docs: private boolean checkForKnownValue(Instruction obj) {
          if (trackValueNumbers) {
              try {
                  // See if the value number loaded here is a known value
                  ValueNumberFrame vnaFrameAfter = vnaDataflow.getFactAfterLocation(getLocation());
                  if (vnaFrameAfter.isValid()) {
                      ValueNumber tosVN = vnaFrameAfter.getTopValue();
                      IsNullValue knownValue = getFrame().getKnownValue(tosVN);
                      if (knownValue != null) {
                          // System.out.println("Produce known value!");
                          // The value produced by this instruction is known.
                          // Push the known value.
                          modelNormalInstruction(obj, getNumWordsConsumed(obj), 0);
                          produce(knownValue);
                          return true;
                      }
                  }
              } catch (DataflowAnalysisException e) {
                  // Ignore...
              }
          }
          return false;
      }