[#99211] Fix scheduler lost trigger - virtualization

Signed-off-by: Igor Zaworski <izaworski@antmicro.com>

src/CMakeLists.txt

@@ -369,6 +369,7 @@ set(COMMON_SOURCES
     V3Unroll.cpp
     V3UnrollGen.cpp
     V3VariableOrder.cpp
+    V3Virtual.cpp
     V3Waiver.cpp
     V3Width.cpp
     V3WidthCommit.cpp

src/Makefile_obj.in

@@ -348,6 +348,7 @@ RAW_OBJS_PCH_ASTNOMT = \
   V3Unknown.o \
   V3Unroll.o \
   V3UnrollGen.o \
+  V3Virtual.o \
   V3Width.o \
   V3WidthCommit.o \
   V3WidthSel.o \

src/V3SchedTiming.cpp

@@ -29,6 +29,7 @@
 #include "V3AstUserAllocator.h"
 #include "V3EmitCBase.h"
 #include "V3Sched.h"
+#include "V3Virtual.h"
 
 #include <unordered_map>
 
@@ -192,6 +193,8 @@ class AwaitVisitor final : public VNVisitor {
     AstNodeStmt*& m_postUpdatesr;  // Post updates for the trigger eval function
     // Additional var sensitivities
     std::map<const AstVarScope*, std::set<AstSenTree*>>& m_externalDomains;
+    std::unique_ptr<V3ClassesGraphWrapper>
+        m_classGraphp;  // class graph to get possibly called functions from a virtual call
     std::set<AstSenTree*> m_processDomains;  // Sentrees from the current process
     // Variables written by suspendable processes
     std::set<AstVarScope*> m_writtenBySuspendable;
@@ -307,7 +310,12 @@ class AwaitVisitor final : public VNVisitor {
     void visit(AstNodeCCall* const nodep) override {
         iterateChildren(nodep);
         // We need to visit bodies of non-inlined functions
-        visitCalledCFunc(nodep->funcp());
+        const auto& cfuncps = m_classGraphp->getCallPossibleCFuncs(nodep);
+        if (cfuncps.empty()) {
+            visitCalledCFunc(nodep->funcp());
+        } else {
+            for (AstCFunc* const cfuncp : cfuncps) visitCalledCFunc(cfuncp);
+        }
     }
     void visit(AstCFunc* const nodep) override {
         const auto& value = m_cfuncsCache(nodep);
@@ -369,7 +377,8 @@ public:
         : m_scopeTopp{nodep->topScopep()->scopep()}
         , m_lbs{lbs}
         , m_postUpdatesr{postUpdatesr}
-        , m_externalDomains{externalDomains} {
+        , m_externalDomains{externalDomains}
+        , m_classGraphp{V3Virtual::buildClassGraph(nodep)} {
         iterate(nodep);
     }
     ~AwaitVisitor() override {

src/V3Virtual.cpp

@@ -0,0 +1,226 @@
+// -*- mode: C++; c-file-style: "cc-mode" -*-
+//*************************************************************************
+// DESCRIPTION: Verilator: Virtual function calls - function finder
+//
+// Code available from: https://verilator.org
+//
+//*************************************************************************
+//
+// 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: 2003-2026 Wilson Snyder
+// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+//
+//*************************************************************************
+//
+// Builds a graph of inheritance (implements & extends)
+// Allows for lookups of what AstCFunc may be called
+// due to a virtual function call
+//
+// Current limitation: This only may be called after V3Task
+// when AstNodeFTasks are substituted with AstCFuncs
+//
+//*************************************************************************
+// TODO:
+//  - Probably in future this phase shall have a check for overriding
+//    virtual functions with static functions - currently
+//    there is no such check - it shall happen before V3Task
+//    since it moves static functions outside classes
+//  - This shall check for error that is currently emitted in V3LinkDot
+//    `Class 'Derived' implements 'Base' but is missing implementation
+//     for 'function' (IEEE 1800-2023 8.26)`
+//    Sometimes this error is emitted and it is a false positive
+//    since the following snipped is correct but Verilator emits an error:
+//
+//      class Base;
+//        virtual task foo();
+//        endtask
+//      endclass
+//
+//      interface class Iface;
+//        pure virtual task foo();
+//      endclass
+//
+//      class Derived extends Base implements Iface;
+//        // This is legal as it is but Verilator fails
+//      endclass
+//
+//    Mentioned `IEEE 1800-2023 8.26` says:
+//    `When an interface class is implemented by a class, the required
+//     implementations of interface class methods may be
+//     provided by inherited virtual method implementations.`
+//
+//  Therefore, this shall probably become a full phase
+//  and check for those errors somewhere before V3Task
+//*************************************************************************
+
+#include "V3PchAstNoMT.h"  // VL_MT_DISABLED_CODE_UNIT
+
+#include "V3Virtual.h"
+
+VL_DEFINE_DEBUG_FUNCTIONS;
+
+class V3ClassGraphVertex final : public V3GraphVertex {
+    VL_RTTI_IMPL(V3ClassGraphVertex, V3GraphVertex)
+    friend class ClassGraphBuilderVisitor;
+    enum Virtualization : uint8_t {
+        NON_VIRTUAL = 0,  // Not a virtual member function
+        VIRTUAL_IMPLICIT,  // virtual keyword is not next to a function definition the ancestor
+                           // class has such virtual function therefore, it is treated as an
+                           // virtual
+        VIRTUAL,  // function explicitly defined as virtual with a keyword
+        UNDEFINED_VIRTUAL,  // Function not declared in a current class however, it is inherited
+                            // and it is virtual
+        // Note: non-virtual inherited function may not be described with this enum - no need for
+        // now as well as static functions
+    };
+    struct FuncInfo final {
+        AstCFunc* const m_cfuncp;  // pointer to a described function
+        std::unordered_set<AstCFunc*>
+            m_cache;  // set of functions that may be called due to a virtual call
+        Virtualization m_virtualization;  // Whether function is virtual (see Virtualization)
+        bool m_cacheInitialized;  // true when m_cache stores a valid value
+        FuncInfo()
+            : m_cfuncp{nullptr}
+            , m_virtualization{UNDEFINED_VIRTUAL}
+            , m_cacheInitialized{false} {}
+        FuncInfo(AstCFunc* const cfuncp, Virtualization virtualization)
+            : m_cfuncp{cfuncp}
+            , m_virtualization{virtualization}
+            , m_cacheInitialized{false} {}
+    };
+    std::unordered_map<std::string, FuncInfo>
+        m_funcsVirtualization;  // Map from function names to their description
+    const AstClass* const m_classp;  // A class of which the function is a member of
+
+public:
+    explicit V3ClassGraphVertex(V3Graph* const graphp, const AstClass* const classp)
+        : V3GraphVertex{graphp}
+        , m_classp{classp} {}
+    ~V3ClassGraphVertex() override = default;
+
+    std::string name() const override { return m_classp->name(); }
+
+    void addFunc(AstCFunc* const cfuncp) {
+        m_funcsVirtualization.emplace(cfuncp->name(),
+                                      FuncInfo{cfuncp, cfuncp->isVirtual()
+                                                           ? V3ClassGraphVertex::VIRTUAL
+                                                           : V3ClassGraphVertex::NON_VIRTUAL});
+    }
+    void propagateVirt(const V3ClassGraphVertex& from) {
+        for (auto funcs : from.m_funcsVirtualization) {
+            if (funcs.second.m_virtualization == NON_VIRTUAL) continue;
+            auto& vertex = m_funcsVirtualization[funcs.first];
+            if (vertex.m_virtualization == NON_VIRTUAL) vertex.m_virtualization = VIRTUAL_IMPLICIT;
+        }
+    }
+    const std::unordered_set<AstCFunc*>& getCallPossibleCFuncs(const std::string& name) & {
+        auto it = m_funcsVirtualization.find(name);
+        UASSERT(it != m_funcsVirtualization.end(),
+                "Unexpected call - CFunc with name '" << name << "' not found");
+        FuncInfo& info = it->second;
+        if (!info.m_cacheInitialized) {
+            if (info.m_cfuncp) info.m_cache.insert(info.m_cfuncp);
+            if (info.m_virtualization != V3ClassGraphVertex::NON_VIRTUAL) {
+                for (V3GraphEdge& edge : outEdges()) {
+                    V3ClassGraphVertex* const other = edge.top()->as<V3ClassGraphVertex>();
+                    const std::unordered_set<AstCFunc*> otherCalls
+                        = other->getCallPossibleCFuncs(name);
+                    info.m_cache.insert(otherCalls.begin(), otherCalls.end());
+                }
+            }
+            info.m_cacheInitialized = true;
+        }
+        return info.m_cache;
+    }
+};
+
+V3ClassesGraphWrapper::V3ClassesGraphWrapper(
+    std::unique_ptr<V3Graph> graph,
+    std::unordered_map<const AstClass*, V3ClassGraphVertex*> vertexMap)
+    : m_graphp{std::move(graph)}
+    , m_vertexMap{std::move(vertexMap)} {}
+V3ClassesGraphWrapper::~V3ClassesGraphWrapper()
+    = default;  // Must be here because only this translation unit actually knows size
+                // of the V3ClassGraphVertex which is needed for ~unique_ptr()
+
+const std::unordered_set<AstCFunc*>&
+V3ClassesGraphWrapper::getCallPossibleCFuncs(const AstNodeCCall* const callp) const& {
+    // super references and AstCNew shall have AstNodeCCall::funcp() pointing to the only possible
+    // AstCFunc that may be called
+    if (callp->superReference() || VN_IS(callp, CNew)) return m_emptySet;
+    AstNode* nodep = callp->funcp();
+    while (nodep && nodep->backp()
+           && (nodep->backp()->nextp() == nodep || VN_IS(nodep->backp(), Scope))) {
+        nodep = nodep->backp();
+    }
+    AstClass* const classp = VN_CAST(nodep->backp(), Class);
+    if (!classp) return m_emptySet;  // Not under class return empty set
+    auto it = m_vertexMap.find(classp);
+    UASSERT_OBJ(it != m_vertexMap.end(), classp, "Class not mapped");
+    return it->second->getCallPossibleCFuncs(callp->funcp()->name());
+}
+
+// Build a Class graph and returns it in a V3ClassesGraphWrapper
+class ClassGraphBuilderVisitor final : VNVisitor {
+    std::unique_ptr<V3Graph> m_graphp;  // Graph of classes
+    std::unordered_map<const AstClass*, V3ClassGraphVertex*>
+        m_vertexMap;  // Maps classes to their vertices
+    AstClass* m_classp = nullptr;  // Current class
+    V3ClassGraphVertex* m_classVertexp = nullptr;  // vertex corresponding to a current class -
+                                                   // getClassVertex(m_classp) == m_classVertexp
+
+    V3ClassGraphVertex* getClassVertex(const AstClass* const classp) {
+        auto it = m_vertexMap.find(classp);
+        if (it != m_vertexMap.end()) return it->second;
+        return m_vertexMap.emplace(classp, new V3ClassGraphVertex{m_graphp.get(), classp})
+            .first->second;
+    }
+
+    void visit(AstCFunc* const nodep) override {
+        if (!m_classp || nodep->isConstructor() || nodep->isDestructor()) return;
+        UASSERT_OBJ(m_classVertexp, nodep,
+                    "If function is under class m_classVertexp shall be set");
+        m_classVertexp->addFunc(nodep);
+    }
+    void visit(AstClassExtends* const nodep) override {
+        UASSERT_OBJ(m_classVertexp, nodep,
+                    "m_classVertexp shall be set while visiting AstClassExtends");
+        new V3GraphEdge{m_graphp.get(),
+                        getClassVertex(VN_AS(nodep->childDTypep(), ClassRefDType)->classp()),
+                        m_classVertexp, 1};
+    }
+    void visit(AstNodeModule* const nodep) override {
+        VL_RESTORER(m_classp);
+        VL_RESTORER(m_classVertexp);
+        if ((m_classp = VN_CAST(nodep, Class))) m_classVertexp = getClassVertex(m_classp);
+        iterateChildren(nodep);
+    }
+    void visit(AstNode* const nodep) override { iterateChildren(nodep); }
+
+public:
+    explicit ClassGraphBuilderVisitor(AstNetlist* const nodep)
+        : m_graphp{new V3Graph} {
+        iterate(nodep);
+
+        // Propagate virtualization
+        m_graphp->order();
+        for (V3GraphVertex& graphVertex : m_graphp->vertices()) {
+            V3ClassGraphVertex* const vertexp = graphVertex.as<V3ClassGraphVertex>();
+            for (V3GraphEdge& outEdge : vertexp->outEdges()) {
+                V3ClassGraphVertex* const successorp = outEdge.top()->as<V3ClassGraphVertex>();
+                successorp->propagateVirt(*vertexp);
+            }
+        }
+    }
+    ~ClassGraphBuilderVisitor() override = default;
+    std::unique_ptr<V3ClassesGraphWrapper> takeGraph() && {
+        return std::unique_ptr<V3ClassesGraphWrapper>(
+            new V3ClassesGraphWrapper{std::move(m_graphp), std::move(m_vertexMap)});
+    }
+};
+
+std::unique_ptr<V3ClassesGraphWrapper> V3Virtual::buildClassGraph(AstNetlist* netlistp) {
+    return ClassGraphBuilderVisitor{netlistp}.takeGraph();
+}

src/V3Virtual.h

@@ -0,0 +1,64 @@
+// -*- mode: C++; c-file-style: "cc-mode" -*-
+//*************************************************************************
+// DESCRIPTION: Verilator: Virtual function calls - function finder
+//
+// Code available from: https://verilator.org
+//
+//*************************************************************************
+//
+// 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: 2003-2026 Wilson Snyder
+// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+//
+//*************************************************************************
+
+#ifndef VERILATOR_V3VIRTUAL_H_
+#define VERILATOR_V3VIRTUAL_H_
+
+#include "config_build.h"
+#include "verilatedos.h"
+
+#include "V3Ast.h"
+#include "V3Graph.h"
+
+#include <memory>
+#include <unordered_map>
+#include <unordered_set>
+
+//============================================================================
+
+class V3ClassGraphVertex;
+
+// Graph of classes - build by V3Virtual::buildClassGraph() and used to get CFuncs that may be
+// called by a AstNodeCCall (due to virtualization)
+class V3ClassesGraphWrapper final {
+    friend class ClassGraphBuilderVisitor;
+
+    const std::unique_ptr<V3Graph> m_graphp;  // graph of classes
+    const std::unordered_map<const AstClass*, V3ClassGraphVertex*>
+        m_vertexMap;  // Map from AstClass to a corresponding vertex
+    const std::unordered_set<AstCFunc*>
+        m_emptySet;  // Always empty set - used to return a reference to an empty set
+
+    V3ClassesGraphWrapper(std::unique_ptr<V3Graph> graph,
+                          std::unordered_map<const AstClass*, V3ClassGraphVertex*> vertexMap);
+
+public:
+    ~V3ClassesGraphWrapper();
+
+    // Returns possible CFuncs that may be called due to a NodeCCall passed as a callp argument
+    // Warning: returned set may be empty if NodeCCall is a New call or a super call - in such
+    // cases only `callp->funcp()` may be called. Also, if callp is to a non-member function the
+    // set will be empty - post V3Task static functions are not member functions anymore.
+    const std::unordered_set<AstCFunc*>&
+    getCallPossibleCFuncs(const AstNodeCCall* const callp) const&;
+};
+
+class V3Virtual final {
+public:
+    static std::unique_ptr<V3ClassesGraphWrapper> buildClassGraph(AstNetlist*);
+};
+
+#endif  // Guard

test_regress/t/t_sched_noninlined_virt_func_suspendable.py

@@ -0,0 +1,21 @@
+#!/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(verilator_flags2=['--binary', '--stats', '-fno-dfg'])
+
+test.execute()
+
+test.file_grep(test.stats,
+               r'Scheduling, count of non-inlined signal writes in suspendables\s+(\d+)', 7)
+
+test.passes()

test_regress/t/t_sched_noninlined_virt_func_suspendable.v

@@ -0,0 +1,117 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain
+// SPDX-FileCopyrightText: 2026 Antmicro
+// SPDX-License-Identifier: CC0-1.0
+
+// verilog_format: off
+`define stop $stop
+`define checkh(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got='h%x exp='h%x\n", `__FILE__,`__LINE__, (gotv), (expv)); `stop; end while(0)
+// verilog_format: off
+
+class TestBase;
+  virtual function int bar();
+  endfunction
+endclass
+
+interface class D1;
+  pure virtual task run();
+endclass
+
+interface class D2 implements D1;
+  pure virtual task a(bit x = 0);
+endclass
+
+interface class D3 implements D1;
+  pure virtual task b(bit x = 0);
+endclass
+
+interface class D4 implements D2, D3;
+endclass
+
+package pkg;
+  bit [2:0] y3;
+endpackage
+
+module t;
+  bit [2:0] y;
+  bit [2:0] z;
+  assign z[0] = 1'b1;
+  assign z[1] = !(y[0]);
+  assign z[2] = !(|y[1:0]);
+
+  bit [2:0] y2;
+  bit [2:0] z2;
+  assign z2[0] = 1'b1;
+  assign z2[1] = !(y2[0]);
+  assign z2[2] = !(|y2[1:0]);
+
+  import pkg::y3;
+  bit [2:0] z3;
+  assign z3[0] = 1'b1;
+  assign z3[1] = !(y3[0]);
+  assign z3[2] = !(|y3[1:0]);
+
+  bit [2:0] y4;
+  bit [2:0] z4;
+  assign z4[0] = 1'b1;
+  assign z4[1] = !(y4[0]);
+  assign z4[2] = !(|y4[1:0]);
+  class Foo extends TestBase implements D4;
+    function automatic int bar();
+      // verilator no_inline_task
+      y2 = 3'b111;
+      y3 = 3'b111;
+      return 1;
+    endfunction
+    task run();
+      y = 3'b111;
+      #1;
+      `checkh(z, 3'b001);
+      `checkh(z2, 3'b001);
+      `checkh(z3, 3'b001);
+      `checkh(z4, 3'b111);
+    endtask
+    task a(bit x = 0);
+      // verilator no_inline_task
+      y4 = ~y4;
+      #1;
+      if (!x) b(!x);
+    endtask
+    task b(bit x = 0);
+      // verilator no_inline_task
+      if (!x) a(!x);
+    endtask
+  endclass
+  initial begin
+    static Foo inst = new;
+    static TestBase foo = inst;
+    static D3 d3 = inst;
+    static D1 d1 = inst;
+    static D4 d4 = inst;
+    #1;
+    `checkh(z, 3'b111);
+    `checkh(z2, 3'b111);
+    `checkh(z3, 3'b111);
+    `checkh(z4, 3'b111);
+    void'(foo.bar());
+    #1;
+    `checkh(z, 3'b111);
+    `checkh(z2, 3'b001);
+    `checkh(z3, 3'b001);
+    `checkh(z4, 3'b111);
+    d1.run();
+    d4.a();
+    `checkh(z, 3'b001);
+    `checkh(z2, 3'b001);
+    `checkh(z3, 3'b001);
+    `checkh(z4, 3'b001);
+    d3.b();
+    `checkh(z, 3'b001);
+    `checkh(z2, 3'b001);
+    `checkh(z3, 3'b001);
+    `checkh(z4, 3'b111);
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule