Internals: Add isForceable() to VerilatedVarProps

Allows runtime checking whether a signal is forceable without needing to
check the existence of the `__VforceEn` and `__VforceVal` signals. This
will be useful for a later implementation of `vpiForceFlag` for
`vpi_put_value`.

include/verilated.h

@@ -154,7 +154,8 @@ enum VerilatedVarFlags {
     // Flags
     VLVF_PUB_RD = (1 << 8),  // Public readable
     VLVF_PUB_RW = (1 << 9),  // Public writable
-    VLVF_DPI_CLAY = (1 << 10)  // DPI compatible C standard layout
+    VLVF_DPI_CLAY = (1 << 10),  // DPI compatible C standard layout
+    VLVF_FORCEABLE = (1 << 11)  // Forceable
 };
 
 // IEEE 1800-2023 Table 20-6

include/verilated_sym_props.h

@@ -156,6 +156,7 @@ public:
         return bits;
     }
     bool isPublicRW() const { return ((m_vlflags & VLVF_PUB_RW) != 0); }
+    bool isForceable() const { return ((m_vlflags & VLVF_FORCEABLE) != 0); }
     // DPI compatible C standard layout
     bool isDpiCLayout() const { return ((m_vlflags & VLVF_DPI_CLAY) != 0); }
     int udims() const VL_MT_SAFE { return m_unpacked.size(); }

src/V3AstNodes.cpp

@@ -630,6 +630,9 @@ string AstVar::vlEnumDir() const {
     } else if (isSigUserRdPublic()) {
         out += "|VLVF_PUB_RD";
     }
+    if (isForceable()) {
+        out += "|VLVF_FORCEABLE";
+    }
     //
     if (const AstBasicDType* const bdtypep = basicp()) {
         if (bdtypep->keyword().isDpiCLayout()) out += "|VLVF_DPI_CLAY";