Mark RTTI methods as const / pure, so compiler could optimize subsequ…

…ent calls, if necessary. (#5049) * Mark RTTI methods as const / pure, so compiler could optimize subsequent calls, if necessary. Signed-off-by: Anton Korobeynikov <[email protected]> * Add some explanation to RTTI boilerplate Signed-off-by: Anton Korobeynikov <[email protected]> --------- Signed-off-by: Anton Korobeynikov <[email protected]>
p4lang · Dec 13, 2024 · 5dc7f87 · 5dc7f87
1 parent b0f775c
commit 5dc7f87
Showing 1 changed file with 20 additions and 12 deletions.
diff --git a/lib/rtti.h b/lib/rtti.h
@@ -296,18 +296,26 @@ struct Base {
     };                                                                                     \
     DECLARE_TYPEINFO_COMMON(T, ##__VA_ARGS__)
 
-#define DECLARE_TYPEINFO_COMMON(T, ...)                                                        \
- public:                                                                                       \
-    static constexpr T *rttiEnabledMarker(T *);                                                \
-    using TypeInfo = P4::RTTI::TypeInfo<T, ##__VA_ARGS__>;                                     \
-    [[nodiscard]] P4::RTTI::TypeId typeId() const noexcept override { return TypeInfo::id(); } \
-    [[nodiscard]] bool isA(P4::RTTI::TypeId typeId) const noexcept override {                  \
-        return TypeInfo::isA(typeId);                                                          \
-    }                                                                                          \
-                                                                                               \
- protected:                                                                                    \
-    [[nodiscard]] const void *toImpl(P4::RTTI::TypeId typeId) const noexcept override {        \
-        return TypeInfo::isA(typeId) ? TypeInfo::dyn_cast(typeId, this) : nullptr;             \
+// Common typeinfo boilerplate methods. Note that they are marked pure / const, so consecutive
+// calls to is<> / to<> on the same pointer could be eliminated by a compiler.
+//   - typeId() / isA are const as they do not access any global state, they
+//     always return the same value (for same input arguments)
+//   - toImpl() is pure. It only access global state via its arguments (this pointer). So for
+//     the same `this` the result is also the same.
+#define DECLARE_TYPEINFO_COMMON(T, ...)                                                            \
+ public:                                                                                           \
+    static constexpr T *rttiEnabledMarker(T *);                                                    \
+    using TypeInfo = P4::RTTI::TypeInfo<T, ##__VA_ARGS__>;                                         \
+    [[nodiscard, gnu::const]] P4::RTTI::TypeId typeId() const noexcept override {                  \
+        return TypeInfo::id();                                                                     \
+    }                                                                                              \
+    [[nodiscard, gnu::const]] bool isA(P4::RTTI::TypeId typeId) const noexcept override {          \
+        return TypeInfo::isA(typeId);                                                              \
+    }                                                                                              \
+                                                                                                   \
+ protected:                                                                                        \
+    [[nodiscard, gnu::pure]] const void *toImpl(P4::RTTI::TypeId typeId) const noexcept override { \
+        return TypeInfo::isA(typeId) ? TypeInfo::dyn_cast(typeId, this) : nullptr;                 \
     }
 
 #endif /* LIB_RTTI_H_ */