Hi,
On Sat, 19 Nov 2011, Tom de Vries wrote:
> On 11/18/2011 10:29 PM, Eric Botcazou wrote:
> >> For the test-case of PR50764, a dead label is introduced by
> >> fixup_reorder_chain in cfg_layout_finalize, called from
> >> pass_reorder_blocks.
> >
> > I presume that there is no reasonable way of preventing fixup_reorder_chain
> > from introducing it or of teaching fixup_reorder_chain to remove it?
> >
>
> This (untested) patch also removes the dead label for the PR, and I
> think it is safe. ...
cfgrtl.c has already code to delete labels (delete_insn) when appropriate
(can_delete_label_p). Perhaps that can be reused somehow.
> Index: cfglayout.c
> =================================================================== ---
> cfglayout.c (revision 181377) +++ cfglayout.c (working copy) @@ -702,6
> +702,21 @@ relink_block_chain (bool stay_in_cfglayo
> }
>
>
> +static bool
> +forced_label_p (rtx label)
> +{
> + rtx insn, forced_label;
> + for (insn = forced_labels; insn; insn = XEXP (insn, 1))
> + {
> + forced_label = XEXP (insn, 0);
> + if (!LABEL_P (forced_label))
> + continue;
> + if (forced_label == label)
> + return true;
> + }
> + return false;
> +}
That's in_expr_list_p().
> @@ -857,6 +872,12 @@ fixup_reorder_chain (void)
> (e_taken->src, e_taken->dest));
> e_taken->flags |= EDGE_FALLTHRU;
> update_br_prob_note (bb);
> + if (LABEL_NUSES (ret_label) == 0
> + && !LABEL_PRESERVE_P (ret_label)
> + && LABEL_NAME (ret_label) == NULL
> + && !forced_label_p (ret_label)
And this is cfgrtl.c:can_delete_label_p. Note that you actually
can remove labels also if they are !can_delete_label_p, if you use
delete_insn (which you do). It will replace such undeletable labels by a
DELETED_LABEL note.
Ciao,
Michael.
