All the cases fixed are safe as registers hold 32-bit value, but that looks
safer to operate on proper sizes.

Review URL: http://codereview.chromium.org/2017002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4610 ce2b1a6d-e550-0410-aec6-3dcde31c8c00