[Bug tree-optimization/45195] New: incorrect "array subscript above bounds" warning

[Bug tree-optimization/45195] New: incorrect "array subscript above bounds" warning

[rahul at icerasemi dot com]

Using GCC 4.4.1 and the following command, test generates an "array subscript
is above array bounds" warning.

gcc -S -Os test.c -Wall

void foo (int b[2][6])
{
  int i = 0;
  for (i = 0; i < 6; i++)
    {
      int *pb = &b[1][i];
      *pb  = 0;
    }
}


Output from VRP looks like

foo (int[6] * b)
{
  int i;
  unsigned int D.1240;
  unsigned int i.0;

<bb 2>:
  goto <bb 6>;

<bb 3>:
  # i_16 = PHI <i_1(4), i_14(6)>
  i.0_6 = (unsigned int) i_16;
  D.1240_7 = i.0_6 + 6;
  (*b_4(D))[D.1240_7] = 0;       <-- warning generated here
  i_10 = i_16 + 1;

<bb 4>:
  # i_1 = PHI <i_10(3)>
  if (i_1 <= 5)
    goto <bb 3>;
  else
    goto <bb 5>;

<bb 5>:
  return;

<bb 6>:
  # i_14 = PHI <0(2)>
  goto <bb 3>;

}

In the statement (*b_4(D))[D.1240_7] = 0, range of b_4 appears to be [0 5]
while the range of index D.1240_7 is [6 11].


-- 
           Summary: incorrect "array subscript above bounds" warning
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rahul at icerasemi dot com
 GCC build triplet: i686-pc-linux
  GCC host triplet: i686-pc-linux
GCC target triplet: i686-pc-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45195

[Bug tree-optimization/45195] incorrect "array subscript above bounds" warning

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2010-08-05 13:16 -------
Fixed in 4.4.3.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
      Known to work|                            |4.4.3
         Resolution|                            |FIXED
   Target Milestone|---                         |4.4.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45195

[Bug tree-optimization/45195] incorrect "array subscript above bounds" warning

[rahul at icerasemi dot com]

------- Comment #2 from rahul at icerasemi dot com  2010-08-06 08:01 -------
Confirmed, fix for PR41317 avoids forwarding ARRAY_REFs to their use and fixes
this issue. Does this fix hinder any optimizations?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45195