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

[Andrew Pinski]

On Wed, Oct 20, 2021 at 12:54 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> On 10/20/2021 12:58 AM, Richard Biener wrote:
> > On Wed, Oct 20, 2021 at 1:14 AM Jeff Law via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> >>
> >>
> >> 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.
> Yea, that seems like a better routine to use.  Andrew, can you try that?

Yes that is a better routine to use, the patch is in testing right
now.  I should be able to submit it in a few hours.

Thanks,
Andrew

> Jeff