Re: [PATCH] Fix dead_debug_insert_before ICE (PR debug/49522, take 3)

[Eric Botcazou <ebotcazou@adacore.com>]

> So, here is a new patch which doesn't need two loops, just might go a
> little bit backwards to unchain dead_debug_use for the reset insn.
>
> It still needs the change of the gcc_assert (reg) into if (reg == NULL)
> return;, because the dead->used bitmap is with this sometimes a false
> positive (saying that a regno is referenced even when it isn't).
> But here it is IMHO better to occassionaly live with the false positives,
> which just means we'll sometimes once walk the chain in dead_debug_reset
> or dead_debug_insert_before before resetting it, than to recompute the
> bitmap (we'd need a second loop for that, bitmap_clear (debug->used) and
> populate it again).

Fine with me for both points, but move some bits of these explanations to the 
code itself because this isn't obvious.  For example see below.

> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2011-07-07  Jakub Jelinek  <jakub@redhat.com>
>
> 	PR debug/49522
> 	* df-problems.c (dead_debug_reset): Remove dead_debug_uses
> 	referencing debug insns that have been reset.
> 	(dead_debug_insert_before): Don't assert reg is non-NULL,
> 	instead return immediately if it is NULL.
>
> 	* gcc.dg/debug/pr49522.c: New test.

OK, thanks.

> --- gcc/df-problems.c.jj	2011-07-07 02:32:45.928547053 +0200
> +++ gcc/df-problems.c	2011-07-07 09:57:34.846464573 +0200
> @@ -3096,6 +3096,7 @@ static void
>  dead_debug_reset (struct dead_debug *debug, unsigned int dregno)
>  {
>    struct dead_debug_use **tailp = &debug->head;
> +  struct dead_debug_use **insnp = &debug->head;
>    struct dead_debug_use *cur;
>    rtx insn;
>
> @@ -3113,9 +3114,21 @@ dead_debug_reset (struct dead_debug *deb
>  	    debug->to_rescan = BITMAP_ALLOC (NULL);
>  	  bitmap_set_bit (debug->to_rescan, INSN_UID (insn));
>  	  XDELETE (cur);
> +	  if (tailp != insnp && DF_REF_INSN ((*insnp)->use) == insn)
> +	    tailp = insnp;

/* If the current use isn't the first one attached to INSN, go back to this
   first use.  We assume that the uses attached to an insn are adjacent.  */

> +	  while ((cur = *tailp) && DF_REF_INSN (cur->use) == insn)
> +	    {
> +	      *tailp = cur->next;
> +	      XDELETE (cur);
> +	    }
> +	  insnp = tailp;

/* Then remove all the other uses attached to INSN.  */

>  	}
>        else
> -	tailp = &(*tailp)->next;
> +	{
> +	  if (DF_REF_INSN ((*insnp)->use) != DF_REF_INSN (cur->use))
> +	    insnp = tailp;
> +	  tailp = &(*tailp)->next;
> +	}
>      }
>  }
>
> @@ -3174,7 +3187,8 @@ dead_debug_insert_before (struct dead_de
>  	tailp = &(*tailp)->next;
>      }
>
> -  gcc_assert (reg);
> +  if (reg == NULL)
> +    return;

/* We may have dangling bits in debug->used for registers that were part of
   a multi-register use, one component of which has been reset.  */


-- 
Eric Botcazou