ruby_atomic.h: fix old value type of ATOMIC_CAS

* ruby_atomic.h (ATOMIC_CAS): old value to be swapped should be
  same as the destination.  immediate value may need type
  promotion.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52893 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,4 +1,8 @@
-Sat Dec  5 09:25:41 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Sat Dec  5 09:56:50 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ruby_atomic.h (ATOMIC_CAS): old value to be swapped should be
+	  same as the destination.  immediate value may need type
+	  promotion.
 
 	* ruby_atomic.h (ATOMIC_SIZE_CAS): fix the argument order of
 	  InterlockedCompareExchange64.  new value and then old value is

ruby_atomic.h

@@ -10,7 +10,7 @@ typedef unsigned int rb_atomic_t;
 # define ATOMIC_OR(var, val) __atomic_fetch_or(&(var), (val), __ATOMIC_SEQ_CST)
 # define ATOMIC_EXCHANGE(var, val) __atomic_exchange_n(&(var), (val), __ATOMIC_SEQ_CST)
 # define ATOMIC_CAS(var, oldval, newval) \
-({ __typeof__(oldval) oldvaldup = (oldval); /* oldval should not be modified */ \
+({ __typeof__(var) oldvaldup = (oldval); /* oldval should not be modified */ \
    __atomic_compare_exchange_n(&(var), &oldvaldup, (newval), 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
    oldvaldup; })