[Bug tree-optimization/61515] [4.9/5 Regression] Extremely long compile time for generated code

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61515

--- Comment #21 from Richard Biener <rguenth at gcc dot gnu.org> ---
So to recap - apart from really fixing the quadraticness - it would be nice
if we can just disable threading over backedges at -O1, thus for
!flag_expensive_optimizations.  Especially on the 4.9 branch.