On 2/2/23 07:22, Richard Biener wrote:
> On Wed, Feb 1, 2023 at 7:12 PM Andrew MacLeod via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>> We can reset SCEV after we fold, then SCEVs cache shouldn't have
>> anything in it when we go to remove ssa-names in remove_unreachable().
>>
>> We were resetting it later sometimes if we were processing the array
>> bounds warning, so I removed that call and just always reset it now.
>>
>> Bootstraps on x86_64-pc-linux-gnu. Testing running. Assuming no
>> regressions,  OK for trunk?
> +
> +  // SCEV needs to be reset for array bounds, and we do not wish to trigger
> +  // any SCEV lookups when removing unreachable globals, so reset it here.
> +  scev_reset ();
>
> the comment suggests that SCEV queries (aka analyze_scalar_evolution)
> won't return anything after a scev_reset ().  That's not true - instead what
> it does is nuke the SCEV cache.  That's necessary when you
> release SSA names or alter the CFG and you want to avoid followup
> SCEV queries to pick up stale data.
>
> So if remove_and_update_globals performs SCEV queries and eventually
> releases SSA names you cannot remove the second call to scev_reset.
>
> But yes, it's probably substitute_and_fold_engine::substitute_and_fold
> itself that should do a
>
>    if (scev_initialized_p ())
>      scev_reset ();
>
> possibly only in the case it released an SSA name, or removed an
> edge (but that's maybe premature optimization).
>
> Richard.
>
>
Mmm, yeah thats not what I meant to imply.  We can simply reset it 
before trying to process the unreachable globals like so. Maybe we visit 
the  S&F engine next release.. It seems more intrusive than this.

How about this patch?  testing underway.

Andrew