There are only 2 language modes, not 3

src/ast/scopes.h

 // Copyright 2012 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_SCOPES_H_
 #define V8_AST_SCOPES_H_
 
 #include "src/ast/ast.h"
 #include "src/base/hashmap.h"
 #include "src/globals.h"
@@ skipping 212 matching lines @@
 
   // Inform the scope that the corresponding code contains an eval call.
   void RecordEvalCall() { scope_calls_eval_ = true; }
 
   // Inform the scope that the corresponding code uses "super".
   void RecordSuperPropertyUsage() { scope_uses_super_property_ = true; }
 
   // Set the language mode flag (unless disabled by a global flag).
   void SetLanguageMode(LanguageMode language_mode) {
     DCHECK(!is_module_scope() || is_strict(language_mode));
-    language_mode_ = language_mode;
+    set_language_mode(language_mode);
   }
 
   // Set the ASM module flag.
   void SetAsmModule() { asm_module_ = true; }
 
   // Inform the scope that the scope may execute declarations nonlinearly.
   // Currently, the only nonlinear scope is a switch statement. The name is
   // more general in case something else comes up with similar control flow,
   // for example the ability to break out of something which does not have
   // its own lexical scope.
@@ skipping 60 matching lines @@
   bool is_module_scope() const { return scope_type_ == MODULE_SCOPE; }
   bool is_script_scope() const { return scope_type_ == SCRIPT_SCOPE; }
   bool is_catch_scope() const { return scope_type_ == CATCH_SCOPE; }
   bool is_block_scope() const { return scope_type_ == BLOCK_SCOPE; }
   bool is_with_scope() const { return scope_type_ == WITH_SCOPE; }
   bool is_declaration_scope() const { return is_declaration_scope_; }
 
   // Information about which scopes calls eval.
   bool calls_eval() const { return scope_calls_eval_; }
   bool calls_sloppy_eval() const {
-    return scope_calls_eval_ && is_sloppy(language_mode_);
+    return scope_calls_eval_ && is_sloppy(language_mode());
   }
   bool outer_scope_calls_sloppy_eval() const {
     return outer_scope_calls_sloppy_eval_;
   }
   bool asm_module() const { return asm_module_; }
   bool asm_function() const { return asm_function_; }
 
   // Does this scope access "super" property (super.foo).
   bool uses_super_property() const { return scope_uses_super_property_; }
   // Does this scope have the potential to execute declarations non-linearly?
   bool is_nonlinear() const { return scope_nonlinear_; }
 
   // Whether this needs to be represented by a runtime context.
   bool NeedsContext() const {
     // Catch scopes always have heap slots.
     DCHECK(!is_catch_scope() || num_heap_slots() > 0);
     return num_heap_slots() > 0;
   }
 
   // ---------------------------------------------------------------------------
   // Accessors.
 
   // The type of this scope.
   ScopeType scope_type() const { return scope_type_; }
 
   // The language mode of this scope.
-  LanguageMode language_mode() const { return language_mode_; }
+  LanguageMode language_mode() const { return is_strict_ ? STRICT : SLOPPY; }
 
   // inner_scope() and sibling() together implement the inner scope list of a
   // scope. Inner scope points to the an inner scope of the function, and
   // "sibling" points to a next inner scope of the outer scope of this scope.
   Scope* inner_scope() const { return inner_scope_; }
   Scope* sibling() const { return sibling_; }
 
   // The scope immediately surrounding this scope, or NULL.
   Scope* outer_scope() const { return outer_scope_; }
 
@@ skipping 86 matching lines @@
   // Check that all Scopes in the scope tree use the same Zone.
   void CheckZones();
 #endif
 
   // Retrieve `IsSimpleParameterList` of current or outer function.
   bool HasSimpleParameters();
   void set_is_debug_evaluate_scope() { is_debug_evaluate_scope_ = true; }
 
  protected:
   void set_language_mode(LanguageMode language_mode) {
-    language_mode_ = language_mode;
+    is_strict_ = is_strict(language_mode);
   }
 
  private:
   Zone* zone_;
 
   // Scope tree.
   Scope* outer_scope_;  // the immediately enclosing outer scope, or NULL
   Scope* inner_scope_;  // an inner scope of this scope
   Scope* sibling_;  // a sibling inner scope of the outer scope of this scope.
 
@@ skipping 30 matching lines @@
   int num_stack_slots_;
   int num_heap_slots_;
   int num_global_slots_;
 
   // The scope type.
   const ScopeType scope_type_;
 
   // Scope-specific information computed during parsing.
   //
   // The language mode of this scope.
-  STATIC_ASSERT(LANGUAGE_END == 3);
-  LanguageMode language_mode_ : 2;
+  STATIC_ASSERT(LANGUAGE_END == 2);
+  bool is_strict_ : 1;
   // This scope is inside a 'with' of some outer scope.
   bool scope_inside_with_ : 1;
   // This scope or a nested catch scope or with scope contain an 'eval' call. At
   // the 'eval' call site this scope is the declaration scope.
   bool scope_calls_eval_ : 1;
   // This scope uses "super" property ('super.foo').
   bool scope_uses_super_property_ : 1;
   // This scope has a parameter called "arguments".
   bool has_arguments_parameter_ : 1;
   // This scope contains an "use asm" annotation.
@@ skipping 380 matching lines @@
   void AllocateModuleVariables();
 
  private:
   ModuleDescriptor* module_descriptor_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_SCOPES_H_