opt_clean: move unused_bits analysis to kernel/unused_bits.h

backends/edif/edif.cc

@@ -406,7 +406,6 @@ struct EdifBackend : public Backend {
 						auto count_nontrivial_attr = [](Wire *w) {
 							int count = w->attributes.size();
 							count -= w->attributes.count(ID::src);
-							count -= w->attributes.count(ID::unused_bits);
 							return count;
 						};
 

docs/source/using_yosys/synthesis/fsm.rst

@@ -108,9 +108,7 @@ FSM optimization
 The `fsm_opt` pass performs basic optimizations on `$fsm` cells (not including
 state recoding). The following optimizations are performed (in this order):
 
--  Unused control outputs are removed from the `$fsm` cell. The attribute
-   ``unused_bits`` (that is usually set by the `opt_clean` pass) is used to
-   determine which control outputs are unused.
+-  Unused control outputs are removed from the `$fsm` cell.
 
 -  Control inputs that are connected to the same driver are merged.
 

docs/source/using_yosys/synthesis/opt.rst

@@ -203,8 +203,6 @@ Removing unused cells and wires - `opt_clean` pass
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 This pass identifies unused signals and cells and removes them from the design.
-It also creates an ``unused_bits`` attribute on wires with unused bits. This
-attribute can be used for debugging or by other optimization passes.
 
 When to use `opt` or `clean`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

kernel/CMakeLists.txt

@@ -80,6 +80,7 @@ yosys_core(kernel
 	threading.h
 	timinginfo.h
 	topo_scc.h
+	unused_bits.h
 	utils.h
 	version.cc
 	yosys.cc
@@ -145,6 +146,7 @@ yosys_core(kernel
 		sigtools.h
 		threading.h
 		timinginfo.h
+		unused_bits.h
 		utils.h
 		yosys.h
 		yosys_common.h

kernel/constids.inc

@@ -1029,7 +1029,6 @@ X(unsigned_a_i)
 X(unsigned_b)
 X(unsigned_b_i)
 X(unsupported_sva)
-X(unused_bits)
 X(use_dsp)
 X(value)
 X(via_celltype)

kernel/unused_bits.h

@@ -0,0 +1,54 @@
+#ifndef UNUSED_BITS_H
+#define UNUSED_BITS_H
+
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+#include "kernel/newcelltypes.h"
+
+YOSYS_NAMESPACE_BEGIN
+
+struct UnusedBits
+{
+	SigMap sigmap;
+	pool<RTLIL::SigBit> used;
+
+	UnusedBits(RTLIL::Module *module) : sigmap(module)
+	{
+		NewCellTypes ct(module->design);
+		collect_used(module, ct);
+	}
+
+	UnusedBits(RTLIL::Module *module, const NewCellTypes &ct) : sigmap(module)
+	{
+		collect_used(module, ct);
+	}
+
+	void collect_used(RTLIL::Module *module, const NewCellTypes &ct)
+	{
+		for (auto cell : module->cells())
+			for (auto &conn : cell->connections())
+				if (!ct.cell_output(cell->type, conn.first))
+					add_used(conn.second);
+
+		for (auto wire : module->wires())
+			if (wire->port_output)
+				add_used(wire);
+	}
+
+	void add_used(const RTLIL::SigSpec &sig)
+	{
+		for (auto bit : sigmap(sig))
+			if (bit.wire != nullptr)
+				used.insert(bit);
+	}
+
+	bool check(RTLIL::SigBit bit) const
+	{
+		RTLIL::SigBit mapped = sigmap(bit);
+		return mapped.wire != nullptr && !used.count(mapped);
+	}
+};
+
+YOSYS_NAMESPACE_END
+
+#endif

passes/cmds/wrapcell.cc

@@ -19,6 +19,7 @@
 #include "kernel/yosys.h"
 #include "kernel/celltypes.h"
 #include "kernel/sigtools.h"
+#include "kernel/unused_bits.h"
 #include "backends/rtlil/rtlil_backend.h"
 
 USING_YOSYS_NAMESPACE
@@ -190,19 +191,10 @@ struct WrapcellPass : Pass {
 
 		bool tracking_unused = has_fmt_field(name_fmt, "%unused");
 
-		for (auto module : d->selected_modules()) {
-			SigPool unused;
+		NewCellTypes ct_all(d);
 
-			for (auto wire : module->wires())
-			if (wire->has_attribute(ID::unused_bits)) {
-				std::string str = wire->get_string_attribute(ID::unused_bits);
-				for (auto it = str.begin(); it != str.end();) {
-					auto sep = it;
-					for (; sep != str.end() && *sep != ' '; sep++);
-					unused.add(SigBit(wire, std::stoi(std::string(it, sep))));
-					for (it = sep; it != str.end() && *it == ' '; it++);
-				}
-			}
+		for (auto module : d->selected_modules()) {
+			UnusedBits unused(module, ct_all);
 
 			for (auto cell : module->selected_cells()) {
 				Module *subm;

passes/fsm/fsm_expand.cc

@@ -22,6 +22,7 @@
 #include "kernel/sigtools.h"
 #include "kernel/consteval.h"
 #include "kernel/celltypes.h"
+#include "kernel/unused_bits.h"
 #include "fsmdata.h"
 #include <string.h>
 
@@ -32,6 +33,7 @@ struct FsmExpand
 {
 	RTLIL::Module *module;
 	RTLIL::Cell *fsm_cell;
+	UnusedBits& unused_bits;
 	bool full_mode;
 
 	SigMap assign_map;
@@ -127,7 +129,7 @@ struct FsmExpand
 		if (trans_num > limit_transitions)
 		{
 			log("  grown transition table to %d entries -> optimize.\n", trans_num);
-			FsmData::optimize_fsm(fsm_cell, module);
+			FsmData::optimize_fsm(fsm_cell, module, unused_bits);
 			already_optimized = true;
 
 			trans_num = fsm_cell->parameters[ID::TRANS_NUM].as_int();
@@ -218,7 +220,7 @@ struct FsmExpand
 		fsm_data.copy_to_cell(fsm_cell);
 	}
 
-	FsmExpand(RTLIL::Cell *cell, RTLIL::Design *design, RTLIL::Module *mod, bool full)
+	FsmExpand(RTLIL::Cell *cell, RTLIL::Design *design, RTLIL::Module *mod, UnusedBits& unused_bits, bool full) : unused_bits(unused_bits)
 	{
 		module = mod;
 		fsm_cell = cell;
@@ -257,7 +259,7 @@ struct FsmExpand
 			module->remove(c);
 
 		if (merged_set.size() > 0 && !already_optimized)
-			FsmData::optimize_fsm(fsm_cell, module);
+			FsmData::optimize_fsm(fsm_cell, module, unused_bits);
 
 		log("  merged %d cells into FSM.\n", GetSize(merged_set));
 	}
@@ -296,12 +298,13 @@ struct FsmExpandPass : public Pass {
 		extra_args(args, argidx, design);
 
 		for (auto mod : design->selected_modules()) {
+			UnusedBits unused_bits(mod);
 			std::vector<RTLIL::Cell*> fsm_cells;
 			for (auto cell : mod->selected_cells())
 				if (cell->type == ID($fsm))
 					fsm_cells.push_back(cell);
 			for (auto c : fsm_cells) {
-				FsmExpand fsm_expand(c, design, mod, full_mode);
+				FsmExpand fsm_expand(c, design, mod, unused_bits, full_mode);
 				fsm_expand.execute();
 			}
 		}

passes/fsm/fsm_opt.cc

@@ -22,8 +22,8 @@
 #include "kernel/sigtools.h"
 #include "kernel/consteval.h"
 #include "kernel/celltypes.h"
+#include "kernel/unused_bits.h"
 #include "fsmdata.h"
-#include <string.h>
 
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
@@ -33,6 +33,7 @@ struct FsmOpt
 	FsmData fsm_data;
 	RTLIL::Cell *cell;
 	RTLIL::Module *module;
+	UnusedBits& unused_bits;
 
 	void opt_unreachable_states()
 	{
@@ -79,21 +80,7 @@ struct FsmOpt
 
 	bool signal_is_unused(RTLIL::SigSpec sig)
 	{
-		RTLIL::SigBit bit = sig.as_bit();
-
-		if (bit.wire == NULL || bit.wire->attributes.count(ID::unused_bits) == 0)
-			return false;
-
-		char *str = strdup(bit.wire->attributes[ID::unused_bits].decode_string().c_str());
-		for (char *tok = strtok(str, " "); tok != NULL; tok = strtok(NULL, " ")) {
-			if (tok[0] && bit.offset == atoi(tok)) {
-				free(str);
-				return true;
-			}
-		}
-		free(str);
-
-		return false;
+		return unused_bits.check(sig.as_bit());
 	}
 
 	void opt_const_and_unused_inputs()
@@ -294,7 +281,7 @@ struct FsmOpt
 		}
 	}
 
-	FsmOpt(RTLIL::Cell *cell, RTLIL::Module *module)
+	FsmOpt(RTLIL::Cell *cell, RTLIL::Module *module, UnusedBits& unused_bits) : unused_bits(unused_bits)
 	{
 		log("Optimizing FSM `%s' from module `%s'.\n", cell->name, module->name);
 
@@ -318,9 +305,9 @@ struct FsmOpt
 
 PRIVATE_NAMESPACE_END
 
-void YOSYS_NAMESPACE_PREFIX FsmData::optimize_fsm(RTLIL::Cell *cell, RTLIL::Module *module)
+void YOSYS_NAMESPACE_PREFIX FsmData::optimize_fsm(RTLIL::Cell *cell, RTLIL::Module *module, UnusedBits& unused_bits)
 {
-	FsmOpt fsmopt(cell, module);
+	FsmOpt fsmopt(cell, module, unused_bits);
 }
 
 PRIVATE_NAMESPACE_BEGIN
@@ -343,10 +330,12 @@ struct FsmOptPass : public Pass {
 		log_header(design, "Executing FSM_OPT pass (simple optimizations of FSMs).\n");
 		extra_args(args, 1, design);
 
-		for (auto mod : design->selected_modules())
+		for (auto mod : design->selected_modules()) {
+			UnusedBits unused_bits(mod);
 			for (auto cell : mod->selected_cells())
 				if (cell->type == ID($fsm))
-					FsmData::optimize_fsm(cell, mod);
+					FsmData::optimize_fsm(cell, mod, unused_bits);
+		}
 	}
 } FsmOptPass;
 

passes/fsm/fsmdata.h

@@ -21,6 +21,7 @@
 #define FSMDATA_H
 
 #include "kernel/yosys.h"
+#include "kernel/unused_bits.h"
 
 YOSYS_NAMESPACE_BEGIN
 
@@ -155,7 +156,7 @@ struct FsmData
 	}
 
 	// implemented in fsm_opt.cc
-	static void optimize_fsm(RTLIL::Cell *cell, RTLIL::Module *module);
+	static void optimize_fsm(RTLIL::Cell *cell, RTLIL::Module *module, UnusedBits& unused_bits);
 };
 
 YOSYS_NAMESPACE_END

passes/opt/opt_clean/wires.cc

@@ -86,7 +86,6 @@ int count_nontrivial_wire_attrs(RTLIL::Wire *w)
 	count -= w->attributes.count(ID::src);
 	count -= w->attributes.count(ID::hdlname);
 	count -= w->attributes.count(ID::scopename);
-	count -= w->attributes.count(ID::unused_bits);
 	return count;
 }
 
@@ -168,13 +167,6 @@ bool check_any(const ShardedSigPool &sigs, const RTLIL::SigSpec &spec) {
 	return false;
 }
 
-bool check_all(const ShardedSigPool &sigs, const RTLIL::SigSpec &spec) {
-	for (SigBit b : spec)
-		if (sigs.find({b, b.hash_top().yield()}) == nullptr)
-			return false;
-	return true;
-}
-
 struct UpdateConnection {
 	RTLIL::Cell *cell;
 	RTLIL::IdString port;
@@ -328,33 +320,28 @@ struct DeferredUpdates {
 };
 struct UsedSignals {
 	// here, "connected" means "driven or driving something"
-	// meanwhile, "used" means "driving something"
 	// sigmapped
 	ShardedSigPool connected;
 	// pre-sigmapped
 	ShardedSigPool raw_connected;
-	// sigmapped
-	ShardedSigPool used;
 
 	void clear(ParallelDispatchThreadPool::Subpool &subpool) {
 		subpool.run([this](const ParallelDispatchThreadPool::RunCtx &ctx) {
 			connected.clear(ctx);
 			raw_connected.clear(ctx);
-			used.clear(ctx);
 		});
 	}
 };
 
-DeferredUpdates analyse_connectivity(UsedSignals& used, SigConnKinds& sig_analysis, const AnalysisContext& actx, CleanRunContext &clean_ctx) {
+DeferredUpdates analyse_connectivity(UsedSignals& used, SigConnKinds& sig_analysis, const AnalysisContext& actx) {
 	DeferredUpdates deferred(actx.subpool);
 	ShardedSigPool::Builder conn_builder(actx.subpool);
 	ShardedSigPool::Builder raw_conn_builder(actx.subpool);
-	ShardedSigPool::Builder used_builder(actx.subpool);
 
 	// gather the usage information for cells and update cell connections with the altered sigmap
 	// also gather the usage information for ports, wires with `keep`
 	// also gather init bits
-	actx.subpool.run([&deferred, &conn_builder, &raw_conn_builder, &used_builder, &sig_analysis, &actx, &clean_ctx](const ParallelDispatchThreadPool::RunCtx &ctx) {
+	actx.subpool.run([&deferred, &conn_builder, &raw_conn_builder, &sig_analysis, &actx](const ParallelDispatchThreadPool::RunCtx &ctx) {
 		// Parallel destruction of these sharded structures
 		sig_analysis.clear(ctx);
 
@@ -366,8 +353,6 @@ DeferredUpdates analyse_connectivity(UsedSignals& used, SigConnKinds& sig_analys
 					deferred.update_connections.insert(ctx, {cell, port, spec});
 				add_spec(raw_conn_builder, ctx, spec);
 				add_spec(conn_builder, ctx, spec);
-				if (!clean_ctx.ct_all.cell_output(cell->type, port))
-					add_spec(used_builder, ctx, spec);
 			}
 		}
 		for (int i : ctx.item_range(actx.mod->wires_size())) {
@@ -377,8 +362,6 @@ DeferredUpdates analyse_connectivity(UsedSignals& used, SigConnKinds& sig_analys
 				add_spec(raw_conn_builder, ctx, sig);
 				actx.assign_map.apply(sig);
 				add_spec(conn_builder, ctx, sig);
-				if (!wire->port_input)
-					add_spec(used_builder, ctx, sig);
 			}
 			if (wire->get_bool_attribute(ID::keep)) {
 				RTLIL::SigSpec sig = RTLIL::SigSpec(wire);
@@ -390,12 +373,11 @@ DeferredUpdates analyse_connectivity(UsedSignals& used, SigConnKinds& sig_analys
 				deferred.initialized_wires.insert(ctx, wire);
 		}
 	});
-	actx.subpool.run([&conn_builder, &raw_conn_builder, &used_builder](const ParallelDispatchThreadPool::RunCtx &ctx) {
+	actx.subpool.run([&conn_builder, &raw_conn_builder](const ParallelDispatchThreadPool::RunCtx &ctx) {
 		conn_builder.process(ctx);
 		raw_conn_builder.process(ctx);
-		used_builder.process(ctx);
 	});
-	used = {conn_builder, raw_conn_builder, used_builder};
+	used = {conn_builder, raw_conn_builder};
 	return deferred;
 }
 
@@ -404,14 +386,10 @@ struct WireDeleter {
 	ShardedVector<RTLIL::Wire*> remove_init;
 	ShardedVector<std::pair<RTLIL::Wire*, RTLIL::Const>> set_init;
 	ShardedVector<RTLIL::SigSig> new_connections;
-	ShardedVector<RTLIL::Wire*> remove_unused_bits;
-	ShardedVector<std::pair<RTLIL::Wire*, RTLIL::Const>> set_unused_bits;
 	WireDeleter(UsedSignals& used_sig_analysis, bool purge_mode, const AnalysisContext& actx) :
 		remove_init(actx.subpool),
 		set_init(actx.subpool),
-		new_connections(actx.subpool),
-		remove_unused_bits(actx.subpool),
-		set_unused_bits(actx.subpool) {
+		new_connections(actx.subpool) {
 		ShardedVector<RTLIL::Wire*> del_wires(actx.subpool);
 		actx.subpool.run([&actx, purge_mode, &del_wires, &used_sig_analysis, this](const ParallelDispatchThreadPool::RunCtx &ctx) {
 			for (int i : ctx.item_range(actx.mod->wires_size())) {
@@ -471,32 +449,6 @@ struct WireDeleter {
 					} else
 						if (init_changed)
 							set_init.insert(ctx, {wire, std::move(initval)});
-
-					std::string unused_bits;
-					if (!check_all(used_sig_analysis.used, s2)) {
-						for (int i = 0; i < GetSize(s2); i++) {
-							if (s2[i].wire == NULL)
-								continue;
-							SigBit b = s2[i];
-							if (used_sig_analysis.used.find({b, b.hash_top().yield()}) == nullptr) {
-								if (!unused_bits.empty())
-									unused_bits += " ";
-								unused_bits += stringf("%d", i);
-							}
-						}
-					}
-					if (unused_bits.empty() || wire->port_id != 0) {
-						if (wire->attributes.count(ID::unused_bits))
-							remove_unused_bits.insert(ctx, wire);
-					} else {
-						RTLIL::Const unused_bits_const(std::move(unused_bits));
-						if (wire->attributes.count(ID::unused_bits)) {
-							RTLIL::Const &unused_bits_attr = wire->attributes.at(ID::unused_bits);
-							if (unused_bits_attr != unused_bits_const)
-								set_unused_bits.insert(ctx, {wire, std::move(unused_bits_const)});
-						} else
-							set_unused_bits.insert(ctx, {wire, std::move(unused_bits_const)});
-					}
 				}
 			}
 		});
@@ -511,10 +463,6 @@ struct WireDeleter {
 			p.first->attributes[ID::init] = std::move(p.second);
 		for (auto &conn : new_connections)
 			mod->connect(std::move(conn));
-		for (RTLIL::Wire *wire : remove_unused_bits)
-			wire->attributes.erase(ID::unused_bits);
-		for (auto &p : set_unused_bits)
-			p.first->attributes[ID::unused_bits] = std::move(p.second);
 	}
 	int delete_wires(RTLIL::Module* mod, bool verbose) {
 		int deleted_and_unreported = 0;
@@ -557,7 +505,7 @@ bool rmunused_module_signals(RTLIL::Module *module, ParallelDispatchThreadPool::
 	module->connections_.clear();
 
 	UsedSignals used;
-	DeferredUpdates deferred = analyse_connectivity(used, conn_kinds, actx, clean_ctx);
+	DeferredUpdates deferred = analyse_connectivity(used, conn_kinds, actx);
 	fixup_cell_ports(deferred.update_connections);
 	// Rip up and re-apply init attributes onto representative wires with x-bits
 	// in place of unset init bits

passes/opt/wreduce.cc

@@ -453,7 +453,6 @@ struct WreduceWorker
 	{
 		int count = w->attributes.size();
 		count -= w->attributes.count(ID::src);
-		count -= w->attributes.count(ID::unused_bits);
 		return count;
 	}