Cleanup unconditional jumps and forwarder blocks before reordering

[Jan Hubicka <jh at suse dot cz>]

Hi,
this patch adds function to kill unconditional jumps and forwarder blocks
in the bb-reroder CFG representation as disucssed earlier.  It simplifies
future algorithm for better graph layout and slightly improves current one
as well - it should also make the cfg_cleanup after reordering obsolette
except for BB merging, but I first want to do more testing first.

Regtested/bootstrapped i686 togeter with other today patches, testing
Sparc and PPC in meantime.

Thu Aug 30 15:27:07 CEST 2001  Jan Hubicka  <jh@suse.cz>

	* bb-reorder.c (cleanup_unconditional_jumps): New function.
	(reorder_basic_blocks): Use it.

*** bb-reorder.c.orig	Sun Aug  5 17:58:25 2001
--- bb-reorder.c	Thu Aug 30 15:06:34 2001
*************** static rtx get_next_bb_note		PARAMS ((rt
*** 196,201 ****
--- 199,273 ----
  static rtx get_prev_bb_note		PARAMS ((rtx));
  
  void verify_insn_chain			PARAMS ((void));
+ static void cleanup_unconditional_jumps	PARAMS ((void));
+ 
+ /* Remove any unconditional jumps and forwarder block creating fallthru
+    edges instead.  During BB reordering fallthru edges are not required
+    to target next basic block in the linear CFG layout, so the unconditional
+    jumps are not needed.  */
+    
+ 
+ static void
+ cleanup_unconditional_jumps ()
+ {
+   int i;
+   for (i = 0; i < n_basic_blocks; i++)
+     {
+       basic_block bb = BASIC_BLOCK (i);
+ 
+       if (!bb->succ)
+ 	continue;
+       if (bb->succ->flags & EDGE_FALLTHRU)
+ 	continue;
+       if (!bb->succ->succ_next)
+ 	{
+ 	  rtx insn;
+ 	  if (GET_CODE (bb->head) != CODE_LABEL && forwarder_block_p (bb))
+ 	    {
+ 	      basic_block prev = BASIC_BLOCK (--i);
+ 
+ 	      if (rtl_dump_file)
+ 		fprintf (rtl_dump_file, "Removing forwarder BB %i\n",
+ 			 bb->index);
+ 
+ 	      redirect_edge_succ (bb->pred, bb->succ->dest);
+ 	      flow_delete_block (bb);
+ 	      bb = prev;
+ 	    }
+ 	  else if (simplejump_p (bb->end))
+ 	    {
+ 	      rtx jump = bb->end;
+ 	      bb->end = PREV_INSN (jump);
+ 	      if (rtl_dump_file)
+ 		fprintf (rtl_dump_file, "Removing jump %i in BB %i\n",
+ 			 INSN_UID (jump), bb->index);
+ 	      flow_delete_insn (jump);
+ 	      bb->succ->flags |= EDGE_FALLTHRU;
+ 	    }
+ 	  else
+ 	    continue;
+ 
+ 	  /* Cleanup barriers and verify that there are no tablejumps
+ 	     in a way.  */
+ 	  insn = NEXT_INSN (bb->end);
+ 	  while (insn
+ 		 && (GET_CODE (insn) != NOTE
+ 		     || NOTE_LINE_NUMBER (insn) != NOTE_INSN_BASIC_BLOCK))
+ 	    {
+ 	      rtx next = NEXT_INSN (insn);
+ 
+ 	      if (GET_CODE (insn) == BARRIER)
+ 		delete_barrier (insn);
+ 	      else if (GET_CODE (insn) == CODE_LABEL)
+ 		;
+ 	      else if (GET_CODE (insn) != NOTE)
+ 		abort ();
+ 
+ 	      insn = next;
+ 	    }
+ 	}
+     }
+ }
  
  /* Skip over inter-block insns occurring after BB which are typically
     associated with BB (e.g., barriers). If there are any such insns,
*************** reorder_basic_blocks ()
*** 1393,1400 ****
  
    build_scope_forest (&forest);
    remove_scope_notes ();
! 
    record_effective_endpoints ();
    make_reorder_chain ();
    fixup_reorder_chain ();
  
--- 1759,1766 ----
  
    build_scope_forest (&forest);
    remove_scope_notes ();
!   cleanup_unconditional_jumps ();
    record_effective_endpoints ();
    make_reorder_chain ();
    fixup_reorder_chain ();