RFR(XXS): 8227117: normal interpreter table is not restored after single stepping with TLH

[Daniel D. Daugherty]

Greetings,

Robbin recently discovered this issue with Thread Local Handshakes. Since
he's not available at the moment, I'm handling the issue:

     JDK-8227117 normal interpreter table is not restored after single 
stepping with TLH
     https://bugs.openjdk.java.net/browse/JDK-8227117

When using Thread Local Handshakes, the normal interpreter table is
not restored after single stepping. This issue is caused by the
VM_ChangeSingleStep VM-op relying on SafepointSynchronize::end() to
restore the normal interpreter table for the "off" case.

Prior to Thread Local Handshakes, this was a valid assumption to make.
SafepointSynchronize::end() has been refactored into
disarm_safepoint() and it only calls Interpreter::ignore_safepoints()
on the global safepoint branch. That matches up with the call to
Interpreter::notice_safepoints() that is also on the global safepoint
branch.

The solution is for the VM_ChangeSingleStep VM-op for the "off" case
to call Interpreter::ignore_safepoints() directly.

Here's the webrev URL:

http://cr.openjdk.java.net/~dcubed/8227117-webrev/0_for_jdk14/

The fix is just a small addition to VM_ChangeSingleStep::doit():

    if (_on) {
      Interpreter::notice_safepoints();
+  } else {
+    Interpreter::ignore_safepoints();
    }

Everything else is just new logging support for future debugging of
interpreter table management and single stepping.

Tested this fix with Mach5 Tier[1-3] on the standard Oracle platforms.
Mach5 Tier[4-6] on standard Oracle platforms is running now.

Thanks, in advance, for questions, comments or suggestions.

Dan