[libc++] Fix the LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT setting

[ldionne]

Summary

When the __config_site header is generated, but LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT
wasn't specified, _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT would be defined
to 0, which was the NonUnique RTTI comparison implementation. The intent
was to use the Unique RTTI comparison implementation in that case, which
caused https://llvm.org/PR45549.

Instead, use a proper "switch" to select the RTTI comparison implementation.
Note that 0 can't be used as a value, because that is treated the same
by CMake as a variable that is just not defined.

[davezarzycki]

This change breaks building on Fedora 32 with clang-10 (as shipped by Fedora). Can we revert this or commit a quick fix?

FAIL: libc++ :: libcxx/modules/clocale_exports.compile.pass.cpp (55739 of 64166)

• TEST 'libc++ :: libcxx/modules/clocale_exports.compile.pass.cpp' FAILED ****

Script:

: 'COMPILED WITH'; /usr/bin/clang++ /home/dave/s/lp/libcxx/test/libcxx/modules/clocale_exports.compile.pass.cpp -v -std=c++2a -include /home/dave/s/lp/libcxx/test/support/nasty_macros.h -nostdinc++ -I/home/dave/s/lp/libcxx/include -I/tmp/_update_lc/r/projects/libcxx/include/c++build -DSTDC_FORMAT_MACROS -DSTDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -I/home/dave/s/lp/libcxx/test/support -Werror -Wall -Wextra -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -Wshadow -Wno-unused-command-line-argument -Wno-attributes -Wno-pessimizing-move -Wno-c++11-extensions -Wno-user-defined-literals -Wno-noexcept-type -Wsign-compare -Wunused-variable -Wunused-parameter -Wunreachable-code -Wno-unused-local-typedef -fcoroutines-ts -Werror=thread-safety -Wuser-defined-warnings -fmodules -fsyntax-only

Exit Code: 1

Command Output (stderr):

clang version 10.0.0 (Fedora 10.0.0-1.fc32)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/10
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/10
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
(in-process)
"/usr/bin/clang-10" -cc1 -triple x86_64-unknown-linux-gnu -fsyntax-only -disable-free -disable-llvm-verifier -discard-value-names -main-file-name clocale_exports.compile.pass.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=all -fmath-errno -fno-rounding-math -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v -nostdinc++ -resource-dir /usr/lib64/clang/10.0.0 -include /home/dave/s/lp/libcxx/test/support/nasty_macros.h -I /home/dave/s/lp/libcxx/include -I /tmp/_update_lc/r/projects/libcxx/include/c++build -D STDC_FORMAT_MACROS -D STDC_LIMIT_MACROS -D STDC_CONSTANT_MACROS -I /home/dave/s/lp/libcxx/test/support -D _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -internal-isystem /usr/local/include -internal-isystem /usr/lib64/clang/10.0.0/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -Werror -Wall -Wextra -Wshadow -Wno-unused-command-line-argument -Wno-attributes -Wno-pessimizing-move -Wno-c++11-extensions -Wno-user-defined-literals -Wno-noexcept-type -Wsign-compare -Wunused-variable -Wunused-parameter -Wunreachable-code -Wno-unused-local-typedef -Werror=thread-safety -Wuser-defined-warnings -std=c++2a -fdeprecated-macro -fdebug-compilation-dir /tmp/_update_lc/r/projects/libcxx/test/libcxx/modules -ferror-limit 19 -fmessage-length 0 -fcoroutines-ts -fgnuc-version=4.2.1 -fmodules -fimplicit-module-maps -fmodules-cache-path=/tmp/org.llvm.clang.dave/ModuleCache -fmodules-validate-system-headers -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -faddrsig -x c++ /home/dave/s/lp/libcxx/test/libcxx/modules/clocale_exports.compile.pass.cpp
clang -cc1 version 10.0.0 based upon LLVM 10.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/home/dave/s/lp/libcxx/include
/tmp/_update_lc/r/projects/libcxx/include/c++build
/home/dave/s/lp/libcxx/test/support
/usr/local/include
/usr/lib64/clang/10.0.0/include
/usr/include
End of search list.
clang -cc1 version 10.0.0 based upon LLVM 10.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/home/dave/s/lp/libcxx/include
/tmp/_update_lc/r/projects/libcxx/include/c++build
/home/dave/s/lp/libcxx/test/support
/usr/local/include
/usr/lib64/clang/10.0.0/include
/usr/include
End of search list.
clang -cc1 version 10.0.0 based upon LLVM 10.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/home/dave/s/lp/libcxx/include
/tmp/_update_lc/r/projects/libcxx/include/c++build
/home/dave/s/lp/libcxx/test/support
/usr/local/include
/usr/lib64/clang/10.0.0/include
/usr/include
End of search list.
While building module 'std' imported from /home/dave/s/lp/libcxx/test/libcxx/modules/clocale_exports.compile.pass.cpp:22:
In file included from <module-includes>:31:
In file included from /home/dave/s/lp/libcxx/include/complex.h:28:
In file included from /home/dave/s/lp/libcxx/include/ccomplex:20:
In file included from /home/dave/s/lp/libcxx/include/complex:247:
In file included from /home/dave/s/lp/libcxx/include/sstream:173:
In file included from /home/dave/s/lp/libcxx/include/ostream:138:
In file included from /home/dave/s/lp/libcxx/include/ios:215:
In file included from /home/dave/s/lp/libcxx/include/locale:14:
In file included from /home/dave/s/lp/libcxx/include/string:506:
In file included from /home/dave/s/lp/libcxx/include/string_view:175:
In file included from /home/dave/s/lp/libcxx/include/__string:57:
In file included from /home/dave/s/lp/libcxx/include/algorithm:643:
In file included from /home/dave/s/lp/libcxx/include/memory:668:
/home/dave/s/lp/libcxx/include/typeinfo:267:5: error: invalid configuration for _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION

error invalid configuration for _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION

^

/home/dave/s/lp/libcxx/include/typeinfo:269:6: error: C++ requires a type specifier for all declarations

__impl;
^

/home/dave/s/lp/libcxx/include/typeinfo:280:5: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

__impl::__type_name_t __type_name;
^

/home/dave/s/lp/libcxx/include/typeinfo:284:21: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

: __type_name(__impl::__string_to_type_name(__n)) {}
              ^

/home/dave/s/lp/libcxx/include/typeinfo:293:14: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

return __impl::__type_name_to_string(__type_name);
       ^

/home/dave/s/lp/libcxx/include/typeinfo:299:14: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

return __impl::__lt(__type_name, __arg.__type_name);
       ^

/home/dave/s/lp/libcxx/include/typeinfo:305:14: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

return __impl::__hash(__type_name);
       ^

/home/dave/s/lp/libcxx/include/typeinfo:311:14: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

return __impl::__eq(__type_name, __arg.__type_name);
       ^

/home/dave/s/lp/libcxx/test/libcxx/modules/clocale_exports.compile.pass.cpp:22:10: fatal error: could not build module 'std'
#include <clocale>
~~~~~~~~^
9 errors generated.

---

FAIL: libc++ :: libcxx/modules/cinttypes_exports.compile.pass.cpp (56023 of 64166)

• TEST 'libc++ :: libcxx/modules/cinttypes_exports.compile.pass.cpp' FAILED ****

Script:

: 'COMPILED WITH'; /usr/bin/clang++ /home/dave/s/lp/libcxx/test/libcxx/modules/cinttypes_exports.compile.pass.cpp -v -std=c++2a -include /home/dave/s/lp/libcxx/test/support/nasty_macros.h -nostdinc++ -I/home/dave/s/lp/libcxx/include -I/tmp/_update_lc/r/projects/libcxx/include/c++build -DSTDC_FORMAT_MACROS -DSTDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -I/home/dave/s/lp/libcxx/test/support -Werror -Wall -Wextra -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -Wshadow -Wno-unused-command-line-argument -Wno-attributes -Wno-pessimizing-move -Wno-c++11-extensions -Wno-user-defined-literals -Wno-noexcept-type -Wsign-compare -Wunused-variable -Wunused-parameter -Wunreachable-code -Wno-unused-local-typedef -fcoroutines-ts -Werror=thread-safety -Wuser-defined-warnings -fmodules -fsyntax-only

Exit Code: 1

Command Output (stderr):

clang version 10.0.0 (Fedora 10.0.0-1.fc32)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/10
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/10
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
(in-process)
"/usr/bin/clang-10" -cc1 -triple x86_64-unknown-linux-gnu -fsyntax-only -disable-free -disable-llvm-verifier -discard-value-names -main-file-name cinttypes_exports.compile.pass.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=all -fmath-errno -fno-rounding-math -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v -nostdinc++ -resource-dir /usr/lib64/clang/10.0.0 -include /home/dave/s/lp/libcxx/test/support/nasty_macros.h -I /home/dave/s/lp/libcxx/include -I /tmp/_update_lc/r/projects/libcxx/include/c++build -D STDC_FORMAT_MACROS -D STDC_LIMIT_MACROS -D STDC_CONSTANT_MACROS -I /home/dave/s/lp/libcxx/test/support -D _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -internal-isystem /usr/local/include -internal-isystem /usr/lib64/clang/10.0.0/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -Werror -Wall -Wextra -Wshadow -Wno-unused-command-line-argument -Wno-attributes -Wno-pessimizing-move -Wno-c++11-extensions -Wno-user-defined-literals -Wno-noexcept-type -Wsign-compare -Wunused-variable -Wunused-parameter -Wunreachable-code -Wno-unused-local-typedef -Werror=thread-safety -Wuser-defined-warnings -std=c++2a -fdeprecated-macro -fdebug-compilation-dir /tmp/_update_lc/r/projects/libcxx/test/libcxx/modules -ferror-limit 19 -fmessage-length 0 -fcoroutines-ts -fgnuc-version=4.2.1 -fmodules -fimplicit-module-maps -fmodules-cache-path=/tmp/org.llvm.clang.dave/ModuleCache -fmodules-validate-system-headers -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -faddrsig -x c++ /home/dave/s/lp/libcxx/test/libcxx/modules/cinttypes_exports.compile.pass.cpp
clang -cc1 version 10.0.0 based upon LLVM 10.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/home/dave/s/lp/libcxx/include
/tmp/_update_lc/r/projects/libcxx/include/c++build
/home/dave/s/lp/libcxx/test/support
/usr/local/include
/usr/lib64/clang/10.0.0/include
/usr/include
End of search list.
clang -cc1 version 10.0.0 based upon LLVM 10.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/home/dave/s/lp/libcxx/include
/tmp/_update_lc/r/projects/libcxx/include/c++build
/home/dave/s/lp/libcxx/test/support
/usr/local/include
/usr/lib64/clang/10.0.0/include
/usr/include
End of search list.
clang -cc1 version 10.0.0 based upon LLVM 10.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/home/dave/s/lp/libcxx/include
/tmp/_update_lc/r/projects/libcxx/include/c++build
/home/dave/s/lp/libcxx/test/support
/usr/local/include
/usr/lib64/clang/10.0.0/include
/usr/include
End of search list.
While building module 'std' imported from /home/dave/s/lp/libcxx/test/libcxx/modules/cinttypes_exports.compile.pass.cpp:22:
In file included from <module-includes>:31:
In file included from /home/dave/s/lp/libcxx/include/complex.h:28:
In file included from /home/dave/s/lp/libcxx/include/ccomplex:20:
In file included from /home/dave/s/lp/libcxx/include/complex:247:
In file included from /home/dave/s/lp/libcxx/include/sstream:173:
In file included from /home/dave/s/lp/libcxx/include/ostream:138:
In file included from /home/dave/s/lp/libcxx/include/ios:215:
In file included from /home/dave/s/lp/libcxx/include/locale:14:
In file included from /home/dave/s/lp/libcxx/include/string:506:
In file included from /home/dave/s/lp/libcxx/include/string_view:175:
In file included from /home/dave/s/lp/libcxx/include/__string:57:
In file included from /home/dave/s/lp/libcxx/include/algorithm:643:
In file included from /home/dave/s/lp/libcxx/include/memory:668:
/home/dave/s/lp/libcxx/include/typeinfo:267:5: error: invalid configuration for _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION

error invalid configuration for _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION

^

/home/dave/s/lp/libcxx/include/typeinfo:269:6: error: C++ requires a type specifier for all declarations

__impl;
^

/home/dave/s/lp/libcxx/include/typeinfo:280:5: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

__impl::__type_name_t __type_name;
^

/home/dave/s/lp/libcxx/include/typeinfo:284:21: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

: __type_name(__impl::__string_to_type_name(__n)) {}
              ^

/home/dave/s/lp/libcxx/include/typeinfo:293:14: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

return __impl::__type_name_to_string(__type_name);
       ^

/home/dave/s/lp/libcxx/include/typeinfo:299:14: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

return __impl::__lt(__type_name, __arg.__type_name);
       ^

/home/dave/s/lp/libcxx/include/typeinfo:305:14: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

return __impl::__hash(__type_name);
       ^

/home/dave/s/lp/libcxx/include/typeinfo:311:14: error: 'std::type_info::__impl' (aka 'int') is not a class, namespace, or enumeration

return __impl::__eq(__type_name, __arg.__type_name);
       ^

/home/dave/s/lp/libcxx/test/libcxx/modules/cinttypes_exports.compile.pass.cpp:22:10: fatal error: could not build module 'std'
#include <cinttypes>
~~~~~~~~^
9 errors generated.

---

---

Failing Tests (2):

libc++ :: libcxx/modules/cinttypes_exports.compile.pass.cpp
libc++ :: libcxx/modules/clocale_exports.compile.pass.cpp

Testing Time: 167.45s

Unsupported Tests  : 12368
Expected Passes    : 51643
Expected Failures  :   153
Unexpected Failures:     2

10 warning(s) in tests
FAILED: CMakeFiles/check-all

[ldionne]

Thanks for the heads up. I've been looking at the issue without being able to reproduce it on a recent clang -- so far I think this is a modules cache issue.

libcxx/CMakeLists.txt

 
 set(LIBCXX_ABI_VERSION "1" CACHE STRING "ABI version of libc++. Can be either 1 or 2, where 2 is currently not stable. Defaults to 1.")
 set(LIBCXX_ABI_NAMESPACE "" CACHE STRING "The inline ABI namespace used by libc++. It defaults to __n where `n` is the current ABI version.")
 option(LIBCXX_ABI_UNSTABLE "Unstable ABI of libc++." OFF)
 option(LIBCXX_ABI_FORCE_ITANIUM "Ignore auto-detection and force use of the Itanium ABI.")
 option(LIBCXX_ABI_FORCE_MICROSOFT "Ignore auto-detection and force use of the Microsoft ABI.")
 
 
-set(LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT  "" CACHE STRING
-  "Whether typeinfo names are expected to be unique. Defining this option overrides the default configuration in the library.")
-set(MERGED_TYPEINFO_VALUES ";ON;OFF")
-set_property(CACHE LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT PROPERTY STRINGS ${MERGED_TYPEINFO_DEFAULTS})
-list(FIND MERGED_TYPEINFO_VALUES "${LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT}" IS_VALID_DEFAULT)
+set(LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION "" CACHE STRING "The implementation of typeinfo comparison to use.")
+set(TYPEINFO_COMPARISON_VALUES ";1;2")
+set_property(CACHE LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION PROPERTY STRINGS ${TYPEINFO_COMPARISON_VALUES})
+list(FIND TYPEINFO_COMPARISON_VALUES "${LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION}" IS_VALID_DEFAULT)
 if (${IS_VALID_DEFAULT} EQUAL -1)
-  message(FATAL_ERROR "Value '${LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT}' is not a valid value for
-          LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT")
+  message(FATAL_ERROR "Value '${LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION}' is not a valid value for
+          LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION")
 endif()
 
 option(LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT "Enable per TU ABI insulation by default. To be used by vendors." OFF)
 set(LIBCXX_ABI_DEFINES "" CACHE STRING "A semicolon separated list of ABI macros to define in the site config header.")
 option(LIBCXX_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)
 set(LIBCXX_LIBCPPABI_VERSION "2" CACHE STRING "Version of libc++abi's ABI to re-export from libc++ when re-exporting is enabled.
                                                Note that this is not related to the version of libc++'s ABI itself!")
 

 config_define_if(LIBCXX_ABI_FORCE_MICROSOFT _LIBCPP_ABI_FORCE_MICROSOFT)
 config_define_if(LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT _LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT)
 config_define_if_not(LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE)
 config_define_if_not(LIBCXX_ENABLE_STDIN _LIBCPP_HAS_NO_STDIN)
 config_define_if_not(LIBCXX_ENABLE_STDOUT _LIBCPP_HAS_NO_STDOUT)
 config_define_if_not(LIBCXX_ENABLE_THREADS _LIBCPP_HAS_NO_THREADS)
 config_define_if_not(LIBCXX_ENABLE_MONOTONIC_CLOCK _LIBCPP_HAS_NO_MONOTONIC_CLOCK)
 config_define_if_not(LIBCXX_ENABLE_THREAD_UNSAFE_C_FUNCTIONS _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS)
-if (NOT LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT STREQUAL "")
-  config_define("${LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT}" _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT)
+if (NOT LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION STREQUAL "")
+  config_define("${LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION}" _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION)
 endif()
 
 config_define_if(LIBCXX_HAS_PTHREAD_API _LIBCPP_HAS_THREAD_API_PTHREAD)
 config_define_if(LIBCXX_HAS_EXTERNAL_THREAD_API _LIBCPP_HAS_THREAD_API_EXTERNAL)
 config_define_if(LIBCXX_HAS_WIN32_THREAD_API _LIBCPP_HAS_THREAD_API_WIN32)
 config_define_if(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY _LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL)
 config_define_if(LIBCXX_HAS_MUSL_LIBC _LIBCPP_HAS_MUSL_LIBC)
 config_define_if(LIBCXX_NO_VCRUNTIME _LIBCPP_NO_VCRUNTIME)

libcxx/cmake/caches/Apple.cmake

 set(CMAKE_BUILD_TYPE MinSizeRel CACHE STRING "")
 set(CMAKE_POSITION_INDEPENDENT_CODE OFF CACHE BOOL "")
 
 set(LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
 set(LIBCXX_ENABLE_ASSERTIONS OFF CACHE BOOL "")
 set(LIBCXX_ABI_VERSION "1" CACHE STRING "")
 set(LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_STATIC OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_SHARED ON CACHE BOOL "")
-set(LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT ON CACHE STRING "")
+set(LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION "1" CACHE STRING "")
 set(LIBCXX_CXX_ABI libcxxabi CACHE STRING "")
 set(LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS OFF CACHE BOOL "")
 set(LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT ON CACHE BOOL "")
 
 set(LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS ON CACHE BOOL "")
 set(LIBCXXABI_ENABLE_PIC OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_ASSERTIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_FORGIVING_DYNAMIC_CAST ON CACHE BOOL "")

libcxx/docs/BuildingLibcxx.rst

 .. option:: LIBCXX_ABI_DEFINES:STRING
 
   **Default**: ``""``
 
   A semicolon-separated list of ABI macros to persist in the site config header.
   See ``include/__config`` for the list of ABI macros.
 
 
-.. option:: LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT
+.. option:: LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION
 
-  **Default**: ``None``. When defined this option overrides the libraries default configuration
-  for whether merged type info names are present.
+  **Default**: ``None``, which lets the library figure out which implementation
+  to use based on the object format.
 
+  This setting defines what implementation to use for comparing typeinfo objects.
+  There are two main implementations, which differ on whether we make the assumption
+  that type info names for a type have been fully merged are unique across the entire
+  program. This may not be the case for libraries built with ``-Bsymbolic`` or due to
+  compiler or linker bugs (Ex. llvm.org/PR37398).
 
-  Build ``std::type_info`` with the assumption that type info names for a type have been fully
-  merged are unique across the entire program. This may not be the case for libraries built with
-  ``-Bsymbolic`` or due to compiler or linker bugs (Ex. llvm.org/PR37398).
 
-  When the value is ``ON`` typeinfo comparisons compare only the pointer value, otherwise ``strcmp``
-  is used as a fallback.
+  When the value is set to ``1``, we assume that typeinfos are unique across the
+  whole program, and typeinfo comparisons compare only the pointer value.
+
+  When the value is set to ``2``, we do not assume that typeinfos are unique across
+  the whole program. We first compare the pointers, and then use ``strcmp`` on the
+  typeinfo names as a fallback.
 
 
 .. _LLVM-specific variables:
 
 LLVM-specific options
 ---------------------
 
 .. option:: LLVM_LIBDIR_SUFFIX:STRING

libcxx/include/__config

 #ifndef _LIBCPP_HIDE_FROM_ABI_PER_TU
 #  ifndef _LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT
 #    define _LIBCPP_HIDE_FROM_ABI_PER_TU 0
 #  else
 #    define _LIBCPP_HIDE_FROM_ABI_PER_TU 1
 #  endif
 #endif
 
-#ifndef _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT
+#ifndef _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION
 #  ifdef _LIBCPP_OBJECT_FORMAT_COFF // Windows binaries can't merge typeinfos.
-#    define _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT 0
+#    define _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION 2
 #  else
      // TODO: This isn't strictly correct on ELF platforms due to llvm.org/PR37398
      // And we should consider defaulting to OFF.
-#    define _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT 1
+#    define _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION 1
 #  endif
 #endif
 
 #ifndef _LIBCPP_HIDE_FROM_ABI
 #  if _LIBCPP_HIDE_FROM_ABI_PER_TU
 #    define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_INTERNAL_LINKAGE
 #  else
 #    define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION

libcxx/include/__config_site.in

 #cmakedefine _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 #cmakedefine _LIBCPP_HAS_MUSL_LIBC
 #cmakedefine _LIBCPP_HAS_THREAD_API_PTHREAD
 #cmakedefine _LIBCPP_HAS_THREAD_API_EXTERNAL
 #cmakedefine _LIBCPP_HAS_THREAD_API_WIN32
 #cmakedefine _LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL
 #cmakedefine _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS
 #cmakedefine _LIBCPP_NO_VCRUNTIME
-#ifndef _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT
-#cmakedefine01 _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT
+#ifndef _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION
+#cmakedefine _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION @_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION@
 #endif
 #cmakedefine _LIBCPP_ABI_NAMESPACE @_LIBCPP_ABI_NAMESPACE@
 #cmakedefine _LIBCPP_HAS_PARALLEL_ALGORITHMS
 
 @_LIBCPP_ABI_DEFINES@
 
 #endif // _LIBCPP_CONFIG_SITE

libcxx/include/typeinfo

 
 #else // !defined(_LIBCPP_ABI_MICROSOFT)
 
 // ========================================================================== //
 //                           Implementations
 // ========================================================================== //
 // ------------------------------------------------------------------------- //
 //                               Unique
+//               (_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION = 1)
 // ------------------------------------------------------------------------- //
 // This implementation of type_info assumes a unique copy of the RTTI for a
 // given type inside a program. This is a valid assumption when abiding to
 // Itanium ABI (http://itanium-cxx-abi.github.io/cxx-abi/abi.html#vtable-components).
 // Under this assumption, we can always compare the addresses of the type names
 // to implement equality-comparison of type_infos instead of having to perform
 // a deep string comparison.
 // -------------------------------------------------------------------------- //
 //                             NonUnique
+//               (_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION = 2)
 // -------------------------------------------------------------------------- //
 // This implementation of type_info does not assume there is always a unique
 // copy of the RTTI for a given type inside a program. For various reasons
 // the linker may have failed to merge every copy of a types RTTI
 // (For example: -Bsymbolic or llvm.org/PR37398). Under this assumption, two
 // type_infos are equal if their addresses are equal or if a deep string
 // comparison is equal.
 // -------------------------------------------------------------------------- //
 //                          NonUniqueARMRTTIBit
+// (selected on ARM64 regardless of _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION)
 // -------------------------------------------------------------------------- //
 // This implementation of type_info does not assume always a unique copy of
 // the RTTI for a given type inside a program. It packs the pointer to the
 // type name into a uintptr_t and reserves the high bit of that pointer (which
 // is assumed to be free for use under the ABI in use) to represent whether
 // that specific copy of the RTTI can be assumed unique inside the program.
 // To implement equality-comparison of type_infos, we check whether BOTH
 // type_infos are guaranteed unique, and if so, we simply compare the addresses
private:
     static bool __is_type_name_unique(__type_name_t __lhs, __type_name_t __rhs) _NOEXCEPT {
       return !((__lhs & __rhs) & __non_unique_rtti_bit::value);
     }
   };
 
   typedef
 #if defined(__APPLE__) && defined(__LP64__) && !defined(__x86_64__)
     __non_unique_arm_rtti_bit_impl
-#elif _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT == 0
-    __non_unique_impl
-#elif _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT == 1
+#elif _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION == 1
     __unique_impl
+#elif _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION == 2
+    __non_unique_impl
 #else
-#   error invalid configuration for _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT
+#   error invalid configuration for _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION
 #endif
      __impl;
 };
 
 class _LIBCPP_EXCEPTION_ABI type_info
 {
   type_info& operator=(const type_info&);
   type_info(const type_info&);

libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.apple.compile.pass.cpp

 // We don't really want to require 'darwin' here -- instead we'd like to express
 // that this test requires the flavor of libc++ built by Apple, which we don't
 // have a clear way to express right now. If another flavor of libc++ was built
 // targetting Apple platforms without assuming merged RTTI, this test would fail.
 // REQUIRES: darwin
 
 #include <typeinfo>
 
-#if !defined(_LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT)
-#   error "_LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT should be defined on Apple platforms"
+#if !defined(_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION)
+#   error "_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION should be defined on Apple platforms"
 #endif
 
-#if _LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT != 1
-#   error "_LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT should be 1 (assume RTTI is merged) on Apple platforms"
+#if _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION != 1
+#   error "_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION should be 1 (assume RTTI is merged) on Apple platforms"
 #endif

libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.merged.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: -fno-rtti
 
 // FILE_DEPENDENCIES: %t.exe
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu1.o -DTU1 -D_LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=1
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu2.o -DTU2 -D_LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=1
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.main.o -DMAIN -D_LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=1
+// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu1.o -DTU1 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=1
+// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu2.o -DTU2 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=1
+// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.main.o -DMAIN -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=1
 // RUN: %{cxx} %t.tu1.o %t.tu2.o %t.main.o %{flags} %{link_flags} -o %t.exe
 // RUN: %{exec} %t.exe
 
 #include <cassert>
 #include <typeindex>
 #include <vector>
 
 extern std::vector<std::type_index> registry;

libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.unmerged.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: -fno-rtti
 
 // FILE_DEPENDENCIES: %t.exe
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu1.o -DTU1 -D_LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=0
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu2.o -DTU2 -D_LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=0
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.main.o -DMAIN -D_LIBCPP_HAS_MERGED_TYPEINFO_NAMES_DEFAULT=0
+// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu1.o -DTU1 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=2
+// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu2.o -DTU2 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=2
+// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.main.o -DMAIN -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=2
 // RUN: %{cxx} %t.tu1.o %t.tu2.o %t.main.o %{flags} %{link_flags} -o %t.exe
 // RUN: %{exec} %t.exe
 
 #include <cassert>
 #include <typeindex>
 #include <vector>
 
 extern std::vector<std::type_index> registry;