From f66df9e70ebdd9b54a7af667eb7c904047e35532 Mon Sep 17 00:00:00 2001
From: Nick Brereton <85175726+nbstrike@users.noreply.github.com>
Date: Fri, 27 Mar 2026 14:31:03 -0400
Subject: [PATCH] Fix `disable iff` imply-delay statement linking (#7337)

---
 src/V3AssertPre.cpp                           | 11 +++-
 .../t/t_property_disable_iff_midreset.py      | 18 ++++++
 .../t/t_property_disable_iff_midreset.v       | 56 +++++++++++++++++++
 3 files changed, 82 insertions(+), 3 deletions(-)
 create mode 100755 test_regress/t/t_property_disable_iff_midreset.py
 create mode 100644 test_regress/t/t_property_disable_iff_midreset.v

diff --git a/src/V3AssertPre.cpp b/src/V3AssertPre.cpp
index cd8868632..f65ca8b24 100644
--- a/src/V3AssertPre.cpp
+++ b/src/V3AssertPre.cpp
@@ -493,7 +493,9 @@ private:
         }
         if (m_disableSeqIfp) {
             AstIf* const disableSeqIfp = m_disableSeqIfp->cloneTree(false);
-            disableSeqIfp->addThensp(nodep->nextp()->unlinkFrBackWithNext());
+            AstNode* const continuationsp = nodep->nextp()->unlinkFrBackWithNext();
+            // Keep continuation statements in a proper statement-list container.
+            disableSeqIfp->addThensp(new AstBegin{flp, "", continuationsp, true});
             nodep->addNextHere(disableSeqIfp);
         }
         nodep->replaceWith(beginp);
@@ -931,7 +933,7 @@ private:
             // */ }
             AstBegin* const bodyp = pexprp->bodyp();
             AstNode* const origStmtsp = bodyp->stmtsp()->unlinkFrBackWithNext();
-            AstIf* const guardp = new AstIf{flp, condp, origStmtsp};
+            AstIf* const guardp = new AstIf{flp, condp, new AstBegin{flp, "", origStmtsp, true}};
             bodyp->addStmtsp(guardp);
             nodep->replaceWith(pexprp);
             // Don't iterate pexprp here -- it was already iterated when created
@@ -1043,11 +1045,14 @@ private:
             AstVar* const initialCntp = new AstVar{flp, VVarType::BLOCKTEMP, "__VinitialCnt",
                                                    nodep->findBasicDType(VBasicDTypeKwd::UINT32)};
             initialCntp->lifetime(VLifetime::AUTOMATIC_EXPLICIT);
-            bodyp->stmtsp()->addHereThisAsNext(initialCntp);
             AstAssign* const assignp
                 = new AstAssign{flp, new AstVarRef{flp, initialCntp, VAccess::WRITE},
                                 readCntRefp->cloneTree(false)};
+            // Prepend to the sequence body to keep statement list structure valid.
+            AstNode* const origStmtsp = bodyp->stmtsp()->unlinkFrBackWithNext();
+            bodyp->addStmtsp(initialCntp);
             initialCntp->addNextHere(assignp);
+            assignp->addNextHere(origStmtsp);
 
             m_disableSeqIfp
                 = new AstIf{flp, new AstEq{flp, new AstVarRef{flp, initialCntp, VAccess::READ},
diff --git a/test_regress/t/t_property_disable_iff_midreset.py b/test_regress/t/t_property_disable_iff_midreset.py
new file mode 100755
index 000000000..35e44000c
--- /dev/null
+++ b/test_regress/t/t_property_disable_iff_midreset.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# 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-FileCopyrightText: 2026 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile(timing_loop=True, verilator_flags2=['--assert', '--timing'])
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_property_disable_iff_midreset.v b/test_regress/t/t_property_disable_iff_midreset.v
new file mode 100644
index 000000000..e82e9ea46
--- /dev/null
+++ b/test_regress/t/t_property_disable_iff_midreset.v
@@ -0,0 +1,56 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// 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-FileCopyrightText: 2026 Wilson Snyder
+// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+// verilog_format: off
+`define stop $stop
+`define checkd(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d: got=%0d exp=%0d (%s !== %s)\n", `__FILE__,`__LINE__, (gotv), (expv), `"gotv`", `"expv`"); `stop; end while(0);
+// verilog_format: on
+
+module t (
+    input clk
+);
+
+  int cyc = 0;
+  bit rst = 0;
+  bit start = 0;
+  bit done = 0;
+
+  int fails_a = 0;
+  int fails_b = 0;
+
+  // First launch at cyc==2 should be canceled by reset pulse in the middle.
+  assert property (@(posedge clk) disable iff (rst) (cyc == 2) |-> ##2 done)
+  else fails_a++;
+
+  // Second launch at cyc==8 has no reset pulse in flight and should fail once.
+  assert property (@(posedge clk) disable iff (rst) (cyc == 8) |-> ##2 done)
+  else fails_b++;
+
+  always @(posedge clk) begin
+    cyc <= cyc + 1;
+
+    // Defaults
+    start <= 0;
+    done <= 0;
+
+    if (cyc == 2) start <= 1;
+    if (cyc == 8) start <= 1;
+
+    // Mid-window reset pulse for first launch.
+    if (cyc == 3) rst <= 1;
+    if (cyc == 4) rst <= 0;
+
+    if (cyc == 16) begin
+      `checkd(fails_a, 0);
+      `checkd(fails_b, 1);
+      $write("*-* All Finished *-*\n");
+      $finish;
+    end
+  end
+
+endmodule