PVS-Studio warning V610 for Clang

static Ty getEmptyKey() {
  intptr_t Val = -1;
  Val <<= PointerLikeTypeTraits<PointerTy>::NumLowBitsAvailable;
  return Ty(reinterpret_cast<PointerTy>(Val),
            IntType((1 << IntBits)-1));
}

This suspicious code was found in Clang project by PVS-Studio static code analyzer.
Warning message is:
V610 Undefined behavior. Check the shift operator '<<=. The left operand 'Val' is negative. pointerintpair.h 139

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/