[Bug tree-optimization/72772] Missed SCEV after pass reordering@236440

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72772

--- Comment #2 from amker at gcc dot gnu.org ---
(In reply to Richard Biener from comment #1)
> Note that for some odd reason creating the preheader causes the PHI to appar.
> Fixing that would be appreciated - it's the make_forwarder_block CFG hook
> that causes this.  Not sure why create_preheader doesn't special-case the
> single_entry != NULL case by simply splitting the edge.
> 
Thanks.  I am also testing patch to simplify_using_initial_conditions and
loop_exits_before_oveflow.  I think they worth fixing too because patches are
kind like a simplification.  Anyway I will send for comment once passes
bootstrap&test.