From e20a57b09ed3efd79fd893035c8f70747e5b3efa Mon Sep 17 00:00:00 2001
From: Mike Inouye <mikeinouye@google.com>
Date: Wed, 13 May 2026 10:57:18 -0700
Subject: [PATCH] Reuse knowledge_t and pass by reference

---
 passes/opt/opt_muxtree.cc | 56 ++++++++++++++++++++-------------------
 1 file changed, 29 insertions(+), 27 deletions(-)

diff --git a/passes/opt/opt_muxtree.cc b/passes/opt/opt_muxtree.cc
index 8bf151e71..4c07f61d8 100644
--- a/passes/opt/opt_muxtree.cc
+++ b/passes/opt/opt_muxtree.cc
@@ -200,6 +200,29 @@ struct OptMuxtreeWorker
 				root_muxes.at(driving_mux) = true;
 	}
 
+	struct knowledge_t
+	{
+		// Known inactive signals
+		// The payload is a reference counter used to manage the list
+		// When it is non-zero, the signal in known to be inactive
+		// When it reaches zero, the map element is removed
+		std::vector<int> known_inactive;
+
+		// database of known active signals
+		std::vector<int> known_active;
+
+		// this is just used to keep track of visited muxes in order to prohibit
+		// endless recursion in mux loops
+		std::vector<bool> visited_muxes;
+
+		// Initialize with the maximum possible sizes
+		knowledge_t(int num_bits, int num_muxes) {
+			known_inactive.assign(num_bits, 0);
+			known_active.assign(num_bits, 0);
+			visited_muxes.assign(num_muxes, false);
+		}
+	};
+
 	OptMuxtreeWorker(RTLIL::Design *design, RTLIL::Module *module) :
 			design(design), module(module), assign_map(module), removed_count(0)
 	{
@@ -227,11 +250,13 @@ struct OptMuxtreeWorker
 
 		populate_roots();
 
+		knowledge_t shared_knowledge(GetSize(bit2info), GetSize(mux2info));
+
 		for (int mux_idx = 0; mux_idx < GetSize(root_muxes); mux_idx++)
 			if (root_muxes.at(mux_idx)) {
 				log_debug("    Root of a mux tree: %s%s\n", log_id(mux2info[mux_idx].cell), root_enable_muxes.at(mux_idx) ? " (pure)" : "");
 				root_mux_rerun.erase(mux_idx);
-				eval_root_mux(mux_idx);
+				eval_root_mux(shared_knowledge, mux_idx);
 				if (glob_evals_left == 0) {
 					log("  Giving up (too many iterations)\n");
 					return;
@@ -243,7 +268,7 @@ struct OptMuxtreeWorker
 			log_debug("    Root of a mux tree: %s (rerun as non-pure)\n", log_id(mux2info[mux_idx].cell));
 			log_assert(root_enable_muxes.at(mux_idx));
 			root_mux_rerun.erase(mux_idx);
-			eval_root_mux(mux_idx);
+			eval_root_mux(shared_knowledge, mux_idx);
 			if (glob_evals_left == 0) {
 				log("  Giving up (too many iterations)\n");
 				return;
@@ -334,29 +359,6 @@ struct OptMuxtreeWorker
 		return results;
 	}
 
-	struct knowledge_t
-	{
-		// Known inactive signals
-		// The payload is a reference counter used to manage the list
-		// When it is non-zero, the signal in known to be inactive
-		// When it reaches zero, the map element is removed
-		std::vector<int> known_inactive;
-
-		// database of known active signals
-		std::vector<int> known_active;
-
-		// this is just used to keep track of visited muxes in order to prohibit
-		// endless recursion in mux loops
-		std::vector<bool> visited_muxes;
-
-		// Initialize with the maximum possible sizes
-		knowledge_t(int num_bits, int num_muxes) {
-			known_inactive.assign(num_bits, 0);
-			known_active.assign(num_bits, 0);
-			visited_muxes.assign(num_muxes, false);
-		}
-	};
-
 	static void activate_port(knowledge_t &knowledge, int port_idx, const muxinfo_t &muxinfo) {
 		// First, mark all other ports inactive
 		for (int i = 0; i < GetSize(muxinfo.ports); i++) {
@@ -579,14 +581,14 @@ struct OptMuxtreeWorker
 		}
 	}
 
-	void eval_root_mux(int mux_idx)
+	void eval_root_mux(knowledge_t &knowledge, int mux_idx)
 	{
 		log_assert(glob_evals_left > 0);
-		knowledge_t knowledge(GetSize(bit2info), GetSize(mux2info));
 		knowledge.visited_muxes[mux_idx] = true;
 		limits_t limits = {};
 		limits.do_mark_ports_observable = root_enable_muxes.at(mux_idx);
 		eval_mux(knowledge, mux_idx, limits);
+		knowledge.visited_muxes[mux_idx] = false;
 	}
 };