[LLVMdev] Old-style code generators broken?

[Chris Lattner]

On Mon, 15 May 2006, Vladimir Prus wrote:
> it looks like old-style code generators can no longer work with LLVM CVS,
> because:
>
> 1. The TableGen uses the DAG from instruction to computed the number of
> operands written in generated tables, and when there's no DAG, writes 0.
>
> 2. MachineInstructions::addRegOperand checks for maximum number of operands.
>
> So, when not using DAGS in TableGen input, addRegOperand asserts on adding
> the very first operand to any instruction.

Right, as the code generators have improved, we've added a lot more 
checking and other code to the code generator.

> If that was an explicit decision, maybe docs should be updated to say so?

Yup it's an explicit decision, and updated docs are welcome.  If you have 
an instruction that takes a variable number of operands, use of the 
variable_ops marker in an operand list will disable the checks above (the 
computed number of operands is set as -1).  For example, the PPC backend 
uses:

...
   def BL  : IForm<18, 0, 1, (ops calltarget:$func, variable_ops),
                   "bl $func", BrB, []>;
...

-Chris

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