struct obstack obst; /**< An obstack for temporary storage. */
be_ra_chordal_opts_t *opts; /**< A pointer to the chordal ra options. */
firm_dbg_module_t *dbg; /**< Debug module for the chordal register allocator. */
- be_irg_t *birg; /**< Backend IRG session. */
+ const be_irg_t *birg; /**< Back-end IRG session. */
dom_front_info_t *dom_front; /**< Dominance frontiers. */
ir_graph *irg; /**< The graph under examination. */
const arch_register_class_t *cls; /**< The current register class. */