> 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 <ja...@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
