elision of volatile field load with empty usages

[Garcia Gutierrez Miguel Alfredo]

In general, a field-load with empty usages on a definitely-non-null is candidate for elision.

However, what about volatile fields? Currently, elision is done (see excerpt below)

  public final class LoadFieldNode extends AccessFieldNode implements Canonicalizable, VirtualizableRoot {
      ...
      public Node canonical(CanonicalizerTool tool) {
          if (usages().isEmpty() && (isStatic() || ObjectStamp.isObjectNonNull(object().stamp()))) {
              return null;
          }
          ...
      ...

Instead, the JMM leads me to believe the "volatile-effect" should remain, even if the actual loaded value isn't needed.

To get that effect without actually loading anything (this is another, related question) Is it possible to have memory brackets without any intervening ReadNode (or WriteNode)? ("memory brackets" as in the snippet below, reproduced from HotSpotLoweringProvider, LoadFieldNode case)

            if (loadField.isVolatile()) {
                MembarNode preMembar = graph.add(new MembarNode(JMM_PRE_VOLATILE_READ));
                graph.addBeforeFixed(memoryRead, preMembar);
                MembarNode postMembar = graph.add(new MembarNode(JMM_POST_VOLATILE_READ));
                graph.addAfterFixed(memoryRead, postMembar);
            }


--
Miguel Garcia
Swiss Federal Institute of Technology
EPFL - IC - LAMP1 - INR 328 - Station 14
CH-1015 Lausanne - Switzerland
http://lamp.epfl.ch/~magarcia/