eliminate_contiguous.cpp

#include <migraphx/eliminate_contiguous.hpp>
#include <migraphx/program.hpp>
#include <migraphx/instruction.hpp>
#include <migraphx/iterator_for.hpp>
#include <migraphx/ranges.hpp>
#include <migraphx/stringutils.hpp>
#include <migraphx/op/contiguous.hpp>
#include <migraphx/op/identity.hpp>
#include <utility>

namespace migraphx {
inline namespace MIGRAPHX_INLINE_NS {

static bool try_compute_shape(instruction_ref ins,
                              const std::vector<shape>& inputs,
                              const std::vector<module_ref>& mods)
{
    try
    {
        shape new_shape = ins->get_operator().compute_shape(inputs, mods);
        // If the output shape is a standard shape, no need to try its output
        if(new_shape.standard())
        {
            return true;
        }

        // if no changes for the shape, the contiguous can also be removed
        if(new_shape == ins->get_shape())
        {
            return true;
        }

        auto outputs = ins->outputs();
        // If the current instruction has no output, it means it is the last
        // instruction and generates a non-standard output shape, and the last
        // output shape is different from the case with the contiguous operator
        if(outputs.empty())
        {
            return false;
        }

        for(auto output : outputs)
        {
            auto args = output->inputs();
            std::vector<shape> input_shapes(args.size());
            std::transform(args.begin(), args.end(), input_shapes.begin(), [&](auto& arg) {
                return (arg == ins) ? new_shape : arg->get_shape();
            });

            if(!try_compute_shape(output, input_shapes, mods))
            {
                return false;
            }
        }
    }
    catch(...)
    {
        return false;
    }

    return true;
}

static bool try_compute_shape(instruction_ref ins,
                              const std::vector<instruction_ref>& args,
                              const std::vector<module_ref>& mods)
{
    auto inputs = to_shapes(args);
    return try_compute_shape(ins, inputs, mods);
}

template<class F>
static void remove_contiguous(const std::string& op_name, module& m, F f)
{
    auto last = std::prev(m.end());
    for(auto ins : iterator_for(m))
    {
        // return instruction should have inputs with standard shape
        if(ins->name() == "@return")
            continue;

        if (ins != last and ins->outputs().empty())
            continue;

        if (not f(ins))
            continue;

        // Make a copy so we can modify it while we iterate
        auto args     = ins->inputs();
        auto new_args = args;
        auto mod_args = ins->module_inputs();
        for(auto arg : ins->inputs())
        {
            if(arg->name() != op_name)
                continue;
            auto prev = arg->inputs().front();
            replace(new_args, arg, prev);
            if(try_compute_shape(ins, new_args, mod_args))
            {
                instruction::replace_argument(ins, arg, prev);
            }
            else if(prev->can_eval())
            {
                auto c = op::contiguous{};
                auto r = c.compute(c.compute_shape({prev->get_shape()}), {prev->eval()});

                auto l = m.add_literal(r.get_shape(), r.data());
                m.replace_instruction(arg, l);
            }
        }
    }
}

void eliminate_contiguous::apply(module& m) const
{
    // Skip contiguous from splits first
    remove_contiguous(op_name, m, [](auto ins) { 
        if (ins->name() != "slice")
            return true;
        return (ins->inputs().front()->outputs().size() == 1);
    });
    remove_contiguous(op_name, m, [](auto) { return true; });
}

} // namespace MIGRAPHX_INLINE_NS
} // namespace migraphx