opt_lut: leave intact LUTs with cascade feeding module outputs.

[yosys.git] / passes / opt / opt_lut.cc

/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  Copyright (C) 2018  whitequark <whitequark@whitequark.org>
 *
 *  Permission to use, copy, modify, and/or distribute this software for any
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 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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#include "kernel/yosys.h"
#include "kernel/sigtools.h"
#include "kernel/modtools.h"

USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN

struct OptLutWorker
{
        dict<IdString, dict<int, IdString>> &dlogic;
        RTLIL::Module *module;
        ModIndex index;
        SigMap sigmap;

        pool<RTLIL::Cell*> luts;
        dict<RTLIL::Cell*, int> luts_arity;
        dict<RTLIL::Cell*, pool<RTLIL::Cell*>> luts_dlogics;
        dict<RTLIL::Cell*, pool<int>> luts_dlogic_inputs;

        int combined_count = 0;

        bool evaluate_lut(RTLIL::Cell *lut, dict<SigBit, bool> inputs)
        {
                SigSpec lut_input = sigmap(lut->getPort("\\A"));
                int lut_width = lut->getParam("\\WIDTH").as_int();
                Const lut_table = lut->getParam("\\LUT");
                int lut_index = 0;

                for (int i = 0; i < lut_width; i++)
                {
                        SigBit input = sigmap(lut_input[i]);
                        if (inputs.count(input))
                        {
                                lut_index |= inputs[input] << i;
                        }
                        else
                        {
                                lut_index |= SigSpec(lut_input[i]).as_bool() << i;
                        }
                }

                return lut_table.extract(lut_index).as_int();
        }

        void show_stats_by_arity()
        {
                dict<int, int> arity_counts;
                dict<IdString, int> dlogic_counts;
                int max_arity = 0;

                for (auto lut_arity : luts_arity)
                {
                        max_arity = max(max_arity, lut_arity.second);
                        arity_counts[lut_arity.second]++;
                }

                for (auto &lut_dlogics : luts_dlogics)
                {
                        for (auto &lut_dlogic : lut_dlogics.second)
                        {
                                dlogic_counts[lut_dlogic->type]++;
                        }
                }

                log("Number of LUTs: %8zu\n", luts.size());
                for (int arity = 1; arity <= max_arity; arity++)
                {
                        if (arity_counts[arity])
                                log("  %d-LUT %16d\n", arity, arity_counts[arity]);
                }
                for (auto &dlogic_count : dlogic_counts)
                {
                        log("  with %-12s %4d\n", dlogic_count.first.c_str(), dlogic_count.second);
                }
        }

        OptLutWorker(dict<IdString, dict<int, IdString>> &dlogic, RTLIL::Module *module, int limit) :
                dlogic(dlogic), module(module), index(module), sigmap(module)
        {
                log("Discovering LUTs.\n");
                for (auto cell : module->selected_cells())
                {
                        if (cell->type == "$lut")
                        {
                                int lut_width = cell->getParam("\\WIDTH").as_int();
                                SigSpec lut_input = cell->getPort("\\A");
                                int lut_arity = 0;

                                log("Found $lut\\WIDTH=%d cell %s.%s.\n", lut_width, log_id(module), log_id(cell));
                                luts.insert(cell);

                                // First, find all dedicated logic we're connected to. This results in an overapproximation
                                // of such connections.
                                pool<RTLIL::Cell*> lut_all_dlogics;
                                for (int i = 0; i < lut_width; i++)
                                {
                                        SigBit bit = lut_input[i];
                                        for (auto &port : index.query_ports(bit))
                                        {
                                                if (dlogic.count(port.cell->type))
                                                {
                                                        auto &dlogic_map = dlogic[port.cell->type];
                                                        if (dlogic_map.count(i))
                                                        {
                                                                if (port.port == dlogic_map[i])
                                                                {
                                                                        lut_all_dlogics.insert(port.cell);
                                                                }
                                                        }
                                                }
                                        }
                                }

                                // Second, make sure that the connection to dedicated logic is legal. If it is not legal,
                                // it means one of the two things:
                                //   * The connection is spurious. I.e. this is dedicated logic that will be packed
                                //     with some other LUT, and it just happens to be conected to this LUT as well.
                                //   * The connection is illegal.
                                // In either of these cases, we don't need to concern ourselves with preserving the connection
                                // between this LUT and this dedicated logic cell.
                                pool<RTLIL::Cell*> lut_legal_dlogics;
                                pool<int> lut_dlogic_inputs;
                                for (auto lut_dlogic : lut_all_dlogics)
                                {
                                        auto &dlogic_map = dlogic[lut_dlogic->type];
                                        bool legal = true;
                                        for (auto &dlogic_conn : dlogic_map)
                                        {
                                                if (lut_width <= dlogic_conn.first)
                                                {
                                                        log("  LUT has illegal connection to %s cell %s.%s.\n", lut_dlogic->type.c_str(), log_id(module), log_id(lut_dlogic));
                                                        log("    LUT input A[%d] not present.\n", dlogic_conn.first);
                                                        legal = false;
                                                        break;
                                                }
                                                if (sigmap(lut_input[dlogic_conn.first]) != sigmap(lut_dlogic->getPort(dlogic_conn.second)))
                                                {
                                                        log("  LUT has illegal connection to %s cell %s.%s.\n", lut_dlogic->type.c_str(), log_id(module), log_id(lut_dlogic));
                                                        log("    LUT input A[%d] (wire %s) not connected to %s port %s (wire %s).\n", dlogic_conn.first, log_signal(lut_input[dlogic_conn.first]), lut_dlogic->type.c_str(), dlogic_conn.second.c_str(), log_signal(lut_dlogic->getPort(dlogic_conn.second)));
                                                        legal = false;
                                                        break;
                                                }
                                        }

                                        if (legal)
                                        {
                                                log("  LUT has legal connection to %s cell %s.%s.\n", lut_dlogic->type.c_str(), log_id(module), log_id(lut_dlogic));
                                                lut_legal_dlogics.insert(lut_dlogic);
                                                for (auto &dlogic_conn : dlogic_map)
                                                        lut_dlogic_inputs.insert(dlogic_conn.first);
                                        }
                                }

                                // Third, determine LUT arity. An n-wide LUT that has k constant inputs and m inputs shared with dedicated
                                // logic implements an (n-k-m)-ary function.
                                for (int i = 0; i < lut_width; i++)
                                {
                                        SigBit bit = lut_input[i];
                                        if (bit.wire || lut_dlogic_inputs.count(i))
                                                lut_arity++;
                                }

                                log("  Cell implements a %d-LUT.\n", lut_arity);
                                luts_arity[cell] = lut_arity;
                                luts_dlogics[cell] = lut_legal_dlogics;
                                luts_dlogic_inputs[cell] = lut_dlogic_inputs;
                        }
                }
                show_stats_by_arity();

                log("\n");
                log("Combining LUTs.\n");
                pool<RTLIL::Cell*> worklist = luts;
                while (worklist.size())
                {
                        if (limit == 0)
                        {
                                log("Limit reached.\n");
                                break;
                        }

                        auto lutA = worklist.pop();
                        SigSpec lutA_input = sigmap(lutA->getPort("\\A"));
                        SigSpec lutA_output = sigmap(lutA->getPort("\\Y")[0]);
                        int lutA_width = lutA->getParam("\\WIDTH").as_int();
                        int lutA_arity = luts_arity[lutA];
                        pool<int> &lutA_dlogic_inputs = luts_dlogic_inputs[lutA];

                        auto lutA_output_ports = index.query_ports(lutA->getPort("\\Y"));
                        if (lutA_output_ports.size() != 2)
                                continue;

                        for (auto &port : lutA_output_ports)
                        {
                                if (port.cell == lutA)
                                        continue;

                                if (luts.count(port.cell))
                                {
                                        auto lutB = port.cell;
                                        SigSpec lutB_input = sigmap(lutB->getPort("\\A"));
                                        SigSpec lutB_output = sigmap(lutB->getPort("\\Y")[0]);
                                        int lutB_width = lutB->getParam("\\WIDTH").as_int();
                                        int lutB_arity = luts_arity[lutB];
                                        pool<int> &lutB_dlogic_inputs = luts_dlogic_inputs[lutB];

                                        log("Found %s.%s (cell A) feeding %s.%s (cell B).\n", log_id(module), log_id(lutA), log_id(module), log_id(lutB));

                                        if (index.query_is_output(lutA->getPort("\\Y")))
                                        {
                                                log("  Not combining LUTs (cascade connection feeds module output).\n");
                                                continue;
                                        }

                                        pool<SigBit> lutA_inputs;
                                        pool<SigBit> lutB_inputs;
                                        for (auto &bit : lutA_input)
                                        {
                                                if (bit.wire)
                                                        lutA_inputs.insert(sigmap(bit));
                                        }
                                        for (auto &bit : lutB_input)
                                        {
                                                if (bit.wire)
                                                        lutB_inputs.insert(sigmap(bit));
                                        }

                                        pool<SigBit> common_inputs;
                                        for (auto &bit : lutA_inputs)
                                        {
                                                if (lutB_inputs.count(bit))
                                                        common_inputs.insert(bit);
                                        }

                                        int lutM_arity = lutA_arity + lutB_arity - 1 - common_inputs.size();
                                        if (lutA_dlogic_inputs.size())
                                                log("  Cell A is a %d-LUT with %zu dedicated connections. ", lutA_arity, lutA_dlogic_inputs.size());
                                        else
                                                log("  Cell A is a %d-LUT. ", lutA_arity);
                                        if (lutB_dlogic_inputs.size())
                                                log("Cell B is a %d-LUT with %zu dedicated connections.\n", lutB_arity, lutB_dlogic_inputs.size());
                                        else
                                                log("Cell B is a %d-LUT.\n", lutB_arity);
                                        log("  Cells share %zu input(s) and can be merged into one %d-LUT.\n", common_inputs.size(), lutM_arity);

                                        const int COMBINE_A = 1, COMBINE_B = 2, COMBINE_EITHER = COMBINE_A | COMBINE_B;
                                        int combine_mask = 0;
                                        if (lutM_arity > lutA_width)
                                        {
                                                log("  Not combining LUTs into cell A (combined LUT wider than cell A).\n");
                                        }
                                        else if (lutB_dlogic_inputs.size() > 0)
                                        {
                                                log("  Not combining LUTs into cell A (cell B is connected to dedicated logic).\n");
                                        }
                                        else if (lutB->get_bool_attribute("\\lut_keep"))
                                        {
                                                log("  Not combining LUTs into cell A (cell B has attribute \\lut_keep).\n");
                                        }
                                        else
                                        {
                                                combine_mask |= COMBINE_A;
                                        }
                                        if (lutM_arity > lutB_width)
                                        {
                                                log("  Not combining LUTs into cell B (combined LUT wider than cell B).\n");
                                        }
                                        else if (lutA_dlogic_inputs.size() > 0)
                                        {
                                                log("  Not combining LUTs into cell B (cell A is connected to dedicated logic).\n");
                                        }
                                        else if (lutA->get_bool_attribute("\\lut_keep"))
                                        {
                                                log("  Not combining LUTs into cell B (cell A has attribute \\lut_keep).\n");
                                        }
                                        else
                                        {
                                                combine_mask |= COMBINE_B;
                                        }

                                        int combine = combine_mask;
                                        if (combine == COMBINE_EITHER)
                                        {
                                                log("  Can combine into either cell.\n");
                                                if (lutA_arity == 1)
                                                {
                                                        log("    Cell A is a buffer or inverter, combining into cell B.\n");
                                                        combine = COMBINE_B;
                                                }
                                                else if (lutB_arity == 1)
                                                {
                                                        log("    Cell B is a buffer or inverter, combining into cell A.\n");
                                                        combine = COMBINE_A;
                                                }
                                                else
                                                {
                                                        log("    Arbitrarily combining into cell A.\n");
                                                        combine = COMBINE_A;
                                                }
                                        }

                                        RTLIL::Cell *lutM, *lutR;
                                        pool<SigBit> lutM_inputs, lutR_inputs;
                                        pool<int> lutM_dlogic_inputs;
                                        if (combine == COMBINE_A)
                                        {
                                                log("  Combining LUTs into cell A.\n");
                                                lutM = lutA;
                                                lutM_inputs = lutA_inputs;
                                                lutM_dlogic_inputs = lutA_dlogic_inputs;
                                                lutR = lutB;
                                                lutR_inputs = lutB_inputs;
                                        }
                                        else if (combine == COMBINE_B)
                                        {
                                                log("  Combining LUTs into cell B.\n");
                                                lutM = lutB;
                                                lutM_inputs = lutB_inputs;
                                                lutM_dlogic_inputs = lutB_dlogic_inputs;
                                                lutR = lutA;
                                                lutR_inputs = lutA_inputs;
                                        }
                                        else
                                        {
                                                log("  Cannot combine LUTs.\n");
                                                continue;
                                        }

                                        pool<SigBit> lutR_unique;
                                        for (auto &bit : lutR_inputs)
                                        {
                                                if (!common_inputs.count(bit) && bit != lutA_output)
                                                        lutR_unique.insert(bit);
                                        }

                                        int lutM_width = lutM->getParam("\\WIDTH").as_int();
                                        SigSpec lutM_input = sigmap(lutM->getPort("\\A"));
                                        std::vector<SigBit> lutM_new_inputs;
                                        for (int i = 0; i < lutM_width; i++)
                                        {
                                                bool input_unused = false;
                                                if (sigmap(lutM_input[i]) == lutA_output)
                                                        input_unused = true;
                                                if (!lutM_input[i].wire && !lutM_dlogic_inputs.count(i))
                                                        input_unused = true;

                                                if (input_unused && lutR_unique.size())
                                                {
                                                        SigBit new_input = lutR_unique.pop();
                                                        log("    Connecting input %d as %s.\n", i, log_signal(new_input));
                                                        lutM_new_inputs.push_back(new_input);
                                                }
                                                else if (sigmap(lutM_input[i]) == lutA_output)
                                                {
                                                        log("    Disconnecting cascade input %d.\n", i);
                                                        lutM_new_inputs.push_back(SigBit());
                                                }
                                                else
                                                {
                                                        log("    Leaving input %d as %s.\n", i, log_signal(lutM_input[i]));
                                                        lutM_new_inputs.push_back(lutM_input[i]);
                                                }
                                        }
                                        log_assert(lutR_unique.size() == 0);

                                        RTLIL::Const lutM_new_table(State::Sx, 1 << lutM_width);
                                        for (int eval = 0; eval < 1 << lutM_width; eval++)
                                        {
                                                dict<SigBit, bool> eval_inputs;
                                                for (size_t i = 0; i < lutM_new_inputs.size(); i++)
                                                {
                                                        eval_inputs[lutM_new_inputs[i]] = (eval >> i) & 1;
                                                }
                                                eval_inputs[lutA_output] = evaluate_lut(lutA, eval_inputs);
                                                lutM_new_table[eval] = (RTLIL::State) evaluate_lut(lutB, eval_inputs);
                                        }

                                        log("  Cell A truth table: %s.\n", lutA->getParam("\\LUT").as_string().c_str());
                                        log("  Cell B truth table: %s.\n", lutB->getParam("\\LUT").as_string().c_str());
                                        log("  Merged truth table: %s.\n", lutM_new_table.as_string().c_str());

                                        lutM->setParam("\\LUT", lutM_new_table);
                                        lutM->setPort("\\A", lutM_new_inputs);
                                        lutM->setPort("\\Y", lutB_output);

                                        luts_arity[lutM] = lutM_arity;
                                        luts.erase(lutR);
                                        luts_arity.erase(lutR);
                                        lutR->module->remove(lutR);

                                        worklist.insert(lutM);
                                        worklist.erase(lutR);

                                        combined_count++;
                                        if (limit > 0)
                                                limit--;
                                }
                        }
                }
                show_stats_by_arity();
        }
};

static void split(std::vector<std::string> &tokens, const std::string &text, char sep)
{
        size_t start = 0, end = 0;
        while ((end = text.find(sep, start)) != std::string::npos) {
                tokens.push_back(text.substr(start, end - start));
                start = end + 1;
        }
        tokens.push_back(text.substr(start));
}

struct OptLutPass : public Pass {
        OptLutPass() : Pass("opt_lut", "optimize LUT cells") { }
        void help() YS_OVERRIDE
        {
                //   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
                log("\n");
                log("    opt_lut [options] [selection]\n");
                log("\n");
                log("This pass combines cascaded $lut cells with unused inputs.\n");
                log("\n");
                log("    -dlogic <type>:<cell-port>=<LUT-input>[:<cell-port>=<LUT-input>...]\n");
                log("        preserve connections to dedicated logic cell <type> that has ports\n");
                log("        <cell-port> connected to LUT inputs <LUT-input>. this includes\n");
                log("        the case where both LUT and dedicated logic input are connected to\n");
                log("        the same constant.\n");
                log("\n");
                log("    -limit N\n");
                log("        only perform the first N combines, then stop. useful for debugging.\n");
                log("\n");
        }
        void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
        {
                log_header(design, "Executing OPT_LUT pass (optimize LUTs).\n");

                dict<IdString, dict<int, IdString>> dlogic;
                int limit = -1;

                size_t argidx;
                for (argidx = 1; argidx < args.size(); argidx++)
                {
                        if (args[argidx] == "-dlogic" && argidx+1 < args.size())
                        {
                                std::vector<std::string> tokens;
                                split(tokens, args[++argidx], ':');
                                if (tokens.size() < 2)
                                        log_cmd_error("The -dlogic option requires at least one connection.\n");
                                IdString type = "\\" + tokens[0];
                                for (auto it = tokens.begin() + 1; it != tokens.end(); ++it) {
                                        std::vector<std::string> conn_tokens;
                                        split(conn_tokens, *it, '=');
                                        if (conn_tokens.size() != 2)
                                                log_cmd_error("Invalid format of -dlogic signal mapping.\n");
                                        IdString logic_port = "\\" + conn_tokens[0];
                                        int lut_input = atoi(conn_tokens[1].c_str());
                                        dlogic[type][lut_input] = logic_port;
                                }
                                continue;
                        }
                        if (args[argidx] == "-limit" && argidx + 1 < args.size())
                        {
                                limit = atoi(args[++argidx].c_str());
                                continue;
                        }
                        break;
                }
                extra_args(args, argidx, design);

                int total_count = 0;
                for (auto module : design->selected_modules())
                {
                        OptLutWorker worker(dlogic, module, limit - total_count);
                        total_count += worker.combined_count;
                }
                if (total_count)
                        design->scratchpad_set_bool("opt.did_something", true);
                log("\n");
                log("Combined %d LUTs.\n", total_count);
        }
} OptLutPass;

PRIVATE_NAMESPACE_END