Compiled Wolfram language functions list?

Questions
1

I am not clear on which Wolfram language functions are actually ‘compiled’. It would be nice if a list of ‘Compile-compatible’ functions was available as it would allow determining, a priori, whether to invest the time in rewriting the code (in a form suitable to Compile). Such a list existed long time ago, but I am not able to find it any longer.

On the same topic, I seem to remember that there is a way to take an existing piece of code and process it without modifications. Am I mistaken? If not, how does that work?

2

For list type:

Compile`CompilerFunctions[] // Sort

You will find it discussed at
https://mathematica.stackexchange.com/questions/1096/list-of-compilable-functions

to make sure your not calling main evaluate after compilation type

<< CompiledFunctionTools`;
CompilePrint[yourfun]
3

Thank you for the link, it is quite informative.