Source

File: wp-includes/revision.php

function _wp_post_revision_data( $post = array(), $autosave = false ) {
	if ( ! is_array( $post ) ) {
		$post = get_post( $post, ARRAY_A );
	}

	$fields = _wp_post_revision_fields( $post );

	$revision_data = array();

	foreach ( array_intersect( array_keys( $post ), array_keys( $fields ) ) as $field ) {
		$revision_data[ $field ] = $post[ $field ];
	}

	$revision_data['post_parent']   = $post['ID'];
	$revision_data['post_status']   = 'inherit';
	$revision_data['post_type']     = 'revision';
	$revision_data['post_name']     = $autosave ? "$post[ID]-autosave-v1" : "$post[ID]-revision-v1"; // "1" is the revisioning system version.
	$revision_data['post_date']     = isset( $post['post_modified'] ) ? $post['post_modified'] : '';
	$revision_data['post_date_gmt'] = isset( $post['post_modified_gmt'] ) ? $post['post_modified_gmt'] : '';

	return $revision_data;
}