diff --git a/Makefile b/Makefile
index 33ff74fa4..a181a9fc2 100644
--- a/Makefile
+++ b/Makefile
@@ -953,6 +953,7 @@ MK_TEST_DIRS += tests/verilog
 
 # Tests that don't generate .mk
 SH_TEST_DIRS =
+SH_TEST_DIRS += tests/csa_tree
 SH_TEST_DIRS += tests/simple
 SH_TEST_DIRS += tests/simple_abc9
 SH_TEST_DIRS += tests/hana
diff --git a/passes/opt/Makefile.inc b/passes/opt/Makefile.inc
index e7b62fc6a..1d7833b31 100644
--- a/passes/opt/Makefile.inc
+++ b/passes/opt/Makefile.inc
@@ -23,6 +23,7 @@ OBJS += passes/opt/opt_ffinv.o
 OBJS += passes/opt/pmux2shiftx.o
 OBJS += passes/opt/muxpack.o
 OBJS += passes/opt/opt_balance_tree.o
+OBJS += passes/opt/csa_tree.o
 
 OBJS += passes/opt/peepopt.o
 GENFILES += passes/opt/peepopt_pm.h
diff --git a/passes/opt/csa_tree.cc b/passes/opt/csa_tree.cc
new file mode 100644
index 000000000..de2e28901
--- /dev/null
+++ b/passes/opt/csa_tree.cc
@@ -0,0 +1,517 @@
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+#include "kernel/macc.h"
+
+#include <queue>
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+struct Operand {
+	SigSpec sig;
+	bool is_signed;
+	bool negate;
+};
+
+struct CsaTreeWorker
+{
+	Module* module;
+	SigMap sigmap;
+
+	dict<SigBit, pool<Cell*>> bit_consumers;
+	dict<SigBit, int> fanout;
+
+	pool<Cell*> addsub_cells;
+	pool<Cell*> alu_cells;
+	pool<Cell*> macc_cells;
+
+	CsaTreeWorker(Module* module) : module(module), sigmap(module) {}
+
+	static bool is_addsub(Cell* cell)
+	{
+		return cell->type == ID($add) || cell->type == ID($sub);
+	}
+
+	static bool is_alu(Cell* cell)
+	{
+		return cell->type == ID($alu);
+	}
+
+	static bool is_macc(Cell* cell)
+	{
+		return cell->type == ID($macc) || cell->type == ID($macc_v2);
+	}
+
+	bool alu_is_subtract(Cell* cell)
+	{
+		SigSpec bi = sigmap(cell->getPort(ID::BI));
+		SigSpec ci = sigmap(cell->getPort(ID::CI));
+		return GetSize(bi) == 1 && bi[0] == State::S1 && GetSize(ci) == 1 && ci[0] == State::S1;
+	}
+
+	bool alu_is_add(Cell* cell)
+	{
+		SigSpec bi = sigmap(cell->getPort(ID::BI));
+		SigSpec ci = sigmap(cell->getPort(ID::CI));
+		return GetSize(bi) == 1 && bi[0] == State::S0 && GetSize(ci) == 1 && ci[0] == State::S0;
+	}
+
+	bool alu_is_chainable(Cell* cell)
+	{
+		if (!(alu_is_add(cell) || alu_is_subtract(cell)))
+			return false;
+
+		for (auto bit : sigmap(cell->getPort(ID::X)))
+			if (fanout.count(bit) && fanout[bit] > 0)
+				return false;
+		for (auto bit : sigmap(cell->getPort(ID::CO)))
+			if (fanout.count(bit) && fanout[bit] > 0)
+				return false;
+
+		return true;
+	}
+
+	bool is_chainable(Cell* cell)
+	{
+		return is_addsub(cell) || (is_alu(cell) && alu_is_chainable(cell));
+	}
+
+	void classify_cells()
+	{
+		for (auto cell : module->cells()) {
+			if (is_addsub(cell))
+				addsub_cells.insert(cell);
+			else if (is_alu(cell))
+				alu_cells.insert(cell);
+			else if (is_macc(cell))
+				macc_cells.insert(cell);
+		}
+	}
+
+	void build_fanout_map()
+	{
+		for (auto cell : module->cells())
+			for (auto& conn : cell->connections())
+				if (cell->input(conn.first))
+					for (auto bit : sigmap(conn.second))
+						bit_consumers[bit].insert(cell);
+
+		for (auto& pair : bit_consumers)
+			fanout[pair.first] = pair.second.size();
+
+		for (auto wire : module->wires())
+			if (wire->port_output)
+				for (auto bit : sigmap(SigSpec(wire)))
+					fanout[bit]++;
+	}
+
+	Cell* sole_chainable_consumer(SigSpec sig, const pool<Cell*>& candidates)
+	{
+		Cell* consumer = nullptr;
+		for (auto bit : sig) {
+			if (!fanout.count(bit) || fanout[bit] != 1)
+				return nullptr;
+			if (!bit_consumers.count(bit) || bit_consumers[bit].size() != 1)
+				return nullptr;
+
+			Cell* c = *bit_consumers[bit].begin();
+			if (!candidates.count(c))
+				return nullptr;
+
+			if (consumer == nullptr)
+				consumer = c;
+			else if (consumer != c)
+				return nullptr;
+		}
+		return consumer;
+	}
+
+	dict<Cell*, Cell*> find_parents(const pool<Cell*>& candidates)
+	{
+		dict<Cell*, Cell*> parent_of;
+		for (auto cell : candidates) {
+			Cell* consumer = sole_chainable_consumer(
+				sigmap(cell->getPort(ID::Y)), candidates);
+			if (consumer && consumer != cell)
+				parent_of[cell] = consumer;
+		}
+		return parent_of;
+	}
+
+	pool<Cell*> collect_chain(Cell* root, const dict<Cell*, pool<Cell*>>& children_of)
+	{
+		pool<Cell*> chain;
+		std::queue<Cell*> q;
+		q.push(root);
+		while (!q.empty()) {
+			Cell* cur = q.front(); q.pop();
+			if (!chain.insert(cur).second)
+				continue;
+			auto it = children_of.find(cur);
+			if (it != children_of.end())
+				for (auto child : it->second)
+					q.push(child);
+		}
+		return chain;
+	}
+
+	pool<SigBit> internal_bits(const pool<Cell*>& chain)
+	{
+		pool<SigBit> bits;
+		for (auto cell : chain)
+			for (auto bit : sigmap(cell->getPort(ID::Y)))
+				bits.insert(bit);
+		return bits;
+	}
+
+	static bool overlaps(SigSpec sig, const pool<SigBit>& bits)
+	{
+		for (auto bit : sig)
+			if (bits.count(bit))
+				return true;
+		return false;
+	}
+
+	bool feeds_subtracted_port(Cell* child, Cell* parent)
+	{
+		bool parent_subtracts;
+		if (parent->type == ID($sub))
+			parent_subtracts = true;
+		else if (is_alu(parent))
+			parent_subtracts = alu_is_subtract(parent);
+		else
+			return false;
+
+		if (!parent_subtracts)
+			return false;
+
+		SigSpec child_y  = sigmap(child->getPort(ID::Y));
+		SigSpec parent_b = sigmap(parent->getPort(ID::B));
+		for (auto bit : child_y)
+			for (auto pbit : parent_b)
+				if (bit == pbit)
+					return true;
+		return false;
+	}
+
+	std::vector<Operand> extract_chain_operands(
+		const pool<Cell*>& chain,
+		Cell* root,
+		const dict<Cell*, Cell*>& parent_of,
+		int& correction
+	) {
+		pool<SigBit> chain_bits = internal_bits(chain);
+		dict<Cell*, bool> negated;
+		negated[root] = false;
+		{
+			std::queue<Cell*> q;
+			q.push(root);
+			while (!q.empty()) {
+				Cell* cur = q.front(); q.pop();
+				for (auto cell : chain) {
+					if (!parent_of.count(cell) || parent_of.at(cell) != cur)
+						continue;
+					if (negated.count(cell))
+						continue;
+					negated[cell] = negated[cur] ^ feeds_subtracted_port(cell, cur);
+					q.push(cell);
+				}
+			}
+		}
+
+		std::vector<Operand> operands;
+		correction = 0;
+
+		for (auto cell : chain) {
+			bool cell_neg;
+			if (negated.count(cell))
+				cell_neg = negated[cell];
+			else
+				cell_neg = false;
+
+			SigSpec a = sigmap(cell->getPort(ID::A));
+			SigSpec b = sigmap(cell->getPort(ID::B));
+			bool a_signed = cell->getParam(ID::A_SIGNED).as_bool();
+			bool b_signed = cell->getParam(ID::B_SIGNED).as_bool();
+			bool b_sub = (cell->type == ID($sub)) || (is_alu(cell) && alu_is_subtract(cell));
+
+			if (!overlaps(a, chain_bits)) {
+				bool neg = cell_neg;
+				operands.push_back({a, a_signed, neg});
+				if (neg) correction++;
+			}
+			if (!overlaps(b, chain_bits)) {
+				bool neg = cell_neg ^ b_sub;
+				operands.push_back({b, b_signed, neg});
+				if (neg) correction++;
+			}
+		}
+		return operands;
+	}
+
+	bool extract_macc_operands(Cell* cell, std::vector<Operand>& operands, int& correction)
+	{
+		Macc macc(cell);
+		correction = 0;
+
+		for (auto& term : macc.terms) {
+			if (GetSize(term.in_b) != 0)
+				return false;
+			operands.push_back({term.in_a, term.is_signed, term.do_subtract});
+			if (term.do_subtract)
+				correction++;
+		}
+		return true;
+	}
+
+	SigSpec extend_operand(SigSpec sig, bool is_signed, int width)
+	{
+		if (GetSize(sig) < width) {
+			SigBit pad;
+			if (is_signed && GetSize(sig) > 0)
+				pad = sig[GetSize(sig) - 1];
+			else
+				pad = State::S0;
+			sig.append(SigSpec(pad, width - GetSize(sig)));
+		}
+		if (GetSize(sig) > width)
+			sig = sig.extract(0, width);
+		return sig;
+	}
+
+	SigSpec emit_not(SigSpec sig, int width)
+	{
+		SigSpec out = module->addWire(NEW_ID, width);
+		Cell* inv = module->addCell(NEW_ID, ID($not));
+		inv->setParam(ID::A_SIGNED, false);
+		inv->setParam(ID::A_WIDTH, width);
+		inv->setParam(ID::Y_WIDTH, width);
+		inv->setPort(ID::A, sig);
+		inv->setPort(ID::Y, out);
+		return out;
+	}
+
+	std::pair<SigSpec, SigSpec> emit_fa(SigSpec a, SigSpec b, SigSpec c, int width)
+	{
+		SigSpec sum  = module->addWire(NEW_ID, width);
+		SigSpec cout = module->addWire(NEW_ID, width);
+
+		Cell* fa = module->addCell(NEW_ID, ID($fa));
+		fa->setParam(ID::WIDTH, width);
+		fa->setPort(ID::A, a);
+		fa->setPort(ID::B, b);
+		fa->setPort(ID::C, c);
+		fa->setPort(ID::X, cout);
+		fa->setPort(ID::Y, sum);
+
+		SigSpec carry;
+		carry.append(State::S0);
+		carry.append(cout.extract(0, width - 1));
+		return {sum, carry};
+	}
+
+	void emit_final_add(SigSpec a, SigSpec b, SigSpec y, int width)
+	{
+		Cell* add = module->addCell(NEW_ID, ID($add));
+		add->setParam(ID::A_SIGNED, false);
+		add->setParam(ID::B_SIGNED, false);
+		add->setParam(ID::A_WIDTH, width);
+		add->setParam(ID::B_WIDTH, width);
+		add->setParam(ID::Y_WIDTH, width);
+		add->setPort(ID::A, a);
+		add->setPort(ID::B, b);
+		add->setPort(ID::Y, y);
+	}
+
+	struct DepthSig {
+		SigSpec sig;
+		int depth;
+	};
+
+	std::pair<SigSpec, SigSpec> reduce_wallace(std::vector<SigSpec>& sigs, int width, int& fa_count)
+	{
+		std::vector<DepthSig> ops;
+		ops.reserve(sigs.size());
+		for (auto& s : sigs)
+			ops.push_back({s, 0});
+
+		fa_count = 0;
+
+		for (int level = 0; ops.size() > 2; level++) {
+			log_assert(level <= 100);
+
+			std::vector<DepthSig> ready, waiting;
+			for (auto& op : ops) {
+				if (op.depth <= level)
+					ready.push_back(op);
+				else
+					waiting.push_back(op);
+			}
+
+			if (ready.size() < 3) continue;
+
+			std::vector<DepthSig> next;
+			size_t i = 0;
+			while (i + 2 < ready.size()) {
+				auto [sum, carry] = emit_fa(ready[i].sig, ready[i + 1].sig, ready[i + 2].sig, width);
+				int d = std::max({ready[i].depth, ready[i + 1].depth,ready[i + 2].depth}) + 1;
+				next.push_back({sum, d});
+				next.push_back({carry, d});
+				fa_count++;
+				i += 3;
+			}
+			for (; i < ready.size(); i++)
+				next.push_back(ready[i]);
+			for (auto& op : waiting)
+				next.push_back(op);
+
+			ops = std::move(next);
+		}
+
+		log_assert(ops.size() == 2);
+		log("    Tree depth: %d FA levels + 1 final add\n",
+			std::max(ops[0].depth, ops[1].depth));
+		return {ops[0].sig, ops[1].sig};
+	}
+
+	void replace_with_csa_tree(
+		std::vector<Operand>& operands,
+		SigSpec result_y,
+		int correction,
+		const char* desc
+	) {
+		int width = GetSize(result_y);
+		std::vector<SigSpec> extended;
+		extended.reserve(operands.size() + 1);
+
+		for (auto& op : operands) {
+			SigSpec s = extend_operand(op.sig, op.is_signed, width);
+			if (op.negate)
+				s = emit_not(s, width);
+			extended.push_back(s);
+		}
+
+		if (correction > 0)
+			extended.push_back(SigSpec(correction, width));
+
+		int fa_count;
+		auto [a, b] = reduce_wallace(extended, width, fa_count);
+
+		log("  %s → %d $fa + 1 $add (%d operands, module %s)\n",
+			desc, fa_count, (int)operands.size(), log_id(module));
+
+		emit_final_add(a, b, result_y, width);
+	}
+
+	void process_chains()
+	{
+		pool<Cell*> candidates;
+		for (auto cell : addsub_cells)
+			candidates.insert(cell);
+		for (auto cell : alu_cells)
+			if (alu_is_chainable(cell))
+				candidates.insert(cell);
+
+		if (candidates.empty())
+			return;
+
+		auto parent_of = find_parents(candidates);
+
+		dict<Cell*, pool<Cell*>> children_of;
+		pool<Cell*> has_parent;
+		for (auto& [child, parent] : parent_of) {
+			children_of[parent].insert(child);
+			has_parent.insert(child);
+		}
+
+		pool<Cell*> processed;
+		for (auto root : candidates) {
+			if (has_parent.count(root) || processed.count(root))
+				continue;
+
+			pool<Cell*> chain = collect_chain(root, children_of);
+			if (chain.size() < 2)
+				continue;
+
+			for (auto c : chain)
+				processed.insert(c);
+
+			int correction;
+			auto operands = extract_chain_operands(
+				chain, root, parent_of, correction);
+			if (operands.size() < 3)
+				continue;
+
+			replace_with_csa_tree(operands, root->getPort(ID::Y),
+				correction, "Replaced add/sub chain");
+			for (auto cell : chain)
+				module->remove(cell);
+		}
+	}
+
+	void process_maccs()
+	{
+		for (auto cell : macc_cells) {
+			std::vector<Operand> operands;
+			int correction;
+			if (!extract_macc_operands(cell, operands, correction))
+				continue;
+			if (operands.size() < 3)
+				continue;
+
+			replace_with_csa_tree(operands, cell->getPort(ID::Y),
+				correction, "Replaced $macc");
+			module->remove(cell);
+		}
+	}
+
+	void run()
+	{
+		classify_cells();
+
+		if (addsub_cells.empty() && alu_cells.empty() && macc_cells.empty())
+			return;
+
+		build_fanout_map();
+		process_chains();
+		process_maccs();
+	}
+};
+
+struct CsaTreePass : public Pass {
+	CsaTreePass() : Pass("csa_tree",
+		"convert add/sub/macc chains to carry-save adder trees") {}
+
+	void help() override
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    csa_tree [selection]\n");
+		log("\n");
+		log("This pass replaces chains of $add/$sub cells, $alu cells (with constant\n");
+		log("BI/CI), and $macc/$macc_v2 cells (without multiplications) with carry-save\n");
+		log("adder trees using $fa cells and a single final $add.\n");
+		log("\n");
+		log("The tree uses Wallace-tree scheduling: at each level, ready operands are\n");
+		log("grouped into triplets and compressed via full adders, giving\n");
+		log("O(log_{1.5} N) depth for N input operands.\n");
+		log("\n");
+	}
+
+	void execute(std::vector<std::string> args, RTLIL::Design* design) override
+	{
+		log_header(design, "Executing CSA_TREE pass.\n");
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++)
+			break;
+		extra_args(args, argidx, design);
+
+		for (auto module : design->selected_modules()) {
+			CsaTreeWorker worker(module);
+			worker.run();
+		}
+	}
+} CsaTreePass;
+
+PRIVATE_NAMESPACE_END
diff --git a/techlibs/common/synth.cc b/techlibs/common/synth.cc
index 0623bf43d..1490c6adc 100644
--- a/techlibs/common/synth.cc
+++ b/techlibs/common/synth.cc
@@ -67,6 +67,10 @@ struct SynthPass : public ScriptPass {
 		log("    -booth\n");
 		log("        run the booth pass to map $mul to Booth encoded multipliers\n");
 		log("\n");
+		log("    -csa\n");
+		log("        run the csa_tree pass to convert $add/$sub chains and $macc cells to\n");
+		log("        carry-save adder trees.\n");
+		log("\n");
 		log("    -noalumacc\n");
 		log("        do not run 'alumacc' pass. i.e. keep arithmetic operators in\n");
 		log("        their direct form ($add, $sub, etc.).\n");
@@ -108,7 +112,7 @@ struct SynthPass : public ScriptPass {
 	}
 
 	string top_module, fsm_opts, memory_opts, abc;
-	bool autotop, flatten, noalumacc, nofsm, noabc, noshare, flowmap, booth, hieropt, relative_share;
+	bool autotop, flatten, noalumacc, nofsm, noabc, noshare, flowmap, booth, csa, hieropt, relative_share;
 	int lut;
 	std::vector<std::string> techmap_maps;
 
@@ -127,6 +131,7 @@ struct SynthPass : public ScriptPass {
 		noshare = false;
 		flowmap = false;
 		booth = false;
+		csa = false;
 		hieropt = false;
 		relative_share = false;
 		abc = "abc";
@@ -187,7 +192,10 @@ struct SynthPass : public ScriptPass {
 				booth = true;
 				continue;
 			}
-
+			if (args[argidx] == "-csa") {
+				csa = true;
+				continue;
+			}
 			if (args[argidx] == "-nordff") {
 				memory_opts += " -nordff";
 				continue;
@@ -289,6 +297,8 @@ struct SynthPass : public ScriptPass {
 				run("booth", "    (if -booth)");
 			if (!noalumacc)
 				run("alumacc", "  (unless -noalumacc)");
+			if (csa || help_mode)
+				run("csa_tree", " (if -csa)");
 			if (!noshare)
 				run("share", "    (unless -noshare)");
 			run("opt" + hieropt_flag);
@@ -301,7 +311,7 @@ struct SynthPass : public ScriptPass {
 			run("memory_map");
 			run("opt -full");
 			if (help_mode) {
-				run(techmap_cmd, "                  (unless -extra-map)");	
+				run(techmap_cmd, "                  (unless -extra-map)");
 				run(techmap_cmd + " -map +/techmap.v -map <inject>", "  (if -extra-map)");
 			} else {
 				std::string techmap_opts;
diff --git a/tests/csa_tree/csa_tree_add_chains.ys b/tests/csa_tree/csa_tree_add_chains.ys
new file mode 100644
index 000000000..46e5868a9
--- /dev/null
+++ b/tests/csa_tree/csa_tree_add_chains.ys
@@ -0,0 +1,61 @@
+read_verilog <<EOT
+module add3(
+	input [7:0] a, b, c,
+	output [7:0] y
+);
+	assign y = a + b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add5(
+	input [11:0] a, b, c, d, e,
+	output [11:0] y
+);
+	assign y = a + b + c + d + e;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add8(
+	input [15:0] a, b, c, d, e, f, g, h,
+	output [15:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add16(
+	input [15:0] a0, a1, a2, a3, a4, a5, a6, a7,
+	input [15:0] a8, a9, a10, a11, a12, a13, a14, a15,
+	output [15:0] y
+);
+	assign y = a0 + a1 + a2 + a3 + a4 + a5 + a6 + a7
+	+ a8 + a9 + a10 + a11 + a12 + a13 + a14 + a15;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 14 t:$fa
+select -assert-count 1 t:$add
+design -reset
diff --git a/tests/csa_tree/csa_tree_alu_chains.ys b/tests/csa_tree/csa_tree_alu_chains.ys
new file mode 100644
index 000000000..ada1368dc
--- /dev/null
+++ b/tests/csa_tree/csa_tree_alu_chains.ys
@@ -0,0 +1,96 @@
+read_verilog <<EOT
+module alu_add3(
+	input [7:0] a, b, c,
+	output [7:0] y
+);
+	assign y = a + b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 1 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+design -reset
+
+read_verilog <<EOT
+module alu_add4(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+design -reset
+
+read_verilog <<EOT
+module alu_add5(
+	input [11:0] a, b, c, d, e,
+	output [11:0] y
+);
+	assign y = a + b + c + d + e;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+design -reset
+
+read_verilog <<EOT
+module alu_add8(
+	input [15:0] a, b, c, d, e, f, g, h,
+	output [15:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+design -reset
+
+read_verilog <<EOT
+module alu_add16(
+	input [15:0] a0, a1, a2, a3, a4, a5, a6, a7,
+	input [15:0] a8, a9, a10, a11, a12, a13, a14, a15,
+	output [15:0] y
+);
+	assign y = a0 + a1 + a2 + a3 + a4 + a5 + a6 + a7
+	+ a8 + a9 + a10 + a11 + a12 + a13 + a14 + a15;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 14 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+design -reset
diff --git a/tests/csa_tree/csa_tree_alu_macc_edge_cases.ys b/tests/csa_tree/csa_tree_alu_macc_edge_cases.ys
new file mode 100644
index 000000000..6751a58ed
--- /dev/null
+++ b/tests/csa_tree/csa_tree_alu_macc_edge_cases.ys
@@ -0,0 +1,285 @@
+read_verilog <<EOT
+module alu_add2(
+	input [7:0] a, b,
+	output [7:0] y
+);
+	assign y = a + b;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+select -assert-none t:$fa
+select -assert-none t:$add
+select -assert-none t:$sub
+select -assert-count 1 t:$alu
+design -reset
+
+read_verilog <<EOT
+module alu_sub2(
+	input [7:0] a, b,
+	output [7:0] y
+);
+	assign y = a - b;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+select -assert-none t:$fa
+select -assert-none t:$add
+select -assert-none t:$sub
+select -assert-count 1 t:$alu
+design -reset
+
+read_verilog <<EOT
+module alu_compare(
+	input [7:0] a, b,
+	output y
+);
+	assign y = (a < b);
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+select -assert-none t:$fa
+select -assert-none t:$add
+select -assert-none t:$sub
+select -assert-count 1 t:$alu
+design -reset
+
+read_verilog <<EOT
+module macc_mul(
+	input [7:0] a, b, c,
+	output [15:0] y
+);
+	assign y = a * b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-none t:$fa
+select -assert-min 1 t:$macc t:$macc_v2 %u
+design -reset
+
+read_verilog <<EOT
+module alu_fanout(
+	input [7:0] a, b, c,
+	output [7:0] mid, y
+);
+	wire [7:0] ab = a + b;
+	assign mid = ab;
+	assign y = ab + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-none t:$fa
+select -assert-count 2 t:$alu
+design -reset
+
+read_verilog <<EOT
+module macc_2port(
+	input [7:0] a, b,
+	output [7:0] y
+);
+	assign y = a + b;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-none t:$fa
+design -reset
+
+read_verilog <<EOT
+module alu_idempotent(
+	input [15:0] a, b, c, d, e, f, g, h,
+	output [15:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+
+csa_tree
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$sub
+select -assert-none t:$alu
+
+csa_tree
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$sub
+select -assert-none t:$alu
+design -reset
+
+read_verilog <<EOT
+module alu_mixed_width(
+	input [7:0] a,
+	input [3:0] b,
+	input [15:0] c,
+	input [7:0] d,
+	output [15:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module alu_signed(
+	input signed [7:0] a, b, c, d,
+	output signed [9:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module fir_4tap_alu(
+	input clk,
+	input [15:0] x, c0, c1, c2, c3,
+	output reg [31:0] y
+);
+	reg [15:0] x1, x2, x3;
+	always @(posedge clk) begin
+		x1 <= x;
+		x2 <= x1;
+		x3 <= x2;
+	end
+
+	wire [31:0] sum = x*c0 + x1*c1 + x2*c2 + x3*c3;
+	always @(posedge clk) y <= sum;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-min 1 t:$dff
+design -reset
+
+read_verilog <<EOT
+module alu_mixed_sign(
+	input signed [7:0] a,
+	input [7:0] b,
+	input signed [7:0] c,
+	output signed [9:0] y
+);
+	assign y = a + b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 1 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module alu_wide32(
+	input [31:0] a, b, c, d,
+	output [31:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module alu_single(
+	input [7:0] a,
+	output [7:0] y
+);
+	assign y = a;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+select -assert-none t:$fa
+select -assert-none t:$add
+select -assert-none t:$sub
+select -assert-none t:$alu
+design -reset
+
+read_verilog <<EOT
+module macc_mul_survives(
+	input [7:0] a, b, c, d,
+	output [15:0] y
+);
+	assign y = a * b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-none t:$fa
+select -assert-min 1 t:$macc t:$macc_v2 %u
+design -reset
diff --git a/tests/csa_tree/csa_tree_alu_macc_equiv.ys b/tests/csa_tree/csa_tree_alu_macc_equiv.ys
new file mode 100644
index 000000000..a8c60ac1a
--- /dev/null
+++ b/tests/csa_tree/csa_tree_alu_macc_equiv.ys
@@ -0,0 +1,179 @@
+read_verilog <<EOT
+module equiv_alu_add3(
+	input [3:0] a, b, c,
+	output [3:0] y
+);
+	assign y = a + b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_alu_add4(
+	input [3:0] a, b, c, d,
+	output [3:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_alu_add8(
+	input [3:0] a, b, c, d, e, f, g, h,
+	output [3:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_alu_signed(
+	input signed [3:0] a, b, c, d,
+	output signed [5:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_alu_sub_mixed(
+	input [3:0] a, b, c, d,
+	output [3:0] y
+);
+	assign y = a + b - c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+equiv_opt csa_tree
+design -load postopt
+select -assert-min 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_alu_sub_all(
+	input [3:0] a, b, c, d,
+	output [3:0] y
+);
+	assign y = a - b - c - d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+equiv_opt csa_tree
+design -load postopt
+select -assert-min 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_macc_add3(
+	input [3:0] a, b, c,
+	output [3:0] y
+);
+	assign y = a + b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_macc_add4(
+	input [3:0] a, b, c, d,
+	output [3:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_macc_add8(
+	input [3:0] a, b, c, d, e, f, g, h,
+	output [3:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_macc_signed(
+	input signed [3:0] a, b, c, d,
+	output signed [5:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
diff --git a/tests/csa_tree/csa_tree_alu_macc_sim.ys b/tests/csa_tree/csa_tree_alu_macc_sim.ys
new file mode 100644
index 000000000..7f76ac476
--- /dev/null
+++ b/tests/csa_tree/csa_tree_alu_macc_sim.ys
@@ -0,0 +1,116 @@
+read_verilog <<EOT
+module sim_alu_add4(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+
+sat -set a 1 -set b 2 -set c 3 -set d 4 -prove y 10
+sat -set a 0 -set b 0 -set c 0 -set d 0 -prove y 0
+sat -set a 255 -set b 1 -set c 0 -set d 0 -prove y 0
+sat -set a 100 -set b 50 -set c 25 -set d 25 -prove y 200
+sat -set a 255 -set b 255 -set c 255 -set d 255 -prove y 252
+design -reset
+
+read_verilog <<EOT
+module sim_alu_sub_mixed(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b - c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+
+sat -set a 10 -set b 20 -set c 5 -set d 3 -prove y 28
+sat -set a 0 -set b 0 -set c 0 -set d 0 -prove y 0
+sat -set a 100 -set b 50 -set c 30 -set d 10 -prove y 130
+design -reset
+
+read_verilog <<EOT
+module sim_alu_sub_all(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a - b - c - d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+
+sat -set a 100 -set b 10 -set c 20 -set d 30 -prove y 40
+sat -set a 0 -set b 0 -set c 0 -set d 0 -prove y 0
+sat -set a 255 -set b 1 -set c 1 -set d 1 -prove y 252
+design -reset
+
+read_verilog <<EOT
+module sim_macc_add4(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+
+sat -set a 1 -set b 2 -set c 3 -set d 4 -prove y 10
+sat -set a 0 -set b 0 -set c 0 -set d 0 -prove y 0
+sat -set a 255 -set b 1 -set c 0 -set d 0 -prove y 0
+sat -set a 100 -set b 50 -set c 25 -set d 25 -prove y 200
+design -reset
+
+read_verilog <<EOT
+module sim_macc_add8(
+	input [7:0] a, b, c, d, e, f, g, h,
+	output [7:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+
+sat -set a 1 -set b 2 -set c 3 -set d 4 -set e 5 -set f 6 -set g 7 -set h 8 -prove y 36
+sat -set a 0 -set b 0 -set c 0 -set d 0 -set e 0 -set f 0 -set g 0 -set h 0 -prove y 0
+sat -set a 32 -set b 32 -set c 32 -set d 32 -set e 32 -set f 32 -set g 32 -set h 32 -prove y 0
+design -reset
+
+read_verilog <<EOT
+module sim_macc_sub_mixed(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b - c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+
+sat -set a 10 -set b 20 -set c 5 -set d 3 -prove y 28
+sat -set a 0 -set b 0 -set c 0 -set d 0 -prove y 0
+sat -set a 100 -set b 50 -set c 30 -set d 10 -prove y 130
+design -reset
diff --git a/tests/csa_tree/csa_tree_alu_sub_chains.ys b/tests/csa_tree/csa_tree_alu_sub_chains.ys
new file mode 100644
index 000000000..c7ff5663a
--- /dev/null
+++ b/tests/csa_tree/csa_tree_alu_sub_chains.ys
@@ -0,0 +1,79 @@
+read_verilog <<EOT
+module alu_sub_3op(
+	input [7:0] a, b, c,
+	output [7:0] y
+);
+	assign y = a - b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module alu_sub_mixed(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b - c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module alu_sub_all(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a - b - c - d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module alu_sub_signed(
+	input signed [7:0] a, b, c, d,
+	output signed [9:0] y
+);
+	assign y = a + b - c - d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt_clean
+csa_tree
+opt_clean
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$alu
+select -assert-none t:$sub
+design -reset
diff --git a/tests/csa_tree/csa_tree_edge_cases.ys b/tests/csa_tree/csa_tree_edge_cases.ys
new file mode 100644
index 000000000..1031f6c2c
--- /dev/null
+++ b/tests/csa_tree/csa_tree_edge_cases.ys
@@ -0,0 +1,147 @@
+read_verilog <<EOT
+module add_1bit(
+	input a, b, c,
+	output [1:0] y
+);
+	assign y = a + b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add_1bit_wide(
+	input a, b, c, d,
+	output [3:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add_wide_out(
+	input [7:0] a, b, c, d,
+	output [31:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add_mixed(
+	input [7:0] a,
+	input [3:0] b,
+	input [15:0] c,
+	input [7:0] d,
+	output [15:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add_signed(
+	input signed [7:0] a, b, c, d,
+	output signed [9:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add_repeated(
+	input [7:0] a,
+	output [7:0] y
+);
+	assign y = a + a + a + a;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add_const(
+	input [7:0] a, b, c,
+	output [7:0] y
+);
+	assign y = a + b + c + 8'd42;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add_two(
+	input [7:0] a, b, c, d, e, f, g, h,
+	output [7:0] y1, y2
+);
+	assign y1 = a + b + c + d;
+	assign y2 = e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 4 t:$fa
+select -assert-count 2 t:$add
+design -reset
+
+read_verilog <<EOT
+module fir_4tap(
+	input clk,
+	input [15:0] x, c0, c1, c2, c3,
+	output reg [31:0] y
+);
+	reg [15:0] x1, x2, x3;
+	always @(posedge clk) begin
+		x1 <= x;
+		x2 <= x1;
+		x3 <= x2;
+	end
+
+	wire [31:0] sum = x*c0 + x1*c1 + x2*c2 + x3*c3;
+	always @(posedge clk) y <= sum;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
diff --git a/tests/csa_tree/csa_tree_equiv.ys b/tests/csa_tree/csa_tree_equiv.ys
new file mode 100644
index 000000000..e208af6c8
--- /dev/null
+++ b/tests/csa_tree/csa_tree_equiv.ys
@@ -0,0 +1,178 @@
+read_verilog <<EOT
+module equiv_add3(
+	input [3:0] a, b, c,
+	output [3:0] y
+);
+	assign y = a + b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_add4(
+	input [3:0] a, b, c, d,
+	output [3:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_add5(
+	input [3:0] a, b, c, d, e,
+	output [3:0] y
+);
+	assign y = a + b + c + d + e;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_add8(
+	input [3:0] a, b, c, d, e, f, g, h,
+	output [3:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_signed(
+	input signed [3:0] a, b, c, d,
+	output signed [5:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_mixed(
+	input [1:0] a,
+	input [3:0] b,
+	input [5:0] c,
+	output [5:0] y
+);
+	assign y = a + b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_sub_mixed(
+	input [3:0] a, b, c, d,
+	output [3:0] y
+);
+	assign y = a + b - c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_sub_all(
+	input [3:0] a, b, c, d,
+	output [3:0] y
+);
+	assign y = a - b - c - d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_sub_3op(
+	input [3:0] a, b, c,
+	output [3:0] y
+);
+	assign y = a - b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_sub_signed(
+	input signed [3:0] a, b, c, d,
+	output signed [5:0] y
+);
+	assign y = a + b - c - d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module equiv_double_neg(
+	input [3:0] a, b, c,
+	output [3:0] y
+);
+	wire [3:0] ab = a - b;
+	assign y = c - ab;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+equiv_opt csa_tree
+design -load postopt
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+design -reset
diff --git a/tests/csa_tree/csa_tree_idempotent.ys b/tests/csa_tree/csa_tree_idempotent.ys
new file mode 100644
index 000000000..dfe098597
--- /dev/null
+++ b/tests/csa_tree/csa_tree_idempotent.ys
@@ -0,0 +1,19 @@
+read_verilog <<EOT
+module add8(
+	input [15:0] a, b, c, d, e, f, g, h,
+	output [15:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+
+csa_tree
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+
+csa_tree
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$sub
diff --git a/tests/csa_tree/csa_tree_macc.ys b/tests/csa_tree/csa_tree_macc.ys
new file mode 100644
index 000000000..4c2490e34
--- /dev/null
+++ b/tests/csa_tree/csa_tree_macc.ys
@@ -0,0 +1,133 @@
+read_verilog <<EOT
+module macc_add3(
+	input [7:0] a, b, c,
+	output [7:0] y
+);
+	assign y = a + b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-count 1 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$macc t:$macc_v2 %u
+design -reset
+
+read_verilog <<EOT
+module macc_add4(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$macc t:$macc_v2 %u
+design -reset
+
+read_verilog <<EOT
+module macc_add5(
+	input [11:0] a, b, c, d, e,
+	output [11:0] y
+);
+	assign y = a + b + c + d + e;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$macc t:$macc_v2 %u
+design -reset
+
+read_verilog <<EOT
+module macc_add8(
+	input [15:0] a, b, c, d, e, f, g, h,
+	output [15:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-count 6 t:$fa
+select -assert-count 1 t:$add
+select -assert-none t:$macc t:$macc_v2 %u
+design -reset
+
+read_verilog <<EOT
+module macc_sub_mixed(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b - c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-none t:$macc t:$macc_v2 %u
+select -assert-min 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module macc_const(
+	input [7:0] a, b, c,
+	output [7:0] y
+);
+	assign y = a + b + c + 8'd42;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-none t:$macc t:$macc_v2 %u
+select -assert-min 1 t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module macc_two(
+	input [7:0] a, b, c, d, e, f, g, h,
+	output [7:0] y1, y2
+);
+	assign y1 = a + b + c + d;
+	assign y2 = e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+alumacc
+opt
+csa_tree
+opt_clean
+select -assert-none t:$macc t:$macc_v2 %u
+select -assert-count 4 t:$fa
+select -assert-count 2 t:$add
+design -reset
diff --git a/tests/csa_tree/csa_tree_negative.ys b/tests/csa_tree/csa_tree_negative.ys
new file mode 100644
index 000000000..1cdcf3deb
--- /dev/null
+++ b/tests/csa_tree/csa_tree_negative.ys
@@ -0,0 +1,77 @@
+read_verilog <<EOT
+module add2(
+	input [7:0] a, b,
+	output [7:0] y
+);
+	assign y = a + b;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-none t:$fa
+select -assert-count 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add_fanout(
+	input [7:0] a, b, c,
+	output [7:0] mid, y
+);
+	wire [7:0] ab = a + b;
+	assign mid = ab;
+	assign y = ab + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-none t:$fa
+design -reset
+
+read_verilog <<EOT
+module sub2(
+	input [7:0] a, b,
+	output [7:0] y
+);
+	assign y = a - b;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-none t:$fa
+select -assert-count 1 t:$sub
+design -reset
+
+read_verilog <<EOT
+module add_multi_const(
+	input [7:0] x,
+	output [7:0] y
+);
+	assign y = 8'd1 + 8'd2 + 8'd3 + x;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-none t:$fa
+select -assert-max 1 t:$add
+design -reset
+
+read_verilog <<EOT
+module add_partial(
+	input [7:0] a, b, c, d, e,
+	output [7:0] mid, y
+);
+	wire [7:0] ab = a + b;
+	assign mid = ab;
+	assign y = ab + c + d + e;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 2 t:$add
+design -reset
diff --git a/tests/csa_tree/csa_tree_sim.ys b/tests/csa_tree/csa_tree_sim.ys
new file mode 100644
index 000000000..7f6cbd1c8
--- /dev/null
+++ b/tests/csa_tree/csa_tree_sim.ys
@@ -0,0 +1,72 @@
+read_verilog <<EOT
+module sim_add4(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b + c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+
+sat -set a 1 -set b 2 -set c 3 -set d 4 -prove y 10
+sat -set a 0 -set b 0 -set c 0 -set d 0 -prove y 0
+sat -set a 255 -set b 1 -set c 0 -set d 0 -prove y 0
+sat -set a 100 -set b 50 -set c 25 -set d 25 -prove y 200
+sat -set a 255 -set b 255 -set c 255 -set d 255 -prove y 252
+design -reset
+
+read_verilog <<EOT
+module sim_sub_mixed(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b - c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+
+sat -set a 10 -set b 20 -set c 5 -set d 3 -prove y 28
+sat -set a 0 -set b 0 -set c 0 -set d 0 -prove y 0
+sat -set a 100 -set b 50 -set c 30 -set d 10 -prove y 130
+sat -set a 1 -set b 1 -set c 255 -set d 1 -prove y 4
+design -reset
+
+read_verilog <<EOT
+module sim_sub_all(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a - b - c - d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+
+sat -set a 100 -set b 10 -set c 20 -set d 30 -prove y 40
+sat -set a 0 -set b 0 -set c 0 -set d 0 -prove y 0
+sat -set a 255 -set b 1 -set c 1 -set d 1 -prove y 252
+design -reset
+
+read_verilog <<EOT
+module sim_double_neg(
+	input [7:0] a, b, c,
+	output [7:0] y
+);
+	wire [7:0] ab = a - b;
+	assign y = c - ab;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+
+sat -set a 30 -set b 20 -set c 10 -prove y 0
+sat -set a 50 -set b 25 -set c 100 -prove y 75
+sat -set a 0 -set b 0 -set c 0 -prove y 0
+sat -set a 255 -set b 1 -set c 1 -prove y 3
+design -reset
diff --git a/tests/csa_tree/csa_tree_sub_chains.ys b/tests/csa_tree/csa_tree_sub_chains.ys
new file mode 100644
index 000000000..7f7ac1c34
--- /dev/null
+++ b/tests/csa_tree/csa_tree_sub_chains.ys
@@ -0,0 +1,102 @@
+read_verilog <<EOT
+module sub_3op(
+	input [7:0] a, b, c,
+	output [7:0] y
+);
+	assign y = a - b + c;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+select -assert-count 1 t:$not
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module sub_mixed(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a + b - c + d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+select -assert-count 1 t:$not
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module sub_all(
+	input [7:0] a, b, c, d,
+	output [7:0] y
+);
+	assign y = a - b - c - d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+select -assert-count 3 t:$not
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module sub_5op(
+	input [11:0] a, b, c, d, e,
+	output [11:0] y
+);
+	assign y = a - b + c - d + e;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 4 t:$fa
+select -assert-count 1 t:$add
+select -assert-count 2 t:$not
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module sub_signed(
+	input signed [7:0] a, b, c, d,
+	output signed [9:0] y
+);
+	assign y = a + b - c - d;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 3 t:$fa
+select -assert-count 1 t:$add
+select -assert-count 2 t:$not
+select -assert-none t:$sub
+design -reset
+
+read_verilog <<EOT
+module sub_double_neg(
+	input [7:0] a, b, c,
+	output [7:0] y
+);
+	wire [7:0] ab = a - b;
+	assign y = c - ab;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+csa_tree
+select -assert-count 2 t:$fa
+select -assert-count 1 t:$add
+select -assert-count 1 t:$not
+select -assert-none t:$sub
+design -reset
diff --git a/tests/csa_tree/csa_tree_synth.ys b/tests/csa_tree/csa_tree_synth.ys
new file mode 100644
index 000000000..2ed1fe32c
--- /dev/null
+++ b/tests/csa_tree/csa_tree_synth.ys
@@ -0,0 +1,70 @@
+# Assert against abc synth with and without csa, hopefully prevent regressions
+# Baseline
+read_verilog <<EOT
+module bench(
+	input [7:0] a, b, c, d, e, f, g, h,
+	output [7:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+opt
+techmap
+abc -g AND,OR,XOR
+select -assert-min 236 t:$_AND_ t:$_OR_ t:$_XOR_ %u
+design -reset
+
+# With csa_tree
+read_verilog <<EOT
+module bench(
+	input [7:0] a, b, c, d, e, f, g, h,
+	output [7:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+opt
+csa_tree
+techmap
+abc -g AND,OR,XOR
+select -assert-max 235 t:$_AND_ t:$_OR_ t:$_XOR_ %u
+design -reset
+
+# Depth-otimal baseline
+read_verilog <<EOT
+module bench(
+	input [7:0] a, b, c, d, e, f, g, h,
+	output [7:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+opt
+techmap
+abc -D 1
+select -assert-min 240 t:$_AND_ t:$_NAND_ t:$_OR_ t:$_NOR_ t:$_XOR_ t:$_XNOR_ t:$_NOT_ %u
+design -reset
+
+# Depth-optimal with csa_tree
+read_verilog <<EOT
+module bench(
+	input [7:0] a, b, c, d, e, f, g, h,
+	output [7:0] y
+);
+	assign y = a + b + c + d + e + f + g + h;
+endmodule
+EOT
+hierarchy -auto-top
+proc
+opt
+csa_tree
+techmap
+abc -D 1
+select -assert-max 236 t:$_AND_ t:$_NAND_ t:$_OR_ t:$_NOR_ t:$_XOR_ t:$_XNOR_ t:$_NOT_ %u
+design -reset
diff --git a/tests/csa_tree/run-test.sh b/tests/csa_tree/run-test.sh
new file mode 100755
index 000000000..0ef575c48
--- /dev/null
+++ b/tests/csa_tree/run-test.sh
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+source ../common-env.sh
+set -e
+for x in *.ys; do
+	echo "Running $x.."
+	../../yosys -ql ${x%.ys}.log $x
+done