Need to check that at least single bit is cleared for unsigned nodes
before reducing their size. Otherwise they might be treated as signed in
signed nodes.
This reverts commit 74e07ab523122d6a8347b25770062ab331b6bb84.
It might be that Mask.getBitWidth() == Mask.countl_zero() (32 in my
case) and zero bitwidth2 causes the crash.
Need to check that at least single bit is cleared for unsigned nodes
before reducing their size. Otherwise they might be treated as signed in
signed nodes.
