Re: [PATCH 1/2] Implementation of new RISCV optimizations pass: fold-mem-offsets.

[Philipp Tomsich <philipp.tomsich@vrull.eu>]

On Thu, 25 May 2023 at 16:14, Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> On 5/25/23 07:50, Richard Biener wrote:
> > On Thu, May 25, 2023 at 3:32 PM Jeff Law via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> >>
> >>
> >>
> >> On 5/25/23 07:01, Richard Biener via Gcc-patches wrote:
> >>> On Thu, May 25, 2023 at 2:36 PM Manolis Tsamis <manolis.tsamis@vrull.eu> wrote:
> >>>>
> >>>> Implementation of the new RISC-V optimization pass for memory offset
> >>>> calculations, documentation and testcases.
> >>>
> >>> Why do fwprop or combine not what you want to do?

At least for stack variables, the virtual-stack-vars is not resolved
until reload.
So combine will be running much too early to be of any use (and I
haven't recently looked at whether one of the propagation passes runs
after).

Philipp.

> >> I think a lot of them end up coming from register elimination.
> >
> > Why isn't this a problem for other targets then?  Or maybe it is and this
> > shouldn't be a machine specific pass?  Maybe postreload-gcse should
> > perform strength reduction (I can't think of any other post reload pass
> > that would do something even remotely related).
> It is to some degree.  I ran into similar problems at my prior employer.
>   We ended up working around it in the target files in a different way
> -- which didn't work when I quickly tried it on RISC-V.
>
> Seems like it would be worth another investigative step as part of the
> evaluation of this patch.  I wasn't at 100% when I did that poking
> around many months ago.
>
> Jeff