From 90079c2974c40fb9758c3e5a5733f3255fe3435b Mon Sep 17 00:00:00 2001
From: Ryszard Rozak <rrozak@antmicro.com>
Date: Wed, 23 Aug 2023 12:08:22 +0200
Subject: [PATCH] Fix nested assignments on the LHS (#4435)

---
 src/V3Timing.cpp                              | 24 ++++++--------
 .../t/t_timing_nested_assignment_on_lhs.pl    | 25 +++++++++++++++
 .../t/t_timing_nested_assignment_on_lhs.v     | 31 +++++++++++++++++++
 3 files changed, 65 insertions(+), 15 deletions(-)
 create mode 100755 test_regress/t/t_timing_nested_assignment_on_lhs.pl
 create mode 100644 test_regress/t/t_timing_nested_assignment_on_lhs.v

diff --git a/src/V3Timing.cpp b/src/V3Timing.cpp
index 0cca7835a..b886b2ed9 100644
--- a/src/V3Timing.cpp
+++ b/src/V3Timing.cpp
@@ -415,25 +415,19 @@ private:
 
     // METHODS
     // Find net delay on the LHS of an assignment
-    AstDelay* getLhsNetDelay(AstNodeAssign* nodep) const {
-        bool foundWrite = false;
-        AstDelay* delayp = nullptr;
-        nodep->lhsp()->foreach([&](const AstNodeVarRef* const refp) {
-            if (!refp->access().isWriteOrRW()) return;
-            UASSERT_OBJ(!foundWrite, nodep, "Should only be one variable written to on the LHS");
-            foundWrite = true;
-            if (refp->varp()->delayp()) {
-                delayp = refp->varp()->delayp();
-                delayp->unlinkFrBack();
-            }
-        });
-        return delayp;
+    AstDelay* getLhsNetDelayRecurse(const AstNodeExpr* const nodep) const {
+        if (const AstNodeVarRef* const refp = VN_CAST(nodep, NodeVarRef)) {
+            if (refp->varp()->delayp()) return refp->varp()->delayp()->unlinkFrBack();
+        } else if (const AstSel* const selp = VN_CAST(nodep, Sel)) {
+            return getLhsNetDelayRecurse(selp->fromp());
+        }
+        return nullptr;
     }
     // Transform an assignment with an intra timing control into a timing control with the
     // assignment under it
     AstNode* factorOutTimingControl(AstNodeAssign* nodep) const {
         AstNode* stmtp = nodep;
-        AstDelay* delayp = getLhsNetDelay(nodep);
+        AstDelay* delayp = getLhsNetDelayRecurse(nodep->lhsp());
         FileLine* const flp = nodep->fileline();
         AstNode* const controlp = nodep->timingControlp();
         if (controlp) {
@@ -955,7 +949,7 @@ private:
         replaceWithIntermediate(nodep->rhsp(), m_intraValueNames.get(nodep));
     }
     void visit(AstAssignW* nodep) override {
-        AstDelay* const netDelayp = getLhsNetDelay(nodep);
+        AstDelay* const netDelayp = getLhsNetDelayRecurse(nodep->lhsp());
         if (!netDelayp && !nodep->timingControlp()) return;
         // This assignment will be converted to an always. In some cases this may generate an
         // UNOPTFLAT, e.g.: assign #1 clk = ~clk. We create a temp var for the LHS of this
diff --git a/test_regress/t/t_timing_nested_assignment_on_lhs.pl b/test_regress/t/t_timing_nested_assignment_on_lhs.pl
new file mode 100755
index 000000000..0ebdb8a45
--- /dev/null
+++ b/test_regress/t/t_timing_nested_assignment_on_lhs.pl
@@ -0,0 +1,25 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2023 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(simulator => 1);
+
+top_filename("t/t_net_delay.v");
+
+compile(
+    timing_loop => 1,
+    verilator_flags2 => ["--timing"],
+    );
+
+execute(
+    check_finished => 1,
+    );
+
+ok(1);
+1;
diff --git a/test_regress/t/t_timing_nested_assignment_on_lhs.v b/test_regress/t/t_timing_nested_assignment_on_lhs.v
new file mode 100644
index 000000000..1bacb5579
--- /dev/null
+++ b/test_regress/t/t_timing_nested_assignment_on_lhs.v
@@ -0,0 +1,31 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2023 by Antmicro Ltd.
+// SPDX-License-Identifier: CC0-1.0
+
+class uvm_object_wrapper;
+   function string get_type_name;
+      return "abcd";
+   endfunction
+endclass
+
+class uvm_default_factory;
+   int m_type_names[string];
+   virtual function int register;
+      uvm_object_wrapper obj;
+      string name;
+      m_type_names[(name = obj.get_type_name())] = 1;
+      return m_type_names[name];
+   endfunction
+endclass
+
+module t;
+   initial begin
+      uvm_default_factory u = new;
+      if (u.register() != 1) $stop;
+      #1; // Needed only visit assignments in V3Timing
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule