Why does clang boundless recursion terminate?

Asked Nov 16 '16 at 22:50

Active Nov 16 '16 at 22:54

Viewed 29 times

With tail-call optimisation enabled via -O2, the following program runs endlessly using GCC, as expected. With Clang however, the program terminates, and outputs a value; apparently different each time. Does anyone know why?

#include <iostream>

int rec()
{
  return 1 + rec();
}

int main(int argc, char *argv[])
{
  int r;
  r = rec();
  std::cout << r << '\n';
  return 0;
}

asked Nov 16 '16 at 22:50

user2023370

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The compiler may assume your program terminates after a finite time, so if it doesn't, you are in the compilers hands. Not much more to say. – Baum mit Augen Nov 16 '16 at 22:52
I think this is answered here:http://stackoverflow.com/questions/18478078/clang-infinite-tail-recursion-optimization – Nathan Monteleone Nov 16 '16 at 22:54
There is a side-effect though, right? The result of the call to rec? – user2023370 Nov 16 '16 at 22:57
Your function is not tail-recursive. – Barmar Nov 16 '16 at 23:09
1

A tail-recursive function has to return the result of the recursive call directly, it can't use it as the argument to another function or operator. – Barmar Nov 16 '16 at 23:10

Why does clang boundless recursion terminate?

0 Answers0