fsm_detect: Add a cache to avoid excessive CPU usage for big mux networks.

Fixes #1634.

1 files changed, 17 insertions, 9 deletions

diff --git a/passes/fsm/fsm_detect.cc b/passes/fsm/fsm_detect.cc
index fb3896669..a1c8067b4 100644
--- a/passes/fsm/fsm_detect.cc
+++ b/passes/fsm/fsm_detect.cc
@@ -34,13 +34,20 @@ 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, pool<Cell*> &recursion_monitor)
+static bool check_state_mux_tree(RTLIL::SigSpec old_sig, RTLIL::SigSpec sig, pool<Cell*> &recursion_monitor, dict<RTLIL::SigSpec, bool> &mux_tree_cache)
 {
+	if (mux_tree_cache.find(sig) != mux_tree_cache.end())
+		return mux_tree_cache.at(sig);
+
 	if (sig.is_fully_const() || old_sig == sig) {
+ret_true:
+		mux_tree_cache[sig] = true;
 		return true;
 	}
 
 	if (sig_at_port.check_any(assign_map(sig))) {
+ret_false:
+		mux_tree_cache[sig] = false;
 		return false;
 	}
 
@@ -49,13 +56,13 @@ static bool check_state_mux_tree(RTLIL::SigSpec old_sig, RTLIL::SigSpec sig, poo
 	for (auto &cellport : cellport_list)
 	{
 		if ((cellport.first->type != "$mux" && cellport.first->type != "$pmux") || cellport.second != "\\Y") {
-			return false;
+			goto ret_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;
+			goto ret_false;
 		}
 
 		recursion_monitor.insert(cellport.first);
@@ -63,22 +70,22 @@ static bool check_state_mux_tree(RTLIL::SigSpec old_sig, RTLIL::SigSpec sig, poo
 		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, mux_tree_cache)) {
 			recursion_monitor.erase(cellport.first);
-			return false;
+			goto ret_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, mux_tree_cache)) {
 				recursion_monitor.erase(cellport.first);
-				return false;
+				goto ret_false;
 			}
 
 		recursion_monitor.erase(cellport.first);
 		muxtree_cells.insert(cellport.first);
 	}
 
-	return true;
+	goto ret_true;
 }
 
 static bool check_state_users(RTLIL::SigSpec sig)
@@ -143,11 +150,12 @@ static void detect_fsm(RTLIL::Wire *wire)
 		pool<Cell*> recursion_monitor;
 		RTLIL::SigSpec sig_q = assign_map(cellport.first->getPort("\\Q"));
 		RTLIL::SigSpec sig_d = assign_map(cellport.first->getPort("\\D"));
+		dict<RTLIL::SigSpec, bool> mux_tree_cache;
 
 		if (sig_q != assign_map(wire))
 			continue;
 
-		looks_like_state_reg = check_state_mux_tree(sig_q, sig_d, recursion_monitor);
+		looks_like_state_reg = check_state_mux_tree(sig_q, sig_d, recursion_monitor, mux_tree_cache);
 		looks_like_good_state_reg = check_state_users(sig_q);
 
 		if (!looks_like_state_reg)