From 7e67f738440620bee1c087c39dc7411e8e57e972 Mon Sep 17 00:00:00 2001
From: Krzysztof Bieganski <kbieganski@antmicro.com>
Date: Tue, 16 Dec 2025 00:09:45 +0100
Subject: [PATCH] Fix process reference giving no return statement error
 (#6767) (#6823)

---
 src/V3EmitCFunc.h                  |  6 ++++++
 src/V3SchedTiming.cpp              | 14 --------------
 src/V3Timing.cpp                   | 21 +++++++--------------
 test_regress/t/t_process_always.py | 18 ++++++++++++++++++
 test_regress/t/t_process_always.v  | 15 +++++++++++++++
 5 files changed, 46 insertions(+), 28 deletions(-)
 create mode 100755 test_regress/t/t_process_always.py
 create mode 100644 test_regress/t/t_process_always.v

diff --git a/src/V3EmitCFunc.h b/src/V3EmitCFunc.h
index da2ba68ec..de139ee6b 100644
--- a/src/V3EmitCFunc.h
+++ b/src/V3EmitCFunc.h
@@ -475,6 +475,12 @@ public:
 
         m_usevlSelfRef = false;
 
+        if (nodep->isCoroutine()) {
+            // Sometimes coroutines don't have co_awaits,
+            // so emit a co_return at the end to avoid compile errors.
+            puts("co_return;");
+        }
+
         puts("}\n");
         if (nodep->ifdef() != "") puts("#endif  // " + nodep->ifdef() + "\n");
     }
diff --git a/src/V3SchedTiming.cpp b/src/V3SchedTiming.cpp
index 581424a5d..19c6b2d38 100644
--- a/src/V3SchedTiming.cpp
+++ b/src/V3SchedTiming.cpp
@@ -316,7 +316,6 @@ class TransformForksVisitor final : public VNVisitor {
     // STATE
     bool m_inClass = false;  // Are we in a class?
     bool m_beginHasAwaits = false;  // Does the current begin have awaits?
-    bool m_awaitMoved = false;  // Has the current function lost awaits?
     AstFork* m_forkp = nullptr;  // Current fork
     AstCFunc* m_funcp = nullptr;  // Current function
 
@@ -373,14 +372,7 @@ class TransformForksVisitor final : public VNVisitor {
     void visit(AstCFunc* nodep) override {
         VL_RESTORER(m_funcp);
         m_funcp = nodep;
-        m_awaitMoved = false;
         iterateChildren(nodep);
-        // cppcheck-suppress knownConditionTrueFalse
-        if (nodep->isCoroutine() && m_awaitMoved
-            && !nodep->stmtsp()->exists([](AstCAwait*) { return true; })) {
-            // co_return at the end (either that or a co_await is required in a coroutine
-            nodep->addStmtsp(new AstCStmt{nodep->fileline(), "co_return;"});
-        }
     }
     void visit(AstVar* nodep) override {
         if (!m_forkp) nodep->user1(true);
@@ -459,12 +451,6 @@ class TransformForksVisitor final : public VNVisitor {
             newfuncp->setNeedProcess();
             newfuncp->addStmtsp(new AstCStmt{flp, "vlProcess->state(VlProcess::FINISHED);"});
         }
-        if (!m_beginHasAwaits) {
-            // co_return at the end (either that or a co_await is required in a coroutine
-            newfuncp->addStmtsp(new AstCStmt{flp, "co_return;"});
-        } else {
-            m_awaitMoved = true;
-        }
         remapLocals(newfuncp, callp);
     }
     void visit(AstCAwait* nodep) override {
diff --git a/src/V3Timing.cpp b/src/V3Timing.cpp
index 6c9f2cb46..885eacb3a 100644
--- a/src/V3Timing.cpp
+++ b/src/V3Timing.cpp
@@ -859,21 +859,14 @@ class TimingControlVisitor final : public VNVisitor {
                 nodep->addStmtsp(cstmtp);
             }
         }
-        AstNode* firstCoStmtp = nullptr;  // First co_* statement in the function
-        nodep->exists([&](AstCAwait* const awaitp) -> bool { return (firstCoStmtp = awaitp); });
-        if (!firstCoStmtp) {
-            // It's a coroutine but has no awaits (a class method that overrides/is
-            // overridden by a suspendable, but doesn't have any awaits itself). Add a
-            // co_return at the end (either that or a co_await is required in a
-            // coroutine)
-            firstCoStmtp = new AstCStmt{nodep->fileline(), "co_return;"};
-            nodep->addStmtsp(firstCoStmtp);
-        }
         if (nodep->dpiExportImpl()) {
-            // A DPI-exported coroutine won't be able to block the calling code
-            // Error on the await node; fall back to the function node
-            firstCoStmtp->v3warn(E_UNSUPPORTED,
-                                 "Unsupported: Timing controls inside DPI-exported tasks");
+            nodep->exists([](AstCAwait* const awaitp) -> bool {
+                // A DPI-exported coroutine won't be able to block the calling code
+                // Error on the await node; fall back to the function node
+                awaitp->v3warn(E_UNSUPPORTED,
+                               "Unsupported: Timing controls inside DPI-exported tasks");
+                return true;
+            });
         }
     }
     void visit(AstNodeCCall* nodep) override {
diff --git a/test_regress/t/t_process_always.py b/test_regress/t/t_process_always.py
new file mode 100755
index 000000000..c6e56559a
--- /dev/null
+++ b/test_regress/t/t_process_always.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(verilator_flags2=["--binary"])
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_process_always.v b/test_regress/t/t_process_always.v
new file mode 100644
index 000000000..f4d49a8f2
--- /dev/null
+++ b/test_regress/t/t_process_always.v
@@ -0,0 +1,15 @@
+// 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
+
+module t;
+  always something();
+
+  function void something();
+    void'(process::self());
+    $write("*-* All Finished *-*\n");
+    $finish;
+  endfunction
+endmodule