Internals: Add AstUserNAllocator utility classes.

These utility classes can be used to hang advanced data structures off
AstNode user*u() pointers, and they take care of memory management for
the client. Use via the call operator().

src/V3Ast.h

@@ -26,6 +26,7 @@
 #include "V3Global.h"
 
 #include <cmath>
+#include <type_traits>
 #include <unordered_set>
 
 #include "V3Ast__gen_classes.h"  // From ./astgen
@@ -1141,10 +1142,14 @@ public:
     explicit VNUser(void* p) { m_u.up = p; }
     ~VNUser() = default;
     // Casters
-    WidthVP* c() const { return reinterpret_cast<WidthVP*>(m_u.up); }
-    VSymEnt* toSymEnt() const { return reinterpret_cast<VSymEnt*>(m_u.up); }
-    AstNode* toNodep() const { return reinterpret_cast<AstNode*>(m_u.up); }
-    V3GraphVertex* toGraphVertex() const { return reinterpret_cast<V3GraphVertex*>(m_u.up); }
+    template <class T>  //
+    typename std::enable_if<std::is_pointer<T>::value, T>::type to() const {
+        return reinterpret_cast<T>(m_u.up);
+    }
+    WidthVP* c() const { return to<WidthVP*>(); }
+    VSymEnt* toSymEnt() const { return to<VSymEnt*>(); }
+    AstNode* toNodep() const { return to<AstNode*>(); }
+    V3GraphVertex* toGraphVertex() const { return to<V3GraphVertex*>(); }
     int toInt() const { return m_u.ui; }
     static VNUser fromInt(int i) { return VNUser(i); }
 };

src/V3AstUserAllocator.h

@@ -0,0 +1,119 @@
+// -*- mode: C++; c-file-style: "cc-mode" -*-
+//*************************************************************************
+// DESCRIPTION: Verilator: Utility to hang advanced data structures of
+// AstNode::user*p() pointers with automatic memory management.
+//
+// Code available from: https://verilator.org
+//
+//*************************************************************************
+//
+// Copyright 2003-2021 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
+//
+//*************************************************************************
+
+#ifndef VERILATOR_V3ASTUSERALLOCATOR_H_
+#define VERILATOR_V3ASTUSERALLOCATOR_H_
+
+#include "config_build.h"
+#include "verilatedos.h"
+
+#include "V3Ast.h"
+
+#include <type_traits>
+#include <vector>
+
+template <class T_Node, class T_Data, int T_UserN> class AstUserAllocatorBase VL_NOT_FINAL {
+    static_assert(1 <= T_UserN && T_UserN <= 5, "Wrong user pointer number");
+    static_assert(std::is_base_of<AstNode, T_Node>::value, "T_Node must be an AstNode type");
+
+private:
+    std::vector<T_Data*> m_allocated;
+
+    inline T_Data* getUserp(T_Node* nodep) const {
+        // This simplifies statically as T_UserN is constant. In C++17, use 'if constexpr'.
+        if (T_UserN == 1) {
+            VNUser user = nodep->user1u();
+            return user.to<T_Data*>();
+        } else if (T_UserN == 2) {
+            VNUser user = nodep->user2u();
+            return user.to<T_Data*>();
+        } else if (T_UserN == 3) {
+            VNUser user = nodep->user3u();
+            return user.to<T_Data*>();
+        } else if (T_UserN == 4) {
+            VNUser user = nodep->user4u();
+            return user.to<T_Data*>();
+        } else {
+            VNUser user = nodep->user5u();
+            return user.to<T_Data*>();
+        }
+    }
+
+    inline void setUserp(T_Node* nodep, T_Data* userp) const {
+        // This simplifies statically as T_UserN is constant. In C++17, use 'if constexpr'.
+        if (T_UserN == 1) {
+            nodep->user1u(VNUser(userp));
+        } else if (T_UserN == 2) {
+            nodep->user2u(VNUser(userp));
+        } else if (T_UserN == 3) {
+            nodep->user3u(VNUser(userp));
+        } else if (T_UserN == 4) {
+            nodep->user4u(VNUser(userp));
+        } else {
+            nodep->user5u(VNUser(userp));
+        }
+    }
+
+protected:
+    AstUserAllocatorBase() {
+        // This simplifies statically as T_UserN is constant. In C++17, use 'if constexpr'.
+        if (T_UserN == 1) {
+            AstUser1InUse::check();
+        } else if (T_UserN == 2) {
+            AstUser2InUse::check();
+        } else if (T_UserN == 3) {
+            AstUser3InUse::check();
+        } else if (T_UserN == 4) {
+            AstUser4InUse::check();
+        } else {
+            AstUser5InUse::check();
+        }
+    }
+
+    virtual ~AstUserAllocatorBase() {
+        // Delete all allocated data structures
+        for (T_Data* const p : m_allocated) { delete p; }
+    }
+
+public:
+    // Get a reference to the user data
+    T_Data& operator()(T_Node* nodep) {
+        T_Data* userp = getUserp(nodep);
+        if (!userp) {
+            userp = new T_Data;
+            m_allocated.push_back(userp);
+            setUserp(nodep, userp);
+        }
+        return *userp;
+    }
+};
+
+// User pointer allocator classes. T_Node is the type of node the allocator should be applied to
+// and is simply there for a bit of extra type safety. T_Data is the type of the data structure
+// managed by the allocator.
+template <class T_Node, class T_Data>
+class AstUser1Allocator final : public AstUserAllocatorBase<T_Node, T_Data, 1> {};
+template <class T_Node, class T_Data>
+class AstUser2Allocator final : public AstUserAllocatorBase<T_Node, T_Data, 2> {};
+template <class T_Node, class T_Data>
+class AstUser3Allocator final : public AstUserAllocatorBase<T_Node, T_Data, 3> {};
+template <class T_Node, class T_Data>
+class AstUser4Allocator final : public AstUserAllocatorBase<T_Node, T_Data, 4> {};
+template <class T_Node, class T_Data>
+class AstUser5Allocator final : public AstUserAllocatorBase<T_Node, T_Data, 5> {};
+
+#endif  // Guard