[Bug tree-optimization/65443] Don't peel last iteration from loop in transform_to_exit_first_loop

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65443

--- Comment #3 from vries at gcc dot gnu.org ---
(In reply to vries from comment #2)
> The problem with this transformation is that '_20 + 1' might overflow,
> that's what the comment 'This may need some additional preconditioning in
> case NIT = ~0' refers to.

AFAIU, we might also move 'ivtmp_6 = ivtmp_y + 1' to the end of bb4. That way
it's not triggered at loop entry, as before the transformation,  eliminating
the need for '_20 + 1'.