[Calyx] IfOp's group has to be a CombGroupOp?

[jiahanxie353]

Does IfOp's Group has to be a CombGroupOp, as required here?

What if we have some examples like:

  func.func @main(%arg0 : i32) {
    %two = arith.constant 2: i32
    %rem = arith.remui %arg0, %two : i32
    %cond0 = arith.cmpi eq, %arg0, %rem : i32

    scf.if %cond0 {
      some operations
    } else {
      some operations
    }

where %cond0 involves comparing the out of remui_pipe_op, which is not combinational?

What was the original design criteria? I believe @mortbopet is the original author. Also tagging @rachitnigam @cgyurgyik

[cgyurgyik]

This was probably a requirement that existed when this was initially implemented: https://docs.calyxir.org/lang/ref.html#if

[jiahanxie353]

This was probably a requirement that existed when this was initially implemented: https://docs.calyxir.org/lang/ref.html#if

Ahh indeed, thanks for pointing that out!

Is it true that if statements with with groups is still an ongoing discussion: calyxir/calyx#1699?

Semantically, I believe my example makes sense, where one of the lhs/rhs of the comparison is a result of some operation, which can be either a combinational circuit or sequential ones (like multi_pipe_op/divi_pipe_op/remui_pipe_op, since the upstream tools should be unaware if an operation is implemented combinationally or sequentially in hardware?).

As separate question, is there any workaround over this Well-formedness check, so that we can still have if %cond with comb_group, and that comb_group somehow compares remui_pipe_op.out with %arg0 combinationally?

[rachitnigam]

No, for non-combinational computations, you need to manually perform the computation in a group, store the value in a register, and then use the value of the register to perform the computation. For example:

compute_cond; // computes rem and store in reg
if reg.out { ... } else { ... }