WordPress at a glance
function is not described

wp_favicon_request() WP 3.0.0

Don't load all of WordPress when handling a favicon.ico request.

Instead, send the headers for a zero-length favicon and bail.

No Hooks.

Return

Nothing (null).

Usage

wp_favicon_request();

Code of wp favicon request: wp-includes/load.php VER 5.0.3

<?php
function wp_favicon_request() {
	if ( '/favicon.ico' == $_SERVER['REQUEST_URI'] ) {
		header('Content-Type: image/vnd.microsoft.icon');
		exit;
	}
}