More degenerate flow graphs breaking if_convert.

[Jeffrey A Law]

  In message < 200006101218.NAA05435@cam-mail2.cambridge.arm.com >you write:
  > 
  > Richard,
  > 
  > Remember that you checked in the following to fix a degenerate flow graph 
  > problem that caused if_convert to get lost?
  > 
  > 	2000-05-15  Richard Henderson  <rth@cygnus.com>
  >         * toplev.c (rest_of_compilation): Run full jump pass before
  >         find_basic_blocks of flow2.
  > 
  > Well, I've now found a case where this is still insufficient.
[ ... ]
I wonder if using a more modern dead code elimination algorithm would solve
this problem such as the one outlined in Morgan's book.  Presumably what is
causing the problem is the cascading effect of dead code elimination and
jump optimizations -- which I believe is handled by Morgan's dead code
elimination algorithm.

jeff