From aa28a8d1e180e09ec2d9686b518f12c8fa7090d6 Mon Sep 17 00:00:00 2001
From: Wilson Snyder <wsnyder@wsnyder.org>
Date: Sat, 6 Sep 2025 08:35:07 -0400
Subject: [PATCH] Fix cell scoping performance (#6059).

---
 Changes           |  1 +
 docs/spelling.txt |  1 +
 src/V3Scope.cpp   | 36 ++++++++++++++++++++----------------
 3 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/Changes b/Changes
index e998f6257..c92e1b1b7 100644
--- a/Changes
+++ b/Changes
@@ -17,6 +17,7 @@ Verilator 5.041 devel
 * Improve automatic selection of logic for DFG synthesis (#6370). [Geza Lore]
 * Improve `covergroup with function sample` handling  (#6387). [Jakub Wasilewski]
 * Optimize dead functions without references (#6380). [Artur Bieniek, Antmicro Ltd.]
+* Fix cell scoping performance (#6059). [Jerry Tianchen]
 * Fix while loop hang on timing-delayed assignment (#6343) (#6354). [Krzysztof Bieganski, Antmicro Ltd.]
 * Fix driver analysis of partially assigned variables (#6364) (#6378). [Geza Lore]
 * Fix V3Hash MacOS ambiguity (#6350). [Lan Zongwei]
diff --git a/docs/spelling.txt b/docs/spelling.txt
index 99593957d..47e4310a1 100644
--- a/docs/spelling.txt
+++ b/docs/spelling.txt
@@ -428,6 +428,7 @@ Terpstra
 Thiede
 Thierry
 Thyer
+Tianchen
 Tianrui
 Tichelaar
 Timi
diff --git a/src/V3Scope.cpp b/src/V3Scope.cpp
index 560e1b40e..bbb691e89 100644
--- a/src/V3Scope.cpp
+++ b/src/V3Scope.cpp
@@ -115,23 +115,27 @@ class ScopeVisitor final : public VNVisitor {
             nodep, scopename, m_aboveScopep, m_aboveCellp};
         if (VN_IS(nodep, Package)) m_packageScopes.emplace(nodep, m_scopep);
 
-        // Now for each child cell, iterate the module this cell points to
+        // Get list of cells before we edit, to avoid excess visits (issue #6059)
+        std::deque<AstCell*> cells;
         for (AstNode* cellnextp = nodep->stmtsp(); cellnextp; cellnextp = cellnextp->nextp()) {
-            if (AstCell* const cellp = VN_CAST(cellnextp, Cell)) {
-                VL_RESTORER(m_scopep);  // Protects m_scopep set in called module
-                // which is "above" in this code, but later in code execution order
-                VL_RESTORER(m_aboveCellp);
-                VL_RESTORER(m_aboveScopep);
-                {
-                    m_aboveCellp = cellp;
-                    m_aboveScopep = m_scopep;
-                    AstNodeModule* const modp = cellp->modp();
-                    UASSERT_OBJ(modp, cellp, "Unlinked mod");
-                    iterate(modp);  // Recursive call to visit(AstNodeModule)
-                    if (VN_IS(modp, Iface)) {
-                        // Remember newly created scope
-                        cellp->user2p(m_scopep);
-                    }
+            if (AstCell* const cellp = VN_CAST(cellnextp, Cell)) cells.push_back(cellp);
+        }
+
+        // Now for each child cell, iterate the module this cell points to
+        for (AstCell* const cellp : cells) {
+            VL_RESTORER(m_scopep);  // Protects m_scopep set in called module
+            // which is "above" in this code, but later in code execution order
+            VL_RESTORER(m_aboveCellp);
+            VL_RESTORER(m_aboveScopep);
+            {
+                m_aboveCellp = cellp;
+                m_aboveScopep = m_scopep;
+                AstNodeModule* const modp = cellp->modp();
+                UASSERT_OBJ(modp, cellp, "Unlinked mod");
+                iterate(modp);  // Recursive call to visit(AstNodeModule)
+                if (VN_IS(modp, Iface)) {
+                    // Remember newly created scope
+                    cellp->user2p(m_scopep);
                 }
             }
         }