From a689cdc6edc9542fbe6b758b89f49ccdc7bb5200 Mon Sep 17 00:00:00 2001
From: "Emil J. Tywoniak" <emil@tywoniak.eu>
Date: Sat, 30 May 2026 01:37:49 +0200
Subject: [PATCH] patch: don't track root cell deletions for perf

---
 kernel/unstable/patch.cc | 8 ++++++--
 kernel/unstable/patch.h  | 3 ++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/unstable/patch.cc b/kernel/unstable/patch.cc
index ba06a470e..a2cf467ad 100644
--- a/kernel/unstable/patch.cc
+++ b/kernel/unstable/patch.cc
@@ -88,7 +88,7 @@ struct SrcCollector {
 	}
 };
 
-void Patch::gc(Cell* old_cell) {
+void Patch::gc(Cell* old_cell, bool track) {
 	log_debug("gc %s\n", old_cell->name);
 	if (old_cell->type.in(ID($input_port), ID($output_port), ID($public)))
 		return;
@@ -119,9 +119,13 @@ void Patch::gc(Cell* old_cell) {
 		}
 	}
 	log_debug("\tremove %s\n", old_cell->name);
+	// Only track recursively-removed cells. The top-level patched cell is the
+	// caller's current iteration variable and won't be re-encountered.
+	if (track && removed_cells)
+		removed_cells->insert(old_cell);
 	old_cell->module->remove(old_cell);
 	for (auto input : inputs)
-		gc(input);
+		gc(input, /*track=*/true);
 }
 
 Wire* Patch::commit_wire(std::unique_ptr<Wire> wire) {
diff --git a/kernel/unstable/patch.h b/kernel/unstable/patch.h
index ba38a4dcc..eea9ab685 100644
--- a/kernel/unstable/patch.h
+++ b/kernel/unstable/patch.h
@@ -10,7 +10,7 @@ YOSYS_NAMESPACE_BEGIN
 struct RTLIL::Patch : public CellAdderMixin<RTLIL::Patch>
 {
 private:
-	void gc(Cell* old_cell);
+	void gc(Cell* old_cell, bool track = false);
 
 protected:
 	void add(RTLIL::Wire *wire);
@@ -25,6 +25,7 @@ protected:
 public:
 	Module* mod;
 	SigMap* map;
+	pool<Cell*>* removed_cells = nullptr;
 	vector<std::unique_ptr<Wire>> wires_ = {};
 	vector<std::unique_ptr<Cell>> cells_ = {};