8337657: AArch64: No need for acquire fence in safepoint poll during JNI calls

Reviewed-by: phh

Author: Dmitry Chuyko

src/hotspot/cpu/aarch64/sharedRuntime_aarch64.cpp

@@ -1883,16 +1883,8 @@ nmethod* SharedRuntime::generate_native_wrapper(MacroAssembler* masm,
 
   // Check for safepoint operation in progress and/or pending suspend requests.
   {
-    // We need an acquire here to ensure that any subsequent load of the
-    // global SafepointSynchronize::_state flag is ordered after this load
-    // of the thread-local polling word.  We don't want this poll to
-    // return false (i.e. not safepointing) and a later poll of the global
-    // SafepointSynchronize::_state spuriously to return true.
-    //
-    // This is to avoid a race when we're in a native->Java transition
-    // racing the code which wakes up from a safepoint.
-
-    __ safepoint_poll(safepoint_in_progress, true /* at_return */, true /* acquire */, false /* in_nmethod */);
+    // No need for acquire as Java threads always disarm themselves.
+    __ safepoint_poll(safepoint_in_progress, true /* at_return */, false /* acquire */, false /* in_nmethod */);
     __ ldrw(rscratch1, Address(rthread, JavaThread::suspend_flags_offset()));
     __ cbnzw(rscratch1, safepoint_in_progress);
     __ bind(safepoint_in_progress_done);

src/hotspot/cpu/aarch64/templateInterpreterGenerator_aarch64.cpp

@@ -1413,15 +1413,8 @@ address TemplateInterpreterGenerator::generate_native_entry(bool synchronized) {
   {
     Label L, Continue;
 
-    // We need an acquire here to ensure that any subsequent load of the
-    // global SafepointSynchronize::_state flag is ordered after this load
-    // of the thread-local polling word.  We don't want this poll to
-    // return false (i.e. not safepointing) and a later poll of the global
-    // SafepointSynchronize::_state spuriously to return true.
-    //
-    // This is to avoid a race when we're in a native->Java transition
-    // racing the code which wakes up from a safepoint.
-    __ safepoint_poll(L, true /* at_return */, true /* acquire */, false /* in_nmethod */);
+    // No need for acquire as Java threads always disarm themselves.
+    __ safepoint_poll(L, true /* at_return */, false /* acquire */, false /* in_nmethod */);
     __ ldrw(rscratch2, Address(rthread, JavaThread::suspend_flags_offset()));
     __ cbz(rscratch2, Continue);
     __ bind(L);