[llvm] [RISCV] Reduce duplicate code for calling SimplifyDemandedBits. (PR #131711)

[Craig Topper via llvm-commits]

topperc wrote:

> Should update the PR title

Maybe "[RISCV] Call SimplifyDemandedBits on the scalar input of vmv_x_s_vl"

https://github.com/llvm/llvm-project/pull/131711