Method setDef

chapter11/src/main/java/com/seaofnodes/simple/node/Node.java:158–175

Change a def into a Node. Keeps the edges correct, by removing the corresponding use->def edge. This may make the original def go dead. This function is co-recursive with #kill. This method is the normal path for altering a Node, because it does the proper d

(int idx, Node new_def )

     * @return new_def for flow coding
     */
    public Node setDef(int idx, Node new_def ) {
        unlock();
        Node old_def = in(idx);
        if( old_def == new_def ) return new_def; // No change
        // If new def is not null, add the corresponding def->use edge
        // This needs to happen before removing the old node's def->use edge as
        // the new_def might get killed if the old node kills it recursively.
        if( new_def != null )
            new_def.addUse(this);
        // Set the new_def over the old (killed) edge
        _inputs.set(idx,new_def);
        if( old_def != null &&  // If the old def exists, remove a def->use edge
            old_def.delUse(this) ) // If we removed the last use, the old def is now dead
            old_def.kill();     // Kill old def
        moveDepsToWorklist();
        // Return self for easy flow-coding
        return new_def;
    }

    // Remove the numbered input, compressing the inputs in-place.  This
    // shuffles the order deterministically - which is suitable for Region and