Extend mask value to 64 bits before taking its complement and assert when mask is
too large to apply in the small case (previously the extra words were silently ignored).
http://reviews.llvm.org/D11890
Patch by James Touton!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247972 91177308-0d34-0410-b5e6-96231b3b80d8