Fix virtual interface null checks (#5391)

include/verilated_types.h

@@ -1787,12 +1787,16 @@ public:
 };
 
 //===================================================================
-// Represents the null pointer. Used for setting VlClassRef to null instead of
+// Represents the null pointer. Used for:
-// via nullptr_t, to prevent the implicit conversion of 0 to nullptr.
+// * setting VlClassRef to null instead of via nullptr_t, to prevent the implicit conversion of 0
+//   to nullptr,
+// * comparing interface pointers to null.
 
 struct VlNull final {
     operator bool() const { return false; }
+    bool operator==(void* ptr) const { return !ptr; }
 };
+inline bool operator==(void* ptr, VlNull) { return !ptr; }
 
 //===================================================================
 // Verilog class reference container

src/V3AstNodeDType.h

@@ -876,8 +876,8 @@ public:
     AstNodeDType* skipRefToConstp() const override { return (AstNodeDType*)this; }
     AstNodeDType* skipRefToEnump() const override { return (AstNodeDType*)this; }
     bool similarDType(const AstNodeDType* samep) const override { return this == samep; }
-    int widthAlignBytes() const override { return 1; }
+    int widthAlignBytes() const override { return 0; }
-    int widthTotalBytes() const override { return 1; }
+    int widthTotalBytes() const override { return 0; }
     bool isVirtual() const { return m_virtual; }
     void isVirtual(bool flag) {
         m_virtual = flag;

src/V3Width.cpp

@@ -2744,7 +2744,6 @@ class WidthVisitor final : public VNVisitor {
         UINFO(5, "   IFACEREF " << nodep << endl);
         userIterateChildren(nodep, m_vup);
         nodep->dtypep(nodep);
-        nodep->widthForce(1, 1);  // Not really relevant
         UINFO(4, "dtWidthed " << nodep << endl);
     }
     void visit(AstNodeUOrStructDType* nodep) override {
@@ -7024,7 +7023,7 @@ class WidthVisitor final : public VNVisitor {
                 = new AstNeqD{nodep->fileline(), VN_AS(underp, NodeExpr),
                               new AstConst{nodep->fileline(), AstConst::RealDouble{}, 0.0}};
             linker.relink(newp);
-        } else if (VN_IS(underVDTypep, ClassRefDType)
+        } else if (VN_IS(underVDTypep, ClassRefDType) || VN_IS(underVDTypep, IfaceRefDType)
                    || (VN_IS(underVDTypep, BasicDType)
                        && VN_AS(underVDTypep, BasicDType)->keyword() == VBasicDTypeKwd::CHANDLE)) {
             // Allow warning-free "if (handle)"

test_regress/t/t_interface_virtual.v

@@ -34,6 +34,9 @@ module t (/*AUTOARG*/);
    initial begin
       va = ia;
       vb = ia;
+
+      if (va == null) $stop;
+
       $display("va==vb? %b", va==vb);
       $display("va!=vb? %b", va!=vb);
       vb = ib;
@@ -53,6 +56,8 @@ module t (/*AUTOARG*/);
       $display("va.addr=%x", va.addr, " va.data=%x", va.data, " ia.addr=%x", ia.addr, " ia.data=%x", ia.data);
       $display("vb.addr=%x", vb.addr, " vb.data=%x", vb.data, " ib.addr=%x", ib.addr, " ib.data=%x", ib.data);
 
+      if (ca.fa) $stop;
+
       ca.fa = ia;
       ca.fb = ib;
       cb.fa = ib;
@@ -60,6 +65,10 @@ module t (/*AUTOARG*/);
       gen.x[0] = va;
       gen.x[1] = vb;
 
+      if (ca == null) $stop;
+      if (ca.fa == null) $stop;
+      if (!ca.fa ) $stop;
+
       pa = va;
       pb = vb;