Issue #1742 - Remove the ambiguous portions of gc that dealt with tagged pointers for shapes.

Nobody likes "isNullLike(obj)" when trying to garbage collect. It either is or
is not. Master Yoda would be pleased with this change.

js/src/gc/Barrier.h

@@ -261,8 +261,6 @@ struct InternalBarrierMethods<T*>
 {
     static bool isMarkable(T* v) { return v != nullptr; }
 
-    static bool isMarkableTaggedPointer(T* v) { return !IsNullTaggedPointer(v); }
-
     static void preBarrier(T* v) { T::writeBarrierPre(v); }
 
     static void postBarrier(T** vp, T* prev, T* next) { T::writeBarrierPost(vp, prev, next); }
@@ -282,7 +280,6 @@ template <>
 struct InternalBarrierMethods<Value>
 {
     static bool isMarkable(const Value& v) { return v.isGCThing(); }
-    static bool isMarkableTaggedPointer(const Value& v) { return isMarkable(v); }
 
     static void preBarrier(const Value& v) {
         DispatchTyped(PreBarrierFunctor<Value>(), v);
@@ -318,7 +315,6 @@ template <>
 struct InternalBarrierMethods<jsid>
 {
     static bool isMarkable(jsid id) { return JSID_IS_GCTHING(id); }
-    static bool isMarkableTaggedPointer(jsid id) { return isMarkable(id); }
 
     static void preBarrier(jsid id) { DispatchTyped(PreBarrierFunctor<jsid>(), id); }
     static void postBarrier(jsid* idp, jsid prev, jsid next) {}

js/src/gc/Heap.h

@@ -317,10 +317,6 @@ class TenuredCell : public Cell
     MOZ_ALWAYS_INLINE void unmark(uint32_t color) const;
     MOZ_ALWAYS_INLINE void copyMarkBitsFrom(const TenuredCell* src);
 
-    // Note: this is in TenuredCell because JSObject subclasses are sometimes
-    // used tagged.
-    static MOZ_ALWAYS_INLINE bool isNullLike(const Cell* thing) { return !thing; }
-
     // Access to the arena.
     inline Arena* arena() const;
     inline AllocKind getAllocKind() const;
@@ -1302,7 +1298,7 @@ TenuredCell::isInsideZone(JS::Zone* zone) const
 TenuredCell::readBarrier(TenuredCell* thing)
 {
     MOZ_ASSERT(!CurrentThreadIsIonCompiling());
-    MOZ_ASSERT(!isNullLike(thing));
+    MOZ_ASSERT(thing);
 
     // It would be good if barriers were never triggered during collection, but
     // at the moment this can happen e.g. when rekeying tables containing
@@ -1335,7 +1331,6 @@ AssertSafeToSkipBarrier(TenuredCell* thing);
 TenuredCell::writeBarrierPre(TenuredCell* thing)
 {
     MOZ_ASSERT(!CurrentThreadIsIonCompiling());
-    MOZ_ASSERT_IF(thing, !isNullLike(thing));
     if (!thing)
         return;
 

js/src/gc/Marking.cpp

@@ -501,7 +501,7 @@ void
 js::TraceNullableRoot(JSTracer* trc, T* thingp, const char* name)
 {
     AssertRootMarkingPhase(trc);
-    if (InternalBarrierMethods<T>::isMarkableTaggedPointer(*thingp))
+    if (InternalBarrierMethods<T>::isMarkable(*thingp))
         DispatchToTracer(trc, ConvertToBase(thingp), name);
 }
 

js/src/gc/Marking.h

@@ -414,14 +414,6 @@ ToMarkable(Cell* cell)
     return cell;
 }
 
-// Return true if the pointer is nullptr, or if it is a tagged pointer to
-// nullptr.
-MOZ_ALWAYS_INLINE bool
-IsNullTaggedPointer(void* p)
-{
-    return uintptr_t(p) <= LargestTaggedNullCellPointer;
-}
-
 // Wrap a GC thing pointer into a new Value or jsid. The type system enforces
 // that the thing pointer is a wrappable type.
 template <typename S, typename T>

js/src/jsobj.h

@@ -299,7 +299,6 @@ class JSObject : public js::gc::Cell
 
     static const JS::TraceKind TraceKind = JS::TraceKind::Object;
     static const size_t MaxTagBits = 3;
-    static bool isNullLike(const JSObject* obj) { return uintptr_t(obj) < (1 << MaxTagBits); }
 
     MOZ_ALWAYS_INLINE JS::Zone* zone() const {
         return group_->zone();
@@ -635,7 +634,6 @@ struct JSObject_Slots16 : JSObject { void* data[3]; js::Value fslots[16]; };
 /* static */ MOZ_ALWAYS_INLINE void
 JSObject::readBarrier(JSObject* obj)
 {
-    MOZ_ASSERT_IF(obj, !isNullLike(obj));
     if (obj && obj->isTenured())
         obj->asTenured().readBarrier(&obj->asTenured());
 }
@@ -643,7 +641,6 @@ JSObject::readBarrier(JSObject* obj)
 /* static */ MOZ_ALWAYS_INLINE void
 JSObject::writeBarrierPre(JSObject* obj)
 {
-    MOZ_ASSERT_IF(obj, !isNullLike(obj));
     if (obj && obj->isTenured())
         obj->asTenured().writeBarrierPre(&obj->asTenured());
 }
@@ -652,8 +649,6 @@ JSObject::writeBarrierPre(JSObject* obj)
 JSObject::writeBarrierPost(void* cellp, JSObject* prev, JSObject* next)
 {
     MOZ_ASSERT(cellp);
-    MOZ_ASSERT_IF(next, !IsNullTaggedPointer(next));
-    MOZ_ASSERT_IF(prev, !IsNullTaggedPointer(prev));
 
     // If the target needs an entry, add it.
     js::gc::StoreBuffer* buffer;

js/src/vm/String.h

@@ -521,7 +521,7 @@ class JSString : public js::gc::TenuredCell
     }
 
     static MOZ_ALWAYS_INLINE void writeBarrierPre(JSString* thing) {
-        if (isNullLike(thing) || thing->isPermanentAtom())
+        if (!thing || thing->isPermanentAtom())
             return;
 
         TenuredCell::writeBarrierPre(thing);

js/src/vm/TaggedProto.h

@@ -68,10 +68,6 @@ struct InternalBarrierMethods<TaggedProto>
 
     static void readBarrier(const TaggedProto& proto);
 
-    static bool isMarkableTaggedPointer(TaggedProto proto) {
-        return proto.isObject();
-    }
-
     static bool isMarkable(TaggedProto proto) {
         return proto.isObject();
     }