あるファイルに使われている関数を数えて返す ref: http://qiita.com/items/2013

file0.php

<?php
$filename = '/path/to/file.php';
$contents = file_get_contents($filename);
$tokens = token_get_all($contents);

$functions = array();

while ( count($tokens) > 0 )
{
    $token = array_shift($tokens);

    if ( $token[0] !== T_STRING )
    {
        continue;
    }

    $isFunction = false;

    while ( count($tokens) > 0 )
    {
        $_token = array_shift($tokens);

        if ( $_token[0] === T_WHITESPACE )
        {
            continue;
        }
        else
        {
            if ( $_token[0] === '(' )
            {
                $isFunction = true;
            }

            break;
        }
    }

    if ( $isFunction === true )
    {
        $functions[] = $token[1];
    }
}

$functions = array_count_values($functions);
arsort($functions);
print_r($functions);