[runtime] Update SavedClassVariable in ScopeInfo

ScopeInfo will contain either inlined (array) local names or
a hash table (names => index) containing the local names.

If we have the local names inlined, we should save the class
variable context slot index.

If we have a hash table instead, we should save the class
variable offset in the internal hash table storage.

Bug: v8:12315
Change-Id: Ifd9ae4f285d11fc034e8560c8558038b38a474fb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3386599Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78621}

src/ast/scopes.cc

@@ -206,11 +206,10 @@ ClassScope::ClassScope(IsolateT* isolate, Zone* zone,
 
   // If the class variable is context-allocated and its index is
   // saved for deserialization, deserialize it.
-  if (scope_info->HasSavedClassVariableIndex()) {
-    int index = scope_info->SavedClassVariableContextLocalIndex();
-    DCHECK_GE(index, 0);
-    DCHECK_LT(index, scope_info->ContextLocalCount());
-    String name = scope_info->ContextLocalName(index);
+  if (scope_info->HasSavedClassVariable()) {
+    String name;
+    int index;
+    std::tie(name, index) = scope_info->SavedClassVariable();
     DCHECK_EQ(scope_info->ContextLocalMode(index), VariableMode::kConst);
     DCHECK_EQ(scope_info->ContextLocalInitFlag(index),
               InitializationFlag::kNeedsInitialization);

src/diagnostics/objects-printer.cc

@@ -2350,7 +2350,7 @@ void ScopeInfo::ScopeInfoPrint(std::ostream& os) {
     os << "\n - receiver: " << ReceiverVariableBits::decode(flags);
   }
   if (HasClassBrand()) os << "\n - has class brand";
-  if (HasSavedClassVariableIndex()) os << "\n - has saved class variable index";
+  if (HasSavedClassVariable()) os << "\n - has saved class variable";
   if (HasNewTarget()) os << "\n - needs new target";
   if (HasFunctionName()) {
     os << "\n - function name(" << FunctionVariableBits::decode(flags) << "): ";

src/objects/scope-info.cc

@@ -204,8 +204,7 @@ Handle<ScopeInfo> ScopeInfo::Create(IsolateT* isolate, Zone* zone, Scope* scope,
         DeclarationScopeBit::encode(scope->is_declaration_scope()) |
         ReceiverVariableBits::encode(receiver_info) |
         HasClassBrandBit::encode(has_brand) |
-        HasSavedClassVariableIndexBit::encode(
-            should_save_class_variable_index) |
+        HasSavedClassVariableBit::encode(should_save_class_variable_index) |
         HasNewTargetBit::encode(has_new_target) |
         FunctionVariableBits::encode(function_name_info) |
         HasInferredFunctionNameBit::encode(has_inferred_function_name) |
@@ -397,8 +396,7 @@ Handle<ScopeInfo> ScopeInfo::CreateForWithScope(
       DeclarationScopeBit::encode(false) |
       ReceiverVariableBits::encode(VariableAllocationInfo::NONE) |
       HasClassBrandBit::encode(false) |
-      HasSavedClassVariableIndexBit::encode(false) |
-      HasNewTargetBit::encode(false) |
+      HasSavedClassVariableBit::encode(false) | HasNewTargetBit::encode(false) |
       FunctionVariableBits::encode(VariableAllocationInfo::NONE) |
       IsAsmModuleBit::encode(false) | HasSimpleParametersBit::encode(true) |
       FunctionKindBits::encode(FunctionKind::kNormalFunction) |
@@ -471,8 +469,7 @@ Handle<ScopeInfo> ScopeInfo::CreateForBootstrapping(Isolate* isolate,
       ReceiverVariableBits::encode(is_script ? VariableAllocationInfo::CONTEXT
                                              : VariableAllocationInfo::UNUSED) |
       HasClassBrandBit::encode(false) |
-      HasSavedClassVariableIndexBit::encode(false) |
-      HasNewTargetBit::encode(false) |
+      HasSavedClassVariableBit::encode(false) | HasNewTargetBit::encode(false) |
       FunctionVariableBits::encode(is_empty_function
                                        ? VariableAllocationInfo::UNUSED
                                        : VariableAllocationInfo::NONE) |
@@ -685,8 +682,8 @@ bool ScopeInfo::HasClassBrand() const {
   return HasClassBrandBit::decode(Flags());
 }
 
-bool ScopeInfo::HasSavedClassVariableIndex() const {
-  return HasSavedClassVariableIndexBit::decode(Flags());
+bool ScopeInfo::HasSavedClassVariable() const {
+  return HasSavedClassVariableBit::decode(Flags());
 }
 
 bool ScopeInfo::HasNewTarget() const {
@@ -919,12 +916,21 @@ int ScopeInfo::ContextSlotIndex(ScopeInfo scope_info, String name,
   return -1;
 }
 
-int ScopeInfo::SavedClassVariableContextLocalIndex() const {
-  if (HasSavedClassVariableIndexBit::decode(Flags())) {
-    int index = saved_class_variable_info();
-    return index - Context::MIN_CONTEXT_SLOTS;
+std::pair<String, int> ScopeInfo::SavedClassVariable() const {
+  DCHECK(HasSavedClassVariableBit::decode(Flags()));
+  if (HasInlinedLocalNames()) {
+    // The saved class variable info corresponds to the context slot index.
+    int index = saved_class_variable_info() - Context::MIN_CONTEXT_SLOTS;
+    DCHECK_GE(index, 0);
+    DCHECK_LT(index, ContextLocalCount());
+    String name = ContextLocalName(index);
+    return std::make_pair(name, index);
+  } else {
+    // The saved class variable info corresponds to the offset in the hash
+    // table storage.
+    // TODO(victorgomes, v8:12315): Implement this once we have a hash table.
+    UNREACHABLE();
   }
-  return -1;
 }
 
 int ScopeInfo::ReceiverContextSlotIndex() const {

src/objects/scope-info.h

@@ -91,9 +91,9 @@ class ScopeInfo : public TorqueGeneratedScopeInfo<ScopeInfo, HeapObject> {
   // Does this scope has class brand (for private methods)?
   bool HasClassBrand() const;
 
-  // Does this scope contain a saved class variable context local slot index
-  // for checking receivers of static private methods?
-  bool HasSavedClassVariableIndex() const;
+  // Does this scope contain a saved class variable for checking receivers of
+  // static private methods?
+  bool HasSavedClassVariable() const;
 
   // Does this scope declare a "new.target" binding?
   bool HasNewTarget() const;
@@ -140,6 +140,12 @@ class ScopeInfo : public TorqueGeneratedScopeInfo<ScopeInfo, HeapObject> {
 
   SourceTextModuleInfo ModuleDescriptorInfo() const;
 
+  // Return true if the local names are inlined in the scope info object.
+  bool HasInlinedLocalNames() const {
+    // TODO(victorgomes, v8:12315): Currently, local names are always inlined.
+    return true;
+  }
+
   // Return the name of the given context local.
   String ContextLocalName(int var) const;
 
@@ -193,11 +199,10 @@ class ScopeInfo : public TorqueGeneratedScopeInfo<ScopeInfo, HeapObject> {
   // Returns the first parameter context slot index.
   int ParametersStartIndex() const;
 
-  // Lookup support for serialized scope info.  Returns the index of the
-  // saved class variable in context local slots if scope is a class scope
+  // Lookup support for serialized scope info.  Returns the name and index of
+  // the saved class variable in context local slots if scope is a class scope
   // and it contains static private methods that may be accessed.
-  // Otherwise returns a value < 0.
-  int SavedClassVariableContextLocalIndex() const;
+  std::pair<String, int> SavedClassVariable() const;
 
   FunctionKind function_kind() const;
 

src/objects/scope-info.tq

@@ -54,7 +54,7 @@ bitfield struct ScopeFlags extends uint31 {
   declaration_scope: bool: 1 bit;
   receiver_variable: VariableAllocationInfo: 2 bit;
   has_class_brand: bool: 1 bit;
-  has_saved_class_variable_index: bool: 1 bit;
+  has_saved_class_variable: bool: 1 bit;
   has_new_target: bool: 1 bit;
   // TODO(cbruni): Combine with function variable field when only storing the
   // function name.
@@ -119,8 +119,9 @@ extern class ScopeInfo extends HeapObject {
 
   // If the scope is a class scope and it has static private methods that
   // may be accessed directly or through eval, one slot is reserved to hold
-  // the context slot index for the class variable.
-  saved_class_variable_info?[flags.has_saved_class_variable_index]: Smi;
+  // the offset in the field storage of the hash table (or the slot index if
+  // local names are inlined) for the class variable.
+  saved_class_variable_info?[flags.has_saved_class_variable]: Smi;
 
   // If the scope belongs to a named function expression this part contains
   // information about the function variable. It always occupies two array

src/web-snapshot/web-snapshot.cc

@@ -1346,7 +1346,7 @@ Handle<ScopeInfo> WebSnapshotDeserializer::CreateScopeInfo(
       ScopeInfo::DeclarationScopeBit::encode(false) |
       ScopeInfo::ReceiverVariableBits::encode(VariableAllocationInfo::NONE) |
       ScopeInfo::HasClassBrandBit::encode(false) |
-      ScopeInfo::HasSavedClassVariableIndexBit::encode(false) |
+      ScopeInfo::HasSavedClassVariableBit::encode(false) |
       ScopeInfo::HasNewTargetBit::encode(false) |
       ScopeInfo::FunctionVariableBits::encode(VariableAllocationInfo::NONE) |
       ScopeInfo::HasInferredFunctionNameBit::encode(false) |