libcxx: Use vcruntime declarations for typeinfo on Windows.

[pcc]

Summary

We need to use the vcruntime declarations on Windows to avoid an ODR
violation involving rtti.obj, which provides the definition of the runtime function
implementing dynamic_cast and depends on the vcruntime implementations of
bad_cast and bad_typeid.

[EricWF]

Is this really a "fix" or does it just hide the ODR issue?

[mclow.lists]

I'd like to call attention to http://libcxxabi.llvm.org, specifically the FAQ entry: Why are the destructors for the standard exception classes defined in libc++abi? They're just empty, can't they be defined inline?

[pcc]

Is this really a "fix" or does it just hide the ODR issue?

You're right, there is an ODR issue. I'll see if it can be solved by using the definitions of these classes from vcruntime_typeinfo.h on Windows. Fixing this in the case where _LIBCPP_NO_VCRUNTIME is defined seems more tricky; I'll leave the situation as is there.

I'd like to call attention to http://libcxxabi.llvm.org, specifically the FAQ entry: Why are the destructors for the standard exception classes defined in libc++abi? They're just empty, can't they be defined inline?

I have read that FAQ entry, but it doesn't seem directly applicable on Windows whose ABI uses a string comparison for type_info comparisons.

[pcc]

• Use typeinfo declarations from vcruntime

[pcc]

Ping.

[compnerd]

I think that this is reasonable to unblock the use of libc++ with and without vcruntime headers. The one thing that I wish was slightly cleaner is not your fault.

libcxx/src/typeinfo.cpp

53 ↗

(On Diff #130343)

I wish that there was a reasonable way to split this logic up.

include/typeinfo

 #ifdef _LIBCPP_NO_EXCEPTIONS
 #include <cstdlib>
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
+#if defined(_LIBCPP_ABI_MICROSOFT) && !defined(_LIBCPP_NO_VCRUNTIME)
+#include <vcruntime_typeinfo.h>
+#else
+
 #if !defined(_LIBCPP_ABI_MICROSOFT)
 #if defined(_LIBCPP_NONUNIQUE_RTTI_BIT)
 #define _LIBCPP_HAS_NONUNIQUE_TYPEINFO
 #else
 #define _LIBCPP_HAS_UNIQUE_TYPEINFO
 #endif
 #endif
 

 public:
     bad_typeid() _NOEXCEPT;
     virtual ~bad_typeid() _NOEXCEPT;
     virtual const char* what() const _NOEXCEPT;
 };
 
 }  // std
 
+#endif // defined(_LIBCPP_ABI_MICROSOFT) && !defined(_LIBCPP_NO_VCRUNTIME)
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 _LIBCPP_NORETURN inline _LIBCPP_ALWAYS_INLINE
 void __throw_bad_cast()
 {
 #ifndef _LIBCPP_NO_EXCEPTIONS
     throw bad_cast();
 #else
   _VSTD::abort();
 #endif
 }
 _LIBCPP_END_NAMESPACE_STD
 
 #endif  // __LIBCPP_TYPEINFO

src/support/runtime/exception_msvc.ipp

 }
 
 const char*
 bad_array_length::what() const _NOEXCEPT
 {
     return "bad_array_length";
 }
 
+#if defined(_LIBCPP_NO_VCRUNTIME)
 bad_cast::bad_cast() _NOEXCEPT
 {
 }
 
 bad_cast::~bad_cast() _NOEXCEPT
 {
 }
 

 }
 
 const char *
 bad_typeid::what() const _NOEXCEPT
 {
   return "std::bad_typeid";
 }
 
-#if defined(_LIBCPP_NO_VCRUNTIME)
 exception::~exception() _NOEXCEPT
 {
 }
 
 const char* exception::what() const _NOEXCEPT
 {
   return "std::exception";
 }

src/typeinfo.cpp

 //===------------------------- typeinfo.cpp -------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "typeinfo"
 
-#if defined(_LIBCPP_ABI_MICROSOFT)
+#if defined(_LIBCPP_ABI_MICROSOFT) && defined(_LIBCPP_NO_VCRUNTIME)
 #include <string.h>
 
 int std::type_info::__compare(const type_info &__rhs) const _NOEXCEPT {
   if (&__data == &__rhs.__data)
     return 0;
   return strcmp(&__data.__decorated_name[1], &__rhs.__data.__decorated_name[1]);
 }
 
#endif
 
   return value;
 }
 #endif // _LIBCPP_ABI_MICROSOFT
 
 // FIXME: Remove __APPLE__ default here once buildit is gone.
 // FIXME: Remove the _LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY configuration.
 #if (!defined(LIBCXX_BUILDING_LIBCXXABI) && !defined(LIBCXXRT) &&              \
-     !defined(__GLIBCXX__) && !defined(__APPLE__)) ||                          \
+     !defined(__GLIBCXX__) && !defined(__APPLE__) &&                           \
+     !(defined(_LIBCPP_ABI_MICROSOFT) && !defined(_LIBCPP_NO_VCRUNTIME))) ||   \
     defined(_LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY)
 std::type_info::~type_info()
 {
 }
 #endif