RFA: Use fixup_fallthru_exit_predecessor only for !HAVE_prologue targets, and only after reload

[Joern Rennecke]

> Joern,
> 
> 	With your patch I am seeing a large number of new testcase
> failures on PowerPC of the form:
> 
> /gcc/dje/src/gcc/testsuite/gcc.c-torture/compile/20020309-2.c:16: internal compiler error: in fixup_reorder_chain, at cfglayout.c:740

What are the exact options?  I've tried this with the powerpc-eabisim
configuration, and -O0, -O1 and -O2 succeed.  -O3 segfaults in the
label_for_bb call in line 735 (what gdb thinks) / 736 (actual).
When I make the obvious fix for this segfault, it goes on to an ICE
in line 740.

2004-06-15  J"orn Rennecke <joern.rennecke@superh.com>

	* cfglayout.c (fixup_reorder_chain): Handle case where the
	destination od E_TAKEN is EXIT_BLOCK_PTR.

Index: cfglayout.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cfglayout.c,v
retrieving revision 1.60
diff -p -r1.60 cfglayout.c
*** cfglayout.c	14 Jun 2004 12:09:07 -0000	1.60
--- cfglayout.c	14 Jun 2004 23:15:59 -0000
*************** fixup_reorder_chain (void)
*** 733,745 ****
  	      /* Otherwise we can try to invert the jump.  This will
  		 basically never fail, however, keep up the pretense.  */
  	      else if (invert_jump (bb_end_insn,
! 				    label_for_bb (e_fall->dest), 0))
  		{
  #ifdef ENABLE_CHECKING
  		  if (!could_fall_through (e_taken->src, e_taken->dest))
  		    abort ();
  #endif
- 		  e_fall->flags &= ~EDGE_FALLTHRU;
  		  e_taken->flags |= EDGE_FALLTHRU;
  		  update_br_prob_note (bb);
  		  continue;
--- 733,747 ----
  	      /* Otherwise we can try to invert the jump.  This will
  		 basically never fail, however, keep up the pretense.  */
  	      else if (invert_jump (bb_end_insn,
! 				    (e_fall->dest == EXIT_BLOCK_PTR
! 				     ? NULL_RTX
! 				     : label_for_bb (e_fall->dest)), 0))
  		{
+ 		  e_fall->flags &= ~EDGE_FALLTHRU;
  #ifdef ENABLE_CHECKING
  		  if (!could_fall_through (e_taken->src, e_taken->dest))
  		    abort ();
  #endif
  		  e_taken->flags |= EDGE_FALLTHRU;
  		  update_br_prob_note (bb);
  		  continue;