11.10 Sequence iterators

Sequence iterators are convenience constructs for iterating through statements in a sequence. Given a sequence SEQ, here is a typical use of gimple sequence iterators:

gimple_stmt_iterator gsi;
for (gsi = gsi_start (seq); !gsi_end_p (gsi); gsi_next (&gsi))
  {
    gimple g = gsi_stmt (gsi);
    /* Do something with gimple statement G.  */
  }

Backward iterations are possible:

        for (gsi = gsi_last (seq); !gsi_end_p (gsi); gsi_prev (&gsi))

Forward and backward iterations on basic blocks are possible with gsi_start_bb and gsi_last_bb.

In the documentation below we sometimes refer to enum gsi_iterator_update. The valid options for this enumeration are:

• GSI_NEW_STMT Only valid when a single statement is added. Move the iterator to it.
• GSI_SAME_STMT Leave the iterator at the same statement.
• GSI_CONTINUE_LINKING Move iterator to whatever position is suitable for linking other statements in the same direction.

Below is a list of the functions used to manipulate and use statement iterators.

GIMPLE function: gimple_stmt_iterator gsi_start (gimple_seq seq)

Return a new iterator pointing to the sequence SEQ’s first statement. If SEQ is empty, the iterator’s basic block is NULL. Use gsi_start_bb instead when the iterator needs to always have the correct basic block set.

GIMPLE function: gimple_stmt_iterator gsi_start_bb (basic_block bb)

Return a new iterator pointing to the first statement in basic block BB.

GIMPLE function: gimple_stmt_iterator gsi_last (gimple_seq seq)

Return a new iterator initially pointing to the last statement of sequence SEQ. If SEQ is empty, the iterator’s basic block is NULL. Use gsi_last_bb instead when the iterator needs to always have the correct basic block set.

GIMPLE function: gimple_stmt_iterator gsi_last_bb (basic_block bb)

Return a new iterator pointing to the last statement in basic block BB.

GIMPLE function: bool gsi_end_p (gimple_stmt_iterator i)

Return TRUE if at the end of I.

GIMPLE function: bool gsi_one_before_end_p (gimple_stmt_iterator i)

Return TRUE if we’re one statement before the end of I.

GIMPLE function: void gsi_next (gimple_stmt_iterator *i)

Advance the iterator to the next gimple statement.

GIMPLE function: void gsi_prev (gimple_stmt_iterator *i)

Advance the iterator to the previous gimple statement.

GIMPLE function: gimple gsi_stmt (gimple_stmt_iterator i)

Return the current stmt.

GIMPLE function: gimple_stmt_iterator gsi_after_labels (basic_block bb)

Return a block statement iterator that points to the first non-label statement in block BB.

GIMPLE function: gimple * gsi_stmt_ptr (gimple_stmt_iterator *i)

Return a pointer to the current stmt.

GIMPLE function: basic_block gsi_bb (gimple_stmt_iterator i)

Return the basic block associated with this iterator.

GIMPLE function: gimple_seq gsi_seq (gimple_stmt_iterator i)

Return the sequence associated with this iterator.

GIMPLE function: void gsi_remove (gimple_stmt_iterator *i, bool remove_eh_info)

Remove the current stmt from the sequence. The iterator is updated to point to the next statement. When REMOVE_EH_INFO is true we remove the statement pointed to by iterator I from the EH tables. Otherwise we do not modify the EH tables. Generally, REMOVE_EH_INFO should be true when the statement is going to be removed from the IL and not reinserted elsewhere.

GIMPLE function: void gsi_link_seq_before (gimple_stmt_iterator *i, gimple_seq seq, enum gsi_iterator_update mode)

Links the sequence of statements SEQ before the statement pointed by iterator I. MODE indicates what to do with the iterator after insertion (see enum gsi_iterator_update above).

GIMPLE function: void gsi_link_before (gimple_stmt_iterator *i, gimple g, enum gsi_iterator_update mode)

Links statement G before the statement pointed-to by iterator I. Updates iterator I according to MODE.

GIMPLE function: void gsi_link_seq_after (gimple_stmt_iterator *i, gimple_seq seq, enum gsi_iterator_update mode)

Links sequence SEQ after the statement pointed-to by iterator I. MODE is as in gsi_insert_after.

GIMPLE function: void gsi_link_after (gimple_stmt_iterator *i, gimple g, enum gsi_iterator_update mode)

Links statement G after the statement pointed-to by iterator I. MODE is as in gsi_insert_after.

GIMPLE function: gimple_seq gsi_split_seq_after (gimple_stmt_iterator i)

Move all statements in the sequence after I to a new sequence. Return this new sequence.

GIMPLE function: gimple_seq gsi_split_seq_before (gimple_stmt_iterator *i)

Move all statements in the sequence before I to a new sequence. Return this new sequence.

GIMPLE function: void gsi_replace (gimple_stmt_iterator *i, gimple stmt, bool update_eh_info)

Replace the statement pointed-to by I to STMT. If UPDATE_EH_INFO is true, the exception handling information of the original statement is moved to the new statement.

GIMPLE function: void gsi_insert_before (gimple_stmt_iterator *i, gimple stmt, enum gsi_iterator_update mode)

Insert statement STMT before the statement pointed-to by iterator I, update STMT’s basic block and scan it for new operands. MODE specifies how to update iterator I after insertion (see enum gsi_iterator_update).

GIMPLE function: void gsi_insert_seq_before (gimple_stmt_iterator *i, gimple_seq seq, enum gsi_iterator_update mode)

Like gsi_insert_before, but for all the statements in SEQ.

GIMPLE function: void gsi_insert_after (gimple_stmt_iterator *i, gimple stmt, enum gsi_iterator_update mode)

Insert statement STMT after the statement pointed-to by iterator I, update STMT’s basic block and scan it for new operands. MODE specifies how to update iterator I after insertion (see enum gsi_iterator_update).

GIMPLE function: void gsi_insert_seq_after (gimple_stmt_iterator *i, gimple_seq seq, enum gsi_iterator_update mode)

Like gsi_insert_after, but for all the statements in SEQ.

GIMPLE function: gimple_stmt_iterator gsi_for_stmt (gimple stmt)

Finds iterator for STMT.

GIMPLE function: void gsi_move_after (gimple_stmt_iterator *from, gimple_stmt_iterator *to)

Move the statement at FROM so it comes right after the statement at TO.

GIMPLE function: void gsi_move_before (gimple_stmt_iterator *from, gimple_stmt_iterator *to)

Move the statement at FROM so it comes right before the statement at TO.

GIMPLE function: void gsi_move_to_bb_end (gimple_stmt_iterator *from, basic_block bb)

Move the statement at FROM to the end of basic block BB.

GIMPLE function: void gsi_insert_on_edge (edge e, gimple stmt)

Add STMT to the pending list of edge E. No actual insertion is made until a call to gsi_commit_edge_inserts() is made.

GIMPLE function: void gsi_insert_seq_on_edge (edge e, gimple_seq seq)

Add the sequence of statements in SEQ to the pending list of edge E. No actual insertion is made until a call to gsi_commit_edge_inserts() is made.

GIMPLE function: basic_block gsi_insert_on_edge_immediate (edge e, gimple stmt)

Similar to gsi_insert_on_edge+gsi_commit_edge_inserts. If a new block has to be created, it is returned.

GIMPLE function: void gsi_commit_one_edge_insert (edge e, basic_block *new_bb)

Commit insertions pending at edge E. If a new block is created, set NEW_BB to this block, otherwise set it to NULL.

GIMPLE function: void gsi_commit_edge_inserts (void)

This routine will commit all pending edge insertions, creating any new basic blocks which are necessary.