# HG changeset patch
# User glaubitz
# Date 1511960308 -3600
#      Wed Nov 29 13:58:28 2017 +0100
# Node ID 0ca256ed11d7018438b285830dd674ffc2eb1977
# Parent  461e9c898e80c32160b36878be97cee47654cdba
8192123: Zero should use compiler built-ins for atomics on linux-arm

diff --git a/src/hotspot/os_cpu/linux_zero/atomic_linux_zero.hpp b/src/hotspot/os_cpu/linux_zero/atomic_linux_zero.hpp
--- a/src/hotspot/os_cpu/linux_zero/atomic_linux_zero.hpp
+++ b/src/hotspot/os_cpu/linux_zero/atomic_linux_zero.hpp
@@ -30,67 +30,6 @@
 
 // Implementation of class atomic
 
-#ifdef ARM
-
-/*
- * __kernel_cmpxchg
- *
- * Atomically store newval in *ptr if *ptr is equal to oldval for user space.
- * Return zero if *ptr was changed or non-zero if no exchange happened.
- * The C flag is also set if *ptr was changed to allow for assembly
- * optimization in the calling code.
- *
- */
-
-typedef int (__kernel_cmpxchg_t)(int oldval, int newval, volatile int *ptr);
-#define __kernel_cmpxchg (*(__kernel_cmpxchg_t *) 0xffff0fc0)
-
-
-
-/* Perform an atomic compare and swap: if the current value of `*PTR'
-   is OLDVAL, then write NEWVAL into `*PTR'.  Return the contents of
-   `*PTR' before the operation.*/
-static inline int arm_compare_and_swap(int newval,
-                                       volatile int *ptr,
-                                       int oldval) {
-  for (;;) {
-      int prev = *ptr;
-      if (prev != oldval)
-        return prev;
-
-      if (__kernel_cmpxchg (prev, newval, ptr) == 0)
-        // Success.
-        return prev;
-
-      // We failed even though prev == oldval.  Try again.
-    }
-}
-
-/* Atomically add an int to memory.  */
-static inline int arm_add_and_fetch(int add_value, volatile int *ptr) {
-  for (;;) {
-      // Loop until a __kernel_cmpxchg succeeds.
-
-      int prev = *ptr;
-
-      if (__kernel_cmpxchg (prev, prev + add_value, ptr) == 0)
-        return prev + add_value;
-    }
-}
-
-/* Atomically write VALUE into `*PTR' and returns the previous
-   contents of `*PTR'.  */
-static inline int arm_lock_test_and_set(int newval, volatile int *ptr) {
-  for (;;) {
-      // Loop until a __kernel_cmpxchg succeeds.
-      int prev = *ptr;
-
-      if (__kernel_cmpxchg (prev, newval, ptr) == 0)
-        return prev;
-    }
-}
-#endif // ARM
-
 template<size_t byte_size>
 struct Atomic::PlatformAdd
   : Atomic::AddAndFetch<Atomic::PlatformAdd<byte_size> >
@@ -105,11 +44,7 @@
   STATIC_ASSERT(4 == sizeof(I));
   STATIC_ASSERT(4 == sizeof(D));
 
-#ifdef ARM
-  return add_using_helper<int>(arm_add_and_fetch, add_value, dest);
-#else
   return __sync_add_and_fetch(dest, add_value);
-#endif // ARM
 }
 
 template<>
@@ -117,7 +52,6 @@
 inline D Atomic::PlatformAdd<8>::add_and_fetch(I add_value, D volatile* dest) const {
   STATIC_ASSERT(8 == sizeof(I));
   STATIC_ASSERT(8 == sizeof(D));
-
   return __sync_add_and_fetch(dest, add_value);
 }
 
@@ -126,9 +60,6 @@
 inline T Atomic::PlatformXchg<4>::operator()(T exchange_value,
                                              T volatile* dest) const {
   STATIC_ASSERT(4 == sizeof(T));
-#ifdef ARM
-  return xchg_using_helper<int>(arm_lock_test_and_set, exchange_value, dest);
-#else
   // __sync_lock_test_and_set is a bizarrely named atomic exchange
   // operation.  Note that some platforms only support this with the
   // limitation that the only valid value to store is the immediate
@@ -140,7 +71,6 @@
   // barrier.
   __sync_synchronize();
   return result;
-#endif // ARM
 }
 
 template<>
@@ -164,11 +94,7 @@
                                                 T compare_value,
                                                 cmpxchg_memory_order order) const {
   STATIC_ASSERT(4 == sizeof(T));
-#ifdef ARM
-  return cmpxchg_using_helper<int>(arm_compare_and_swap, exchange_value, dest, compare_value);
-#else
   return __sync_val_compare_and_swap(dest, compare_value, exchange_value);
-#endif // ARM
 }
 
 template<>