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

[Renato Golin via Phabricator via llvm-commits]

rengolin added a comment.

In D57504#1725429 <https://reviews.llvm.org/D57504#1725429>, @cameron.mcinally wrote:

> But it just seems silly to me to implement something twice: Occam's razor. We'll have to work the kinks out somewhere -- so why not push directly to the goal...


I see where you're coming from, but hindsight is 20/20. Implementing something twice, when the first one is a prototype means you can make a lot of mistakes on the first iteration.

If the cost of changing the IR outweighs the prototyping costs (it usually does), than the overall cost is lower, even if for a longer period.

The current proposals are interlinked, so I don't think there will be combinatorial explosion, or even multiplication of intrinsics. I hope that we'll figure out the best way to represent that into IR sooner because of that.

This is not the first time that we try to get those into IR proper, either. All previous times we started with "change the IR" approach and could never get into agreement.

Intrinsics give us the prototype route: low implementation cost, low impact, easy to clean up later. It does add clutter in between, but that impact can also be limited to one or two targets of the willing sub-communities.

LLVM is a very fast moving target, stopping the world to get the IR "right" doesn't work.

A good example to look for is the scalable vector IR changes that have gone through multiple attempts and are going on for many years and still not complete...

These things take time, rushing it usually backfires. :)


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