From 246e362717f23bb8cfbd22c33728d6517b7d3d8f Mon Sep 17 00:00:00 2001
From: Clifford Wolf <clifford@clifford.at>
Date: Tue, 18 Aug 2015 14:17:50 +0200
Subject: [PATCH] Bugfix in fsm_detect for complex muxtrees

---
 passes/fsm/fsm_detect.cc | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/passes/fsm/fsm_detect.cc b/passes/fsm/fsm_detect.cc
index 7a621b567..feeaa347c 100644
--- a/passes/fsm/fsm_detect.cc
+++ b/passes/fsm/fsm_detect.cc
@@ -34,7 +34,7 @@ static SigSet<sig2driver_entry_t> sig2driver, sig2user;
 static std::set<RTLIL::Cell*> muxtree_cells;
 static SigPool sig_at_port;
 
-static bool check_state_mux_tree(RTLIL::SigSpec old_sig, RTLIL::SigSpec sig, SigPool &recursion_monitor)
+static bool check_state_mux_tree(RTLIL::SigSpec old_sig, RTLIL::SigSpec sig, pool<Cell*> &recursion_monitor)
 {
 	if (sig_at_port.check_any(assign_map(sig)))
 		return false;
@@ -42,31 +42,39 @@ static bool check_state_mux_tree(RTLIL::SigSpec old_sig, RTLIL::SigSpec sig, Sig
 	if (sig.is_fully_const() || old_sig == sig)
 		return true;
 
-	if (recursion_monitor.check_any(sig)) {
-		log_warning("logic loop in mux tree at signal %s in module %s.\n",
-				log_signal(sig), RTLIL::id2cstr(module->name));
-		return false;
-	}
-
-	recursion_monitor.add(sig);
-
 	std::set<sig2driver_entry_t> cellport_list;
 	sig2driver.find(sig, cellport_list);
-	for (auto &cellport : cellport_list) {
+	for (auto &cellport : cellport_list)
+	{
 		if ((cellport.first->type != "$mux" && cellport.first->type != "$pmux") || cellport.second != "\\Y")
 			return false;
+
+		if (recursion_monitor.count(cellport.first)) {
+			log_warning("logic loop in mux tree at signal %s in module %s.\n",
+					log_signal(sig), RTLIL::id2cstr(module->name));
+			return false;
+		}
+
+		recursion_monitor.insert(cellport.first);
+
 		RTLIL::SigSpec sig_a = assign_map(cellport.first->getPort("\\A"));
 		RTLIL::SigSpec sig_b = assign_map(cellport.first->getPort("\\B"));
-		if (!check_state_mux_tree(old_sig, sig_a, recursion_monitor))
+
+		if (!check_state_mux_tree(old_sig, sig_a, recursion_monitor)) {
+			recursion_monitor.erase(cellport.first);
 			return false;
+		}
+
 		for (int i = 0; i < sig_b.size(); i += sig_a.size())
-			if (!check_state_mux_tree(old_sig, sig_b.extract(i, sig_a.size()), recursion_monitor))
+			if (!check_state_mux_tree(old_sig, sig_b.extract(i, sig_a.size()), recursion_monitor)) {
+				recursion_monitor.erase(cellport.first);
 				return false;
+			}
+
+		recursion_monitor.erase(cellport.first);
 		muxtree_cells.insert(cellport.first);
 	}
 
-	recursion_monitor.del(sig);
-
 	return true;
 }
 
@@ -111,7 +119,7 @@ static void detect_fsm(RTLIL::Wire *wire)
 		if ((cellport.first->type != "$dff" && cellport.first->type != "$adff") || cellport.second != "\\Q")
 			continue;
 		muxtree_cells.clear();
-		SigPool recursion_monitor;
+		pool<Cell*> recursion_monitor;
 		RTLIL::SigSpec sig_q = assign_map(cellport.first->getPort("\\Q"));
 		RTLIL::SigSpec sig_d = assign_map(cellport.first->getPort("\\D"));
 		if (sig_q == RTLIL::SigSpec(wire) && check_state_mux_tree(sig_q, sig_d, recursion_monitor) && check_state_users(sig_q)) {
-- 
2.30.2