[Bug tree-optimization/68576] scev failed for loop auto parallelize

[amker.cheng at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68576

--- Comment #6 from bin.cheng <amker.cheng at gmail dot com> ---
Hmm, at least for this case, lim should be aware that lim candidate doesn't
invoke undefined overflow when it is not executed after entering target loop. 
Thus we don't need to rewrite it in unsigned arithmetic.