Merge pull request #2632 from zachjs/width-limit

[yosys.git] / frontends / ast / genrtlil.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.
 *
 *  ---
 *
 *  This is the AST frontend library.
 *
 *  The AST frontend library is not a frontend on it's own but provides a
 *  generic abstract syntax tree (AST) abstraction for HDL code and can be
 *  used by HDL frontends. See "ast.h" for an overview of the API and the
 *  Verilog frontend for an usage example.
 *
 */

#include "kernel/log.h"
#include "kernel/utils.h"
#include "libs/sha1/sha1.h"
#include "ast.h"

#include <sstream>
#include <stdarg.h>
#include <algorithm>

YOSYS_NAMESPACE_BEGIN

using namespace AST;
using namespace AST_INTERNAL;

// helper function for creating RTLIL code for unary operations
static RTLIL::SigSpec uniop2rtlil(AstNode *that, IdString type, int result_width, const RTLIL::SigSpec &arg, bool gen_attributes = true)
{
        IdString name = stringf("%s$%s:%d$%d", type.c_str(), that->filename.c_str(), that->location.first_line, autoidx++);
        RTLIL::Cell *cell = current_module->addCell(name, type);
        set_src_attr(cell, that);

        RTLIL::Wire *wire = current_module->addWire(cell->name.str() + "_Y", result_width);
        set_src_attr(wire, that);
        wire->is_signed = that->is_signed;

        if (gen_attributes)
                for (auto &attr : that->attributes) {
                        if (attr.second->type != AST_CONSTANT)
                                log_file_error(that->filename, that->location.first_line, "Attribute `%s' with non-constant value!\n", attr.first.c_str());
                        cell->attributes[attr.first] = attr.second->asAttrConst();
                }

        cell->parameters[ID::A_SIGNED] = RTLIL::Const(that->children[0]->is_signed);
        cell->parameters[ID::A_WIDTH] = RTLIL::Const(arg.size());
        cell->setPort(ID::A, arg);

        cell->parameters[ID::Y_WIDTH] = result_width;
        cell->setPort(ID::Y, wire);
        return wire;
}

// helper function for extending bit width (preferred over SigSpec::extend() because of correct undef propagation in ConstEval)
static void widthExtend(AstNode *that, RTLIL::SigSpec &sig, int width, bool is_signed)
{
        if (width <= sig.size()) {
                sig.extend_u0(width, is_signed);
                return;
        }

        IdString name = stringf("$extend$%s:%d$%d", that->filename.c_str(), that->location.first_line, autoidx++);
        RTLIL::Cell *cell = current_module->addCell(name, ID($pos));
        set_src_attr(cell, that);

        RTLIL::Wire *wire = current_module->addWire(cell->name.str() + "_Y", width);
        set_src_attr(wire, that);
        wire->is_signed = that->is_signed;

        if (that != NULL)
                for (auto &attr : that->attributes) {
                        if (attr.second->type != AST_CONSTANT)
                                log_file_error(that->filename, that->location.first_line, "Attribute `%s' with non-constant value!\n", attr.first.c_str());
                        cell->attributes[attr.first] = attr.second->asAttrConst();
                }

        cell->parameters[ID::A_SIGNED] = RTLIL::Const(is_signed);
        cell->parameters[ID::A_WIDTH] = RTLIL::Const(sig.size());
        cell->setPort(ID::A, sig);

        cell->parameters[ID::Y_WIDTH] = width;
        cell->setPort(ID::Y, wire);
        sig = wire;
}

// helper function for creating RTLIL code for binary operations
static RTLIL::SigSpec binop2rtlil(AstNode *that, IdString type, int result_width, const RTLIL::SigSpec &left, const RTLIL::SigSpec &right)
{
        IdString name = stringf("%s$%s:%d$%d", type.c_str(), that->filename.c_str(), that->location.first_line, autoidx++);
        RTLIL::Cell *cell = current_module->addCell(name, type);
        set_src_attr(cell, that);

        RTLIL::Wire *wire = current_module->addWire(cell->name.str() + "_Y", result_width);
        set_src_attr(wire, that);
        wire->is_signed = that->is_signed;

        for (auto &attr : that->attributes) {
                if (attr.second->type != AST_CONSTANT)
                        log_file_error(that->filename, that->location.first_line, "Attribute `%s' with non-constant value!\n", attr.first.c_str());
                cell->attributes[attr.first] = attr.second->asAttrConst();
        }

        cell->parameters[ID::A_SIGNED] = RTLIL::Const(that->children[0]->is_signed);
        cell->parameters[ID::B_SIGNED] = RTLIL::Const(that->children[1]->is_signed);

        cell->parameters[ID::A_WIDTH] = RTLIL::Const(left.size());
        cell->parameters[ID::B_WIDTH] = RTLIL::Const(right.size());

        cell->setPort(ID::A, left);
        cell->setPort(ID::B, right);

        cell->parameters[ID::Y_WIDTH] = result_width;
        cell->setPort(ID::Y, wire);
        return wire;
}

// helper function for creating RTLIL code for multiplexers
static RTLIL::SigSpec mux2rtlil(AstNode *that, const RTLIL::SigSpec &cond, const RTLIL::SigSpec &left, const RTLIL::SigSpec &right)
{
        log_assert(cond.size() == 1);

        std::stringstream sstr;
        sstr << "$ternary$" << that->filename << ":" << that->location.first_line << "$" << (autoidx++);

        RTLIL::Cell *cell = current_module->addCell(sstr.str(), ID($mux));
        set_src_attr(cell, that);

        RTLIL::Wire *wire = current_module->addWire(cell->name.str() + "_Y", left.size());
        set_src_attr(wire, that);
        wire->is_signed = that->is_signed;

        for (auto &attr : that->attributes) {
                if (attr.second->type != AST_CONSTANT)
                        log_file_error(that->filename, that->location.first_line, "Attribute `%s' with non-constant value!\n", attr.first.c_str());
                cell->attributes[attr.first] = attr.second->asAttrConst();
        }

        cell->parameters[ID::WIDTH] = RTLIL::Const(left.size());

        cell->setPort(ID::A, right);
        cell->setPort(ID::B, left);
        cell->setPort(ID::S, cond);
        cell->setPort(ID::Y, wire);

        return wire;
}

// helper class for rewriting simple lookahead references in AST always blocks
struct AST_INTERNAL::LookaheadRewriter
{
        dict<IdString, pair<AstNode*, AstNode*>> lookaheadids;

        void collect_lookaheadids(AstNode *node)
        {
                if (node->lookahead) {
                        log_assert(node->type == AST_IDENTIFIER);
                        if (!lookaheadids.count(node->str)) {
                                AstNode *wire = new AstNode(AST_WIRE);
                                for (auto c : node->id2ast->children)
                                        wire->children.push_back(c->clone());
                                wire->str = stringf("$lookahead%s$%d", node->str.c_str(), autoidx++);
                                wire->attributes[ID::nosync] = AstNode::mkconst_int(1, false);
                                wire->is_logic = true;
                                while (wire->simplify(true, false, false, 1, -1, false, false)) { }
                                current_ast_mod->children.push_back(wire);
                                lookaheadids[node->str] = make_pair(node->id2ast, wire);
                                wire->genRTLIL();
                        }
                }

                for (auto child : node->children)
                        collect_lookaheadids(child);
        }

        bool has_lookaheadids(AstNode *node)
        {
                if (node->type == AST_IDENTIFIER && lookaheadids.count(node->str) != 0)
                        return true;

                for (auto child : node->children)
                        if (has_lookaheadids(child))
                                return true;

                return false;
        }

        bool has_nonlookaheadids(AstNode *node)
        {
                if (node->type == AST_IDENTIFIER && lookaheadids.count(node->str) == 0)
                        return true;

                for (auto child : node->children)
                        if (has_nonlookaheadids(child))
                                return true;

                return false;
        }

        void rewrite_lookaheadids(AstNode *node, bool lhs = false)
        {
                if (node->type == AST_ASSIGN_LE)
                {
                        if (has_lookaheadids(node->children[0]))
                        {
                                if (has_nonlookaheadids(node->children[0]))
                                        log_error("incompatible mix of lookahead and non-lookahead IDs in LHS expression.\n");

                                rewrite_lookaheadids(node->children[0], true);
                                node->type = AST_ASSIGN_EQ;
                        }

                        rewrite_lookaheadids(node->children[1], lhs);
                        return;
                }

                if (node->type == AST_IDENTIFIER && (node->lookahead || lhs)) {
                        AstNode *newwire = lookaheadids.at(node->str).second;
                        node->str = newwire->str;
                        node->id2ast = newwire;
                        lhs = false;
                }

                for (auto child : node->children)
                        rewrite_lookaheadids(child, lhs);
        }

        LookaheadRewriter(AstNode *top)
        {
                // top->dumpAst(NULL, "REWRITE-BEFORE> ");
                // top->dumpVlog(NULL, "REWRITE-BEFORE> ");

                AstNode *block = nullptr;

                for (auto c : top->children)
                        if (c->type == AST_BLOCK) {
                                log_assert(block == nullptr);
                                block = c;
                        }
                log_assert(block != nullptr);

                collect_lookaheadids(block);
                rewrite_lookaheadids(block);

                for (auto it : lookaheadids)
                {
                        AstNode *ref_orig = new AstNode(AST_IDENTIFIER);
                        ref_orig->str = it.second.first->str;
                        ref_orig->id2ast = it.second.first;
                        ref_orig->was_checked = true;

                        AstNode *ref_temp = new AstNode(AST_IDENTIFIER);
                        ref_temp->str = it.second.second->str;
                        ref_temp->id2ast = it.second.second;
                        ref_temp->was_checked = true;

                        AstNode *init_assign = new AstNode(AST_ASSIGN_EQ, ref_temp->clone(), ref_orig->clone());
                        AstNode *final_assign = new AstNode(AST_ASSIGN_LE, ref_orig, ref_temp);

                        block->children.insert(block->children.begin(), init_assign);
                        block->children.push_back(final_assign);
                }

                // top->dumpAst(NULL, "REWRITE-AFTER> ");
                // top->dumpVlog(NULL, "REWRITE-AFTER> ");
        }
};

// helper class for converting AST always nodes to RTLIL processes
struct AST_INTERNAL::ProcessGenerator
{
        // input and output structures
        AstNode *always;
        RTLIL::SigSpec initSyncSignals;
        RTLIL::Process *proc;
        RTLIL::SigSpec outputSignals;

        // This always points to the RTLIL::CaseRule being filled at the moment
        RTLIL::CaseRule *current_case;

        // This map contains the replacement pattern to be used in the right hand side
        // of an assignment. E.g. in the code "foo = bar; foo = func(foo);" the foo in the right
        // hand side of the 2nd assignment needs to be replace with the temporary signal holding
        // the value assigned in the first assignment. So when the first assignment is processed
        // the according information is appended to subst_rvalue_from and subst_rvalue_to.
        stackmap<RTLIL::SigBit, RTLIL::SigBit> subst_rvalue_map;

        // This map contains the replacement pattern to be used in the left hand side
        // of an assignment. E.g. in the code "always @(posedge clk) foo <= bar" the signal bar
        // should not be connected to the signal foo. Instead it must be connected to the temporary
        // signal that is used as input for the register that drives the signal foo.
        stackmap<RTLIL::SigBit, RTLIL::SigBit> subst_lvalue_map;

        // The code here generates a number of temporary signal for each output register. This
        // map helps generating nice numbered names for all this temporary signals.
        std::map<RTLIL::Wire*, int> new_temp_count;

        // Buffer for generating the init action
        RTLIL::SigSpec init_lvalue, init_rvalue;

        ProcessGenerator(AstNode *always, RTLIL::SigSpec initSyncSignalsArg = RTLIL::SigSpec()) : always(always), initSyncSignals(initSyncSignalsArg)
        {
                // rewrite lookahead references
                LookaheadRewriter la_rewriter(always);

                // generate process and simple root case
                proc = new RTLIL::Process;
                set_src_attr(proc, always);
                proc->name = stringf("$proc$%s:%d$%d", always->filename.c_str(), always->location.first_line, autoidx++);
                for (auto &attr : always->attributes) {
                        if (attr.second->type != AST_CONSTANT)
                                log_file_error(always->filename, always->location.first_line, "Attribute `%s' with non-constant value!\n",
                                                attr.first.c_str());
                        proc->attributes[attr.first] = attr.second->asAttrConst();
                }
                current_module->processes[proc->name] = proc;
                current_case = &proc->root_case;

                // create initial temporary signal for all output registers
                RTLIL::SigSpec subst_lvalue_from, subst_lvalue_to;
                collect_lvalues(subst_lvalue_from, always, true, true);
                subst_lvalue_to = new_temp_signal(subst_lvalue_from);
                subst_lvalue_map = subst_lvalue_from.to_sigbit_map(subst_lvalue_to);

                bool found_global_syncs = false;
                bool found_anyedge_syncs = false;
                for (auto child : always->children)
                {
                        if ((child->type == AST_POSEDGE || child->type == AST_NEGEDGE) && GetSize(child->children) == 1 && child->children.at(0)->type == AST_IDENTIFIER &&
                                        child->children.at(0)->id2ast && child->children.at(0)->id2ast->type == AST_WIRE && child->children.at(0)->id2ast->get_bool_attribute(ID::gclk)) {
                                found_global_syncs = true;
                        }
                        if (child->type == AST_EDGE) {
                                if (GetSize(child->children) == 1 && child->children.at(0)->type == AST_IDENTIFIER && child->children.at(0)->str == "\\$global_clock")
                                        found_global_syncs = true;
                                else
                                        found_anyedge_syncs = true;
                        }
                }

                if (found_anyedge_syncs) {
                        if (found_global_syncs)
                                log_file_error(always->filename, always->location.first_line, "Found non-synthesizable event list!\n");
                        log("Note: Assuming pure combinatorial block at %s in\n", always->loc_string().c_str());
                        log("compliance with IEC 62142(E):2005 / IEEE Std. 1364.1(E):2002. Recommending\n");
                        log("use of @* instead of @(...) for better match of synthesis and simulation.\n");
                }

                // create syncs for the process
                bool found_clocked_sync = false;
                for (auto child : always->children)
                        if (child->type == AST_POSEDGE || child->type == AST_NEGEDGE) {
                                if (GetSize(child->children) == 1 && child->children.at(0)->type == AST_IDENTIFIER && child->children.at(0)->id2ast &&
                                                child->children.at(0)->id2ast->type == AST_WIRE && child->children.at(0)->id2ast->get_bool_attribute(ID::gclk))
                                        continue;
                                found_clocked_sync = true;
                                if (found_global_syncs || found_anyedge_syncs)
                                        log_file_error(always->filename, always->location.first_line, "Found non-synthesizable event list!\n");
                                RTLIL::SyncRule *syncrule = new RTLIL::SyncRule;
                                syncrule->type = child->type == AST_POSEDGE ? RTLIL::STp : RTLIL::STn;
                                syncrule->signal = child->children[0]->genRTLIL();
                                if (GetSize(syncrule->signal) != 1)
                                        log_file_error(always->filename, always->location.first_line, "Found posedge/negedge event on a signal that is not 1 bit wide!\n");
                                addChunkActions(syncrule->actions, subst_lvalue_from, subst_lvalue_to, true);
                                proc->syncs.push_back(syncrule);
                        }
                if (proc->syncs.empty()) {
                        RTLIL::SyncRule *syncrule = new RTLIL::SyncRule;
                        syncrule->type = found_global_syncs ? RTLIL::STg : RTLIL::STa;
                        syncrule->signal = RTLIL::SigSpec();
                        addChunkActions(syncrule->actions, subst_lvalue_from, subst_lvalue_to, true);
                        proc->syncs.push_back(syncrule);
                }

                // create initial assignments for the temporary signals
                if ((flag_nolatches || always->get_bool_attribute(ID::nolatches) || current_module->get_bool_attribute(ID::nolatches)) && !found_clocked_sync) {
                        subst_rvalue_map = subst_lvalue_from.to_sigbit_dict(RTLIL::SigSpec(RTLIL::State::Sx, GetSize(subst_lvalue_from)));
                } else {
                        addChunkActions(current_case->actions, subst_lvalue_to, subst_lvalue_from);
                }

                // process the AST
                for (auto child : always->children)
                        if (child->type == AST_BLOCK)
                                processAst(child);

                if (initSyncSignals.size() > 0)
                {
                        RTLIL::SyncRule *sync = new RTLIL::SyncRule;
                        sync->type = RTLIL::SyncType::STi;
                        proc->syncs.push_back(sync);

                        log_assert(init_lvalue.size() == init_rvalue.size());

                        int offset = 0;
                        for (auto &init_lvalue_c : init_lvalue.chunks()) {
                                RTLIL::SigSpec lhs = init_lvalue_c;
                                RTLIL::SigSpec rhs = init_rvalue.extract(offset, init_lvalue_c.width);
                                remove_unwanted_lvalue_bits(lhs, rhs);
                                sync->actions.push_back(RTLIL::SigSig(lhs, rhs));
                                offset += lhs.size();
                        }
                }

                outputSignals = RTLIL::SigSpec(subst_lvalue_from);
        }

        void remove_unwanted_lvalue_bits(RTLIL::SigSpec &lhs, RTLIL::SigSpec &rhs)
        {
                RTLIL::SigSpec new_lhs, new_rhs;

                log_assert(GetSize(lhs) == GetSize(rhs));
                for (int i = 0; i < GetSize(lhs); i++) {
                        if (lhs[i].wire == nullptr)
                                continue;
                        new_lhs.append(lhs[i]);
                        new_rhs.append(rhs[i]);
                }

                lhs = new_lhs;
                rhs = new_rhs;
        }

        // create new temporary signals
        RTLIL::SigSpec new_temp_signal(RTLIL::SigSpec sig)
        {
                std::vector<RTLIL::SigChunk> chunks = sig.chunks();

                for (int i = 0; i < GetSize(chunks); i++)
                {
                        RTLIL::SigChunk &chunk = chunks[i];
                        if (chunk.wire == NULL)
                                continue;

                        std::string wire_name;
                        do {
                                wire_name = stringf("$%d%s[%d:%d]", new_temp_count[chunk.wire]++,
                                                chunk.wire->name.c_str(), chunk.width+chunk.offset-1, chunk.offset);;
                                if (chunk.wire->name.str().find('$') != std::string::npos)
                                        wire_name += stringf("$%d", autoidx++);
                        } while (current_module->wires_.count(wire_name) > 0);

                        RTLIL::Wire *wire = current_module->addWire(wire_name, chunk.width);
                        set_src_attr(wire, always);

                        chunk.wire = wire;
                        chunk.offset = 0;
                }

                return chunks;
        }

        // recursively traverse the AST and collect all assigned signals
        void collect_lvalues(RTLIL::SigSpec &reg, AstNode *ast, bool type_eq, bool type_le, bool run_sort_and_unify = true)
        {
                switch (ast->type)
                {
                case AST_CASE:
                        for (auto child : ast->children)
                                if (child != ast->children[0]) {
                                        log_assert(child->type == AST_COND || child->type == AST_CONDX || child->type == AST_CONDZ);
                                        collect_lvalues(reg, child, type_eq, type_le, false);
                                }
                        break;

                case AST_COND:
                case AST_CONDX:
                case AST_CONDZ:
                case AST_ALWAYS:
                case AST_INITIAL:
                        for (auto child : ast->children)
                                if (child->type == AST_BLOCK)
                                        collect_lvalues(reg, child, type_eq, type_le, false);
                        break;

                case AST_BLOCK:
                        for (auto child : ast->children) {
                                if (child->type == AST_ASSIGN_EQ && type_eq)
                                        reg.append(child->children[0]->genRTLIL());
                                if (child->type == AST_ASSIGN_LE && type_le)
                                        reg.append(child->children[0]->genRTLIL());
                                if (child->type == AST_CASE || child->type == AST_BLOCK)
                                        collect_lvalues(reg, child, type_eq, type_le, false);
                        }
                        break;

                default:
                        log_abort();
                }

                if (run_sort_and_unify) {
                        std::set<RTLIL::SigBit> sorted_reg;
                        for (auto bit : reg)
                                if (bit.wire)
                                        sorted_reg.insert(bit);
                        reg = RTLIL::SigSpec(sorted_reg);
                }
        }

        // remove all assignments to the given signal pattern in a case and all its children.
        // e.g. when the last statement in the code "a = 23; if (b) a = 42; a = 0;" is processed this
        // function is called to clean up the first two assignments as they are overwritten by
        // the third assignment.
        void removeSignalFromCaseTree(const RTLIL::SigSpec &pattern, RTLIL::CaseRule *cs)
        {
                for (auto it = cs->actions.begin(); it != cs->actions.end(); it++)
                        it->first.remove2(pattern, &it->second);

                for (auto it = cs->switches.begin(); it != cs->switches.end(); it++)
                        for (auto it2 = (*it)->cases.begin(); it2 != (*it)->cases.end(); it2++)
                                removeSignalFromCaseTree(pattern, *it2);
        }

        // add an assignment (aka "action") but split it up in chunks. this way huge assignments
        // are avoided and the generated $mux cells have a more "natural" size.
        void addChunkActions(std::vector<RTLIL::SigSig> &actions, RTLIL::SigSpec lvalue, RTLIL::SigSpec rvalue, bool inSyncRule = false)
        {
                if (inSyncRule && initSyncSignals.size() > 0) {
                        init_lvalue.append(lvalue.extract(initSyncSignals));
                        init_rvalue.append(lvalue.extract(initSyncSignals, &rvalue));
                        lvalue.remove2(initSyncSignals, &rvalue);
                }
                log_assert(lvalue.size() == rvalue.size());

                int offset = 0;
                for (auto &lvalue_c : lvalue.chunks()) {
                        RTLIL::SigSpec lhs = lvalue_c;
                        RTLIL::SigSpec rhs = rvalue.extract(offset, lvalue_c.width);
                        if (inSyncRule && lvalue_c.wire && lvalue_c.wire->get_bool_attribute(ID::nosync))
                                rhs = RTLIL::SigSpec(RTLIL::State::Sx, rhs.size());
                        remove_unwanted_lvalue_bits(lhs, rhs);
                        actions.push_back(RTLIL::SigSig(lhs, rhs));
                        offset += lhs.size();
                }
        }

        // recursively process the AST and fill the RTLIL::Process
        void processAst(AstNode *ast)
        {
                switch (ast->type)
                {
                case AST_BLOCK:
                        for (auto child : ast->children)
                                processAst(child);
                        break;

                case AST_ASSIGN_EQ:
                case AST_ASSIGN_LE:
                        {
                                RTLIL::SigSpec unmapped_lvalue = ast->children[0]->genRTLIL(), lvalue = unmapped_lvalue;
                                RTLIL::SigSpec rvalue = ast->children[1]->genWidthRTLIL(lvalue.size(), &subst_rvalue_map.stdmap());

                                pool<SigBit> lvalue_sigbits;
                                for (int i = 0; i < GetSize(lvalue); i++) {
                                        if (lvalue_sigbits.count(lvalue[i]) > 0) {
                                                unmapped_lvalue.remove(i);
                                                lvalue.remove(i);
                                                rvalue.remove(i--);
                                        } else
                                                lvalue_sigbits.insert(lvalue[i]);
                                }

                                lvalue.replace(subst_lvalue_map.stdmap());

                                if (ast->type == AST_ASSIGN_EQ) {
                                        for (int i = 0; i < GetSize(unmapped_lvalue); i++)
                                                subst_rvalue_map.set(unmapped_lvalue[i], rvalue[i]);
                                }

                                removeSignalFromCaseTree(lvalue, current_case);
                                remove_unwanted_lvalue_bits(lvalue, rvalue);
                                current_case->actions.push_back(RTLIL::SigSig(lvalue, rvalue));
                        }
                        break;

                case AST_CASE:
                        {
                                RTLIL::SwitchRule *sw = new RTLIL::SwitchRule;
                                set_src_attr(sw, ast);
                                sw->signal = ast->children[0]->genWidthRTLIL(-1, &subst_rvalue_map.stdmap());
                                current_case->switches.push_back(sw);

                                for (auto &attr : ast->attributes) {
                                        if (attr.second->type != AST_CONSTANT)
                                                log_file_error(ast->filename, ast->location.first_line, "Attribute `%s' with non-constant value!\n", attr.first.c_str());
                                        sw->attributes[attr.first] = attr.second->asAttrConst();
                                }

                                RTLIL::SigSpec this_case_eq_lvalue;
                                collect_lvalues(this_case_eq_lvalue, ast, true, false);

                                RTLIL::SigSpec this_case_eq_ltemp = new_temp_signal(this_case_eq_lvalue);

                                RTLIL::SigSpec this_case_eq_rvalue = this_case_eq_lvalue;
                                this_case_eq_rvalue.replace(subst_rvalue_map.stdmap());

                                RTLIL::CaseRule *default_case = NULL;
                                RTLIL::CaseRule *last_generated_case = NULL;
                                for (auto child : ast->children)
                                {
                                        if (child == ast->children[0])
                                                continue;
                                        log_assert(child->type == AST_COND || child->type == AST_CONDX || child->type == AST_CONDZ);

                                        subst_lvalue_map.save();
                                        subst_rvalue_map.save();

                                        for (int i = 0; i < GetSize(this_case_eq_lvalue); i++)
                                                subst_lvalue_map.set(this_case_eq_lvalue[i], this_case_eq_ltemp[i]);

                                        RTLIL::CaseRule *backup_case = current_case;
                                        current_case = new RTLIL::CaseRule;
                                        set_src_attr(current_case, child);
                                        last_generated_case = current_case;
                                        addChunkActions(current_case->actions, this_case_eq_ltemp, this_case_eq_rvalue);
                                        for (auto node : child->children) {
                                                if (node->type == AST_DEFAULT)
                                                        default_case = current_case;
                                                else if (node->type == AST_BLOCK)
                                                        processAst(node);
                                                else
                                                        current_case->compare.push_back(node->genWidthRTLIL(sw->signal.size(), &subst_rvalue_map.stdmap()));
                                        }
                                        if (default_case != current_case)
                                                sw->cases.push_back(current_case);
                                        else
                                                log_assert(current_case->compare.size() == 0);
                                        current_case = backup_case;

                                        subst_lvalue_map.restore();
                                        subst_rvalue_map.restore();
                                }

                                if (last_generated_case != NULL && ast->get_bool_attribute(ID::full_case) && default_case == NULL) {
                        #if 0
                                        // this is a valid transformation, but as optimization it is premature.
                                        // better: add a default case that assigns 'x' to everything, and let later
                                        // optimizations take care of the rest
                                        last_generated_case->compare.clear();
                        #else
                                        default_case = new RTLIL::CaseRule;
                                        addChunkActions(default_case->actions, this_case_eq_ltemp, SigSpec(State::Sx, GetSize(this_case_eq_rvalue)));
                                        sw->cases.push_back(default_case);
                        #endif
                                } else {
                                        if (default_case == NULL) {
                                                default_case = new RTLIL::CaseRule;
                                                addChunkActions(default_case->actions, this_case_eq_ltemp, this_case_eq_rvalue);
                                        }
                                        sw->cases.push_back(default_case);
                                }

                                for (int i = 0; i < GetSize(this_case_eq_lvalue); i++)
                                        subst_rvalue_map.set(this_case_eq_lvalue[i], this_case_eq_ltemp[i]);

                                this_case_eq_lvalue.replace(subst_lvalue_map.stdmap());
                                removeSignalFromCaseTree(this_case_eq_lvalue, current_case);
                                addChunkActions(current_case->actions, this_case_eq_lvalue, this_case_eq_ltemp);
                        }
                        break;

                case AST_WIRE:
                        log_file_error(ast->filename, ast->location.first_line, "Found reg declaration in block without label!\n");
                        break;

                case AST_ASSIGN:
                        log_file_error(ast->filename, ast->location.first_line, "Found continous assignment in always/initial block!\n");
                        break;

                case AST_PARAMETER:
                case AST_LOCALPARAM:
                        log_file_error(ast->filename, ast->location.first_line, "Found parameter declaration in block without label!\n");
                        break;

                case AST_NONE:
                case AST_TCALL:
                case AST_FOR:
                        break;

                default:
                        // ast->dumpAst(NULL, "ast> ");
                        // current_ast_mod->dumpAst(NULL, "mod> ");
                        log_abort();
                }
        }
};

// detect sign and width of an expression
void AstNode::detectSignWidthWorker(int &width_hint, bool &sign_hint, bool *found_real)
{
        std::string type_name;
        bool sub_sign_hint = true;
        int sub_width_hint = -1;
        int this_width = 0;
        AstNode *range = NULL;
        AstNode *id_ast = NULL;

        bool local_found_real = false;
        if (found_real == NULL)
                found_real = &local_found_real;

        switch (type)
        {
        case AST_NONE:
                // unallocated enum, ignore
                break;
        case AST_CONSTANT:
                width_hint = max(width_hint, int(bits.size()));
                if (!is_signed)
                        sign_hint = false;
                break;

        case AST_REALVALUE:
                *found_real = true;
                width_hint = max(width_hint, 32);
                break;

        case AST_IDENTIFIER:
                id_ast = id2ast;
                if (id_ast == NULL && current_scope.count(str))
                        id_ast = current_scope.at(str);
                if (!id_ast)
                        log_file_error(filename, location.first_line, "Failed to resolve identifier %s for width detection!\n", str.c_str());
                if (id_ast->type == AST_PARAMETER || id_ast->type == AST_LOCALPARAM || id_ast->type == AST_ENUM_ITEM) {
                        if (id_ast->children.size() > 1 && id_ast->children[1]->range_valid) {
                                this_width = id_ast->children[1]->range_left - id_ast->children[1]->range_right + 1;
                        } else
                        if (id_ast->children[0]->type != AST_CONSTANT)
                                while (id_ast->simplify(true, false, false, 1, -1, false, true)) { }
                        if (id_ast->children[0]->type == AST_CONSTANT)
                                this_width = id_ast->children[0]->bits.size();
                        else
                                log_file_error(filename, location.first_line, "Failed to detect width for parameter %s!\n", str.c_str());
                        if (children.size() != 0)
                                range = children[0];
                } else if (id_ast->type == AST_WIRE || id_ast->type == AST_AUTOWIRE) {
                        if (!id_ast->range_valid) {
                                if (id_ast->type == AST_AUTOWIRE)
                                        this_width = 1;
                                else {
                                        // current_ast_mod->dumpAst(NULL, "mod> ");
                                        // log("---\n");
                                        // id_ast->dumpAst(NULL, "decl> ");
                                        // dumpAst(NULL, "ref> ");
                                        log_file_error(filename, location.first_line, "Failed to detect width of signal access `%s'!\n", str.c_str());
                                }
                        } else {
                                this_width = id_ast->range_left - id_ast->range_right + 1;
                                if (children.size() != 0)
                                        range = children[0];
                        }
                } else if (id_ast->type == AST_GENVAR) {
                        this_width = 32;
                } else if (id_ast->type == AST_MEMORY) {
                        if (!id_ast->children[0]->range_valid)
                                log_file_error(filename, location.first_line, "Failed to detect width of memory access `%s'!\n", str.c_str());
                        this_width = id_ast->children[0]->range_left - id_ast->children[0]->range_right + 1;
                        if (children.size() > 1)
                                range = children[1];
                } else
                        log_file_error(filename, location.first_line, "Failed to detect width for identifier %s!\n", str.c_str());
                if (range) {
                        if (range->children.size() == 1)
                                this_width = 1;
                        else if (!range->range_valid) {
                                AstNode *left_at_zero_ast = children[0]->children[0]->clone();
                                AstNode *right_at_zero_ast = children[0]->children.size() >= 2 ? children[0]->children[1]->clone() : left_at_zero_ast->clone();
                                while (left_at_zero_ast->simplify(true, true, false, 1, -1, false, false)) { }
                                while (right_at_zero_ast->simplify(true, true, false, 1, -1, false, false)) { }
                                if (left_at_zero_ast->type != AST_CONSTANT || right_at_zero_ast->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "Unsupported expression on dynamic range select on signal `%s'!\n", str.c_str());
                                this_width = abs(int(left_at_zero_ast->integer - right_at_zero_ast->integer)) + 1;
                                delete left_at_zero_ast;
                                delete right_at_zero_ast;
                        } else
                                this_width = range->range_left - range->range_right + 1;
                        sign_hint = false;
                }
                width_hint = max(width_hint, this_width);
                if (!id_ast->is_signed)
                        sign_hint = false;
                break;

        case AST_TO_BITS:
                while (children[0]->simplify(true, false, false, 1, -1, false, false) == true) { }
                if (children[0]->type != AST_CONSTANT)
                        log_file_error(filename, location.first_line, "Left operand of tobits expression is not constant!\n");
                children[1]->detectSignWidthWorker(sub_width_hint, sign_hint);
                width_hint = max(width_hint, children[0]->bitsAsConst().as_int());
                break;

        case AST_TO_SIGNED:
                children.at(0)->detectSignWidthWorker(width_hint, sub_sign_hint);
                break;

        case AST_TO_UNSIGNED:
                children.at(0)->detectSignWidthWorker(width_hint, sub_sign_hint);
                sign_hint = false;
                break;

        case AST_SELFSZ:
                sub_width_hint = 0;
                children.at(0)->detectSignWidthWorker(sub_width_hint, sign_hint);
                break;

        case AST_CAST_SIZE:
                while (children.at(0)->simplify(true, false, false, 1, -1, false, false)) { }
                if (children.at(0)->type != AST_CONSTANT)
                        log_file_error(filename, location.first_line, "Static cast with non constant expression!\n");
                children.at(1)->detectSignWidthWorker(width_hint, sign_hint);
                width_hint = children.at(0)->bitsAsConst().as_int();
                if (width_hint <= 0)
                        log_file_error(filename, location.first_line, "Static cast with zero or negative size!\n");
                break;

        case AST_CONCAT:
                for (auto child : children) {
                        sub_width_hint = 0;
                        sub_sign_hint = true;
                        child->detectSignWidthWorker(sub_width_hint, sub_sign_hint);
                        this_width += sub_width_hint;
                }
                width_hint = max(width_hint, this_width);
                sign_hint = false;
                break;

        case AST_REPLICATE:
                while (children[0]->simplify(true, false, false, 1, -1, false, true) == true) { }
                if (children[0]->type != AST_CONSTANT)
                        log_file_error(filename, location.first_line, "Left operand of replicate expression is not constant!\n");
                children[1]->detectSignWidthWorker(sub_width_hint, sub_sign_hint);
                width_hint = max(width_hint, children[0]->bitsAsConst().as_int() * sub_width_hint);
                sign_hint = false;
                break;

        case AST_NEG:
        case AST_BIT_NOT:
        case AST_POS:
                children[0]->detectSignWidthWorker(width_hint, sign_hint, found_real);
                break;

        case AST_BIT_AND:
        case AST_BIT_OR:
        case AST_BIT_XOR:
        case AST_BIT_XNOR:
                for (auto child : children)
                        child->detectSignWidthWorker(width_hint, sign_hint, found_real);
                break;

        case AST_REDUCE_AND:
        case AST_REDUCE_OR:
        case AST_REDUCE_XOR:
        case AST_REDUCE_XNOR:
        case AST_REDUCE_BOOL:
                width_hint = max(width_hint, 1);
                sign_hint = false;
                break;

        case AST_SHIFT_LEFT:
        case AST_SHIFT_RIGHT:
        case AST_SHIFT_SLEFT:
        case AST_SHIFT_SRIGHT:
        case AST_SHIFTX:
        case AST_SHIFT:
        case AST_POW:
                children[0]->detectSignWidthWorker(width_hint, sign_hint, found_real);
                break;

        case AST_LT:
        case AST_LE:
        case AST_EQ:
        case AST_NE:
        case AST_EQX:
        case AST_NEX:
        case AST_GE:
        case AST_GT:
                width_hint = max(width_hint, 1);
                sign_hint = false;
                break;

        case AST_ADD:
        case AST_SUB:
        case AST_MUL:
        case AST_DIV:
        case AST_MOD:
                for (auto child : children)
                        child->detectSignWidthWorker(width_hint, sign_hint, found_real);
                break;

        case AST_LOGIC_AND:
        case AST_LOGIC_OR:
        case AST_LOGIC_NOT:
                width_hint = max(width_hint, 1);
                sign_hint = false;
                break;

        case AST_TERNARY:
                children.at(1)->detectSignWidthWorker(width_hint, sign_hint, found_real);
                children.at(2)->detectSignWidthWorker(width_hint, sign_hint, found_real);
                break;

        case AST_MEMRD:
                if (!id2ast->is_signed)
                        sign_hint = false;
                if (!id2ast->children[0]->range_valid)
                        log_file_error(filename, location.first_line, "Failed to detect width of memory access `%s'!\n", str.c_str());
                this_width = id2ast->children[0]->range_left - id2ast->children[0]->range_right + 1;
                width_hint = max(width_hint, this_width);
                break;

        case AST_FCALL:
                if (str == "\\$anyconst" || str == "\\$anyseq" || str == "\\$allconst" || str == "\\$allseq") {
                        if (GetSize(children) == 1) {
                                while (children[0]->simplify(true, false, false, 1, -1, false, true) == true) { }
                                if (children[0]->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "System function %s called with non-const argument!\n",
                                                        RTLIL::unescape_id(str).c_str());
                                width_hint = max(width_hint, int(children[0]->asInt(true)));
                        }
                        break;
                }
                if (str == "\\$past") {
                        if (GetSize(children) > 0) {
                                sub_width_hint = 0;
                                sub_sign_hint = true;
                                children.at(0)->detectSignWidthWorker(sub_width_hint, sub_sign_hint);
                                width_hint = max(width_hint, sub_width_hint);
                                sign_hint = false;
                        }
                        break;
                }
                if (current_scope.count(str))
                {
                        // This width detection is needed for function calls which are
                        // unelaborated, which currently only applies to calls to recursive
                        // functions reached by unevaluated ternary branches.
                        const AstNode *func = current_scope.at(str);
                        if (func->type != AST_FUNCTION)
                                log_file_error(filename, location.first_line, "Function call to %s resolved to something that isn't a function!\n", RTLIL::unescape_id(str).c_str());
                        const AstNode *wire = nullptr;
                        for (const AstNode *child : func->children)
                                if (child->str == func->str) {
                                        wire = child;
                                        break;
                                }
                        log_assert(wire && wire->type == AST_WIRE);
                        sign_hint = wire->is_signed;
                        width_hint = 1;
                        if (!wire->children.empty())
                        {
                                log_assert(wire->children.size() == 1);
                                const AstNode *range = wire->children.at(0);
                                log_assert(range->type == AST_RANGE && range->children.size() == 2);
                                AstNode *left = range->children.at(0)->clone();
                                AstNode *right = range->children.at(1)->clone();
                                while (left->simplify(true, false, false, 1, -1, false, true)) { }
                                while (right->simplify(true, false, false, 1, -1, false, true)) { }
                                if (left->type != AST_CONSTANT || right->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "Function %s has non-constant width!",
                                                        RTLIL::unescape_id(str).c_str());
                                width_hint = abs(int(left->asInt(true) - right->asInt(true)));
                                delete left;
                                delete right;
                        }
                        break;
                }
                YS_FALLTHROUGH

        // everything should have been handled above -> print error if not.
        default:
                for (auto f : log_files)
                        current_ast_mod->dumpAst(f, "verilog-ast> ");
                log_file_error(filename, location.first_line, "Don't know how to detect sign and width for %s node!\n", type2str(type).c_str());
        }

        if (*found_real)
                sign_hint = true;
}

// detect sign and width of an expression
void AstNode::detectSignWidth(int &width_hint, bool &sign_hint, bool *found_real)
{
        width_hint = -1;
        sign_hint = true;
        if (found_real)
                *found_real = false;
        detectSignWidthWorker(width_hint, sign_hint, found_real);

        constexpr int kWidthLimit = 1 << 24;
        if (width_hint >= kWidthLimit)
                log_file_error(filename, location.first_line,
                        "Expression width %d exceeds implementation limit of %d!\n",
                        width_hint, kWidthLimit);
}

static void check_unique_id(RTLIL::Module *module, RTLIL::IdString id,
                const AstNode *node, const char *to_add_kind)
{
        auto already_exists = [&](const RTLIL::AttrObject *existing, const char *existing_kind) {
                std::string src = existing->get_string_attribute(ID::src);
                std::string location_str = "earlier";
                if (!src.empty())
                        location_str = "at " + src;
                log_file_error(node->filename, node->location.first_line,
                        "Cannot add %s `%s' because a %s with the same name was already created %s!\n",
                        to_add_kind, id.c_str(), existing_kind, location_str.c_str());
        };

        if (const RTLIL::Wire *wire = module->wire(id))
                already_exists(wire, "signal");
        if (const RTLIL::Cell *cell = module->cell(id))
                already_exists(cell, "cell");
        if (module->processes.count(id))
                already_exists(module->processes.at(id), "process");
        if (module->memories.count(id))
                already_exists(module->memories.at(id), "memory");
}

// create RTLIL from an AST node
// all generated cells, wires and processes are added to the module pointed to by 'current_module'
// when the AST node is an expression (AST_ADD, AST_BIT_XOR, etc.), the result signal is returned.
//
// note that this function is influenced by a number of global variables that might be set when
// called from genWidthRTLIL(). also note that this function recursively calls itself to transform
// larger expressions into a netlist of cells.
RTLIL::SigSpec AstNode::genRTLIL(int width_hint, bool sign_hint)
{
        // in the following big switch() statement there are some uses of
        // Clifford's Device (http://www.clifford.at/cfun/cliffdev/). In this
        // cases this variable is used to hold the type of the cell that should
        // be instantiated for this type of AST node.
        IdString type_name;

        current_filename = filename;

        switch (type)
        {
        // simply ignore this nodes.
        // they are either leftovers from simplify() or are referenced by other nodes
        // and are only accessed here thru this references
        case AST_NONE:
        case AST_TASK:
        case AST_FUNCTION:
        case AST_DPI_FUNCTION:
        case AST_AUTOWIRE:
        case AST_DEFPARAM:
        case AST_GENVAR:
        case AST_GENFOR:
        case AST_GENBLOCK:
        case AST_GENIF:
        case AST_GENCASE:
        case AST_PACKAGE:
        case AST_ENUM:
        case AST_MODPORT:
        case AST_MODPORTMEMBER:
        case AST_TYPEDEF:
        case AST_STRUCT:
        case AST_UNION:
                break;
        case AST_INTERFACEPORT: {
                // If a port in a module with unknown type is found, mark it with the attribute 'is_interface'
                // This is used by the hierarchy pass to know when it can replace interface connection with the individual
                // signals.
                RTLIL::IdString id = str;
                check_unique_id(current_module, id, this, "interface port");
                RTLIL::Wire *wire = current_module->addWire(id, 1);
                set_src_attr(wire, this);
                wire->start_offset = 0;
                wire->port_id = port_id;
                wire->port_input = true;
                wire->port_output = true;
                wire->set_bool_attribute(ID::is_interface);
                if (children.size() > 0) {
                        for(size_t i=0; i<children.size();i++) {
                                if(children[i]->type == AST_INTERFACEPORTTYPE) {
                                        std::pair<std::string,std::string> res = AST::split_modport_from_type(children[i]->str);
                                        wire->attributes[ID::interface_type] = res.first;
                                        if (res.second != "")
                                                wire->attributes[ID::interface_modport] = res.second;
                                        break;
                                }
                        }
                }
                wire->upto = 0;
                }
                break;
        case AST_INTERFACEPORTTYPE:
                break;

        // remember the parameter, needed for example in techmap
        case AST_PARAMETER:
                current_module->avail_parameters(str);
                if (GetSize(children) >= 1 && children[0]->type == AST_CONSTANT) {
                        current_module->parameter_default_values[str] = children[0]->asParaConst();
                }
                YS_FALLTHROUGH
        case AST_LOCALPARAM:
                if (flag_pwires)
                {
                        if (GetSize(children) < 1 || children[0]->type != AST_CONSTANT)
                                log_file_error(filename, location.first_line, "Parameter `%s' with non-constant value!\n", str.c_str());

                        RTLIL::Const val = children[0]->bitsAsConst();
                        RTLIL::IdString id = str;
                        check_unique_id(current_module, id, this, "pwire");
                        RTLIL::Wire *wire = current_module->addWire(id, GetSize(val));
                        current_module->connect(wire, val);
                        wire->is_signed = children[0]->is_signed;

                        set_src_attr(wire, this);
                        wire->attributes[type == AST_PARAMETER ? ID::parameter : ID::localparam] = 1;

                        for (auto &attr : attributes) {
                                if (attr.second->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "Attribute `%s' with non-constant value!\n", attr.first.c_str());
                                wire->attributes[attr.first] = attr.second->asAttrConst();
                        }
                }
                break;

        // create an RTLIL::Wire for an AST_WIRE node
        case AST_WIRE: {
                        if (!range_valid)
                                log_file_error(filename, location.first_line, "Signal `%s' with non-constant width!\n", str.c_str());

                        if (!(range_left + 1 >= range_right))
                                log_file_error(filename, location.first_line, "Signal `%s' with invalid width range %d!\n", str.c_str(), range_left - range_right + 1);

                        RTLIL::IdString id = str;
                        check_unique_id(current_module, id, this, "signal");
                        RTLIL::Wire *wire = current_module->addWire(id, range_left - range_right + 1);
                        set_src_attr(wire, this);
                        wire->start_offset = range_right;
                        wire->port_id = port_id;
                        wire->port_input = is_input;
                        wire->port_output = is_output;
                        wire->upto = range_swapped;
                        wire->is_signed = is_signed;

                        for (auto &attr : attributes) {
                                if (attr.second->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "Attribute `%s' with non-constant value!\n", attr.first.c_str());
                                wire->attributes[attr.first] = attr.second->asAttrConst();
                        }

                        if (is_wand) wire->set_bool_attribute(ID::wand);
                        if (is_wor)  wire->set_bool_attribute(ID::wor);
                }
                break;

        // create an RTLIL::Memory for an AST_MEMORY node
        case AST_MEMORY: {
                        log_assert(children.size() >= 2);
                        log_assert(children[0]->type == AST_RANGE);
                        log_assert(children[1]->type == AST_RANGE);

                        if (!children[0]->range_valid || !children[1]->range_valid)
                                log_file_error(filename, location.first_line, "Memory `%s' with non-constant width or size!\n", str.c_str());

                        RTLIL::Memory *memory = new RTLIL::Memory;
                        set_src_attr(memory, this);
                        memory->name = str;
                        memory->width = children[0]->range_left - children[0]->range_right + 1;
                        if (children[1]->range_right < children[1]->range_left) {
                                memory->start_offset = children[1]->range_right;
                                memory->size = children[1]->range_left - children[1]->range_right + 1;
                        } else {
                                memory->start_offset = children[1]->range_left;
                                memory->size = children[1]->range_right - children[1]->range_left + 1;
                        }
                        check_unique_id(current_module, memory->name, this, "memory");
                        current_module->memories[memory->name] = memory;

                        for (auto &attr : attributes) {
                                if (attr.second->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "Attribute `%s' with non-constant value!\n", attr.first.c_str());
                                memory->attributes[attr.first] = attr.second->asAttrConst();
                        }
                }
                break;

        // simply return the corresponding RTLIL::SigSpec for an AST_CONSTANT node
        case AST_CONSTANT:
        case AST_REALVALUE:
                {
                        if (width_hint < 0)
                                detectSignWidth(width_hint, sign_hint);
                        is_signed = sign_hint;

                        if (type == AST_CONSTANT) {
                                if (is_unsized) {
                                        return RTLIL::SigSpec(bitsAsUnsizedConst(width_hint));
                                } else {
                                        return RTLIL::SigSpec(bitsAsConst());
                                }
                        }

                        RTLIL::SigSpec sig = realAsConst(width_hint);
                        log_file_warning(filename, location.first_line, "converting real value %e to binary %s.\n", realvalue, log_signal(sig));
                        return sig;
                }

        // simply return the corresponding RTLIL::SigSpec for an AST_IDENTIFIER node
        // for identifiers with dynamic bit ranges (e.g. "foo[bar]" or "foo[bar+3:bar]") a
        // shifter cell is created and the output signal of this cell is returned
        case AST_IDENTIFIER:
                {
                        RTLIL::Wire *wire = NULL;
                        RTLIL::SigChunk chunk;
                        bool is_interface = false;

                        int add_undef_bits_msb = 0;
                        int add_undef_bits_lsb = 0;

                        log_assert(id2ast != nullptr);

                        if (id2ast->type == AST_AUTOWIRE && current_module->wires_.count(str) == 0) {
                                RTLIL::Wire *wire = current_module->addWire(str);
                                set_src_attr(wire, this);
                                wire->name = str;
                                if (flag_autowire)
                                        log_file_warning(filename, location.first_line, "Identifier `%s' is implicitly declared.\n", str.c_str());
                                else
                                        log_file_error(filename, location.first_line, "Identifier `%s' is implicitly declared and `default_nettype is set to none.\n", str.c_str());
                        }
                        else if (id2ast->type == AST_PARAMETER || id2ast->type == AST_LOCALPARAM || id2ast->type == AST_ENUM_ITEM) {
                                if (id2ast->children[0]->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "Parameter %s does not evaluate to constant value!\n", str.c_str());
                                chunk = RTLIL::Const(id2ast->children[0]->bits);
                                goto use_const_chunk;
                        }
                        else if ((id2ast->type == AST_WIRE || id2ast->type == AST_AUTOWIRE || id2ast->type == AST_MEMORY) && current_module->wires_.count(str) != 0) {
                                RTLIL::Wire *current_wire = current_module->wire(str);
                                if (current_wire->get_bool_attribute(ID::is_interface))
                                        is_interface = true;
                                // Ignore
                        }
                        // If an identifier is found that is not already known, assume that it is an interface:
                        else if (1) { // FIXME: Check if sv_mode first?
                                is_interface = true;
                        }
                        else {
                                log_file_error(filename, location.first_line, "Identifier `%s' doesn't map to any signal!\n", str.c_str());
                        }

                        if (id2ast->type == AST_MEMORY)
                                log_file_error(filename, location.first_line, "Identifier `%s' does map to an unexpanded memory!\n", str.c_str());

                        // If identifier is an interface, create a RTLIL::SigSpec with a dummy wire with a attribute called 'is_interface'
                        // This makes it possible for the hierarchy pass to see what are interface connections and then replace them
                        // with the individual signals:
                        if (is_interface) {
                                IdString dummy_wire_name = stringf("$dummywireforinterface%s", str.c_str());
                                RTLIL::Wire *dummy_wire = current_module->wire(dummy_wire_name);
                                if (!dummy_wire) {
                                        dummy_wire = current_module->addWire(dummy_wire_name);
                                        dummy_wire->set_bool_attribute(ID::is_interface);
                                }
                                return dummy_wire;
                        }

                        wire = current_module->wires_[str];
                        chunk.wire = wire;
                        chunk.width = wire->width;
                        chunk.offset = 0;

                use_const_chunk:
                        if (children.size() != 0) {
                                if (children[0]->type != AST_RANGE)
                                        log_file_error(filename, location.first_line, "Single range expected.\n");
                                int source_width = id2ast->range_left - id2ast->range_right + 1;
                                int source_offset = id2ast->range_right;
                                if (!children[0]->range_valid) {
                                        AstNode *left_at_zero_ast = children[0]->children[0]->clone();
                                        AstNode *right_at_zero_ast = children[0]->children.size() >= 2 ? children[0]->children[1]->clone() : left_at_zero_ast->clone();
                                        while (left_at_zero_ast->simplify(true, true, false, 1, -1, false, false)) { }
                                        while (right_at_zero_ast->simplify(true, true, false, 1, -1, false, false)) { }
                                        if (left_at_zero_ast->type != AST_CONSTANT || right_at_zero_ast->type != AST_CONSTANT)
                                                log_file_error(filename, location.first_line, "Unsupported expression on dynamic range select on signal `%s'!\n", str.c_str());
                                        int width = abs(int(left_at_zero_ast->integer - right_at_zero_ast->integer)) + 1;
                                        AstNode *fake_ast = new AstNode(AST_NONE, clone(), children[0]->children.size() >= 2 ?
                                                        children[0]->children[1]->clone() : children[0]->children[0]->clone());
                                        fake_ast->children[0]->delete_children();

                                        int fake_ast_width = 0;
                                        bool fake_ast_sign = true;
                                        fake_ast->children[1]->detectSignWidth(fake_ast_width, fake_ast_sign);
                                        RTLIL::SigSpec shift_val = fake_ast->children[1]->genRTLIL(fake_ast_width, fake_ast_sign);

                                        if (id2ast->range_right != 0) {
                                                shift_val = current_module->Sub(NEW_ID, shift_val, id2ast->range_right, fake_ast_sign);
                                                fake_ast->children[1]->is_signed = true;
                                        }
                                        if (id2ast->range_swapped) {
                                                shift_val = current_module->Sub(NEW_ID, RTLIL::SigSpec(source_width - width), shift_val, fake_ast_sign);
                                                fake_ast->children[1]->is_signed = true;
                                        }
                                        if (GetSize(shift_val) >= 32)
                                                fake_ast->children[1]->is_signed = true;
                                        RTLIL::SigSpec sig = binop2rtlil(fake_ast, ID($shiftx), width, fake_ast->children[0]->genRTLIL(), shift_val);
                                        delete left_at_zero_ast;
                                        delete right_at_zero_ast;
                                        delete fake_ast;
                                        return sig;
                                } else {
                                        chunk.width = children[0]->range_left - children[0]->range_right + 1;
                                        chunk.offset = children[0]->range_right - source_offset;
                                        if (id2ast->range_swapped)
                                                chunk.offset = (id2ast->range_left - id2ast->range_right + 1) - (chunk.offset + chunk.width);
                                        if (chunk.offset >= source_width || chunk.offset + chunk.width < 0) {
                                                if (chunk.width == 1)
                                                        log_file_warning(filename, location.first_line, "Range select out of bounds on signal `%s': Setting result bit to undef.\n",
                                                                        str.c_str());
                                                else
                                                        log_file_warning(filename, location.first_line, "Range select [%d:%d] out of bounds on signal `%s': Setting all %d result bits to undef.\n",
                                                                        children[0]->range_left, children[0]->range_right, str.c_str(), chunk.width);
                                                chunk = RTLIL::SigChunk(RTLIL::State::Sx, chunk.width);
                                        } else {
                                                if (chunk.width + chunk.offset > source_width) {
                                                        add_undef_bits_msb = (chunk.width + chunk.offset) - source_width;
                                                        chunk.width -= add_undef_bits_msb;
                                                }
                                                if (chunk.offset < 0) {
                                                        add_undef_bits_lsb = -chunk.offset;
                                                        chunk.width -= add_undef_bits_lsb;
                                                        chunk.offset += add_undef_bits_lsb;
                                                }
                                                if (add_undef_bits_lsb)
                                                        log_file_warning(filename, location.first_line, "Range [%d:%d] select out of bounds on signal `%s': Setting %d LSB bits to undef.\n",
                                                                        children[0]->range_left, children[0]->range_right, str.c_str(), add_undef_bits_lsb);
                                                if (add_undef_bits_msb)
                                                        log_file_warning(filename, location.first_line, "Range [%d:%d] select out of bounds on signal `%s': Setting %d MSB bits to undef.\n",
                                                                        children[0]->range_left, children[0]->range_right, str.c_str(), add_undef_bits_msb);
                                        }
                                }
                        }

                        RTLIL::SigSpec sig = { RTLIL::SigSpec(RTLIL::State::Sx, add_undef_bits_msb), chunk, RTLIL::SigSpec(RTLIL::State::Sx, add_undef_bits_lsb) };

                        if (genRTLIL_subst_ptr)
                                sig.replace(*genRTLIL_subst_ptr);

                        is_signed = children.size() > 0 ? false : id2ast->is_signed && sign_hint;
                        return sig;
                }

        // just pass thru the signal. the parent will evaluate the is_signed property and interpret the SigSpec accordingly
        case AST_TO_SIGNED:
        case AST_TO_UNSIGNED:
        case AST_SELFSZ: {
                        RTLIL::SigSpec sig = children[0]->genRTLIL();
                        if (sig.size() < width_hint)
                                sig.extend_u0(width_hint, sign_hint);
                        is_signed = sign_hint;
                        return sig;
        }

        // changing the size of signal can be done directly using RTLIL::SigSpec
        case AST_CAST_SIZE: {
                        RTLIL::SigSpec size = children[0]->genRTLIL();
                        RTLIL::SigSpec sig = children[1]->genRTLIL();
                        if (!size.is_fully_const())
                                log_file_error(filename, location.first_line, "Static cast with non constant expression!\n");
                        int width = size.as_int();
                        if (width <= 0)
                                log_file_error(filename, location.first_line, "Static cast with zero or negative size!\n");
                        sig.extend_u0(width, sign_hint);
                        is_signed = sign_hint;
                        return sig;
                }

        // concatenation of signals can be done directly using RTLIL::SigSpec
        case AST_CONCAT: {
                        RTLIL::SigSpec sig;
                        for (auto it = children.begin(); it != children.end(); it++)
                                sig.append((*it)->genRTLIL());
                        if (sig.size() < width_hint)
                                sig.extend_u0(width_hint, false);
                        return sig;
                }

        // replication of signals can be done directly using RTLIL::SigSpec
        case AST_REPLICATE: {
                        RTLIL::SigSpec left = children[0]->genRTLIL();
                        RTLIL::SigSpec right = children[1]->genRTLIL();
                        if (!left.is_fully_const())
                                log_file_error(filename, location.first_line, "Left operand of replicate expression is not constant!\n");
                        int count = left.as_int();
                        RTLIL::SigSpec sig;
                        for (int i = 0; i < count; i++)
                                sig.append(right);
                        if (sig.size() < width_hint)
                                sig.extend_u0(width_hint, false);
                        is_signed = false;
                        return sig;
                }

        // generate cells for unary operations: $not, $pos, $neg
        if (0) { case AST_BIT_NOT: type_name = ID($not); }
        if (0) { case AST_POS:     type_name = ID($pos); }
        if (0) { case AST_NEG:     type_name = ID($neg); }
                {
                        RTLIL::SigSpec arg = children[0]->genRTLIL(width_hint, sign_hint);
                        is_signed = children[0]->is_signed;
                        int width = arg.size();
                        if (width_hint > 0) {
                                width = width_hint;
                                widthExtend(this, arg, width, is_signed);
                        }
                        return uniop2rtlil(this, type_name, width, arg);
                }

        // generate cells for binary operations: $and, $or, $xor, $xnor
        if (0) { case AST_BIT_AND:  type_name = ID($and); }
        if (0) { case AST_BIT_OR:   type_name = ID($or); }
        if (0) { case AST_BIT_XOR:  type_name = ID($xor); }
        if (0) { case AST_BIT_XNOR: type_name = ID($xnor); }
                {
                        if (width_hint < 0)
                                detectSignWidth(width_hint, sign_hint);
                        RTLIL::SigSpec left = children[0]->genRTLIL(width_hint, sign_hint);
                        RTLIL::SigSpec right = children[1]->genRTLIL(width_hint, sign_hint);
                        int width = max(left.size(), right.size());
                        if (width_hint > 0)
                                width = width_hint;
                        is_signed = children[0]->is_signed && children[1]->is_signed;
                        return binop2rtlil(this, type_name, width, left, right);
                }

        // generate cells for unary operations: $reduce_and, $reduce_or, $reduce_xor, $reduce_xnor
        if (0) { case AST_REDUCE_AND:  type_name = ID($reduce_and); }
        if (0) { case AST_REDUCE_OR:   type_name = ID($reduce_or); }
        if (0) { case AST_REDUCE_XOR:  type_name = ID($reduce_xor); }
        if (0) { case AST_REDUCE_XNOR: type_name = ID($reduce_xnor); }
                {
                        RTLIL::SigSpec arg = children[0]->genRTLIL();
                        RTLIL::SigSpec sig = uniop2rtlil(this, type_name, max(width_hint, 1), arg);
                        return sig;
                }

        // generate cells for unary operations: $reduce_bool
        // (this is actually just an $reduce_or, but for clarity a different cell type is used)
        if (0) { case AST_REDUCE_BOOL:  type_name = ID($reduce_bool); }
                {
                        RTLIL::SigSpec arg = children[0]->genRTLIL();
                        RTLIL::SigSpec sig = arg.size() > 1 ? uniop2rtlil(this, type_name, max(width_hint, 1), arg) : arg;
                        return sig;
                }

        // generate cells for binary operations: $shl, $shr, $sshl, $sshr
        if (0) { case AST_SHIFT_LEFT:   type_name = ID($shl); }
        if (0) { case AST_SHIFT_RIGHT:  type_name = ID($shr); }
        if (0) { case AST_SHIFT_SLEFT:  type_name = ID($sshl); }
        if (0) { case AST_SHIFT_SRIGHT: type_name = ID($sshr); }
        if (0) { case AST_SHIFTX:       type_name = ID($shiftx); }
        if (0) { case AST_SHIFT:        type_name = ID($shift); }
                {
                        if (width_hint < 0)
                                detectSignWidth(width_hint, sign_hint);
                        RTLIL::SigSpec left = children[0]->genRTLIL(width_hint, sign_hint);
                        RTLIL::SigSpec right = children[1]->genRTLIL();
                        int width = width_hint > 0 ? width_hint : left.size();
                        is_signed = children[0]->is_signed;
                        return binop2rtlil(this, type_name, width, left, right);
                }

        // generate cells for binary operations: $pow
        case AST_POW:
                {
                        int right_width;
                        bool right_signed;
                        children[1]->detectSignWidth(right_width, right_signed);
                        if (width_hint < 0)
                                detectSignWidth(width_hint, sign_hint);
                        RTLIL::SigSpec left = children[0]->genRTLIL(width_hint, sign_hint);
                        RTLIL::SigSpec right = children[1]->genRTLIL(right_width, right_signed);
                        int width = width_hint > 0 ? width_hint : left.size();
                        is_signed = children[0]->is_signed;
                        if (!flag_noopt && left.is_fully_const() && left.as_int() == 2 && !right_signed)
                                return binop2rtlil(this, ID($shl), width, RTLIL::SigSpec(1, left.size()), right);
                        return binop2rtlil(this, ID($pow), width, left, right);
                }

        // generate cells for binary operations: $lt, $le, $eq, $ne, $ge, $gt
        if (0) { case AST_LT:  type_name = ID($lt); }
        if (0) { case AST_LE:  type_name = ID($le); }
        if (0) { case AST_EQ:  type_name = ID($eq); }
        if (0) { case AST_NE:  type_name = ID($ne); }
        if (0) { case AST_EQX: type_name = ID($eqx); }
        if (0) { case AST_NEX: type_name = ID($nex); }
        if (0) { case AST_GE:  type_name = ID($ge); }
        if (0) { case AST_GT:  type_name = ID($gt); }
                {
                        int width = max(width_hint, 1);
                        width_hint = -1, sign_hint = true;
                        children[0]->detectSignWidthWorker(width_hint, sign_hint);
                        children[1]->detectSignWidthWorker(width_hint, sign_hint);
                        RTLIL::SigSpec left = children[0]->genRTLIL(width_hint, sign_hint);
                        RTLIL::SigSpec right = children[1]->genRTLIL(width_hint, sign_hint);
                        RTLIL::SigSpec sig = binop2rtlil(this, type_name, width, left, right);
                        return sig;
                }

        // generate cells for binary operations: $add, $sub, $mul, $div, $mod
        if (0) { case AST_ADD: type_name = ID($add); }
        if (0) { case AST_SUB: type_name = ID($sub); }
        if (0) { case AST_MUL: type_name = ID($mul); }
        if (0) { case AST_DIV: type_name = ID($div); }
        if (0) { case AST_MOD: type_name = ID($mod); }
                {
                        if (width_hint < 0)
                                detectSignWidth(width_hint, sign_hint);
                        RTLIL::SigSpec left = children[0]->genRTLIL(width_hint, sign_hint);
                        RTLIL::SigSpec right = children[1]->genRTLIL(width_hint, sign_hint);
                #if 0
                        int width = max(left.size(), right.size());
                        if (width > width_hint && width_hint > 0)
                                width = width_hint;
                        if (width < width_hint) {
                                if (type == AST_ADD || type == AST_SUB || type == AST_DIV)
                                        width++;
                                if (type == AST_SUB && (!children[0]->is_signed || !children[1]->is_signed))
                                        width = width_hint;
                                if (type == AST_MUL)
                                        width = min(left.size() + right.size(), width_hint);
                        }
                #else
                        int width = max(max(left.size(), right.size()), width_hint);
                #endif
                        is_signed = children[0]->is_signed && children[1]->is_signed;
                        return binop2rtlil(this, type_name, width, left, right);
                }

        // generate cells for binary operations: $logic_and, $logic_or
        if (0) { case AST_LOGIC_AND: type_name = ID($logic_and); }
        if (0) { case AST_LOGIC_OR:  type_name = ID($logic_or); }
                {
                        RTLIL::SigSpec left = children[0]->genRTLIL();
                        RTLIL::SigSpec right = children[1]->genRTLIL();
                        return binop2rtlil(this, type_name, max(width_hint, 1), left, right);
                }

        // generate cells for unary operations: $logic_not
        case AST_LOGIC_NOT:
                {
                        RTLIL::SigSpec arg = children[0]->genRTLIL();
                        return uniop2rtlil(this, ID($logic_not), max(width_hint, 1), arg);
                }

        // generate multiplexer for ternary operator (aka ?:-operator)
        case AST_TERNARY:
                {
                        if (width_hint < 0)
                                detectSignWidth(width_hint, sign_hint);
                        is_signed = sign_hint;

                        RTLIL::SigSpec cond = children[0]->genRTLIL();
                        RTLIL::SigSpec sig;

                        if (cond.is_fully_def())
                        {
                                if (cond.as_bool()) {
                                        sig = children[1]->genRTLIL(width_hint, sign_hint);
                                        log_assert(is_signed == children[1]->is_signed);
                                } else {
                                        sig = children[2]->genRTLIL(width_hint, sign_hint);
                                        log_assert(is_signed == children[2]->is_signed);
                                }

                                widthExtend(this, sig, sig.size(), is_signed);
                        }
                        else
                        {
                                RTLIL::SigSpec val1 = children[1]->genRTLIL(width_hint, sign_hint);
                                RTLIL::SigSpec val2 = children[2]->genRTLIL(width_hint, sign_hint);

                                if (cond.size() > 1)
                                        cond = uniop2rtlil(this, ID($reduce_bool), 1, cond, false);

                                int width = max(val1.size(), val2.size());
                                log_assert(is_signed == children[1]->is_signed);
                                log_assert(is_signed == children[2]->is_signed);
                                widthExtend(this, val1, width, is_signed);
                                widthExtend(this, val2, width, is_signed);

                                sig = mux2rtlil(this, cond, val1, val2);
                        }

                        if (sig.size() < width_hint)
                                sig.extend_u0(width_hint, sign_hint);
                        return sig;
                }

        // generate $memrd cells for memory read ports
        case AST_MEMRD:
                {
                        std::stringstream sstr;
                        sstr << "$memrd$" << str << "$" << filename << ":" << location.first_line << "$" << (autoidx++);

                        RTLIL::Cell *cell = current_module->addCell(sstr.str(), ID($memrd));
                        set_src_attr(cell, this);

                        RTLIL::Wire *wire = current_module->addWire(cell->name.str() + "_DATA", current_module->memories[str]->width);
                        set_src_attr(wire, this);

                        int mem_width, mem_size, addr_bits;
                        is_signed = id2ast->is_signed;
                        wire->is_signed = is_signed;
                        id2ast->meminfo(mem_width, mem_size, addr_bits);

                        RTLIL::SigSpec addr_sig = children[0]->genRTLIL();

                        cell->setPort(ID::CLK, RTLIL::SigSpec(RTLIL::State::Sx, 1));
                        cell->setPort(ID::EN, RTLIL::SigSpec(RTLIL::State::Sx, 1));
                        cell->setPort(ID::ADDR, addr_sig);
                        cell->setPort(ID::DATA, RTLIL::SigSpec(wire));

                        cell->parameters[ID::MEMID] = RTLIL::Const(str);
                        cell->parameters[ID::ABITS] = RTLIL::Const(GetSize(addr_sig));
                        cell->parameters[ID::WIDTH] = RTLIL::Const(wire->width);

                        cell->parameters[ID::CLK_ENABLE] = RTLIL::Const(0);
                        cell->parameters[ID::CLK_POLARITY] = RTLIL::Const(0);
                        cell->parameters[ID::TRANSPARENT] = RTLIL::Const(0);

                        if (!sign_hint)
                                is_signed = false;

                        return RTLIL::SigSpec(wire);
                }

        // generate $memwr cells for memory write ports
        case AST_MEMWR:
        case AST_MEMINIT:
                {
                        std::stringstream sstr;
                        sstr << (type == AST_MEMWR ? "$memwr$" : "$meminit$") << str << "$" << filename << ":" << location.first_line << "$" << (autoidx++);

                        RTLIL::Cell *cell = current_module->addCell(sstr.str(), type == AST_MEMWR ? ID($memwr) : ID($meminit));
                        set_src_attr(cell, this);

                        int mem_width, mem_size, addr_bits;
                        id2ast->meminfo(mem_width, mem_size, addr_bits);

                        int num_words = 1;
                        if (type == AST_MEMINIT) {
                                if (children[2]->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "Memory init with non-constant word count!\n");
                                num_words = int(children[2]->asInt(false));
                                cell->parameters[ID::WORDS] = RTLIL::Const(num_words);
                        }

                        SigSpec addr_sig = children[0]->genRTLIL();

                        cell->setPort(ID::ADDR, addr_sig);
                        cell->setPort(ID::DATA, children[1]->genWidthRTLIL(current_module->memories[str]->width * num_words));

                        cell->parameters[ID::MEMID] = RTLIL::Const(str);
                        cell->parameters[ID::ABITS] = RTLIL::Const(GetSize(addr_sig));
                        cell->parameters[ID::WIDTH] = RTLIL::Const(current_module->memories[str]->width);

                        if (type == AST_MEMWR) {
                                cell->setPort(ID::CLK, RTLIL::SigSpec(RTLIL::State::Sx, 1));
                                cell->setPort(ID::EN, children[2]->genRTLIL());
                                cell->parameters[ID::CLK_ENABLE] = RTLIL::Const(0);
                                cell->parameters[ID::CLK_POLARITY] = RTLIL::Const(0);
                        }

                        cell->parameters[ID::PRIORITY] = RTLIL::Const(autoidx-1);
                }
                break;

        // generate $assert cells
        case AST_ASSERT:
        case AST_ASSUME:
        case AST_LIVE:
        case AST_FAIR:
        case AST_COVER:
                {
                        IdString celltype;
                        if (type == AST_ASSERT) celltype = ID($assert);
                        if (type == AST_ASSUME) celltype = ID($assume);
                        if (type == AST_LIVE) celltype = ID($live);
                        if (type == AST_FAIR) celltype = ID($fair);
                        if (type == AST_COVER) celltype = ID($cover);

                        log_assert(children.size() == 2);

                        RTLIL::SigSpec check = children[0]->genRTLIL();
                        if (GetSize(check) != 1)
                                check = current_module->ReduceBool(NEW_ID, check);

                        RTLIL::SigSpec en = children[1]->genRTLIL();
                        if (GetSize(en) != 1)
                                en = current_module->ReduceBool(NEW_ID, en);

                        IdString cellname;
                        if (str.empty())
                                cellname = stringf("%s$%s:%d$%d", celltype.c_str(), filename.c_str(), location.first_line, autoidx++);
                        else
                                cellname = str;

                        check_unique_id(current_module, cellname, this, "procedural assertion");
                        RTLIL::Cell *cell = current_module->addCell(cellname, celltype);
                        set_src_attr(cell, this);

                        for (auto &attr : attributes) {
                                if (attr.second->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "Attribute `%s' with non-constant value!\n", attr.first.c_str());
                                cell->attributes[attr.first] = attr.second->asAttrConst();
                        }

                        cell->setPort(ID::A, check);
                        cell->setPort(ID::EN, en);
                }
                break;

        // add entries to current_module->connections for assignments (outside of always blocks)
        case AST_ASSIGN:
                {
                        RTLIL::SigSpec left = children[0]->genRTLIL();
                        RTLIL::SigSpec right = children[1]->genWidthRTLIL(left.size());
                        if (left.has_const()) {
                                RTLIL::SigSpec new_left, new_right;
                                for (int i = 0; i < GetSize(left); i++)
                                        if (left[i].wire) {
                                                new_left.append(left[i]);
                                                new_right.append(right[i]);
                                        }
                                log_file_warning(filename, location.first_line, "Ignoring assignment to constant bits:\n"
                                                "    old assignment: %s = %s\n    new assignment: %s = %s.\n",
                                                log_signal(left), log_signal(right),
                                                log_signal(new_left), log_signal(new_right));
                                left = new_left;
                                right = new_right;
                        }
                        current_module->connect(RTLIL::SigSig(left, right));
                }
                break;

        // create an RTLIL::Cell for an AST_CELL
        case AST_CELL:
                {
                        int port_counter = 0, para_counter = 0;

                        RTLIL::IdString id = str;
                        check_unique_id(current_module, id, this, "cell");
                        RTLIL::Cell *cell = current_module->addCell(id, "");
                        set_src_attr(cell, this);
                        // Set attribute 'module_not_derived' which will be cleared again after the hierarchy pass
                        cell->set_bool_attribute(ID::module_not_derived);

                        for (auto it = children.begin(); it != children.end(); it++) {
                                AstNode *child = *it;
                                if (child->type == AST_CELLTYPE) {
                                        cell->type = child->str;
                                        if (flag_icells && cell->type.begins_with("\\$"))
                                                cell->type = cell->type.substr(1);
                                        continue;
                                }
                                if (child->type == AST_PARASET) {
                                        int extra_const_flags = 0;
                                        IdString paraname = child->str.empty() ? stringf("$%d", ++para_counter) : child->str;
                                        if (child->children[0]->type == AST_REALVALUE) {
                                                log_file_warning(filename, location.first_line, "Replacing floating point parameter %s.%s = %f with string.\n",
                                                                log_id(cell), log_id(paraname), child->children[0]->realvalue);
                                                extra_const_flags = RTLIL::CONST_FLAG_REAL;
                                                auto strnode = AstNode::mkconst_str(stringf("%f", child->children[0]->realvalue));
                                                strnode->cloneInto(child->children[0]);
                                                delete strnode;
                                        }
                                        if (child->children[0]->type != AST_CONSTANT)
                                                log_file_error(filename, location.first_line, "Parameter %s.%s with non-constant value!\n",
                                                                log_id(cell), log_id(paraname));
                                        cell->parameters[paraname] = child->children[0]->asParaConst();
                                        cell->parameters[paraname].flags |= extra_const_flags;
                                        continue;
                                }
                                if (child->type == AST_ARGUMENT) {
                                        RTLIL::SigSpec sig;
                                        if (child->children.size() > 0) {
                                                AstNode *arg = child->children[0];
                                                int local_width_hint = -1;
                                                bool local_sign_hint = false;
                                                // don't inadvertently attempt to detect the width of interfaces
                                                if (arg->type != AST_IDENTIFIER || !arg->id2ast || arg->id2ast->type != AST_CELL)
                                                        arg->detectSignWidth(local_width_hint, local_sign_hint);
                                                sig = arg->genRTLIL(local_width_hint, local_sign_hint);
                                                log_assert(local_sign_hint == arg->is_signed);
                                                if (sig.is_wire()) {
                                                        // if the resulting SigSpec is a wire, its
                                                        // signedness should match that of the AstNode
                                                        log_assert(arg->is_signed == sig.as_wire()->is_signed);
                                                } else if (arg->is_signed) {
                                                        // non-trivial signed nodes are indirected through
                                                        // signed wires to enable sign extension
                                                        RTLIL::IdString wire_name = NEW_ID;
                                                        RTLIL::Wire *wire = current_module->addWire(wire_name, GetSize(sig));
                                                        wire->is_signed = true;
                                                        current_module->connect(wire, sig);
                                                        sig = wire;
                                                }
                                        }
                                        if (child->str.size() == 0) {
                                                char buf[100];
                                                snprintf(buf, 100, "$%d", ++port_counter);
                                                cell->setPort(buf, sig);
                                        } else {
                                                cell->setPort(child->str, sig);
                                        }
                                        continue;
                                }
                                log_abort();
                        }
                        for (auto &attr : attributes) {
                                if (attr.second->type != AST_CONSTANT)
                                        log_file_error(filename, location.first_line, "Attribute `%s' with non-constant value.\n", attr.first.c_str());
                                cell->attributes[attr.first] = attr.second->asAttrConst();
                        }
                        if (cell->type == ID($specify2)) {
                                int src_width = GetSize(cell->getPort(ID::SRC));
                                int dst_width = GetSize(cell->getPort(ID::DST));
                                bool full = cell->getParam(ID::FULL).as_bool();
                                if (!full && src_width != dst_width)
                                        log_file_error(filename, location.first_line, "Parallel specify SRC width does not match DST width.\n");
                                cell->setParam(ID::SRC_WIDTH, Const(src_width));
                                cell->setParam(ID::DST_WIDTH, Const(dst_width));
                        }
                        else if (cell->type ==  ID($specify3)) {
                                int dat_width = GetSize(cell->getPort(ID::DAT));
                                int dst_width = GetSize(cell->getPort(ID::DST));
                                if (dat_width != dst_width)
                                        log_file_error(filename, location.first_line, "Specify DAT width does not match DST width.\n");
                                int src_width = GetSize(cell->getPort(ID::SRC));
                                cell->setParam(ID::SRC_WIDTH, Const(src_width));
                                cell->setParam(ID::DST_WIDTH, Const(dst_width));
                        }
                        else if (cell->type == ID($specrule)) {
                                int src_width = GetSize(cell->getPort(ID::SRC));
                                int dst_width = GetSize(cell->getPort(ID::DST));
                                cell->setParam(ID::SRC_WIDTH, Const(src_width));
                                cell->setParam(ID::DST_WIDTH, Const(dst_width));
                        }
                }
                break;

        // use ProcessGenerator for always blocks
        case AST_ALWAYS: {
                        AstNode *always = this->clone();
                        ProcessGenerator generator(always);
                        ignoreThisSignalsInInitial.append(generator.outputSignals);
                        delete always;
                } break;

        case AST_INITIAL: {
                        AstNode *always = this->clone();
                        ProcessGenerator generator(always, ignoreThisSignalsInInitial);
                        delete always;
                } break;

        case AST_TECALL: {
                        int sz = children.size();
                        if (str == "$info") {
                                if (sz > 0)
                                        log_file_info(filename, location.first_line, "%s.\n", children[0]->str.c_str());
                                else
                                        log_file_info(filename, location.first_line, "\n");
                        } else if (str == "$warning") {
                                if (sz > 0)
                                        log_file_warning(filename, location.first_line, "%s.\n", children[0]->str.c_str());
                                else
                                        log_file_warning(filename, location.first_line, "\n");
                        } else if (str == "$error") {
                                if (sz > 0)
                                        log_file_error(filename, location.first_line, "%s.\n", children[0]->str.c_str());
                                else
                                        log_file_error(filename, location.first_line, "\n");
                        } else if (str == "$fatal") {
                                // TODO: 1st parameter, if exists, is 0,1 or 2, and passed to $finish()
                                // if no parameter is given, default value is 1
                                // dollar_finish(sz ? children[0] : 1);
                                // perhaps create & use log_file_fatal()
                                if (sz > 0)
                                        log_file_error(filename, location.first_line, "FATAL: %s.\n", children[0]->str.c_str());
                                else
                                        log_file_error(filename, location.first_line, "FATAL.\n");
                        } else {
                                log_file_error(filename, location.first_line, "Unknown elabortoon system task '%s'.\n", str.c_str());
                        }
                } break;

        case AST_FCALL: {
                        if (str == "\\$anyconst" || str == "\\$anyseq" || str == "\\$allconst" || str == "\\$allseq")
                        {
                                string myid = stringf("%s$%d", str.c_str() + 1, autoidx++);
                                int width = width_hint;

                                if (GetSize(children) > 1)
                                        log_file_error(filename, location.first_line, "System function %s got %d arguments, expected 1 or 0.\n",
                                                        RTLIL::unescape_id(str).c_str(), GetSize(children));

                                if (GetSize(children) == 1) {
                                        if (children[0]->type != AST_CONSTANT)
                                                log_file_error(filename, location.first_line, "System function %s called with non-const argument!\n",
                                                                RTLIL::unescape_id(str).c_str());
                                        width = children[0]->asInt(true);
                                }

                                if (width <= 0)
                                        log_file_error(filename, location.first_line, "Failed to detect width of %s!\n", RTLIL::unescape_id(str).c_str());

                                Cell *cell = current_module->addCell(myid, str.substr(1));
                                set_src_attr(cell, this);
                                cell->parameters[ID::WIDTH] = width;

                                if (attributes.count(ID::reg)) {
                                        auto &attr = attributes.at(ID::reg);
                                        if (attr->type != AST_CONSTANT)
                                                log_file_error(filename, location.first_line, "Attribute `reg' with non-constant value!\n");
                                        cell->attributes[ID::reg] =  attr->asAttrConst();
                                }

                                Wire *wire = current_module->addWire(myid + "_wire", width);
                                set_src_attr(wire, this);
                                cell->setPort(ID::Y, wire);

                                is_signed = sign_hint;
                                return SigSpec(wire);
                        }
                }
                YS_FALLTHROUGH

        // everything should have been handled above -> print error if not.
        default:
                for (auto f : log_files)
                        current_ast_mod->dumpAst(f, "verilog-ast> ");
                type_name = type2str(type);
                log_file_error(filename, location.first_line, "Don't know how to generate RTLIL code for %s node!\n", type_name.c_str());
        }

        return RTLIL::SigSpec();
}

// this is a wrapper for AstNode::genRTLIL() when a specific signal width is requested and/or
// signals must be substituted before being used as input values (used by ProcessGenerator)
// note that this is using some global variables to communicate this special settings to AstNode::genRTLIL().
RTLIL::SigSpec AstNode::genWidthRTLIL(int width, const dict<RTLIL::SigBit, RTLIL::SigBit> *new_subst_ptr)
{
        const dict<RTLIL::SigBit, RTLIL::SigBit> *backup_subst_ptr = genRTLIL_subst_ptr;

        if (new_subst_ptr)
                genRTLIL_subst_ptr = new_subst_ptr;

        bool sign_hint = true;
        int width_hint = width;
        detectSignWidthWorker(width_hint, sign_hint);
        RTLIL::SigSpec sig = genRTLIL(width_hint, sign_hint);

        genRTLIL_subst_ptr = backup_subst_ptr;

        if (width >= 0)
                sig.extend_u0(width, is_signed);

        return sig;
}

YOSYS_NAMESPACE_END