[Bug rtl-optimization/106187] armhf: Miscompilation at O2 level (O0 / O1 are working)

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106187

--- Comment #44 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to rguenther@suse.de from comment #43)
> On Mon, 25 Jul 2022, rearnsha at gcc dot gnu.org wrote:
> 
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106187
> > 
> > --- Comment #42 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
> > That would be unfortunate, it removes a lot of pointless loads in this case;
> > and even the store it removes ought to be safe, if it weren't for the corrupted
> > alias info that results (the values /are/ the same).
> 
> We only need to scrap the case removing _stores_, removing loads is
> all fine.  And the fix would, in this case, cause us to preserve
> the store anyway (but I expect there are cases where we can detect
> the store can be safely removed as well)

Btw, there's pass_rtl_dse2 after postreload which may be able to catch
most of the important cases as well and it already received the "fix"
(and has the info we need readily available).