EH flow analysis

[Jeffrey A Law]

  In message < u9k9g89ft8.fsf@yorick.cygnus.com >you write:
  > Mike's earlier patch fixes the flow information, but flow still doesn't
  > delete all unreachable handlers.  Another jump (and exception_optimize)
  > pass will delete the rest, but that doesn't happen again until the very end
  > of compilation, when we've already aborted because we saw a use of a dead
  > pseudo.
  > 
  > Here's a patch that fixes this test case in a pessimistic way, by assuming
  > for the purposes of flow analysis that all handlers are reachable from all
  > calls.  A better solution will be to only note that the innermost handler
  > is reachable, and make flow delete all unreachable code; then we can do
  > away with exception_optimize.
  > 
  > Tue Sep 23 09:01:38 1997  Jason Merrill  <jason@yorick.cygnus.com>
  > 
  > 	* flow.c (find_basic_blocks): Mark calls as potentially jumping
  > 	to the EH labels.
I've installed this patch.

If we need/want to refine it later we can.

I noted while looking at this patch that we don't have any
docs in invoke.texi for asynchronous_exceptions.

jeff