php know in which file a function or class is declared

Last week prestahop became terribly slow, to understand what the problem was, I opened the index.php file and commented on a few lines of code I found what the function was like from this problem. Entering this function I found the line of code that slows everything, is a function. I'm entering deeper into the code to find the slowness but look for functions in thousands of files only using the "grep" function I do not think is the right method, too slow. What do you advise me to do? are there any IDEs (for linux) where I can click on the function and automatically open the file at the point where the function is declared? Thank you.