[Bug tree-optimization/31130] [4.3 Regression] VRP no longer derives range for division after negation

["ian at airs dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from ian at airs dot com  2007-03-12 17:08 -------
First test case:

int f(int a)
{
  if (a < 0)
    a = -a;
  return a < 0;
}

As far as I can tell the behaviour of this test case in VRP is unchanged by the
patch in this PR.  And the code is still fully optimized.

Second test case:

int f(int a)
{
  if (a < 0)
    a = -a;
  if (a < 0)
    a = -a;
  return a < 0;
}

In my tests the second conditional is removed during the VRP pass with or
without the patch in this PR.  It is cleaned up by jump threading.

Third test case:

extern void link_error ();
void foo (int a)
{
  if (a < 0)
    {
      int y;
      a *=-2;
      y  = a / 7;
      if (y > 1 << 30)
        link_error ();
    }
}

int main()
{
  return 0;
}

I agree that VRP does not sort this out, although the final generated code is
fine.  I personally think the overflow infinity code does the right thing here.

Fourth test case:

extern void link_error ();
void foo (int a)
{
  if (a < 0)
    {
      int y;
      y  = -a / 7;
      if (y > 1 << 30)
        link_error ();
    }
}

This does give a warning with -Wstrict-overflow=4


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31130