[PATCH] D40209: [DAGCombiner] eliminate shuffle of insert element

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

> I don't think we need any legality checking because the new insert is identical to the existing insert except that it may have a different constant insertion operand.

We should probably document this rule somewhere... I mean, it makes sense, but it's not obvious given that we allow the legality to vary based on whether the index is constant, and some targets have operations like movss which could be modeled as an insert_vector_elt.


https://reviews.llvm.org/D40209