From 9cc218db3eaa1b275f89714c0e8e371b96e500ca Mon Sep 17 00:00:00 2001
From: Adrien Le Masle <14968086+adrienlemasle@users.noreply.github.com>
Date: Thu, 1 Jun 2023 13:43:17 +0100
Subject: [PATCH] Fix incorrect multi-driven lint warning (#4231) (#4248)

---
 src/V3DfgAstToDfg.cpp                      | 25 +++++-----
 test_regress/t/t_incorrect_multi_driven.pl | 21 ++++++++
 test_regress/t/t_incorrect_multi_driven.v  | 56 ++++++++++++++++++++++
 3 files changed, 91 insertions(+), 11 deletions(-)
 create mode 100755 test_regress/t/t_incorrect_multi_driven.pl
 create mode 100644 test_regress/t/t_incorrect_multi_driven.v

diff --git a/src/V3DfgAstToDfg.cpp b/src/V3DfgAstToDfg.cpp
index 78a598742..da265a1ff 100644
--- a/src/V3DfgAstToDfg.cpp
+++ b/src/V3DfgAstToDfg.cpp
@@ -334,17 +334,20 @@ class AstToDfgVisitor final : public VNVisitor {
                     const uint32_t bEnd = b.m_lsb + bWidth;
                     const uint32_t overlapEnd = std::min(aEnd, bEnd) - 1;
 
-                    varp->varp()->v3warn(  //
-                        MULTIDRIVEN,
-                        "Bits ["  //
-                            << overlapEnd << ":" << b.m_lsb << "] of signal "
-                            << varp->varp()->prettyNameQ()
-                            << " have multiple combinational drivers\n"
-                            << a.m_fileline->warnOther() << "... Location of first driver\n"
-                            << a.m_fileline->warnContextPrimary() << '\n'
-                            << b.m_fileline->warnOther() << "... Location of other driver\n"
-                            << b.m_fileline->warnContextSecondary() << varp->varp()->warnOther()
-                            << "... Only the first driver will be respected");
+                    if (a.m_fileline->operatorCompare(*b.m_fileline) != 0) {
+                        varp->varp()->v3warn(  //
+                            MULTIDRIVEN,
+                            "Bits ["  //
+                                << overlapEnd << ":" << b.m_lsb << "] of signal "
+                                << varp->varp()->prettyNameQ()
+                                << " have multiple combinational drivers\n"
+                                << a.m_fileline->warnOther() << "... Location of first driver\n"
+                                << a.m_fileline->warnContextPrimary() << '\n'
+                                << b.m_fileline->warnOther() << "... Location of other driver\n"
+                                << b.m_fileline->warnContextSecondary()
+                                << varp->varp()->warnOther()
+                                << "... Only the first driver will be respected");
+                    }
 
                     // If the first driver completely covers the range of the second driver,
                     // we can just delete the second driver completely, otherwise adjust the
diff --git a/test_regress/t/t_incorrect_multi_driven.pl b/test_regress/t/t_incorrect_multi_driven.pl
new file mode 100755
index 000000000..0fc71f8e9
--- /dev/null
+++ b/test_regress/t/t_incorrect_multi_driven.pl
@@ -0,0 +1,21 @@
+#!/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(linter => 1);
+
+top_filename("t/t_incorrect_multi_driven.v");
+
+lint(
+    fails => 0
+    );
+
+ok(1);
+1;
diff --git a/test_regress/t/t_incorrect_multi_driven.v b/test_regress/t/t_incorrect_multi_driven.v
new file mode 100644
index 000000000..3020398db
--- /dev/null
+++ b/test_regress/t/t_incorrect_multi_driven.v
@@ -0,0 +1,56 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2023 by Adrien Le Masle.
+// SPDX-License-Identifier: CC0-1.0
+
+interface test_if #(parameter int AA = 2, BB=5);
+
+   logic [AA-1 : 0]     a;
+   logic [BB-1 : 0]     b;
+   logic                c;
+   logic                d;
+
+   modport slave (input  a,
+                  input  b,
+                  input  c,
+                  input  d);
+
+   modport master (output a,
+                   output b,
+                   output c,
+                   output d);
+
+endinterface : test_if
+
+module test
+  (input logic [28:0]  a,
+   output logic [28:0] b);
+
+   always_comb begin
+      b = a;
+   end
+endmodule
+
+module multi_driven
+  (
+   input logic [20-1 : 0] data_in,
+   output logic [20-1 : 0] data_out,
+   test_if.slave  test_if_in,
+   test_if.master test_if_out
+   );
+
+   test test_inst
+     (
+      .a({data_in,
+          test_if_in.a,
+          test_if_in.b,
+          test_if_in.c,
+          test_if_in.d}),
+      .b({data_out,
+          test_if_out.a,
+          test_if_out.b,
+          test_if_out.c,
+          test_if_out.d}));
+
+endmodule;