[PATCH] D93860: [SLP] delete unused pairwise reduction option

[Pengfei Wang via Phabricator via llvm-commits]

pengfei added a comment.

In D93860#2475028 <https://reviews.llvm.org/D93860#2475028>, @spatel wrote:

> In D93860#2473348 <https://reviews.llvm.org/D93860#2473348>, @pengfei wrote:
>
>> Hi Sanjay, pairwise reduction seems not adopted by any targets. But do we need to consider the FMF here? I found LangRef says the intrinsic is sequential for fadd and fmul if `reassoc` flag is not set.
>
> Hi @pengfei - 
> Sorry for the delayed reply - I did not get an email notification for your comment here in Phab.
>
> We do not need to care about FMF directly here because neither of these shuffle variations corresponds to "sequential" reduction of the elements. In other words, we should require `reassoc` (at the least) to form an fadd or fmul reduction that is expected to need any shuffles. Let me know if you see any holes in that theory.
>
> One motivation for this cleanup is to correct bugs with using/propagating FMF (that was also true for D87416 <https://reviews.llvm.org/D87416>). For example - https://llvm.org/PR35538

Thanks for explanation. I was confused it with reduction intrinsics. I noticed `tryToReduce` sets fast flag instead of requires. Is that the problem you mentioned? By the way, can we build reduction intrinsics directly here instead of doing shuffle?


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