[RISCV] Allow vslidedown.vx in isExtractSubvectorCheap for half VT case#114886

preames merged 3 commits intollvm:mainllvm/llvm-project:mainfrom

preames:pr-riscv-is-subvector-extract-cheap-vxpreames/llvm-project:pr-riscv-is-subvector-extract-cheap-vxCopy head branch name to clipboard