[Bug tree-optimization/57858] AVX2: ymm used for div, not for sqrt

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57858

--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> ---
-fno-tree-pre lets it vectorize sqr as well. PRE creates a jump to the middle
of the loop body, which is nice but prevents vectorization.