[llvm] [RISCV][VLOPT] Skip EMUL if it is unknown before entering EMULAndEEWAreEqual (PR #139670)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

Would it be better if we just handle the nullopt EMUL case in `EMULAndEEWAreEqual`? Does it work if we just replace it with

```c++
  static bool EMULAndEEWAreEqual(const OperandInfo &A, const OperandInfo &B) {
    return A.Log2EEW == B.Log2EEW && A.EMUL == B.EMUL;
  }
```

https://github.com/llvm/llvm-project/pull/139670