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.
> 
> jeff

Aha! I see now. I will try disabling that chunk of code, and testing.

Incidentially, MD_CAN_REDIRECT_BRANCH is already used in reorg in one
other place, in steal_delay_list_from_target():

#ifdef MD_CAN_REDIRECT_BRANCH
  /* On some targets, branches with delay slots can have a limited
     displacement.  Give the back end a chance to tell us we can't do
     this.  */
  if (! MD_CAN_REDIRECT_BRANCH (insn, XVECEXP (seq, 0, 0)))
    return delay_list;
#endif

This should probably be fixed as well.

Toshi