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Date: Thu, 05 Aug 2010 12:21:00 -0000
Subject: [Bug tree-optimization/45195]  New: incorrect "array subscript above bounds" warning
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From: "rahul at icerasemi dot com" <gcc-bugzilla@gcc.gnu.org>
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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