public PhysicalContext optimize() throws SemanticException {
    for (PhysicalPlanResolver r : resolvers) {
      pctx = r.resolve(pctx);
    }
    return pctx;
  }
invoke all the resolvers one-by-one, and alter the physical plan.

@return PhysicalContext
@throws SemanticException
ql/src/java/org/apache/hadoop/hive/ql/optimizer/physical/PhysicalOptimizer.java