[libc++abi] Reuse libc++'s refstring.h header instead of copying it

This has been a long-standing TODO item, however we have now been requiring
a monorepo layout to build libc++ and libc++abi for a while now. Hence,
we can fix this code duplication issue now.

Note that it's still not super pretty to reach into libc++ to include
headers, but it's better than having duplicated code which can get out
of sync.

libcxxabi/src/include/refstring.h

@@ -1,131 +0,0 @@
-//===------------------------ __refstring ---------------------------------===//
-//
-// 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
-//
-//===----------------------------------------------------------------------===//
-
-// FIXME: This file is copied from libcxx/src/include/refstring.h. Instead of
-// duplicating the file in libc++abi we should require that the libc++ sources
-// are available when building libc++abi.
-
-#ifndef _LIBCPPABI_REFSTRING_H
-#define _LIBCPPABI_REFSTRING_H
-
-#include <__config>
-#include <stdexcept>
-#include <cstddef>
-#include <cstring>
-#ifdef __APPLE__
-#include <dlfcn.h>
-#include <mach-o/dyld.h>
-#endif
-#include "atomic_support.h"
-
-_LIBCPP_BEGIN_NAMESPACE_STD
-
-namespace __refstring_imp { namespace {
-typedef int count_t;
-
-struct _Rep_base {
-    std::size_t len;
-    std::size_t cap;
-    count_t     count;
-};
-
-inline _Rep_base* rep_from_data(const char *data_) noexcept {
-    char *data = const_cast<char *>(data_);
-    return reinterpret_cast<_Rep_base *>(data - sizeof(_Rep_base));
-}
-
-inline char * data_from_rep(_Rep_base *rep) noexcept {
-    char *data = reinterpret_cast<char *>(rep);
-    return data + sizeof(*rep);
-}
-
-#if defined(__APPLE__)
-inline
-const char* compute_gcc_empty_string_storage() _NOEXCEPT
-{
-    void* handle = dlopen("/usr/lib/libstdc++.6.dylib", RTLD_NOLOAD);
-    if (handle == nullptr)
-        return nullptr;
-    void* sym = dlsym(handle, "_ZNSs4_Rep20_S_empty_rep_storageE");
-    if (sym == nullptr)
-        return nullptr;
-    return data_from_rep(reinterpret_cast<_Rep_base *>(sym));
-}
-
-inline
-const char*
-get_gcc_empty_string_storage() _NOEXCEPT
-{
-    static const char* p = compute_gcc_empty_string_storage();
-    return p;
-}
-#endif
-
-}} // namespace __refstring_imp
-
-using namespace __refstring_imp;
-
-inline
-__libcpp_refstring::__libcpp_refstring(const char* msg) {
-    std::size_t len = strlen(msg);
-    _Rep_base* rep = static_cast<_Rep_base *>(::operator new(sizeof(*rep) + len + 1));
-    rep->len = len;
-    rep->cap = len;
-    rep->count = 0;
-    char *data = data_from_rep(rep);
-    std::memcpy(data, msg, len + 1);
-    __imp_ = data;
-}
-
-inline
-__libcpp_refstring::__libcpp_refstring(const __libcpp_refstring &s) _NOEXCEPT
-    : __imp_(s.__imp_)
-{
-    if (__uses_refcount())
-        __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
-}
-
-inline
-__libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring const& s) _NOEXCEPT {
-    bool adjust_old_count = __uses_refcount();
-    struct _Rep_base *old_rep = rep_from_data(__imp_);
-    __imp_ = s.__imp_;
-    if (__uses_refcount())
-        __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
-    if (adjust_old_count)
-    {
-        if (__libcpp_atomic_add(&old_rep->count, count_t(-1)) < 0)
-        {
-            ::operator delete(old_rep);
-        }
-    }
-    return *this;
-}
-
-inline
-__libcpp_refstring::~__libcpp_refstring() {
-    if (__uses_refcount()) {
-        _Rep_base* rep = rep_from_data(__imp_);
-        if (__libcpp_atomic_add(&rep->count, count_t(-1)) < 0) {
-            ::operator delete(rep);
-        }
-    }
-}
-
-inline
-bool __libcpp_refstring::__uses_refcount() const {
-#ifdef __APPLE__
-    return __imp_ != get_gcc_empty_string_storage();
-#else
-    return true;
-#endif
-}
-
-_LIBCPP_END_NAMESPACE_STD
-
-#endif //_LIBCPPABI_REFSTRING_H

libcxxabi/src/stdlib_stdexcept.cpp

@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "include/refstring.h"
+#include "../../libcxx/src/include/refstring.h"
 #include "stdexcept"
 #include "new"
 #include <cstdlib>