Preparse inner functions (new try)

This is an overly pessimistic approach where PreParser only keeps
track of unresolved variables, but doesn't declare anything. This
will result in context-allocating variables in the outer function
unnecessarily, if the variable names clash with variable names
used by the inner function (even if the variables are not the
same). However, we have been unable to prove that this approach
wouldn't be good enough for the practical purposes.

Fixes after the previous try ( https://codereview.chromium.org/2322243002/ ):
Keep the context-allocation decision stable when compiling fully eagerly.

Tests which exercise this functionality:
mjsunit/fixed-context-shapes-when-recompiling.js

Design document (chromium):

https://docs.google.com/a/chromium.org/document/d/1rRv5JJZ0JpOZAZN2CSUwZPFJiBAdRnTiSYhazseNHFg/edit?usp=sharing

BUG=

Review-Url: https://codereview.chromium.org/2352593002
Cr-Commit-Position: refs/heads/master@{#39719}

src/ast/scopes.cc

@@ -1073,12 +1073,14 @@ void DeclarationScope::AllocateVariables(ParseInfo* info, AnalyzeMode mode) {
   }
 }
 
-bool Scope::AllowsLazyParsing() const {
-  // If we are inside a block scope, we must parse eagerly to find out how
-  // to allocate variables on the block scope. At this point, declarations may
-  // not have yet been parsed.
+bool Scope::AllowsLazyParsingWithoutUnresolvedVariables() const {
+  // If we are inside a block scope, we must find unresolved variables in the
+  // inner scopes to find out how to allocate variables on the block scope. At
+  // this point, declarations may not have yet been parsed.
   for (const Scope* s = this; s != nullptr; s = s->outer_scope_) {
     if (s->is_block_scope()) return false;
+    // TODO(marja): Refactor parsing modes: also add s->is_function_scope()
+    // here.
   }
   return true;
 }
@@ -1178,7 +1180,7 @@ Scope* Scope::GetOuterScopeWithContext() {
 
 Handle<StringSet> DeclarationScope::CollectNonLocals(
     ParseInfo* info, Handle<StringSet> non_locals) {
-  VariableProxy* free_variables = FetchFreeVariables(this, info);
+  VariableProxy* free_variables = FetchFreeVariables(this, true, info);
   for (VariableProxy* proxy = free_variables; proxy != nullptr;
        proxy = proxy->next_unresolved()) {
     non_locals = StringSet::Add(non_locals, proxy->name());
@@ -1191,8 +1193,9 @@ void DeclarationScope::AnalyzePartially(DeclarationScope* migrate_to,
   // Try to resolve unresolved variables for this Scope and migrate those which
   // cannot be resolved inside. It doesn't make sense to try to resolve them in
   // the outer Scopes here, because they are incomplete.
-  for (VariableProxy* proxy = FetchFreeVariables(this); proxy != nullptr;
-       proxy = proxy->next_unresolved()) {
+  for (VariableProxy* proxy =
+           FetchFreeVariables(this, !FLAG_lazy_inner_functions);
+       proxy != nullptr; proxy = proxy->next_unresolved()) {
     DCHECK(!proxy->is_resolved());
     VariableProxy* copy = ast_node_factory->CopyVariableProxy(proxy);
     migrate_to->AddUnresolved(copy);
@@ -1515,6 +1518,29 @@ void Scope::ResolveVariable(ParseInfo* info, VariableProxy* proxy) {
   DCHECK(!proxy->is_resolved());
   Variable* var = LookupRecursive(proxy, nullptr);
   ResolveTo(info, proxy, var);
+
+  if (FLAG_lazy_inner_functions) {
+    if (info != nullptr && info->is_native()) return;
+    // Pessimistically force context allocation for all variables to which inner
+    // scope variables could potentially resolve to.
+    Scope* scope = GetClosureScope()->outer_scope_;
+    while (scope != nullptr && scope->scope_info_.is_null()) {
+      var = scope->LookupLocal(proxy->raw_name());
+      if (var != nullptr) {
+        // Since we don't lazy parse inner arrow functions, inner functions
+        // cannot refer to the outer "this".
+        if (!var->is_dynamic() && !var->is_this() &&
+            !var->has_forced_context_allocation()) {
+          var->ForceContextAllocation();
+          var->set_is_used();
+          // We don't know what the (potentially lazy parsed) inner function
+          // does with the variable; pessimistically assume that it's assigned.
+          var->set_maybe_assigned();
+        }
+      }
+      scope = scope->outer_scope_;
+    }
+  }
 }
 
 void Scope::ResolveTo(ParseInfo* info, VariableProxy* proxy, Variable* var) {
@@ -1560,13 +1586,16 @@ void Scope::ResolveVariablesRecursively(ParseInfo* info) {
 }
 
 VariableProxy* Scope::FetchFreeVariables(DeclarationScope* max_outer_scope,
-                                         ParseInfo* info,
+                                         bool try_to_resolve, ParseInfo* info,
                                          VariableProxy* stack) {
   for (VariableProxy *proxy = unresolved_, *next = nullptr; proxy != nullptr;
        proxy = next) {
     next = proxy->next_unresolved();
     DCHECK(!proxy->is_resolved());
-    Variable* var = LookupRecursive(proxy, max_outer_scope->outer_scope());
+    Variable* var = nullptr;
+    if (try_to_resolve) {
+      var = LookupRecursive(proxy, max_outer_scope->outer_scope());
+    }
     if (var == nullptr) {
       proxy->set_next_unresolved(stack);
       stack = proxy;
@@ -1579,7 +1608,8 @@ VariableProxy* Scope::FetchFreeVariables(DeclarationScope* max_outer_scope,
   unresolved_ = nullptr;
 
   for (Scope* scope = inner_scope_; scope != nullptr; scope = scope->sibling_) {
-    stack = scope->FetchFreeVariables(max_outer_scope, info, stack);
+    stack =
+        scope->FetchFreeVariables(max_outer_scope, try_to_resolve, info, stack);
   }
 
   return stack;

src/ast/scopes.h

@@ -342,8 +342,9 @@ class Scope: public ZoneObject {
   int StackLocalCount() const;
   int ContextLocalCount() const;
 
-  // Determine if we can parse a function literal in this scope lazily.
-  bool AllowsLazyParsing() const;
+  // Determine if we can parse a function literal in this scope lazily without
+  // caring about the unresolved variables within.
+  bool AllowsLazyParsingWithoutUnresolvedVariables() const;
 
   // The number of contexts between this and scope; zero if this == scope.
   int ContextChainLength(Scope* scope) const;
@@ -538,6 +539,7 @@ class Scope: public ZoneObject {
   // list along the way, so full resolution cannot be done afterwards.
   // If a ParseInfo* is passed, non-free variables will be resolved.
   VariableProxy* FetchFreeVariables(DeclarationScope* max_outer_scope,
+                                    bool try_to_resolve = true,
                                     ParseInfo* info = nullptr,
                                     VariableProxy* stack = nullptr);
 

src/flag-definitions.h

@@ -837,6 +837,7 @@ DEFINE_BOOL(trace_maps, false, "trace map creation")
 // parser.cc
 DEFINE_BOOL(allow_natives_syntax, false, "allow natives syntax")
 DEFINE_BOOL(trace_parse, false, "trace parsing and preparsing")
+DEFINE_BOOL(lazy_inner_functions, true, "enable lazy parsing inner functions")
 
 // simulator-arm.cc, simulator-arm64.cc and simulator-mips.cc
 DEFINE_BOOL(trace_sim, false, "Trace simulator execution")

src/parsing/parser-base.h

@@ -3915,13 +3915,17 @@ ParserBase<Impl>::ParseArrowFunctionLiteral(
       // Multiple statement body
       Consume(Token::LBRACE);
       DCHECK_EQ(scope(), formal_parameters.scope);
-      bool is_lazily_parsed = (mode() == PARSE_LAZILY &&
-                               formal_parameters.scope->AllowsLazyParsing());
+      bool is_lazily_parsed =
+          (mode() == PARSE_LAZILY &&
+           formal_parameters.scope
+               ->AllowsLazyParsingWithoutUnresolvedVariables());
+      // TODO(marja): consider lazy-parsing inner arrow functions too. is_this
+      // handling in Scope::ResolveVariable needs to change.
       if (is_lazily_parsed) {
         Scanner::BookmarkScope bookmark(scanner());
         bookmark.Set();
         LazyParsingResult result = impl()->SkipLazyFunctionBody(
-            &materialized_literal_count, &expected_property_count, true,
+            &materialized_literal_count, &expected_property_count, false, true,
             CHECK_OK);
 
         if (formal_parameters.materialized_literals_count > 0) {

src/parsing/parser.cc

@@ -122,11 +122,17 @@ class DiscardableZoneScope {
     if (use_temp_zone) {
       parser_->fni_ = &fni_;
       parser_->zone_ = temp_zone;
+      if (parser_->reusable_preparser_ != nullptr) {
+        parser_->reusable_preparser_->zone_ = temp_zone;
+      }
     }
   }
   ~DiscardableZoneScope() {
     parser_->fni_ = prev_fni_;
     parser_->zone_ = prev_zone_;
+    if (parser_->reusable_preparser_ != nullptr) {
+      parser_->reusable_preparser_->zone_ = prev_zone_;
+    }
   }
 
  private:
@@ -2683,7 +2689,9 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
   // These are all things we can know at this point, without looking at the
   // function itself.
 
-  // In addition, we need to distinguish between these cases:
+  // We separate between lazy parsing top level functions and lazy parsing inner
+  // functions, because the latter needs to do more work. In particular, we need
+  // to track unresolved variables to distinguish between these cases:
   // (function foo() {
   //   bar = function() { return 1; }
   //  })();
@@ -2695,17 +2703,18 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
 
   // Now foo will be parsed eagerly and compiled eagerly (optimization: assume
   // parenthesis before the function means that it will be called
-  // immediately). The inner function *must* be parsed eagerly to resolve the
-  // possible reference to the variable in foo's scope. However, it's possible
-  // that it will be compiled lazily.
-
-  // To make this additional case work, both Parser and PreParser implement a
-  // logic where only top-level functions will be parsed lazily.
-  bool is_lazily_parsed = mode() == PARSE_LAZILY &&
-                          scope()->AllowsLazyParsing() &&
-                          !function_state_->next_function_is_parenthesized();
-
-  // Determine whether the function body can be discarded after parsing.
+  // immediately). bar can be parsed lazily, but we need to parse it in a mode
+  // that tracks unresolved variables.
+  DCHECK_IMPLIES(mode() == PARSE_LAZILY, FLAG_lazy);
+  DCHECK_IMPLIES(mode() == PARSE_LAZILY, allow_lazy());
+  DCHECK_IMPLIES(mode() == PARSE_LAZILY, extension_ == nullptr);
+
+  bool is_lazy_top_level_function =
+      mode() == PARSE_LAZILY &&
+      eager_compile_hint == FunctionLiteral::kShouldLazyCompile &&
+      scope()->AllowsLazyParsingWithoutUnresolvedVariables();
+
+  // Determine whether we can still lazy parse the inner function.
   // The preconditions are:
   // - Lazy compilation has to be enabled.
   // - Neither V8 natives nor native function declarations can be allowed,
@@ -2720,11 +2729,16 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
   // - The function literal shouldn't be hinted to eagerly compile.
   // - For asm.js functions the body needs to be available when module
   //   validation is active, because we examine the entire module at once.
+
+  // Inner functions will be parsed using a temporary Zone. After parsing, we
+  // will migrate unresolved variable into a Scope in the main Zone.
+  // TODO(marja): Refactor parsing modes: simplify this.
   bool use_temp_zone =
-      !is_lazily_parsed && allow_lazy() &&
+      !is_lazy_top_level_function && allow_lazy() &&
       function_type == FunctionLiteral::kDeclaration &&
       eager_compile_hint != FunctionLiteral::kShouldEagerCompile &&
       !(FLAG_validate_asm && scope()->IsAsmModule());
+  bool is_lazy_inner_function = use_temp_zone && FLAG_lazy_inner_functions;
 
   DeclarationScope* main_scope = nullptr;
   if (use_temp_zone) {
@@ -2800,35 +2814,38 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
     // which says whether we need to create an arguments adaptor frame).
     if (formals.has_rest) arity--;
 
-    // Eager or lazy parse?
-    // If is_lazily_parsed, we'll parse lazily. We'll call SkipLazyFunctionBody,
-    // which may decide to abort lazy parsing if it suspects that wasn't a good
-    // idea. If so (in which case the parser is expected to have backtracked),
-    // or if we didn't try to lazy parse in the first place, we'll have to parse
-    // eagerly.
-    if (is_lazily_parsed) {
+    // Eager or lazy parse? If is_lazy_top_level_function, we'll parse
+    // lazily. We'll call SkipLazyFunctionBody, which may decide to abort lazy
+    // parsing if it suspects that wasn't a good idea. If so (in which case the
+    // parser is expected to have backtracked), or if we didn't try to lazy
+    // parse in the first place, we'll have to parse eagerly.
+    if (is_lazy_top_level_function || is_lazy_inner_function) {
       Scanner::BookmarkScope bookmark(scanner());
       bookmark.Set();
-      LazyParsingResult result =
-          SkipLazyFunctionBody(&materialized_literal_count,
-                               &expected_property_count, true, CHECK_OK);
+      LazyParsingResult result = SkipLazyFunctionBody(
+          &materialized_literal_count, &expected_property_count,
+          is_lazy_inner_function, is_lazy_top_level_function, CHECK_OK);
 
       materialized_literal_count += formals.materialized_literals_count +
                                     function_state.materialized_literal_count();
 
       if (result == kLazyParsingAborted) {
+        DCHECK(is_lazy_top_level_function);
         bookmark.Apply();
         // Trigger eager (re-)parsing, just below this block.
-        is_lazily_parsed = false;
+        is_lazy_top_level_function = false;
 
         // This is probably an initialization function. Inform the compiler it
         // should also eager-compile this function, and that we expect it to be
         // used once.
         eager_compile_hint = FunctionLiteral::kShouldEagerCompile;
         should_be_used_once_hint = true;
+      } else if (is_lazy_inner_function) {
+        DCHECK(main_scope != scope);
+        scope->AnalyzePartially(main_scope, &previous_zone_ast_node_factory);
       }
     }
-    if (!is_lazily_parsed) {
+    if (!is_lazy_top_level_function && !is_lazy_inner_function) {
       body = ParseEagerFunctionBody(function_name, pos, formals, kind,
                                     function_type, CHECK_OK);
 
@@ -2838,6 +2855,8 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
         // If the preconditions are correct the function body should never be
         // accessed, but do this anyway for better behaviour if they're wrong.
         body = nullptr;
+        DCHECK(main_scope != scope);
+        scope->AnalyzePartially(main_scope, &previous_zone_ast_node_factory);
       }
     }
 
@@ -2867,11 +2886,6 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
     }
     has_duplicate_parameters =
         !classifier()->is_valid_formal_parameter_list_without_duplicates();
-
-    if (use_temp_zone) {
-      DCHECK(main_scope != scope);
-      scope->AnalyzePartially(main_scope, &previous_zone_ast_node_factory);
-    }
   }  // DiscardableZoneScope goes out of scope.
 
   FunctionLiteral::ParameterFlag duplicate_parameters =
@@ -2922,14 +2936,16 @@ Expression* Parser::ParseAsyncFunctionExpression(bool* ok) {
 
 Parser::LazyParsingResult Parser::SkipLazyFunctionBody(
     int* materialized_literal_count, int* expected_property_count,
-    bool may_abort, bool* ok) {
+    bool is_inner_function, bool may_abort, bool* ok) {
   if (produce_cached_parse_data()) CHECK(log_);
 
   int function_block_pos = position();
   DeclarationScope* scope = this->scope()->AsDeclarationScope();
   DCHECK(scope->is_function_scope());
   scope->set_is_lazily_parsed(true);
-  if (consume_cached_parse_data() && !cached_parse_data_->rejected()) {
+  // Inner functions are not part of the cached data.
+  if (!is_inner_function && consume_cached_parse_data() &&
+      !cached_parse_data_->rejected()) {
     // If we have cached data, we use it to skip parsing the function body. The
     // data contains the information we need to construct the lazy function.
     FunctionEntry entry =
@@ -2956,7 +2972,7 @@ Parser::LazyParsingResult Parser::SkipLazyFunctionBody(
   // AST. This gathers the data needed to build a lazy function.
   SingletonLogger logger;
   PreParser::PreParseResult result =
-      ParseLazyFunctionBodyWithPreParser(&logger, may_abort);
+      ParseLazyFunctionBodyWithPreParser(&logger, is_inner_function, may_abort);
   // Return immediately if pre-parser decided to abort parsing.
   if (result == PreParser::kPreParseAbort) {
     scope->set_is_lazily_parsed(false);
@@ -2983,7 +2999,7 @@ Parser::LazyParsingResult Parser::SkipLazyFunctionBody(
   SetLanguageMode(scope, logger.language_mode());
   if (logger.uses_super_property()) scope->RecordSuperPropertyUsage();
   if (logger.calls_eval()) scope->RecordEvalCall();
-  if (produce_cached_parse_data()) {
+  if (!is_inner_function && produce_cached_parse_data()) {
     DCHECK(log_);
     // Position right after terminal '}'.
     int body_end = scanner()->location().end_pos;
@@ -3255,8 +3271,10 @@ ZoneList<Statement*>* Parser::ParseEagerFunctionBody(
     const AstRawString* function_name, int pos,
     const ParserFormalParameters& parameters, FunctionKind kind,
     FunctionLiteral::FunctionType function_type, bool* ok) {
-  // Everything inside an eagerly parsed function will be parsed eagerly
-  // (see comment above).
+  // Everything inside an eagerly parsed function will be parsed eagerly (see
+  // comment above). Lazy inner functions are handled separately and they won't
+  // require the mode to be PARSE_LAZILY (see ParseFunctionLiteral).
+  // TODO(marja): Refactor parsing modes: remove this.
   ParsingModeScope parsing_mode(this, PARSE_EAGERLY);
   ZoneList<Statement*>* result = new(zone()) ZoneList<Statement*>(8, zone());
 
@@ -3427,7 +3445,7 @@ ZoneList<Statement*>* Parser::ParseEagerFunctionBody(
 }
 
 PreParser::PreParseResult Parser::ParseLazyFunctionBodyWithPreParser(
-    SingletonLogger* logger, bool may_abort) {
+    SingletonLogger* logger, bool is_inner_function, bool may_abort) {
   // This function may be called on a background thread too; record only the
   // main thread preparse times.
   if (pre_parse_timer_ != NULL) {
@@ -3452,10 +3470,36 @@ PreParser::PreParseResult Parser::ParseLazyFunctionBodyWithPreParser(
     SET_ALLOW(harmony_class_fields);
 #undef SET_ALLOW
   }
-  PreParser::PreParseResult result = reusable_preparser_->PreParseLazyFunction(
-      language_mode(), function_state_->kind(),
-      scope()->AsDeclarationScope()->has_simple_parameters(), parsing_module_,
-      logger, may_abort, use_counts_);
+  // Aborting inner function preparsing would leave scopes in an inconsistent
+  // state; we don't parse inner functions in the abortable mode anyway.
+  DCHECK(!is_inner_function || !may_abort);
+
+  FunctionKind kind = function_state_->kind();
+  PreParser::PreParseResult result;
+  if (!is_inner_function) {
+    // If we don't need to look at the scope, construct a dummy scope chain
+    // which is not connected to the real scope chain.
+    LanguageMode mode = language_mode();
+    bool has_simple_parameters =
+        scope()->AsDeclarationScope()->has_simple_parameters();
+    DeclarationScope* top_scope = NewScriptScope();
+    top_scope->SetLanguageMode(mode);
+    FunctionState top_state(&function_state_, &scope_state_, top_scope,
+                            kNormalFunction);
+    DeclarationScope* function_scope = NewFunctionScope(kind);
+    if (!has_simple_parameters) {
+      function_scope->SetHasNonSimpleParameters();
+    }
+    result = reusable_preparser_->PreParseLazyFunction(
+        kind, function_scope, parsing_module_, logger, is_inner_function,
+        may_abort, use_counts_);
+  } else {
+    // Detaching the scopes created by PreParser from the Scope chain must be
+    // done above (see ParseFunctionLiteral & AnalyzePartially).
+    result = reusable_preparser_->PreParseLazyFunction(
+        kind, scope()->AsDeclarationScope(), parsing_module_, logger,
+        is_inner_function, may_abort, use_counts_);
+  }
   if (pre_parse_timer_ != NULL) {
     pre_parse_timer_->Stop();
   }

src/parsing/parser.h

@@ -484,10 +484,11 @@ class Parser : public ParserBase<Parser> {
   // in order to force the function to be eagerly parsed, after all.
   LazyParsingResult SkipLazyFunctionBody(int* materialized_literal_count,
                                          int* expected_property_count,
-                                         bool may_abort, bool* ok);
+                                         bool is_inner_function, bool may_abort,
+                                         bool* ok);
 
   PreParser::PreParseResult ParseLazyFunctionBodyWithPreParser(
-      SingletonLogger* logger, bool may_abort);
+      SingletonLogger* logger, bool is_inner_function, bool may_abort);
 
   Block* BuildParameterInitializationBlock(
       const ParserFormalParameters& parameters, bool* ok);
@@ -1063,6 +1064,9 @@ class Parser : public ParserBase<Parser> {
   }
 
   // Parser's private field members.
+  friend class DiscardableZoneScope;  // Uses reusable_preparser_.
+  // FIXME(marja): Make reusable_preparser_ always use its own temp Zone (call
+  // DeleteAll after each function), so this won't be needed.
 
   Scanner scanner_;
   PreParser* reusable_preparser_;

src/parsing/preparser.cc

@@ -38,8 +38,10 @@ namespace internal {
 #define CHECK_OK CHECK_OK_VALUE(Statement::Default())
 #define CHECK_OK_VOID CHECK_OK_VALUE(this->Void())
 
-PreParserIdentifier PreParser::GetSymbol() const {
-  switch (scanner()->current_token()) {
+namespace {
+
+PreParserIdentifier GetSymbolHelper(Scanner* scanner) {
+  switch (scanner->current_token()) {
     case Token::ENUM:
       return PreParserIdentifier::Enum();
     case Token::AWAIT:
@@ -55,34 +57,46 @@ PreParserIdentifier PreParser::GetSymbol() const {
     case Token::ASYNC:
       return PreParserIdentifier::Async();
     default:
-      if (scanner()->UnescapedLiteralMatches("eval", 4))
+      if (scanner->UnescapedLiteralMatches("eval", 4))
         return PreParserIdentifier::Eval();
-      if (scanner()->UnescapedLiteralMatches("arguments", 9))
+      if (scanner->UnescapedLiteralMatches("arguments", 9))
         return PreParserIdentifier::Arguments();
-      if (scanner()->UnescapedLiteralMatches("undefined", 9))
+      if (scanner->UnescapedLiteralMatches("undefined", 9))
         return PreParserIdentifier::Undefined();
-      if (scanner()->LiteralMatches("prototype", 9))
+      if (scanner->LiteralMatches("prototype", 9))
         return PreParserIdentifier::Prototype();
-      if (scanner()->LiteralMatches("constructor", 11))
+      if (scanner->LiteralMatches("constructor", 11))
         return PreParserIdentifier::Constructor();
       return PreParserIdentifier::Default();
   }
 }
 
+}  // unnamed namespace
+
+PreParserIdentifier PreParser::GetSymbol() const {
+  PreParserIdentifier symbol = GetSymbolHelper(scanner());
+  if (track_unresolved_variables_) {
+    const AstRawString* result = scanner()->CurrentSymbol(ast_value_factory());
+    DCHECK_NOT_NULL(result);
+    symbol.string_ = result;
+  }
+  return symbol;
+}
+
 PreParser::PreParseResult PreParser::PreParseLazyFunction(
-    LanguageMode language_mode, FunctionKind kind, bool has_simple_parameters,
-    bool parsing_module, ParserRecorder* log, bool may_abort, int* use_counts) {
+    FunctionKind kind, DeclarationScope* function_scope, bool parsing_module,
+    ParserRecorder* log, bool is_inner_function, bool may_abort,
+    int* use_counts) {
   parsing_module_ = parsing_module;
   log_ = log;
   use_counts_ = use_counts;
-  // Lazy functions always have trivial outer scopes (no with/catch scopes).
+  DCHECK(!track_unresolved_variables_);
+  track_unresolved_variables_ = is_inner_function;
+
+  // The caller passes the function_scope which is not yet inserted into the
+  // scope_state_. All scopes above the function_scope are ignored by the
+  // PreParser.
   DCHECK_NULL(scope_state_);
-  DeclarationScope* top_scope = NewScriptScope();
-  FunctionState top_state(&function_state_, &scope_state_, top_scope,
-                          kNormalFunction);
-  scope()->SetLanguageMode(language_mode);
-  DeclarationScope* function_scope = NewFunctionScope(kind);
-  if (!has_simple_parameters) function_scope->SetHasNonSimpleParameters();
   FunctionState function_state(&function_state_, &scope_state_, function_scope,
                                kind);
   DCHECK_EQ(Token::LBRACE, scanner()->current_token());
@@ -90,6 +104,7 @@ PreParser::PreParseResult PreParser::PreParseLazyFunction(
   int start_position = peek_position();
   LazyParsingResult result = ParseLazyFunctionLiteralBody(may_abort, &ok);
   use_counts_ = nullptr;
+  track_unresolved_variables_ = false;
   if (result == kLazyParsingAborted) {
     return kPreParseAbort;
   } else if (stack_overflow()) {
@@ -340,6 +355,21 @@ void PreParser::ParseAsyncArrowSingleExpressionBody(PreParserStatementList body,
   body->Add(PreParserStatement::ExpressionStatement(return_value), zone());
 }
 
+PreParserExpression PreParser::ExpressionFromIdentifier(
+    PreParserIdentifier name, int start_position, int end_position,
+    InferName infer) {
+  if (track_unresolved_variables_) {
+    AstNodeFactory factory(ast_value_factory());
+    // Setting the Zone is necessary because zone_ might be the temp Zone, and
+    // AstValueFactory doesn't know about it.
+    factory.set_zone(zone());
+    DCHECK_NOT_NULL(name.string_);
+    scope()->NewUnresolved(&factory, name.string_, start_position, end_position,
+                           NORMAL_VARIABLE);
+  }
+  return PreParserExpression::FromIdentifier(name);
+}
+
 #undef CHECK_OK
 #undef CHECK_OK_CUSTOM
 

src/parsing/preparser.h

@@ -112,10 +112,12 @@ class PreParserIdentifier {
     kAsyncIdentifier
   };
 
-  explicit PreParserIdentifier(Type type) : type_(type) {}
+  explicit PreParserIdentifier(Type type) : type_(type), string_(nullptr) {}
   Type type_;
-
+  // Only non-nullptr when PreParser.track_unresolved_variables_ is true.
+  const AstRawString* string_;
   friend class PreParserExpression;
+  friend class PreParser;
 };
 
 
@@ -774,7 +776,8 @@ class PreParser : public ParserBase<PreParser> {
             ParserRecorder* log, uintptr_t stack_limit)
       : ParserBase<PreParser>(zone, scanner, stack_limit, NULL,
                               ast_value_factory, log),
-        use_counts_(nullptr) {}
+        use_counts_(nullptr),
+        track_unresolved_variables_(false) {}
 
   // Pre-parse the program from the character stream; returns true on
   // success (even if parsing failed, the pre-parse data successfully
@@ -820,10 +823,10 @@ class PreParser : public ParserBase<PreParser> {
   // keyword and parameters, and have consumed the initial '{'.
   // At return, unless an error occurred, the scanner is positioned before the
   // the final '}'.
-  PreParseResult PreParseLazyFunction(LanguageMode language_mode,
-                                      FunctionKind kind,
-                                      bool has_simple_parameters,
+  PreParseResult PreParseLazyFunction(FunctionKind kind,
+                                      DeclarationScope* function_scope,
                                       bool parsing_module, ParserRecorder* log,
+                                      bool track_unresolved_variables,
                                       bool may_abort, int* use_counts);
 
  private:
@@ -850,9 +853,9 @@ class PreParser : public ParserBase<PreParser> {
       const PreParserFormalParameters& parameters, FunctionKind kind,
       FunctionLiteral::FunctionType function_type, bool* ok);
 
-  V8_INLINE LazyParsingResult
-  SkipLazyFunctionBody(int* materialized_literal_count,
-                       int* expected_property_count, bool may_abort, bool* ok) {
+  V8_INLINE LazyParsingResult SkipLazyFunctionBody(
+      int* materialized_literal_count, int* expected_property_count,
+      bool track_unresolved_variables, bool may_abort, bool* ok) {
     UNREACHABLE();
     return kLazyParsingComplete;
   }
@@ -1304,11 +1307,9 @@ class PreParser : public ParserBase<PreParser> {
     return PreParserExpression::Default();
   }
 
-  V8_INLINE PreParserExpression ExpressionFromIdentifier(
+  PreParserExpression ExpressionFromIdentifier(
       PreParserIdentifier name, int start_position, int end_position,
-      InferName infer = InferName::kYes) {
-    return PreParserExpression::FromIdentifier(name);
-  }
+      InferName infer = InferName::kYes);
 
   V8_INLINE PreParserExpression ExpressionFromString(int pos) {
     if (scanner()->UnescapedLiteralMatches("use strict", 10)) {
@@ -1417,6 +1418,7 @@ class PreParser : public ParserBase<PreParser> {
   // Preparser's private field members.
 
   int* use_counts_;
+  bool track_unresolved_variables_;
 };
 
 PreParserExpression PreParser::SpreadCall(PreParserExpression function,

test/cctest/test-parsing.cc

@@ -38,6 +38,7 @@
 #include "src/ast/ast.h"
 #include "src/compiler.h"
 #include "src/execution.h"
+#include "src/flags.h"
 #include "src/isolate.h"
 #include "src/objects.h"
 #include "src/parsing/parse-info.h"
@@ -3416,7 +3417,14 @@ TEST(InnerAssignment) {
         bool expected = outers[i].assigned || inners[j].assigned;
         CHECK(var != NULL);
         CHECK(var->is_used() || !expected);
-        CHECK((var->maybe_assigned() == i::kMaybeAssigned) == expected);
+        bool is_maybe_assigned = var->maybe_assigned() == i::kMaybeAssigned;
+        if (i::FLAG_lazy_inner_functions) {
+          // If we parse inner functions lazily, allow being pessimistic about
+          // maybe_assigned.
+          CHECK(is_maybe_assigned || (is_maybe_assigned == expected));
+        } else {
+          CHECK(is_maybe_assigned == expected);
+        }
       }
     }
   }

test/mjsunit/debug-function-scopes.js

@@ -87,7 +87,6 @@ var f3 = (function F1(invisible_parameter) {
     var invisible2 = 2;
     return (function F3() {
       var visible2 = 20;
-      var invisible2 = 3;
       return (function () {return visible1 + visible2 + visible1a;});
     })();
   })();

test/mjsunit/debug-scopes.js

@@ -157,20 +157,20 @@ function CheckScopeChainNames(names, exec_state) {
 }
 
 
-// Check that the content of the scope is as expected. For functions just check
-// that there is a function.
-function CheckScopeContent(content, number, exec_state) {
+// Check that the scope contains at least minimum_content. For functions just
+// check that there is a function.
+function CheckScopeContent(minimum_content, number, exec_state) {
   var scope = exec_state.frame().scope(number);
-  var count = 0;
-  for (var p in content) {
+  var minimum_count = 0;
+  for (var p in minimum_content) {
     var property_mirror = scope.scopeObject().property(p);
     assertFalse(property_mirror.isUndefined(), 'property ' + p + ' not found in scope');
-    if (typeof(content[p]) === 'function') {
+    if (typeof(minimum_content[p]) === 'function') {
       assertTrue(property_mirror.value().isFunction());
     } else {
-      assertEquals(content[p], property_mirror.value().value(), 'property ' + p + ' has unexpected value');
+      assertEquals(minimum_content[p], property_mirror.value().value(), 'property ' + p + ' has unexpected value');
     }
-    count++;
+    minimum_count++;
   }
 
   // 'arguments' and might be exposed in the local and closure scope. Just
@@ -186,14 +186,14 @@ function CheckScopeContent(content, number, exec_state) {
   // Temporary variables introduced by the parser have not been materialized.
   assertTrue(scope.scopeObject().property('').isUndefined());
 
-  if (count != scope_size) {
+  if (scope_size < minimum_count) {
     print('Names found in scope:');
     var names = scope.scopeObject().propertyNames();
     for (var i = 0; i < names.length; i++) {
       print(names[i]);
     }
   }
-  assertEquals(count, scope_size);
+  assertTrue(scope_size >= minimum_count);
 
   // Get the debug command processor.
   var dcp = exec_state.debugCommandProcessor("unspecified_running_state");

test/mjsunit/lazy-inner-functions.js

+// Copyright 2016 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.
+
+// Flags: --min-preparse-length 1
+
+(function TestLazyInnerFunctionCallsEval() {
+  var i = (function eager_outer() {
+    var a = 41; // Should be context-allocated
+    function lazy_inner() {
+      return eval("a");
+    }
+    return lazy_inner;
+  })();
+  assertEquals(41, i());
+})();