From 9ed93e210b14658eeb059c143a4894e5df88220d Mon Sep 17 00:00:00 2001
From: "Emil J. Tywoniak" <emil@tywoniak.eu>
Date: Fri, 5 Jun 2026 13:36:53 +0200
Subject: [PATCH] rtlil: add per-Design src meta vector + freelist

---
 kernel/rtlil.cc | 20 ++++++++++++++++++++
 kernel/rtlil.h  | 16 ++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index 469c9eeee..1fc91be8c 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -1078,6 +1078,26 @@ namespace {
 	}
 }
 
+uint32_t RTLIL::Design::alloc_obj_meta()
+{
+	if (!obj_meta_free_.empty()) {
+		uint32_t idx = obj_meta_free_.back();
+		obj_meta_free_.pop_back();
+		obj_meta_src_[idx] = Twine::Null;
+		return idx;
+	}
+	uint32_t idx = static_cast<uint32_t>(obj_meta_src_.size());
+	obj_meta_src_.push_back(Twine::Null);
+	return idx;
+}
+
+void RTLIL::Design::free_obj_meta(uint32_t idx)
+{
+	log_assert(idx < obj_meta_src_.size());
+	log_assert(obj_meta_src_[idx] == Twine::Null);
+	obj_meta_free_.push_back(idx);
+}
+
 void RTLIL::Design::merge_src(RTLIL::AttrObject *target, const RTLIL::AttrObject *source)
 {
 	std::vector<Twine::Id> ids;
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index b28b73115..ae6cbb3f8 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -1993,6 +1993,22 @@ struct RTLIL::Design
 	// via cell->module->design->src_twines.
 	TwinePool src_twines;
 
+	// Per-object src metadata, indexed by AttrObject::meta_idx_. Holds the
+	// Twine::Id for an object's src — the future home of any other per-
+	// object cold metadata we want to evacuate from inline storage (e.g.
+	// name once IdString/Twine unify). Freed slots are recycled via
+	// obj_meta_free_ (LIFO), mirroring TwinePool's freelist.
+	//
+	// alloc_obj_meta returns a fresh index whose entry is Twine::Null;
+	// free_obj_meta requires the slot's src_id to already have been
+	// released via src_twines.release() — the freelist only handles
+	// the index itself, not the referenced pool slot.
+	std::vector<Twine::Id> obj_meta_src_;
+	std::vector<uint32_t> obj_meta_free_;
+
+	uint32_t alloc_obj_meta();
+	void free_obj_meta(uint32_t idx);
+
 	// Resolve a stored src-attribute string to its flat path:line.col
 	// representation. If `raw` is a twine reference ("@N") returns
 	// src_twines.flatten(N); otherwise returns `raw` unchanged. Backends