Re: [PATCH 4/4] Improve maybe_remove_writeonly_store to do a simple DCE for defining statement

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Oct 20, 2021 at 1:14 AM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
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> On 10/18/2021 10:54 PM, apinski--- via Gcc-patches wrote:
> > From: Andrew Pinski <apinski@marvell.com>
> >
> > Instead of putting a full blow DCE after execute_fixup_cfg, it makes sense
> > to try to remove the defining statement for the store that is being removed.
> > Right now we only handle PHI node statements as there needs no extra checks
> > except for it is only used once in the store statement.
> >
> > gcc/ChangeLog:
> >
> >       * tree-cfg.c (maybe_remove_writeonly_store): Remove defining
> >       (PHI) statement of the store if possible.
> This is the only part that I consider at all controversial.
>
> Is the case you're trying to handle such that you have to eliminate the
> PHI immediately and can't wait until the next DCE pass?
>
> If so and we want to go this direction, should we pull this out into a
> little routine?   I'm a bit surprised we don't already have one or more
> that do basically the same thing.

We have simple_dce_from_worklist for this which you'd seed with
the SSA rhs of the removed stores.

Richard.

>
> Jeff
>