Flattening and remove ifelse adds instructions with empty call stacks

[sirasistant]

Aim

Profiling where all the constraints in the program come from

Expected Behavior

Every ACIR opcode should have a call stack associated with it

Bug

Some ACIR opcodes in the program have no call stack associated. I've added a condition in the SSA printer to figure out wich instructions in SSA do not have any call stack associated.

I've tracked down these instructions to some optimization steps:

• flatten_cfg.rs: Explicitely uses CallStack::new() for instructions related with the if condition. A solution to this might be to add call_stack to JmpIf in the same way Jmp and Return have call stacks, to associated the emitted instructions with.
• value_merger.rs::merge_numeric_values: This seems to be emitting some Cast and mul instructions with no call stack associated, because sometimes the if value and the else value have no call stack associated. I guess this can happen when the if else values don't come from previous instructions, such as being block params or constants
• remove_if_else.rs: Seems to be emitting array_get instructions with no call_stack, presumably from value_merger::merge_array_values that has a explicit CallStack::new() when emitting an ArrayGet

In the case we can't track down the instructions to a specific location instruction, it'd be good to at least use the call stack of the function being processed, allowing users to at least track that the instruction comes from a given function call, even though they might not know which part of the function being called generated it 🤔

To Reproduce

Modify this code in printer.rs

/// Display an arbitrary instruction
pub(crate) fn display_instruction(
    function: &Function,
    instruction: InstructionId,
    f: &mut Formatter,
) -> Result {
    // instructions are always indented within a function
    write!(f, "    ")?;

    let results = function.dfg.instruction_results(instruction);
    if !results.is_empty() {
        write!(f, "{} = ", value_list(function, results))?;
    }

    display_instruction_inner(function, &function.dfg[instruction], f, instruction)
}

fn display_instruction_inner(
    function: &Function,
    instruction: &Instruction,
    f: &mut Formatter,
    instruction_id: InstructionId,
) -> Result {
    let show = |id| value(function, id);

    let call_stack = function.dfg.get_call_stack(instruction_id);

    if call_stack.is_empty() {
        write!(f, "NO CALL STACK ")?;
    }

And compile a large program such as aztec protocol circuits or the token contract transfer function with show ssa enabled.

Project Impact

None

Impact Context

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Workaround

None

Workaround Description

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Additional Context

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Installation Method

None

Nargo Version

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NoirJS Version

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