[PATCH] D79078: [VectorCombine] Leave reduction operation to SLP

Wed Apr 29 06:24:06 PDT 2020

junparser added a comment.

In D79078#2009922 <https://reviews.llvm.org/D79078#2009922>, @lebedev.ri wrote:

> In D79078#2009883 <https://reviews.llvm.org/D79078#2009883>, @junparser wrote:
>
> > In D79078#2009814 <https://reviews.llvm.org/D79078#2009814>, @lebedev.ri wrote:
> >
> > > This needs a phase-ordering test.
> >
> >
> > For now vector-combine is executed before slp in both legacy pm and new pm with O2 <https://reviews.llvm.org/owners/package/2/>, so either we handle it here or slp can handle this kind of pattern.
>
>
> I'm not really sure what you mean.
>  We clearly have phase-ordering issue, and we should have a test that shows it.

Thanks, now i know what you mean.

> 
> 
>>> Why shouldn't SLPVectorizer be taught about that pattern instead?
>> 
>> I think we can handle this in SLP, however it may much hard than doing here? I'm not sure.
> 
> It would be best to enhance SLP rather than adding potentially-numerous semi-arbitrarily bailout elsewhere, i think.

make sense,  will check this later.

Repository:
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https://reviews.llvm.org/D79078