[PATCH] D103882: [CostModel][AArch64] Make loads/stores of <vscale x 1 x eltty> expensive.

[Sander de Smalen via Phabricator via llvm-commits]

sdesmalen added a comment.

In D103882#2805707 <https://reviews.llvm.org/D103882#2805707>, @dmgreen wrote:

> Why 9999? Why not an invalid cost? I thought that was what invalid was for, so we didn't need hacky random numbers like this.

We've chosen not to conflate legalization and cost-modelling, so that the cost-model must return a valid cost when the legalization phase says that a given VF is legal to use. The benefit of that is that it guards the requirement to have a complete (albeit not necessarily accurate) cost-model. For SVE a VF of `vscale x 1` is legal in principle, meaning that we should be able to code-generate it. But because our code-generator is incomplete, we want to avoid using these VFs. I haven't added an interface to query the minimum legal VF, since I know we'll remove that interface at some point. The LV will expect all costs calculated to be Valid and will fail this assertion otherwise. So basically `return <magic number>` is just a temporary stop-gap to avoid failing that (and other) assertion failures.

Does that make more sense?


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