diff --git a/kernel/hashlib.h b/kernel/hashlib.h
index 92188a220..70e9736f7 100644
--- a/kernel/hashlib.h
+++ b/kernel/hashlib.h
@@ -114,7 +114,7 @@ public:
 		return;
 	}
 	[[nodiscard]]
-	hash_t yield() {
+	hash_t yield() const {
 		return (hash_t)state;
 	}
 
@@ -373,7 +373,11 @@ public:
 	commutative_hash() {
 		buckets.fill(0);
 	}
-	void eat(Hasher h) {
+	template <typename T>
+	void eat(const T &obj) {
+		eat(hash_ops<T>::hash(obj));
+	}
+	void eat(const Hasher &h) {
 		Hasher::hash_t v = h.yield();
 		size_t index = v & (buckets.size() - 1);
 		buckets[index] += v;
diff --git a/passes/opt/opt_merge.cc b/passes/opt/opt_merge.cc
index fbfdb9b63..ded0e7360 100644
--- a/passes/opt/opt_merge.cc
+++ b/passes/opt/opt_merge.cc
@@ -33,6 +33,9 @@
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
 
+template <typename T, typename U>
+inline Hasher hash_pair(const T &t, const U &u) { return hash_ops<std::pair<T, U>>::hash(t, u); }
+
 struct OptMergeWorker
 {
 	RTLIL::Design *design;
@@ -51,7 +54,7 @@ struct OptMergeWorker
 
 		hashlib::commutative_hash comm;
 		for (int i = 0; i < s_width; i++)
-			comm.eat(hash_ops<std::pair<SigBit, SigSpec>>::hash({sig_s[i], sig_b.extract(i*width, width)}));
+			comm.eat(hash_pair(sig_s[i], sig_b.extract(i*width, width)));
 
 		return comm.hash_into(h);
 	}
@@ -86,8 +89,8 @@ struct OptMergeWorker
 		if (cell->type.in(ID($and), ID($or), ID($xor), ID($xnor), ID($add), ID($mul),
 				ID($logic_and), ID($logic_or), ID($_AND_), ID($_OR_), ID($_XOR_))) {
 			hashlib::commutative_hash comm;
-			comm.eat(hash_ops<RTLIL::SigSpec>::hash(assign_map(cell->getPort(ID::A))));
-			comm.eat(hash_ops<RTLIL::SigSpec>::hash(assign_map(cell->getPort(ID::B))));
+			comm.eat(assign_map(cell->getPort(ID::A)));
+			comm.eat(assign_map(cell->getPort(ID::B)));
 			h = comm.hash_into(h);
 		} else if (cell->type.in(ID($reduce_xor), ID($reduce_xnor))) {
 			SigSpec a = assign_map(cell->getPort(ID::A));
@@ -107,7 +110,7 @@ struct OptMergeWorker
 			for (const auto& [port, sig] : cell->connections()) {
 				if (cell->output(port))
 					continue;
-				comm.eat(hash_ops<std::pair<IdString, SigSpec>>::hash(port, assign_map(sig)));
+				comm.eat(hash_pair(port, assign_map(sig)));
 			}
 			h = comm.hash_into(h);
 			if (RTLIL::builtin_ff_cell_types().count(cell->type))
@@ -120,7 +123,7 @@ struct OptMergeWorker
 	{
 		hashlib::commutative_hash comm;
 		for (const auto& param : cell->parameters) {
-			comm.eat(hash_ops<std::pair<IdString, Const>>::hash(param));
+			comm.eat(param);
 		}
 		return comm.hash_into(h);
 	}