From eb114eb96f0039b5989e8b7077274b0759c82490 Mon Sep 17 00:00:00 2001
From: Yilou Wang <wangyilou123@gmail.com>
Date: Fri, 27 Mar 2026 15:18:09 +0100
Subject: [PATCH] Fix wait() hang in interface with always @* using
 process::self() and VIF function calls

---
 src/V3Timing.cpp                   |  7 ++-
 src/V3Width.cpp                    | 10 +++++
 test_regress/t/t_wait_iface_vif.py | 18 ++++++++
 test_regress/t/t_wait_iface_vif.v  | 71 ++++++++++++++++++++++++++++++
 4 files changed, 105 insertions(+), 1 deletion(-)
 create mode 100755 test_regress/t/t_wait_iface_vif.py
 create mode 100755 test_regress/t/t_wait_iface_vif.v

diff --git a/src/V3Timing.cpp b/src/V3Timing.cpp
index 316a9c642..602b7de06 100644
--- a/src/V3Timing.cpp
+++ b/src/V3Timing.cpp
@@ -892,7 +892,12 @@ class TimingControlVisitor final : public VNVisitor {
         m_underProcedure = true;
         // Workaround for killing `always` processes (doing that is pretty much UB)
         // TODO: Disallow killing `always` at runtime (throw an error)
-        if (hasFlags(nodep, T_HAS_PROC)) addFlags(nodep, T_SUSPENDEE);
+        // Do not make combinational always blocks (always @*) suspendable just because
+        // they need process context (e.g. for uvm_fatal's process::self()). Combo blocks
+        // have no timing controls and would spin forever as coroutines.
+        if (hasFlags(nodep, T_HAS_PROC)
+            && !(m_activep && m_activep->sentreep() && m_activep->sentreep()->hasCombo()))
+            addFlags(nodep, T_SUSPENDEE);
 
         iterateChildren(nodep);
         if (hasFlags(nodep, T_HAS_PROC)) nodep->setNeedProcess();
diff --git a/src/V3Width.cpp b/src/V3Width.cpp
index a4a8c0c2d..f5b1244a8 100644
--- a/src/V3Width.cpp
+++ b/src/V3Width.cpp
@@ -4464,6 +4464,16 @@ class WidthVisitor final : public VNVisitor {
         if (AstNodeFTask* const ftaskp
             = VN_CAST(m_memberMap.findMember(ifacep, nodep->name()), NodeFTask)) {
             UINFO(5, __FUNCTION__ << "AstNodeFTask" << nodep);
+            // When a function/task is called through a virtual interface, its body may
+            // write to interface member variables. Mark all members as sensIfacep so
+            // optimization passes do not constant-fold them across instances.
+            if (adtypep->isVirtual()) {
+                for (AstNode* itemp = ifacep->stmtsp(); itemp; itemp = itemp->nextp()) {
+                    if (AstVar* const mvarp = VN_CAST(itemp, Var)) {
+                        mvarp->sensIfacep(ifacep);
+                    }
+                }
+            }
             userIterate(ftaskp, nullptr);
             if (ftaskp->isStatic()) {
                 AstArg* const argsp = nodep->argsp();
diff --git a/test_regress/t/t_wait_iface_vif.py b/test_regress/t/t_wait_iface_vif.py
new file mode 100755
index 000000000..557b1b992
--- /dev/null
+++ b/test_regress/t/t_wait_iface_vif.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: 2025 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile(verilator_flags2=['--binary', '--timing', '--timescale 1ns/1ps'])
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_wait_iface_vif.v b/test_regress/t/t_wait_iface_vif.v
new file mode 100755
index 000000000..efdc2a65c
--- /dev/null
+++ b/test_regress/t/t_wait_iface_vif.v
@@ -0,0 +1,71 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain.
+// SPDX-FileCopyrightText: 2025 PlanV GmbH
+// SPDX-License-Identifier: CC0-1.0
+/* verilator lint_off ZERODLY */
+
+interface my_if();
+  logic clk;
+  realtime clk_period;
+  bit clk_active = 0;
+
+  initial begin
+    wait (clk_active);
+    forever begin
+      #(clk_period);
+      if (clk_active) begin
+        case (clk)
+          1'b0: clk = 1'b1;
+          default: clk = 1'b0;
+        endcase
+      end
+    end
+  end
+
+  // always @* with process::self() must not become a spinning coroutine
+  always @* begin
+    if (clk_active && clk_period == 0.0) begin
+      automatic process p = process::self();
+      $display("%m: active with 0 period (proc=%p)", p);
+      $stop;
+    end
+  end
+
+  function void set_period(realtime p);
+    clk_period = p;
+  endfunction
+
+  function void start_clk();
+    if (clk_period) clk_active = 1;
+  endfunction
+endinterface
+
+class Driver;
+  virtual my_if vif;
+
+  task run();
+    vif.set_period(5ns);
+    #10;
+    vif.start_clk();
+  endtask
+endclass
+
+module t;
+  my_if intf();
+
+  initial begin
+    automatic Driver d = new;
+    d.vif = intf;
+    d.run();
+    repeat (4) @(posedge intf.clk);
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+
+  initial begin
+    #1000;
+    $display("TIMEOUT");
+    $stop;
+  end
+endmodule