[Bug tree-optimization/25985] [4.2 Regression] with optimization integer math fails

[rakdver at gcc dot gnu dot org]

------- Comment #6 from rakdver at gcc dot gnu dot org  2006-03-16 03:15 -------
Actually, my previous comment is wrong, it is ivcanon (more precisely, # of
iterations analysis).  Consider this testcase:

#include <stdio.h>

void bla(int x)
{
  if (x < -100)
   exit (0);
}

int main(void)
{
  int bits = 25;
  while (bits) {
      printf ("%d\n", bits);
      bla(bits);
      bits -= 8;
  }
  return 0;
}

We note that bits is signed, therefore it cannot overflow, and conclude the
loop must be finite.  Using this assumption, we conclude it iterates two times.
However, this would only be correct if the loop were exited through this
particular exit, as these examples demonstrate.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25985