[llvm] [GISEL] Add G_SPLAT_VECTOR_PARTS to represent 64-bit splat vectors on… (PR #86970)

[Craig Topper via llvm-commits]

topperc wrote:

This node exists in SelectionDAG because type legalization and op legalization are separate steps. That's not true in GISel where there's only one legalizer. There's no G_SPLAT_VECTOR_PARTS instruction in RISC-V. So if the legalizer in GISel creates a G_SPLAT_VECTOR_PARTS when does it get removed?

https://github.com/llvm/llvm-project/pull/86970