[Bug tree-optimization/77283] [7 Regression] Revision 238005 disables loop unrolling

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77283

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
I'm reasonably happy with the PHI logic so I am going to test it.  It's quite
on the do-more-duplicating side for memory references (just uses the virtual
operand PHI to see if there are any loads/stores in the joiner).

For the case of

  if (a)
    i = i + 1;
  else
    ...;
  j = i + 1;

thus CSE opportunities on one/both paths this is something that PRE catches
already.  So we're not actually looking for CSE opportunities but opportunities
for simplification or DCE/DSE.