Support disabling a fork from outside that fork (#6174)

include/verilated_std.sv

@@ -175,6 +175,14 @@ package std;
 `endif
       endtask
 
+      static task killQueue(ref process processQueue[$]);
+`ifdef VERILATOR_TIMING
+         while (processQueue.size() > 0) begin
+            processQueue.pop_back().kill();
+         end
+`endif
+      endtask
+
       // Two process references are equal if the different classes' containing
       // m_process are equal. Can't yet use <=> as the base class template
       // comparisons doesn't define <=> as they don't yet require --timing and C++20.

src/V3AstNodeOther.h

@@ -1974,7 +1974,7 @@ class AstVar final : public AstNode {
     bool m_isConst : 1;  // Table contains constant data
     bool m_isContinuously : 1;  // Ever assigned continuously (for force/release)
     bool m_hasStrengthAssignment : 1;  // Is on LHS of assignment with strength specifier
-    bool m_isStatic : 1;  // Static C variable (for Verilog see instead isAutomatic)
+    bool m_isStatic : 1;  // Static C variable (for Verilog see instead lifetime())
     bool m_isPulldown : 1;  // Tri0
     bool m_isPullup : 1;  // Tri1
     bool m_isIfaceParent : 1;  // dtype is reference to interface present in this module

src/V3LinkJump.cpp

@@ -35,6 +35,7 @@
 
 #include "V3AstUserAllocator.h"
 #include "V3Error.h"
+#include "V3UniqueNames.h"
 
 #include <vector>
 
@@ -60,6 +61,8 @@ class LinkJumpVisitor final : public VNVisitor {
     int m_modRepeatNum = 0;  // Repeat counter
     VOptionBool m_unrollFull;  // Pragma full, disable, or default unrolling
     std::vector<AstNodeBlock*> m_blockStack;  // All begin blocks above current node
+    V3UniqueNames m_queueNames{
+        "__VprocessQueue"};  // Names for queues needed for 'disable' handling
 
     // METHODS
     AstJumpLabel* findAddLabel(AstNode* nodep, bool endOfIter) {
@@ -159,6 +162,29 @@ class LinkJumpVisitor final : public VNVisitor {
         if (AstNode* const refp = nodep->op4p()) addPrefixToBlocksRecurse(prefix, refp);
         if (AstNode* const refp = nodep->nextp()) addPrefixToBlocksRecurse(prefix, refp);
     }
+    static AstNode* getMemberp(const AstNodeModule* const nodep, const std::string& name) {
+        for (AstNode* itemp = nodep->stmtsp(); itemp; itemp = itemp->nextp()) {
+            if (itemp->name() == name) return itemp;
+        }
+        return nullptr;
+    }
+    bool existsBlockAbove(const std::string& name) const {
+        for (const AstNodeBlock* const stackp : vlstd::reverse_view(m_blockStack)) {
+            if (stackp->name() == name) return true;
+        }
+        return false;
+    }
+    static AstStmtExpr* getQueuePushProcessSelfp(AstVarRef* const queueRefp) {
+        // Constructs queue.push_back(std::process::self()) statement
+        FileLine* const fl = queueRefp->fileline();
+        AstClass* const processClassp
+            = VN_AS(getMemberp(v3Global.rootp()->stdPackagep(), "process"), Class);
+        AstFunc* const selfMethodp = VN_AS(getMemberp(processClassp, "self"), Func);
+        AstFuncRef* const processSelfp = new AstFuncRef{fl, selfMethodp, nullptr};
+        processSelfp->classOrPackagep(processClassp);
+        return new AstStmtExpr{
+            fl, new AstMethodCall{fl, queueRefp, "push_back", new AstArg{fl, "", processSelfp}}};
+    }
 
     // VISITORS
     void visit(AstNodeModule* nodep) override {
@@ -338,22 +364,65 @@ class LinkJumpVisitor final : public VNVisitor {
     void visit(AstDisable* nodep) override {
         UINFO(8, "   DISABLE " << nodep);
         AstNode* const targetp = nodep->targetp();
+        FileLine* const fl = nodep->fileline();
         UASSERT_OBJ(targetp, nodep, "Unlinked disable statement");
         if (VN_IS(targetp, Task)) {
             nodep->v3warn(E_UNSUPPORTED, "Unsupported: disabling task by name");
-        } else if (VN_IS(targetp, Fork)) {
-            nodep->v3warn(E_UNSUPPORTED, "Unsupported: disabling fork by name");
-        } else if (AstBegin* const beginp = VN_CAST(targetp, Begin)) {
-            const std::string targetName = beginp->name();
-            bool aboveBlock = false;
-            for (AstNodeBlock* const stackp : vlstd::reverse_view(m_blockStack)) {
-                UINFO(9, "    UNDERBLK  " << stackp);
-                if (stackp->name() == targetName) {
-                    aboveBlock = true;
-                    break;
+        } else if (AstFork* const forkp = VN_CAST(targetp, Fork)) {
+            // 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.
+            if (existsBlockAbove(forkp->name())) {
+                nodep->v3warn(E_UNSUPPORTED, "Unsupported: disabling fork from within same fork");
+            }
+            if (m_ftaskp) {
+                nodep->v3warn(E_UNSUPPORTED, "Unsupported: disabling fork from task / function");
+            }
+            AstPackage* const topPkgp = v3Global.rootp()->dollarUnitPkgAddp();
+            AstClass* const processClassp
+                = VN_AS(getMemberp(v3Global.rootp()->stdPackagep(), "process"), Class);
+            // Declare queue of processes (as a global variable for simplicity)
+            AstVar* const processQueuep = new AstVar{
+                fl, VVarType::VAR, m_queueNames.get(forkp->name()), VFlagChildDType{},
+                new AstQueueDType{fl, VFlagChildDType{},
+                                  new AstClassRefDType{fl, processClassp, nullptr}, nullptr}};
+            processQueuep->lifetime(VLifetime::STATIC);
+            topPkgp->addStmtsp(processQueuep);
+
+            AstVarRef* const queueWriteRefp
+                = new AstVarRef{fl, topPkgp, processQueuep, VAccess::WRITE};
+            AstStmtExpr* const pushCurrentProcessp = getQueuePushProcessSelfp(queueWriteRefp);
+
+            for (AstNode* forkItemp = forkp->stmtsp(); forkItemp; forkItemp = forkItemp->nextp()) {
+                // Add push_back statement at the beginning of each fork.
+                // Wrap into begin block if needed
+                AstBegin* beginp = VN_CAST(forkItemp, Begin);
+                if (!beginp) {
+                    beginp = new AstBegin{fl, "", nullptr};
+                    forkItemp->replaceWith(beginp);
+                    beginp->addStmtsp(forkItemp);
+                    // In order to continue the iteration
+                    forkItemp = beginp;
+                }
+                if (pushCurrentProcessp->backp()) {
+                    beginp->stmtsp()->addHereThisAsNext(pushCurrentProcessp->cloneTree(false));
+                } else {
+                    beginp->stmtsp()->addHereThisAsNext(pushCurrentProcessp);
                 }
             }
-            if (aboveBlock) {
+
+            AstVarRef* const queueRefp
+                = new AstVarRef{fl, topPkgp, processQueuep, VAccess::READWRITE};
+            AstTaskRef* const killQueueCall
+                = new AstTaskRef{fl, VN_AS(getMemberp(processClassp, "killQueue"), Task),
+                                 new AstArg{fl, "", queueRefp}};
+            killQueueCall->classOrPackagep(processClassp);
+            nodep->addNextHere(new AstStmtExpr{fl, killQueueCall});
+        } else if (AstBegin* const beginp = VN_CAST(targetp, Begin)) {
+            const std::string targetName = beginp->name();
+            if (existsBlockAbove(targetName)) {
                 if (beginp->user3()) {
                     nodep->v3warn(E_UNSUPPORTED,
                                   "Unsupported: disabling block that contains a fork");

src/V3ParseImp.h

@@ -293,12 +293,12 @@ public:
     void dumpInputsFile() VL_MT_DISABLED;
     void dumpTokensAhead(int line) VL_MT_DISABLED;
     static void candidatePli(VSpellCheck* spellerp) VL_MT_DISABLED;
+    void importIfInStd(FileLine* fileline, const string& id);
 
 private:
     void preprocDumps(std::ostream& os);
     void lexFile(const string& modname) VL_MT_DISABLED;
     void yylexReadTok() VL_MT_DISABLED;
-    void importIfInStd(FileLine* fileline, const string& id);
     void tokenPull() VL_MT_DISABLED;
     void tokenPipeline() VL_MT_DISABLED;  // Internal; called from tokenToBison
     int tokenPipelineId(int token) VL_MT_DISABLED;

src/verilog.y

@@ -3754,7 +3754,9 @@ statement_item<nodep>:          // IEEE: statement_item
         //                      // IEEE: disable_statement
         |       yDISABLE yFORK ';'                      { $$ = new AstDisableFork{$1}; }
         |       yDISABLE idDottedSel ';'
-                        { $$ = new AstDisable{$1, $2}; }
+                        { $$ = new AstDisable{$1, $2};
+                          PARSEP->importIfInStd($1, "process");
+                        }
         //                      // IEEE: event_trigger
         |       yP_MINUSGT expr ';'
                         { $$ = new AstFireEvent{$1, $2, false}; }

test_regress/t/t_disable.out

@@ -1,4 +1,4 @@
-%Error-UNSUPPORTED: t/t_disable.v:11:10: Unsupported: disabling fork by name
+%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

test_regress/t/t_disable_outside.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_outside.v

@@ -0,0 +1,26 @@
+// 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
+      begin : blk
+         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
+   end
+endmodule

test_regress/t/t_disable_outside2.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_outside2.v

@@ -0,0 +1,29 @@
+// 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
+      for (int i = 0; i < 3; i++) begin
+         begin : blk
+            int x = 0;
+            fork : fork_blk
+               begin
+                  x = 1;
+                  #2;
+                  x = 2;
+               end
+            join_none
+            #1;
+            if (i < 2) disable fork_blk;
+            #2;
+            if (i < 2 && x != 1) $stop;
+            if (i == 2 && x != 2) $stop;
+         end
+      end
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule

test_regress/t/t_disable_within_task_unsup.out

@@ -0,0 +1,5 @@
+%Error-UNSUPPORTED: t/t_disable_within_task_unsup.v:8:4: Unsupported: disabling fork from task / function
+    8 |    disable t.init.fork_blk;
+      |    ^~~~~~~
+                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+%Error: Exiting due to

test_regress/t/t_disable_within_task_unsup.py

@@ -0,0 +1,16 @@
+#!/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.lint(verilator_flags2=['--timing'], fails=True, expect_filename=test.golden_filename)
+
+test.passes()

test_regress/t/t_disable_within_task_unsup.v

@@ -0,0 +1,31 @@
+// 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
+
+task disable_fork_blk;
+   disable t.init.fork_blk;
+endtask
+
+module t(/*AUTOARG*/);
+
+   initial begin : init
+      int x = 0;
+      fork : fork_blk
+         begin
+            x = 1;
+            disable_fork_blk();
+            x = 2;
+         end
+         begin
+            #1;
+            x = 3;
+         end
+      join
+      if (x != 1) $stop;
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+
+endmodule