[llvm] [RISCV] Fix crash costing cttz.elts without fixed-length RVV. (PR #226181)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

The attached test case is +zve32x which only implies zvl32b, and the RISC-V backend doesn't really support codegen for that case. 

Returning invalid for a scalarized intrinsic is fine FWIW, but can you update the PR title/description to say "Fix crash costing cttz.elts with zvl32b"

https://github.com/llvm/llvm-project/pull/226181