PVS-Studio warning V610 for glibc

static void init_cacheinfo (void)
{
  ....
  count_mask = ~(-1 << (count_mask + 1));
  ....
}

This suspicious code was found in glibc project by PVS-Studio static code analyzer.
Warning message is:
V610 Undefined behavior. Check the shift operator '<<. The left operand '-1' is negative. cacheinfo.c 645

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/