diff --git a/.github/workflows/wheels.yml b/.github/workflows/wheels.yml
index 8139b5af5..9450534be 100644
--- a/.github/workflows/wheels.yml
+++ b/.github/workflows/wheels.yml
@@ -66,6 +66,7 @@ jobs:
         run: |
           mkdir -p bison
           curl -L https://ftpmirror.gnu.org/gnu/bison/bison-3.8.2.tar.gz | tar --strip-components=1 -xzC bison
+          sed -i 's/-Werror=unused//g' Makefile
       ## Software installed by default in GitHub Action Runner VMs:
       ##  https://github.com/actions/runner-images
       - if: ${{ matrix.os.family == 'macos' }}
diff --git a/CHANGELOG b/CHANGELOG
index 01faf44c2..61b221bc9 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -2,9 +2,22 @@
 List of major changes and improvements between releases
 =======================================================
 
-Yosys 0.65 .. Yosys 0.66-dev
+Yosys 0.66 .. Yosys 0.67-dev
 --------------------------
 
+Yosys 0.65 .. Yosys 0.66
+--------------------------
+ * Various
+    - C++ compiler with C++20 support is required.
+    - Please be aware that next release will also
+      migrate to CMake build system.
+ 
+ * New commands and options
+    - Added "lattice_dsp_nexus" pass for Lattice Nexus
+      DSP inference.
+    - Added "-scopename" option to "synth_gatemate" pass
+      that is propagated to "flatten".
+
 Yosys 0.64 .. Yosys 0.65
 --------------------------
  * New commands and options
diff --git a/Makefile b/Makefile
index 6ee34070d..8bb1c0b2a 100644
--- a/Makefile
+++ b/Makefile
@@ -161,7 +161,7 @@ ifeq ($(OS), Haiku)
 CXXFLAGS += -D_DEFAULT_SOURCE
 endif
 
-YOSYS_VER := 0.65
+YOSYS_VER := 0.66
 
 ifneq (, $(shell command -v git 2>/dev/null))
 ifneq (, $(shell git rev-parse --git-dir 2>/dev/null))
diff --git a/docs/source/conf.py b/docs/source/conf.py
index b85c391db..92975d3df 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -6,7 +6,7 @@ import os
 project = 'YosysHQ Yosys'
 author = 'YosysHQ GmbH'
 copyright ='2026 YosysHQ GmbH'
-yosys_ver = "0.65"
+yosys_ver = "0.66"
 
 # select HTML theme
 html_theme = 'furo-ys'
diff --git a/frontends/ast/genrtlil.cc b/frontends/ast/genrtlil.cc
index 718d5aa23..f7c5bb7bd 100644
--- a/frontends/ast/genrtlil.cc
+++ b/frontends/ast/genrtlil.cc
@@ -406,18 +406,6 @@ struct AST_INTERNAL::ProcessGenerator
 				if (GetSize(syncrule->signal) != 1)
 					always->input_error("Found posedge/negedge event on a signal that is not 1 bit wide!\n");
 				addChunkActions(syncrule->actions, subst_lvalue_from, subst_lvalue_to, true);
-				// Automatic (nosync) variables must not become flip-flops: remove
-				// them from clocked sync rules so that proc_dff does not infer
-				// an unnecessary register for a purely combinational temporary.
-				syncrule->actions.erase(
-					std::remove_if(syncrule->actions.begin(), syncrule->actions.end(),
-						[](const RTLIL::SigSig &ss) {
-							for (auto &chunk : ss.first.chunks())
-								if (chunk.wire && chunk.wire->get_bool_attribute(ID::nosync))
-									return true;
-							return false;
-						}),
-					syncrule->actions.end());
 				proc->syncs.push_back(syncrule);
 			}
 		if (proc->syncs.empty()) {
diff --git a/passes/opt/opt_clean/opt_clean.cc b/passes/opt/opt_clean/opt_clean.cc
index 87597d721..24085c34e 100644
--- a/passes/opt/opt_clean/opt_clean.cc
+++ b/passes/opt/opt_clean/opt_clean.cc
@@ -19,6 +19,7 @@
 
 #include "kernel/register.h"
 #include "kernel/log.h"
+#include "kernel/log_help.h"
 #include "passes/opt/opt_clean/opt_clean.h"
 
 USING_YOSYS_NAMESPACE
@@ -43,6 +44,12 @@ void rmunused_module(RTLIL::Module *module, bool rminit, CleanRunContext &clean_
 
 struct OptCleanPass : public Pass {
 	OptCleanPass() : Pass("opt_clean", "remove unused cells and wires") { }
+	bool formatted_help() override
+	{
+		auto *help = PrettyHelp::get_current();
+		help->set_group("passes/opt");
+		return false;
+	}
 	void help() override
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
@@ -99,6 +106,12 @@ struct OptCleanPass : public Pass {
 
 struct CleanPass : public Pass {
 	CleanPass() : Pass("clean", "remove unused cells and wires") { }
+	bool formatted_help() override
+	{
+		auto *help = PrettyHelp::get_current();
+		help->set_group("passes/opt");
+		return false;
+	}
 	void help() override
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
diff --git a/techlibs/gatemate/synth_gatemate.cc b/techlibs/gatemate/synth_gatemate.cc
index f7cdcbd12..6861b6780 100644
--- a/techlibs/gatemate/synth_gatemate.cc
+++ b/techlibs/gatemate/synth_gatemate.cc
@@ -56,6 +56,9 @@ struct SynthGateMatePass : public ScriptPass
 		log("    -noflatten\n");
 		log("        do not flatten design before synthesis.\n");
 		log("\n");
+		log("    -scopename\n");
+		log("        create 'scopename' attributes when flattening the netlist.\n");
+		log("\n");
 		log("    -nobram\n");
 		log("        do not use CC_BRAM_20K or CC_BRAM_40K cells in output netlist.\n");
 		log("\n");
@@ -94,7 +97,7 @@ struct SynthGateMatePass : public ScriptPass
 	}
 
 	string top_opt, vlog_file, json_file;
-	bool noflatten, nobram, noaddf, nomult, nomx4, nomx8, luttree, dff, retime, noiopad, noclkbuf, abc_new;
+	bool noflatten, scopename, nobram, noaddf, nomult, nomx4, nomx8, luttree, dff, retime, noiopad, noclkbuf, abc_new;
 
 	void clear_flags() override
 	{
@@ -102,6 +105,7 @@ struct SynthGateMatePass : public ScriptPass
 		vlog_file = "";
 		json_file = "";
 		noflatten = false;
+		scopename = false;
 		nobram = false;
 		noaddf = false;
 		nomult = false;
@@ -147,6 +151,10 @@ struct SynthGateMatePass : public ScriptPass
 				noflatten = true;
 				continue;
 			}
+			if (args[argidx] == "-scopename") {
+				scopename = true;
+				continue;
+			}
 			if (args[argidx] == "-nobram") {
 				nobram = true;
 				continue;
@@ -220,7 +228,8 @@ struct SynthGateMatePass : public ScriptPass
 			run("proc");
 			if (!noflatten) {
 				run("check");
-				run("flatten");
+				std::string flatten_args = scopename ? " -scopename" : "";
+				run("flatten" + flatten_args);
 			}
 			run("tribuf -logic");
 			run("deminout");
diff --git a/techlibs/lattice/Makefile.inc b/techlibs/lattice/Makefile.inc
index 9084472cf..1fb150e6c 100644
--- a/techlibs/lattice/Makefile.inc
+++ b/techlibs/lattice/Makefile.inc
@@ -1,6 +1,7 @@
 
 OBJS += techlibs/lattice/synth_lattice.o
 OBJS += techlibs/lattice/lattice_gsr.o
+OBJS += techlibs/lattice/lattice_dsp_nexus.o
 
 $(eval $(call add_share_file,share/lattice,techlibs/lattice/cells_ff.vh))
 $(eval $(call add_share_file,share/lattice,techlibs/lattice/cells_io.vh))
@@ -50,3 +51,10 @@ $(eval $(call add_share_file_and_rename,share/ecp5,techlibs/lattice/cells_bb_ecp
 $(eval $(call add_share_file,share/nexus,techlibs/lattice/parse_init.vh))
 $(eval $(call add_share_file_and_rename,share/nexus,techlibs/lattice/cells_sim_nexus.v,cells_sim.v))
 $(eval $(call add_share_file_and_rename,share/nexus,techlibs/lattice/cells_bb_nexus.v,cells_xtra.v))
+
+techlibs/lattice/%_pm.h: passes/pmgen/pmgen.py techlibs/lattice/%.pmg
+	$(P) mkdir -p $(dir $@) && $(PYTHON_EXECUTABLE) $< -o $@ -p $(notdir $*) $(filter-out $<,$^)
+
+GENFILES += techlibs/lattice/lattice_dsp_nexus_pm.h
+techlibs/lattice/lattice_dsp_nexus.o: techlibs/lattice/lattice_dsp_nexus_pm.h
+$(eval $(call add_extra_objs,techlibs/lattice/lattice_dsp_nexus_pm.h))
diff --git a/techlibs/lattice/dsp_map_nexus.v b/techlibs/lattice/dsp_map_nexus.v
index b12528309..61d2d96a8 100644
--- a/techlibs/lattice/dsp_map_nexus.v
+++ b/techlibs/lattice/dsp_map_nexus.v
@@ -77,3 +77,75 @@ module \$__NX_MUL9X9 (input [8:0] A, input [8:0] B, output [17:0] Y);
 		.Z(Y)
 	);
 endmodule
+
+module \$__NX_MAC18X18 (input [17:0] A, input [17:0] B, input [47:0] C, output [53:0] Y);
+
+	parameter A_WIDTH = 18;
+	parameter B_WIDTH = 18;
+	parameter C_WIDTH = 48;
+	parameter Y_WIDTH = 48;
+	parameter A_SIGNED = 0;
+	parameter B_SIGNED = 0;
+	parameter SUBTRACT = 0;
+
+	MULTADDSUB18X18 #(
+		.REGINPUTA("BYPASS"),
+		.REGINPUTB("BYPASS"),
+		.REGINPUTC("BYPASS"),
+		.REGOUTPUT("BYPASS")
+	) _TECHMAP_REPLACE_ (
+		.A(A), 
+		.B(B), 
+		.C({6'b0, C}),
+		.SIGNED(A_SIGNED ? 1'b1 : 1'b0), 
+		.ADDSUB(SUBTRACT ? 1'b1 : 1'b0),
+		.Z(Y)
+	);
+endmodule
+
+module \$__NX_PREADD18X18 (input [17:0] A, input [17:0] B, input [17:0] C, input CLK, output [35:0] Y);
+
+	parameter PIPELINED = 0;
+	parameter A_SIGNED = 0;
+	parameter B_SIGNED = 0;
+	parameter C_SIGNED = 0;
+
+	MULTPREADD18X18 #(
+		.REGINPUTA("BYPASS"),
+		.REGINPUTB("BYPASS"),
+		.REGINPUTC("BYPASS"),
+		.REGOUTPUT(PIPELINED ? "REGISTER" : "BYPASS")
+	) _TECHMAP_REPLACE_ (
+		.A(A),
+		.B(B),
+		.C(C),
+		.CLK(CLK),
+		.SIGNEDA(A_SIGNED ? 1'b1 : 1'b0),
+		.SIGNEDB(B_SIGNED ? 1'b1 : 1'b0),
+		.SIGNEDC(C_SIGNED ? 1'b1 : 1'b0),
+		.Z(Y)
+	);
+endmodule
+
+module \$__NX_MAC9X9WIDE_4LANE (input [8:0] A0, B0, A1, B1, A2, B2, A3, B3, output [53:0] Y);
+
+	parameter SIGNED = 0;
+
+	MULTADDSUB9X9WIDE #(
+		.REGINPUTAB0("BYPASS"),
+		.REGINPUTAB1("BYPASS"),
+		.REGINPUTAB2("BYPASS"),
+		.REGINPUTAB3("BYPASS"),
+		.REGINPUTC("BYPASS"),
+		.REGOUTPUT("BYPASS")
+	) _TECHMAP_REPLACE_ (
+		.A0(A0), .B0(B0),
+		.A1(A1), .B1(B1),
+		.A2(A2), .B2(B2),
+		.A3(A3), .B3(B3),
+		.C(54'b0),
+		.SIGNED(SIGNED ? 1'b1 : 1'b0),
+		.ADDSUB(4'b0000),
+		.Z(Y)
+	);
+endmodule
diff --git a/techlibs/lattice/lattice_dsp_nexus.cc b/techlibs/lattice/lattice_dsp_nexus.cc
new file mode 100644
index 000000000..d072c552d
--- /dev/null
+++ b/techlibs/lattice/lattice_dsp_nexus.cc
@@ -0,0 +1,36 @@
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+#include "techlibs/lattice/lattice_dsp_nexus_pm.h"
+
+struct LatticeDspNexusPass : public Pass {
+	LatticeDspNexusPass() : Pass("lattice_dsp_nexus", "Lattice Nexus DSP inference") { }
+	void help() override
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    lattice_dsp_nexus [options] [selection]\n");
+		log("\n");
+		log("Infer Lattice Nexus sysDSP macrocells (MULTADDSUB18X18, MULTPREADD18X18,\n");
+		log("MULTADDSUB9X9WIDE) from MAC and dot-product patterns.\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) override
+	{
+		log_header(design, "Executing LATTICE_DSP_NEXUS pass.\n");
+		extra_args(args, 1, design);
+
+		for (auto module : design->selected_modules()) {
+			lattice_dsp_nexus_pm pm(module, module->cells());
+			
+			pm.run_nexus_mac9_4lane(); 
+			pm.run_nexus_mac18();
+			pm.run_nexus_preadd18();
+		}
+	}
+} LatticeDspNexusPass;
+
+PRIVATE_NAMESPACE_END
\ No newline at end of file
diff --git a/techlibs/lattice/lattice_dsp_nexus.pmg b/techlibs/lattice/lattice_dsp_nexus.pmg
new file mode 100644
index 000000000..5fb828bb9
--- /dev/null
+++ b/techlibs/lattice/lattice_dsp_nexus.pmg
@@ -0,0 +1,208 @@
+pattern nexus_mac18
+
+match mul
+	select mul->type.in($mul)
+	select GetSize(port(mul, \A)) <= 18
+	select GetSize(port(mul, \B)) <= 18
+	select GetSize(port(mul, \Y)) <= 48
+endmatch
+
+match add
+	select add->type.in($add, $sub)
+	select GetSize(port(add, \Y)) <= 48
+	choice <IdString> AB {\A, \B}
+	index <SigBit> port(add, AB)[0] === port(mul, \Y)[0]
+endmatch
+
+code
+	if (mul->getParam(\A_SIGNED).as_bool() != mul->getParam(\B_SIGNED).as_bool()) {
+		reject;
+	}
+
+	{
+		SigSpec mul_out = port(mul, \Y);
+		IdString add_AB;
+
+		if (GetSize(port(add, \A)) >= GetSize(mul_out) && port(add, \A).extract(0, GetSize(mul_out)) == mul_out) {
+			add_AB = \A;
+		} else if (GetSize(port(add, \B)) >= GetSize(mul_out) && port(add, \B).extract(0, GetSize(mul_out)) == mul_out) {
+			add_AB = \B;
+		} else {
+			reject;
+		}
+
+		Cell *mac = module->addCell(NEW_ID, "$__NX_MAC18X18");
+		IdString add_C = (add_AB == \A) ? \B : \A;
+
+		mac->setPort(\A, port(mul, \A));
+		mac->setPort(\B, port(mul, \B));
+		mac->setPort(\C, port(add, add_C));
+		mac->setPort(\Y, port(add, \Y));
+		mac->setParam(\A_SIGNED, mul->getParam(\A_SIGNED)); 
+		mac->setParam(\SUBTRACT, add->type == $sub ? State::S1 : State::S0);
+
+		autoremove(mul);
+		autoremove(add);
+	}
+
+	accept;
+endcode
+
+pattern nexus_preadd18
+
+match preadd
+	select preadd->type.in($add, $sub)
+	select GetSize(port(preadd, \Y)) <= 19
+endmatch
+
+match mul
+	select mul->type.in($mul)
+	select GetSize(port(mul, \Y)) <= 48
+	choice <IdString> mul_AB {\A, \B}
+	index <SigBit> port(mul, mul_AB)[0] === port(preadd, \Y)[0]
+endmatch
+
+match pipe_ff
+	select pipe_ff->type.in($dff, $dffe, $sdff, $sdffe)
+	index <SigBit> port(pipe_ff, \D)[0] === port(mul, \Y)[0]
+	optional
+endmatch
+
+code
+	SigSpec preadd_out = port(preadd, \Y);
+	IdString actual_mul_AB;
+
+	if (GetSize(port(mul, \A)) >= GetSize(preadd_out) && port(mul, \A).extract(0, GetSize(preadd_out)) == preadd_out) {
+		actual_mul_AB = \A;
+	} else if (GetSize(port(mul, \B)) >= GetSize(preadd_out) && port(mul, \B).extract(0, GetSize(preadd_out)) == preadd_out) {
+		actual_mul_AB = \B;
+	} else {
+		reject;
+	}
+
+	{
+		Cell *mac = module->addCell(NEW_ID, "$__NX_PREADD18X18");
+
+		IdString mul_other = (actual_mul_AB == \A) ? \B : \A;
+		IdString sgn_AC = (mul_other == \A) ? \B_SIGNED : \A_SIGNED;
+		IdString sgn_B = (mul_other == \A) ? \A_SIGNED : \B_SIGNED;
+
+		SigSpec sig_A = port(preadd, \A);
+		SigSpec sig_C = port(preadd, \B);
+		SigSpec sig_B = port(mul, mul_other);
+
+		sig_A.extend_u0(18, false);
+		sig_C.extend_u0(18, false);
+		sig_B.extend_u0(18, false);
+
+		mac->setPort(\A, sig_A.extract(0, 18));
+		mac->setPort(\C, sig_C.extract(0, 18));
+		mac->setPort(\B, sig_B.extract(0, 18));
+
+		if (pipe_ff) {
+			mac->setPort(\Y, port(pipe_ff, \Q));
+			mac->setPort(\CLK, port(pipe_ff, \CLK));
+			mac->setParam(\PIPELINED, State::S1);
+		} else {
+			mac->setPort(\Y, port(mul, \Y));
+			mac->setPort(\CLK, State::S0);
+			mac->setParam(\PIPELINED, State::S0);
+		}
+
+		mac->setParam(\A_SIGNED, mul->getParam(sgn_AC));
+		mac->setParam(\B_SIGNED, mul->getParam(sgn_B));
+		mac->setParam(\C_SIGNED, mul->getParam(sgn_AC));
+
+		if (pipe_ff) autoremove(pipe_ff);
+		autoremove(mul);
+		autoremove(preadd);
+	}
+
+	accept;
+endcode
+
+pattern nexus_mac9_4lane
+
+match add_top
+	select add_top->type == $add
+endmatch
+
+match add_mid
+	select add_mid->type == $add
+	index <SigBit> port(add_mid, \Y)[0] === port(add_top, \A)[0]
+endmatch
+
+match add_bot
+	select add_bot->type == $add
+	index <SigBit> port(add_bot, \Y)[0] === port(add_mid, \A)[0]
+endmatch
+
+match mul3
+	select mul3->type == $mul
+	select GetSize(port(mul3, \A)) <= 9 && GetSize(port(mul3, \B)) <= 9
+	index <SigBit> port(mul3, \Y)[0] === port(add_top, \B)[0]
+endmatch
+
+match mul2
+	select mul2->type == $mul
+	select GetSize(port(mul2, \A)) <= 9 && GetSize(port(mul2, \B)) <= 9
+	index <SigBit> port(mul2, \Y)[0] === port(add_mid, \B)[0]
+endmatch
+
+match mul1
+	select mul1->type == $mul
+	select GetSize(port(mul1, \A)) <= 9 && GetSize(port(mul1, \B)) <= 9
+	index <SigBit> port(mul1, \Y)[0] === port(add_bot, \B)[0]
+endmatch
+
+match mul0
+	select mul0->type == $mul
+	select GetSize(port(mul0, \A)) <= 9 && GetSize(port(mul0, \B)) <= 9
+	index <SigBit> port(mul0, \Y)[0] === port(add_bot, \A)[0]
+endmatch
+
+code
+	bool is_signed = mul0->getParam(\A_SIGNED).as_bool();
+
+	if (
+		mul0->getParam(\B_SIGNED).as_bool() != is_signed ||
+		mul1->getParam(\A_SIGNED).as_bool() != is_signed ||
+		mul1->getParam(\B_SIGNED).as_bool() != is_signed ||
+		mul2->getParam(\A_SIGNED).as_bool() != is_signed ||
+		mul2->getParam(\B_SIGNED).as_bool() != is_signed ||
+		mul3->getParam(\A_SIGNED).as_bool() != is_signed ||
+		mul3->getParam(\B_SIGNED).as_bool() != is_signed
+	) {
+		reject;
+	}
+
+	{
+		Cell *mac = module->addCell(NEW_ID, "$__NX_MAC9X9WIDE_4LANE");
+		
+		auto ext9 = [&](SigSpec s) { 
+			s.extend_u0(9, is_signed); 
+			return s;
+		};
+
+		mac->setPort(\A0, ext9(port(mul0, \A)));
+		mac->setPort(\B0, ext9(port(mul0, \B)));
+		mac->setPort(\A1, ext9(port(mul1, \A)));
+		mac->setPort(\B1, ext9(port(mul1, \B)));
+		mac->setPort(\A2, ext9(port(mul2, \A)));
+		mac->setPort(\B2, ext9(port(mul2, \B)));
+		mac->setPort(\A3, ext9(port(mul3, \A)));
+		mac->setPort(\B3, ext9(port(mul3, \B)));
+		mac->setPort(\Y, port(add_top, \Y));
+		mac->setParam(\SIGNED, is_signed ? State::S1 : State::S0);
+
+		autoremove(add_top);
+		autoremove(add_mid);
+		autoremove(add_bot);
+		autoremove(mul0);
+		autoremove(mul1);
+		autoremove(mul2);
+		autoremove(mul3);
+	}
+
+	accept;
+endcode
\ No newline at end of file
diff --git a/techlibs/lattice/synth_lattice.cc b/techlibs/lattice/synth_lattice.cc
index 382dae3d8..43fb7b1c2 100644
--- a/techlibs/lattice/synth_lattice.cc
+++ b/techlibs/lattice/synth_lattice.cc
@@ -425,9 +425,12 @@ struct SynthLatticePass : public ScriptPass
 			run("opt_clean");
 
 			if (help_mode) {
+				run("lattice_dsp_nexus", "(only if -family lifcl/lfd2nx and unless -nodsp)");
 				run("techmap -map +/mul2dsp.v [...]", "(unless -nodsp)");
 				run("techmap -map +/lattice/dsp_map" + dsp_map + ".v", "(unless -nodsp)");
 			} else if (have_dsp && !nodsp) {
+				if (is_nexus)
+					run("lattice_dsp_nexus");
 				for (const auto &rule : dsp_rules) {
 					run(stringf("techmap -map +/mul2dsp.v -D DSP_A_MAXWIDTH=%d -D DSP_B_MAXWIDTH=%d -D DSP_A_MINWIDTH=%d -D DSP_B_MINWIDTH=%d -D DSP_NAME=%s",
 						rule.a_maxwidth, rule.b_maxwidth, rule.a_minwidth, rule.b_minwidth, rule.prim));
diff --git a/tests/arch/nexus/fuse_mac.sv b/tests/arch/nexus/fuse_mac.sv
new file mode 100644
index 000000000..cf16bd261
--- /dev/null
+++ b/tests/arch/nexus/fuse_mac.sv
@@ -0,0 +1,76 @@
+// https://github.com/YosysHQ/yosys/issues/5906
+
+module mac (
+	input  bit         clk, rst,
+	input  bit [17:0]  a, b,
+	input  bit         clear,
+	output bit [47:0]  p
+);
+	bit [17:0] a_r, b_r; bit clear_r; bit [47:0] p_r;
+	always_ff @(posedge clk) begin
+		if (rst) begin a_r<=0; b_r<=0; clear_r<=0; p_r<=0; end
+		else begin
+			a_r<=a; b_r<=b; clear_r<=clear;
+			p_r <= clear_r ? 48'(a_r*b_r) : 48'(p_r + 48'(a_r*b_r));
+		end
+	end
+	assign p = p_r;
+endmodule
+
+module madd_pre (
+	input  bit         clk, rst,
+	input  bit [17:0]  a, b, c, d,
+	output bit [47:0]  p
+);
+	bit [17:0] a_r, b_r, c_r, d_r; bit [47:0] m_r, p_r;
+	always_ff @(posedge clk) begin
+		if (rst) begin a_r<=0; b_r<=0; c_r<=0; d_r<=0; m_r<=0; p_r<=0; end
+		else begin
+			a_r<=a; b_r<=b; c_r<=c; d_r<=d;
+			m_r <= 48'((a_r - d_r) * b_r);
+			p_r <= 48'(m_r + 48'(c_r));
+		end
+	end
+	assign p = p_r;
+endmodule
+
+module dot4 (
+	input  bit         clk, rst,
+	input  bit [8:0]   a0, b0, a1, b1, a2, b2, a3, b3,
+	output bit [19:0]  p
+);
+	bit [8:0]  a0_r, b0_r, a1_r, b1_r, a2_r, b2_r, a3_r, b3_r;
+	bit [19:0] p_r;
+	always_ff @(posedge clk) begin
+		if (rst) begin
+			a0_r<=0; b0_r<=0; a1_r<=0; b1_r<=0;
+			a2_r<=0; b2_r<=0; a3_r<=0; b3_r<=0;
+			p_r<=0;
+		end else begin
+			a0_r<=a0; b0_r<=b0; a1_r<=a1; b1_r<=b1;
+			a2_r<=a2; b2_r<=b2; a3_r<=a3; b3_r<=b3;
+			p_r <= 20'(20'(a0_r*b0_r) + 20'(a1_r*b1_r) + 20'(a2_r*b2_r) + 20'(a3_r*b3_r));
+		end
+	end
+	assign p = p_r;
+endmodule
+
+// Oversized 24x24 MAC
+module neg_mac24 (input clk, clear, input [23:0] a, b, output [47:0] p);
+	reg [23:0] a_r, b_r; reg [47:0] p_r; reg clear_r;
+	always_ff @(posedge clk) begin
+		a_r <= a; b_r <= b; clear_r <= clear;
+		p_r <= clear_r ? 48'(a_r*b_r) : 48'(p_r + 48'(a_r*b_r));
+	end
+	assign p = p_r;
+endmodule
+
+// Dot product with mixed 9x9 and 18x18 lanes
+module neg_dot_mixed (input clk, input [8:0] a0,b0,a1,b1, input [17:0] a2, b2, output [35:0] p);
+	reg [8:0] a0_r,b0_r,a1_r,b1_r; reg [17:0] a2_r, b2_r; reg [35:0] p_r;
+	always_ff @(posedge clk) begin
+		a0_r<=a0; b0_r<=b0; a1_r<=a1; b1_r<=b1; a2_r<=a2; b2_r<=b2;
+		p_r <= 36'(36'(a0_r*b0_r) + 36'(a1_r*b1_r) + 36'(a2_r*b2_r));
+	end
+	assign p = p_r;
+endmodule
diff --git a/tests/arch/nexus/fuse_mac.ys b/tests/arch/nexus/fuse_mac.ys
new file mode 100644
index 000000000..e3e117130
--- /dev/null
+++ b/tests/arch/nexus/fuse_mac.ys
@@ -0,0 +1,35 @@
+read_verilog -sv fuse_mac.sv
+
+design -save pristine
+
+# 18x18 MAC
+design -load pristine
+hierarchy -top mac;
+synth_nexus -family lifcl -top mac
+select -assert-count 1 t:MULTADDSUB18X18
+select -assert-count 0 t:CCU2
+
+# 18x18 pre-add MAC
+design -load pristine
+hierarchy -top madd_pre;
+synth_nexus -family lifcl -top madd_pre
+select -assert-count 1 t:MULTPREADD18X18
+
+# 4-lane 9x9 dot product
+design -load pristine
+hierarchy -top dot4;
+synth_nexus -family lifcl -top dot4
+select -assert-count 1 t:MULTADDSUB9X9WIDE
+
+# 24x24 MAC
+design -load pristine
+hierarchy -top neg_mac24;
+synth_nexus -family lifcl -top neg_mac24
+select -assert-count 0 t:MULTADDSUB18X18
+
+# mixed
+design -load pristine
+hierarchy -top neg_dot_mixed;
+synth_nexus -family lifcl -top neg_dot_mixed
+select -assert-count 0 t:MULTADDSUB9X9WIDE
+select -assert-count 2 t:MULTADDSUB18X18
diff --git a/tests/common.mk b/tests/common.mk
index ef6982514..0e85e9fb9 100644
--- a/tests/common.mk
+++ b/tests/common.mk
@@ -1,9 +1,16 @@
 ROOT_DIR := $(abspath $(dir $(lastword $(MAKEFILE_LIST))))
 BUILD_DIR ?= $(ROOT_DIR)/..
+ifneq ($(wildcard $(ROOT_DIR)/../Makefile.conf),)
+include $(ROOT_DIR)/../Makefile.conf
+endif
 
 SBY   ?= sby
 YOSYS ?= $(BUILD_DIR)/yosys
+ifneq ($(ABCEXTERNAL),)
+ABC	  ?= $(ABCEXTERNAL)
+else
 ABC   ?= $(BUILD_DIR)/yosys-abc
+endif
 YOSYS_FILTERLIB ?= $(BUILD_DIR)/yosys-filterlib
 YOSYS_CONFIG ?= $(BUILD_DIR)/yosys-config
 YOSYS_SMTBMC ?= $(BUILD_DIR)/yosys-smtbmc
diff --git a/tests/verilog/automatic_lifetime.ys b/tests/verilog/automatic_lifetime.ys
index 84e21e088..7df02e67f 100644
--- a/tests/verilog/automatic_lifetime.ys
+++ b/tests/verilog/automatic_lifetime.ys
@@ -15,6 +15,7 @@ module t1(input a, b, c, output reg y);
 endmodule
 EOF
 proc
+opt_clean
 async2sync
 # no state elements for tmp
 select -assert-none t:$dff t:$dlatch %%
@@ -39,6 +40,7 @@ module t2(input [3:0] a, b, input sel, output reg [3:0] y, output reg co);
 endmodule
 EOF
 proc
+opt_clean
 async2sync
 select -assert-none t:$dff t:$dlatch %%
 sat -verify -prove-asserts -show-all
@@ -59,6 +61,7 @@ module t3(input clk, rst, input [7:0] data, output reg [7:0] result);
 endmodule
 EOF
 proc
+opt_clean
 # Exactly one DFF (for result), zero latches, no DFF for tmp
 select -assert-count 1 t:$dff %%
 select -assert-none t:$dlatch %%
@@ -80,6 +83,7 @@ module t4(input [7:0] a, b, input sub, output reg [7:0] y);
 endmodule
 EOF
 proc
+opt_clean
 async2sync
 select -assert-none t:$dff t:$dlatch %%
 sat -verify -prove-asserts -show-all
@@ -100,5 +104,6 @@ module t5(input en, d, output reg q);
 endmodule
 EOF
 proc
+opt_clean
 # No latch for tmp — X propagates instead of old value
 select -assert-none t:$dff t:$dlatch %%