Reapply "[vm, compiler] Treat _uninitializedData/Index as effectively const."

This reverts commit 1d797bd.

TEST=ci
Change-Id: I43a87112cb44239330704e5715051b3988832631
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/401141
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Stephen Adams <[email protected]>

Author: rakudrama

runtime/vm/compiler/backend/constant_propagator.cc

@@ -863,9 +863,10 @@ void ConstantPropagator::VisitLoadIndexedUnsafe(LoadIndexedUnsafeInstr* instr) {
 }
 
 void ConstantPropagator::VisitLoadStaticField(LoadStaticFieldInstr* instr) {
-  // Cannot treat an initialized field as constant because the same code will be
-  // used when the AppAOT or AppJIT starts over with everything uninitialized or
-  // another isolate in the isolate group starts with everything uninitialized.
+  // We cannot generally take the current value for an initialized constant
+  // field because the same code will be used when the AppAOT or AppJIT starts
+  // over with everything uninitialized or another isolate in the isolate group
+  // starts with everything uninitialized.
   SetValue(instr, non_constant_);
 }
 

runtime/vm/compiler/backend/il_serializer.cc

@@ -30,7 +30,11 @@ FlowGraphSerializer::FlowGraphSerializer(NonStreamingWriteStream* stream)
       zone_(Thread::Current()->zone()),
       thread_(Thread::Current()),
       isolate_group_(IsolateGroup::Current()),
-      heap_(IsolateGroup::Current()->heap()) {}
+      heap_(IsolateGroup::Current()->heap()) {
+  // We want to preserve the identity of these, even though they are not const.
+  AddBaseObject(Object::uninitialized_index());
+  AddBaseObject(Object::uninitialized_data());
+}
 
 FlowGraphSerializer::~FlowGraphSerializer() {
   heap_->ResetObjectIdTable();
@@ -43,7 +47,11 @@ FlowGraphDeserializer::FlowGraphDeserializer(
       stream_(stream),
       zone_(Thread::Current()->zone()),
       thread_(Thread::Current()),
-      isolate_group_(IsolateGroup::Current()) {}
+      isolate_group_(IsolateGroup::Current()) {
+  // We want to preserve the identity of these, even though they are not const.
+  AddBaseObject(Object::uninitialized_index());
+  AddBaseObject(Object::uninitialized_data());
+}
 
 ClassPtr FlowGraphDeserializer::GetClassById(classid_t id) const {
   return isolate_group()->class_table()->At(id);
@@ -1392,6 +1400,11 @@ void MoveOperands::Write(FlowGraphSerializer* s) const {
 MoveOperands::MoveOperands(FlowGraphDeserializer* d)
     : dest_(Location::Read(d)), src_(Location::Read(d)) {}
 
+void FlowGraphSerializer::AddBaseObject(const Object& x) {
+  const intptr_t object_index = object_counter_++;
+  heap()->SetObjectId(x.ptr(), object_index + 1);
+}
+
 template <>
 void FlowGraphSerializer::WriteTrait<const Object&>::Write(
     FlowGraphSerializer* s,
@@ -1412,6 +1425,12 @@ void FlowGraphSerializer::WriteTrait<const Object&>::Write(
   s->WriteObjectImpl(x, cid, object_index);
 }
 
+void FlowGraphDeserializer::AddBaseObject(const Object& x) {
+  const intptr_t object_index = object_counter_;
+  object_counter_++;
+  SetObjectAt(object_index, x);
+}
+
 template <>
 const Object& FlowGraphDeserializer::ReadTrait<const Object&>::Read(
     FlowGraphDeserializer* d) {

runtime/vm/compiler/backend/il_serializer.h

@@ -306,6 +306,7 @@ class FlowGraphSerializer : public ValueObject {
   bool can_write_refs() const { return can_write_refs_; }
 
  private:
+  void AddBaseObject(const Object& x);
   void WriteObjectImpl(const Object& x, intptr_t cid, intptr_t object_index);
   bool IsWritten(const Object& obj);
   bool HasEnclosingTypes(const Object& obj);
@@ -499,6 +500,7 @@ class FlowGraphDeserializer : public ValueObject {
   }
 
  private:
+  void AddBaseObject(const Object& x);
   ClassPtr GetClassById(classid_t id) const;
   const Object& ReadObjectImpl(intptr_t cid, intptr_t object_index);
   void SetObjectAt(intptr_t object_index, const Object& object);

runtime/vm/compiler/frontend/kernel_to_il.cc

@@ -1135,6 +1135,8 @@ bool FlowGraphBuilder::IsRecognizedMethodForFlowGraph(
     case MethodRecognizer::kUtf8DecoderScan:
     case MethodRecognizer::kHas63BitSmis:
     case MethodRecognizer::kExtensionStreamHasListener:
+    case MethodRecognizer::kCompactHash_uninitializedIndex:
+    case MethodRecognizer::kCompactHash_uninitializedData:
     case MethodRecognizer::kSmi_hashCode:
     case MethodRecognizer::kMint_hashCode:
     case MethodRecognizer::kDouble_hashCode:
@@ -1746,6 +1748,12 @@ FlowGraph* FlowGraphBuilder::BuildGraphOfRecognizedMethod(
       body += IntToBool();
 #endif  // PRODUCT
     } break;
+    case MethodRecognizer::kCompactHash_uninitializedIndex: {
+      body += Constant(Object::uninitialized_index());
+    } break;
+    case MethodRecognizer::kCompactHash_uninitializedData: {
+      body += Constant(Object::uninitialized_data());
+    } break;
     case MethodRecognizer::kSmi_hashCode: {
       // TODO(dartbug.com/38985): We should make this LoadLocal+Unbox+
       // IntegerHash+Box. Though  this would make use of unboxed values on stack

runtime/vm/compiler/recognized_methods_list.h

@@ -101,6 +101,10 @@ namespace dart {
     ImmutableLinkedHashBase_getIndex, 0xfe7649ae)                              \
   V(CompactHashLibrary, _HashVMImmutableBase, set:_index,                      \
     ImmutableLinkedHashBase_setIndexStoreRelease, 0xcf36944c)                  \
+  V(CompactHashLibrary, ::, get:_uninitializedIndex,                           \
+    CompactHash_uninitializedIndex, 0xa25a79e6)                                \
+  V(CompactHashLibrary, ::, get:_uninitializedData,                            \
+    CompactHash_uninitializedData, 0x06a56b3b)                                 \
   V(DeveloperLibrary, ::, get:extensionStreamHasListener,                      \
     ExtensionStreamHasListener, 0xfa975305)                                    \
   V(DeveloperLibrary, ::, debugger, Debugger, 0xf0aaff14)                      \

runtime/vm/object.cc

@@ -1329,6 +1329,11 @@ void Object::Init(IsolateGroup* isolate_group) {
       KernelBytecode::kVMInternal_ImplicitConstructorClosure);
 #endif  // defined(DART_DYNAMIC_MODULES)
 
+  *uninitialized_index_ =
+      TypedData::New(kTypedDataUint32ArrayCid,
+                     LinkedHashBase::kUninitializedIndexSize, Heap::kOld);
+  *uninitialized_data_ = Array::New(0, Heap::kOld);
+
   // Some thread fields need to be reinitialized as null constants have not been
   // initialized until now.
   thread->ClearStickyError();
@@ -1428,6 +1433,10 @@ void Object::Init(IsolateGroup* isolate_group) {
   ASSERT(implicit_instance_closure_bytecode_->IsBytecode());
   ASSERT(!implicit_constructor_closure_bytecode_->IsSmi());
   ASSERT(implicit_constructor_closure_bytecode_->IsBytecode());
+  ASSERT(!uninitialized_index_->IsSmi());
+  ASSERT(uninitialized_index_->IsTypedData());
+  ASSERT(!uninitialized_data_->IsSmi());
+  ASSERT(uninitialized_data_->IsArray());
 }
 
 void Object::FinishInit(IsolateGroup* isolate_group) {

runtime/vm/object.h

@@ -517,7 +517,9 @@ class Object {
   V(Array, vm_isolate_snapshot_object_table)                                   \
   V(Type, dynamic_type)                                                        \
   V(Type, void_type)                                                           \
-  V(AbstractType, null_abstract_type)
+  V(AbstractType, null_abstract_type)                                          \
+  V(TypedData, uninitialized_index)                                            \
+  V(Array, uninitialized_data)
 
 #define DEFINE_SHARED_READONLY_HANDLE_GETTER(Type, name)                       \
   static const Type& name() {                                                  \
@@ -12147,10 +12149,10 @@ class LinkedHashBase : public Instance {
   virtual uint32_t CanonicalizeHash() const;
   virtual void CanonicalizeFieldsLocked(Thread* thread) const;
 
- protected:
   // Keep this in sync with Dart implementation (lib/compact_hash.dart).
   static constexpr intptr_t kInitialIndexBits = 2;
   static constexpr intptr_t kInitialIndexSize = 1 << (kInitialIndexBits + 1);
+  static constexpr intptr_t kUninitializedIndexSize = 1;
 
  private:
   LinkedHashBasePtr ptr() const { return static_cast<LinkedHashBasePtr>(ptr_); }

runtime/vm/object_store.h

@@ -528,7 +528,7 @@ class ObjectStore {
 #undef DECLARE_LAZY_INIT_ASYNC_GETTER
 #undef DECLARE_LAZY_INIT_ISOLATE_GETTER
 #undef DECLARE_LAZY_INIT_INTERNAL_GETTER
-#undef DECLARE_LAZY_INIT_TYPED_DATA_GETTER
+#undef DECLARE_LAZY_INIT_FFI_GETTER
 
   LibraryPtr bootstrap_library(BootstrapLibraryId index) {
     switch (index) {

sdk/lib/_internal/vm_shared/lib/compact_hash.dart

@@ -360,11 +360,18 @@ mixin _CustomEqualsAndHashCode<K> implements _EqualsAndHashCode {
   bool _equals(Object? e1, Object? e2) => (_equality as Function)(e1, e2);
 }
 
-final _uninitializedIndex = new Uint32List(_HashBase._UNINITIALIZED_INDEX_SIZE);
+@pragma("vm:prefer-inline")
+@pragma("vm:recognized", "other")
+@pragma("vm:exact-result-type", "dart:typed_data#_Uint32List")
+external Uint32List get _uninitializedIndex;
+
 // Note: not const. Const arrays are made immutable by having a different class
 // than regular arrays that throws on element assignment. We want the data field
 // in maps and sets to be monomorphic.
-final _uninitializedData = new List.filled(0, null);
+@pragma("vm:prefer-inline")
+@pragma("vm:recognized", "other")
+@pragma("vm:exact-result-type", "dart:core#_List")
+external List<Object?> get _uninitializedData;
 
 // VM-internalized implementation of a default-constructed LinkedHashMap. Map
 // literals also create instances of this class.