Method hoist_external_inputs

src/module.cpp:1665–1704

Hoists external inputs (instructions not in the dependency chain between start_ins and end_ins) to before start_ins, while preserving topological order

// Hoists external inputs (instructions not in the dependency chain between start_ins and end_ins)
// to before start_ins, while preserving topological order
void module::hoist_external_inputs(instruction_ref start_ins, instruction_ref end_ins)
{
    // get the chain of instructions between start_ins and end_ins, inclusive
    auto fusion_ins = find_instructions_between(start_ins, end_ins, this);

    // move all instructions between start_ins & end_ins that are not in the fusion chain
    // to the start_ins. In order, moving to the same destination, this will naturally preserve
    // the preexisting topological order of the module
    for(auto it = std::next(start_ins); it != end_ins;)
    {
        if(fusion_ins.count(it) == 0)
        {
            // only move if none of its inputs are after start_ins
            bool has_input_in_range =
                std::any_of(it->inputs().begin(), it->inputs().end(), [&](instruction_ref input) {
                    if(not has_instruction(input))
                        return false;
                    // verify: start_ins < input < it
                    return std::find(std::next(start_ins), it, input) != it;
                });

            if(has_input_in_range)
            {
                // input is after start_ins, meaning can't move this instruction
                ++it;
            }
            else
            {
                auto next = std::next(it);
                this->move_instruction(it, start_ins);
                it = next;
            }
        }
        else
        {
            ++it;
        }
    }
    assert(this->validate() == this->end());
}

bool operator==(const module& x, const module& y) { return to_string(x) == to_string(y); }