EXECUTABLE}" "${LIBCXX_SOURCE_DIR}/utils/sym_diff.py"