From dca555b6d7dc39f1d6d53a1a9b3822223e5cd771 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=C5=82omiej=20Chmiel?= <bchmiel@antmicro.com>
Date: Mon, 15 Sep 2025 16:50:31 +0200
Subject: [PATCH] Fix pre/post increments in assertions (#6434)

---
 src/V3LinkInc.cpp              | 15 +++++++-
 test_regress/t/t_assert_pre.py | 18 +++++++++
 test_regress/t/t_assert_pre.v  | 68 ++++++++++++++++++++++++++++++++++
 3 files changed, 99 insertions(+), 2 deletions(-)
 create mode 100755 test_regress/t/t_assert_pre.py
 create mode 100644 test_regress/t/t_assert_pre.v

diff --git a/src/V3LinkInc.cpp b/src/V3LinkInc.cpp
index 2b60ad92c..a8809a6d7 100644
--- a/src/V3LinkInc.cpp
+++ b/src/V3LinkInc.cpp
@@ -47,8 +47,6 @@
 
 #include "V3LinkInc.h"
 
-#include <algorithm>
-
 VL_DEFINE_DEBUG_FUNCTIONS;
 
 //######################################################################
@@ -102,6 +100,19 @@ class LinkIncVisitor final : public VNVisitor {
         m_ftaskp = nodep;
         iterateChildren(nodep);
     }
+    void visit(AstNodeCoverOrAssert* nodep) override {
+        VL_RESTORER(m_insStmtp);
+        m_insStmtp = nodep;
+        iterateAndNextNull(nodep->propp());
+        m_insStmtp = nullptr;
+        // Note: no iterating over sentreep here as they will be ignored anyway
+        if (AstAssert* const assertp = VN_CAST(nodep, Assert)) {
+            iterateAndNextNull(assertp->failsp());
+        } else if (AstAssertIntrinsic* const intrinsicp = VN_CAST(nodep, AssertIntrinsic)) {
+            iterateAndNextNull(intrinsicp->failsp());
+        }
+        iterateAndNextNull(nodep->passsp());
+    }
     void visit(AstWhile* nodep) override {
         // Special, as statements need to be put in different places
         m_insStmtp = nodep;
diff --git a/test_regress/t/t_assert_pre.py b/test_regress/t/t_assert_pre.py
new file mode 100755
index 000000000..f989a35fb
--- /dev/null
+++ b/test_regress/t/t_assert_pre.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_assert_pre.v b/test_regress/t/t_assert_pre.v
new file mode 100644
index 000000000..64ee99eb2
--- /dev/null
+++ b/test_regress/t/t_assert_pre.v
@@ -0,0 +1,68 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Antmicro.
+// SPDX-License-Identifier: CC0-1.0
+
+`define stop $stop
+`define checkh(gotv,
+               expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got=%0x exp=%0x (%s !== %s)\n", `__FILE__,`__LINE__, (gotv), (expv), `"gotv`", `"expv`"); `stop; end while(0);
+
+module t (  /*AUTOARG*/
+    // Inputs
+    clk
+);
+  input clk;
+
+  bit toggle = 0;
+  int inc = 0;
+  int dec = 0;
+
+  assert property (@(negedge clk) not toggle)
+  else ++inc;
+
+  assert property (@(negedge clk) not toggle)
+  else --dec;
+
+  int passsInc = 0;
+  int passsDec = 0;
+
+  assert property (@(negedge clk) not toggle) ++passsInc;
+  else --passsDec;
+
+  assert property (@(negedge clk) not toggle) ++passsInc;
+  cover property (@(negedge clk) not toggle) ++passsInc;
+
+  int inc2 = 0;
+  assert property (@(e) not toggle) begin
+    `checkh(inc2, 0);
+    inc2++;
+    `checkh(inc2,1);
+  end
+  event e;
+
+  int cyc = 0;
+
+  always @(posedge clk) begin
+`ifdef TEST_VERBOSE
+    $write("[%0t] cyc==%0d toggle==%d\n", $time, cyc, toggle);
+`endif
+    if (cyc % 3 == 0) begin
+      toggle <= 1;
+    end else begin
+      toggle <= 0;
+    end
+
+    cyc <= cyc + 1;
+
+    if (cyc == 5) begin
+      ->e;
+      `checkh(inc, 2);
+      `checkh(dec, -2);
+      `checkh(passsInc, 6);
+      `checkh(passsDec, -2);
+      $write("*-* All Finished *-*\n");
+      $finish;
+    end
+  end
+endmodule