[Bug middle-end/66588] combine should try transforming if_then_else of zero_extends into zero_extend of if_then_else

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66588

--- Comment #1 from Uroš Bizjak <ubizjak at gmail dot com> ---
BTW: x86_64 is missing any form of zero-extended cmove.