out of bound warning in non-builtin strcmp() with a fixed argument with two characters.

[Alfonso Cepeda Caballos <cepeda@xxxxxxxxx>]

Hi:

I obtain a warning when compiling the following code:
#include <stdio.h>
#include <string.h>

int main(int argc, char **argv)
{
   printf("%i",strcmp(argv[0],"A")); //  NO warning
   printf("%i",strcmp(argv[0],"AA")); //  warning: array subscript is
above array bounds
   printf("%i",strcmp(argv[0],"AAA")); //  NO warning
   return 0;
}

with:
gcc -O3 -fno-builtin -funsigned-char  -Wall test.c
test.c: In function ‘main’:
test.c:7: warning: array subscript is above array bounds

It only show the warning with this combination options (at least in
linux). If you use signed-char or the strcmp() builtin function, it
doesn't show the warning. And it only shows if the second comparision
string is two bytes length (I mean three with the \0).

Do you know why?

Thanks in advance.

-- 
Alfonso Cepeda