Improve proc full_case detection and handling, fixes #931

Signed-off-by: Clifford Wolf <clifford@clifford.at>

passes/proc/proc_mux.cc

@@ -108,6 +108,7 @@ struct SigSnippets
 
 struct SnippetSwCache
 {
+	dict<RTLIL::SwitchRule*, pool<RTLIL::SigBit>, hash_ptr_ops> full_case_bits_cache;
 	dict<RTLIL::SwitchRule*, pool<int>, hash_ptr_ops> cache;
 	const SigSnippets *snippets;
 	int current_snippet;
@@ -268,6 +269,49 @@ void append_pmux(RTLIL::Module *mod, const RTLIL::SigSpec &signal, const std::ve
 	last_mux_cell->parameters["\\S_WIDTH"] = last_mux_cell->getPort("\\S").size();
 }
 
+const pool<SigBit> &get_full_case_bits(SnippetSwCache &swcache, RTLIL::SwitchRule *sw)
+{
+	if (!swcache.full_case_bits_cache.count(sw))
+	{
+		pool<SigBit> bits;
+
+		if (sw->get_bool_attribute("\\full_case"))
+		{
+			bool first_case = true;
+
+			for (auto cs : sw->cases)
+			{
+				pool<SigBit> case_bits;
+
+				for (auto it : cs->actions) {
+					for (auto bit : it.first)
+						case_bits.insert(bit);
+				}
+
+				for (auto it : cs->switches) {
+					for (auto bit : get_full_case_bits(swcache, it))
+						case_bits.insert(bit);
+				}
+
+				if (first_case) {
+					first_case = false;
+					bits = case_bits;
+				} else {
+					pool<SigBit> new_bits;
+					for (auto bit : bits)
+						if (case_bits.count(bit))
+							new_bits.insert(bit);
+					bits.swap(new_bits);
+				}
+			}
+		}
+
+		bits.swap(swcache.full_case_bits_cache[sw]);
+	}
+
+	return swcache.full_case_bits_cache.at(sw);
+}
+
 RTLIL::SigSpec signal_to_mux_tree(RTLIL::Module *mod, SnippetSwCache &swcache, dict<RTLIL::SwitchRule*, bool, hash_ptr_ops> &swpara,
 		RTLIL::CaseRule *cs, const RTLIL::SigSpec &sig, const RTLIL::SigSpec &defval, bool ifxmode)
 {
@@ -337,6 +381,12 @@ RTLIL::SigSpec signal_to_mux_tree(RTLIL::Module *mod, SnippetSwCache &swcache, d
 			}
 		}
 
+		// mask default bits that are irrelevant because the output is driven by a full case
+		const pool<SigBit> &full_case_bits = get_full_case_bits(swcache, sw);
+		for (int i = 0; i < GetSize(sig); i++)
+			if (full_case_bits.count(sig[i]))
+				result[i] = State::Sx;
+
 		// evaluate in reverse order to give the first entry the top priority
 		RTLIL::SigSpec initial_val = result;
 		RTLIL::Cell *last_mux_cell = NULL;

passes/proc/proc_rmdead.cc

@@ -28,7 +28,7 @@
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
 
-void proc_rmdead(RTLIL::SwitchRule *sw, int &counter)
+void proc_rmdead(RTLIL::SwitchRule *sw, int &counter, int &full_case_counter)
 {
 	BitPatternPool pool(sw->signal);
 
@@ -56,11 +56,16 @@ void proc_rmdead(RTLIL::SwitchRule *sw, int &counter)
 		}
 
 		for (auto switch_it : sw->cases[i]->switches)
-			proc_rmdead(switch_it, counter);
+			proc_rmdead(switch_it, counter, full_case_counter);
 
 		if (is_default)
 			pool.take_all();
 	}
+
+	if (pool.empty() && !sw->get_bool_attribute("\\full_case")) {
+		sw->set_bool_attribute("\\full_case");
+		full_case_counter++;
+	}
 }
 
 struct ProcRmdeadPass : public Pass {
@@ -87,12 +92,15 @@ struct ProcRmdeadPass : public Pass {
 			for (auto &proc_it : mod->processes) {
 				if (!design->selected(mod, proc_it.second))
 					continue;
-				int counter = 0;
+				int counter = 0, full_case_counter = 0;
 				for (auto switch_it : proc_it.second->root_case.switches)
-					proc_rmdead(switch_it, counter);
+					proc_rmdead(switch_it, counter, full_case_counter);
 				if (counter > 0)
 					log("Removed %d dead cases from process %s in module %s.\n", counter,
-							proc_it.first.c_str(), log_id(mod));
+							log_id(proc_it.first), log_id(mod));
+				if (full_case_counter > 0)
+					log("Marked %d switch rules as full_case in process %s in module %s.\n",
+							full_case_counter, log_id(proc_it.first), log_id(mod));
 				total_counter += counter;
 			}
 		}