[llvm] [RISCV] Restrict combineOp_VLToVWOp_VL w/ bf16 to vfwmadd_vl with zvfbfwma (PR #108798)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Do we need to do this check when we check the other users too?
> 
> ```
>     auto AppendUsersIfNeeded = [&Worklist, &Subtarget,                           
>                                 &Inserted](const NodeExtensionHelper &Op) {      
>       if (Op.needToPromoteOtherUsers()) {                                        
>         for (SDNode::use_iterator UI = Op.OrigOperand->use_begin(),              
>                                   UE = Op.OrigOperand->use_end();                
>              UI != UE; ++UI) {                                                   
>           SDNode *TheUse = *UI;                                                  
>           if (!NodeExtensionHelper::isSupportedRoot(TheUse, Subtarget))          
>             return false;                                                        
>           // We only support the first 2 operands of FMA.                        
>           if (UI.getOperandNo() >= 2)                                            
>             return false;                                                        
>           if (Inserted.insert(TheUse).second)                                    
>             Worklist.push_back(TheUse);                                          
>         }                                                                        
>       }                                                                          
>       return true;                                                               
>     }; 
> ```

If I'm reading this right, won't the other users of the extended bf16 ops go back onto the worklist, where they'll then have their LHS/RHS checked through the same NodeExtensionHelper constructor?

https://github.com/llvm/llvm-project/pull/108798