[PATCH] D57504: RFC: Prototype & Roadmap for vector predication in LLVM

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer added a comment.

(not sure if I should continue here or in D69891 <https://reviews.llvm.org/D69891>, will try here first)

Sorry for dipping out of this discussion. I.e. after our "passthru discussion", I wanted to do more homework to make sure a "separate select" would work for us, if we wouldn't miss anything, but then other work happened and never got round to this. But I am still very interested, so dipping back in :-/

> If we had predicated IR instructions, would we want them to have a passthru operand?
> 
>> I think that would probably be a reasonable clean-slate IR design, though I am not at all sure if it would be better.

One of the problems I had that I found it difficult to see all consequences, and answers the sort of questions asked above (also because I haven't yet spend enough time on this). For example, being explicit in IR is in general a good thing to do? So yes, why not a passthru? But then I had the same question as Robin, not sure it would be better. The other thing I would mention again is that I think convenience is a pretty strong argument too, if this is most convenient for at least two / three other architectures, then why not? But then you could argue that it is simple to patch up with a select, and we're going in circles... At least the concern Robin brought up about the select seems to be addressed with the vp.select.


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