gcc/testsuite/algol68/execute/proc-28.a68

# { dg-options "-fstropping=upper" }  #
BEGIN PROC hcf = (INT m, n) INT:
         IF m < n
         THEN hcf (n, m)
         ELIF n = 0
         THEN m
         ELSE hcf (n, m MOD n)
         FI;
      ASSERT (hcf (10, 20) = 10)
END