[llvm-dev] RFC: Promoting experimental reduction intrinsics to first class intrinsics

Philip Reames via llvm-dev llvm-dev at lists.llvm.org
Thu Apr 9 10:04:36 PDT 2020

My experience with them so far is that the code generation for these 
intrinsics is still missing a lot of cases.  Some of them are X86 
specific (the target I look at mostly), but many of them have generic forms.

As one recent example, consider 
https://bugs.llvm.org/show_bug.cgi?id=45378.  (There's nothing special 
about this one other than it was recent.)

I'm not necessarily arguing they can't be promoted from experimental, 
but it would be a much easier case if the code gen was routinely as good 
or better than the scalar forms.  Or to say that a bit differently, if 
we could canonicalize to them in the IR without major regression.  
Having two ways to represent something in the IR without any agreed upon 
canonical form is always sub-optimal.


On 4/7/20 9:59 PM, Amara Emerson via llvm-dev wrote:
> Hi,
> It’s been a few years now since I added some intrinsics for doing vector reductions. We’ve been using them exclusively on AArch64, and I’ve seen some traffic a while ago on list for other targets too. Sander did some work last year to refine the semantics after some discussion.
> Are we at the point where we can drop the “experimental” from the name? IMO all target should begin to transition to using these as the preferred representation for reductions. But for now, I’m only proposing the naming change.
> Cheers,
> Amara
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