[Bug tree-optimization/34169] New: Bad code generated with -O2

[unaiur at gmail dot com]

$ gcc -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.1.3 --program-suffix=-4.1
--enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug
--enable-mpfr --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)
$ gcc -O2 -w p.c -o p ; ./p
Bad
$ gcc -O2 -fno-tree-pre -w p.c -o p ; ./p
$ gcc -O2 -fno-strict-aliasing -w p.c -o p ; ./p
$ cat p.c
int bmemcmp(void *a1, void *a2, unsigned len)
{
        int dwlen = len / 4;
        while (dwlen)
        {
                int res = *(int *)a1 - *(int *)a2;
                if (res)
                        return res;

                --dwlen;
                ++*(int **)&a1;
                ++*(int **)&a2;
        }
        return 0;
}

int main(int argc, char *argv[])
{
        int *p1 = (int*)calloc(sizeof(int), 1024 * 1024 * 4);
        int *p2 = (int*)calloc(sizeof(int), 1024 * 1024 * 4);
        p1[3] = 1;
        if (bmemcmp(p1, p2, 1024 * 1024 * 4) == 0)
                printf("Bad\n");
        return 0;
}


-- 
           Summary: Bad code generated with -O2
           Product: gcc
           Version: 4.1.3
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: unaiur at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34169