Re: [patch] Removal of dead labels

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 5/1/07, Zdenek Dvorak <rakdver@atrey.karlin.mff.cuni.cz> wrote:
> Hello,
>
> with http://gcc.gnu.org/ml/gcc-patches/2007-04/msg01840.html, most of
> the tree labels are unused once cfg is built.  This patch makes us
> remove those dead labels (we still keep user labels even if they are not
> referenced, for debug info).  This saves some peak memory, and the
> optimization passes that traverse all statements are a bit faster, as
> they do not need to skip the labels.
>
> Additionally, the patch makes cfgexpand avoid creating new tree labels.
>
> A few changes to code that did not handle empty blocks
> (apply_return_prediction) or blocks not starting with a label
> (rewrite_use_nonlinear_expr, vect_create_epilog_for_reduction)
> were necessary.
>
> The timings for combine.i compilation (-O2, with checking enabled)
> without and with the patch:
>
>  TOTAL                 :  25.42             0.57            26.00 43480 kB
>  TOTAL                 :  24.48             0.43            25.21 42528 kB
>
> Compilation of preprocessed gcc sources (-O2, checking disabled) is
> faster by about 2-3% with the patch, on all architectures where I tested
> it.  Bootstrapped & regtested on i686, x86_64, ia64 and ppc64-linux.

This is ok.

Thanks,
Richard.

> Zdenek
>
>         * tree-ssa-loop-ivopts.c (rewrite_use_nonlinear_expr): Use
>         bsi_after_labels.  Always insert statements before bsi.
>         * tree-vect-transform.c (vect_create_epilog_for_reduction): Ditto.
>         * predict.c (apply_return_prediction): Check for empty blocks.
>         * cfgexpand.c (lab_rtx_for_bb): New variable.
>         (label_rtx_for_bb): Do not create new tree labels.
>         (expand_gimple_basic_block): Add labels recorded in lab_rtx_for_bb.
>         (tree_expand_cfg): Initialize lab_rtx_for_bb.
>         * tree-cfg.c (build_tree_cfg): Call cleanup_dead_labels after
>         creating edges.
>         (label_for_bb): Add field used.
>         (update_eh_label, main_block_label): Mark the label used.
>         (cleanup_dead_labels): Remove unused labels.