/* Called to notify frontend, that new basic block is being added.
The first parameter - new basic block.
The second parameter - block, after which new basic block is being added,
- or EXIT_BLOCK_PTR, if recovery block is being added,
+ or the exit block, if recovery block is being added,
or NULL, if standalone block is being added. */
void (*add_block) (basic_block, basic_block);