[csa] Add TNode<MaybeObject>.

LoadMaybeWeakField returns a TNode<MaybeObject>, and the only way to extract
values from it is through explicit functions.

BUG=v8:7308

Change-Id: I98da6b715527bb9976b4c78ed9caaa39fbcb3ed5
Reviewed-on: https://chromium-review.googlesource.com/1014106
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52732}

src/code-stub-assembler.cc

@@ -829,6 +829,12 @@ TNode<BoolT> CodeStubAssembler::TaggedIsSmi(SloppyTNode<Object> a) {
                    IntPtrConstant(0));
 }
 
+TNode<BoolT> CodeStubAssembler::TaggedIsSmi(TNode<MaybeObject> a) {
+  return WordEqual(
+      WordAnd(BitcastMaybeObjectToWord(a), IntPtrConstant(kSmiTagMask)),
+      IntPtrConstant(0));
+}
+
 TNode<BoolT> CodeStubAssembler::TaggedIsNotSmi(SloppyTNode<Object> a) {
   return WordNotEqual(
       WordAnd(BitcastTaggedToWord(a), IntPtrConstant(kSmiTagMask)),
@@ -1492,15 +1498,15 @@ TNode<PrototypeInfo> CodeStubAssembler::LoadMapPrototypeInfo(
     SloppyTNode<Map> map, Label* if_no_proto_info) {
   Label if_strong_heap_object(this);
   CSA_ASSERT(this, IsMap(map));
-  Node* maybe_prototype_info =
-      LoadObjectField(map, Map::kTransitionsOrPrototypeInfoOffset);
-  VARIABLE(prototype_info, MachineRepresentation::kTagged);
+  TNode<MaybeObject> maybe_prototype_info =
+      LoadMaybeWeakObjectField(map, Map::kTransitionsOrPrototypeInfoOffset);
+  TVARIABLE(Object, prototype_info);
   DispatchMaybeObject(maybe_prototype_info, if_no_proto_info, if_no_proto_info,
                       if_no_proto_info, &if_strong_heap_object,
                       &prototype_info);
 
   BIND(&if_strong_heap_object);
-  GotoIfNot(WordEqual(LoadMap(prototype_info.value()),
+  GotoIfNot(WordEqual(LoadMap(CAST(prototype_info.value())),
                       LoadRoot(Heap::kPrototypeInfoMapRootIndex)),
             if_no_proto_info);
   return CAST(prototype_info.value());
@@ -1681,49 +1687,62 @@ TNode<Object> CodeStubAssembler::LoadWeakCellValue(
   return value;
 }
 
-void CodeStubAssembler::DispatchMaybeObject(Node* maybe_object, Label* if_smi,
-                                            Label* if_cleared, Label* if_weak,
-                                            Label* if_strong,
-                                            Variable* extracted) {
+void CodeStubAssembler::DispatchMaybeObject(TNode<MaybeObject> maybe_object,
+                                            Label* if_smi, Label* if_cleared,
+                                            Label* if_weak, Label* if_strong,
+                                            TVariable<Object>* extracted) {
   Label inner_if_smi(this), inner_if_strong(this);
 
   GotoIf(TaggedIsSmi(maybe_object), &inner_if_smi);
 
-  GotoIf(WordEqual(maybe_object, IntPtrConstant(reinterpret_cast<intptr_t>(
-                                     HeapObjectReference::ClearedValue()))),
+  GotoIf(WordEqual(BitcastMaybeObjectToWord(maybe_object),
+                   IntPtrConstant(reinterpret_cast<intptr_t>(
+                       HeapObjectReference::ClearedValue()))),
          if_cleared);
 
-  GotoIf(WordEqual(WordAnd(BitcastTaggedToWord(maybe_object),
+  GotoIf(WordEqual(WordAnd(BitcastMaybeObjectToWord(maybe_object),
                            IntPtrConstant(kWeakHeapObjectMask)),
                    IntPtrConstant(0)),
          &inner_if_strong);
 
-  extracted->Bind(
-      BitcastWordToTagged(WordAnd(BitcastTaggedToWord(maybe_object),
-                                  IntPtrConstant(~kWeakHeapObjectMask))));
+  *extracted =
+      BitcastWordToTagged(WordAnd(BitcastMaybeObjectToWord(maybe_object),
+                                  IntPtrConstant(~kWeakHeapObjectMask)));
   Goto(if_weak);
 
   BIND(&inner_if_smi);
-  extracted->Bind(maybe_object);
+  *extracted = ToStrongHeapObjectOrSmi(maybe_object);
   Goto(if_smi);
 
   BIND(&inner_if_strong);
-  extracted->Bind(maybe_object);
+  *extracted = ToStrongHeapObject(maybe_object);
   Goto(if_strong);
 }
 
-Node* CodeStubAssembler::IsStrongHeapObject(Node* value) {
-  return WordEqual(
-      WordAnd(BitcastTaggedToWord(value), IntPtrConstant(kWeakHeapObjectMask)),
-      IntPtrConstant(0));
+TNode<BoolT> CodeStubAssembler::IsStrongHeapObject(TNode<MaybeObject> value) {
+  return WordEqual(WordAnd(BitcastMaybeObjectToWord(value),
+                           IntPtrConstant(kWeakHeapObjectMask)),
+                   IntPtrConstant(0));
+}
+
+TNode<HeapObject> CodeStubAssembler::GetHeapObject(TNode<MaybeObject> value) {
+  return UncheckedCast<HeapObject>(BitcastWordToTagged(WordAnd(
+      BitcastMaybeObjectToWord(value), IntPtrConstant(~kWeakHeapObjectMask))));
 }
 
-Node* CodeStubAssembler::ToStrongHeapObject(Node* value) {
-  return BitcastWordToTagged(WordAnd(BitcastTaggedToWord(value),
-                                     IntPtrConstant(~kWeakHeapObjectMask)));
+TNode<HeapObject> CodeStubAssembler::ToStrongHeapObject(
+    TNode<MaybeObject> value) {
+  AssertIsStrongHeapObject(value);
+  return ReinterpretCast<HeapObject>(value);
 }
 
-TNode<Object> CodeStubAssembler::LoadArrayElement(
+TNode<Object> CodeStubAssembler::ToStrongHeapObjectOrSmi(
+    TNode<MaybeObject> value) {
+  AssertIsStrongHeapObjectOrSmi(value);
+  return ReinterpretCast<Object>(value);
+}
+
+TNode<MaybeObject> CodeStubAssembler::LoadArrayElement(
     SloppyTNode<Object> object, int array_header_size, Node* index_node,
     int additional_offset, ParameterMode parameter_mode,
     LoadSensitivity needs_poisoning) {
@@ -1733,7 +1752,7 @@ TNode<Object> CodeStubAssembler::LoadArrayElement(
   int32_t header_size = array_header_size + additional_offset - kHeapObjectTag;
   TNode<IntPtrT> offset = ElementOffsetFromIndex(index_node, HOLEY_ELEMENTS,
                                                  parameter_mode, header_size);
-  return UncheckedCast<Object>(
+  return UncheckedCast<MaybeObject>(
       Load(MachineType::AnyTagged(), object, offset, needs_poisoning));
 }
 
@@ -1744,8 +1763,9 @@ TNode<Object> CodeStubAssembler::LoadFixedArrayElement(
   // and thus the reasonable assert IsFixedArraySubclass(object) is
   // untrue. TODO(marja): Fix.
   CSA_SLOW_ASSERT(this, IsNotWeakFixedArraySubclass(object));
-  return LoadArrayElement(object, FixedArray::kHeaderSize, index_node,
-                          additional_offset, parameter_mode, needs_poisoning);
+  return ToStrongHeapObjectOrSmi(
+      LoadArrayElement(object, FixedArray::kHeaderSize, index_node,
+                       additional_offset, parameter_mode, needs_poisoning));
 }
 
 TNode<RawPtrT> CodeStubAssembler::LoadFixedTypedArrayBackingStore(
@@ -6943,9 +6963,8 @@ void CodeStubAssembler::LookupLinear(TNode<Name> unique_name,
 
   BuildFastLoop(last_exclusive, first_inclusive,
                 [=](SloppyTNode<IntPtrT> name_index) {
-                  TNode<Name> candidate_name = CAST(
-                      LoadArrayElement(array, Array::kHeaderSize, name_index));
-                  CSA_ASSERT(this, IsStrongHeapObject(candidate_name));
+                  TNode<Name> candidate_name = CAST(ToStrongHeapObject(
+                      LoadArrayElement(array, Array::kHeaderSize, name_index)));
                   *var_name_index = name_index;
                   GotoIf(WordEqual(candidate_name, unique_name), if_found);
                 },
@@ -7014,10 +7033,9 @@ TNode<Name> CodeStubAssembler::GetKey(TNode<Array> array,
                     std::is_base_of<TransitionArray, Array>::value,
                 "T must be a descendant of FixedArray or a TransitionArray");
   const int key_offset = Array::ToKeyIndex(0) * kPointerSize;
-  TNode<Name> key =
-      CAST(LoadArrayElement(array, Array::kHeaderSize,
-                            EntryIndexToIndex<Array>(entry_index), key_offset));
-  CSA_ASSERT(this, IsStrongHeapObject(key));
+  TNode<Name> key = CAST(ToStrongHeapObject(
+      LoadArrayElement(array, Array::kHeaderSize,
+                       EntryIndexToIndex<Array>(entry_index), key_offset)));
   return key;
 }
 
@@ -11442,6 +11460,20 @@ void CodeStubAssembler::InitializeFunctionContext(Node* native_context,
                                     native_context);
 }
 
+void CodeStubAssembler::AssertIsStrongHeapObject(
+    SloppyTNode<MaybeObject> object) {
+  CSA_SLOW_ASSERT(this, WordEqual(WordAnd(BitcastMaybeObjectToWord(object),
+                                          IntPtrConstant(kHeapObjectTagMask)),
+                                  IntPtrConstant(kHeapObjectTag)));
+}
+
+void CodeStubAssembler::AssertIsStrongHeapObjectOrSmi(
+    SloppyTNode<MaybeObject> object) {
+  CSA_SLOW_ASSERT(this, WordEqual(WordAnd(BitcastMaybeObjectToWord(object),
+                                          IntPtrConstant(kWeakHeapObjectMask)),
+                                  IntPtrConstant(0)));
+}
+
 void CodeStubAssembler::AssertIsStrongHeapObject(
     SloppyTNode<HeapObject> object) {
   CSA_SLOW_ASSERT(this, WordEqual(WordAnd(BitcastTaggedToWord(object),

src/code-stub-assembler.h

@@ -436,6 +436,7 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
 
   // Check a value for smi-ness
   TNode<BoolT> TaggedIsSmi(SloppyTNode<Object> a);
+  TNode<BoolT> TaggedIsSmi(TNode<MaybeObject> a);
   TNode<BoolT> TaggedIsNotSmi(SloppyTNode<Object> a);
   // Check that the value is a non-negative smi.
   TNode<BoolT> TaggedIsPositiveSmi(SloppyTNode<Object> a);
@@ -537,6 +538,12 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
   // Load a SMI root, untag it, and convert to Word32.
   Node* LoadAndUntagToWord32Root(Heap::RootListIndex root_index);
 
+  TNode<MaybeObject> LoadMaybeWeakObjectField(SloppyTNode<HeapObject> object,
+                                              int offset) {
+    return UncheckedCast<MaybeObject>(
+        LoadObjectField(object, offset, MachineType::AnyTagged()));
+  }
+
   // Tag a smi and store it.
   Node* StoreAndTagSmi(Node* base, int offset, Node* value);
 
@@ -647,14 +654,16 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
   // pointed to)
   // - a strong reference (jump to "if_strong", "extracted" will be the object
   // pointed to)
-  void DispatchMaybeObject(Node* maybe_object, Label* if_smi, Label* if_cleared,
-                           Label* if_weak, Label* if_strong,
-                           Variable* extracted);
-  Node* IsStrongHeapObject(Node* value);
-  Node* ToStrongHeapObject(Node* value);
+  void DispatchMaybeObject(TNode<MaybeObject> maybe_object, Label* if_smi,
+                           Label* if_cleared, Label* if_weak, Label* if_strong,
+                           TVariable<Object>* extracted);
+  TNode<BoolT> IsStrongHeapObject(TNode<MaybeObject> value);
+  TNode<HeapObject> GetHeapObject(TNode<MaybeObject> value);
+  TNode<HeapObject> ToStrongHeapObject(TNode<MaybeObject> value);
+  TNode<Object> ToStrongHeapObjectOrSmi(TNode<MaybeObject> value);
 
   // Load an array element from a FixedArray / WeakFixedArray.
-  TNode<Object> LoadArrayElement(
+  TNode<MaybeObject> LoadArrayElement(
       SloppyTNode<Object> object, int array_header_size, Node* index,
       int additional_offset = 0,
       ParameterMode parameter_mode = INTPTR_PARAMETERS,
@@ -2290,6 +2299,8 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
   void InitializeFunctionContext(Node* native_context, Node* context,
                                  int slots);
 
+  void AssertIsStrongHeapObject(SloppyTNode<MaybeObject> object);
+  void AssertIsStrongHeapObjectOrSmi(SloppyTNode<MaybeObject> object);
   void AssertIsStrongHeapObject(SloppyTNode<HeapObject> object);
 
  private:

src/compiler/code-assembler.h

@@ -19,6 +19,7 @@
 #include "src/machine-type.h"
 #include "src/objects/data-handler.h"
 #include "src/objects/map.h"
+#include "src/objects/maybe-object.h"
 #include "src/runtime/runtime.h"
 #include "src/zone/zone-containers.h"
 
@@ -156,8 +157,10 @@ template <class T>
 struct is_valid_type_tag {
   static const bool value = std::is_base_of<Object, T>::value ||
                             std::is_base_of<UntaggedT, T>::value ||
+                            std::is_base_of<MaybeObject, T>::value ||
                             std::is_same<ExternalReference, T>::value;
-  static const bool is_tagged = std::is_base_of<Object, T>::value;
+  static const bool is_tagged = std::is_base_of<Object, T>::value ||
+                                std::is_base_of<MaybeObject, T>::value;
 };
 
 template <class T1, class T2>
@@ -485,6 +488,7 @@ TNode<Float64T> Float64Add(TNode<Float64T> a, TNode<Float64T> b);
   V(Float64ExtractLowWord32, Word32T, Float64T)                \
   V(Float64ExtractHighWord32, Word32T, Float64T)               \
   V(BitcastTaggedToWord, IntPtrT, Object)                      \
+  V(BitcastMaybeObjectToWord, IntPtrT, MaybeObject)            \
   V(BitcastWordToTagged, Object, WordT)                        \
   V(BitcastWordToTaggedSigned, Smi, WordT)                     \
   V(TruncateFloat64ToFloat32, Float32T, Float64T)              \

src/compiler/machine-operator.cc

@@ -701,6 +701,14 @@ struct MachineOperatorGlobalCache {
   };
   BitcastTaggedToWordOperator kBitcastTaggedToWord;
 
+  struct BitcastMaybeObjectToWordOperator : public Operator {
+    BitcastMaybeObjectToWordOperator()
+        : Operator(IrOpcode::kBitcastTaggedToWord,
+                   Operator::kEliminatable | Operator::kNoWrite,
+                   "BitcastMaybeObjectToWord", 1, 1, 1, 1, 1, 0) {}
+  };
+  BitcastMaybeObjectToWordOperator kBitcastMaybeObjectToWord;
+
   struct PoisonOnSpeculationTagged : public Operator {
     PoisonOnSpeculationTagged()
         : Operator(IrOpcode::kPoisonOnSpeculationTagged,
@@ -912,6 +920,10 @@ const Operator* MachineOperatorBuilder::BitcastTaggedToWord() {
   return &cache_.kBitcastTaggedToWord;
 }
 
+const Operator* MachineOperatorBuilder::BitcastMaybeObjectToWord() {
+  return &cache_.kBitcastMaybeObjectToWord;
+}
+
 const Operator* MachineOperatorBuilder::DebugAbort() {
   return &cache_.kDebugAbort;
 }

src/compiler/machine-operator.h

@@ -301,6 +301,10 @@ class V8_EXPORT_PRIVATE MachineOperatorBuilder final
   // This operator reinterprets the bits of a tagged pointer as word.
   const Operator* BitcastTaggedToWord();
 
+  // This operator reinterprets the bits of a tagged MaybeObject pointer as
+  // word.
+  const Operator* BitcastMaybeObjectToWord();
+
   // This operator reinterprets the bits of a word as tagged pointer.
   const Operator* BitcastWordToTagged();
 

src/compiler/raw-machine-assembler.h

@@ -578,6 +578,13 @@ class V8_EXPORT_PRIVATE RawMachineAssembler {
     return AddNode(machine()->BitcastTaggedToWord(), a);
 #else
     return a;
+#endif
+  }
+  Node* BitcastMaybeObjectToWord(Node* a) {
+#ifdef ENABLE_VERIFY_CSA
+    return AddNode(machine()->BitcastMaybeObjectToWord(), a);
+#else
+    return a;
 #endif
   }
   Node* BitcastWordToTagged(Node* a) {

src/ic/keyed-store-generic.cc

@@ -684,14 +684,14 @@ void KeyedStoreGenericAssembler::EmitGenericPropertyStore(
       TVARIABLE(Map, var_transition_map);
       Label simple_transition(this), transition_array(this),
           found_handler_candidate(this);
-      TNode<Object> maybe_handler =
-          LoadObjectField(receiver_map, Map::kTransitionsOrPrototypeInfoOffset);
+      TNode<MaybeObject> maybe_handler = LoadMaybeWeakObjectField(
+          receiver_map, Map::kTransitionsOrPrototypeInfoOffset);
 
       // SMI -> slow
       // cleared weak reference -> slow
       // weak reference -> simple_transition
       // strong reference -> transition_array
-      VARIABLE(var_transition_map_or_array, MachineRepresentation::kTagged);
+      TVARIABLE(Object, var_transition_map_or_array);
       DispatchMaybeObject(maybe_handler, slow, slow, &simple_transition,
                           &transition_array, &var_transition_map_or_array);
 
@@ -732,7 +732,7 @@ void KeyedStoreGenericAssembler::EmitGenericPropertyStore(
           const int kKeyToTargetOffset = (TransitionArray::kEntryTargetIndex -
                                           TransitionArray::kEntryKeyIndex) *
                                          kPointerSize;
-          var_transition_map = CAST(ToStrongHeapObject(
+          var_transition_map = CAST(GetHeapObject(
               LoadArrayElement(transitions, WeakFixedArray::kHeaderSize,
                                var_name_index.value(), kKeyToTargetOffset)));
           Goto(&found_handler_candidate);

src/objects/maybe-object-inl.h

@@ -91,6 +91,11 @@ HeapObject* MaybeObject::GetHeapObject() {
   return RemoveWeakHeapObjectMask(reinterpret_cast<HeapObjectReference*>(this));
 }
 
+MaybeObject* MaybeObject::MakeWeak(MaybeObject* object) {
+  DCHECK(object->IsStrongOrWeakHeapObject());
+  return AddWeakHeapObjectMask(object);
+}
+
 }  // namespace internal
 }  // namespace v8
 

src/objects/maybe-object.h

@@ -50,10 +50,7 @@ class MaybeObject {
     return reinterpret_cast<MaybeObject*>(object);
   }
 
-  static MaybeObject* MakeWeak(MaybeObject* object) {
-    DCHECK(object->IsStrongOrWeakHeapObject());
-    return AddWeakHeapObjectMask(object);
-  }
+  static inline MaybeObject* MakeWeak(MaybeObject* object);
 
 #ifdef VERIFY_HEAP
   static void VerifyMaybeObjectPointer(MaybeObject* p);