Support disabling a fork from within that fork (#6314)

src/V3LinkJump.cpp

@@ -180,16 +180,12 @@ class LinkJumpVisitor final : public VNVisitor {
             fl, new AstMethodCall{fl, queueRefp, "push_back", new AstArg{fl, "", processSelfp}}};
     }
     void handleDisableOnFork(AstDisable* const nodep, const std::vector<AstBegin*>& forks) {
-        // The support is limited only to disabling a fork from outside that fork.
-        // It utilizes the process::kill()` method. For each `disable` a queue of processes is
-        // declared. At the beginning of each fork that can be disabled, its process handle is
-        // pushed to the queue. `disable` statement is replaced with calling `kill()` method on
-        // each element of the queue.
+        // The support utilizes the process::kill()` method. For each `disable` a queue of
+        // processes is declared. At the beginning of each fork that can be disabled, its process
+        // handle is pushed to the queue. `disable` statement is replaced with calling `kill()`
+        // method on each element of the queue.
         FileLine* const fl = nodep->fileline();
         const std::string targetName = nodep->targetp()->name();
-        if (existsBlockAbove(targetName)) {
-            nodep->v3warn(E_UNSUPPORTED, "Unsupported: disabling fork from within same fork");
-        }
         if (m_ftaskp) {
             nodep->v3warn(E_UNSUPPORTED, "Unsupported: disabling fork from task / function");
         }
@@ -222,7 +218,15 @@ class LinkJumpVisitor final : public VNVisitor {
             = new AstTaskRef{fl, VN_AS(getMemberp(processClassp, "killQueue"), Task),
                              new AstArg{fl, "", queueRefp}};
         killQueueCall->classOrPackagep(processClassp);
-        nodep->addNextHere(new AstStmtExpr{fl, killQueueCall});
+        AstStmtExpr* const killStmtp = new AstStmtExpr{fl, killQueueCall};
+        nodep->addNextHere(killStmtp);
+        if (existsBlockAbove(targetName)) {
+            // process::kill doesn't kill the current process immediately, because it is in the
+            // running state. Since the current process has to be terminated immediately, we jump
+            // at the end of the fork that is being disabled
+            AstJumpBlock* const jumpBlockp = getJumpBlock(nodep->targetp(), false);
+            killStmtp->addNextHere(new AstJumpGo{fl, jumpBlockp});
+        }
     }
     static bool directlyUnderFork(const AstNode* const nodep) {
         if (nodep->backp()->nextp() == nodep) return directlyUnderFork(nodep->backp());

test_regress/t/t_disable.out

@@ -1,8 +1,5 @@
-%Error-UNSUPPORTED: t/t_disable.v:11:10: Unsupported: disabling fork from within same fork
-   11 |          disable foo;
-      |          ^~~~~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
 %Error-UNSUPPORTED: t/t_disable.v:17:13: Unsupported: disabling block that contains a fork
    17 |             disable forked;
       |             ^~~~~~~
+                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
 %Error: Exiting due to

test_regress/t/t_disable_inside.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(timing_loop=True, verilator_flags2=["--timing"])
+
+test.execute()
+
+test.passes()

test_regress/t/t_disable_inside.v

@@ -0,0 +1,24 @@
+// 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 (  /*AUTOARG*/);
+  initial begin
+    int x = 0;
+    fork : fork_blk
+      begin
+        x = 1;
+        #2;
+        x = 2;
+      end
+    join_none
+    #1;
+    disable fork_blk;
+    #2;
+    if (x != 1) $stop;
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule