[Interpreter] Avoid dereferencing handles on BytecodeGenerator for AST operations.

src/ast/variables.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_AST_VARIABLES_H_
 #define V8_AST_VARIABLES_H_
 
 #include "src/ast/ast-value-factory.h"
 #include "src/zone.h"
 
@@ skipping 37 matching lines @@
     force_context_allocation_ = true;
   }
   bool is_used() { return is_used_; }
   void set_is_used() { is_used_ = true; }
   MaybeAssignedFlag maybe_assigned() const { return maybe_assigned_; }
   void set_maybe_assigned() { maybe_assigned_ = kMaybeAssigned; }
 
   int initializer_position() { return initializer_position_; }
   void set_initializer_position(int pos) { initializer_position_ = pos; }
 
-  bool IsVariable(Handle<String> n) const {
-    return !is_this() && name().is_identical_to(n);
-  }
-
   bool IsUnallocated() const {
     return location_ == VariableLocation::UNALLOCATED;
   }
   bool IsParameter() const { return location_ == VariableLocation::PARAMETER; }
   bool IsStackLocal() const { return location_ == VariableLocation::LOCAL; }
   bool IsStackAllocated() const { return IsParameter() || IsStackLocal(); }
   bool IsContextSlot() const { return location_ == VariableLocation::CONTEXT; }
   bool IsGlobalSlot() const { return location_ == VariableLocation::GLOBAL; }
   bool IsUnallocatedOrGlobalSlot() const {
     return IsUnallocated() || IsGlobalSlot();
@@ skipping 11 matching lines @@
   bool is_function() const { return kind_ == FUNCTION; }
   bool is_this() const { return kind_ == THIS; }
   bool is_arguments() const { return kind_ == ARGUMENTS; }
 
   // For script scopes, the "this" binding is provided by a ScriptContext added
   // to the global's ScriptContextTable.  This binding might not statically
   // resolve to a Variable::THIS binding, instead being DYNAMIC_LOCAL.  However
   // any variable named "this" does indeed refer to a Variable::THIS binding;
   // the grammar ensures this to be the case.  So wherever a "this" binding
   // might be provided by the global, use HasThisName instead of is_this().
-  bool HasThisName(Isolate* isolate) const {
-    return is_this() || *name() == *isolate->factory()->this_string();
+  bool HasThisName(Isolate* isolate,
+                   HandleDereferenceMode deref_mode =
+                       HandleDereferenceMode::kAllowed) const {
+    // Note: it is safe to dereference isolate->factory()->this_string() here
+    // regardless of |deref_mode| because it is a constant root and so will
+    // never be updated or moved.
+    return is_this() ||
+           name_is_identical_to(isolate->factory()->this_string(), deref_mode);
   }
 
   // True if the variable is named eval and not known to be shadowed.
-  bool is_possibly_eval(Isolate* isolate) const {
-    return IsVariable(isolate->factory()->eval_string());
+  bool is_possibly_eval(Isolate* isolate,
+                        HandleDereferenceMode deref_mode =
+                            HandleDereferenceMode::kAllowed) const {
+    // Note: it is safe to dereference isolate->factory()->eval_string() here
+    // regardless of |deref_mode| because it is a constant root and so will
+    // never be updated or moved.
+    return !is_this() &&
+           name_is_identical_to(isolate->factory()->eval_string(), deref_mode);
   }
 
   Variable* local_if_not_shadowed() const {
     DCHECK(mode_ == DYNAMIC_LOCAL && local_if_not_shadowed_ != NULL);
     return local_if_not_shadowed_;
   }
 
   void set_local_if_not_shadowed(Variable* local) {
     local_if_not_shadowed_ = local;
   }
 
   VariableLocation location() const { return location_; }
   int index() const { return index_; }
   InitializationFlag initialization_flag() const {
     return initialization_flag_;
   }
 
   void AllocateTo(VariableLocation location, int index) {
     location_ = location;
     index_ = index;
   }
 
   static int CompareIndex(Variable* const* v, Variable* const* w);
 
  private:
+  bool name_is_identical_to(Handle<Object> object,
+                            HandleDereferenceMode deref_mode) const {
+    if (deref_mode == HandleDereferenceMode::kAllowed) {
+      return *name() == *object;
+    } else {
+      // If handle dereference isn't allowed use the handle address for
+      // identity. This depends on the variable name being internalized in a
+      // CanonicalHandleScope, so that all handles created during the
+      // internalization with identical values have identical locations, and any
+      // handles created which point to roots have the root handle's location.
+      return name().address() == object.address();
+    }
+  }
+
   Scope* scope_;
   const AstRawString* name_;
   VariableMode mode_;
   Kind kind_;
   VariableLocation location_;
   int index_;
   int initializer_position_;
 
   // If this field is set, this variable references the stored locally bound
   // variable, but it might be shadowed by variable bindings introduced by
   // sloppy 'eval' calls between the reference scope (inclusive) and the
   // binding scope (exclusive).
   Variable* local_if_not_shadowed_;
 
   // Usage info.
   bool force_context_allocation_;  // set by variable resolver
   bool is_used_;
   InitializationFlag initialization_flag_;
   MaybeAssignedFlag maybe_assigned_;
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_VARIABLES_H_