llvm dev - Dec 2020 - "Bits value must be constants" when generating ISel from Tablegen

I had two Instruction class definitions in my InstructionFormat TableGen, as
listed below:


```
class InstRI8<bits<8&gt; opcode,string asm,dag outs,dag ins&gt; :
Instruction{
&nbsp; ........
}




class InstRI8222<bits<8&gt; opcode,string asm,dag outs,dag
ins,list<dag&gt; Pat&gt; : Instruction{
&nbsp; ........
&nbsp; let Pattern = Pat;
}


```


However later when initializing those two classes, if I use the following format
to initialize the instruction:
```
def X : InstRI8<...&gt;{
&nbsp; &nbsp;let Pattern = [ ...... ];
}
```
I got a error from Tablegen that says&nbsp;"Bits value must be
constants" for this def.
Using the second Instruction Class which models Pattern as the template argument
works perfectly fine
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