diff --git a/CHANGELOG b/CHANGELOG
index ae7d28236..44d83c1bf 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -13,6 +13,7 @@ Yosys 0.9 .. Yosys 0.9-dev
     - Added "synth_ice40 -abc9" (experimental)
     - Added "synth -abc9" (experimental)
     - Added "script -scriptwire
+    - "synth_xilinx" to now infer wide multiplexers (-widemux <min> to enable)
 
 
 Yosys 0.8 .. Yosys 0.8-dev
diff --git a/backends/aiger/xaiger.cc b/backends/aiger/xaiger.cc
index 632a5c8d5..a1085addf 100644
--- a/backends/aiger/xaiger.cc
+++ b/backends/aiger/xaiger.cc
@@ -21,13 +21,15 @@
 // https://stackoverflow.com/a/46137633
 #ifdef _MSC_VER
 #include <stdlib.h>
-#define __builtin_bswap32 _byteswap_ulong
+#define bswap32 _byteswap_ulong
 #elif defined(__APPLE__)
 #include <libkern/OSByteOrder.h>
-#define __builtin_bswap32 OSSwapInt32
-#elif !defined(__GNUC__)
+#define bswap32 OSSwapInt32
+#elif defined(__GNUC__)
+#define bswap32 __builtin_bswap32
+#else
 #include <cstdint>
-inline uint32_t __builtin_bswap32(uint32_t x)
+inline static uint32_t bswap32(uint32_t x)
 {
 	// https://stackoverflow.com/a/27796212
 	register uint32_t value = number_to_be_reversed;
@@ -145,6 +147,7 @@ struct XAigerWriter
 	{
 		pool<SigBit> undriven_bits;
 		pool<SigBit> unused_bits;
+		pool<SigBit> keep_bits;
 
 		// promote public wires
 		for (auto wire : module->wires())
@@ -183,6 +186,9 @@ struct XAigerWriter
 					unused_bits.insert(bit);
 				}
 
+				if (keep)
+					keep_bits.insert(bit);
+
 				if (wire->port_input || keep) {
 					if (bit != wirebit)
 						alias_map[bit] = wirebit;
@@ -260,7 +266,7 @@ struct XAigerWriter
 				continue;
 			}
 
-			RTLIL::Module* inst_module = !holes_mode ? module->design->module(cell->type) : nullptr;
+			RTLIL::Module* inst_module = module->design->module(cell->type);
 			if (inst_module && inst_module->attributes.count("\\abc_box_id")) {
 				abc_box_seen = true;
 
@@ -319,10 +325,11 @@ struct XAigerWriter
 				}
 			}
 			else {
+				bool cell_known = cell->known();
 				for (const auto &c : cell->connections()) {
 					if (c.second.is_fully_const()) continue;
-					auto is_input = cell->input(c.first);
-					auto is_output = cell->output(c.first);
+					auto is_input = !cell_known || cell->input(c.first);
+					auto is_output = !cell_known || cell->output(c.first);
 					if (!is_input && !is_output)
 						log_error("Connection '%s' on cell '%s' (type '%s') not recognised!\n", log_id(c.first), log_id(cell), log_id(cell->type));
 
@@ -330,12 +337,15 @@ struct XAigerWriter
 						for (auto b : c.second.bits()) {
 							Wire *w = b.wire;
 							if (!w) continue;
-							if (!w->port_output) {
+							if (!w->port_output || !cell_known) {
 								SigBit I = sigmap(b);
 								if (I != b)
 									alias_map[b] = I;
 								output_bits.insert(b);
 								unused_bits.erase(b);
+
+								if (!cell_known)
+									keep_bits.insert(b);
 							}
 						}
 					}
@@ -488,7 +498,7 @@ struct XAigerWriter
 
 							auto jt = input_bits.find(b);
 							if (jt != input_bits.end()) {
-								log_assert(b.wire->attributes.count("\\keep"));
+								log_assert(keep_bits.count(O));
 								input_bits.erase(b);
 							}
 						}
@@ -508,7 +518,7 @@ struct XAigerWriter
 			// with $inout.out suffix, make it a PO driven by the existing inout, and
 			// inherit existing inout's drivers
 			if ((wire->port_input && wire->port_output && !undriven_bits.count(bit))
-					|| wire->attributes.count("\\keep")) {
+					|| keep_bits.count(bit)) {
 				RTLIL::IdString wire_name = wire->name.str() + "$inout.out";
 				RTLIL::Wire *new_wire = module->wire(wire_name);
 				if (!new_wire)
diff --git a/backends/ilang/ilang_backend.cc b/backends/ilang/ilang_backend.cc
index b4ba2b03f..313af7d5c 100644
--- a/backends/ilang/ilang_backend.cc
+++ b/backends/ilang/ilang_backend.cc
@@ -204,6 +204,11 @@ void ILANG_BACKEND::dump_proc_switch(std::ostream &f, std::string indent, const
 
 	for (auto it = sw->cases.begin(); it != sw->cases.end(); ++it)
 	{
+		for (auto ait = (*it)->attributes.begin(); ait != (*it)->attributes.end(); ++ait) {
+			f << stringf("%s  attribute %s ", indent.c_str(), ait->first.c_str());
+			dump_const(f, ait->second);
+			f << stringf("\n");
+		}
 		f << stringf("%s  case ", indent.c_str());
 		for (size_t i = 0; i < (*it)->compare.size(); i++) {
 			if (i > 0)
diff --git a/backends/verilog/verilog_backend.cc b/backends/verilog/verilog_backend.cc
index 827af5d85..087c6fec6 100644
--- a/backends/verilog/verilog_backend.cc
+++ b/backends/verilog/verilog_backend.cc
@@ -364,20 +364,22 @@ void dump_sigspec(std::ostream &f, const RTLIL::SigSpec &sig)
 	}
 }
 
-void dump_attributes(std::ostream &f, std::string indent, dict<RTLIL::IdString, RTLIL::Const> &attributes, char term = '\n', bool modattr = false)
+void dump_attributes(std::ostream &f, std::string indent, dict<RTLIL::IdString, RTLIL::Const> &attributes, char term = '\n', bool modattr = false, bool as_comment = false)
 {
 	if (noattr)
 		return;
+	if (attr2comment)
+		as_comment = true;
 	for (auto it = attributes.begin(); it != attributes.end(); ++it) {
-		f << stringf("%s" "%s %s", indent.c_str(), attr2comment ? "/*" : "(*", id(it->first).c_str());
+		f << stringf("%s" "%s %s", indent.c_str(), as_comment ? "/*" : "(*", id(it->first).c_str());
 		f << stringf(" = ");
 		if (modattr && (it->second == Const(0, 1) || it->second == Const(0)))
 			f << stringf(" 0 ");
 		else if (modattr && (it->second == Const(1, 1) || it->second == Const(1)))
 			f << stringf(" 1 ");
 		else
-			dump_const(f, it->second, -1, 0, false, attr2comment);
-		f << stringf(" %s%c", attr2comment ? "*/" : "*)", term);
+			dump_const(f, it->second, -1, 0, false, as_comment);
+		f << stringf(" %s%c", as_comment ? "*/" : "*)", term);
 	}
 }
 
@@ -1492,12 +1494,14 @@ void dump_proc_switch(std::ostream &f, std::string indent, RTLIL::SwitchRule *sw
 		return;
 	}
 
+	dump_attributes(f, indent, sw->attributes);
 	f << stringf("%s" "casez (", indent.c_str());
 	dump_sigspec(f, sw->signal);
 	f << stringf(")\n");
 
 	bool got_default = false;
 	for (auto it = sw->cases.begin(); it != sw->cases.end(); ++it) {
+		dump_attributes(f, indent + "  ", (*it)->attributes, '\n', /*modattr=*/false, /*as_comment=*/true);
 		if ((*it)->compare.size() == 0) {
 			if (got_default)
 				continue;
@@ -1662,7 +1666,7 @@ void dump_module(std::ostream &f, std::string indent, RTLIL::Module *module)
 		}
 	}
 
-	dump_attributes(f, indent, module->attributes, '\n', true);
+	dump_attributes(f, indent, module->attributes, '\n', /*attr2comment=*/true);
 	f << stringf("%s" "module %s(", indent.c_str(), id(module->name, false).c_str());
 	bool keep_running = true;
 	for (int port_id = 1; keep_running; port_id++) {
diff --git a/frontends/ast/genrtlil.cc b/frontends/ast/genrtlil.cc
index 079fc11e5..571ddd988 100644
--- a/frontends/ast/genrtlil.cc
+++ b/frontends/ast/genrtlil.cc
@@ -504,6 +504,7 @@ struct AST_INTERNAL::ProcessGenerator
 
 					RTLIL::CaseRule *backup_case = current_case;
 					current_case = new RTLIL::CaseRule;
+					current_case->attributes["\\src"] = stringf("%s:%d", child->filename.c_str(), child->linenum);
 					last_generated_case = current_case;
 					addChunkActions(current_case->actions, this_case_eq_ltemp, this_case_eq_rvalue);
 					for (auto node : child->children) {
diff --git a/frontends/ilang/ilang_parser.y b/frontends/ilang/ilang_parser.y
index 44c99906a..b4b9693da 100644
--- a/frontends/ilang/ilang_parser.y
+++ b/frontends/ilang/ilang_parser.y
@@ -282,14 +282,14 @@ proc_stmt:
 	} case_body sync_list TOK_END EOL;
 
 switch_stmt:
-	attr_list TOK_SWITCH sigspec EOL {
+	TOK_SWITCH sigspec EOL {
 		RTLIL::SwitchRule *rule = new RTLIL::SwitchRule;
-		rule->signal = *$3;
+		rule->signal = *$2;
 		rule->attributes = attrbuf;
 		switch_stack.back()->push_back(rule);
 		attrbuf.clear();
-		delete $3;
-	} switch_body TOK_END EOL;
+		delete $2;
+	} attr_list switch_body TOK_END EOL;
 
 attr_list:
 	/* empty */ |
@@ -298,9 +298,11 @@ attr_list:
 switch_body:
 	switch_body TOK_CASE {
 		RTLIL::CaseRule *rule = new RTLIL::CaseRule;
+		rule->attributes = attrbuf;
 		switch_stack.back()->back()->cases.push_back(rule);
 		switch_stack.push_back(&rule->switches);
 		case_stack.push_back(rule);
+		attrbuf.clear();
 	} compare_list EOL case_body {
 		switch_stack.pop_back();
 		case_stack.pop_back();
@@ -319,12 +321,15 @@ compare_list:
 	/* empty */;
 
 case_body:
+	case_body attr_stmt |
 	case_body switch_stmt |
 	case_body assign_stmt |
 	/* empty */;
 
 assign_stmt:
 	TOK_ASSIGN sigspec sigspec EOL {
+		if (attrbuf.size() != 0)
+			rtlil_frontend_ilang_yyerror("dangling attribute");
 		case_stack.back()->actions.push_back(RTLIL::SigSig(*$2, *$3));
 		delete $2;
 		delete $3;
diff --git a/frontends/verilog/verilog_parser.y b/frontends/verilog/verilog_parser.y
index d89b2dc88..0fec445fa 100644
--- a/frontends/verilog/verilog_parser.y
+++ b/frontends/verilog/verilog_parser.y
@@ -1021,13 +1021,8 @@ list_of_specparam_assignments:
 specparam_assignment:
 	ignspec_id '=' constant_mintypmax_expression ;
 
-/*
-pulsestyle_declaration :
-	;
-
-showcancelled_declaration :
-	;
-*/
+ignspec_opt_cond:
+	TOK_IF '(' ignspec_expr ')' | /* empty */;
 
 path_declaration :
 	simple_path_declaration ';'
@@ -1036,8 +1031,8 @@ path_declaration :
 	;
 
 simple_path_declaration :
-	parallel_path_description '=' path_delay_value |
-	full_path_description '=' path_delay_value
+	ignspec_opt_cond parallel_path_description '=' path_delay_value |
+	ignspec_opt_cond full_path_description '=' path_delay_value
 	;
 
 path_delay_value :
@@ -1047,32 +1042,20 @@ path_delay_value :
 	;
 
 list_of_path_delay_extra_expressions :
-/*
-	t_path_delay_expression
-	| trise_path_delay_expression ',' tfall_path_delay_expression
-	| trise_path_delay_expression ',' tfall_path_delay_expression ',' tz_path_delay_expression
-	| t01_path_delay_expression ',' t10_path_delay_expression ',' t0z_path_delay_expression ','
-	  tz1_path_delay_expression ',' t1z_path_delay_expression ',' tz0_path_delay_expression
-	| t01_path_delay_expression ',' t10_path_delay_expression ',' t0z_path_delay_expression ','
-	  tz1_path_delay_expression ',' t1z_path_delay_expression ',' tz0_path_delay_expression ','
-	  t0x_path_delay_expression ',' tx1_path_delay_expression ',' t1x_path_delay_expression ','
-	  tx0_path_delay_expression ',' txz_path_delay_expression ',' tzx_path_delay_expression
-*/
-	',' path_delay_expression
-	|  ',' path_delay_expression ',' path_delay_expression
-	|  ',' path_delay_expression ',' path_delay_expression ','
-	  path_delay_expression ',' path_delay_expression ',' path_delay_expression
-	|  ',' path_delay_expression ',' path_delay_expression ','
-	  path_delay_expression ',' path_delay_expression ',' path_delay_expression ','
-	  path_delay_expression ',' path_delay_expression ',' path_delay_expression ','
-	  path_delay_expression ',' path_delay_expression ',' path_delay_expression
-	;
+	',' path_delay_expression | ',' path_delay_expression list_of_path_delay_extra_expressions;
+
+specify_edge_identifier :
+	TOK_POSEDGE | TOK_NEGEDGE ;
 
 parallel_path_description :
-	'(' specify_input_terminal_descriptor opt_polarity_operator '=' '>' specify_output_terminal_descriptor ')' ;
+	'(' specify_input_terminal_descriptor opt_polarity_operator '=' '>' specify_output_terminal_descriptor ')' |
+	'(' specify_edge_identifier specify_input_terminal_descriptor '=' '>' '(' specify_output_terminal_descriptor opt_polarity_operator ':' ignspec_expr ')' ')' |
+	'(' specify_edge_identifier specify_input_terminal_descriptor '=' '>' '(' specify_output_terminal_descriptor TOK_POS_INDEXED ignspec_expr ')' ')' ;
 
 full_path_description :
-	'(' list_of_path_inputs '*' '>' list_of_path_outputs ')' ;
+	'(' list_of_path_inputs '*' '>' list_of_path_outputs ')' |
+	'(' specify_edge_identifier list_of_path_inputs '*' '>' '(' list_of_path_outputs opt_polarity_operator ':' ignspec_expr ')' ')' |
+	'(' specify_edge_identifier list_of_path_inputs '*' '>' '(' list_of_path_outputs TOK_POS_INDEXED ignspec_expr ')' ')' ;
 
 // This was broken into 2 rules to solve shift/reduce conflicts
 list_of_path_inputs :
@@ -1112,56 +1095,6 @@ system_timing_args :
 	system_timing_arg |
 	system_timing_args ',' system_timing_arg ;
 
-/*
-t_path_delay_expression :
-	path_delay_expression;
-
-trise_path_delay_expression :
-	path_delay_expression;
-
-tfall_path_delay_expression :
-	path_delay_expression;
-
-tz_path_delay_expression :
-	path_delay_expression;
-
-t01_path_delay_expression :
-	path_delay_expression;
-
-t10_path_delay_expression :
-	path_delay_expression;
-
-t0z_path_delay_expression :
-	path_delay_expression;
-
-tz1_path_delay_expression :
-	path_delay_expression;
-
-t1z_path_delay_expression :
-	path_delay_expression;
-
-tz0_path_delay_expression :
-	path_delay_expression;
-
-t0x_path_delay_expression :
-	path_delay_expression;
-
-tx1_path_delay_expression :
-	path_delay_expression;
-
-t1x_path_delay_expression :
-	path_delay_expression;
-
-tx0_path_delay_expression :
-	path_delay_expression;
-
-txz_path_delay_expression :
-	path_delay_expression;
-
-tzx_path_delay_expression :
-	path_delay_expression;
-*/
-
 path_delay_expression :
 	ignspec_constant_expression;
 
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index f4fcf5dcf..82cbfaf28 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -1327,7 +1327,7 @@ public:
 #endif
 };
 
-struct RTLIL::CaseRule
+struct RTLIL::CaseRule : public RTLIL::AttrObject
 {
 	std::vector<RTLIL::SigSpec> compare;
 	std::vector<RTLIL::SigSig> actions;
diff --git a/kernel/yosys.cc b/kernel/yosys.cc
index f95c0127b..a42a7c0b8 100644
--- a/kernel/yosys.cc
+++ b/kernel/yosys.cc
@@ -1273,6 +1273,10 @@ struct ScriptCmdPass : public Pass {
 		log("If only one label is specified (without ':') then only the block\n");
 		log("marked with that label (until the next label) is executed.\n");
 		log("\n");
+		log("In \"-scriptwire\" mode, the commands on the selected wire(s) will be executed\n");
+		log("in the scope of (and thus, relative to) the wires' owning module(s). This\n");
+		log("'-module' mode can be exited by using the 'cd' command.\n");
+		log("\n");
 	}
 	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
diff --git a/manual/CHAPTER_Overview.tex b/manual/CHAPTER_Overview.tex
index 1a25c477f..3009bf2c0 100644
--- a/manual/CHAPTER_Overview.tex
+++ b/manual/CHAPTER_Overview.tex
@@ -331,8 +331,9 @@ to update {\tt \textbackslash{}q}.
 An RTLIL::Process is a container for zero or more RTLIL::SyncRule objects and
 exactly one RTLIL::CaseRule object, which is called the {\it root case}.
 
-An RTLIL::SyncRule object contains an (optional) synchronization condition
-(signal and edge-type) and zero or more assignments (RTLIL::SigSig).
+An RTLIL::SyncRule object contains an (optional) synchronization condition (signal and edge-type) and zero or
+more assignments (RTLIL::SigSig). The {\tt always} synchronization condition is used to break combinatorial
+loops when a latch should be inferred instead.
 
 An RTLIL::CaseRule is a container for zero or more assignments (RTLIL::SigSig)
 and zero or more RTLIL::SwitchRule objects. An RTLIL::SwitchRule objects is a
diff --git a/misc/py_wrap_generator.py b/misc/py_wrap_generator.py
index 9e5727499..66d661fa1 100644
--- a/misc/py_wrap_generator.py
+++ b/misc/py_wrap_generator.py
@@ -779,6 +779,9 @@ class WClass:
 
 			#if self.link_type != link_types.pointer:
 			text += "\n\t\tstatic " + self.name + "* get_py_obj(" + long_name + "* ref)\n\t\t{"
+			text += "\n\t\t\tif(ref == nullptr){"
+			text += "\n\t\t\t\tthrow std::runtime_error(\"" + self.name + " does not exist.\");"
+			text += "\n\t\t\t}"
 			text += "\n\t\t\t" + self.name + "* ret = (" + self.name + "*)malloc(sizeof(" + self.name + "));"
 			if self.link_type == link_types.pointer:
 				text += "\n\t\t\tret->ref_obj = ref;"
diff --git a/passes/cmds/bugpoint.cc b/passes/cmds/bugpoint.cc
index 038ab7c7c..5a47988ec 100644
--- a/passes/cmds/bugpoint.cc
+++ b/passes/cmds/bugpoint.cc
@@ -51,14 +51,14 @@ struct BugpointPass : public Pass {
 		log("        only consider crashes that place this string in the log file.\n");
 		log("\n");
 		log("    -fast\n");
-		log("        run `clean -purge` after each minimization step. converges faster, but\n");
-		log("        produces larger testcases, and may fail to produce any testcase at all if\n");
-		log("        the crash is related to dangling wires.\n");
+		log("        run `proc_clean; clean -purge` after each minimization step. converges\n");
+		log("        faster, but produces larger testcases, and may fail to produce any\n");
+		log("        testcase at all if the crash is related to dangling wires.\n");
 		log("\n");
 		log("    -clean\n");
-		log("        run `clean -purge` before checking testcase and after finishing. produces\n");
-		log("        smaller and more useful testcases, but may fail to produce any testcase\n");
-		log("        at all if the crash is related to dangling wires.\n");
+		log("        run `proc_clean; clean -purge` before checking testcase and after\n");
+		log("        finishing. produces smaller and more useful testcases, but may fail to\n");
+		log("        produce any testcase at all if the crash is related to dangling wires.\n");
 		log("\n");
 		log("    -modules\n");
 		log("        try to remove modules.\n");
@@ -72,6 +72,12 @@ struct BugpointPass : public Pass {
 		log("    -connections\n");
 		log("        try to reconnect ports to 'x.\n");
 		log("\n");
+		log("    -assigns\n");
+		log("        try to remove process assigns from cases.\n");
+		log("\n");
+		log("    -updates\n");
+		log("        try to remove process updates from syncs.\n");
+		log("\n");
 	}
 
 	bool run_yosys(RTLIL::Design *design, string yosys_cmd, string script)
@@ -110,6 +116,7 @@ struct BugpointPass : public Pass {
 		RTLIL::Design *design_copy = new RTLIL::Design;
 		for (auto &it : design->modules_)
 			design_copy->add(it.second->clone());
+		Pass::call(design_copy, "proc_clean -quiet");
 		Pass::call(design_copy, "clean -purge");
 
 		if (do_delete)
@@ -117,7 +124,7 @@ struct BugpointPass : public Pass {
 		return design_copy;
 	}
 
-	RTLIL::Design *simplify_something(RTLIL::Design *design, int &seed, bool stage2, bool modules, bool ports, bool cells, bool connections)
+	RTLIL::Design *simplify_something(RTLIL::Design *design, int &seed, bool stage2, bool modules, bool ports, bool cells, bool connections, bool assigns, bool updates)
 	{
 		RTLIL::Design *design_copy = new RTLIL::Design;
 		for (auto &it : design->modules_)
@@ -225,6 +232,59 @@ struct BugpointPass : public Pass {
 				}
 			}
 		}
+		if (assigns)
+		{
+			for (auto mod : design_copy->modules())
+			{
+				if (mod->get_blackbox_attribute())
+					continue;
+
+				for (auto &pr : mod->processes)
+				{
+					vector<RTLIL::CaseRule*> cases = {&pr.second->root_case};
+					while (!cases.empty())
+					{
+						RTLIL::CaseRule *cs = cases[0];
+						cases.erase(cases.begin());
+						for (auto it = cs->actions.begin(); it != cs->actions.end(); ++it)
+						{
+							if (index++ == seed)
+							{
+								log("Trying to remove assign %s %s in %s.%s.\n", log_signal((*it).first), log_signal((*it).second), mod->name.c_str(), pr.first.c_str());
+								cs->actions.erase(it);
+								return design_copy;
+							}
+						}
+						for (auto &sw : cs->switches)
+							cases.insert(cases.end(), sw->cases.begin(), sw->cases.end());
+					}
+				}
+			}
+		}
+		if (updates)
+		{
+			for (auto mod : design_copy->modules())
+			{
+				if (mod->get_blackbox_attribute())
+					continue;
+
+				for (auto &pr : mod->processes)
+				{
+					for (auto &sy : pr.second->syncs)
+					{
+						for (auto it = sy->actions.begin(); it != sy->actions.end(); ++it)
+						{
+							if (index++ == seed)
+							{
+								log("Trying to remove sync %s update %s %s in %s.%s.\n", log_signal(sy->signal), log_signal((*it).first), log_signal((*it).second), mod->name.c_str(), pr.first.c_str());
+								sy->actions.erase(it);
+								return design_copy;
+							}
+						}
+					}
+				}
+			}
+		}
 		return NULL;
 	}
 
@@ -232,7 +292,7 @@ struct BugpointPass : public Pass {
 	{
 		string yosys_cmd = "yosys", script, grep;
 		bool fast = false, clean = false;
-		bool modules = false, ports = false, cells = false, connections = false, has_part = false;
+		bool modules = false, ports = false, cells = false, connections = false, assigns = false, updates = false, has_part = false;
 
 		size_t argidx;
 		for (argidx = 1; argidx < args.size(); argidx++)
@@ -277,6 +337,16 @@ struct BugpointPass : public Pass {
 				has_part = true;
 				continue;
 			}
+			if (args[argidx] == "-assigns") {
+				assigns = true;
+				has_part = true;
+				continue;
+			}
+			if (args[argidx] == "-updates") {
+				updates = true;
+				has_part = true;
+				continue;
+			}
 			break;
 		}
 		extra_args(args, argidx, design);
@@ -290,6 +360,8 @@ struct BugpointPass : public Pass {
 			ports = true;
 			cells = true;
 			connections = true;
+			assigns = true;
+			updates = true;
 		}
 
 		if (!design->full_selection())
@@ -305,7 +377,7 @@ struct BugpointPass : public Pass {
 		bool found_something = false, stage2 = false;
 		while (true)
 		{
-			if (RTLIL::Design *simplified = simplify_something(crashing_design, seed, stage2, modules, ports, cells, connections))
+			if (RTLIL::Design *simplified = simplify_something(crashing_design, seed, stage2, modules, ports, cells, connections, assigns, updates))
 			{
 				simplified = clean_design(simplified, fast, /*do_delete=*/true);
 
diff --git a/passes/proc/Makefile.inc b/passes/proc/Makefile.inc
index 397fe46a1..4b56979f8 100644
--- a/passes/proc/Makefile.inc
+++ b/passes/proc/Makefile.inc
@@ -1,5 +1,6 @@
 
 OBJS += passes/proc/proc.o
+OBJS += passes/proc/proc_prune.o
 OBJS += passes/proc/proc_clean.o
 OBJS += passes/proc/proc_rmdead.o
 OBJS += passes/proc/proc_init.o
@@ -7,4 +8,3 @@ OBJS += passes/proc/proc_arst.o
 OBJS += passes/proc/proc_mux.o
 OBJS += passes/proc/proc_dlatch.o
 OBJS += passes/proc/proc_dff.o
-
diff --git a/passes/proc/proc.cc b/passes/proc/proc.cc
index ef7cb0f71..a5b4a3112 100644
--- a/passes/proc/proc.cc
+++ b/passes/proc/proc.cc
@@ -37,6 +37,7 @@ struct ProcPass : public Pass {
 		log("\n");
 		log("    proc_clean\n");
 		log("    proc_rmdead\n");
+		log("    proc_prune\n");
 		log("    proc_init\n");
 		log("    proc_arst\n");
 		log("    proc_mux\n");
@@ -83,6 +84,7 @@ struct ProcPass : public Pass {
 		Pass::call(design, "proc_clean");
 		if (!ifxmode)
 			Pass::call(design, "proc_rmdead");
+		Pass::call(design, "proc_prune");
 		Pass::call(design, "proc_init");
 		if (global_arst.empty())
 			Pass::call(design, "proc_arst");
diff --git a/passes/proc/proc_arst.cc b/passes/proc/proc_arst.cc
index b69eba3f9..d069f152a 100644
--- a/passes/proc/proc_arst.cc
+++ b/passes/proc/proc_arst.cc
@@ -172,7 +172,7 @@ restart_proc_arst:
 					sync->type = sync->type == RTLIL::SyncType::STp ? RTLIL::SyncType::ST1 : RTLIL::SyncType::ST0;
 				}
 				for (auto &action : sync->actions) {
-					RTLIL::SigSpec rspec = action.second;
+					RTLIL::SigSpec rspec = assign_map(action.second);
 					RTLIL::SigSpec rval = RTLIL::SigSpec(RTLIL::State::Sm, rspec.size());
 					for (int i = 0; i < GetSize(rspec); i++)
 						if (rspec[i].wire == NULL)
diff --git a/passes/proc/proc_clean.cc b/passes/proc/proc_clean.cc
index 52141a8ec..97f4c6573 100644
--- a/passes/proc/proc_clean.cc
+++ b/passes/proc/proc_clean.cc
@@ -143,7 +143,7 @@ void proc_clean_case(RTLIL::CaseRule *cs, bool &did_something, int &count, int m
 YOSYS_NAMESPACE_END
 PRIVATE_NAMESPACE_BEGIN
 
-void proc_clean(RTLIL::Module *mod, RTLIL::Process *proc, int &total_count)
+void proc_clean(RTLIL::Module *mod, RTLIL::Process *proc, int &total_count, bool quiet)
 {
 	int count = 0;
 	bool did_something = true;
@@ -160,7 +160,7 @@ void proc_clean(RTLIL::Module *mod, RTLIL::Process *proc, int &total_count)
 		did_something = false;
 		proc_clean_case(&proc->root_case, did_something, count, -1);
 	}
-	if (count > 0)
+	if (count > 0 && !quiet)
 		log("Found and cleaned up %d empty switch%s in `%s.%s'.\n", count, count == 1 ? "" : "es", mod->name.c_str(), proc->name.c_str());
 	total_count += count;
 }
@@ -171,7 +171,10 @@ struct ProcCleanPass : public Pass {
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
-		log("    proc_clean [selection]\n");
+		log("    proc_clean [options] [selection]\n");
+		log("\n");
+		log("    -quiet\n");
+		log("        do not print any messages.\n");
 		log("\n");
 		log("This pass removes empty parts of processes and ultimately removes a process\n");
 		log("if it contains only empty structures.\n");
@@ -180,9 +183,20 @@ struct ProcCleanPass : public Pass {
 	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		int total_count = 0;
-		log_header(design, "Executing PROC_CLEAN pass (remove empty switches from decision trees).\n");
+		bool quiet = false;
 
-		extra_args(args, 1, design);
+		if (find(args.begin(), args.end(), "-quiet") == args.end())
+			log_header(design, "Executing PROC_CLEAN pass (remove empty switches from decision trees).\n");
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++)
+		{
+			if (args[argidx] == "-quiet") {
+				quiet = true;
+				continue;
+			}
+		}
+		extra_args(args, argidx, design);
 
 		for (auto mod : design->modules()) {
 			std::vector<RTLIL::IdString> delme;
@@ -191,10 +205,11 @@ struct ProcCleanPass : public Pass {
 			for (auto &proc_it : mod->processes) {
 				if (!design->selected(mod, proc_it.second))
 					continue;
-				proc_clean(mod, proc_it.second, total_count);
+				proc_clean(mod, proc_it.second, total_count, quiet);
 				if (proc_it.second->syncs.size() == 0 && proc_it.second->root_case.switches.size() == 0 &&
 						proc_it.second->root_case.actions.size() == 0) {
-					log("Removing empty process `%s.%s'.\n", log_id(mod), proc_it.second->name.c_str());
+					if (!quiet)
+						log("Removing empty process `%s.%s'.\n", log_id(mod), proc_it.second->name.c_str());
 					delme.push_back(proc_it.first);
 				}
 			}
@@ -204,7 +219,8 @@ struct ProcCleanPass : public Pass {
 			}
 		}
 
-		log("Cleaned up %d empty switch%s.\n", total_count, total_count == 1 ? "" : "es");
+		if (!quiet)
+			log("Cleaned up %d empty switch%s.\n", total_count, total_count == 1 ? "" : "es");
 	}
 } ProcCleanPass;
 
diff --git a/passes/proc/proc_init.cc b/passes/proc/proc_init.cc
index e2dc07e53..462a384b7 100644
--- a/passes/proc/proc_init.cc
+++ b/passes/proc/proc_init.cc
@@ -26,21 +26,7 @@
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
 
-void proc_get_const(RTLIL::SigSpec &sig, RTLIL::CaseRule &rule)
-{
-	log_assert(rule.compare.size() == 0);
-
-	while (1) {
-		RTLIL::SigSpec tmp = sig;
-		for (auto &it : rule.actions)
-			tmp.replace(it.first, it.second);
-		if (tmp == sig)
-			break;
-		sig = tmp;
-	}
-}
-
-void proc_init(RTLIL::Module *mod, RTLIL::Process *proc)
+void proc_init(RTLIL::Module *mod, SigMap &sigmap, RTLIL::Process *proc)
 {
 	bool found_init = false;
 
@@ -53,9 +39,7 @@ void proc_init(RTLIL::Module *mod, RTLIL::Process *proc)
 			for (auto &action : sync->actions)
 			{
 				RTLIL::SigSpec lhs = action.first;
-				RTLIL::SigSpec rhs = action.second;
-
-				proc_get_const(rhs, proc->root_case);
+				RTLIL::SigSpec rhs = sigmap(action.second);
 
 				if (!rhs.is_fully_const())
 					log_cmd_error("Failed to get a constant init value for %s: %s\n", log_signal(lhs), log_signal(rhs));
@@ -120,10 +104,12 @@ struct ProcInitPass : public Pass {
 		extra_args(args, 1, design);
 
 		for (auto mod : design->modules())
-			if (design->selected(mod))
+			if (design->selected(mod)) {
+				SigMap sigmap(mod);
 				for (auto &proc_it : mod->processes)
 					if (design->selected(mod, proc_it.second))
-						proc_init(mod, proc_it.second);
+						proc_init(mod, sigmap, proc_it.second);
+			}
 	}
 } ProcInitPass;
 
diff --git a/passes/proc/proc_mux.cc b/passes/proc/proc_mux.cc
index aac0b121c..d029282fd 100644
--- a/passes/proc/proc_mux.cc
+++ b/passes/proc/proc_mux.cc
@@ -144,7 +144,13 @@ struct SnippetSwCache
 	}
 };
 
-RTLIL::SigSpec gen_cmp(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const std::vector<RTLIL::SigSpec> &compare, RTLIL::SwitchRule *sw, bool ifxmode)
+void apply_attrs(RTLIL::Cell *cell, const RTLIL::SwitchRule *sw, const RTLIL::CaseRule *cs)
+{
+	cell->attributes = sw->attributes;
+	cell->add_strpool_attribute("\\src", cs->get_strpool_attribute("\\src"));
+}
+
+RTLIL::SigSpec gen_cmp(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const std::vector<RTLIL::SigSpec> &compare, RTLIL::SwitchRule *sw, RTLIL::CaseRule *cs, bool ifxmode)
 {
 	std::stringstream sstr;
 	sstr << "$procmux$" << (autoidx++);
@@ -173,7 +179,7 @@ RTLIL::SigSpec gen_cmp(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const s
 		{
 			// create compare cell
 			RTLIL::Cell *eq_cell = mod->addCell(stringf("%s_CMP%d", sstr.str().c_str(), cmp_wire->width), ifxmode ? "$eqx" : "$eq");
-			eq_cell->attributes = sw->attributes;
+			apply_attrs(eq_cell, sw, cs);
 
 			eq_cell->parameters["\\A_SIGNED"] = RTLIL::Const(0);
 			eq_cell->parameters["\\B_SIGNED"] = RTLIL::Const(0);
@@ -199,7 +205,7 @@ RTLIL::SigSpec gen_cmp(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const s
 
 		// reduce cmp vector to one logic signal
 		RTLIL::Cell *any_cell = mod->addCell(sstr.str() + "_ANY", "$reduce_or");
-		any_cell->attributes = sw->attributes;
+		apply_attrs(any_cell, sw, cs);
 
 		any_cell->parameters["\\A_SIGNED"] = RTLIL::Const(0);
 		any_cell->parameters["\\A_WIDTH"] = RTLIL::Const(cmp_wire->width);
@@ -212,7 +218,7 @@ RTLIL::SigSpec gen_cmp(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const s
 	return RTLIL::SigSpec(ctrl_wire);
 }
 
-RTLIL::SigSpec gen_mux(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const std::vector<RTLIL::SigSpec> &compare, RTLIL::SigSpec when_signal, RTLIL::SigSpec else_signal, RTLIL::Cell *&last_mux_cell, RTLIL::SwitchRule *sw, bool ifxmode)
+RTLIL::SigSpec gen_mux(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const std::vector<RTLIL::SigSpec> &compare, RTLIL::SigSpec when_signal, RTLIL::SigSpec else_signal, RTLIL::Cell *&last_mux_cell, RTLIL::SwitchRule *sw, RTLIL::CaseRule *cs, bool ifxmode)
 {
 	log_assert(when_signal.size() == else_signal.size());
 
@@ -224,7 +230,7 @@ RTLIL::SigSpec gen_mux(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const s
 		return when_signal;
 
 	// compare results
-	RTLIL::SigSpec ctrl_sig = gen_cmp(mod, signal, compare, sw, ifxmode);
+	RTLIL::SigSpec ctrl_sig = gen_cmp(mod, signal, compare, sw, cs, ifxmode);
 	if (ctrl_sig.size() == 0)
 		return when_signal;
 	log_assert(ctrl_sig.size() == 1);
@@ -234,7 +240,7 @@ RTLIL::SigSpec gen_mux(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const s
 
 	// create the multiplexer itself
 	RTLIL::Cell *mux_cell = mod->addCell(sstr.str(), "$mux");
-	mux_cell->attributes = sw->attributes;
+	apply_attrs(mux_cell, sw, cs);
 
 	mux_cell->parameters["\\WIDTH"] = RTLIL::Const(when_signal.size());
 	mux_cell->setPort("\\A", else_signal);
@@ -246,7 +252,7 @@ RTLIL::SigSpec gen_mux(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const s
 	return RTLIL::SigSpec(result_wire);
 }
 
-void append_pmux(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const std::vector<RTLIL::SigSpec> &compare, RTLIL::SigSpec when_signal, RTLIL::Cell *last_mux_cell, RTLIL::SwitchRule *sw, bool ifxmode)
+void append_pmux(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const std::vector<RTLIL::SigSpec> &compare, RTLIL::SigSpec when_signal, RTLIL::Cell *last_mux_cell, RTLIL::SwitchRule *sw, RTLIL::CaseRule *cs, bool ifxmode)
 {
 	log_assert(last_mux_cell != NULL);
 	log_assert(when_signal.size() == last_mux_cell->getPort("\\A").size());
@@ -254,7 +260,7 @@ void append_pmux(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const std::ve
 	if (when_signal == last_mux_cell->getPort("\\A"))
 		return;
 
-	RTLIL::SigSpec ctrl_sig = gen_cmp(mod, signal, compare, sw, ifxmode);
+	RTLIL::SigSpec ctrl_sig = gen_cmp(mod, signal, compare, sw, cs, ifxmode);
 	log_assert(ctrl_sig.size() == 1);
 	last_mux_cell->type = "$pmux";
 
@@ -395,9 +401,9 @@ RTLIL::SigSpec signal_to_mux_tree(RTLIL::Module *mod, SnippetSwCache &swcache, d
 			RTLIL::CaseRule *cs2 = sw->cases[case_idx];
 			RTLIL::SigSpec value = signal_to_mux_tree(mod, swcache, swpara, cs2, sig, initial_val, ifxmode);
 			if (last_mux_cell && pgroups[case_idx] == pgroups[case_idx+1])
-				append_pmux(mod, sw->signal, cs2->compare, value, last_mux_cell, sw, ifxmode);
+				append_pmux(mod, sw->signal, cs2->compare, value, last_mux_cell, sw, cs2, ifxmode);
 			else
-				result = gen_mux(mod, sw->signal, cs2->compare, value, result, last_mux_cell, sw, ifxmode);
+				result = gen_mux(mod, sw->signal, cs2->compare, value, result, last_mux_cell, sw, cs2, ifxmode);
 		}
 	}
 
diff --git a/passes/proc/proc_prune.cc b/passes/proc/proc_prune.cc
new file mode 100644
index 000000000..9e00b0a8a
--- /dev/null
+++ b/passes/proc/proc_prune.cc
@@ -0,0 +1,158 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2019  whitequark <whitequark@whitequark.org>
+ *
+ *  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/register.h"
+#include "kernel/sigtools.h"
+#include "kernel/log.h"
+#include <stdlib.h>
+#include <stdio.h>
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+struct PruneWorker
+{
+	RTLIL::Module *module;
+	SigMap sigmap;
+
+	int removed_count = 0, promoted_count = 0;
+
+	PruneWorker(RTLIL::Module *mod) : module(mod), sigmap(mod) {}
+
+	pool<RTLIL::SigBit> do_switch(RTLIL::SwitchRule *sw, pool<RTLIL::SigBit> assigned, pool<RTLIL::SigBit> &affected)
+	{
+		pool<RTLIL::SigBit> all_assigned;
+		bool full_case = sw->get_bool_attribute("\\full_case");
+		bool first = true;
+		for (auto it : sw->cases) {
+			if (it->compare.empty())
+				full_case = true;
+			pool<RTLIL::SigBit> case_assigned = do_case(it, assigned, affected);
+			if (first) {
+				first = false;
+				all_assigned = case_assigned;
+			} else {
+				for (auto &bit : all_assigned)
+					if (!case_assigned[bit])
+						all_assigned.erase(bit);
+			}
+		}
+		if (full_case)
+			assigned.insert(all_assigned.begin(), all_assigned.end());
+		return assigned;
+	}
+
+	pool<RTLIL::SigBit> do_case(RTLIL::CaseRule *cs, pool<RTLIL::SigBit> assigned, pool<RTLIL::SigBit> &affected,
+	                            bool root = false)
+	{
+		for (auto it = cs->switches.rbegin(); it != cs->switches.rend(); ++it) {
+			pool<RTLIL::SigBit> sw_assigned = do_switch((*it), assigned, affected);
+			assigned.insert(sw_assigned.begin(), sw_assigned.end());
+		}
+		pool<RTLIL::SigSig> remove;
+		for (auto it = cs->actions.rbegin(); it != cs->actions.rend(); ++it) {
+			RTLIL::SigSpec lhs = sigmap(it->first);
+			bool redundant = true;
+			for (auto &bit : lhs) {
+				if (bit.wire && !assigned[bit]) {
+					redundant = false;
+					break;
+				}
+			}
+			if (redundant) {
+				removed_count++;
+				remove.insert(*it);
+			} else {
+				if (root) {
+					bool promotable = true;
+					for (auto &bit : lhs) {
+						if (bit.wire && affected[bit]) {
+							promotable = false;
+							break;
+						}
+					}
+					if (promotable) {
+						promoted_count++;
+						module->connect(*it);
+						remove.insert(*it);
+					}
+				}
+				for (auto &bit : lhs)
+					if (bit.wire)
+						assigned.insert(bit);
+				for (auto &bit : lhs)
+					if (bit.wire)
+						affected.insert(bit);
+			}
+		}
+		for (auto it = cs->actions.begin(); it != cs->actions.end(); ) {
+			if (remove[*it]) {
+				it = cs->actions.erase(it);
+			} else it++;
+		}
+		return assigned;
+	}
+
+	void do_process(RTLIL::Process *pr)
+	{
+		pool<RTLIL::SigBit> affected;
+		do_case(&pr->root_case, {}, affected, /*root=*/true);
+	}
+};
+
+struct ProcPrunePass : public Pass {
+	ProcPrunePass() : Pass("proc_prune", "remove redundant assignments") { }
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    proc_prune [selection]\n");
+		log("\n");
+		log("This pass identifies assignments in processes that are always overwritten by\n");
+		log("a later assignment to the same signal and removes them.\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		int total_removed_count = 0, total_promoted_count = 0;
+		log_header(design, "Executing PROC_PRUNE pass (remove redundant assignments in processes).\n");
+
+		extra_args(args, 1, design);
+
+		for (auto mod : design->modules()) {
+			if (!design->selected(mod))
+				continue;
+			PruneWorker worker(mod);
+			for (auto &proc_it : mod->processes) {
+				if (!design->selected(mod, proc_it.second))
+					continue;
+				worker.do_process(proc_it.second);
+			}
+			total_removed_count += worker.removed_count;
+			total_promoted_count += worker.promoted_count;
+		}
+
+		log("Removed %d redundant assignment%s.\n",
+		    total_removed_count, total_removed_count == 1 ? "" : "s");
+		log("Promoted %d assignment%s to connection%s.\n",
+		    total_promoted_count, total_promoted_count == 1 ? "" : "s", total_promoted_count == 1 ? "" : "s");
+	}
+} ProcPrunePass;
+
+PRIVATE_NAMESPACE_END
diff --git a/passes/sat/clk2fflogic.cc b/passes/sat/clk2fflogic.cc
index 49ec795d3..4bb4aa047 100644
--- a/passes/sat/clk2fflogic.cc
+++ b/passes/sat/clk2fflogic.cc
@@ -253,6 +253,13 @@ struct Clk2fflogicPass : public Pass {
 						SigSpec qval = module->Mux(NEW_ID, past_q, past_d, clock_edge);
 						Const rstval = cell->parameters["\\ARST_VALUE"];
 
+						Wire *past_arst = module->addWire(NEW_ID);
+						module->addFf(NEW_ID, arst, past_arst);
+						if (cell->parameters["\\ARST_POLARITY"].as_bool())
+							arst = module->LogicOr(NEW_ID, arst, past_arst);
+						else
+							arst = module->LogicAnd(NEW_ID, arst, past_arst);
+
 						if (cell->parameters["\\ARST_POLARITY"].as_bool())
 							module->addMux(NEW_ID, qval, rstval, arst, sig_q);
 						else
diff --git a/passes/techmap/muxcover.cc b/passes/techmap/muxcover.cc
index c84cfc39a..d53378a29 100644
--- a/passes/techmap/muxcover.cc
+++ b/passes/techmap/muxcover.cc
@@ -632,10 +632,15 @@ struct MuxcoverPass : public Pass {
 		log("Cover trees of $_MUX_ cells with $_MUX{4,8,16}_ cells\n");
 		log("\n");
 		log("    -mux4[=cost], -mux8[=cost], -mux16[=cost]\n");
-		log("        Use the specified types of MUXes (with optional integer costs). If none\n");
-		log("        of these options are given, the effect is the same as if all of them are.\n");
-		log("        Default costs: $_MUX_ = %d, $_MUX4_ = %d,\n", COST_MUX2, COST_MUX4);
-		log("                       $_MUX8_ = %d, $_MUX16_ = %d\n", COST_MUX8, COST_MUX16);
+		log("        Cover $_MUX_ trees using the specified types of MUXes (with optional\n");
+		log("        integer costs). If none of these options are given, the effect is the\n");
+		log("        same as if all of them are.\n");
+		log("        Default costs: $_MUX4_ = %d, $_MUX8_ = %d, \n", COST_MUX4, COST_MUX8);
+		log("                       $_MUX16_ = %d\n", COST_MUX16);
+		log("\n");
+		log("    -mux2=cost\n");
+		log("        Use the specified cost for $_MUX_ cells when making covering decisions.\n");
+		log("        Default cost: $_MUX_ = %d\n", COST_MUX2);
 		log("\n");
 		log("    -dmux=cost\n");
 		log("        Use the specified cost for $_MUX_ cells used in decoders.\n");
@@ -661,6 +666,7 @@ struct MuxcoverPass : public Pass {
 		bool nodecode = false;
 		bool nopartial = false;
 		int cost_dmux = COST_DMUX;
+		int cost_mux2 = COST_MUX2;
 		int cost_mux4 = COST_MUX4;
 		int cost_mux8 = COST_MUX8;
 		int cost_mux16 = COST_MUX16;
@@ -669,11 +675,15 @@ struct MuxcoverPass : public Pass {
 		for (argidx = 1; argidx < args.size(); argidx++)
 		{
 			const auto &arg = args[argidx];
+			if (arg.size() >= 6 && arg.substr(0,6) == "-mux2=") {
+				cost_mux2 = std::stoi(arg.substr(6));
+				continue;
+			}
 			if (arg.size() >= 5 && arg.substr(0,5) == "-mux4") {
 				use_mux4 = true;
 				if (arg.size() > 5) {
 					if (arg[5] != '=') break;
-					cost_mux4 = atoi(arg.substr(6).c_str());
+					cost_mux4 = std::stoi(arg.substr(6));
 				}
 				continue;
 			}
@@ -681,7 +691,7 @@ struct MuxcoverPass : public Pass {
 				use_mux8 = true;
 				if (arg.size() > 5) {
 					if (arg[5] != '=') break;
-					cost_mux8 = atoi(arg.substr(6).c_str());
+					cost_mux8 = std::stoi(arg.substr(6));
 				}
 				continue;
 			}
@@ -689,12 +699,12 @@ struct MuxcoverPass : public Pass {
 				use_mux16 = true;
 				if (arg.size() > 6) {
 					if (arg[6] != '=') break;
-					cost_mux16 = atoi(arg.substr(7).c_str());
+					cost_mux16 = std::stoi(arg.substr(7));
 				}
 				continue;
 			}
 			if (arg.size() >= 6 && arg.substr(0,6) == "-dmux=") {
-				cost_dmux = atoi(arg.substr(6).c_str());
+				cost_dmux = std::stoi(arg.substr(6));
 				continue;
 			}
 			if (arg == "-nodecode") {
@@ -722,6 +732,7 @@ struct MuxcoverPass : public Pass {
 			worker.use_mux8 = use_mux8;
 			worker.use_mux16 = use_mux16;
 			worker.cost_dmux = cost_dmux;
+			worker.cost_mux2 = cost_mux2;
 			worker.cost_mux4 = cost_mux4;
 			worker.cost_mux8 = cost_mux8;
 			worker.cost_mux16 = cost_mux16;
diff --git a/passes/techmap/techmap.cc b/passes/techmap/techmap.cc
index ab0bd3b54..ceb053825 100644
--- a/passes/techmap/techmap.cc
+++ b/passes/techmap/techmap.cc
@@ -649,10 +649,13 @@ struct TechmapWorker
 									unique_bit_id[bit] = unique_bit_id_counter++;
 						}
 
+					// Find highest bit set
 					int bits = 0;
 					for (int i = 0; i < 32; i++)
 						if (((unique_bit_id_counter-1) & (1 << i)) != 0)
 							bits = i;
+					// Increment index by one to get number of bits
+					bits++;
 					if (tpl->avail_parameters.count("\\_TECHMAP_BITS_CONNMAP_"))
 						parameters["\\_TECHMAP_BITS_CONNMAP_"] = bits;
 
diff --git a/techlibs/ecp5/synth_ecp5.cc b/techlibs/ecp5/synth_ecp5.cc
index f16a47f01..9f409ca51 100644
--- a/techlibs/ecp5/synth_ecp5.cc
+++ b/techlibs/ecp5/synth_ecp5.cc
@@ -2,7 +2,7 @@
  *  yosys -- Yosys Open SYnthesis Suite
  *
  *  Copyright (C) 2012 Clifford Wolf <clifford@clifford.at>
- *  Copyright (C) 2018 Clifford Wolf <dave@ds0.me>
+ *  Copyright (C) 2018 David Shah <dave@ds0.me>
  *
  *  Permission to use, copy, modify, and/or distribute this software for any
  *  purpose with or without fee is hereby granted, provided that the above
@@ -199,6 +199,9 @@ struct SynthEcp5Pass : public ScriptPass
 		if (!design->full_selection())
 			log_cmd_error("This command only operates on fully selected designs!\n");
 
+		if (abc9 && retime)
+				log_cmd_error("-retime option not currently compatible with -abc9!\n");
+
 		log_header(design, "Executing SYNTH_ECP5 pass.\n");
 		log_push();
 
diff --git a/techlibs/ice40/synth_ice40.cc b/techlibs/ice40/synth_ice40.cc
index 9dd5d81f7..2c75215cb 100644
--- a/techlibs/ice40/synth_ice40.cc
+++ b/techlibs/ice40/synth_ice40.cc
@@ -227,6 +227,9 @@ struct SynthIce40Pass : public ScriptPass
 		if (device_opt != "hx" && device_opt != "lp" && device_opt !="u")
 			log_cmd_error("Invalid or no device specified: '%s'\n", device_opt.c_str());
 
+		if (abc == "abc9" && retime)
+			log_cmd_error("-retime option not currently compatible with -abc9!\n");
+
 		log_header(design, "Executing SYNTH_ICE40 pass.\n");
 		log_push();
 
@@ -296,7 +299,7 @@ struct SynthIce40Pass : public ScriptPass
 				run("techmap");
 			else
 				run("techmap -map +/techmap.v -map +/ice40/arith_map.v");
-			if ((retime || help_mode) && abc != "abc9")
+			if (retime || help_mode)
 				run(abc + " -dff", "(only if -retime)");
 			run("ice40_opt");
 		}
diff --git a/techlibs/intel/synth_intel.cc b/techlibs/intel/synth_intel.cc
index 639cba2c2..09c9ba3af 100644
--- a/techlibs/intel/synth_intel.cc
+++ b/techlibs/intel/synth_intel.cc
@@ -48,6 +48,8 @@ struct SynthIntelPass : public ScriptPass {
 		log("    -vqm <file>\n");
 		log("        write the design to the specified Verilog Quartus Mapping File. Writing of an\n");
 		log("        output file is omitted if this parameter is not specified.\n");
+		log("        Note that this backend has not been tested and is likely incompatible\n");
+		log("        with recent versions of Quartus.\n");
 		log("\n");
 		log("    -vpr <file>\n");
 		log("        write BLIF files for VPR flow experiments. The synthesized BLIF output file is not\n");
@@ -108,6 +110,7 @@ struct SynthIntelPass : public ScriptPass {
 			}
 			if (args[argidx] == "-vqm" && argidx + 1 < args.size()) {
 				vout_file = args[++argidx];
+				log_warning("The Quartus backend has not been tested recently and is likely incompatible with modern versions of Quartus.\n");
 				continue;
 			}
 			if (args[argidx] == "-vpr" && argidx + 1 < args.size()) {
diff --git a/techlibs/xilinx/Makefile.inc b/techlibs/xilinx/Makefile.inc
index 860fcd88c..c9a3a49fb 100644
--- a/techlibs/xilinx/Makefile.inc
+++ b/techlibs/xilinx/Makefile.inc
@@ -30,6 +30,7 @@ $(eval $(call add_share_file,share/xilinx,techlibs/xilinx/drams_map.v))
 $(eval $(call add_share_file,share/xilinx,techlibs/xilinx/arith_map.v))
 $(eval $(call add_share_file,share/xilinx,techlibs/xilinx/ff_map.v))
 $(eval $(call add_share_file,share/xilinx,techlibs/xilinx/lut_map.v))
+$(eval $(call add_share_file,share/xilinx,techlibs/xilinx/mux_map.v))
 
 $(eval $(call add_share_file,share/xilinx,techlibs/xilinx/abc_ff.v))
 $(eval $(call add_share_file,share/xilinx,techlibs/xilinx/abc_xc7.box))
diff --git a/techlibs/xilinx/abc_xc7.box b/techlibs/xilinx/abc_xc7.box
index 633e2d484..69ff9aeab 100644
--- a/techlibs/xilinx/abc_xc7.box
+++ b/techlibs/xilinx/abc_xc7.box
@@ -3,17 +3,22 @@
 # NB: Inputs/Outputs must be ordered alphabetically
 #     (with exceptions for carry in/out)
 
-# F7BMUX slower than F7AMUX
+# Average across F7[AB]MUX
 # Inputs: I0 I1 S0
 # Outputs: O
-F7BMUX 1 1 3 1
-217 223 296
+F7MUX 1 1 3 1
+204 208 286
 
 # Inputs: I0 I1 S0
 # Outputs: O
 MUXF8 2 1 3 1
 104 94 273
 
+# Inputs: I0 I1 I2 I3 S0 S1
+# Outputs: O
+$__MUXF78 3 1 6 1
+294 297 311 317 390 273
+
 # CARRY4 + CARRY4_[ABCD]X
 # Inputs: CYINIT DI0 DI1 DI2 DI3 S0 S1 S2 S3 CI
 # Outputs:  O0 O1 O2 O3 CO0 CO1 CO2 CO3
@@ -21,7 +26,7 @@ MUXF8 2 1 3 1
 #        input/output and the entire bus has been
 #        moved there overriding the otherwise
 #        alphabetical ordering)
-CARRY4 3 1 10 8
+CARRY4 4 1 10 8
 482 -   -   -   -   223 -   -   -   222
 598 407 -   -   -   400 205 -   -   334
 584 556 537 -   -   523 558 226 -   239
@@ -34,21 +39,21 @@ CARRY4 3 1 10 8
 # SLICEM/A6LUT
 # Inputs: A0 A1 A2 A3 A4 D DPRA0 DPRA1 DPRA2 DPRA3 DPRA4 WCLK WE
 # Outputs: DPO SPO
-RAM32X1D 4 0 13 2
+RAM32X1D 5 0 13 2
 -   -   -   -   -   - 631 472 407 238 127 - -
 631 472 407 238 127 - -   -   -   -   -   - -
 
 # SLICEM/A6LUT
 # Inputs: A0 A1 A2 A3 A4 A5 D DPRA0 DPRA1 DPRA2 DPRA3 DPRA4 DPRA5 WCLK WE
 # Outputs: DPO SPO
-RAM64X1D 5 0 15 2
+RAM64X1D 6 0 15 2
 -   -   -   -   -   -   - 642 631 472 407 238 127 - -
 642 631 472 407 238 127 - -   -   -   -   -   -   - -
 
 # SLICEM/A6LUT + F7[AB]MUX
 # Inputs: A0 A1 A2 A3 A4 A5 A6 D DPRA0 DPRA1 DPRA2 DPRA3 DPRA4 DPRA5 DPRA6 WCLK WE
 # Outputs: DPO SPO
-RAM128X1D 6 0 17 2
+RAM128X1D 7 0 17 2
 -    -    -   -   -   -   -   - 1009 998 839 774 605 494 450 - -
 1047 1036 877 812 643 532 478 - -    -   -   -   -   -   -   - -
 
diff --git a/techlibs/xilinx/cells_map.v b/techlibs/xilinx/cells_map.v
index 9a316fc96..2eb9fa2c1 100644
--- a/techlibs/xilinx/cells_map.v
+++ b/techlibs/xilinx/cells_map.v
@@ -56,7 +56,6 @@ module \$__XILINX_SHREG_ (input C, input D, input [31:0] L, input E, output Q, o
   localparam [DEPTH-1:0] INIT_R = brev(INIT);
 
   parameter _TECHMAP_CONSTMSK_L_ = 0;
-  parameter _TECHMAP_CONSTVAL_L_ = 0;
 
   wire CE;
   generate
@@ -94,11 +93,8 @@ module \$__XILINX_SHREG_ (input C, input D, input [31:0] L, input E, output Q, o
       \$__XILINX_SHREG_ #(.DEPTH(DEPTH-64), .INIT(INIT[DEPTH-64-1:0]), .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl_2 (.C(C), .D(T3), .L(L[4:0]), .E(E), .Q(T4));
       if (&_TECHMAP_CONSTMSK_L_)
         assign Q = T4;
-      else begin
-        MUXF7 fpga_mux_0 (.O(T5), .I0(T0), .I1(T2), .S(L[5]));
-        MUXF7 fpga_mux_1 (.O(T6), .I0(T4), .I1(1'b0 /* unused */), .S(L[5]));
-        MUXF8 fpga_mux_2 (.O(Q), .I0(T5), .I1(T6), .S(L[6]));
-      end
+      else
+        \$__XILINX_MUXF78 fpga_hard_mux (.I0(T0), .I1(T2), .I2(T4), .I3(1'bx), .S0(L[5]), .S1(L[6]), .O(Q));
     end else
     if (DEPTH > 97 && DEPTH < 128) begin
       wire T0, T1, T2, T3, T4, T5, T6, T7, T8;
@@ -108,11 +104,8 @@ module \$__XILINX_SHREG_ (input C, input D, input [31:0] L, input E, output Q, o
       \$__XILINX_SHREG_ #(.DEPTH(DEPTH-96), .INIT(INIT[DEPTH-96-1:0]), .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl_3 (.C(C), .D(T5), .L(L[4:0]), .E(E), .Q(T6));
       if (&_TECHMAP_CONSTMSK_L_)
         assign Q = T6;
-      else begin
-        MUXF7 fpga_mux_0 (.O(T7), .I0(T0), .I1(T2), .S(L[5]));
-        MUXF7 fpga_mux_1 (.O(T8), .I0(T4), .I1(T6), .S(L[5]));
-        MUXF8 fpga_mux_2 (.O(Q), .I0(T7), .I1(T8), .S(L[6]));
-      end
+      else
+        \$__XILINX_MUXF78 fpga_hard_mux (.I0(T0), .I1(T2), .I2(T4), .I3(T6), .S0(L[5]), .S1(L[6]), .O(Q));
     end
     else if (DEPTH == 128) begin
       wire T0, T1, T2, T3, T4, T5, T6;
@@ -122,33 +115,253 @@ module \$__XILINX_SHREG_ (input C, input D, input [31:0] L, input E, output Q, o
       SRLC32E #(.INIT(INIT_R[128-1:96]), .IS_CLK_INVERTED(~CLKPOL[0])) fpga_srl_3 (.A(L[4:0]), .CE(CE), .CLK(C), .D(T5), .Q(T6), .Q31(SO));
       if (&_TECHMAP_CONSTMSK_L_)
         assign Q = T6;
-      else begin
-        wire T7, T8;
-        MUXF7 fpga_mux_0 (.O(T7), .I0(T0), .I1(T2), .S(L[5]));
-        MUXF7 fpga_mux_1 (.O(T8), .I0(T4), .I1(T6), .S(L[5]));
-        MUXF8 fpga_mux_2 (.O(Q), .I0(T7), .I1(T8), .S(L[6]));
-      end
+      else
+        \$__XILINX_MUXF78 fpga_hard_mux (.I0(T0), .I1(T2), .I2(T4), .I3(T6), .S0(L[5]), .S1(L[6]), .O(Q));
     end
-    else if (DEPTH <= 129 && ~&_TECHMAP_CONSTMSK_L_) begin
-      // Handle cases where fixed-length depth is
-      // just 1 over a convenient value
+    // For fixed length, if just 1 over a convenient value, decompose
+    else if (DEPTH <= 129 && &_TECHMAP_CONSTMSK_L_) begin
+      wire T;
+      \$__XILINX_SHREG_ #(.DEPTH(DEPTH-1), .INIT(INIT[DEPTH-1:1]), .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl      (.C(C), .D(D), .L({32{1'b1}}), .E(E), .Q(T));
+      \$__XILINX_SHREG_ #(.DEPTH(1),       .INIT(INIT[0]),         .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl_last (.C(C), .D(T), .L(L), .E(E), .Q(Q));
+    end
+    // For variable length, if just 1 over a convenient value, then bump up one more
+    else if (DEPTH < 129 && ~&_TECHMAP_CONSTMSK_L_)
       \$__XILINX_SHREG_ #(.DEPTH(DEPTH+1), .INIT({INIT,1'b0}), .CLKPOL(CLKPOL), .ENPOL(ENPOL)) _TECHMAP_REPLACE_ (.C(C), .D(D), .L(L), .E(E), .Q(Q));
-    end
     else begin
-      localparam lower_clog2 = $clog2((DEPTH+1)/2);
-      localparam lower_depth = 2 ** lower_clog2;
-      wire T0, T1, T2, T3;
-      if (&_TECHMAP_CONSTMSK_L_) begin
-        \$__XILINX_SHREG_ #(.DEPTH(lower_depth), .INIT(INIT[DEPTH-1:DEPTH-lower_depth]), .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl_0 (.C(C), .D(D), .L(lower_depth-1), .E(E), .Q(T0));
-        \$__XILINX_SHREG_ #(.DEPTH(DEPTH-lower_depth), .INIT(INIT[DEPTH-lower_depth-1:0]), .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl_1 (.C(C), .D(T0), .L(DEPTH-lower_depth-1), .E(E), .Q(Q), .SO(T3));
-      end
-      else begin
-        \$__XILINX_SHREG_ #(.DEPTH(lower_depth), .INIT(INIT[DEPTH-1:DEPTH-lower_depth]), .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl_0 (.C(C), .D(D), .L(L[lower_clog2-1:0]), .E(E), .Q(T0), .SO(T1));
-        \$__XILINX_SHREG_ #(.DEPTH(DEPTH-lower_depth), .INIT(INIT[DEPTH-lower_depth-1:0]), .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl_1 (.C(C), .D(T1), .L(L[lower_clog2-1:0]), .E(E), .Q(T2), .SO(T3));
-        assign Q = L[lower_clog2] ? T2 : T0;
-      end
-      if (DEPTH == 2 * lower_depth)
-          assign SO = T3;
+      localparam depth0 = 128;
+      localparam num_srl128 = DEPTH / depth0;
+      localparam depthN = DEPTH % depth0;
+      wire [num_srl128 + (depthN > 0 ? 1 : 0) - 1:0] T;
+      wire [num_srl128 + (depthN > 0 ? 1 : 0) :0] S;
+      assign S[0] = D;
+      genvar i;
+      for (i = 0; i < num_srl128; i++)
+        \$__XILINX_SHREG_ #(.DEPTH(depth0), .INIT(INIT[DEPTH-1-i*depth0-:depth0]), .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl      (.C(C), .D(S[i]),          .L(L[$clog2(depth0)-1:0]), .E(E), .Q(T[i]), .SO(S[i+1]));
+
+      if (depthN > 0)
+        \$__XILINX_SHREG_ #(.DEPTH(depthN), .INIT(INIT[depthN-1:0]),               .CLKPOL(CLKPOL), .ENPOL(ENPOL)) fpga_srl_last (.C(C), .D(S[num_srl128]), .L(L[$clog2(depth0)-1:0]), .E(E), .Q(T[num_srl128]));
+
+      if (&_TECHMAP_CONSTMSK_L_)
+        assign Q = T[num_srl128 + (depthN > 0 ? 1 : 0) - 1];
+      else
+        assign Q = T[L[DEPTH-1:$clog2(depth0)]];
     end
   endgenerate
 endmodule
+
+`ifdef MIN_MUX_INPUTS
+module \$__XILINX_SHIFTX (A, B, Y);
+  parameter A_SIGNED = 0;
+  parameter B_SIGNED = 0;
+  parameter A_WIDTH = 1;
+  parameter B_WIDTH = 1;
+  parameter Y_WIDTH = 1;
+
+  input [A_WIDTH-1:0] A;
+  input [B_WIDTH-1:0] B;
+  output [Y_WIDTH-1:0] Y;
+
+  parameter [A_WIDTH-1:0] _TECHMAP_CONSTMSK_A_ = 0;
+  parameter [A_WIDTH-1:0] _TECHMAP_CONSTVAL_A_ = 0;
+  parameter [B_WIDTH-1:0] _TECHMAP_CONSTMSK_B_ = 0;
+  parameter [B_WIDTH-1:0] _TECHMAP_CONSTVAL_B_ = 0;
+
+  function integer A_WIDTH_trimmed;
+    input integer start;
+  begin
+    A_WIDTH_trimmed = start;
+    while (A_WIDTH_trimmed > 0 && _TECHMAP_CONSTMSK_A_[A_WIDTH_trimmed-1] && _TECHMAP_CONSTVAL_A_[A_WIDTH_trimmed-1] === 1'bx)
+      A_WIDTH_trimmed = A_WIDTH_trimmed - 1;
+  end
+  endfunction
+
+  generate
+    genvar i, j;
+    // Bit-blast
+    if (Y_WIDTH > 1) begin
+      for (i = 0; i < Y_WIDTH; i++)
+        \$__XILINX_SHIFTX  #(.A_SIGNED(A_SIGNED), .B_SIGNED(B_SIGNED), .A_WIDTH(A_WIDTH-Y_WIDTH+1), .B_WIDTH(B_WIDTH), .Y_WIDTH(1'd1)) bitblast (.A(A[A_WIDTH-Y_WIDTH+i:i]), .B(B), .Y(Y[i]));
+    end
+    // If the LSB of B is constant zero (and Y_WIDTH is 1) then
+    //   we can optimise by removing every other entry from A
+    //   and popping the constant zero from B
+    else if (_TECHMAP_CONSTMSK_B_[0] && !_TECHMAP_CONSTVAL_B_[0]) begin
+      wire [(A_WIDTH+1)/2-1:0] A_i;
+      for (i = 0; i < (A_WIDTH+1)/2; i++)
+        assign A_i[i] = A[i*2];
+      \$__XILINX_SHIFTX  #(.A_SIGNED(A_SIGNED), .B_SIGNED(B_SIGNED), .A_WIDTH((A_WIDTH+1'd1)/2'd2), .B_WIDTH(B_WIDTH-1'd1), .Y_WIDTH(Y_WIDTH)) _TECHMAP_REPLACE_ (.A(A_i), .B(B[B_WIDTH-1:1]), .Y(Y));
+    end
+    // Trim off any leading 1'bx -es in A
+    else if (_TECHMAP_CONSTMSK_A_[A_WIDTH-1] && _TECHMAP_CONSTVAL_A_[A_WIDTH-1] === 1'bx) begin
+      localparam A_WIDTH_new = A_WIDTH_trimmed(A_WIDTH-1);
+      \$__XILINX_SHIFTX  #(.A_SIGNED(A_SIGNED), .B_SIGNED(B_SIGNED), .A_WIDTH(A_WIDTH_new), .B_WIDTH(B_WIDTH), .Y_WIDTH(Y_WIDTH)) _TECHMAP_REPLACE_ (.A(A[A_WIDTH_new-1:0]), .B(B), .Y(Y));
+    end
+    else if (A_WIDTH < `MIN_MUX_INPUTS) begin
+      wire _TECHMAP_FAIL_ = 1;
+    end
+    else if (A_WIDTH == 2) begin
+      MUXF7 fpga_hard_mux (.I0(A[0]), .I1(A[1]), .S(B[0]), .O(Y));
+    end
+    else if (A_WIDTH <= 4) begin
+      wire [4-1:0] Ax;
+      if (A_WIDTH == 4)
+        assign Ax = A;
+      else
+        // Rather than extend with 1'bx which gets flattened to 1'b0
+        // causing the "don't care" status to get lost, extend with
+        // the same driver of F7B.I0 so that we can optimise F7B away
+        // later
+        assign Ax = {A[1], A};
+      \$__XILINX_MUXF78 fpga_hard_mux (.I0(Ax[0]), .I1(Ax[2]), .I2(Ax[1]), .I3(Ax[3]), .S0(B[1]), .S1(B[0]), .O(Y));
+    end
+    // Note that the following decompositions are 'backwards' in that
+    // the LSBs are placed on the hard resources, and the soft resources
+    // are used for MSBs.
+    // This has the effect of more effectively utilising the hard mux;
+    // take for example a 5:1 multiplexer, currently this would map as:
+    //
+    //     A[0] \___  __                             A[0] \__  __
+    //     A[4] /   \|  \       whereas the more     A[1] /  \|  \
+    //     A[1] _____|   |      obvious mapping      A[2] \___|   |
+    //     A[2] _____|   |--    of MSBs to hard      A[3] /   |   |__
+    //     A[3]______|   |      resources would      A[4] ____|   |
+    //               |__/       lead to:             1'bx ____|   |
+    //                ||                                      |__/
+    //                ||                                       ||
+    //              B[1:0]                                   B[1:2]
+    //
+    // Expectation would be that the 'forward' mapping (right) is more
+    // area efficient (consider a 9:1 multiplexer using 2x4:1 multiplexers
+    // on its I0 and I1 inputs, and A[8] and 1'bx on its I2 and I3 inputs)
+    // but that the 'backwards' mapping (left) is more delay efficient
+    // since smaller LUTs are faster than wider ones.
+    else if (A_WIDTH <= 8) begin
+      wire [8-1:0] Ax = {{{8-A_WIDTH}{1'bx}}, A};
+      wire T0 = B[2] ? Ax[4] : Ax[0];
+      wire T1 = B[2] ? Ax[5] : Ax[1];
+      wire T2 = B[2] ? Ax[6] : Ax[2];
+      wire T3 = B[2] ? Ax[7] : Ax[3];
+      \$__XILINX_MUXF78 fpga_hard_mux (.I0(T0), .I1(T2), .I2(T1), .I3(T3), .S0(B[1]), .S1(B[0]), .O(Y));
+    end
+    else if (A_WIDTH <= 16) begin
+      wire [16-1:0] Ax = {{{16-A_WIDTH}{1'bx}}, A};
+      wire T0 = B[2] ? B[3] ? Ax[12] : Ax[4]
+                     : B[3] ? Ax[ 8] : Ax[0];
+      wire T1 = B[2] ? B[3] ? Ax[13] : Ax[5]
+                     : B[3] ? Ax[ 9] : Ax[1];
+      wire T2 = B[2] ? B[3] ? Ax[14] : Ax[6]
+                     : B[3] ? Ax[10] : Ax[2];
+      wire T3 = B[2] ? B[3] ? Ax[15] : Ax[7]
+                     : B[3] ? Ax[11] : Ax[3];
+      \$__XILINX_MUXF78 fpga_hard_mux (.I0(T0), .I1(T2), .I2(T1), .I3(T3), .S0(B[1]), .S1(B[0]), .O(Y));
+    end
+    else begin
+      localparam num_mux16 = (A_WIDTH+15) / 16;
+      localparam clog2_num_mux16 = $clog2(num_mux16);
+      wire [num_mux16-1:0] T;
+      wire [num_mux16*16-1:0] Ax = {{(num_mux16*16-A_WIDTH){1'bx}}, A};
+      for (i = 0; i < num_mux16; i++)
+        \$__XILINX_SHIFTX  #(
+          .A_SIGNED(A_SIGNED),
+          .B_SIGNED(B_SIGNED),
+          .A_WIDTH(16),
+          .B_WIDTH(4),
+          .Y_WIDTH(Y_WIDTH)
+        ) fpga_mux (
+          .A(Ax[i*16+:16]),
+          .B(B[3:0]),
+          .Y(T[i])
+        );
+      \$__XILINX_SHIFTX  #(
+          .A_SIGNED(A_SIGNED),
+          .B_SIGNED(B_SIGNED),
+          .A_WIDTH(num_mux16),
+          .B_WIDTH(clog2_num_mux16),
+          .Y_WIDTH(Y_WIDTH)
+      ) _TECHMAP_REPLACE_ (
+          .A(T),
+          .B(B[B_WIDTH-1-:clog2_num_mux16]),
+          .Y(Y));
+    end
+  endgenerate
+endmodule
+
+(* techmap_celltype = "$__XILINX_SHIFTX" *)
+module _90__XILINX_SHIFTX (A, B, Y);
+  parameter A_SIGNED = 0;
+  parameter B_SIGNED = 0;
+  parameter A_WIDTH = 1;
+  parameter B_WIDTH = 1;
+  parameter Y_WIDTH = 1;
+
+  input [A_WIDTH-1:0] A;
+  input [B_WIDTH-1:0] B;
+  output [Y_WIDTH-1:0] Y;
+
+  \$shiftx  #(.A_SIGNED(A_SIGNED), .B_SIGNED(B_SIGNED), .A_WIDTH(A_WIDTH), .B_WIDTH(B_WIDTH), .Y_WIDTH(Y_WIDTH)) _TECHMAP_REPLACE_ (.A(A), .B(B), .Y(Y));
+endmodule
+
+module \$_MUX_ (A, B, S, Y);
+  input A, B, S;
+  output Y;
+  generate
+    if (`MIN_MUX_INPUTS == 2)
+      \$__XILINX_SHIFTX  #(.A_SIGNED(0), .B_SIGNED(0), .A_WIDTH(2), .B_WIDTH(1), .Y_WIDTH(1)) _TECHMAP_REPLACE_ (.A({B,A}), .B(S), .Y(Y));
+    else
+      wire _TECHMAP_FAIL_ = 1;
+  endgenerate
+endmodule
+
+module \$_MUX4_ (A, B, C, D, S, T, Y);
+  input A, B, C, D, S, T;
+  output Y;
+  \$__XILINX_SHIFTX  #(.A_SIGNED(0), .B_SIGNED(0), .A_WIDTH(4), .B_WIDTH(2), .Y_WIDTH(1)) _TECHMAP_REPLACE_ (.A({D,C,B,A}), .B({T,S}), .Y(Y));
+endmodule
+
+module \$_MUX8_ (A, B, C, D, E, F, G, H, S, T, U, Y);
+  input A, B, C, D, E, F, G, H, S, T, U;
+  output Y;
+  \$__XILINX_SHIFTX  #(.A_SIGNED(0), .B_SIGNED(0), .A_WIDTH(8), .B_WIDTH(3), .Y_WIDTH(1)) _TECHMAP_REPLACE_ (.A({H,G,F,E,D,C,B,A}), .B({U,T,S}), .Y(Y));
+endmodule
+
+module \$_MUX16_ (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, S, T, U, V, Y);
+  input A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, S, T, U, V;
+  output Y;
+  \$__XILINX_SHIFTX  #(.A_SIGNED(0), .B_SIGNED(0), .A_WIDTH(16), .B_WIDTH(4), .Y_WIDTH(1)) _TECHMAP_REPLACE_ (.A({P,O,N,M,L,K,J,I,H,G,F,E,D,C,B,A}), .B({V,U,T,S}), .Y(Y));
+endmodule
+`endif
+
+`ifndef _ABC
+module \$__XILINX_MUXF78 (O, I0, I1, I2, I3, S0, S1);
+  output O;
+  input I0, I1, I2, I3, S0, S1;
+  wire T0, T1;
+  parameter _TECHMAP_BITS_CONNMAP_ = 0;
+  parameter [_TECHMAP_BITS_CONNMAP_-1:0] _TECHMAP_CONNMAP_I0_ = 0;
+  parameter [_TECHMAP_BITS_CONNMAP_-1:0] _TECHMAP_CONNMAP_I1_ = 0;
+  parameter [_TECHMAP_BITS_CONNMAP_-1:0] _TECHMAP_CONNMAP_I2_ = 0;
+  parameter [_TECHMAP_BITS_CONNMAP_-1:0] _TECHMAP_CONNMAP_I3_ = 0;
+  parameter _TECHMAP_CONSTMSK_S0_ = 0;
+  parameter _TECHMAP_CONSTVAL_S0_ = 0;
+  parameter _TECHMAP_CONSTMSK_S1_ = 0;
+  parameter _TECHMAP_CONSTVAL_S1_ = 0;
+  if (_TECHMAP_CONSTMSK_S0_ && _TECHMAP_CONSTVAL_S0_ === 1'b1)
+    assign T0 = I1;
+  else if (_TECHMAP_CONSTMSK_S0_ || _TECHMAP_CONNMAP_I0_ === _TECHMAP_CONNMAP_I1_)
+    assign T0 = I0;
+  else
+    MUXF7 mux7a (.I0(I0), .I1(I1), .S(S0), .O(T0));
+  if (_TECHMAP_CONSTMSK_S0_ && _TECHMAP_CONSTVAL_S0_ === 1'b1)
+    assign T1 = I3;
+  else if (_TECHMAP_CONSTMSK_S0_ || _TECHMAP_CONNMAP_I2_ === _TECHMAP_CONNMAP_I3_)
+    assign T1 = I2;
+  else
+    MUXF7 mux7b (.I0(I2), .I1(I3), .S(S0), .O(T1));
+  if (_TECHMAP_CONSTMSK_S1_ && _TECHMAP_CONSTVAL_S1_ === 1'b1)
+    assign O = T1;
+  else if (_TECHMAP_CONSTMSK_S1_ || (_TECHMAP_CONNMAP_I0_ === _TECHMAP_CONNMAP_I1_ && _TECHMAP_CONNMAP_I1_ === _TECHMAP_CONNMAP_I2_ && _TECHMAP_CONNMAP_I2_ === _TECHMAP_CONNMAP_I3_))
+    assign O = T0;
+  else
+    MUXF8 mux8 (.I0(T0), .I1(T1), .S(S1), .O(O));
+endmodule
+`endif
diff --git a/techlibs/xilinx/cells_sim.v b/techlibs/xilinx/cells_sim.v
index 5a148be01..3937d3536 100644
--- a/techlibs/xilinx/cells_sim.v
+++ b/techlibs/xilinx/cells_sim.v
@@ -169,11 +169,19 @@ module MUXF8(output O, input I0, I1, S);
   assign O = S ? I1 : I0;
 endmodule
 
+`ifdef _ABC
+(* abc_box_id = 3, lib_whitebox *)
+module \$__XILINX_MUXF78 (output O, input I0, I1, I2, I3, S0, S1);
+  assign O = S1 ? (S0 ? I3 : I2)
+                : (S0 ? I1 : I0);
+endmodule
+`endif
+
 module XORCY(output O, input CI, LI);
   assign O = CI ^ LI;
 endmodule
 
-(* abc_box_id = 3, abc_carry="CI,CO", lib_whitebox *)
+(* abc_box_id = 4, abc_carry="CI,CO", lib_whitebox *)
 module CARRY4(output [3:0] CO, O, input CI, CYINIT, input [3:0] DI, S);
   assign O = S ^ {CO[2:0], CI | CYINIT};
   assign CO[0] = S[0] ? CI | CYINIT : DI[0];
@@ -281,7 +289,7 @@ module FDPE_1 (output reg Q, input C, CE, D, PRE);
   always @(negedge C, posedge PRE) if (PRE) Q <= 1'b1; else if (CE) Q <= D;
 endmodule
 
-(* abc_box_id = 4, abc_scc_break="D,WE" *)
+(* abc_box_id = 5, abc_scc_break="D,WE" *)
 module RAM32X1D (
   output DPO, SPO,
   input  D, WCLK, WE,
@@ -299,7 +307,7 @@ module RAM32X1D (
   always @(posedge clk) if (WE) mem[a] <= D;
 endmodule
 
-(* abc_box_id = 5, abc_scc_break="D,WE" *)
+(* abc_box_id = 6, abc_scc_break="D,WE" *)
 module RAM64X1D (
   output DPO, SPO,
   input  D, WCLK, WE,
@@ -317,7 +325,7 @@ module RAM64X1D (
   always @(posedge clk) if (WE) mem[a] <= D;
 endmodule
 
-(* abc_box_id = 6, abc_scc_break="D,WE" *)
+(* abc_box_id = 7, abc_scc_break="D,WE" *)
 module RAM128X1D (
   output       DPO, SPO,
   input        D, WCLK, WE,
diff --git a/techlibs/xilinx/mux_map.v b/techlibs/xilinx/mux_map.v
new file mode 100644
index 000000000..91aaf2118
--- /dev/null
+++ b/techlibs/xilinx/mux_map.v
@@ -0,0 +1,71 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *                2019  Eddie Hung    <eddie@fpgeh.com>
+ *
+ *  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.
+ *
+ */
+
+// The purpose of these mapping rules is to allow preserve all (sufficiently
+// wide) $shiftx cells during 'techmap' so that they can be mapped to hard
+// resources, rather than being bit-blasted to gates during 'techmap'
+// execution
+
+module \$shiftx (A, B, Y);
+  parameter A_SIGNED = 0;
+  parameter B_SIGNED = 0;
+  parameter A_WIDTH = 1;
+  parameter B_WIDTH = 1;
+  parameter Y_WIDTH = 1;
+
+  input [A_WIDTH-1:0] A;
+  input [B_WIDTH-1:0] B;
+  output [Y_WIDTH-1:0] Y;
+
+  parameter [B_WIDTH-1:0] _TECHMAP_CONSTMSK_B_ = 0;
+  parameter [B_WIDTH-1:0] _TECHMAP_CONSTVAL_B_ = 0;
+
+  generate
+    if (B_SIGNED) begin
+      if (_TECHMAP_CONSTMSK_B_[B_WIDTH-1] && (_TECHMAP_CONSTVAL_B_[B_WIDTH-1] == 1'b0 || _TECHMAP_CONSTVAL_B_[B_WIDTH-1] === 1'bx))
+        // Optimisation to remove B_SIGNED if sign bit of B is constant-0
+        \$shiftx #(
+          .A_SIGNED(A_SIGNED),
+          .B_SIGNED(0),
+          .A_WIDTH(A_WIDTH),
+          .B_WIDTH(B_WIDTH-1'd1),
+          .Y_WIDTH(Y_WIDTH)
+        ) _TECHMAP_REPLACE_ (
+          .A(A), .B(B[B_WIDTH-2:0]), .Y(Y)
+        );
+      else
+        wire _TECHMAP_FAIL_ = 1;
+    end
+    else begin
+      if (((A_WIDTH + Y_WIDTH - 1) / Y_WIDTH) < `MIN_MUX_INPUTS)
+        wire _TECHMAP_FAIL_ = 1;
+      else
+        \$__XILINX_SHIFTX #(
+          .A_SIGNED(A_SIGNED),
+          .B_SIGNED(B_SIGNED),
+          .A_WIDTH(A_WIDTH),
+          .B_WIDTH(B_WIDTH),
+          .Y_WIDTH(Y_WIDTH)
+        ) _TECHMAP_REPLACE_ (
+          .A(A), .B(B), .Y(Y)
+        );
+    end
+  endgenerate
+endmodule
diff --git a/techlibs/xilinx/synth_xilinx.cc b/techlibs/xilinx/synth_xilinx.cc
index cdc64db1d..2455c2885 100644
--- a/techlibs/xilinx/synth_xilinx.cc
+++ b/techlibs/xilinx/synth_xilinx.cc
@@ -2,6 +2,7 @@
  *  yosys -- Yosys Open SYnthesis Suite
  *
  *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *            (C) 2019  Eddie Hung    <eddie@fpgeh.com>
  *
  *  Permission to use, copy, modify, and/or distribute this software for any
  *  purpose with or without fee is hereby granted, provided that the above
@@ -25,8 +26,8 @@
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
 
-#define XC7_WIRE_DELAY "300" // Number with which ABC will map a 6-input gate
-                             // to one LUT6 (instead of a LUT5 + LUT2)
+#define XC7_WIRE_DELAY 300 // Number with which ABC will map a 6-input gate
+                           // to one LUT6 (instead of a LUT5 + LUT2)
 
 struct SynthXilinxPass : public ScriptPass
 {
@@ -77,6 +78,11 @@ struct SynthXilinxPass : public ScriptPass
 		log("    -nowidelut\n");
 		log("        do not use MUXF[78] resources to implement LUTs larger than LUT6s\n");
 		log("\n");
+		log("    -widemux <int>\n");
+		log("        enable inference of hard multiplexer resources (MUXF[78]) for muxes at or\n");
+		log("        above this number of inputs (minimum value 2, recommended value >= 5).\n");
+		log("        default: 0 (no inference)\n");
+		log("\n");
 		log("    -run <from_label>:<to_label>\n");
 		log("        only run the commands between the labels (see below). an empty\n");
 		log("        from label is synonymous to 'begin', and empty to label is\n");
@@ -99,6 +105,7 @@ struct SynthXilinxPass : public ScriptPass
 
 	std::string top_opt, edif_file, blif_file, family;
 	bool flatten, retime, vpr, nobram, nodram, nosrl, nocarry, nowidelut, abc9;
+	int widemux;
 
 	void clear_flags() YS_OVERRIDE
 	{
@@ -116,6 +123,7 @@ struct SynthXilinxPass : public ScriptPass
 		nocarry = false;
 		nowidelut = false;
 		abc9 = false;
+		widemux = 0;
 	}
 
 	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
@@ -186,6 +194,10 @@ struct SynthXilinxPass : public ScriptPass
 				nosrl = true;
 				continue;
 			}
+			if (args[argidx] == "-widemux" && argidx+1 < args.size()) {
+				widemux = std::stoi(args[++argidx]);
+				continue;
+			}
 			if (args[argidx] == "-abc9") {
 				abc9 = true;
 				continue;
@@ -195,11 +207,17 @@ struct SynthXilinxPass : public ScriptPass
 		extra_args(args, argidx, design);
 
 		if (family != "xcup" && family != "xcu" && family != "xc7" && family != "xc6s")
-			log_cmd_error("Invalid Xilinx -family setting: %s\n", family.c_str());
+			log_cmd_error("Invalid Xilinx -family setting: '%s'.\n", family.c_str());
+
+		if (widemux != 0 && widemux < 2)
+			log_cmd_error("-widemux value must be 0 or >= 2.\n");
 
 		if (!design->full_selection())
 			log_cmd_error("This command only operates on fully selected designs!\n");
 
+		if (abc9 && retime)
+			log_cmd_error("-retime option not currently compatible with -abc9!\n");
+
 		log_header(design, "Executing SYNTH_XILINX pass.\n");
 		log_push();
 
@@ -212,9 +230,9 @@ struct SynthXilinxPass : public ScriptPass
 	{
 		if (check_label("begin")) {
 			if (vpr)
-				run("read_verilog -lib -D _ABC -D_EXPLICIT_CARRY +/xilinx/cells_sim.v");
+				run("read_verilog -lib -icells -D _ABC -D_EXPLICIT_CARRY +/xilinx/cells_sim.v");
 			else
-				run("read_verilog -lib -D _ABC +/xilinx/cells_sim.v");
+				run("read_verilog -lib -icells -D _ABC +/xilinx/cells_sim.v");
 
 			run("read_verilog -lib +/xilinx/cells_xtra.v");
 
@@ -224,21 +242,41 @@ struct SynthXilinxPass : public ScriptPass
 			run(stringf("hierarchy -check %s", top_opt.c_str()));
 		}
 
-		if (check_label("flatten", "(with '-flatten' only)")) {
-			if (flatten || help_mode) {
-				run("proc");
-				run("flatten");
-			}
-		}
-
 		if (check_label("coarse")) {
-			run("synth -run coarse");
+			run("proc");
+			if (help_mode || flatten)
+				run("flatten", "(if -flatten)");
+			run("opt_expr");
+			run("opt_clean");
+			run("check");
+			run("opt");
+			if (help_mode)
+				run("wreduce [-keepdc]", "(option for '-widemux')");
+			else
+				run("wreduce" + std::string(widemux > 0 ? " -keepdc" : ""));
+			run("peepopt");
+			run("opt_clean");
+
+			if (widemux > 0 || help_mode)
+				run("muxpack", "    ('-widemux' only)");
 
 			// shregmap -tech xilinx can cope with $shiftx and $mux
 			//   cells for identifying variable-length shift registers,
 			//   so attempt to convert $pmux-es to the former
-			if (!nosrl || help_mode)
-				run("pmux2shiftx", "(skip if '-nosrl')");
+			// Also: wide multiplexer inference benefits from this too
+			if (!(nosrl && widemux == 0) || help_mode) {
+				run("pmux2shiftx", "(skip if '-nosrl' and '-widemux=0')");
+				run("clean", "      (skip if '-nosrl' and '-widemux=0')");
+			}
+
+			run("techmap -map +/cmp2lut.v -D LUT_WIDTH=6");
+			run("alumacc");
+			run("share");
+			run("opt");
+			run("fsm");
+			run("opt -fast");
+			run("memory -nomap");
+			run("opt_clean");
 		}
 
 		if (check_label("bram", "(skip if '-nobram')")) {
@@ -256,54 +294,89 @@ struct SynthXilinxPass : public ScriptPass
 		}
 
 		if (check_label("fine")) {
-			run("opt -fast -full");
+			if (widemux > 0)
+				run("opt -fast -mux_bool -undriven -fine"); // Necessary to omit -mux_undef otherwise muxcover
+									    // performs less efficiently
+			else
+				run("opt -fast -full");
 			run("memory_map");
 			run("dffsr2dff");
 			run("dff2dffe");
+			if (help_mode) {
+				run("simplemap t:$mux", "         ('-widemux' only)");
+				run("muxcover <internal options>, ('-widemux' only)");
+			}
+			else if (widemux > 0) {
+				run("simplemap t:$mux");
+				constexpr int cost_mux2 = 100;
+				std::string muxcover_args = stringf(" -nodecode -mux2=%d", cost_mux2);
+				switch (widemux) {
+					case  2: muxcover_args += stringf(" -mux4=%d -mux8=%d -mux16=%d", cost_mux2+1, cost_mux2+2, cost_mux2+3); break;
+					case  3:
+					case  4: muxcover_args += stringf(" -mux4=%d -mux8=%d -mux16=%d", cost_mux2*(widemux-1)-2, cost_mux2*(widemux-1)-1, cost_mux2*(widemux-1)); break;
+					case  5:
+					case  6:
+					case  7:
+					case  8: muxcover_args += stringf(" -mux8=%d -mux16=%d", cost_mux2*(widemux-1)-1, cost_mux2*(widemux-1)); break;
+					case  9:
+					case 10:
+					case 11:
+					case 12:
+					case 13:
+					case 14:
+					case 15:
+					default: muxcover_args += stringf(" -mux16=%d", cost_mux2*(widemux-1)-1); break;
+				}
+				run("muxcover " + muxcover_args);
+			}
 			run("opt -full");
 
 			if (!nosrl || help_mode) {
 				// shregmap operates on bit-level flops, not word-level,
 				//   so break those down here
-				run("simplemap t:$dff t:$dffe", "(skip if '-nosrl')");
+				run("simplemap t:$dff t:$dffe", "       (skip if '-nosrl')");
 				// shregmap with '-tech xilinx' infers variable length shift regs
 				run("shregmap -tech xilinx -minlen 3", "(skip if '-nosrl')");
 			}
 
-			std::string techmap_files = " -map +/techmap.v";
+			std::string techmap_args = " -map +/techmap.v";
 			if (help_mode)
-				techmap_files += " [-map +/xilinx/arith_map.v]";
+				techmap_args += " [-map +/xilinx/mux_map.v]";
+			else if (widemux > 0)
+				techmap_args += stringf(" -D MIN_MUX_INPUTS=%d -map +/xilinx/mux_map.v", widemux);
+			if (help_mode)
+				techmap_args += " [-map +/xilinx/arith_map.v]";
 			else if (!nocarry) {
-				techmap_files += " -map +/xilinx/arith_map.v";
+				techmap_args += " -map +/xilinx/arith_map.v";
 				if (vpr)
-					techmap_files += " -D _EXPLICIT_CARRY";
+					techmap_args += " -D _EXPLICIT_CARRY";
 				else if (abc9)
-					techmap_files += " -D _CLB_CARRY";
+					techmap_args += " -D _CLB_CARRY";
 			}
-			run("techmap " + techmap_files);
+			run("techmap " + techmap_args);
 			run("opt -fast");
 		}
 
 		if (check_label("map_cells")) {
-			if (abc9)
-				run("techmap -map +/techmap.v -map +/xilinx/cells_map.v -D _ABC -map +/xilinx/ff_map.v");
-			else
-				run("techmap -map +/techmap.v -map +/xilinx/cells_map.v");
+			std::string techmap_args = "-map +/techmap.v -D _ABC -map +/xilinx/cells_map.v";
+			if (widemux > 0)
+				techmap_args += stringf(" -D MIN_MUX_INPUTS=%d", widemux);
+			run("techmap " + techmap_args);
 			run("clean");
 		}
 
 		if (check_label("map_luts")) {
 			run("opt_expr -mux_undef");
 			if (help_mode)
-				run("abc -luts 2:2,3,6:5[,10,20] [-dff]", "(skip if 'nowidelut', only for '-retime')");
+				run("abc -luts 2:2,3,6:5[,10,20] [-dff]", "(option for 'nowidelut', option for '-retime')");
 			else if (abc9) {
 				if (family != "xc7")
 					log_warning("'synth_xilinx -abc9' currently supports '-family xc7' only.\n");
 				run("read_verilog -icells -lib +/xilinx/abc_ff.v");
 				if (nowidelut)
-					run("abc9 -lut +/xilinx/abc_xc7_nowide.lut -box +/xilinx/abc_xc7.box -W " + std::string(XC7_WIRE_DELAY) + string(retime ? " -dff" : ""));
+					run("abc9 -lut +/xilinx/abc_xc7_nowide.lut -box +/xilinx/abc_xc7.box -W " + std::to_string(XC7_WIRE_DELAY));
 				else
-					run("abc9 -lut +/xilinx/abc_xc7.lut -box +/xilinx/abc_xc7.box -W " + std::string(XC7_WIRE_DELAY) + string(retime ? " -dff" : ""));
+					run("abc9 -lut +/xilinx/abc_xc7.lut -box +/xilinx/abc_xc7.box -W " + std::to_string(XC7_WIRE_DELAY));
 			}
 			else {
 				if (nowidelut)
diff --git a/tests/simple_abc9/.gitignore b/tests/simple_abc9/.gitignore
new file mode 100644
index 000000000..598951333
--- /dev/null
+++ b/tests/simple_abc9/.gitignore
@@ -0,0 +1,3 @@
+*.v
+*.log
+*.out
diff --git a/tests/various/abc9.v b/tests/various/abc9.v
index 8271cd249..a08b613a8 100644
--- a/tests/various/abc9.v
+++ b/tests/various/abc9.v
@@ -3,3 +3,7 @@ initial o = 1'b0;
 always @*
     o <= ~o;
 endmodule
+
+module abc9_test028(input i, output o);
+unknown u(~i, o);
+endmodule
diff --git a/tests/various/abc9.ys b/tests/various/abc9.ys
index 922f7005d..a84b637d9 100644
--- a/tests/various/abc9.ys
+++ b/tests/various/abc9.ys
@@ -1,4 +1,6 @@
 read_verilog abc9.v
+design -save read
+hierarchy -top abc9_test027
 proc
 design -save gold
 
@@ -12,3 +14,11 @@ design -import gate -as gate
 miter -equiv -flatten -make_assert -make_outputs gold gate miter
 sat -verify -prove-asserts -show-ports miter
 
+design -load read
+hierarchy -top abc9_test028
+proc
+
+abc9 -lut 4
+select -assert-count 1 t:$lut r:LUT=1 r:WIDTH=1 %i %i
+select -assert-count 1 t:unknown
+select -assert-none t:$lut t:unknown %% t: %D
diff --git a/tests/various/async.sh b/tests/various/async.sh
new file mode 100644
index 000000000..7c41d6d94
--- /dev/null
+++ b/tests/various/async.sh
@@ -0,0 +1,11 @@
+#!/bin/bash
+set -ex
+../../yosys -q -o async_syn.v -p 'synth; rename uut syn' async.v
+../../yosys -q -o async_prp.v -p 'prep; rename uut prp' async.v
+../../yosys -q -o async_a2s.v -p 'prep; async2sync; rename uut a2s' async.v
+../../yosys -q -o async_ffl.v -p 'prep; clk2fflogic; rename uut ffl' async.v
+iverilog -o async_sim -DTESTBENCH async.v async_???.v
+vvp -N async_sim > async.out
+tail async.out
+grep PASS async.out
+rm -f async_???.v async_sim async.out async.vcd
diff --git a/tests/various/async.v b/tests/various/async.v
new file mode 100644
index 000000000..c27e30c4b
--- /dev/null
+++ b/tests/various/async.v
@@ -0,0 +1,108 @@
+`define MAXQ 2
+module uut (
+	input clk,
+	input d, r, e,
+	output [`MAXQ:0] q
+);
+	reg q0;
+	always @(posedge clk) begin
+		if (r)
+			q0 <= 0;
+		else if (e)
+			q0 <= d;
+	end
+
+	reg q1;
+	always @(posedge clk, posedge r) begin
+		if (r)
+			q1 <= 0;
+		else if (e)
+			q1 <= d;
+	end
+
+	reg q2;
+	always @(posedge clk, negedge r) begin
+		if (!r)
+			q2 <= 0;
+		else if (!e)
+			q2 <= d;
+	end
+
+	assign q = {q2, q1, q0};
+endmodule
+
+`ifdef TESTBENCH
+module \$ff #(
+	parameter integer WIDTH = 1
+) (
+	input [WIDTH-1:0] D,
+	output reg [WIDTH-1:0] Q
+);
+	wire sysclk = testbench.sysclk;
+	always @(posedge sysclk)
+		Q <= D;
+endmodule
+
+module testbench;
+	reg sysclk;
+	always #5 sysclk = (sysclk === 1'b0);
+
+	reg clk;
+	always @(posedge sysclk) clk = (clk === 1'b0);
+
+	reg d, r, e;
+
+	wire [`MAXQ:0] q_uut;
+	uut uut (.clk(clk), .d(d), .r(r), .e(e), .q(q_uut));
+
+	wire [`MAXQ:0] q_syn;
+	syn syn (.clk(clk), .d(d), .r(r), .e(e), .q(q_syn));
+
+	wire [`MAXQ:0] q_prp;
+	prp prp (.clk(clk), .d(d), .r(r), .e(e), .q(q_prp));
+
+	wire [`MAXQ:0] q_a2s;
+	a2s a2s (.clk(clk), .d(d), .r(r), .e(e), .q(q_a2s));
+
+	wire [`MAXQ:0] q_ffl;
+	ffl ffl (.clk(clk), .d(d), .r(r), .e(e), .q(q_ffl));
+
+	task printq;
+		reg [5*8-1:0] msg;
+		begin
+			msg = "OK";
+			if (q_uut !== q_syn) msg = "SYN";
+			if (q_uut !== q_prp) msg = "PRP";
+			if (q_uut !== q_a2s) msg = "A2S";
+			if (q_uut !== q_ffl) msg = "FFL";
+			$display("%6t %b %b %b %b %b %s", $time, q_uut, q_syn, q_prp, q_a2s, q_ffl, msg);
+			if (msg != "OK") $finish;
+		end
+	endtask
+
+	initial if(0) begin
+		$dumpfile("async.vcd");
+		$dumpvars(0, testbench);
+	end
+
+	initial begin
+		@(posedge clk);
+		d <= 0;
+		r <= 0;
+		e <= 0;
+		@(posedge clk);
+		e <= 1;
+		@(posedge clk);
+		e <= 0;
+		repeat (10000) begin
+			@(posedge clk);
+			printq;
+			d <= $random;
+			r <= $random;
+			e <= $random;
+		end
+		$display("PASS");
+		$finish;
+	end
+endmodule
+`endif
diff --git a/tests/various/run-test.sh b/tests/various/run-test.sh
index d49553ede..92b905765 100755
--- a/tests/various/run-test.sh
+++ b/tests/various/run-test.sh
@@ -4,11 +4,9 @@ for x in *.ys; do
 	echo "Running $x.."
 	../../yosys -ql ${x%.ys}.log $x
 done
-# Run any .sh files in this directory (with the exception of the file - run-test.sh
-shell_tests=$(echo *.sh | sed -e 's/run-test.sh//')
-if [ "$shell_tests" ]; then
-    for s in $shell_tests; do
-        echo "Running $s.."
-        bash $s
-    done
-fi
+for s in *.sh; do
+	if [ "$s" != "run-test.sh" ]; then
+		echo "Running $s.."
+		bash $s
+	fi
+done
diff --git a/tests/various/specify.v b/tests/various/specify.v
index afc421da8..5d44d78f7 100644
--- a/tests/various/specify.v
+++ b/tests/various/specify.v
@@ -7,9 +7,11 @@ module test (
 		if (EN) Q <= D;
 
 	specify
-		if (EN) (CLK *> (Q : D)) = (1, 2:3:4);
+`ifndef SKIP_UNSUPPORTED_IGN_PARSER_CONSTRUCTS
+		if (EN) (posedge CLK *> (Q : D)) = (1, 2:3:4);
 		$setup(D, posedge CLK &&& EN, 5);
 		$hold(posedge CLK, D &&& EN, 6);
+`endif
 	endspecify
 endmodule
 
@@ -28,3 +30,10 @@ module test2 (
 		(B => Q) = 1.5;
 	endspecify
 endmodule
+
+module issue01144(input clk, d, output q);
+specify
+  (posedge clk => (q +: d)) = (3,1);
+  (posedge clk *> (q +: d)) = (3,1);
+endspecify
+endmodule
diff --git a/tests/various/specify.ys b/tests/various/specify.ys
index a5ca07219..00597e1e2 100644
--- a/tests/various/specify.ys
+++ b/tests/various/specify.ys
@@ -54,3 +54,5 @@ equiv_struct
 equiv_induct -seq 5
 equiv_status -assert
 design -reset
+
+read_verilog -DSKIP_UNSUPPORTED_IGN_PARSER_CONSTRUCTS specify.v