[Bug tree-optimization/21959] [4.1 Regression] vrp miscompiles Ada front-end, drops loop exit test in well-defined wrap-around circumstances

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-06-17 
20:37 -------
(In reply to comment #10)
> > No because Ada front-end is creating:
> > signed_char <= 127 which is always true, removing this from fold would not
> > change the problem as it will still be optimized away.
> 
> Where do you see signed_char?  The type 0x556d9144 is unsigned.

Woops, I must have read something wrong.
This is still a bug in the VRP.
C Testcase:
unsigned char c[0xFF];
void f(void)
{
  unsigned char i;
  c[128] = 128;
  i = 0;
  while (1)
  {
    if (((signed char) i) < 0) break;
    c[i] = ' ';
    i++;
  }
}

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dnovillo at gcc dot gnu dot
                   |                            |org
          Component|ada                         |tree-optimization
            Summary|[4.1 Regression] Ada depends|[4.1 Regression] vrp
                   |on signed overflow          |miscompiles Ada front-end,
                   |                            |drops loop exit test in
                   |                            |well-defined wrap-around
                   |                            |circumstances


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21959