Consider

#include <stdio.h>

void foo(int i)
{
        printf("Hello World %d!\n", i);
        printf(&"Hello World %d!\n"[0], i);
        printf(&"Hello World %d!\n"[6], i);
}

> g++-3.3 -c c-format.C -Wformat=2
> g++-3.4 -c c-format.C -Wformat=2
c-format.C: In function `void foo(int)':
c-format.C:6: warning: format not a string literal, argument types not checked
> g++-4.0 -c c-format.C -Wformat=2
c-format.C: In function 'void foo(int)':
c-format.C:6: warning: format not a string literal, argument types not checked
c-format.C:7: warning: format not a string literal, argument types not checked
> g++-4.1 -c c-format.C -Wformat=2
c-format.C: In function 'void foo(int)':
c-format.C:6: warning: format not a string literal, argument types not checked
c-format.C:7: warning: format not a string literal, argument types not checked

so we're getting worse here.  The problem is that c-format.c:check_format_arg
does not handle string literals of the form ADDR_EXPR (ARRAY_REF ( ... )).

This blocks changing the C frontend to emit &a[0] for array-to-pointer decay.