[libcxx] Make sure we can build with -fvisibility=hidden on Linux

[ldionne]

Summary

This commit marks a few functions as hidden and removes them from the ABI list
on Linux such that libc++ can be built with -fvisibility=hidden. The functions
marked as hidden by this patch were exported from the shared object only
because they were implicitly instantiated function templates. It is safe
to stop exporting those symbols from the shared object because nobody could
actually depend on them: implicit instantiations are not taken from shared
objects.

The symbols removed in this commit are basically the same that had been
removed in https://reviews.llvm.org/D53868, but that patch had to be reverted
because it broke the build (because the functions were not marked as hidden
like this patch does).

[ldionne]

I'm shipping this because I have other changes depending on it and we already reviewed the ABI changes in https://reviews.llvm.org/D53868. Please LMK if you have concerns with this patch and I can revert it or fix them post-commit.

include/algorithm

if (__c(*__x4, *__x3))
         }
     }
     return __r;
 }
 
 // stable, 4-10 compares, 0-9 swaps
 
 template <class _Compare, class _ForwardIterator>
+_LIBCPP_HIDDEN
 unsigned
 __sort5(_ForwardIterator __x1, _ForwardIterator __x2, _ForwardIterator __x3,
             _ForwardIterator __x4, _ForwardIterator __x5, _Compare __c)
 {
     unsigned __r = __sort4<_Compare>(__x1, __x2, __x3, __x4, __c);
     if (__c(*__x5, *__x4))
     {
         swap(*__x4, *__x5);

include/locale

virtual iter_type do_get(iter_type __b, iter_type __e, ios_base& __iob,
                              ios_base::iostate& __err, void*& __v) const;
 };
 
 template <class _CharT, class _InputIterator>
 locale::id
 num_get<_CharT, _InputIterator>::id;
 
 template <class _Tp>
-_Tp
+_LIBCPP_HIDDEN _Tp
 __num_get_signed_integral(const char* __a, const char* __a_end,
                           ios_base::iostate& __err, int __base)
 {
     if (__a != __a_end)
     {
         typename remove_reference<decltype(errno)>::type __save_errno = errno;
         errno = 0;
         char *__p2;
if (__a != __a_end)
         }
         return static_cast<_Tp>(__ll);
     }
     __err = ios_base::failbit;
     return 0;
 }
 
 template <class _Tp>
-_Tp
+_LIBCPP_HIDDEN _Tp
 __num_get_unsigned_integral(const char* __a, const char* __a_end,
                             ios_base::iostate& __err, int __base)
 {
     if (__a != __a_end)
     {
         const bool __negate = *__a == '-';
         if (__negate && ++__a == __a_end) {
           __err = ios_base::failbit;

include/string

operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Allocator>& __rhs)
     basic_string<_CharT, _Traits, _Allocator> __r(__rhs.get_allocator());
     typename basic_string<_CharT, _Traits, _Allocator>::size_type __rhs_sz = __rhs.size();
     __r.__init(&__lhs, 1, 1 + __rhs_sz);
     __r.append(__rhs.data(), __rhs_sz);
     return __r;
 }
 
 template<class _CharT, class _Traits, class _Allocator>
+_LIBCPP_INLINE_VISIBILITY
 basic_string<_CharT, _Traits, _Allocator>
 operator+(const basic_string<_CharT, _Traits, _Allocator>& __lhs, const _CharT* __rhs)
 {
     basic_string<_CharT, _Traits, _Allocator> __r(__lhs.get_allocator());
     typename basic_string<_CharT, _Traits, _Allocator>::size_type __lhs_sz = __lhs.size();
     typename basic_string<_CharT, _Traits, _Allocator>::size_type __rhs_sz = _Traits::length(__rhs);
     __r.__init(__lhs.data(), __lhs_sz, __lhs_sz + __rhs_sz);
     __r.append(__rhs, __rhs_sz);

lib/abi/CHANGELOG.TXT

 Afterwards the ABI list should be updated to include the new changes.
 
 New entries should be added directly below the "Version" header.
 
 -----------
 Version 8.0
 -----------
 
-* r345260 - Making libc++ build under -fvisibility=hidden
+* rXXXXXX - Making libc++ build under -fvisibility=hidden on Linux
+
+  The change marks several function templates as hidden. This removes symbols
+  from the shared library, but this is not an ABI break because it's impossible
+  for programs linking against libc++.so to actually depend on that symbol.
+  The reason is that the symbol is exported from the shared library through
+  an implicit instantiation present in the shared object itself only. Furthermore,
+  if a user's shared object was implicitly instantiating one of these functions,
+  marking that symbol as hidden would not be an ABI break for them because none
+  of their users could actually be using the symbol in their dylib (because
+  it's an implicit instantiation).
+
+  x86_64-linux-gnu
+  ----------------
+  Symbol removed: _ZNSt3__125__num_get_signed_integralIlEET_PKcS3_Rji
+  Symbol removed: _ZNSt3__125__num_get_signed_integralIxEET_PKcS3_Rji
+  Symbol removed: _ZNSt3__127__num_get_unsigned_integralIjEET_PKcS3_Rji
+  Symbol removed: _ZNSt3__127__num_get_unsigned_integralImEET_PKcS3_Rji
+  Symbol removed: _ZNSt3__127__num_get_unsigned_integralItEET_PKcS3_Rji
+  Symbol removed: _ZNSt3__127__num_get_unsigned_integralIyEET_PKcS3_Rji
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIaaEEPaEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIccEEPcEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIddEEPdEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIffEEPfEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIhhEEPhEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIiiEEPiEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIjjEEPjEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIllEEPlEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessImmEEPmEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIssEEPsEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIttEEPtEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIwwEEPwEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIxxEEPxEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__17__sort5IRNS_6__lessIyyEEPyEEjT0_S5_S5_S5_S5_T_
+  Symbol removed: _ZNSt3__1plIcNS_11char_traitsIcEENS_9allocatorIcEEEENS_12basic_stringIT_T0_T1_EERKS9_PKS6_
+  Symbol removed: _ZSt18make_exception_ptrINSt3__112future_errorEESt13exception_ptrT_
+
+* r345260 - Making libc++ build under -fvisibility=hidden on Mac OS
 
   The change marks __thread_specific_ptr<__thread_struct>::__at_thread_exit(void*)
   with hidden visibility. This removes a symbol from the shared libraries,
   however this is not an ABI break because it's impossible for programs linking
   against libc++.dylib to actually depend on that symbol. The reason is that
   the symbol is exported from the shared library through an implicit
   instantiation present in the dylib itself only. Furthermore, if a user's
   dylib was implicitly instantiating __thread_specific_ptr<T>::__at_thread_exit

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