[llvm] [RISCV][VLOPT] Support segmented store instructions (PR #155467)

[Luke Lau via llvm-commits]

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lukel97 wrote:

Can we also add a negative test where we have a tuple insert but into the wrong EMUL? e.g.


```
%v = vadd_m2 ...
%imp:vrn2m1 = IMPLICIT_DEF
%ins:vrn2m1 = INSERT_SUBREG %imp, %v, %subreg.sub_vrm2_0
PseudoVSSEG2_E32_V_M1 %ins, $noreg, ...
```

I think this should be rejected with the current code, because the pseudovsseg2 should be added to the checkUsers worklist but fail at the `OperandInfo::areCompatible` check. 

https://github.com/llvm/llvm-project/pull/155467