From 7daf917b51731dd7243dd248db9c8af9f60aa8ab Mon Sep 17 00:00:00 2001
From: Robert O'Callahan <rocallahan@google.com>
Date: Mon, 1 Sep 2025 03:36:03 +0000
Subject: [PATCH] In hash_cell_inputs, avoid constructing an std::pair (which
 requires copying the port IdString)

---
 kernel/hashlib.h        | 6 ++++++
 passes/opt/opt_merge.cc | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/hashlib.h b/kernel/hashlib.h
index 9c53e6687..39530baea 100644
--- a/kernel/hashlib.h
+++ b/kernel/hashlib.h
@@ -188,6 +188,12 @@ template<typename P, typename Q> struct hash_ops<std::pair<P, Q>> {
 		return h;
 	}
 	HASH_TOP_LOOP_FST (const std::pair<P, Q> &a) HASH_TOP_LOOP_SND
+	[[nodiscard]] static inline Hasher hash(const P &p, const Q &q) {
+		Hasher h;
+		h = hash_ops<P>::hash_into(p, h);
+		h = hash_ops<Q>::hash_into(q, h);
+		return h;
+	}
 };
 
 template<typename... T> struct hash_ops<std::tuple<T...>> {
diff --git a/passes/opt/opt_merge.cc b/passes/opt/opt_merge.cc
index ba8168e74..6c81ee241 100644
--- a/passes/opt/opt_merge.cc
+++ b/passes/opt/opt_merge.cc
@@ -107,7 +107,7 @@ 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_ops<std::pair<IdString, SigSpec>>::hash(port, assign_map(sig)));
 			}
 			h = comm.hash_into(h);
 			if (RTLIL::builtin_ff_cell_types().count(cell->type))