yosys/backends/simplec/simplec.cc

/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
 *
 *  Permission to use, copy, modify, and/or distribute this software for any
 *  purpose with or without fee is hereby granted, provided that the above
 *  copyright notice and this permission notice appear in all copies.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include "kernel/yosys.h"
#include "kernel/sigtools.h"
#include "kernel/utils.h"

USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN

struct HierDirtyFlags;

static pool<string> reserved_cids;
static dict<IdString, string> id2cid;

static string cid(IdString id)
{
	if (id2cid.count(id) == 0)
	{
		string s = id.str();
		if (GetSize(s) < 2) log_abort();

		if (s[0] == '\\')
			s = s.substr(1);

		if ('0' <= s[0] && s[0] <= '9') {
			s = "_" + s;
		}

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

		while (reserved_cids.count(s))
			s += "_";

		reserved_cids.insert(s);
		id2cid[id] = s;
	}

	return id2cid.at(id);
}

struct HierDirtyFlags
{
	int dirty;
	Module *module;
	IdString hiername;
	HierDirtyFlags *parent;
	pool<SigBit> dirty_bits;
	pool<Cell*> dirty_cells;
	pool<SigBit> sticky_dirty_bits;
	dict<IdString, HierDirtyFlags*> children;
	string prefix, log_prefix;

	HierDirtyFlags(Module *module, IdString hiername, HierDirtyFlags *parent, const string &prefix, const string &log_prefix) :
			dirty(0), module(module), hiername(hiername), parent(parent), prefix(prefix), log_prefix(log_prefix)
	{
		for (Cell *cell : module->cells()) {
			Module *mod = module->design->module(cell->type);
			if (mod) children[cell->name] = new HierDirtyFlags(mod, cell->name, this,
					prefix + cid(cell->name) + ".", log_prefix + "." + prefix + log_id(cell->name));
		}
	}

	~HierDirtyFlags()
	{
		for (auto &child : children)
			delete child.second;
	}

	void set_dirty(SigBit bit)
	{
		if (dirty_bits.count(bit))
			return;

		dirty_bits.insert(bit);
		sticky_dirty_bits.insert(bit);

		HierDirtyFlags *p = this;
		while (p != nullptr) {
			p->dirty++;
			p = p->parent;
		}
	}

	void unset_dirty(SigBit bit)
	{
		if (dirty_bits.count(bit) == 0)
			return;

		dirty_bits.erase(bit);

		HierDirtyFlags *p = this;
		while (p != nullptr) {
			p->dirty--;
			log_assert(p->dirty >= 0);
			p = p->parent;
		}
	}

	void set_dirty(Cell *cell)
	{
		if (dirty_cells.count(cell))
			return;

		dirty_cells.insert(cell);

		HierDirtyFlags *p = this;
		while (p != nullptr) {
			p->dirty++;
			p = p->parent;
		}
	}

	void unset_dirty(Cell *cell)
	{
		if (dirty_cells.count(cell) == 0)
			return;

		dirty_cells.erase(cell);

		HierDirtyFlags *p = this;
		while (p != nullptr) {
			p->dirty--;
			log_assert(p->dirty >= 0);
			p = p->parent;
		}
	}
};

struct SimplecWorker
{
	bool verbose = false;
	int max_uintsize = 32;

	Design *design;
	dict<Module*, SigMap> sigmaps;

	vector<string> signal_declarations;
	pool<int> generated_sigtypes;

	vector<string> util_declarations;
	pool<string> generated_utils;

	vector<string> struct_declarations;
	pool<IdString> generated_structs;

	vector<string> funct_declarations;

	dict<Module*, dict<SigBit, pool<tuple<Cell*, IdString, int>>>> bit2cell;
	dict<Module*, dict<SigBit, pool<SigBit>>> bit2output;
	dict<Module*, pool<SigBit>> driven_bits;

	dict<Cell*, int> topoidx;

	pool<string> activated_cells;
	pool<string> reactivated_cells;

	SimplecWorker(Design *design) : design(design)
	{
	}

	string sigtype(int n)
	{
		string struct_name = stringf("signal%d_t", n);

		if (generated_sigtypes.count(n) == 0)
		{
			signal_declarations.push_back("");
			signal_declarations.push_back(stringf("#ifndef YOSYS_SIMPLEC_SIGNAL%d_T", n));
			signal_declarations.push_back(stringf("#define YOSYS_SIMPLEC_SIGNAL%d_T", n));
			signal_declarations.push_back(stringf("typedef struct {"));

			for (int k = 8; k <= max_uintsize; k = 2*k)
				if (n <= k && k <= max_uintsize) {
					signal_declarations.push_back(stringf("  uint%d_t value_%d_0 : %d;", k, n-1, n));
					goto end_struct;
				}

			for (int k = 0; k < n; k += max_uintsize) {
				int bits = std::min(max_uintsize, n-k);
				signal_declarations.push_back(stringf("  uint%d_t value_%d_%d : %d;", max_uintsize, k+bits-1, k, bits));
			}

		end_struct:
			signal_declarations.push_back(stringf("} signal%d_t;", n));
			signal_declarations.push_back(stringf("#endif"));
			generated_sigtypes.insert(n);
		}

		return struct_name;
	}

	void util_ifdef_guard(string s)
	{
		for (int i = 0; i < GetSize(s); i++)
			if ('a' <= s[i] && s[i] <= 'z')
				s[i] -= 'a' - 'A';

		util_declarations.push_back("");
		util_declarations.push_back(stringf("#ifndef %s", s.c_str()));
		util_declarations.push_back(stringf("#define %s", s.c_str()));
	}

	string util_get_bit(const string &signame, int n, int idx)
	{
		if (n == 1 && idx == 0)
			return signame + ".value_0_0";

		string util_name = stringf("yosys_simplec_get_bit_%d_of_%d", idx, n);

		if (generated_utils.count(util_name) == 0)
		{
			util_ifdef_guard(util_name);
			util_declarations.push_back(stringf("static inline bool %s(const %s *sig)", util_name.c_str(), sigtype(n).c_str()));
			util_declarations.push_back(stringf("{"));

			int word_idx = idx / max_uintsize, word_offset = idx % max_uintsize;
			string value_name = stringf("value_%d_%d", std::min(n-1, (word_idx+1)*max_uintsize-1), word_idx*max_uintsize);

			util_declarations.push_back(stringf("  return (sig->%s >> %d) & 1;", value_name.c_str(), word_offset));

			util_declarations.push_back(stringf("}"));
			util_declarations.push_back(stringf("#endif"));
			generated_utils.insert(util_name);
		}

		return stringf("%s(&%s)", util_name.c_str(), signame.c_str());
	}

	string util_set_bit(const string &signame, int n, int idx, const string &expr)
	{
		if (n == 1 && idx == 0)
			return stringf("  %s.value_0_0 = %s;", signame.c_str(), expr.c_str());

		string util_name = stringf("yosys_simplec_set_bit_%d_of_%d", idx, n);

		if (generated_utils.count(util_name) == 0)
		{
			util_ifdef_guard(util_name);
			util_declarations.push_back(stringf("static inline void %s(%s *sig, bool value)", util_name.c_str(), sigtype(n).c_str()));
			util_declarations.push_back(stringf("{"));

			int word_idx = idx / max_uintsize, word_offset = idx % max_uintsize;
			string value_name = stringf("value_%d_%d", std::min(n-1, (word_idx+1)*max_uintsize-1), word_idx*max_uintsize);

		#if 0
			util_declarations.push_back(stringf("  if (value)"));
			util_declarations.push_back(stringf("    sig->%s |= 1UL << %d;", value_name.c_str(), word_offset));
			util_declarations.push_back(stringf("  else"));
			util_declarations.push_back(stringf("    sig->%s &= ~(1UL << %d);", value_name.c_str(), word_offset));
		#else
			util_declarations.push_back(stringf("    sig->%s = (sig->%s & ~((uint%d_t)1 << %d)) | ((uint%d_t)value << %d);",
					value_name.c_str(), value_name.c_str(), max_uintsize, word_offset, max_uintsize, word_offset));
		#endif

			util_declarations.push_back(stringf("}"));
			util_declarations.push_back(stringf("#endif"));
			generated_utils.insert(util_name);
		}

		return stringf("  %s(&%s, %s);", util_name.c_str(), signame.c_str(), expr.c_str());
	}

	void create_module_struct(Module *mod)
	{
		if (generated_structs.count(mod->name))
			return;

		generated_structs.insert(mod->name);
		sigmaps[mod].set(mod);

		for (Wire *w : mod->wires())
		{
			if (w->port_output)
				for (auto bit : SigSpec(w))
					bit2output[mod][sigmaps.at(mod)(bit)].insert(bit);
		}

		for (Cell *c : mod->cells())
		{
			for (auto &conn : c->connections())
			{
				if (!c->input(conn.first)) {
					for (auto bit : sigmaps.at(mod)(conn.second))
						driven_bits[mod].insert(bit);
					continue;
				}

				int idx = 0;
				for (auto bit : sigmaps.at(mod)(conn.second))
					bit2cell[mod][bit].insert(tuple<Cell*, IdString, int>(c, conn.first, idx++));
			}

			if (design->module(c->type))
				create_module_struct(design->module(c->type));
		}

		TopoSort<IdString> topo;

		for (Cell *c : mod->cells())
		{
			topo.node(c->name);

			for (auto &conn : c->connections())
			{
				if (!c->input(conn.first))
					continue;

				for (auto bit : sigmaps.at(mod)(conn.second))
				for (auto &it : bit2cell[mod][bit])
					topo.edge(c->name, std::get<0>(it)->name);
			}
		}

		topo.analyze_loops = false;
		topo.sort();

		for (int i = 0; i < GetSize(topo.sorted); i++)
			topoidx[mod->cell(topo.sorted[i])] = i;

		string ifdef_name = stringf("yosys_simplec_%s_state_t", cid(mod->name).c_str());

		for (int i = 0; i < GetSize(ifdef_name); i++)
			if ('a' <= ifdef_name[i] && ifdef_name[i] <= 'z')
				ifdef_name[i] -= 'a' - 'A';

		struct_declarations.push_back("");
		struct_declarations.push_back(stringf("#ifndef %s", ifdef_name.c_str()));
		struct_declarations.push_back(stringf("#define %s", ifdef_name.c_str()));
		struct_declarations.push_back(stringf("struct %s_state_t", cid(mod->name).c_str()));
		struct_declarations.push_back("{");

		struct_declarations.push_back("  // Input Ports");
		for (Wire *w : mod->wires())
			if (w->port_input)
				struct_declarations.push_back(stringf("  %s %s; // %s", sigtype(w->width).c_str(), cid(w->name).c_str(), log_id(w)));

		struct_declarations.push_back("");
		struct_declarations.push_back("  // Output Ports");
		for (Wire *w : mod->wires())
			if (!w->port_input && w->port_output)
				struct_declarations.push_back(stringf("  %s %s; // %s", sigtype(w->width).c_str(), cid(w->name).c_str(), log_id(w)));

		struct_declarations.push_back("");
		struct_declarations.push_back("  // Internal Wires");
		for (Wire *w : mod->wires())
			if (!w->port_input && !w->port_output)
				struct_declarations.push_back(stringf("  %s %s; // %s", sigtype(w->width).c_str(), cid(w->name).c_str(), log_id(w)));

		for (Cell *c : mod->cells())
			if (design->module(c->type))
				struct_declarations.push_back(stringf("  struct %s_state_t %s; // %s", cid(c->type).c_str(), cid(c->name).c_str(), log_id(c)));

		struct_declarations.push_back(stringf("};"));
		struct_declarations.push_back("#endif");
	}

	void eval_cell(HierDirtyFlags *work, Cell *cell)
	{
		if (cell->type.in(ID($_BUF_), ID($_NOT_)))
		{
			SigBit a = sigmaps.at(work->module)(cell->getPort(ID::A));
			SigBit y = sigmaps.at(work->module)(cell->getPort(ID::Y));

			string a_expr = a.wire ? util_get_bit(work->prefix + cid(a.wire->name), a.wire->width, a.offset) : a.data ? "1" : "0";
			string expr;

			if (cell->type == ID($_BUF_))  expr = a_expr;
			if (cell->type == ID($_NOT_))  expr = "!" + a_expr;

			log_assert(y.wire);
			funct_declarations.push_back(util_set_bit(work->prefix + cid(y.wire->name), y.wire->width, y.offset, expr) +
					stringf(" // %s (%s)", log_id(cell), log_id(cell->type)));

			work->set_dirty(y);
			return;
		}

		if (cell->type.in(ID($_AND_), ID($_NAND_), ID($_OR_), ID($_NOR_), ID($_XOR_), ID($_XNOR_), ID($_ANDNOT_), ID($_ORNOT_)))
		{
			SigBit a = sigmaps.at(work->module)(cell->getPort(ID::A));
			SigBit b = sigmaps.at(work->module)(cell->getPort(ID::B));
			SigBit y = sigmaps.at(work->module)(cell->getPort(ID::Y));

			string a_expr = a.wire ? util_get_bit(work->prefix + cid(a.wire->name), a.wire->width, a.offset) : a.data ? "1" : "0";
			string b_expr = b.wire ? util_get_bit(work->prefix + cid(b.wire->name), b.wire->width, b.offset) : b.data ? "1" : "0";
			string expr;

			if (cell->type == ID($_AND_))    expr = stringf("%s & %s",    a_expr.c_str(), b_expr.c_str());
			if (cell->type == ID($_NAND_))   expr = stringf("!(%s & %s)", a_expr.c_str(), b_expr.c_str());
			if (cell->type == ID($_OR_))     expr = stringf("%s | %s",    a_expr.c_str(), b_expr.c_str());
			if (cell->type == ID($_NOR_))    expr = stringf("!(%s | %s)", a_expr.c_str(), b_expr.c_str());
			if (cell->type == ID($_XOR_))    expr = stringf("%s ^ %s",    a_expr.c_str(), b_expr.c_str());
			if (cell->type == ID($_XNOR_))   expr = stringf("!(%s ^ %s)", a_expr.c_str(), b_expr.c_str());
			if (cell->type == ID($_ANDNOT_)) expr = stringf("%s & (!%s)", a_expr.c_str(), b_expr.c_str());
			if (cell->type == ID($_ORNOT_))  expr = stringf("%s | (!%s)", a_expr.c_str(), b_expr.c_str());

			log_assert(y.wire);
			funct_declarations.push_back(util_set_bit(work->prefix + cid(y.wire->name), y.wire->width, y.offset, expr) +
					stringf(" // %s (%s)", log_id(cell), log_id(cell->type)));

			work->set_dirty(y);
			return;
		}

		if (cell->type.in(ID($_AOI3_), ID($_OAI3_)))
		{
			SigBit a = sigmaps.at(work->module)(cell->getPort(ID::A));
			SigBit b = sigmaps.at(work->module)(cell->getPort(ID::B));
			SigBit c = sigmaps.at(work->module)(cell->getPort(ID::C));
			SigBit y = sigmaps.at(work->module)(cell->getPort(ID::Y));

			string a_expr = a.wire ? util_get_bit(work->prefix + cid(a.wire->name), a.wire->width, a.offset) : a.data ? "1" : "0";
			string b_expr = b.wire ? util_get_bit(work->prefix + cid(b.wire->name), b.wire->width, b.offset) : b.data ? "1" : "0";
			string c_expr = c.wire ? util_get_bit(work->prefix + cid(c.wire->name), c.wire->width, c.offset) : c.data ? "1" : "0";
			string expr;

			if (cell->type == ID($_AOI3_)) expr = stringf("!((%s & %s) | %s)", a_expr.c_str(), b_expr.c_str(), c_expr.c_str());
			if (cell->type == ID($_OAI3_)) expr = stringf("!((%s | %s) & %s)", a_expr.c_str(), b_expr.c_str(), c_expr.c_str());

			log_assert(y.wire);
			funct_declarations.push_back(util_set_bit(work->prefix + cid(y.wire->name), y.wire->width, y.offset, expr) +
					stringf(" // %s (%s)", log_id(cell), log_id(cell->type)));

			work->set_dirty(y);
			return;
		}

		if (cell->type.in(ID($_AOI4_), ID($_OAI4_)))
		{
			SigBit a = sigmaps.at(work->module)(cell->getPort(ID::A));
			SigBit b = sigmaps.at(work->module)(cell->getPort(ID::B));
			SigBit c = sigmaps.at(work->module)(cell->getPort(ID::C));
			SigBit d = sigmaps.at(work->module)(cell->getPort(ID::D));
			SigBit y = sigmaps.at(work->module)(cell->getPort(ID::Y));

			string a_expr = a.wire ? util_get_bit(work->prefix + cid(a.wire->name), a.wire->width, a.offset) : a.data ? "1" : "0";
			string b_expr = b.wire ? util_get_bit(work->prefix + cid(b.wire->name), b.wire->width, b.offset) : b.data ? "1" : "0";
			string c_expr = c.wire ? util_get_bit(work->prefix + cid(c.wire->name), c.wire->width, c.offset) : c.data ? "1" : "0";
			string d_expr = d.wire ? util_get_bit(work->prefix + cid(d.wire->name), d.wire->width, d.offset) : d.data ? "1" : "0";
			string expr;

			if (cell->type == ID($_AOI4_)) expr = stringf("!((%s & %s) | (%s & %s))", a_expr.c_str(), b_expr.c_str(), c_expr.c_str(), d_expr.c_str());
			if (cell->type == ID($_OAI4_)) expr = stringf("!((%s | %s) & (%s | %s))", a_expr.c_str(), b_expr.c_str(), c_expr.c_str(), d_expr.c_str());

			log_assert(y.wire);
			funct_declarations.push_back(util_set_bit(work->prefix + cid(y.wire->name), y.wire->width, y.offset, expr) +
					stringf(" // %s (%s)", log_id(cell), log_id(cell->type)));

			work->set_dirty(y);
			return;
		}

		if (cell->type.in(ID($_MUX_), ID($_NMUX_)))
		{
			SigBit a = sigmaps.at(work->module)(cell->getPort(ID::A));
			SigBit b = sigmaps.at(work->module)(cell->getPort(ID::B));
			SigBit s = sigmaps.at(work->module)(cell->getPort(ID::S));
			SigBit y = sigmaps.at(work->module)(cell->getPort(ID::Y));

			string a_expr = a.wire ? util_get_bit(work->prefix + cid(a.wire->name), a.wire->width, a.offset) : a.data ? "1" : "0";
			string b_expr = b.wire ? util_get_bit(work->prefix + cid(b.wire->name), b.wire->width, b.offset) : b.data ? "1" : "0";
			string s_expr = s.wire ? util_get_bit(work->prefix + cid(s.wire->name), s.wire->width, s.offset) : s.data ? "1" : "0";

			// casts to bool are a workaround for CBMC bug (https://github.com/diffblue/cbmc/issues/933)
			string expr = stringf("%s ? %s(bool)%s : %s(bool)%s", s_expr.c_str(),
					cell->type == ID($_NMUX_) ? "!" : "", b_expr.c_str(),
					cell->type == ID($_NMUX_) ? "!" : "", a_expr.c_str());

			log_assert(y.wire);
			funct_declarations.push_back(util_set_bit(work->prefix + cid(y.wire->name), y.wire->width, y.offset, expr) +
					stringf(" // %s (%s)", log_id(cell), log_id(cell->type)));

			work->set_dirty(y);
			return;
		}

		log_error("No C model for %s available at the moment (FIXME).\n", log_id(cell->type));
	}

	void eval_dirty(HierDirtyFlags *work)
	{
		while (work->dirty)
		{
			if (verbose && (!work->dirty_bits.empty() || !work->dirty_cells.empty()))
				log("  In %s:\n", work->log_prefix.c_str());

			while (!work->dirty_bits.empty() || !work->dirty_cells.empty())
			{
				if (!work->dirty_bits.empty())
				{
					SigSpec dirtysig(work->dirty_bits);
					dirtysig.sort_and_unify();

					for (SigChunk chunk : dirtysig.chunks()) {
						if (chunk.wire == nullptr)
							continue;
						if (verbose)
							log("    Propagating %s.%s[%d:%d].\n", work->log_prefix.c_str(), log_id(chunk.wire), chunk.offset+chunk.width-1, chunk.offset);
						funct_declarations.push_back(stringf("  // Updated signal in %s: %s", work->log_prefix.c_str(), log_signal(chunk)));
					}

					for (SigBit bit : dirtysig)
					{
						if (bit2output[work->module].count(bit) && work->parent)
							for (auto outbit : bit2output[work->module][bit])
							{
								Module *parent_mod = work->parent->module;
								Cell *parent_cell = parent_mod->cell(work->hiername);

								IdString port_name = outbit.wire->name;
								int port_offset = outbit.offset;
								SigBit parent_bit = sigmaps.at(parent_mod)(parent_cell->getPort(port_name)[port_offset]);

								log_assert(bit.wire && parent_bit.wire);
								funct_declarations.push_back(util_set_bit(work->parent->prefix + cid(parent_bit.wire->name), parent_bit.wire->width, parent_bit.offset,
										util_get_bit(work->prefix + cid(bit.wire->name), bit.wire->width, bit.offset)));
								work->parent->set_dirty(parent_bit);

								if (verbose)
									log("      Propagating %s.%s[%d] -> %s.%s[%d].\n", work->log_prefix.c_str(), log_id(bit.wire), bit.offset,
											work->parent->log_prefix.c_str(), log_id(parent_bit.wire), parent_bit.offset);
							}

						for (auto &port : bit2cell[work->module][bit])
						{
							if (work->children.count(std::get<0>(port)->name))
							{
								HierDirtyFlags *child = work->children.at(std::get<0>(port)->name);
								SigBit child_bit = sigmaps.at(child->module)(SigBit(child->module->wire(std::get<1>(port)), std::get<2>(port)));
								log_assert(bit.wire && child_bit.wire);

								funct_declarations.push_back(util_set_bit(work->prefix + cid(child->hiername) + "." + cid(child_bit.wire->name),
										child_bit.wire->width, child_bit.offset, util_get_bit(work->prefix + cid(bit.wire->name), bit.wire->width, bit.offset)));
								child->set_dirty(child_bit);

								if (verbose)
									log("      Propagating %s.%s[%d] -> %s.%s.%s[%d].\n", work->log_prefix.c_str(), log_id(bit.wire), bit.offset,
											work->log_prefix.c_str(), log_id(std::get<0>(port)), log_id(child_bit.wire), child_bit.offset);
							} else {
								if (verbose)
									log("      Marking cell %s.%s (via %s.%s[%d]).\n", work->log_prefix.c_str(), log_id(std::get<0>(port)),
											work->log_prefix.c_str(), log_id(bit.wire), bit.offset);
								work->set_dirty(std::get<0>(port));
							}
						}
						work->unset_dirty(bit);
					}
				}

				if (!work->dirty_cells.empty())
				{
					Cell *cell = nullptr;
					for (auto c : work->dirty_cells)
						if (cell == nullptr || topoidx.at(cell) < topoidx.at(c))
							cell = c;

					string hiername = work->log_prefix + "." + log_id(cell);

					if (verbose)
						log("    Evaluating %s (%s, best of %d).\n", hiername.c_str(), log_id(cell->type), GetSize(work->dirty_cells));

					if (activated_cells.count(hiername))
						reactivated_cells.insert(hiername);
					activated_cells.insert(hiername);

					eval_cell(work, cell);
					work->unset_dirty(cell);
				}
			}

			for (auto &child : work->children)
				eval_dirty(child.second);
		}
	}

	void eval_sticky_dirty(HierDirtyFlags *work)
	{
		Module *mod = work->module;

		for (Wire *w : mod->wires())
		for (SigBit bit : SigSpec(w))
		{
			SigBit canonical_bit = sigmaps.at(mod)(bit);

			if (canonical_bit == bit)
				continue;

			if (work->sticky_dirty_bits.count(canonical_bit) == 0)
				continue;

			if (bit.wire == nullptr || canonical_bit.wire == nullptr)
				continue;

			funct_declarations.push_back(util_set_bit(work->prefix + cid(bit.wire->name), bit.wire->width, bit.offset,
					util_get_bit(work->prefix + cid(canonical_bit.wire->name), canonical_bit.wire->width, canonical_bit.offset).c_str()));

			if (verbose)
				log("  Propagating alias %s.%s[%d] -> %s.%s[%d].\n",
						work->log_prefix.c_str(), log_id(canonical_bit.wire), canonical_bit.offset,
						work->log_prefix.c_str(), log_id(bit.wire), bit.offset);
		}

		work->sticky_dirty_bits.clear();

		for (auto &child : work->children)
			eval_sticky_dirty(child.second);
	}

	void make_func(HierDirtyFlags *work, const string &func_name, const vector<string> &preamble)
	{
		log("Generating function %s():\n", func_name.c_str());

		activated_cells.clear();
		reactivated_cells.clear();

		funct_declarations.push_back("");
		funct_declarations.push_back(stringf("static void %s(struct %s_state_t *state)", func_name.c_str(), cid(work->module->name).c_str()));
		funct_declarations.push_back("{");
		for (auto &line : preamble)
			funct_declarations.push_back(line);
		eval_dirty(work);
		eval_sticky_dirty(work);
		funct_declarations.push_back("}");

		log("  Activated %d cells (%d activated more than once).\n", GetSize(activated_cells), GetSize(reactivated_cells));
	}

	void eval_init(HierDirtyFlags *work, vector<string> &preamble)
	{
		Module *module = work->module;

		for (Wire *w : module->wires())
		{
			if (w->attributes.count(ID::init))
			{
				SigSpec sig = sigmaps.at(module)(w);
				Const val = w->attributes.at(ID::init);
				val.bits.resize(GetSize(sig), State::Sx);

				for (int i = 0; i < GetSize(sig); i++)
					if (val[i] == State::S0 || val[i] == State::S1) {
						SigBit bit = sig[i];
						preamble.push_back(util_set_bit(work->prefix + cid(bit.wire->name), bit.wire->width, bit.offset, val == State::S1 ? "true" : "false"));
						work->set_dirty(bit);
					}
			}

			for (SigBit bit : SigSpec(w))
			{
				SigBit val = sigmaps.at(module)(bit);

				if (val == State::S0 || val == State::S1)
					preamble.push_back(util_set_bit(work->prefix + cid(bit.wire->name), bit.wire->width, bit.offset, val == State::S1 ? "true" : "false"));

				if (driven_bits.at(module).count(val) == 0)
					work->set_dirty(val);
			}
		}

		work->set_dirty(State::S0);
		work->set_dirty(State::S1);

		for (auto &child : work->children)
			eval_init(child.second, preamble);
	}

	void make_init_func(HierDirtyFlags *work)
	{
		vector<string> preamble;
		eval_init(work, preamble);
		make_func(work, cid(work->module->name) + "_init", preamble);
	}

	void make_eval_func(HierDirtyFlags *work)
	{
		Module *mod = work->module;
		vector<string> preamble;

		for (Wire *w : mod->wires()) {
			if (w->port_input)
				for (SigBit bit : sigmaps.at(mod)(w))
					work->set_dirty(bit);
		}

		make_func(work, cid(work->module->name) + "_eval", preamble);
	}

	void make_tick_func(HierDirtyFlags* /* work */)
	{
		// FIXME
	}

	void run(Module *mod)
	{
		create_module_struct(mod);

		HierDirtyFlags work(mod, IdString(), nullptr, "state->", log_id(mod->name));

		make_init_func(&work);
		make_eval_func(&work);
		make_tick_func(&work);
	}

	void write(std::ostream &f)
	{
		f << "#include <stdint.h>" << std::endl;
		f << "#include <stdbool.h>" << std::endl;

		for (auto &line : signal_declarations)
			f << line << std::endl;

		for (auto &line : util_declarations)
			f << line << std::endl;

		for (auto &line : struct_declarations)
			f << line << std::endl;

		for (auto &line : funct_declarations)
			f << line << std::endl;
	}
};

struct SimplecBackend : public Backend {
	SimplecBackend() : Backend("simplec", "convert design to simple C code") { }
	void help() override
	{
		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
		log("\n");
		log("    write_simplec [options] [filename]\n");
		log("\n");
		log("Write simple C code for simulating the design. The C code written can be used to\n");
		log("simulate the design in a C environment, but the purpose of this command is to\n");
		log("generate code that works well with C-based formal verification.\n");
		log("\n");
		log("    -verbose\n");
		log("        this will print the recursive walk used to export the modules.\n");
		log("\n");
		log("    -i8, -i16, -i32, -i64\n");
		log("        set the maximum integer bit width to use in the generated code.\n");
		log("\n");
		log("THIS COMMAND IS UNDER CONSTRUCTION\n");
		log("\n");
	}
	void execute(std::ostream *&f, std::string filename, std::vector<std::string> args, RTLIL::Design *design) override
	{
		reserved_cids.clear();
		id2cid.clear();

		SimplecWorker worker(design);

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

		size_t argidx;
		for (argidx = 1; argidx < args.size(); argidx++)
		{
			if (args[argidx] == "-verbose") {
				worker.verbose = true;
				continue;
			}
			if (args[argidx] == "-i8") {
				worker.max_uintsize = 8;
				continue;
			}
			if (args[argidx] == "-i16") {
				worker.max_uintsize = 16;
				continue;
			}
			if (args[argidx] == "-i32") {
				worker.max_uintsize = 32;
				continue;
			}
			if (args[argidx] == "-i64") {
				worker.max_uintsize = 64;
				continue;
			}
			break;
		}
		extra_args(f, filename, args, argidx);

		Module *topmod = design->top_module();

		if (topmod == nullptr)
			log_error("Current design has no top module.\n");

		worker.run(topmod);
		worker.write(*f);
	}
} SimplecBackend;

PRIVATE_NAMESPACE_END