[Bug tree-optimization/66522] New: 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

            Bug ID: 66522
           Summary: handle casts in nr of iterations in
                    try_transform_to_exit_first_loop_alt
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

There's a todo in try_transform_to_exit_first_loop_alt:
...
      /* There is a number of test-cases for which we don't get an alt_bound
         here: they're listed here, with the lhs of the last stmt as the nit:
         libgomp.graphite/force-parallel-1.c:
         _21 = (signed long) N_6(D);
         _19 = _21 + -1;
         _7 = (unsigned long) _19;
         libgomp.graphite/force-parallel-2.c:
         _33 = (signed long) N_9(D);
         _16 = _33 + -1;
         _37 = (unsigned long) _16;
         libgomp.graphite/force-parallel-5.c:
         <bb 6>:
         # graphite_IV.5_46 = PHI <0(5), graphite_IV.5_47(11)>
         <bb 7>:
         _33 = (unsigned long) graphite_IV.5_46;
         g++.dg/tree-ssa/pr34355.C:
         _2 = (unsigned int) i_9;
         _3 = 4 - _2;
         gcc.dg/pr53849.c:
         _5 = d.0_11 + -2;
         _18 = (unsigned int) _5;
         We will be able to handle some of these cases, if we can determine
when
         it's safe to look past casts.  */
...

I'm running into this todo for a trivial fortran test-case
gcc/testsuite/gfortran.dg/parloops-exit-first-loop-alt.f95:
...
! { dg-additional-options "-O2" }
! { dg-require-effective-target pthread }
! { dg-additional-options "-ftree-parallelize-loops=2" }
! { dg-additional-options "-fdump-tree-parloops" }

! Variable bound, vector addition.

subroutine foo(nr)
  integer, intent(in)       :: nr
  integer, parameter         :: n = 1000
  integer, dimension (0:n-1) :: a, b, c
  common a, b, c
  integer                    :: ii

  do ii = 0, nr - 1
     c(ii) = a(ii) + b(ii) + 25
  end do
end subroutine foo

! Three times 'plus 25'
! - one in f._loopfn.0
! - one in the parallel
! - one in the low iteration count loop
! Crucially, none for a peeled off last iteration following the parallel.
! { dg-final { scan-tree-dump-times "(?n) \\+ 25;" 3 "parloops" } }
...

The scan-tree-dump-times currently fails, so
try_transform_to_exit_first_loop_alt is failing.