[llvm] [RISCV] Fix crash when unrolling loop containing vector instructions (PR #83384)

[Fraser Cormack via llvm-commits]

================
@@ -0,0 +1,53 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
----------------
frasercrmck wrote:

Is `rvv-invalid-cost` the best name for this test? It might make people think there's an invalid cost when using `+v`.

https://github.com/llvm/llvm-project/pull/83384