[libc++] Replace __sync_* functions with __libcpp_atomic_* functions

Summary:
This patch replaces __sync_* with __libcpp_atomic_* and adds a wrapper
function for __atomic_exchange to support _LIBCPP_HAS_NO_THREADS.

Reviewers: EricWF, jroelofs, mclow.lists, compnerd

Reviewed By: EricWF, compnerd

Subscribers: compnerd, efriedma, cfe-commits, joerg, llvm-commits

Differential Revision: https://reviews.llvm.org/D35235

llvm-svn: 313694

2 files changed, 24 insertions, 4 deletions

diff --git a/libcxx/src/include/atomic_support.h b/libcxx/src/include/atomic_support.h
index 08847e63070..ccd8d78d3d7 100644
--- a/libcxx/src/include/atomic_support.h
+++ b/libcxx/src/include/atomic_support.h
@@ -16,6 +16,7 @@
 #if defined(__clang__) && __has_builtin(__atomic_load_n)             \
                        && __has_builtin(__atomic_store_n)            \
                        && __has_builtin(__atomic_add_fetch)          \
+                       && __has_builtin(__atomic_exchange_n)         \
                        && __has_builtin(__atomic_compare_exchange_n) \
                        && defined(__ATOMIC_RELAXED)                  \
                        && defined(__ATOMIC_CONSUME)                  \
@@ -84,6 +85,14 @@ _ValueType __libcpp_atomic_add(_ValueType* __val, _AddType __a,
 
 template <class _ValueType>
 inline _LIBCPP_INLINE_VISIBILITY
+_ValueType __libcpp_atomic_exchange(_ValueType* __target,
+                                    _ValueType __value, int __order = _AO_Seq)
+{
+    return __atomic_exchange_n(__target, __value, __order);
+}
+
+template <class _ValueType>
+inline _LIBCPP_INLINE_VISIBILITY
 bool __libcpp_atomic_compare_exchange(_ValueType* __val,
     _ValueType* __expected, _ValueType __after,
     int __success_order = _AO_Seq,
@@ -137,6 +146,16 @@ _ValueType __libcpp_atomic_add(_ValueType* __val, _AddType __a,
 
 template <class _ValueType>
 inline _LIBCPP_INLINE_VISIBILITY
+_ValueType __libcpp_atomic_exchange(_ValueType* __target,
+                                    _ValueType __value, int __order = _AO_Seq)
+{
+    _ValueType old = *__target;
+    *__target = __value;
+    return old;
+}
+
+template <class _ValueType>
+inline _LIBCPP_INLINE_VISIBILITY
 bool __libcpp_atomic_compare_exchange(_ValueType* __val,
     _ValueType* __expected, _ValueType __after,
     int = 0, int = 0)
diff --git a/libcxx/src/include/refstring.h b/libcxx/src/include/refstring.h
index f0d5b4456da..702f2b7388d 100644
--- a/libcxx/src/include/refstring.h
+++ b/libcxx/src/include/refstring.h
@@ -18,6 +18,7 @@
 #include <dlfcn.h>
 #include <mach-o/dyld.h>
 #endif
+#include "atomic_support.h"
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -83,7 +84,7 @@ __libcpp_refstring::__libcpp_refstring(const __libcpp_refstring &s) _NOEXCEPT
     : __imp_(s.__imp_)
 {
     if (__uses_refcount())
-        __sync_add_and_fetch(&rep_from_data(__imp_)->count, 1);
+        __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
 }
 
 inline
@@ -92,10 +93,10 @@ __libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring const& s) _
     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);
+        __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
     if (adjust_old_count)
     {
-        if (__sync_add_and_fetch(&old_rep->count, count_t(-1)) < 0)
+        if (__libcpp_atomic_add(&old_rep->count, count_t(-1)) < 0)
         {
             ::operator delete(old_rep);
         }
@@ -107,7 +108,7 @@ 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) {
+        if (__libcpp_atomic_add(&rep->count, count_t(-1)) < 0) {
             ::operator delete(rep);
         }
     }