[libc++] Fix modules build - Rework __refstring definition

Summary:
`__libcpp_refstring` currently has two different definitions. First there is the complete definition in `<__refstring>` but there is also a second in  `<stdexcept>`.  The historical reason for this split is because both libc++ and libc++abi need to see the inline definitions of __libcpp_refstrings methods, but the `<stdexcept>` header doesn't.  However this is an ODR violation and breaks the modules build.

This patch fixes the issue by creating a single class definition in `<stdexcept>` and changing `<__refstring>` to contain only the inline method definitions. This way both `libcxx/src/stdexcept.cpp` and `libcxxabi/src/stdexcept.cpp` see the same declaration in `<stdexcept>` and definitions in `<__refstring>`

Reviewers: mclow.lists, EricWF

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D25603

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@285100 91177308-0d34-0410-b5e6-96231b3b80d8

include/__refstring

@@ -11,6 +11,7 @@
 #define _LIBCPP___REFSTRING
 
 #include <__config>
+#include <stdexcept>
 #include <cstddef>
 #include <cstring>
 #ifdef __APPLE__
@@ -20,39 +21,28 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-class _LIBCPP_HIDDEN __libcpp_refstring
-{
-private:
-    const char* str_;
-
+namespace __refstring_imp { namespace {
 typedef int count_t;
 
-    struct _Rep_base
-    {
+struct _Rep_base {
     std::size_t len;
     std::size_t cap;
     count_t     count;
 };
 
-    static
-    _Rep_base*
-    rep_from_data(const char *data_) _NOEXCEPT
-    {
+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));
 }
-    static
-    char *
-    data_from_rep(_Rep_base *rep) _NOEXCEPT
-    {
+
+inline char * data_from_rep(_Rep_base *rep) noexcept {
     char *data = reinterpret_cast<char *>(rep);
     return data + sizeof(*rep);
 }
 
-#ifdef __APPLE__
-    static
-    const char*
-    compute_gcc_empty_string_storage() _NOEXCEPT
+#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)
@@ -63,29 +53,21 @@ private:
     return data_from_rep(reinterpret_cast<_Rep_base *>(sym));
 }
 
-    static
+inline
 const char*
 get_gcc_empty_string_storage() _NOEXCEPT
 {
     static const char* p = compute_gcc_empty_string_storage();
     return p;
 }
-
-    bool
-    uses_refcount() const
-    {
-        return str_ != get_gcc_empty_string_storage();
-    }
-#else
-    bool
-    uses_refcount() const
-    {
-        return true;
-    }
 #endif
 
-public:
-    explicit __libcpp_refstring(const char* msg) {
+}} // 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;
@@ -93,22 +75,24 @@ public:
     rep->count = 0;
     char *data = data_from_rep(rep);
     std::memcpy(data, msg, len + 1);
-        str_ = data;
+    __imp_ = data;
 }
 
-    __libcpp_refstring(const __libcpp_refstring& s) _NOEXCEPT : str_(s.str_)
+inline
+__libcpp_refstring::__libcpp_refstring(const __libcpp_refstring &s) _NOEXCEPT
+    : __imp_(s.__imp_)
 {
-        if (uses_refcount())
-            __sync_add_and_fetch(&rep_from_data(str_)->count, 1);
+    if (__uses_refcount())
+        __sync_add_and_fetch(&rep_from_data(__imp_)->count, 1);
 }
 
-    __libcpp_refstring& operator=(const __libcpp_refstring& s) _NOEXCEPT
-    {
-        bool adjust_old_count = uses_refcount();
-        struct _Rep_base *old_rep = rep_from_data(str_);
-        str_ = s.str_;
-        if (uses_refcount())
-            __sync_add_and_fetch(&rep_from_data(str_)->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())
+        __sync_add_and_fetch(&rep_from_data(__imp_)->count, 1);
     if (adjust_old_count)
     {
         if (__sync_add_and_fetch(&old_rep->count, count_t(-1)) < 0)
@@ -119,20 +103,24 @@ public:
     return *this;
 }
 
-    ~__libcpp_refstring()
-    {
-        if (uses_refcount())
-        {
-            _Rep_base* rep = rep_from_data(str_);
-            if (__sync_add_and_fetch(&rep->count, count_t(-1)) < 0)
-            {
+inline
+__libcpp_refstring::~__libcpp_refstring() {
+    if (__uses_refcount()) {
+        _Rep_base* rep = rep_from_data(__imp_);
+        if (__sync_add_and_fetch(&rep->count, count_t(-1)) < 0) {
             ::operator delete(rep);
         }
     }
 }
 
-    const char* c_str() const _NOEXCEPT {return str_;}
-};
+inline
+bool __libcpp_refstring::__uses_refcount() const {
+#ifdef __APPLE__
+    return __imp_ != get_gcc_empty_string_storage();
+#else
+    return true;
+#endif
+}
 
 _LIBCPP_END_NAMESPACE_STD
 

include/stdexcept

@@ -53,17 +53,23 @@ public:
 #pragma GCC system_header
 #endif
 
-#ifndef _LIBCPP___REFSTRING
 _LIBCPP_BEGIN_NAMESPACE_STD
-class _LIBCPP_HIDDEN __libcpp_refstring {
-#ifdef __clang__
-    const char *__imp_ __attribute__((__unused__)); // only clang emits a warning
-#else
+
+class _LIBCPP_HIDDEN __libcpp_refstring
+{
     const char* __imp_;
-#endif
+
+    bool __uses_refcount() const;
+public:
+    explicit __libcpp_refstring(const char* msg);
+    __libcpp_refstring(const __libcpp_refstring& s) _NOEXCEPT;
+    __libcpp_refstring& operator=(const __libcpp_refstring& s) _NOEXCEPT;
+    ~__libcpp_refstring();
+
+    const char* c_str() const _NOEXCEPT {return __imp_;}
 };
+
 _LIBCPP_END_NAMESPACE_STD
-#endif
 
 namespace std  // purposefully not using versioning namespace
 {

src/stdexcept.cpp

@@ -7,11 +7,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "__refstring"
 #include "stdexcept"
 #include "new"
 #include "string"
 #include "system_error"
+#include "__refstring"
 
 /* For _LIBCPPABI_VERSION */
 #if defined(LIBCXX_BUILDING_LIBCXXABI) || defined(__APPLE__) || defined(LIBCXXRT)
@@ -20,6 +20,7 @@
 
 static_assert(sizeof(std::__libcpp_refstring) == sizeof(const char *), "");
 
+
 namespace std  // purposefully not using versioning namespace
 {