Re: PATCH: reorg branch displacement fix

[tm <tm at mail dot kloo dot net>]

On Fri, 1 Nov 2002, Jeff Law wrote:

> In message <Pine.LNX.4.21.0210311508160.3016-100000@mail.kloo.net>, tm writes:
>  >
>  >This fixes the problem mentioned in:
>  >
>  >http://gcc.gnu.org/ml/gcc-bugs/2002-06/msg00896.html
>  >
>  >When a conditional branch jumps to an unconditional branch, reorg will
>  >thread the branch without checking if the conditional branch has enough
>  >displacement bits to branch to the target.
>  >
>  >This patch uses MD_CAN_REDIRECT_BRANCH (as suggested by Joern in followup
>  >messages to original message) to implement the substitution checking.
>  >
>  >Please review and if correct, commit as I don't have CVS access.
>  >
>  >Toshi
>  >
>  >Thu Oct 31  Toshiyasu Morita  <toshiyasu.morita@hsa.hitachi.com>
>  >
>  >	* reorg.c (relax_delay_slots): Don't thread conditional jump
>  >        through unconditional jump if the conditional jump can't reach
>  >        the branch target on this processor target.
> This is wrong.  reorg does not and should not be checking branch displacements.
> That is a problem for shorten-branches and the backend.
> 

Okay, here's a revised patch:

2002-10-31  Toshiyasu Morita  <toshiyasu.morita@hsa.hitachi.com>

	* reorg.c (relax_delay_slots): Don't thread conditional branches.

*** reorg.c.bak	Thu Oct 31 13:38:29 2002
--- reorg.c	Fri Nov  1 13:13:20 2002
*************** relax_delay_slots (first)
*** 3277,3300 ****
  
        if (target_label)
  	{
! 	  /* If this jump goes to another unconditional jump, thread it, but
! 	     don't convert a jump into a RETURN here.  */
! 	  trial = follow_jumps (target_label);
! 	  /* We use next_real_insn instead of next_active_insn, so that
! 	     the special USE insns emitted by reorg won't be ignored.
! 	     If they are ignored, then they will get deleted if target_label
! 	     is now unreachable, and that would cause mark_target_live_regs
! 	     to fail.  */
! 	  trial = prev_label (next_real_insn (trial));
! 	  if (trial == 0 && target_label != 0)
! 	    trial = find_end_label ();
! 
! 	  if (trial != target_label
! 	      && redirect_with_delay_slots_safe_p (delay_insn, trial, insn))
! 	    {
! 	      reorg_redirect_jump (delay_insn, trial);
! 	      target_label = trial;
! 	    }
  
  	  /* If the first insn at TARGET_LABEL is redundant with a previous
  	     insn, redirect the jump to the following insn process again.  */
--- 3277,3285 ----
  
        if (target_label)
  	{
!           /* Code previously here to thread unconditional jumps was deleted
!              because it caused problems and this should be handled by
!              shorten_branches and/or machine_dependent_reorg anyway.  */
  
  	  /* If the first insn at TARGET_LABEL is redundant with a previous
  	     insn, redirect the jump to the following insn process again.  */