Bug 339858 arm64 recognize dmb sy. Data Memory Barrier full SYstem variant.

git-svn-id: svn://svn.valgrind.org/vex/trunk@2975 8f6e269a-dfd6-0310-a8e1-e2731360e62c
diff --git a/priv/guest_arm64_toIR.c b/priv/guest_arm64_toIR.c
index 2aa145c..5ebe0a6 100644
--- a/priv/guest_arm64_toIR.c
+++ b/priv/guest_arm64_toIR.c
@@ -5537,6 +5537,11 @@
       DIP("isb\n");
       return True;
    }
+   if (INSN(31,0) == 0xD5033FBF) {
+      stmt(IRStmt_MBE(Imbe_Fence));
+      DIP("dmb sy\n");
+      return True;
+   }
    if (INSN(31,0) == 0xD5033BBF) {
       stmt(IRStmt_MBE(Imbe_Fence));
       DIP("dmb ish\n");