Source

File: wp-includes/class-wp-comment.php

public static function get_instance( $id ) {
		global $wpdb;

		$comment_id = (int) $id;
		if ( ! $comment_id ) {
			return false;
		}

		$_comment = wp_cache_get( $comment_id, 'comment' );

		if ( ! $_comment ) {
			$_comment = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM $wpdb->comments WHERE comment_ID = %d LIMIT 1", $comment_id ) );

			if ( ! $_comment ) {
				return false;
			}

			wp_cache_add( $_comment->comment_ID, $_comment, 'comment' );
		}

		return new WP_Comment( $_comment );
	}