     */
    void init(unsigned size, SimpleFreeList *_freeList, RegIndex _zeroReg);

    /**
     * Pair of a physical register and a physical register.  Used to
     * return the physical register that a logical register has been
     * renamed to, and the previous physical register that the same
     * logical register was previously mapped to.
     */
    typedef std::pair<PhysRegIdPtr, PhysRegIdPtr> RenameInfo;

    /**
     * Tell rename map to get a new free physical register to remap