[llvm] [RISCV][VLOPT] Fix operand check in isVectorOpUsedAsScalarOp (PR #112253)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> > IIUC, I think this is saying we only need to preserve elements of the passthru depending on tail policy. I think we could maybe treat the destination as a scalar operand if the policy is TA?
> 
> If I'm reading this right it shouldn't matter if we mark the destination operand as scalar or not because isVectorOpUsedAsScalarOp is only called on users.
> 
> The passthru operand might be checked, but if the policy is TA then I think we still need to preserve it. Because tail agnostic still somewhat defined (it has to be either the same as the passthru or all ones), which is separate from "tail undefined" when we have an undef passthru.

Okay, LGTM.

https://github.com/llvm/llvm-project/pull/112253