Bug 1421152 - Add a checked cast method to TenuredCell. r=jonco

js/src/gc/AtomMarking.cpp

@@ -237,15 +237,14 @@ AtomMarkingRuntime::atomIsMarked(Zone* zone, TenuredCell* thing)
     if (!thing)
         return true;
 
-    JS::TraceKind kind = thing->getTraceKind();
-    if (kind == JS::TraceKind::String) {
-        JSString* str = static_cast<JSString*>(thing);
-        if (str->isAtom())
-            return atomIsMarked(zone, &str->asAtom());
-        return true;
+    if (thing->is<JSString>()) {
+        JSString* str = thing->as<JSString>();
+        return str->isAtom() ? atomIsMarked(zone, &str->asAtom()) : true;
     }
-    if (kind == JS::TraceKind::Symbol)
-        return atomIsMarked(zone, static_cast<JS::Symbol*>(thing));
+
+    if (thing->is<JS::Symbol>())
+        return atomIsMarked(zone, thing->as<JS::Symbol>());
+
     return true;
 }
 

js/src/gc/Cell.h

@@ -138,6 +138,23 @@ class TenuredCell : public Cell
         return JS::shadow::Zone::asShadowZone(zoneFromAnyThread());
     }
 
+    template <class T>
+    inline bool is() const {
+        return getTraceKind() == JS::MapTypeToTraceKind<T>::kind;
+    }
+
+    template<class T>
+    inline T* as() {
+        MOZ_ASSERT(is<T>());
+        return static_cast<T*>(this);
+    }
+
+    template <class T>
+    inline const T* as() const {
+        MOZ_ASSERT(is<T>());
+        return static_cast<const T*>(this);
+    }
+
     static MOZ_ALWAYS_INLINE void readBarrier(TenuredCell* thing);
     static MOZ_ALWAYS_INLINE void writeBarrierPre(TenuredCell* thing);
 

js/src/gc/Marking.cpp

@@ -2016,7 +2016,8 @@ inline T*
 MarkStack::TaggedPtr::as() const
 {
     MOZ_ASSERT(tag() == MapTypeToMarkStackTag<T*>::value);
-    MOZ_ASSERT(ptr()->asTenured().getTraceKind() == MapTypeToTraceKind<T>::kind);
+    MOZ_ASSERT(ptr()->isTenured());
+    MOZ_ASSERT(ptr()->is<T>());
     return static_cast<T*>(ptr());
 }
 
@@ -2024,7 +2025,8 @@ inline JSObject*
 MarkStack::TaggedPtr::asValueArrayObject() const
 {
     MOZ_ASSERT(tag() == ValueArrayTag);
-    MOZ_ASSERT(ptr()->asTenured().getTraceKind() == JS::TraceKind::Object);
+    MOZ_ASSERT(ptr()->isTenured());
+    MOZ_ASSERT(ptr()->is<JSObject>());
     return static_cast<JSObject*>(ptr());
 }
 
@@ -2032,7 +2034,8 @@ inline JSObject*
 MarkStack::TaggedPtr::asSavedValueArrayObject() const
 {
     MOZ_ASSERT(tag() == SavedValueArrayTag);
-    MOZ_ASSERT(ptr()->asTenured().getTraceKind() == JS::TraceKind::Object);
+    MOZ_ASSERT(ptr()->isTenured());
+    MOZ_ASSERT(ptr()->is<JSObject>());
     return static_cast<JSObject*>(ptr());
 }
 
@@ -2040,7 +2043,8 @@ inline JSRope*
 MarkStack::TaggedPtr::asTempRope() const
 {
     MOZ_ASSERT(tag() == TempRopeTag);
-    MOZ_ASSERT(ptr()->asTenured().getTraceKind() == JS::TraceKind::String);
+    MOZ_ASSERT(ptr()->isTenured());
+    MOZ_ASSERT(ptr()->is<JSString>());
     return static_cast<JSRope*>(ptr());
 }