substr() -> compare()

[yosys.git] / backends / firrtl / firrtl.cc

/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
 *
 *  Permission to use, copy, modify, and/or distribute this software for any
 *  purpose with or without fee is hereby granted, provided that the above
 *  copyright notice and this permission notice appear in all copies.
 *
 *  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.
 *
 */

#include "kernel/rtlil.h"
#include "kernel/register.h"
#include "kernel/sigtools.h"
#include "kernel/celltypes.h"
#include "kernel/cellaigs.h"
#include "kernel/log.h"
#include <algorithm>
#include <string>
#include <regex>
#include <vector>
#include <cmath>

USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN

pool<string> used_names;
dict<IdString, string> namecache;
int autoid_counter;

typedef unsigned FDirection;
static const FDirection FD_NODIRECTION = 0x0;
static const FDirection FD_IN = 0x1;
static const FDirection FD_OUT = 0x2;
static const FDirection FD_INOUT = 0x3;
static const int FIRRTL_MAX_DSH_WIDTH_ERROR = 20; // For historic reasons, this is actually one greater than the maximum allowed shift width

// Get a port direction with respect to a specific module.
FDirection getPortFDirection(IdString id, Module *module)
{
        Wire *wire = module->wires_.at(id);
        FDirection direction = FD_NODIRECTION;
        if (wire && wire->port_id)
        {
                if (wire->port_input)
                        direction |= FD_IN;
                if (wire->port_output)
                        direction |= FD_OUT;
        }
        return direction;
}

string next_id()
{
        string new_id;

        while (1) {
                new_id = stringf("_%d", autoid_counter++);
                if (used_names.count(new_id) == 0) break;
        }

        used_names.insert(new_id);
        return new_id;
}

const char *make_id(IdString id)
{
        if (namecache.count(id) != 0)
                return namecache.at(id).c_str();

        string new_id = log_id(id);

        for (int i = 0; i < GetSize(new_id); i++)
        {
                char &ch = new_id[i];
                if ('a' <= ch && ch <= 'z') continue;
                if ('A' <= ch && ch <= 'Z') continue;
                if ('0' <= ch && ch <= '9' && i != 0) continue;
                if ('_' == ch) continue;
                ch = '_';
        }

        while (used_names.count(new_id) != 0)
                new_id += '_';

        namecache[id] = new_id;
        used_names.insert(new_id);
        return namecache.at(id).c_str();
}

struct FirrtlWorker
{
        Module *module;
        std::ostream &f;

        dict<SigBit, pair<string, int>> reverse_wire_map;
        string unconn_id;
        RTLIL::Design *design;
        std::string indent;

        // Define read/write ports and memories.
        // We'll collect their definitions and emit the corresponding FIRRTL definitions at the appropriate point in module construction.
        // For the moment, we don't handle $readmemh or $readmemb.
        // These will be part of a subsequent PR.
        struct read_port {
                string name;
                bool clk_enable;
                bool clk_parity;
                bool transparent;
                RTLIL::SigSpec clk;
                RTLIL::SigSpec ena;
                RTLIL::SigSpec addr;
                read_port(string name, bool clk_enable, bool clk_parity, bool transparent, RTLIL::SigSpec clk, RTLIL::SigSpec ena, RTLIL::SigSpec addr) : name(name), clk_enable(clk_enable), clk_parity(clk_parity), transparent(transparent), clk(clk), ena(ena), addr(addr) {
                        // Current (3/13/2019) conventions:
                        //  generate a constant 0 for clock and a constant 1 for enable if they are undefined.
                        if (!clk.is_fully_def())
                                this->clk = SigSpec(State::S0);
                        if (!ena.is_fully_def())
                                this->ena = SigSpec(State::S1);
                }
                string gen_read(const char * indent) {
                        string addr_expr = make_expr(addr);
                        string ena_expr = make_expr(ena);
                        string clk_expr = make_expr(clk);
                        string addr_str = stringf("%s%s.addr <= %s\n", indent, name.c_str(), addr_expr.c_str());
                        string ena_str = stringf("%s%s.en <= %s\n", indent, name.c_str(), ena_expr.c_str());
                        string clk_str = stringf("%s%s.clk <= asClock(%s)\n", indent, name.c_str(), clk_expr.c_str());
                        return addr_str + ena_str + clk_str;
                }
        };
        struct write_port : read_port {
                RTLIL::SigSpec mask;
                write_port(string name, bool clk_enable, bool clk_parity, bool transparent, RTLIL::SigSpec clk, RTLIL::SigSpec ena, RTLIL::SigSpec addr, RTLIL::SigSpec mask) : read_port(name, clk_enable, clk_parity, transparent, clk, ena, addr), mask(mask) {
                        if (!clk.is_fully_def())
                                this->clk = SigSpec(RTLIL::Const(0));
                        if (!ena.is_fully_def())
                                this->ena = SigSpec(RTLIL::Const(0));
                        if (!mask.is_fully_def())
                                this->ena = SigSpec(RTLIL::Const(1));
                }
                string gen_read(const char * /* indent */) {
                        log_error("gen_read called on write_port: %s\n", name.c_str());
                        return stringf("gen_read called on write_port: %s\n", name.c_str());
                }
                string gen_write(const char * indent) {
                        string addr_expr = make_expr(addr);
                        string ena_expr = make_expr(ena);
                        string clk_expr = make_expr(clk);
                        string mask_expr = make_expr(mask);
                        string mask_str = stringf("%s%s.mask <= %s\n", indent, name.c_str(), mask_expr.c_str());
                        string addr_str = stringf("%s%s.addr <= %s\n", indent, name.c_str(), addr_expr.c_str());
                        string ena_str = stringf("%s%s.en <= %s\n", indent, name.c_str(), ena_expr.c_str());
                        string clk_str = stringf("%s%s.clk <= asClock(%s)\n", indent, name.c_str(), clk_expr.c_str());
                        return addr_str + ena_str + clk_str + mask_str;
                }
        };
        /* Memories defined within this module. */
        struct memory {
                Cell *pCell;                                    // for error reporting
                string name;                                    // memory name
                int abits;                                              // number of address bits
                int size;                                               // size (in units) of the memory
                int width;                                              // size (in bits) of each element
                int read_latency;
                int write_latency;
                vector<read_port> read_ports;
                vector<write_port> write_ports;
                std::string init_file;
                std::string init_file_srcFileSpec;
                string srcLine;
                memory(Cell *pCell, string name, int abits, int size, int width) : pCell(pCell), name(name), abits(abits), size(size), width(width), read_latency(0), write_latency(1), init_file(""), init_file_srcFileSpec("") {
                        // Provide defaults for abits or size if one (but not the other) is specified.
                        if (this->abits == 0 && this->size != 0) {
                                this->abits = ceil_log2(this->size);
                        } else if (this->abits != 0 && this->size == 0) {
                                this->size = 1 << this->abits;
                        }
                        // Sanity-check this construction.
                        if (this->name == "") {
                                log_error("Nameless memory%s\n", this->atLine());
                        }
                        if (this->abits == 0 && this->size == 0) {
                                log_error("Memory %s has zero address bits and size%s\n", this->name.c_str(), this->atLine());
                        }
                        if (this->width == 0) {
                                log_error("Memory %s has zero width%s\n", this->name.c_str(), this->atLine());
                        }
                 }
                // We need a default constructor for the dict insert.
           memory() : pCell(0), read_latency(0), write_latency(1), init_file(""), init_file_srcFileSpec(""){}

                const char *atLine() {
                        if (srcLine == "") {
                                if (pCell) {
                                        auto p = pCell->attributes.find("\\src");
                                        srcLine = " at " + p->second.decode_string();
                                }
                        }
                        return srcLine.c_str();
                }
                void add_memory_read_port(read_port &rp) {
                        read_ports.push_back(rp);
                }
                void add_memory_write_port(write_port &wp) {
                        write_ports.push_back(wp);
                }
                void add_memory_file(std::string init_file, std::string init_file_srcFileSpec) {
                        this->init_file = init_file;
                        this->init_file_srcFileSpec = init_file_srcFileSpec;
                }

        };
        dict<string, memory> memories;

        void register_memory(memory &m)
        {
                memories[m.name] = m;
        }

        void register_reverse_wire_map(string id, SigSpec sig)
        {
                for (int i = 0; i < GetSize(sig); i++)
                        reverse_wire_map[sig[i]] = make_pair(id, i);
        }

        FirrtlWorker(Module *module, std::ostream &f, RTLIL::Design *theDesign) : module(module), f(f), design(theDesign), indent("    ")
        {
        }

        static string make_expr(const SigSpec &sig)
        {
                string expr;

                for (auto chunk : sig.chunks())
                {
                        string new_expr;

                        if (chunk.wire == nullptr)
                        {
                                std::vector<RTLIL::State> bits = chunk.data;
                                new_expr = stringf("UInt<%d>(\"h", GetSize(bits));

                                while (GetSize(bits) % 4 != 0)
                                        bits.push_back(State::S0);

                                for (int i = GetSize(bits)-4; i >= 0; i -= 4)
                                {
                                        int val = 0;
                                        if (bits[i+0] == State::S1) val += 1;
                                        if (bits[i+1] == State::S1) val += 2;
                                        if (bits[i+2] == State::S1) val += 4;
                                        if (bits[i+3] == State::S1) val += 8;
                                        new_expr.push_back(val < 10 ? '0' + val : 'a' + val - 10);
                                }

                                new_expr += "\")";
                        }
                        else if (chunk.offset == 0 && chunk.width == chunk.wire->width)
                        {
                                new_expr = make_id(chunk.wire->name);
                        }
                        else
                        {
                                string wire_id = make_id(chunk.wire->name);
                                new_expr = stringf("bits(%s, %d, %d)", wire_id.c_str(), chunk.offset + chunk.width - 1, chunk.offset);
                        }

                        if (expr.empty())
                                expr = new_expr;
                        else
                                expr = "cat(" + new_expr + ", " + expr + ")";
                }

                return expr;
        }

        std::string fid(RTLIL::IdString internal_id)
        {
                return make_id(internal_id);
        }

        std::string cellname(RTLIL::Cell *cell)
        {
                return fid(cell->name).c_str();
        }

        void process_instance(RTLIL::Cell *cell, vector<string> &wire_exprs)
        {
                std::string cell_type = fid(cell->type);
                std::string instanceOf;
                // If this is a parameterized module, its parent module is encoded in the cell type
                if (cell->type.begins_with("$paramod"))
                {
                        std::string::iterator it;
                        for (it = cell_type.begin(); it < cell_type.end(); it++)
                        {
                                switch (*it) {
                                        case '\\': /* FALL_THROUGH */
                                        case '=': /* FALL_THROUGH */
                                        case '\'': /* FALL_THROUGH */
                                        case '$': instanceOf.append("_"); break;
                                        default: instanceOf.append(1, *it); break;
                                }
                        }
                }
                else
                {
                        instanceOf = cell_type;
                }

                std::string cell_name = cellname(cell);
                std::string cell_name_comment;
                if (cell_name != fid(cell->name))
                        cell_name_comment = " /* " + fid(cell->name) + " */ ";
                else
                        cell_name_comment = "";
                // Find the module corresponding to this instance.
                auto instModule = design->module(cell->type);
                // If there is no instance for this, just return.
                if (instModule == NULL)
                {
                        log_warning("No instance for %s.%s\n", cell_type.c_str(), cell_name.c_str());
                        return;
                }
                wire_exprs.push_back(stringf("%s" "inst %s%s of %s", indent.c_str(), cell_name.c_str(), cell_name_comment.c_str(), instanceOf.c_str()));

                for (auto it = cell->connections().begin(); it != cell->connections().end(); ++it) {
                        if (it->second.size() > 0) {
                                const SigSpec &secondSig = it->second;
                                const std::string firstName = cell_name + "." + make_id(it->first);
                                const std::string secondExpr = make_expr(secondSig);
                                // Find the direction for this port.
                                FDirection dir = getPortFDirection(it->first, instModule);
                                std::string sourceExpr, sinkExpr;
                                const SigSpec *sinkSig = nullptr;
                                switch (dir) {
                                        case FD_INOUT:
                                                log_warning("Instance port connection %s.%s is INOUT; treating as OUT\n", cell_type.c_str(), log_signal(it->second));
                                                /* FALLTHRU */
                                        case FD_OUT:
                                                sourceExpr = firstName;
                                                sinkExpr = secondExpr;
                                                sinkSig = &secondSig;
                                                break;
                                        case FD_NODIRECTION:
                                                log_warning("Instance port connection %s.%s is NODIRECTION; treating as IN\n", cell_type.c_str(), log_signal(it->second));
                                                /* FALLTHRU */
                                        case FD_IN:
                                                sourceExpr = secondExpr;
                                                sinkExpr = firstName;
                                                break;
                                        default:
                                                log_error("Instance port %s.%s unrecognized connection direction 0x%x !\n", cell_type.c_str(), log_signal(it->second), dir);
                                                break;
                                }
                                // Check for subfield assignment.
                                std::string bitsString = "bits(";
                                if (sinkExpr.compare(0, bitsString.length(), bitsString) == 0) {
                                        if (sinkSig == nullptr)
                                                log_error("Unknown subfield %s.%s\n", cell_type.c_str(), sinkExpr.c_str());
                                        // Don't generate the assignment here.
                                        // Add the source and sink to the "reverse_wire_map" and we'll output the assignment
                                        //  as part of the coalesced subfield assignments for this wire.
                                        register_reverse_wire_map(sourceExpr, *sinkSig);
                                } else {
                                        wire_exprs.push_back(stringf("\n%s%s <= %s", indent.c_str(), sinkExpr.c_str(), sourceExpr.c_str()));
                                }
                        }
                }
                wire_exprs.push_back(stringf("\n"));

        }

        // Given an expression for a shift amount, and a maximum width,
        //  generate the FIRRTL expression for equivalent dynamic shift taking into account FIRRTL shift semantics.
        std::string gen_dshl(const string b_expr, const int b_width)
        {
                string result = b_expr;
                if (b_width >= FIRRTL_MAX_DSH_WIDTH_ERROR) {
                        int max_shift_width_bits = FIRRTL_MAX_DSH_WIDTH_ERROR - 1;
                        string max_shift_string = stringf("UInt<%d>(%d)", max_shift_width_bits, (1<<max_shift_width_bits) - 1);
                        // Deal with the difference in semantics between FIRRTL and verilog
                        result = stringf("mux(gt(%s, %s), %s, bits(%s, %d, 0))", b_expr.c_str(), max_shift_string.c_str(), max_shift_string.c_str(), b_expr.c_str(), max_shift_width_bits - 1);
                }
                return result;
        }

        void run()
        {
                f << stringf("  module %s:\n", make_id(module->name));
                vector<string> port_decls, wire_decls, cell_exprs, wire_exprs;

                for (auto wire : module->wires())
                {
                        const auto wireName = make_id(wire->name);
                        // If a wire has initial data, issue a warning since FIRRTL doesn't currently support it.
                        if (wire->attributes.count("\\init")) {
                                log_warning("Initial value (%s) for (%s.%s) not supported\n",
                                                        wire->attributes.at("\\init").as_string().c_str(),
                                                        log_id(module), log_id(wire));
                        }
                        if (wire->port_id)
                        {
                                if (wire->port_input && wire->port_output)
                                        log_error("Module port %s.%s is inout!\n", log_id(module), log_id(wire));
                                port_decls.push_back(stringf("    %s %s: UInt<%d>\n", wire->port_input ? "input" : "output",
                                                wireName, wire->width));
                        }
                        else
                        {
                                wire_decls.push_back(stringf("    wire %s: UInt<%d>\n", wireName, wire->width));
                        }
                }

                for (auto cell : module->cells())
                {
                        static Const ndef(0, 0);

                    // Is this cell is a module instance?
                        if (cell->type[0] != '$')
                        {
                                process_instance(cell, wire_exprs);
                                continue;
                        }
                        // Not a module instance. Set up cell properties
                        bool extract_y_bits = false;            // Assume no extraction of final bits will be required.
                        int a_width = cell->parameters.at("\\A_WIDTH", ndef).as_int();  // The width of "A"
                        int b_width = cell->parameters.at("\\B_WIDTH", ndef).as_int();  // The width of "A"
                        const int y_width = cell->parameters.at("\\Y_WIDTH", ndef).as_int();    // The width of the result
                        const bool a_signed = cell->parameters.at("\\A_SIGNED", ndef).as_bool();
                        const bool b_signed = cell->parameters.at("\\B_SIGNED", ndef).as_bool();
                        bool firrtl_is_signed = a_signed;       // The result is signed (subsequent code may change this).
                        int firrtl_width = 0;
                        string primop;
                        bool always_uint = false;
                        string y_id = make_id(cell->name);

                        if (cell->type.in("$not", "$logic_not", "$neg", "$reduce_and", "$reduce_or", "$reduce_xor", "$reduce_bool", "$reduce_xnor"))
                        {
                                string a_expr = make_expr(cell->getPort("\\A"));
                                wire_decls.push_back(stringf("    wire %s: UInt<%d>\n", y_id.c_str(), y_width));

                                if (a_signed) {
                                        a_expr = "asSInt(" + a_expr + ")";
                                }

                                // Don't use the results of logical operations (a single bit) to control padding
                                if (!(cell->type.in("$eq", "$eqx", "$gt", "$ge", "$lt", "$le", "$ne", "$nex", "$reduce_bool", "$logic_not") && y_width == 1) ) {
                                        a_expr = stringf("pad(%s, %d)", a_expr.c_str(), y_width);
                                }

                                // Assume the FIRRTL width is a single bit.
                                firrtl_width = 1;
                                if (cell->type == "$not") primop = "not";
                                else if (cell->type == "$neg") {
                                        primop = "neg";
                                        firrtl_is_signed = true;        // Result of "neg" is signed (an SInt).
                                        firrtl_width = a_width;
                                } else if (cell->type == "$logic_not") {
                                        primop = "eq";
                                        a_expr = stringf("%s, UInt(0)", a_expr.c_str());
                                }
                                else if (cell->type == "$reduce_and") primop = "andr";
                                else if (cell->type == "$reduce_or") primop = "orr";
                                else if (cell->type == "$reduce_xor") primop = "xorr";
                                else if (cell->type == "$reduce_xnor") {
                                        primop = "not";
                                        a_expr = stringf("xorr(%s)", a_expr.c_str());
                                }
                                else if (cell->type == "$reduce_bool") {
                                        primop = "neq";
                                        // Use the sign of the a_expr and its width as the type (UInt/SInt) and width of the comparand.
                                        a_expr = stringf("%s, %cInt<%d>(0)", a_expr.c_str(), a_signed ? 'S' : 'U', a_width);
                                }

                                string expr = stringf("%s(%s)", primop.c_str(), a_expr.c_str());

                                if ((firrtl_is_signed && !always_uint))
                                        expr = stringf("asUInt(%s)", expr.c_str());

                                cell_exprs.push_back(stringf("    %s <= %s\n", y_id.c_str(), expr.c_str()));
                                register_reverse_wire_map(y_id, cell->getPort("\\Y"));

                                continue;
                        }
                        if (cell->type.in("$add", "$sub", "$mul", "$div", "$mod", "$xor", "$xnor", "$and", "$or", "$eq", "$eqx",
                                                          "$gt", "$ge", "$lt", "$le", "$ne", "$nex", "$shr", "$sshr", "$sshl", "$shl",
                                                          "$logic_and", "$logic_or", "$pow"))
                        {
                                string a_expr = make_expr(cell->getPort("\\A"));
                                string b_expr = make_expr(cell->getPort("\\B"));
                                wire_decls.push_back(stringf("    wire %s: UInt<%d>\n", y_id.c_str(), y_width));

                                if (a_signed) {
                                        a_expr = "asSInt(" + a_expr + ")";
                                        // Expand the "A" operand to the result width
                                        if (a_width < y_width) {
                                                a_expr = stringf("pad(%s, %d)", a_expr.c_str(), y_width);
                                                a_width = y_width;
                                        }
                                }
                                // Shift amount is always unsigned, and needn't be padded to result width,
                                //  otherwise, we need to cast the b_expr appropriately
                                if (b_signed && !cell->type.in("$shr", "$sshr", "$shl", "$sshl", "$pow")) {
                                        b_expr = "asSInt(" + b_expr + ")";
                                        // Expand the "B" operand to the result width
                                        if (b_width < y_width) {
                                                b_expr = stringf("pad(%s, %d)", b_expr.c_str(), y_width);
                                                b_width = y_width;
                                        }
                                }

                                // For the arithmetic ops, expand operand widths to result widths befor performing the operation.
                                // This corresponds (according to iverilog) to what verilog compilers implement.
                                if (cell->type.in("$add", "$sub", "$mul", "$div", "$mod", "$xor", "$xnor", "$and", "$or"))
                                {
                                        if (a_width < y_width) {
                                                a_expr = stringf("pad(%s, %d)", a_expr.c_str(), y_width);
                                                a_width = y_width;
                                        }
                                        if (b_width < y_width) {
                                                b_expr = stringf("pad(%s, %d)", b_expr.c_str(), y_width);
                                                b_width = y_width;
                                        }
                                }
                                // Assume the FIRRTL width is the width of "A"
                                firrtl_width = a_width;
                                auto a_sig = cell->getPort("\\A");

                                if (cell->type == "$add") {
                                        primop = "add";
                                        firrtl_is_signed = a_signed | b_signed;
                                        firrtl_width = max(a_width, b_width);
                                } else if (cell->type == "$sub") {
                                        primop = "sub";
                                        firrtl_is_signed = true;
                                        int a_widthInc = (!a_signed && b_signed) ? 2 : (a_signed && !b_signed) ? 1 : 0;
                                        int b_widthInc = (a_signed && !b_signed) ? 2 : (!a_signed && b_signed) ? 1 : 0;
                                        firrtl_width = max(a_width + a_widthInc, b_width + b_widthInc);
                                } else if (cell->type == "$mul") {
                                        primop = "mul";
                                        firrtl_is_signed = a_signed | b_signed;
                                        firrtl_width = a_width + b_width;
                                } else if (cell->type == "$div") {
                                        primop = "div";
                                        firrtl_is_signed = a_signed | b_signed;
                                        firrtl_width = a_width;
                                } else if (cell->type == "$mod") {
                                        primop = "rem";
                                        firrtl_width = min(a_width, b_width);
                                } else if (cell->type == "$and") {
                                        primop = "and";
                                        always_uint = true;
                                        firrtl_width = max(a_width, b_width);
                                }
                                else if (cell->type == "$or" ) {
                                        primop =  "or";
                                        always_uint = true;
                                        firrtl_width = max(a_width, b_width);
                                }
                                else if (cell->type == "$xor") {
                                        primop = "xor";
                                        always_uint = true;
                                        firrtl_width = max(a_width, b_width);
                                }
                                else if (cell->type == "$xnor") {
                                        primop = "xnor";
                                        always_uint = true;
                                        firrtl_width = max(a_width, b_width);
                                }
                                else if ((cell->type == "$eq") | (cell->type == "$eqx")) {
                                        primop = "eq";
                                        always_uint = true;
                                        firrtl_width = 1;
                            }
                                else if ((cell->type == "$ne") | (cell->type == "$nex")) {
                                        primop = "neq";
                                        always_uint = true;
                                        firrtl_width = 1;
                                }
                                else if (cell->type == "$gt") {
                                        primop = "gt";
                                        always_uint = true;
                                        firrtl_width = 1;
                                }
                                else if (cell->type == "$ge") {
                                        primop = "geq";
                                        always_uint = true;
                                        firrtl_width = 1;
                                }
                                else if (cell->type == "$lt") {
                                        primop = "lt";
                                        always_uint = true;
                                        firrtl_width = 1;
                                }
                                else if (cell->type == "$le") {
                                        primop = "leq";
                                        always_uint = true;
                                        firrtl_width = 1;
                                }
                                else if ((cell->type == "$shl") | (cell->type == "$sshl")) {
                                        // FIRRTL will widen the result (y) by the amount of the shift.
                                        // We'll need to offset this by extracting the un-widened portion as Verilog would do.
                                        extract_y_bits = true;
                                        // Is the shift amount constant?
                                        auto b_sig = cell->getPort("\\B");
                                        if (b_sig.is_fully_const()) {
                                                primop = "shl";
                                                int shift_amount = b_sig.as_int();
                                                b_expr = std::to_string(shift_amount);
                                                firrtl_width = a_width + shift_amount;
                                        } else {
                                                primop = "dshl";
                                                // Convert from FIRRTL left shift semantics.
                                                b_expr = gen_dshl(b_expr, b_width);
                                                firrtl_width = a_width + (1 << b_width) - 1;
                                        }
                                }
                                else if ((cell->type == "$shr") | (cell->type == "$sshr")) {
                                        // We don't need to extract a specific range of bits.
                                        extract_y_bits = false;
                                        // Is the shift amount constant?
                                        auto b_sig = cell->getPort("\\B");
                                        if (b_sig.is_fully_const()) {
                                                primop = "shr";
                                                int shift_amount = b_sig.as_int();
                                                b_expr = std::to_string(shift_amount);
                                                firrtl_width = max(1, a_width - shift_amount);
                                        } else {
                                                primop = "dshr";
                                                firrtl_width = a_width;
                                        }
                                        // We'll need to do some special fixups if the source (and thus result) is signed.
                                        if (firrtl_is_signed) {
                                                // If this is a "logical" shift right, pretend the source is unsigned.
                                                if (cell->type == "$shr") {
                                                        a_expr = "asUInt(" + a_expr + ")";
                                                }
                                        }
                                }
                                else if ((cell->type == "$logic_and")) {
                                        primop = "and";
                                        a_expr = "neq(" + a_expr + ", UInt(0))";
                                        b_expr = "neq(" + b_expr + ", UInt(0))";
                                        always_uint = true;
                                        firrtl_width = 1;
                                }
                                else if ((cell->type == "$logic_or")) {
                                        primop = "or";
                                        a_expr = "neq(" + a_expr + ", UInt(0))";
                                        b_expr = "neq(" + b_expr + ", UInt(0))";
                                        always_uint = true;
                                        firrtl_width = 1;
                                }
                                else if ((cell->type == "$pow")) {
                                        if (a_sig.is_fully_const() && a_sig.as_int() == 2) {
                                                // We'll convert this to a shift. To simplify things, change the a_expr to "1"
                                                //      so we can use b_expr directly as a shift amount.
                                                // Only support 2 ** N (i.e., shift left)
                                                // FIRRTL will widen the result (y) by the amount of the shift.
                                                // We'll need to offset this by extracting the un-widened portion as Verilog would do.
                                                a_expr = firrtl_is_signed ? "SInt(1)" : "UInt(1)";
                                                extract_y_bits = true;
                                                // Is the shift amount constant?
                                                auto b_sig = cell->getPort("\\B");
                                                if (b_sig.is_fully_const()) {
                                                        primop = "shl";
                                                        int shiftAmount = b_sig.as_int();
                                                        if (shiftAmount < 0) {
                                                                log_error("Negative power exponent - %d: %s.%s\n", shiftAmount, log_id(module), log_id(cell));
                                                        }
                                                        b_expr = std::to_string(shiftAmount);
                                                        firrtl_width = a_width + shiftAmount;
                                                } else {
                                                        primop = "dshl";
                                                        // Convert from FIRRTL left shift semantics.
                                                        b_expr = gen_dshl(b_expr, b_width);
                                                        firrtl_width = a_width + (1 << b_width) - 1;
                                                }
                                        } else {
                                                log_error("Non power 2: %s.%s\n", log_id(module), log_id(cell));
                                        }
                                }

                                if (!cell->parameters.at("\\B_SIGNED").as_bool()) {
                                        b_expr = "asUInt(" + b_expr + ")";
                                }

                                string expr;
                                // Deal with $xnor == ~^ (not xor)
                                if (primop == "xnor") {
                                        expr = stringf("not(xor(%s, %s))", a_expr.c_str(), b_expr.c_str());
                                } else {
                                        expr = stringf("%s(%s, %s)", primop.c_str(), a_expr.c_str(), b_expr.c_str());
                                }

                                // Deal with FIRRTL's "shift widens" semantics, or the need to widen the FIRRTL result.
                                // If the operation is signed, the FIRRTL width will be 1 one bit larger.
                                if (extract_y_bits) {
                                        expr = stringf("bits(%s, %d, 0)", expr.c_str(), y_width - 1);
                                } else if (firrtl_is_signed && (firrtl_width + 1) < y_width) {
                                        expr = stringf("pad(%s, %d)", expr.c_str(), y_width);
                                }

                                if ((firrtl_is_signed && !always_uint))
                                        expr = stringf("asUInt(%s)", expr.c_str());

                                cell_exprs.push_back(stringf("    %s <= %s\n", y_id.c_str(), expr.c_str()));
                                register_reverse_wire_map(y_id, cell->getPort("\\Y"));

                                continue;
                        }

                        if (cell->type.in("$mux"))
                        {
                                int width = cell->parameters.at("\\WIDTH").as_int();
                                string a_expr = make_expr(cell->getPort("\\A"));
                                string b_expr = make_expr(cell->getPort("\\B"));
                                string s_expr = make_expr(cell->getPort("\\S"));
                                wire_decls.push_back(stringf("    wire %s: UInt<%d>\n", y_id.c_str(), width));

                                string expr = stringf("mux(%s, %s, %s)", s_expr.c_str(), b_expr.c_str(), a_expr.c_str());

                                cell_exprs.push_back(stringf("    %s <= %s\n", y_id.c_str(), expr.c_str()));
                                register_reverse_wire_map(y_id, cell->getPort("\\Y"));

                                continue;
                        }

                        if (cell->type.in("$mem"))
                        {
                                string mem_id = make_id(cell->name);
                                int abits = cell->parameters.at("\\ABITS").as_int();
                                int width = cell->parameters.at("\\WIDTH").as_int();
                                int size = cell->parameters.at("\\SIZE").as_int();
                                memory m(cell, mem_id, abits, size, width);
                                int rd_ports = cell->parameters.at("\\RD_PORTS").as_int();
                                int wr_ports = cell->parameters.at("\\WR_PORTS").as_int();

                                Const initdata = cell->parameters.at("\\INIT");
                                for (State bit : initdata.bits)
                                        if (bit != State::Sx)
                                                log_error("Memory with initialization data: %s.%s\n", log_id(module), log_id(cell));

                                Const rd_clk_enable = cell->parameters.at("\\RD_CLK_ENABLE");
                                Const wr_clk_enable = cell->parameters.at("\\WR_CLK_ENABLE");
                                Const wr_clk_polarity = cell->parameters.at("\\WR_CLK_POLARITY");

                                int offset = cell->parameters.at("\\OFFSET").as_int();
                                if (offset != 0)
                                        log_error("Memory with nonzero offset: %s.%s\n", log_id(module), log_id(cell));

                                for (int i = 0; i < rd_ports; i++)
                                {
                                        if (rd_clk_enable[i] != State::S0)
                                                log_error("Clocked read port %d on memory %s.%s.\n", i, log_id(module), log_id(cell));

                                        SigSpec addr_sig = cell->getPort("\\RD_ADDR").extract(i*abits, abits);
                                        SigSpec data_sig = cell->getPort("\\RD_DATA").extract(i*width, width);
                                        string addr_expr = make_expr(addr_sig);
                                        string name(stringf("%s.r%d", m.name.c_str(), i));
                                        bool clk_enable = false;
                                        bool clk_parity = true;
                                        bool transparency = false;
                                        SigSpec ena_sig = RTLIL::SigSpec(RTLIL::State::S1, 1);
                                        SigSpec clk_sig = RTLIL::SigSpec(RTLIL::State::S0, 1);
                                        read_port rp(name, clk_enable, clk_parity, transparency, clk_sig, ena_sig, addr_sig);
                                        m.add_memory_read_port(rp);
                                        cell_exprs.push_back(rp.gen_read(indent.c_str()));
                                        register_reverse_wire_map(stringf("%s.data", name.c_str()), data_sig);
                                }

                                for (int i = 0; i < wr_ports; i++)
                                {
                                        if (wr_clk_enable[i] != State::S1)
                                                log_error("Unclocked write port %d on memory %s.%s.\n", i, log_id(module), log_id(cell));

                                        if (wr_clk_polarity[i] != State::S1)
                                                log_error("Negedge write port %d on memory %s.%s.\n", i, log_id(module), log_id(cell));

                                        string name(stringf("%s.w%d", m.name.c_str(), i));
                                        bool clk_enable = true;
                                        bool clk_parity = true;
                                        bool transparency = false;
                                        SigSpec addr_sig =cell->getPort("\\WR_ADDR").extract(i*abits, abits);
                                        string addr_expr = make_expr(addr_sig);
                                        SigSpec data_sig =cell->getPort("\\WR_DATA").extract(i*width, width);
                                        string data_expr = make_expr(data_sig);
                                        SigSpec clk_sig = cell->getPort("\\WR_CLK").extract(i);
                                        string clk_expr = make_expr(clk_sig);

                                        SigSpec wen_sig = cell->getPort("\\WR_EN").extract(i*width, width);
                                        string wen_expr = make_expr(wen_sig[0]);

                                        for (int i = 1; i < GetSize(wen_sig); i++)
                                                if (wen_sig[0] != wen_sig[i])
                                                        log_error("Complex write enable on port %d on memory %s.%s.\n", i, log_id(module), log_id(cell));

                                        SigSpec mask_sig = RTLIL::SigSpec(RTLIL::State::S1, 1);
                                        write_port wp(name, clk_enable, clk_parity, transparency, clk_sig, wen_sig[0], addr_sig, mask_sig);
                                        m.add_memory_write_port(wp);
                                        cell_exprs.push_back(stringf("%s%s.data <= %s\n", indent.c_str(), name.c_str(), data_expr.c_str()));
                                        cell_exprs.push_back(wp.gen_write(indent.c_str()));
                                }
                                register_memory(m);
                                continue;
                        }

                        if (cell->type.in("$memwr", "$memrd", "$meminit"))
                        {
                                std::string cell_type = fid(cell->type);
                                std::string mem_id = make_id(cell->parameters["\\MEMID"].decode_string());
                                int abits = cell->parameters.at("\\ABITS").as_int();
                                int width = cell->parameters.at("\\WIDTH").as_int();
                                memory *mp = nullptr;
                                if (cell->type == "$meminit" ) {
                                        log_error("$meminit (%s.%s.%s) currently unsupported\n", log_id(module), log_id(cell), mem_id.c_str());
                                } else {
                                        // It's a $memwr or $memrd. Remember the read/write port parameters for the eventual FIRRTL memory definition.
                                        auto addrSig = cell->getPort("\\ADDR");
                                        auto dataSig = cell->getPort("\\DATA");
                                        auto enableSig = cell->getPort("\\EN");
                                        auto clockSig = cell->getPort("\\CLK");
                                        Const clk_enable = cell->parameters.at("\\CLK_ENABLE");
                                        Const clk_polarity = cell->parameters.at("\\CLK_POLARITY");

                                        // Do we already have an entry for this memory?
                                        if (memories.count(mem_id) == 0) {
                                                memory m(cell, mem_id, abits, 0, width);
                                                register_memory(m);
                                        }
                                        mp = &memories.at(mem_id);
                                        int portNum = 0;
                                        bool transparency = false;
                                        string data_expr = make_expr(dataSig);
                                        if (cell->type.in("$memwr")) {
                                                portNum = (int) mp->write_ports.size();
                                                write_port wp(stringf("%s.w%d", mem_id.c_str(), portNum), clk_enable.as_bool(), clk_polarity.as_bool(),  transparency, clockSig, enableSig, addrSig, dataSig);
                                                mp->add_memory_write_port(wp);
                                                cell_exprs.push_back(stringf("%s%s.data <= %s\n", indent.c_str(), wp.name.c_str(), data_expr.c_str()));
                                                cell_exprs.push_back(wp.gen_write(indent.c_str()));
                                        } else if (cell->type.in("$memrd")) {
                                                portNum = (int) mp->read_ports.size();
                                                read_port rp(stringf("%s.r%d", mem_id.c_str(), portNum), clk_enable.as_bool(), clk_polarity.as_bool(),  transparency, clockSig, enableSig, addrSig);
                                                mp->add_memory_read_port(rp);
                                                cell_exprs.push_back(rp.gen_read(indent.c_str()));
                                                register_reverse_wire_map(stringf("%s.data", rp.name.c_str()), dataSig);
                                        }
                                }
                                continue;
                        }

                        if (cell->type.in("$dff"))
                        {
                                bool clkpol = cell->parameters.at("\\CLK_POLARITY").as_bool();
                                if (clkpol == false)
                                        log_error("Negative edge clock on FF %s.%s.\n", log_id(module), log_id(cell));

                                int width = cell->parameters.at("\\WIDTH").as_int();
                                string expr = make_expr(cell->getPort("\\D"));
                                string clk_expr = "asClock(" + make_expr(cell->getPort("\\CLK")) + ")";

                                wire_decls.push_back(stringf("    reg %s: UInt<%d>, %s\n", y_id.c_str(), width, clk_expr.c_str()));

                                cell_exprs.push_back(stringf("    %s <= %s\n", y_id.c_str(), expr.c_str()));
                                register_reverse_wire_map(y_id, cell->getPort("\\Q"));

                                continue;
                        }

                        // This may be a parameterized module - paramod.
                        if (cell->type.begins_with("$paramod"))
                        {
                                process_instance(cell, wire_exprs);
                                continue;
                        }
                        if (cell->type == "$shiftx") {
                                // assign y = a[b +: y_width];
                                // We'll extract the correct bits as part of the primop.

                                string a_expr = make_expr(cell->getPort("\\A"));
                                // Get the initial bit selector
                                string b_expr = make_expr(cell->getPort("\\B"));
                                wire_decls.push_back(stringf("    wire %s: UInt<%d>\n", y_id.c_str(), y_width));

                                if (cell->getParam("\\B_SIGNED").as_bool()) {
                                        // Use validif to constrain the selection (test the sign bit)
                                        auto b_string = b_expr.c_str();
                                        int b_sign = cell->parameters.at("\\B_WIDTH").as_int() - 1;
                                        b_expr = stringf("validif(not(bits(%s, %d, %d)), %s)", b_string, b_sign, b_sign, b_string);
                                }
                                string expr = stringf("dshr(%s, %s)", a_expr.c_str(), b_expr.c_str());

                                cell_exprs.push_back(stringf("    %s <= %s\n", y_id.c_str(), expr.c_str()));
                                register_reverse_wire_map(y_id, cell->getPort("\\Y"));
                                continue;
                        }
                        if (cell->type == "$shift") {
                                // assign y = a >> b;
                                //  where b may be negative

                                string a_expr = make_expr(cell->getPort("\\A"));
                                string b_expr = make_expr(cell->getPort("\\B"));
                                auto b_string = b_expr.c_str();
                                string expr;
                                wire_decls.push_back(stringf("    wire %s: UInt<%d>\n", y_id.c_str(), y_width));

                                if (cell->getParam("\\B_SIGNED").as_bool()) {
                                        // We generate a left or right shift based on the sign of b.
                                        std::string dshl = stringf("bits(dshl(%s, %s), 0, %d)", a_expr.c_str(), gen_dshl(b_expr, b_width).c_str(), y_width);
                                        std::string dshr = stringf("dshr(%s, %s)", a_expr.c_str(), b_string);
                                        expr = stringf("mux(%s < 0, %s, %s)",
                                                                         b_string,
                                                                         dshl.c_str(),
                                                                         dshr.c_str()
                                                                         );
                                } else {
                                        expr = stringf("dshr(%s, %s)", a_expr.c_str(), b_string);
                                }
                                cell_exprs.push_back(stringf("    %s <= %s\n", y_id.c_str(), expr.c_str()));
                                register_reverse_wire_map(y_id, cell->getPort("\\Y"));
                                continue;
                        }
                        if (cell->type == "$pos") {
                                // assign y = a;
//                              printCell(cell);
                                string a_expr = make_expr(cell->getPort("\\A"));
                                // Verilog appears to treat the result as signed, so if the result is wider than "A",
                                //  we need to pad.
                                if (a_width < y_width) {
                                        a_expr = stringf("pad(%s, %d)", a_expr.c_str(), y_width);
                                }
                                wire_decls.push_back(stringf("    wire %s: UInt<%d>\n", y_id.c_str(), y_width));
                                cell_exprs.push_back(stringf("    %s <= %s\n", y_id.c_str(), a_expr.c_str()));
                                register_reverse_wire_map(y_id, cell->getPort("\\Y"));
                                continue;
                        }
                        log_warning("Cell type not supported: %s (%s.%s)\n", log_id(cell->type), log_id(module), log_id(cell));
                }

                for (auto conn : module->connections())
                {
                        string y_id = next_id();
                        int y_width =  GetSize(conn.first);
                        string expr = make_expr(conn.second);

                        wire_decls.push_back(stringf("    wire %s: UInt<%d>\n", y_id.c_str(), y_width));
                        cell_exprs.push_back(stringf("    %s <= %s\n", y_id.c_str(), expr.c_str()));
                        register_reverse_wire_map(y_id, conn.first);
                }

                for (auto wire : module->wires())
                {
                        string expr;

                        if (wire->port_input)
                                continue;

                        int cursor = 0;
                        bool is_valid = false;
                        bool make_unconn_id = false;

                        while (cursor < wire->width)
                        {
                                int chunk_width = 1;
                                string new_expr;

                                SigBit start_bit(wire, cursor);

                                if (reverse_wire_map.count(start_bit))
                                {
                                        pair<string, int> start_map = reverse_wire_map.at(start_bit);

                                        while (cursor+chunk_width < wire->width)
                                        {
                                                SigBit stop_bit(wire, cursor+chunk_width);

                                                if (reverse_wire_map.count(stop_bit) == 0)
                                                        break;

                                                pair<string, int> stop_map = reverse_wire_map.at(stop_bit);
                                                stop_map.second -= chunk_width;

                                                if (start_map != stop_map)
                                                        break;

                                                chunk_width++;
                                        }

                                        new_expr = stringf("bits(%s, %d, %d)", start_map.first.c_str(),
                                                        start_map.second + chunk_width - 1, start_map.second);
                                        is_valid = true;
                                }
                                else
                                {
                                        if (unconn_id.empty()) {
                                                unconn_id = next_id();
                                                make_unconn_id = true;
                                        }
                                        new_expr = unconn_id;
                                }

                                if (expr.empty())
                                        expr = new_expr;
                                else
                                        expr = "cat(" + new_expr + ", " + expr + ")";

                                cursor += chunk_width;
                        }

                        if (is_valid) {
                                if (make_unconn_id) {
                                        wire_decls.push_back(stringf("    wire %s: UInt<1>\n", unconn_id.c_str()));
                                        wire_decls.push_back(stringf("    %s is invalid\n", unconn_id.c_str()));
                                }
                                wire_exprs.push_back(stringf("    %s <= %s\n", make_id(wire->name), expr.c_str()));
                        } else {
                                if (make_unconn_id) {
                                        unconn_id.clear();
                                }
                                wire_decls.push_back(stringf("    %s is invalid\n", make_id(wire->name)));
                        }
                }

                for (auto str : port_decls)
                        f << str;

                f << stringf("\n");

                for (auto str : wire_decls)
                        f << str;

                f << stringf("\n");

                // If we have any memory definitions, output them.
                for (auto kv : memories) {
                        memory &m = kv.second;
                        f << stringf("    mem %s:\n", m.name.c_str());
                        f << stringf("      data-type => UInt<%d>\n", m.width);
                        f << stringf("      depth => %d\n", m.size);
                        for (int i = 0; i < (int) m.read_ports.size(); i += 1) {
                                f << stringf("      reader => r%d\n", i);
                        }
                        for (int i = 0; i < (int) m.write_ports.size(); i += 1) {
                                f << stringf("      writer => w%d\n", i);
                        }
                        f << stringf("      read-latency => %d\n", m.read_latency);
                        f << stringf("      write-latency => %d\n", m.write_latency);
                        f << stringf("      read-under-write => undefined\n");
                }
                f << stringf("\n");

                for (auto str : cell_exprs)
                        f << str;

                f << stringf("\n");

                for (auto str : wire_exprs)
                        f << str;
        }
};

struct FirrtlBackend : public Backend {
        FirrtlBackend() : Backend("firrtl", "write design to a FIRRTL file") { }
        void help() YS_OVERRIDE
        {
                //   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
                log("\n");
                log("    write_firrtl [options] [filename]\n");
                log("\n");
                log("Write a FIRRTL netlist of the current design.\n");
                log("The following commands are executed by this command:\n");
                log("        pmuxtree\n");
                log("\n");
        }
        void execute(std::ostream *&f, std::string filename, std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
        {
                size_t argidx = args.size();    // We aren't expecting any arguments.

                // If we weren't explicitly passed a filename, use the last argument (if it isn't a flag).
                if (filename == "") {
                        if (argidx > 0 && args[argidx - 1][0] != '-') {
                                // extra_args and friends need to see this argument.
                                argidx -= 1;
                                filename = args[argidx];
                        }
                }
                extra_args(f, filename, args, argidx);

                if (!design->full_selection())
                        log_cmd_error("This command only operates on fully selected designs!\n");

                log_header(design, "Executing FIRRTL backend.\n");
                log_push();

                Pass::call(design, stringf("pmuxtree"));

                namecache.clear();
                autoid_counter = 0;

                // Get the top module, or a reasonable facsimile - we need something for the circuit name.
                Module *top = design->top_module();
                Module *last = nullptr;
                // Generate module and wire names.
                for (auto module : design->modules()) {
                        make_id(module->name);
                        last = module;
                        if (top == nullptr && module->get_bool_attribute("\\top")) {
                                top = module;
                        }
                        for (auto wire : module->wires())
                                if (wire->port_id)
                                        make_id(wire->name);
                }

                if (top == nullptr)
                        top = last;

                *f << stringf("circuit %s:\n", make_id(top->name));

                for (auto module : design->modules())
                {
                        FirrtlWorker worker(module, *f, design);
                        worker.run();
                }

                namecache.clear();
                autoid_counter = 0;
        }
} FirrtlBackend;

PRIVATE_NAMESPACE_END