yosys/passes/opt/pmux2shiftx.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

struct Pmux2ShiftxPass : public Pass {
	Pmux2ShiftxPass() : Pass("pmux2shiftx", "transform $pmux cells to $shiftx cells") { }
	void help() YS_OVERRIDE
	{
		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
		log("\n");
		log("    pmux2shiftx [selection]\n");
		log("\n");
		log("This pass transforms $pmux cells to $shiftx cells.\n");
		log("\n");
	}
	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
	{
		log_header(design, "Executing PMUX2SHIFTX pass.\n");

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

		for (auto module : design->selected_modules())
		{
			SigMap sigmap(module);

			dict<SigBit, pair<SigSpec, Const>> eqdb;

			for (auto cell : module->selected_cells())
			{
				if (cell->type == "$eq")
				{
					dict<SigBit, State> bits;

					SigSpec A = sigmap(cell->getPort("\\A"));
					SigSpec B = sigmap(cell->getPort("\\B"));

					int a_width = cell->getParam("\\A_WIDTH").as_int();
					int b_width = cell->getParam("\\B_WIDTH").as_int();

					if (a_width < b_width) {
						bool a_signed = cell->getParam("\\A_SIGNED").as_int();
						A.extend_u0(b_width, a_signed);
					}

					if (b_width < a_width) {
						bool b_signed = cell->getParam("\\B_SIGNED").as_int();
						B.extend_u0(a_width, b_signed);
					}

					for (int i = 0; i < GetSize(A); i++) {
						SigBit a_bit = A[i], b_bit = B[i];
						if (b_bit.wire && !a_bit.wire) {
							std::swap(a_bit, b_bit);
						}
						if (!a_bit.wire || b_bit.wire)
							goto next_cell;
						if (bits.count(a_bit))
							goto next_cell;
						bits[a_bit] = b_bit.data;
					}

					if (GetSize(bits) > 20)
						goto next_cell;

					bits.sort();
					pair<SigSpec, Const> entry;

					for (auto it : bits) {
						entry.first.append_bit(it.first);
						entry.second.bits.push_back(it.second);
					}

					eqdb[sigmap(cell->getPort("\\Y")[0])] = entry;
					goto next_cell;
				}

				if (cell->type == "$logic_not")
				{
					dict<SigBit, State> bits;

					SigSpec A = sigmap(cell->getPort("\\A"));

					for (int i = 0; i < GetSize(A); i++)
						bits[A[i]] = State::S0;

					bits.sort();
					pair<SigSpec, Const> entry;

					for (auto it : bits) {
						entry.first.append_bit(it.first);
						entry.second.bits.push_back(it.second);
					}

					eqdb[sigmap(cell->getPort("\\Y")[0])] = entry;
					goto next_cell;
				}
		next_cell:;
			}

			for (auto cell : module->selected_cells())
			{
				if (cell->type != "$pmux")
					continue;

				string src = cell->get_src_attribute();
				int width = cell->getParam("\\WIDTH").as_int();
				int width_bits = ceil_log2(width);
				int extwidth = width;

				while (extwidth & (extwidth-1))
					extwidth++;

				dict<SigSpec, pool<int>> seldb;

				SigSpec S = sigmap(cell->getPort("\\S"));
				for (int i = 0; i < GetSize(S); i++)
				{
					if (!eqdb.count(S[i]))
						continue;

					auto &entry = eqdb.at(S[i]);
					seldb[entry.first].insert(i);
				}

				if (seldb.empty())
					continue;

				log("Inspecting $pmux cell %s/%s.\n", log_id(module), log_id(cell));
				log("  data width: %d (next power-of-2 = %d, log2 = %d)\n", width, extwidth, width_bits);

				SigSpec updated_S = cell->getPort("\\S");
				SigSpec updated_B = cell->getPort("\\B");

			#if 1
				for (auto &it : seldb) {
					string msg = stringf("seldb: %s ->", log_signal(it.first));
					for (int i : it.second)
						msg += stringf(" %d(%s)", i, log_signal(eqdb.at(S[i]).second));
					log("  %s\n", msg.c_str());
				}
			#endif

				while (!seldb.empty())
				{
					// pick the largest entry in seldb
					SigSpec sig = seldb.begin()->first;
					for (auto &it : seldb) {
						if (GetSize(sig) < GetSize(it.first))
							sig = it.first;
						else if (GetSize(seldb.at(sig)) < GetSize(it.second))
							sig = it.first;
					}

					log("  checking ctrl signal %s\n", log_signal(sig));

					// find the relevant choices
					dict<Const, int> choices;
					vector<int> onescnt(GetSize(sig));
					for (int i : seldb.at(sig)) {
						Const val = eqdb.at(S[i]).second;
						choices[val] = i;
						for (int k = 0; k < GetSize(val); k++)
							if (val[k] == State::S1)
								onescnt[k] |= 1;
							else
								onescnt[k] |= 2;
					}

					// TBD: also find choices that are using signals that are subsets of the bits in "sig"

					// find the best permutation
					vector<pair<int, int>> perm(GetSize(sig));
					for (int i = 0; i < GetSize(onescnt); i++)
						perm[i] = make_pair(onescnt[i], i);
					// TBD: this is not the best permutation
					std::sort(perm.rbegin(), perm.rend());

					// permutated sig
					Const perm_xormask(State::S0, GetSize(sig));
					SigSpec perm_sig(State::S0, GetSize(sig));
					for (int i = 0; i < GetSize(sig); i++) {
						if (perm[i].first == 1)
							perm_xormask[i] = State::S1;
						perm_sig[i] = sig[perm[i].second];
					}

					log("    best permutation: %s\n", log_signal(perm_sig));
					log("    best xor mask: %s\n", log_signal(perm_xormask));

					// permutated choices
					int min_choice = 1 << 30;
					int max_choice = -1;
					dict<Const, int> perm_choices;

					for (auto &it : choices)
					{
						Const &old_c = it.first;
						Const new_c(State::S0, GetSize(old_c));

						for (int i = 0; i < GetSize(old_c); i++)
							new_c[i] = old_c[perm[i].second];

						Const new_c_before_xor = new_c;
						new_c = const_xor(new_c, perm_xormask, false, false, GetSize(new_c));

						perm_choices[new_c] = it.second;

						min_choice = std::min(min_choice, new_c.as_int());
						max_choice = std::max(max_choice, new_c.as_int());

						log("      %s -> %s -> %s\n", log_signal(old_c), log_signal(new_c_before_xor), log_signal(new_c));
					}

					log("    choices: %d\n", GetSize(choices));
					log("    min choice: %d\n", min_choice);
					log("    max choice: %d\n", max_choice);
					log("    range density: %d%%\n", 100*GetSize(choices)/(max_choice-min_choice+1));
					log("    absolute density: %d%%\n", 100*GetSize(choices)/(max_choice+1));

					bool full_case = (min_choice == 0) && (max_choice == (1 << GetSize(sig))-1) && (max_choice+1 == GetSize(choices));
					log("    full case: %s\n", full_case ? "true" : "false");

					// use arithmetic offset if density is less than 30%
					Const offset(State::S0, GetSize(sig));
					if (3*GetSize(choices) < max_choice && 3*GetSize(choices) >= (max_choice-min_choice))
					{
						log("    using offset method.\n");

						offset = Const(min_choice, GetSize(sig));
						min_choice -= offset.as_int();
						max_choice -= offset.as_int();

						dict<Const, int> new_perm_choices;
						for (auto &it : perm_choices)
							new_perm_choices[const_sub(it.first, offset, false, false, GetSize(sig))] = it.second;
						perm_choices.swap(new_perm_choices);
					}

					// ignore cases with a absolute density of less than 30%
					if (3*GetSize(choices) < max_choice) {
						log("    insufficient density.\n");
						seldb.erase(sig);
						continue;
					}

					// creat cmp signal
					SigSpec cmp = perm_sig;
					if (perm_xormask.as_bool())
						cmp = module->Xor(NEW_ID, cmp, perm_xormask, false, src);
					if (offset.as_bool())
						cmp = module->Sub(NEW_ID, cmp, offset, false, src);

					// create enable signal
					SigBit en = State::S1;
					if (!full_case) {
						Const enable_mask(State::S0, max_choice+1);
						for (auto &it : perm_choices)
							enable_mask[it.first.as_int()] = State::S1;
						en = module->addWire(NEW_ID);
						module->addShift(NEW_ID, enable_mask, cmp, en, false, src);
					}

					// create data signal
					SigSpec data(State::Sx, (max_choice+1)*extwidth);
					for (auto &it : perm_choices) {
						int position = it.first.as_int()*extwidth;
						int data_index = it.second;
						data.replace(position, cell->getPort("\\B").extract(data_index*width, width));
						updated_S[data_index] = State::S0;
						updated_B.replace(data_index*width, SigSpec(State::Sx, width));
					}

					// create shiftx cell
					SigSpec shifted_cmp = {cmp, SigSpec(State::S0, width_bits)};
					SigSpec outsig = module->addWire(NEW_ID, width);
					Cell *c = module->addShiftx(NEW_ID, data, shifted_cmp, outsig, false, src);
					updated_S.append(en);
					updated_B.append(outsig);
					log("    created $shiftx cell %s.\n", log_id(c));

					// remove this sig and continue with the next block
					seldb.erase(sig);
				}

				// update $pmux cell
				cell->setPort("\\S", updated_S);
				cell->setPort("\\B", updated_B);
				cell->setParam("\\S_WIDTH", GetSize(updated_S));
			}
		}
	}
} Pmux2ShiftxPass;

PRIVATE_NAMESPACE_END