yosys/passes/pmgen/peepopt_dffmux.pmg

pattern dffmux

state <IdString> cemuxAB rstmuxBA
state <SigSpec> sigD

match dff
	select dff->type == $dff
	select GetSize(port(dff, \D)) > 1
endmatch

code sigD
	sigD = port(dff, \D);
endcode

match rstmux
	select rstmux->type == $mux
	select GetSize(port(rstmux, \Y)) > 1
	index <SigSpec> port(rstmux, \Y) === sigD
	choice <IdString> BA {\B, \A}
	select port(rstmux, BA).is_fully_const()
	set rstmuxBA BA
	semioptional
endmatch

code sigD
	if (rstmux)
		sigD = port(rstmux, rstmuxBA == \B ? \A : \B);
endcode

match cemux
	select cemux->type == $mux
	select GetSize(port(cemux, \Y)) > 1
	index <SigSpec> port(cemux, \Y) === sigD
	choice <IdString> AB {\A, \B}
	index <SigSpec> port(cemux, AB) === port(dff, \Q)
	set cemuxAB AB
	semioptional
endmatch

code
	if (!cemux && !rstmux)
		reject;
endcode

code
	Const rst;
	SigSpec D;
	if (cemux) {
		D = port(cemux, cemuxAB == \A ? \B : \A);
		if (rstmux)
			rst = port(rstmux, rstmuxBA).as_const();
		else
			rst = Const(State::Sx, GetSize(D));
	}
	else {
		log_assert(rstmux);
		D = port(rstmux, rstmuxBA  == \B ? \A : \B);
		rst = port(rstmux, rstmuxBA).as_const();
	}
	SigSpec Q = port(dff, \Q);
	int width = GetSize(D);

	SigSpec &dffD = dff->connections_.at(\D);
	SigSpec &dffQ = dff->connections_.at(\Q);
	Const init;
	for (const auto &b : Q) {
		auto it = b.wire->attributes.find(\init);
		init.bits.push_back(it == b.wire->attributes.end() ? State::Sx : it->second[b.offset]);
	}

	auto cmpx = [=](State lhs, State rhs) {
		if (lhs == State::Sx || rhs == State::Sx)
			return true;
		return lhs == rhs;
	};

	int i = width;
	while (i > 2) {
		i--;
		if (D[i] != D[i-1])
			break;
		if (!cmpx(rst[i], rst[i-1]))
			break;
		if (!cmpx(init[i], init[i-1]))
			break;
		if (!cmpx(rst[i], init[i]))
			break;
		module->connect(Q[i], Q[i-1]);
		did_something = true;
	}
	if (i < width-1) {
		if (cemux) {
			SigSpec &ceA = cemux->connections_.at(\A);
			SigSpec &ceB = cemux->connections_.at(\B);
			SigSpec &ceY = cemux->connections_.at(\Y);
			ceA.remove(i, width-i);
			ceB.remove(i, width-i);
			ceY.remove(i, width-i);
			cemux->fixup_parameters();
		}
		dffD.remove(i, width-i);
		dffQ.remove(i, width-i);
		dff->fixup_parameters();

		log("dffcemux pattern in %s: dff=%s, cemux=%s; removed top %d bits.\n", log_id(module), log_id(dff), log_id(cemux), width-i);
		accept;
	}
	else if (cemux) {
		SigSpec &ceA = cemux->connections_.at(\A);
		SigSpec &ceB = cemux->connections_.at(\B);
		SigSpec &ceY = cemux->connections_.at(\Y);

		int count = 0;
		for (int i = width-1; i >= 0; i--) {
			if (D[i].wire)
				continue;
			Wire *w = Q[i].wire;
			auto it = w->attributes.find(\init);
			State init;
			if (it != w->attributes.end())
				init = it->second[Q[i].offset];
			else
				init = State::Sx;

			if (init == State::Sx || init == D[i].data) {
				count++;
				module->connect(Q[i], D[i]);
				ceA.remove(i);
				ceB.remove(i);
				ceY.remove(i);
				dffD.remove(i);
				dffQ.remove(i);
			}
		}
		if (count > 0) {
			did_something = true;
			cemux->fixup_parameters();
			dff->fixup_parameters();
			log("dffcemux pattern in %s: dff=%s, cemux=%s; removed %d constant bits.\n", log_id(module), log_id(dff), log_id(cemux), count);
		}

		accept;
	}
endcode