[Bug tree-optimization/66522] handle casts in nr of iterations in try_transform_to_exit_first_loop_alt

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66522

--- Comment #1 from vries at gcc dot gnu.org ---
Created attachment 35772
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35772&action=edit
tentative patch