Fix a few use-after-free issues

[Jeff Law <law at redhat dot com>]

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This fixes a couple use-after-free problems and one use-after-free
non-problem.

In cfgrtl.c, redirect_branch_edge may delete its first argument, so this
code is clearly erroneous:

  	  e->flags &= ~EDGE_FALLTHRU;
  	  redirected = redirect_branch_edge (e, dest);
  	  gcc_assert (redirected);
 	  e->flags |= EDGE_FALLTHRU;
 	  df_set_bb_dirty (e->src);
 	  return e;

This fix is obvious, use REDIRECTED rather than E after the call to
redirect_branch_edge.

Similarly for redirect_edge_succ_nodup in this fragment:

        ret = redirect_edge_succ_nodup (e, dest);
        if (dump_file)
  	fprintf (dump_file, "Fallthru edge %i->%i redirected to %i\n",
 		 e->src->index, e->dest->index, dest->index);
      }
Luckily in this case the use-after-free only occurs when dumping, so it
won't typically affect end users.


The non-problem is this code in cfg.c:

        if (s->probability > REG_BR_PROB_BASE)
  	s->probability = REG_BR_PROB_BASE;
        s->count += e->count;
        remove_edge (e);
        redirect_edge_var_map_dup (s, e);
        e = s;

remove_edge frees E, when we then use in redirect_edge_var_map_dup.
Luckily we only care about the pointer value of E which doesn't change.
 Regardless, I fixed this to keep the static checkers quiet.

Bootstrapped and regression tested on x86_64-unknown-linux-gnu.  Ok for
the trunk?

Jeff
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