Hi Richard,
Thank you for the detailed review.
We discovered this issue while testing bw_mem benchmarks, where
signed integer
reductions showed significant performance regression. I attempted
a quick fix,
but I now understand my approach doesn't align with your
architectural direction
and has correctness issues.
I'll wait for your refactoring work instead. If I can help with
testing or any
part of the implementation, please let me know.
Thanks again for the guidance.
Zhongyao
On Fri, Oct 10, 2025 at 6:10 PM Richard Biener <rguent...@suse.de> wrote:
>
> On Fri, 10 Oct 2025, Zhongyao Chen wrote:
>
> > Enable SLP vectorization for signed integer reductions by teaching the
> > vectorizer to walk PLUS_EXPR trees directly, complementing reassociation
> > which skips signed types due to undefined overflow semantics.
>
> Thanks for working on this. Note this is not the direction I want
> the code to do - instead vect_is_simple_reduction should no longer
> decide on what is a reduction chain and what not but SLP discovery
> should (I started some refactoring there to work towards this a
> few weeks ago but got distracted). On the SLP side there's the
> vect_slp_linearize_chain toolbox that could be extended for this.
>
> That said, what I did not get to yet is to move reduction chain
> discovery to vect_analyze_slp () time, thus get rid of
> loop_vinfo->reduction_chains and only work from the reductions.
>
> What seems to be missing with your attempt is that if we re-associate
> signed operations, we have to perform the operations in an unsigned
> type.
>
> Richard.
>
