[PATCH] D129302: [RISCV] Mark vsadd(u)_vl as commutable

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

> I haven't fully dug in to understand why, but I suspect it's because of a difference in how we represent splats (splat_vector vs build_vector).

To close this. I believe it's because fixed vector uses build_vector of constants for the "step vector" while scalable vector uses the step_vector ISD node. The build_vector being all constants is canonicalized to the RHS. For the step_vector case there is no canonicalization preference so it keeps the order the node was created with which had the splat on the RHS.


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  https://reviews.llvm.org/D129302/new/

https://reviews.llvm.org/D129302