[llvm] [IR][RISCV] Remove @llvm.experimental.vp.splat (PR #171084)

[Craig Topper via llvm-commits]

topperc wrote:

Do we need to add AutoUpgrade support for compatibility with old bitcode? I don't know if the experimental allows us to skip that if it was used by an in-tree pass.

https://github.com/llvm/llvm-project/pull/171084