From d10e841b56d0e7f08d5e0eb65c8237fc9554a183 Mon Sep 17 00:00:00 2001
From: Todd Strader <todd.strader@gmail.com>
Date: Wed, 17 Dec 2025 13:51:40 -0500
Subject: [PATCH] Skip properties for expression coverage (#6830)

---
 src/V3Coverage.cpp                            |   3 +-
 .../t/t_assert_implication_coverage.py        |  18 +++
 .../t/t_assert_implication_coverage.v         | 116 ++++++++++++++++++
 3 files changed, 136 insertions(+), 1 deletion(-)
 create mode 100755 test_regress/t/t_assert_implication_coverage.py
 create mode 100644 test_regress/t/t_assert_implication_coverage.v

diff --git a/src/V3Coverage.cpp b/src/V3Coverage.cpp
index c3770e421..f3a7d797d 100644
--- a/src/V3Coverage.cpp
+++ b/src/V3Coverage.cpp
@@ -359,7 +359,8 @@ class CoverageVisitor final : public VNVisitor {
         VL_RESTORER(m_state);
         VL_RESTORER(m_exprStmtsp);
         VL_RESTORER(m_inToggleOff);
-        m_exprStmtsp = nodep;
+        // skip properties for expresison coverage
+        if (!VN_IS(nodep, Property)) m_exprStmtsp = nodep;
         m_inToggleOff = true;
         createHandle(nodep);
         iterateChildren(nodep);
diff --git a/test_regress/t/t_assert_implication_coverage.py b/test_regress/t/t_assert_implication_coverage.py
new file mode 100755
index 000000000..4674cc9c1
--- /dev/null
+++ b/test_regress/t/t_assert_implication_coverage.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 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(verilator_flags2=['--assert --cc --coverage'])
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_assert_implication_coverage.v b/test_regress/t/t_assert_implication_coverage.v
new file mode 100644
index 000000000..edc613f52
--- /dev/null
+++ b/test_regress/t/t_assert_implication_coverage.v
@@ -0,0 +1,116 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2025 by Wilson Snyder
+// SPDX-License-Identifier: CC0-1.0
+
+module t (/*AUTOARG*/
+  // Inputs
+  clk
+);
+
+  input clk;
+  integer cyc; initial cyc=1;
+
+  Test test (
+    /*AUTOINST*/
+    // Inputs
+    .clk(clk),
+    .cyc(cyc)
+  );
+
+  always @ (posedge clk) begin
+    if (cyc!=0) begin
+      cyc <= cyc + 1;
+`ifdef TEST_VERBOSE
+      $display("cyc=%0d", cyc);
+`endif
+      if (cyc==10) begin
+        $write("*-* All Finished *-*\n");
+        $finish;
+      end
+    end
+  end
+
+endmodule
+
+// Interface for data validation with coverage
+interface data_valid_if (input logic clk);
+  logic enable_invalid_data_checks;
+  logic valid;
+  logic [7:0] data;
+
+  property dataIsKnownWhenValid;
+    @(posedge clk) enable_invalid_data_checks & valid |-> !$isunknown(data);
+  endproperty
+
+  assert_dataIsKnownWhenValid: assert property (dataIsKnownWhenValid)
+    else $error("Data contains unknown values when valid is asserted");
+
+endinterface
+
+module Test
+  (
+   input clk,
+   input integer cyc
+   );
+
+  logic rst_n;
+
+  // Instantiate the interface
+  data_valid_if dv_if(clk);
+
+  // Reset logic
+  initial begin
+    rst_n = 0;
+    dv_if.enable_invalid_data_checks = 0;
+  end
+
+  always @(posedge clk) begin
+    if (cyc == 1) begin
+      rst_n <= 1'b1;
+    end
+  end
+
+  // Stimulus: Enable checks after reset
+  always @(posedge clk) begin
+    if (cyc == 2) begin
+      dv_if.enable_invalid_data_checks <= 1'b1;
+    end
+  end
+
+  // Simulate data transactions
+  always @(posedge clk) begin
+    case (cyc)
+      3: begin
+        dv_if.valid <= 1'b0;
+        dv_if.data <= 8'h00;
+      end
+      4: begin
+        dv_if.valid <= 1'b1;
+        dv_if.data <= 8'hAA;  // Valid data
+      end
+      5: begin
+        dv_if.valid <= 1'b1;
+        dv_if.data <= 8'h55;  // Valid data
+      end
+      6: begin
+        dv_if.valid <= 1'b0;
+        dv_if.data <= 8'hxx;  // Unknown OK when valid=0
+      end
+      7: begin
+        dv_if.valid <= 1'b1;
+        dv_if.data <= 8'hFF;  // Valid data
+      end
+      8: begin
+        dv_if.valid <= 1'b0;
+        dv_if.data <= 8'h00;
+      end
+      default: begin
+        dv_if.valid <= 1'b0;
+        dv_if.data <= 8'h00;
+      end
+    endcase
+  end
+
+endmodule