yosys/passes/opt/muxpack.cc

/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  Copyright (C) 2012  Claire Xenia Wolf <claire@yosyshq.com>
 *                2019  Eddie Hung    <eddie@fpgeh.com>
 *
 *  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"

USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN

struct ExclusiveDatabase
{
	Module *module;
	const SigMap &sigmap;

	dict<SigBit, std::pair<SigSpec,std::vector<Const>>> sig_cmp_prev;

	ExclusiveDatabase(Module *module, const SigMap &sigmap) : module(module), sigmap(sigmap)
	{
		SigSpec const_sig, nonconst_sig;
		SigBit y_port;
		pool<Cell*> reduce_or;
		for (auto cell : module->cells()) {
			if (cell->type == ID($eq)) {
				nonconst_sig = sigmap(cell->getPort(ID::A));
				const_sig = sigmap(cell->getPort(ID::B));
				if (!const_sig.is_fully_const()) {
					if (!nonconst_sig.is_fully_const())
						continue;
					std::swap(nonconst_sig, const_sig);
				}
				y_port = sigmap(cell->getPort(ID::Y));
			}
			else if (cell->type == ID($logic_not)) {
				nonconst_sig = sigmap(cell->getPort(ID::A));
				const_sig = Const(State::S0, GetSize(nonconst_sig));
				y_port = sigmap(cell->getPort(ID::Y));
			}
			else if (cell->type == ID($reduce_or)) {
				reduce_or.insert(cell);
				continue;
			}
			else continue;

			log_assert(!nonconst_sig.empty());
			log_assert(!const_sig.empty());
			sig_cmp_prev[y_port] = std::make_pair(nonconst_sig,std::vector<Const>{const_sig.as_const()});
		}

		for (auto cell : reduce_or) {
			nonconst_sig = SigSpec();
			std::vector<Const> values;
			SigSpec a_port = sigmap(cell->getPort(ID::A));
			for (auto bit : a_port) {
				auto it = sig_cmp_prev.find(bit);
				if (it == sig_cmp_prev.end()) {
					nonconst_sig = SigSpec();
					break;
				}
				if (nonconst_sig.empty())
					nonconst_sig = it->second.first;
				else if (nonconst_sig != it->second.first) {
					nonconst_sig = SigSpec();
					break;
				}
				for (auto value : it->second.second)
					values.push_back(value);
			}
			if (nonconst_sig.empty())
				continue;
			y_port = sigmap(cell->getPort(ID::Y));
			sig_cmp_prev[y_port] = std::make_pair(nonconst_sig,std::move(values));
		}
	}

	bool query(const SigSpec &sig) const
	{
		SigSpec nonconst_sig;
		pool<Const> const_values;

		for (auto bit : sig) {
			auto it = sig_cmp_prev.find(bit);
			if (it == sig_cmp_prev.end())
				return false;

			if (nonconst_sig.empty())
				nonconst_sig = it->second.first;
			else if (nonconst_sig != it->second.first)
				return false;

			for (auto value : it->second.second)
				if (!const_values.insert(value).second)
					return false;
		}

		return true;
	}
};


struct MuxpackWorker
{
	Module *module;
	SigMap sigmap;

	int mux_count, pmux_count;

	pool<Cell*> remove_cells;

	dict<SigSpec, Cell*> sig_chain_next;
	dict<SigSpec, Cell*> sig_chain_prev;
	pool<SigBit> sigbit_with_non_chain_users;
	pool<Cell*> chain_start_cells;
	pool<Cell*> candidate_cells;

	ExclusiveDatabase excl_db;

	void make_sig_chain_next_prev()
	{
		for (auto wire : module->wires())
		{
			if (wire->port_output || wire->get_bool_attribute(ID::keep)) {
				for (auto bit : sigmap(wire))
					sigbit_with_non_chain_users.insert(bit);
			}
		}

		for (auto cell : module->cells())
		{
			if (cell->type.in(ID($mux), ID($pmux)) && !cell->get_bool_attribute(ID::keep))
			{
				SigSpec a_sig = sigmap(cell->getPort(ID::A));
				SigSpec b_sig;
				if (cell->type == ID($mux))
					b_sig = sigmap(cell->getPort(ID::B));
				SigSpec y_sig = sigmap(cell->getPort(ID::Y));
   
				if (sig_chain_next.count(a_sig))
					for (auto a_bit : a_sig)
						sigbit_with_non_chain_users.insert(a_bit);
				else {
					sig_chain_next[a_sig] = cell;
					candidate_cells.insert(cell);
				}

				if (!b_sig.empty()) {
					if (sig_chain_next.count(b_sig))
						for (auto b_bit : b_sig)
							sigbit_with_non_chain_users.insert(b_bit);
					else {
						sig_chain_next[b_sig] = cell;
						candidate_cells.insert(cell);
					}
				}

				sig_chain_prev[y_sig] = cell;
				continue;
			}

			for (auto conn : cell->connections())
				if (cell->input(conn.first))
					for (auto bit : sigmap(conn.second))
						sigbit_with_non_chain_users.insert(bit);
		}
	}

	void find_chain_start_cells()
	{
		for (auto cell : candidate_cells)
		{
			log_debug("Considering %s (%s)\n", log_id(cell), log_id(cell->type));

			SigSpec a_sig = sigmap(cell->getPort(ID::A));
			if (cell->type == ID($mux)) {
				SigSpec b_sig = sigmap(cell->getPort(ID::B));
				if (sig_chain_prev.count(a_sig) + sig_chain_prev.count(b_sig) != 1)
					goto start_cell;

				if (!sig_chain_prev.count(a_sig))
					a_sig = b_sig;
			}
			else if (cell->type == ID($pmux)) {
				if (!sig_chain_prev.count(a_sig))
					goto start_cell;
			}
			else log_abort();

			for (auto bit : a_sig)
				if (sigbit_with_non_chain_users.count(bit))
					goto start_cell;

			{
				Cell *prev_cell = sig_chain_prev.at(a_sig);
				log_assert(prev_cell);
				SigSpec s_sig = sigmap(cell->getPort(ID::S));
				s_sig.append(sigmap(prev_cell->getPort(ID::S)));
				if (!excl_db.query(s_sig))
					goto start_cell;
			}

			continue;

		start_cell:
			chain_start_cells.insert(cell);
		}
	}

	vector<Cell*> create_chain(Cell *start_cell)
	{
		vector<Cell*> chain;

		Cell *c = start_cell;
		while (c != nullptr)
		{
			chain.push_back(c);

			SigSpec y_sig = sigmap(c->getPort(ID::Y));

			if (sig_chain_next.count(y_sig) == 0)
				break;

			c = sig_chain_next.at(y_sig);
			if (chain_start_cells.count(c) != 0)
				break;
		}

		return chain;
	}

	void process_chain(vector<Cell*> &chain)
	{
		if (GetSize(chain) < 2)
			return;

		int cursor = 0;
		while (cursor < GetSize(chain))
		{
			int cases = GetSize(chain) - cursor;

			Cell *first_cell = chain[cursor];
			dict<int, SigBit> taps_dict;

			if (cases < 2) {
				cursor++;
				continue;
			}

			Cell *last_cell = chain[cursor+cases-1];

			log("Converting %s.%s ... %s.%s to a pmux with %d cases.\n",
				log_id(module), log_id(first_cell), log_id(module), log_id(last_cell), cases);

			mux_count += cases;
			pmux_count += 1;

			first_cell->type = ID($pmux);
			SigSpec b_sig = first_cell->getPort(ID::B);
			SigSpec s_sig = first_cell->getPort(ID::S);

			for (int i = 1; i < cases; i++) {
				Cell* prev_cell = chain[cursor+i-1];
				Cell* cursor_cell = chain[cursor+i];
				if (sigmap(prev_cell->getPort(ID::Y)) == sigmap(cursor_cell->getPort(ID::A))) {
					b_sig.append(cursor_cell->getPort(ID::B));
					s_sig.append(cursor_cell->getPort(ID::S));
				}
				else {
					log_assert(cursor_cell->type == ID($mux));
					b_sig.append(cursor_cell->getPort(ID::A));
					s_sig.append(module->LogicNot(NEW_ID, cursor_cell->getPort(ID::S)));
				}
				remove_cells.insert(cursor_cell);
			}

			first_cell->setPort(ID::B, b_sig);
			first_cell->setPort(ID::S, s_sig);
			first_cell->setParam(ID::S_WIDTH, GetSize(s_sig));
			first_cell->setPort(ID::Y, last_cell->getPort(ID::Y));

			cursor += cases;
		}
	}

	void cleanup()
	{
		for (auto cell : remove_cells)
			module->remove(cell);

		remove_cells.clear();
		sig_chain_next.clear();
		sig_chain_prev.clear();
		chain_start_cells.clear();
		candidate_cells.clear();
	}

	MuxpackWorker(Module *module) :
			module(module), sigmap(module), mux_count(0), pmux_count(0), excl_db(module, sigmap)
	{
		make_sig_chain_next_prev();
		find_chain_start_cells();

		for (auto c : chain_start_cells) {
			vector<Cell*> chain = create_chain(c);
			process_chain(chain);
		}

		cleanup();
	}
};

struct MuxpackPass : public Pass {
	MuxpackPass() : Pass("muxpack", "$mux/$pmux cascades to $pmux") { }
	void help() override
	{
		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
		log("\n");
		log("    muxpack [selection]\n");
		log("\n");
		log("This pass converts cascaded chains of $pmux cells (e.g. those create from case\n");
		log("constructs) and $mux cells (e.g. those created by if-else constructs) into\n");
		log("$pmux cells.\n");
		log("\n");
		log("This optimisation is conservative --- it will only pack $mux or $pmux cells\n");
		log("whose select lines are driven by '$eq' cells with other such cells if it can be\n");
		log("certain that their select inputs are mutually exclusive.\n");
		log("\n");
	}
	void execute(std::vector<std::string> args, RTLIL::Design *design) override
	{
		log_header(design, "Executing MUXPACK pass ($mux cell cascades to $pmux).\n");

		size_t argidx;
		for (argidx = 1; argidx < args.size(); argidx++)
		{
			break;
		}
		extra_args(args, argidx, design);

		int mux_count = 0;
		int pmux_count = 0;

		for (auto module : design->selected_modules()) {
			MuxpackWorker worker(module);
			mux_count += worker.mux_count;
			pmux_count += worker.pmux_count;
		}

		log("Converted %d (p)mux cells into %d pmux cells.\n", mux_count, pmux_count);
	}
} MuxpackPass;

PRIVATE_NAMESPACE_END