dataflow/src/main/java/org/checkerframework/dataflow/analysis/Store.java

package org.checkerframework.dataflow.analysis;

import org.checkerframework.dataflow.cfg.visualize.CFGVisualizer;
import org.checkerframework.dataflow.expression.JavaExpression;

/**
 * A store is used to keep track of the information that the org.checkerframework.dataflow analysis
 * has accumulated at any given point in time.
 *
 * @param <S> the type of the store returned by {@code copy} and that is used in {@code
 *     leastUpperBound}. Usually it is the implementing class itself, e.g. in {@code T extends
 *     Store<T>}.
 */
public interface Store<S extends Store<S>> {

  // We maintain a then store and an else store before each basic block.
  // When they are identical (by reference equality), they can be treated
  // as a regular unconditional store.
  // Once we have some information for both the then and else store, we
  // create a TransferInput for the block and allow it to be analyzed.
  public static enum Kind {
    THEN,
    ELSE,
    BOTH
  }

  /** A flow rule describes how stores flow along one edge between basic blocks. */
  public static enum FlowRule {
    /**
     * The normal case: then store flows to the then store, and else store flows to the else store.
     */
    EACH_TO_EACH,
    /** Then store flows to both then and else of successor. */
    THEN_TO_BOTH,
    /** Else store flows to both then and else of successor. */
    ELSE_TO_BOTH,
    /** Then store flows to the then of successor. Else store is ignored. */
    THEN_TO_THEN,
    /** Else store flows to the else of successor. Then store is ignored. */
    ELSE_TO_ELSE,
    /** Both stores flow to the then of successor. */
    BOTH_TO_THEN,
    /** Both stores flow to the else of successor. */
    BOTH_TO_ELSE,
  }

  /**
   * Returns an exact copy of this store.
   *
   * @return an exact copy of this store
   */
  S copy();

  /**
   * Compute the least upper bound of two stores.
   *
   * <p><em>Important</em>: This method must fulfill the following contract:
   *
   * <ul>
   *   <li>Does not change {@code this}.
   *   <li>Does not change {@code other}.
   *   <li>Returns a fresh object which is not aliased yet.
   *   <li>Returns an object of the same (dynamic) type as {@code this}, even if the signature is
   *       more permissive.
   *   <li>Is commutative.
   * </ul>
   */
  S leastUpperBound(S other);

  /**
   * Compute an upper bound of two stores that is wider than the least upper bound of the two
   * stores. Used to jump to a higher abstraction to allow faster termination of the fixed point
   * computations in {@link Analysis}. {@code previous} must be the previous store.
   *
   * <p>A particular analysis might not require widening and should implement this method by calling
   * leastUpperBound.
   *
   * <p><em>Important</em>: This method must fulfill the following contract:
   *
   * <ul>
   *   <li>Does not change {@code this}.
   *   <li>Does not change {@code previous}.
   *   <li>Returns a fresh object which is not aliased yet.
   *   <li>Returns an object of the same (dynamic) type as {@code this}, even if the signature is
   *       more permissive.
   *   <li>Is commutative.
   * </ul>
   *
   * @param previous must be the previous store
   */
  S widenedUpperBound(S previous);

  /**
   * Can the objects {@code a} and {@code b} be aliases? Returns a conservative answer (i.e.,
   * returns {@code true} if not enough information is available to determine aliasing).
   */
  boolean canAlias(JavaExpression a, JavaExpression b);

  /**
   * Delegate visualization responsibility to a visualizer.
   *
   * @param viz the visualizer to visualize this store
   * @return the String representation of this store
   */
  String visualize(CFGVisualizer<?, S, ?> viz);
}