[Bug tree-optimization/57600] Turn 2 comparisons into 1 with the min

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57600

--- Comment #4 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #3)
> Perhaps we want to perform it just during ifcvt once it is rolled into
> vectorizer and works on an on-the-side bb?  Then it wouldn't affect
> non-vectorized code.

We would miss some useful cases (in the original testcase, the transformation
is worth it even without vectorizing), but at least it would make regressions
unlikely...