Re: Edges, predictions, and GC crashes ...

[Ulrich Weigand <uweigand at de dot ibm dot com>]

Jan Hubicka wrote:

> I've comitted the attached patch.  I didn't suceed to reproduce your
> failures, but Danny reported it fixes his and it bootstrap/regtests
> i686-pc-gnu-linux.

Thanks; this does fix one crash on s390x, but doesn't fix the
pass57-frag crashes on s390.

What happens is that after the predictions are created, but before 
remove_edge is called, the edge is modified in rtl_split_block
(called from tree_expand_cfg):

  /* Redirect the outgoing edges.  */
  new_bb->succs = bb->succs;
  bb->succs = NULL;
  FOR_EACH_EDGE (e, ei, new_bb->succs)
    e->src = new_bb;

Now the 'src' link points to a different basic block, but the old
basic block still has the prediction pointing to the edge.

When remove_edge is finally called, your new code tries to find
and remove the prediction from the *new* basic block's prediction
list -- but it still remains on the old one's list ...

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  Linux on zSeries Development
  Ulrich.Weigand@de.ibm.com