With -O3, I get an apparently incorrect "array subscript is above array bounds" warning when a multidimensional array is passed to a function and accessed in a loop:

$ /home/tmp/u/rjpeters/gcc-svn-install/bin/gcc -v
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: /home/tmp/u/rjpeters/gcc-svn/configure --enable-languages=c,c++ --enable-checking=yes --enable-__cxa_atexit --with-mpfr=/home/tmp/u/rjpeters/mpfr-2.2.1-install --with-gmp=/home/tmp/u/rjpeters/gmp-4.2.1-install --prefix=/home/tmp/u/rjpeters/gcc-svn-install
Thread model: posix
gcc version 4.4.0 20080220 (experimental) [trunk revision 129827] (GCC)

$ cat bug2.c
#include <stdio.h>

static void test1(char f[][64], const int n)
{
  int i;
  for (i = 0; i < n; ++i)
    printf("%s", f[i]); /* warning here */
  printf("\n");
}

static void test2(char f[][64])
{
  int i;
  for (i = 0; i < 4; ++i)
    printf("%s", f[i]); /* warning here */
  printf("\n");
}

static void test3(char f[][64])
{
  printf("%s", f[0]);
  printf("%s", f[1]);
  printf("%s", f[2]);
  printf("%s", f[3]); /* NOTE: no warning here */
  printf("\n");
}

int main()
{
  char f[4][64] = { "a", "b", "c", "d" };

  test1(f, 4);
  test2(f);
  test3(f);

  return 0;
}

$ /home/tmp/u/rjpeters/gcc-svn-install/bin/gcc -Wall -O3 bug2.c
bug2.c: In function ‘main’:
bug2.c:7: warning: array subscript is above array bounds
bug2.c:7: warning: array subscript is above array bounds
bug2.c:15: warning: array subscript is above array bounds
bug2.c:15: warning: array subscript is above array bounds

$ ./a.out
abcd
abcd
abcd

The fact that there are two warnings each at lines 7 and 14 suggests that somehow the last two iterations of the unrolled loop are considered as out-of-bounds; however, the generated code is apparently correct, at least judging by the runtime output of the program.

I don't see these warnings with "gcc version 4.1.1 20060724 (prerelease) (4.1.1-3mdk)".

Thanks,
Rob