[Bug tree-optimization/67842] New: Incorrect check in sese.h:bb_in_region

["miyuki at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67842

            Bug ID: 67842
           Summary: Incorrect check in sese.h:bb_in_region
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: ice-checking
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: miyuki at gcc dot gnu.org
  Target Milestone: ---

>From discussion on the mailing list:
https://gcc.gnu.org/ml/gcc-patches/2015-09/msg00615.html

The function bb_in_region contains the following check guarded by
ENABLE_CHECKING:

    edge e;
    edge_iterator ei;

    /* Check that there are no edges coming in the region: all the
       predecessors of EXIT are dominated by ENTRY.  */
    FOR_EACH_EDGE (e, ei, exit->preds)
      dominated_by_p (CDI_DOMINATORS, e->src, entry);

dominated_by_p is a pure function, so the check has no effect. If it is changed
to
      gcc_assert (dominated_by_p (CDI_DOMINATORS, e->src, entry));

It starts to ICE on several testcases, for example gcc.dg/graphite/block-1.c.