From 5c1d7f3ce95e7b242e8f7d6f2b0f68f1b34a9754 Mon Sep 17 00:00:00 2001
From: Wilson Snyder <wsnyder@wsnyder.org>
Date: Mon, 28 Jul 2025 02:20:57 -0400
Subject: [PATCH] Fix negate of wide structure selections (#6186).

---
 Changes                           |  3 ++-
 src/V3Cast.cpp                    |  9 +++++++--
 test_regress/t/t_struct_negate.py | 18 ++++++++++++++++++
 test_regress/t/t_struct_negate.v  | 19 +++++++++++++++++++
 4 files changed, 46 insertions(+), 3 deletions(-)
 create mode 100755 test_regress/t/t_struct_negate.py
 create mode 100644 test_regress/t/t_struct_negate.v

diff --git a/Changes b/Changes
index b0265165d..dbc9eb50d 100644
--- a/Changes
+++ b/Changes
@@ -47,9 +47,10 @@ Verilator 5.039 devel
 * Fix virtual interface member propagation (#6175) (#6184). [Yilou Wang]
 * Fix `--coverage-expr` null pointer dereference (#6181). [Igor Zaworski, Antmicro Ltd.]
 * Fix conflicting function/class name linking error (#6182). [Igor Zaworski, Antmicro Ltd.]
-* Fix automatic task variables in unrolled loops with forks (#6194) (#6201). [Danny Oler]
+* Fix negate of wide structure selections (#6186).
 * Fix VPI signal range order (#6189) (#6200). [Ibrahim Burak Yorulmaz]
 * Fix structure select causing 'Wide Op' error (#6191). [Danny Oler]
+* Fix automatic task variables in unrolled loops with forks (#6194) (#6201). [Danny Oler]
 * Fix 'driver same component' assertion (#6211) (#6215). [Geza Lore]
 * Fix `--stats` overridden by skipping identical build (#6220). [Geza Lore]
 * Fix MODDUP with duplicate packages to take first package (#6222).
diff --git a/src/V3Cast.cpp b/src/V3Cast.cpp
index 1cdd43a4d..9795de230 100644
--- a/src/V3Cast.cpp
+++ b/src/V3Cast.cpp
@@ -173,13 +173,13 @@ class CastVisitor final : public VNVisitor {
     void visit(AstNegate* nodep) override {
         iterateChildren(nodep);
         nodep->user1(nodep->lhsp()->user1());
-        if (nodep->lhsp()->widthMin() == 1) {
+        if (nodep->lhsp()->widthMin() == 1 && !nodep->lhsp()->isWide()) {
             // We want to avoid a GCC "converting of negative value" warning
             // from our expansion of
             //    out = {32{a<b}}  =>   out = - (a<b)
             insertCast(nodep->lhsp(), castSize(nodep));
         } else {
-            ensureCast(nodep->lhsp());
+            if (nodep->sizeMattersLhs()) ensureCast(nodep->lhsp());
         }
     }
     void visit(AstVarRef* nodep) override {
@@ -221,6 +221,11 @@ class CastVisitor final : public VNVisitor {
     void visit(AstMemberSel* nodep) override {
         iterateChildren(nodep);
         ensureNullChecked(nodep->fromp());
+        nodep->user1(true);
+    }
+    void visit(AstStructSel* nodep) override {
+        iterateChildren(nodep);
+        nodep->user1(true);
     }
 
     // NOPs
diff --git a/test_regress/t/t_struct_negate.py b/test_regress/t/t_struct_negate.py
new file mode 100755
index 000000000..f989a35fb
--- /dev/null
+++ b/test_regress/t/t_struct_negate.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2025 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
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile()
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_struct_negate.v b/test_regress/t/t_struct_negate.v
new file mode 100644
index 000000000..6803ef09a
--- /dev/null
+++ b/test_regress/t/t_struct_negate.v
@@ -0,0 +1,19 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+module t (
+    input  logic signed [64:0] i_x,
+    output logic signed [64:0] o_y
+);
+  struct {logic signed [64:0] m_x;} s;
+  assign s.m_x = i_x;
+  assign o_y = -s.m_x;
+  initial begin
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+
+endmodule