### 12.12 Statement and operand traversals

There are two functions available for walking statements and sequences: `walk_gimple_stmt` and `walk_gimple_seq`, accordingly, and a third function for walking the operands in a statement: `walk_gimple_op`.

GIMPLE function: tree walk_gimple_stmt (gimple_stmt_iterator *gsi, walk_stmt_fn callback_stmt, walk_tree_fn callback_op, struct walk_stmt_info *wi)

  This function is used to walk the current statement in `GSI`, optionally using traversal state stored in `WI`. If `WI` is `NULL`, no state is kept during the traversal.

  The callback `CALLBACK_STMT` is called. If `CALLBACK_STMT` returns true, it means that the callback function has handled all the operands of the statement and it is not necessary to walk its operands.

  If `CALLBACK_STMT` is `NULL` or it returns false, `CALLBACK_OP` is called on each operand of the statement via `walk_gimple_op`. If `walk_gimple_op` returns non-`NULL` for any operand, the remaining operands are not scanned.

  The return value is that returned by the last call to `walk_gimple_op`, or `NULL_TREE` if no `CALLBACK_OP` is specified.

GIMPLE function: tree walk_gimple_op (gimple stmt, walk_tree_fn callback_op, struct walk_stmt_info *wi)

  Use this function to walk the operands of statement `STMT`. Every operand is walked via `walk_tree` with optional state information in `WI`.

  `CALLBACK_OP` is called on each operand of `STMT` via `walk_tree`. Additional parameters to `walk_tree` must be stored in `WI`. For each operand `OP`, `walk_tree` is called as:

      walk_tree (&OP, CALLBACK_OP, WI, PSET)

  If `CALLBACK_OP` returns non-`NULL` for an operand, the remaining operands are not scanned. The return value is that returned by the last call to `walk_tree`, or `NULL_TREE` if no `CALLBACK_OP` is specified.

GIMPLE function: tree walk_gimple_seq (gimple_seq seq, walk_stmt_fn callback_stmt, walk_tree_fn callback_op, struct walk_stmt_info *wi)

  This function walks all the statements in the sequence `SEQ` calling `walk_gimple_stmt` on each one. `WI` is as in `walk_gimple_stmt`. If `walk_gimple_stmt` returns non-`NULL`, the walk is stopped and the value returned. Otherwise, all the statements are walked and `NULL_TREE` returned.