Allocate script scopes using a separate constructor

This avoids checking for outer_scope == nullptr in Scope::Scope

BUG=v8:5209

Review-Url: https://codereview.chromium.org/2266973002
Cr-Commit-Position: refs/heads/master@{#38812}

src/ast/scopes.cc

@@ -77,6 +77,16 @@ void SloppyBlockFunctionMap::Declare(Zone* zone, const AstRawString* name,
 // ----------------------------------------------------------------------------
 // Implementation of Scope
 
+Scope::Scope(Zone* zone)
+    : zone_(zone),
+      outer_scope_(nullptr),
+      variables_(zone),
+      ordered_variables_(4, zone),
+      decls_(4, zone),
+      scope_type_(SCRIPT_SCOPE) {
+  SetDefaults();
+}
+
 Scope::Scope(Zone* zone, Scope* outer_scope, ScopeType scope_type)
     : zone_(zone),
       outer_scope_(outer_scope),
@@ -84,17 +94,12 @@ Scope::Scope(Zone* zone, Scope* outer_scope, ScopeType scope_type)
       ordered_variables_(4, zone),
       decls_(4, zone),
       scope_type_(scope_type) {
+  DCHECK_NE(SCRIPT_SCOPE, scope_type);
   SetDefaults();
-  if (outer_scope == nullptr) {
-    // If the outer scope is null, this cannot be a with scope. The outermost
-    // scope must be a script scope.
-    DCHECK_EQ(SCRIPT_SCOPE, scope_type);
-  } else {
-    set_language_mode(outer_scope->language_mode());
-    force_context_allocation_ =
-        !is_function_scope() && outer_scope->has_forced_context_allocation();
-    outer_scope_->AddInnerScope(this);
-  }
+  set_language_mode(outer_scope->language_mode());
+  force_context_allocation_ =
+      !is_function_scope() && outer_scope->has_forced_context_allocation();
+  outer_scope_->AddInnerScope(this);
 }
 
 Scope::Snapshot::Snapshot(Scope* scope)
@@ -103,6 +108,15 @@ Scope::Snapshot::Snapshot(Scope* scope)
       top_unresolved_(scope->unresolved_),
       top_temp_(scope->GetClosureScope()->temps()->length()) {}
 
+DeclarationScope::DeclarationScope(Zone* zone)
+    : Scope(zone),
+      function_kind_(kNormalFunction),
+      temps_(4, zone),
+      params_(4, zone),
+      sloppy_block_function_map_(zone) {
+  SetDefaults();
+}
+
 DeclarationScope::DeclarationScope(Zone* zone, Scope* outer_scope,
                                    ScopeType scope_type,
                                    FunctionKind function_kind)
@@ -112,7 +126,7 @@ DeclarationScope::DeclarationScope(Zone* zone, Scope* outer_scope,
       params_(4, zone),
       sloppy_block_function_map_(zone) {
   SetDefaults();
-  if (outer_scope != nullptr) asm_function_ = outer_scope_->IsAsmModule();
+  asm_function_ = outer_scope_->IsAsmModule();
 }
 
 ModuleScope::ModuleScope(Zone* zone, DeclarationScope* script_scope,

src/ast/scopes.h

@@ -443,6 +443,9 @@ class Scope: public ZoneObject {
   void set_is_debug_evaluate_scope() { is_debug_evaluate_scope_ = true; }
 
  protected:
+  // Creates a script scope.
+  explicit Scope(Zone* zone);
+
   void set_language_mode(LanguageMode language_mode) {
     is_strict_ = is_strict(language_mode);
   }
@@ -657,6 +660,8 @@ class DeclarationScope : public Scope {
                    FunctionKind function_kind = kNormalFunction);
   DeclarationScope(Zone* zone, Scope* inner_scope, ScopeType scope_type,
                    Handle<ScopeInfo> scope_info);
+  // Creates a script scope.
+  explicit DeclarationScope(Zone* zone);
 
   bool IsDeclaredParameter(const AstRawString* name) {
     // If IsSimpleParameterList is false, duplicate parameters are not allowed,

src/parsing/parser-base.h

@@ -607,7 +607,7 @@ class ParserBase : public Traits {
   };
 
   DeclarationScope* NewScriptScope() {
-    return new (zone()) DeclarationScope(zone(), nullptr, SCRIPT_SCOPE);
+    return new (zone()) DeclarationScope(zone());
   }
 
   DeclarationScope* NewVarblockScope() {

test/cctest/test-parsing.cc

@@ -3393,8 +3393,7 @@ TEST(SerializationOfMaybeAssignmentFlag) {
   const i::AstRawString* name = avf.GetOneByteString("result");
   i::Handle<i::String> str = name->string();
   CHECK(str->IsInternalizedString());
-  i::DeclarationScope* script_scope =
-      new (&zone) i::DeclarationScope(&zone, nullptr, i::SCRIPT_SCOPE);
+  i::DeclarationScope* script_scope = new (&zone) i::DeclarationScope(&zone);
   i::Scope* s = i::Scope::DeserializeScopeChain(
       isolate, &zone, context, script_scope, &avf,
       i::Scope::DeserializationMode::kKeepScopeInfo);
@@ -3441,8 +3440,7 @@ TEST(IfArgumentsArrayAccessedThenParametersMaybeAssigned) {
   i::AstValueFactory avf(&zone, isolate->heap()->HashSeed());
   avf.Internalize(isolate);
 
-  i::DeclarationScope* script_scope =
-      new (&zone) i::DeclarationScope(&zone, nullptr, i::SCRIPT_SCOPE);
+  i::DeclarationScope* script_scope = new (&zone) i::DeclarationScope(&zone);
   i::Scope* s = i::Scope::DeserializeScopeChain(
       isolate, &zone, context, script_scope, &avf,
       i::Scope::DeserializationMode::kKeepScopeInfo);