yosys/passes/techmap/muxcover.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"

USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN

#define COST_MUX2  100
#define COST_MUX4  220
#define COST_MUX8  460
#define COST_MUX16 940

struct MuxcoverWorker
{
	Module *module;
	SigMap sigmap;

	struct newmux_t
	{
		int cost;
		vector<SigBit> inputs, selects;
		newmux_t() : cost(0) {}
	};

	struct tree_t
	{
		SigBit root;
		dict<SigBit, Cell*> muxes;
		dict<SigBit, newmux_t> newmuxes;
	};

	vector<tree_t> tree_list;

	dict<tuple<SigBit, SigBit, SigBit>, tuple<SigBit, pool<SigBit>, bool>> decode_mux_cache;
	dict<SigBit, tuple<SigBit, SigBit, SigBit>> decode_mux_reverse_cache;
	int decode_mux_counter;

	bool use_mux4;
	bool use_mux8;
	bool use_mux16;
	bool nodecode;

	MuxcoverWorker(Module *module) : module(module), sigmap(module)
	{
		use_mux4 = false;
		use_mux8 = false;
		use_mux16 = false;
		nodecode = false;
		decode_mux_counter = 0;
	}

	void treeify()
	{
		pool<SigBit> roots;
		pool<SigBit> used_once;
		dict<SigBit, Cell*> sig_to_mux;

		for (auto wire : module->wires()) {
			if (!wire->port_output)
				continue;
			for (auto bit : sigmap(wire))
				roots.insert(bit);
		}

		for (auto cell : module->cells()) {
			for (auto conn : cell->connections()) {
				if (!cell->input(conn.first))
					continue;
				for (auto bit : sigmap(conn.second)) {
					if (used_once.count(bit) || cell->type != "$_MUX_" || conn.first == "\\S")
						roots.insert(bit);
					used_once.insert(bit);
				}
			}
			if (cell->type == "$_MUX_")
				sig_to_mux[sigmap(cell->getPort("\\Y"))] = cell;
		}

		log("  Treeifying %d MUXes:\n", GetSize(sig_to_mux));

		roots.sort();
		for (auto rootsig : roots)
		{
			tree_t tree;
			tree.root = rootsig;

			pool<SigBit> wavefront;
			wavefront.insert(rootsig);

			while (!wavefront.empty()) {
				SigBit bit = wavefront.pop();
				if (sig_to_mux.count(bit) && (bit == rootsig || !roots.count(bit))) {
					Cell *c = sig_to_mux.at(bit);
					tree.muxes[bit] = c;
					wavefront.insert(sigmap(c->getPort("\\A")));
					wavefront.insert(sigmap(c->getPort("\\B")));
				}
			}

			if (!tree.muxes.empty()) {
				log("    Found tree with %d MUXes at root %s.\n", GetSize(tree.muxes), log_signal(tree.root));
				tree_list.push_back(tree);
			}
		}

		log("    Finished treeification: Found %d trees.\n", GetSize(tree_list));
	}

	bool follow_muxtree(SigBit &ret_bit, tree_t &tree, SigBit bit, const char *path)
	{
		if (*path) {
			if (tree.muxes.count(bit) == 0)
				return false;
			char port_name[3] = {'\\', *path, 0};
			return follow_muxtree(ret_bit, tree, sigmap(tree.muxes.at(bit)->getPort(port_name)), path+1);
		} else {
			ret_bit = bit;
			return true;
		}
	}

	int prepare_decode_mux(SigBit &A, SigBit B, SigBit sel, SigBit bit)
	{
		if (A == B)
			return 0;

		tuple<SigBit, SigBit, SigBit> key(A, B, sel);
		if (decode_mux_cache.count(key) == 0) {
			auto &entry = decode_mux_cache[key];
			std::get<0>(entry) = module->addWire(NEW_ID);
			std::get<2>(entry) = false;
			decode_mux_reverse_cache[std::get<0>(entry)] = key;
		}

		auto &entry = decode_mux_cache[key];
		A = std::get<0>(entry);
		std::get<1>(entry).insert(bit);

		if (std::get<2>(entry))
			return 0;

		return COST_MUX2 / GetSize(std::get<1>(entry));
	}

	void implement_decode_mux(SigBit ctrl_bit)
	{
		if (decode_mux_reverse_cache.count(ctrl_bit) == 0)
			return;

		auto &key = decode_mux_reverse_cache.at(ctrl_bit);
		auto &entry = decode_mux_cache[key];

		if (std::get<2>(entry))
			return;

		implement_decode_mux(std::get<0>(key));
		implement_decode_mux(std::get<1>(key));

		module->addMuxGate(NEW_ID, std::get<0>(key), std::get<1>(key), std::get<2>(key), ctrl_bit);
		std::get<2>(entry) = true;
		decode_mux_counter++;
	}

	int find_best_cover(tree_t &tree, SigBit bit)
	{
		if (tree.newmuxes.count(bit)) {
			return tree.newmuxes.at(bit).cost;
		}

		SigBit A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P;
		SigBit S1, S2, S3, S4, S5, S6, S7, S8;
		SigBit T1, T2, T3, T4;
		SigBit U1, U2;
		SigBit V1;

		newmux_t best_mux;
		bool ok = true;

		// 2-Input MUX

		ok = ok && follow_muxtree(A, tree, bit, "A");
		ok = ok && follow_muxtree(B, tree, bit, "B");

		ok = ok && follow_muxtree(S1, tree, bit, "S");

		if (ok)
		{
			newmux_t mux;

			mux.inputs.push_back(A);
			mux.inputs.push_back(B);
			mux.selects.push_back(S1);

			mux.cost += COST_MUX2;
			mux.cost += find_best_cover(tree, A);
			mux.cost += find_best_cover(tree, B);

			best_mux = mux;
		}

		// 4-Input MUX

		if (use_mux4)
		{
			ok = ok && follow_muxtree(A, tree, bit, "AA");
			ok = ok && follow_muxtree(B, tree, bit, "AB");
			ok = ok && follow_muxtree(C, tree, bit, "BA");
			ok = ok && follow_muxtree(D, tree, bit, "BB");

			ok = ok && follow_muxtree(S1, tree, bit, "AS");
			ok = ok && follow_muxtree(S2, tree, bit, "BS");

			if (nodecode)
				ok = ok && S1 == S2;

			ok = ok && follow_muxtree(T1, tree, bit, "S");

			if (ok)
			{
				newmux_t mux;

				mux.inputs.push_back(A);
				mux.inputs.push_back(B);
				mux.inputs.push_back(C);
				mux.inputs.push_back(D);

				mux.cost += prepare_decode_mux(S1, S2, T1, bit);

				mux.selects.push_back(S1);
				mux.selects.push_back(T1);

				mux.cost += COST_MUX4;
				mux.cost += find_best_cover(tree, A);
				mux.cost += find_best_cover(tree, B);
				mux.cost += find_best_cover(tree, C);
				mux.cost += find_best_cover(tree, D);

				if (best_mux.cost > mux.cost)
					best_mux = mux;
			}
		}

		// 8-Input MUX

		if (use_mux8)
		{
			ok = ok && follow_muxtree(A, tree, bit, "AAA");
			ok = ok && follow_muxtree(B, tree, bit, "AAB");
			ok = ok && follow_muxtree(C, tree, bit, "ABA");
			ok = ok && follow_muxtree(D, tree, bit, "ABB");
			ok = ok && follow_muxtree(E, tree, bit, "BAA");
			ok = ok && follow_muxtree(F, tree, bit, "BAB");
			ok = ok && follow_muxtree(G, tree, bit, "BBA");
			ok = ok && follow_muxtree(H, tree, bit, "BBB");

			ok = ok && follow_muxtree(S1, tree, bit, "AAS");
			ok = ok && follow_muxtree(S2, tree, bit, "ABS");
			ok = ok && follow_muxtree(S3, tree, bit, "BAS");
			ok = ok && follow_muxtree(S4, tree, bit, "BBS");

			if (nodecode)
				ok = ok && S1 == S2 && S2 == S3 && S3 == S4;

			ok = ok && follow_muxtree(T1, tree, bit, "AS");
			ok = ok && follow_muxtree(T2, tree, bit, "BS");

			if (nodecode)
				ok = ok && T1 == T2;

			ok = ok && follow_muxtree(U1, tree, bit, "S");

			if (ok)
			{
				newmux_t mux;

				mux.inputs.push_back(A);
				mux.inputs.push_back(B);
				mux.inputs.push_back(C);
				mux.inputs.push_back(D);
				mux.inputs.push_back(E);
				mux.inputs.push_back(F);
				mux.inputs.push_back(G);
				mux.inputs.push_back(H);

				mux.cost += prepare_decode_mux(S1, S2, T1, bit);
				mux.cost += prepare_decode_mux(S3, S4, T2, bit);
				mux.cost += prepare_decode_mux(S1, S3, U1, bit);

				mux.cost += prepare_decode_mux(T1, T2, U1, bit);

				mux.selects.push_back(S1);
				mux.selects.push_back(T1);
				mux.selects.push_back(U1);

				mux.cost += COST_MUX8;
				mux.cost += find_best_cover(tree, A);
				mux.cost += find_best_cover(tree, B);
				mux.cost += find_best_cover(tree, C);
				mux.cost += find_best_cover(tree, D);
				mux.cost += find_best_cover(tree, E);
				mux.cost += find_best_cover(tree, F);
				mux.cost += find_best_cover(tree, G);
				mux.cost += find_best_cover(tree, H);

				if (best_mux.cost > mux.cost)
					best_mux = mux;
			}
		}

		// 16-Input MUX

		if (use_mux16)
		{
			ok = ok && follow_muxtree(A, tree, bit, "AAAA");
			ok = ok && follow_muxtree(B, tree, bit, "AAAB");
			ok = ok && follow_muxtree(C, tree, bit, "AABA");
			ok = ok && follow_muxtree(D, tree, bit, "AABB");
			ok = ok && follow_muxtree(E, tree, bit, "ABAA");
			ok = ok && follow_muxtree(F, tree, bit, "ABAB");
			ok = ok && follow_muxtree(G, tree, bit, "ABBA");
			ok = ok && follow_muxtree(H, tree, bit, "ABBB");
			ok = ok && follow_muxtree(I, tree, bit, "BAAA");
			ok = ok && follow_muxtree(J, tree, bit, "BAAB");
			ok = ok && follow_muxtree(K, tree, bit, "BABA");
			ok = ok && follow_muxtree(L, tree, bit, "BABB");
			ok = ok && follow_muxtree(M, tree, bit, "BBAA");
			ok = ok && follow_muxtree(N, tree, bit, "BBAB");
			ok = ok && follow_muxtree(O, tree, bit, "BBBA");
			ok = ok && follow_muxtree(P, tree, bit, "BBBB");

			ok = ok && follow_muxtree(S1, tree, bit, "AAAS");
			ok = ok && follow_muxtree(S2, tree, bit, "AABS");
			ok = ok && follow_muxtree(S3, tree, bit, "ABAS");
			ok = ok && follow_muxtree(S4, tree, bit, "ABBS");
			ok = ok && follow_muxtree(S5, tree, bit, "BAAS");
			ok = ok && follow_muxtree(S6, tree, bit, "BABS");
			ok = ok && follow_muxtree(S7, tree, bit, "BBAS");
			ok = ok && follow_muxtree(S8, tree, bit, "BBBS");

			if (nodecode)
				ok = ok && S1 == S2 && S2 == S3 && S3 == S4 && S4 == S5 && S5 == S6 && S6 == S7 && S7 == S8;

			ok = ok && follow_muxtree(T1, tree, bit, "AAS");
			ok = ok && follow_muxtree(T2, tree, bit, "ABS");
			ok = ok && follow_muxtree(T3, tree, bit, "BAS");
			ok = ok && follow_muxtree(T4, tree, bit, "BBS");

			if (nodecode)
				ok = ok && T1 == T2 && T2 == T3 && T3 == T4;

			ok = ok && follow_muxtree(U1, tree, bit, "AS");
			ok = ok && follow_muxtree(U2, tree, bit, "BS");

			if (nodecode)
				ok = ok && U1 == U2;

			ok = ok && follow_muxtree(V1, tree, bit, "S");

			if (ok)
			{
				newmux_t mux;

				mux.inputs.push_back(A);
				mux.inputs.push_back(B);
				mux.inputs.push_back(C);
				mux.inputs.push_back(D);
				mux.inputs.push_back(E);
				mux.inputs.push_back(F);
				mux.inputs.push_back(G);
				mux.inputs.push_back(H);
				mux.inputs.push_back(I);
				mux.inputs.push_back(J);
				mux.inputs.push_back(K);
				mux.inputs.push_back(L);
				mux.inputs.push_back(M);
				mux.inputs.push_back(N);
				mux.inputs.push_back(O);
				mux.inputs.push_back(P);

				mux.cost += prepare_decode_mux(S1, S2, T1, bit);
				mux.cost += prepare_decode_mux(S3, S4, T2, bit);
				mux.cost += prepare_decode_mux(S5, S6, T3, bit);
				mux.cost += prepare_decode_mux(S7, S8, T4, bit);
				mux.cost += prepare_decode_mux(S1, S3, U1, bit);
				mux.cost += prepare_decode_mux(S5, S7, U2, bit);
				mux.cost += prepare_decode_mux(S1, S5, V1, bit);

				mux.cost += prepare_decode_mux(T1, T2, U1, bit);
				mux.cost += prepare_decode_mux(T3, T4, U2, bit);
				mux.cost += prepare_decode_mux(T1, T3, V1, bit);

				mux.cost += prepare_decode_mux(U1, U2, V1, bit);

				mux.selects.push_back(S1);
				mux.selects.push_back(T1);
				mux.selects.push_back(U1);
				mux.selects.push_back(V1);

				mux.cost += COST_MUX16;
				mux.cost += find_best_cover(tree, A);
				mux.cost += find_best_cover(tree, B);
				mux.cost += find_best_cover(tree, C);
				mux.cost += find_best_cover(tree, D);
				mux.cost += find_best_cover(tree, E);
				mux.cost += find_best_cover(tree, F);
				mux.cost += find_best_cover(tree, G);
				mux.cost += find_best_cover(tree, H);
				mux.cost += find_best_cover(tree, I);
				mux.cost += find_best_cover(tree, J);
				mux.cost += find_best_cover(tree, K);
				mux.cost += find_best_cover(tree, L);
				mux.cost += find_best_cover(tree, M);
				mux.cost += find_best_cover(tree, N);
				mux.cost += find_best_cover(tree, O);
				mux.cost += find_best_cover(tree, P);

				if (best_mux.cost > mux.cost)
					best_mux = mux;
			}
		}

		tree.newmuxes[bit] = best_mux;
		return best_mux.cost;
	}

	void implement_best_cover(tree_t &tree, SigBit bit, int count_muxes_by_type[4])
	{
		newmux_t mux = tree.newmuxes.at(bit);

		for (auto inbit : mux.inputs)
			implement_best_cover(tree, inbit, count_muxes_by_type);

		for (auto selbit : mux.selects)
			implement_decode_mux(selbit);

		if (GetSize(mux.inputs) == 0)
			return;

		if (GetSize(mux.inputs) == 2) {
			count_muxes_by_type[0]++;
			Cell *cell = module->addCell(NEW_ID, "$_MUX_");
			cell->setPort("\\A", mux.inputs[0]);
			cell->setPort("\\B", mux.inputs[1]);
			cell->setPort("\\S", mux.selects[0]);
			cell->setPort("\\Y", bit);
			return;
		}

		if (GetSize(mux.inputs) == 4) {
			count_muxes_by_type[1]++;
			Cell *cell = module->addCell(NEW_ID, "$_MUX4_");
			cell->setPort("\\A", mux.inputs[0]);
			cell->setPort("\\B", mux.inputs[1]);
			cell->setPort("\\C", mux.inputs[2]);
			cell->setPort("\\D", mux.inputs[3]);
			cell->setPort("\\S", mux.selects[0]);
			cell->setPort("\\T", mux.selects[1]);
			cell->setPort("\\Y", bit);
			return;
		}

		if (GetSize(mux.inputs) == 8) {
			count_muxes_by_type[2]++;
			Cell *cell = module->addCell(NEW_ID, "$_MUX8_");
			cell->setPort("\\A", mux.inputs[0]);
			cell->setPort("\\B", mux.inputs[1]);
			cell->setPort("\\C", mux.inputs[2]);
			cell->setPort("\\D", mux.inputs[3]);
			cell->setPort("\\E", mux.inputs[4]);
			cell->setPort("\\F", mux.inputs[5]);
			cell->setPort("\\G", mux.inputs[6]);
			cell->setPort("\\H", mux.inputs[7]);
			cell->setPort("\\S", mux.selects[0]);
			cell->setPort("\\T", mux.selects[1]);
			cell->setPort("\\U", mux.selects[2]);
			cell->setPort("\\Y", bit);
			return;
		}

		if (GetSize(mux.inputs) == 16) {
			count_muxes_by_type[3]++;
			Cell *cell = module->addCell(NEW_ID, "$_MUX16_");
			cell->setPort("\\A", mux.inputs[0]);
			cell->setPort("\\B", mux.inputs[1]);
			cell->setPort("\\C", mux.inputs[2]);
			cell->setPort("\\D", mux.inputs[3]);
			cell->setPort("\\E", mux.inputs[4]);
			cell->setPort("\\F", mux.inputs[5]);
			cell->setPort("\\G", mux.inputs[6]);
			cell->setPort("\\H", mux.inputs[7]);
			cell->setPort("\\I", mux.inputs[8]);
			cell->setPort("\\J", mux.inputs[9]);
			cell->setPort("\\K", mux.inputs[10]);
			cell->setPort("\\L", mux.inputs[11]);
			cell->setPort("\\M", mux.inputs[12]);
			cell->setPort("\\N", mux.inputs[13]);
			cell->setPort("\\O", mux.inputs[14]);
			cell->setPort("\\P", mux.inputs[15]);
			cell->setPort("\\S", mux.selects[0]);
			cell->setPort("\\T", mux.selects[1]);
			cell->setPort("\\U", mux.selects[2]);
			cell->setPort("\\V", mux.selects[3]);
			cell->setPort("\\Y", bit);
			return;
		}

		log_abort();
	}

	void treecover(tree_t &tree)
	{
		int count_muxes_by_type[4] = {0, 0, 0, 0};
		find_best_cover(tree, tree.root);
		implement_best_cover(tree, tree.root, count_muxes_by_type);
		log("    Replaced tree at %s: %d MUX2, %d MUX4, %d MUX8, %d MUX16\n", log_signal(tree.root),
				count_muxes_by_type[0], count_muxes_by_type[1], count_muxes_by_type[2], count_muxes_by_type[3]);
		for (auto &it : tree.muxes)
			module->remove(it.second);
	}

	void run()
	{
		log("Covering MUX trees in module %s..\n", log_id(module));

		treeify();

		log("  Covering trees:\n");

		// pre-fill cache of decoder muxes
		if (!nodecode)
			for (auto &tree : tree_list) {
				find_best_cover(tree, tree.root);
				tree.newmuxes.clear();
			}

		for (auto &tree : tree_list)
			treecover(tree);

		if (!nodecode)
			log("  Added a total of %d decoder MUXes.\n", decode_mux_counter);
	}
};

struct MuxcoverPass : public Pass {
	MuxcoverPass() : Pass("muxcover", "cover trees of MUX cells with wider MUXes") { }
	virtual void help()
	{
		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
		log("\n");
		log("    muxcover [options] [selection]\n");
		log("\n");
		log("Cover trees of $_MUX_ cells with $_MUX{4,8,16}_ cells\n");
		log("\n");
		log("    -mux4, -mux8, -mux16\n");
		log("        Use the specified types of MUXes. If none of those options are used,\n");
		log("        the effect is the same as if all of them where used.\n");
		log("\n");
		log("    -nodecode\n");
		log("        Do not insert decoder logic. This reduces the number of possible\n");
		log("        substitutions, but guarantees that the resulting circuit is not\n");
		log("        less efficient than the original circuit.\n");
		log("\n");
	}
	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
	{
		log_header(design, "Executing MUXCOVER pass (mapping to wider MUXes).\n");

		bool use_mux4 = false;
		bool use_mux8 = false;
		bool use_mux16 = false;
		bool nodecode = false;

		size_t argidx;
		for (argidx = 1; argidx < args.size(); argidx++)
		{
			if (args[argidx] == "-mux4") {
				use_mux4 = true;
				continue;
			}
			if (args[argidx] == "-mux8") {
				use_mux8 = true;
				continue;
			}
			if (args[argidx] == "-mux16") {
				use_mux16 = true;
				continue;
			}
			if (args[argidx] == "-nodecode") {
				nodecode = true;
				continue;
			}
			break;
		}
		extra_args(args, argidx, design);

		if (!use_mux4 && !use_mux8 && !use_mux16) {
			use_mux4 = true;
			use_mux8 = true;
			use_mux16 = true;
		}

		for (auto module : design->selected_modules())
		{
			MuxcoverWorker worker(module);
			worker.use_mux4 = use_mux4;
			worker.use_mux8 = use_mux8;
			worker.use_mux16 = use_mux16;
			worker.nodecode = nodecode;
			worker.run();
		}
	}
} MuxcoverPass;

PRIVATE_NAMESPACE_END