obvious try_optimize_cfg and verify_flow_info fixes

[Jan Hubicka <jh at suse dot cz>]

Hi,
this patch contains two fixes I decided to install as obvious.
FIrst one is causing crash on m68k bootstrap (if you are patient enought).
When the trivially dead blocks happends to be chained, the test afterwards
travels NULL pointer.

Second part just cleans up the diagnostics a bit, as I've forgot to do that
before installing the patch.

Honza

Thu Jul 12 17:42:53 CEST 2001  Jan Hubicka  <jh@suse.cz>
	* flow.c (try_optimize_cfg): Delete whole chain of trivially dead
	basic blocks.
	(verify_flow_info): Make diagnostics prettier.

Index: flow.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/flow.c,v
retrieving revision 1.420
diff -c -3 -p -r1.420 flow.c
*** flow.c	2001/07/12 14:52:51	1.420
--- flow.c	2001/07/12 15:33:48
*************** try_optimize_cfg (mode)
*** 3653,3662 ****
  	  edge s;
  	  int changed_here = 0;
  
! 	  /* Delete trivially dead basic block.  */
! 	  if (b->pred == NULL)
  	    {
! 	      c = BASIC_BLOCK (i - 1);
  	      if (rtl_dump_file)
  		fprintf (rtl_dump_file, "Deleting block %i.\n", b->index);
  	      flow_delete_block (b);
--- 3653,3662 ----
  	  edge s;
  	  int changed_here = 0;
  
! 	  /* Delete trivially dead basic blocks.  */
! 	  while (b->pred == NULL)
  	    {
! 	      c = BASIC_BLOCK (b->index - 1);
  	      if (rtl_dump_file)
  		fprintf (rtl_dump_file, "Deleting block %i.\n", b->index);
  	      flow_delete_block (b);
*************** verify_flow_info ()
*** 7923,7945 ****
  	      && (e->src->index + 1 != e->dest->index
  		  || !can_fallthru (e->src, e->dest)))
  	    {
! 	      fprintf (stderr,
! 		       "verify_flow_info: Incorrect fallthru edge %i->%i\n",
! 		       e->src->index, e->dest->index);
! 	      fflush (stderr);
  	      err = 1;
  	    }
  	    
  	  if (e->src != bb)
  	    {
! 	      fprintf (stderr,
! 		       "verify_flow_info: Basic block %d succ edge is corrupted\n",
! 		       bb->index);
  	      fprintf (stderr, "Predecessor: ");
  	      dump_edge_info (stderr, e, 0);
  	      fprintf (stderr, "\nSuccessor: ");
  	      dump_edge_info (stderr, e, 1);
! 	      fflush (stderr);
  	      err = 1;
  	    }
  	  if (e->dest != EXIT_BLOCK_PTR)
--- 7923,7942 ----
  	      && (e->src->index + 1 != e->dest->index
  		  || !can_fallthru (e->src, e->dest)))
  	    {
! 	      error ("verify_flow_info: Incorrect fallthru edge %i->%i",
! 		     e->src->index, e->dest->index);
  	      err = 1;
  	    }
  	    
  	  if (e->src != bb)
  	    {
! 	      error ("verify_flow_info: Basic block %d succ edge is corrupted",
! 		     bb->index);
  	      fprintf (stderr, "Predecessor: ");
  	      dump_edge_info (stderr, e, 0);
  	      fprintf (stderr, "\nSuccessor: ");
  	      dump_edge_info (stderr, e, 1);
! 	      fprintf (stderr, "\n");
  	      err = 1;
  	    }
  	  if (e->dest != EXIT_BLOCK_PTR)