Parse eagerly inside block scopes.

Only this way we can precisely determine how to allocate let variables
inside the scope.

R=rossberg@chromium.org
BUG=v8:4255
LOG=N

Review URL: https://codereview.chromium.org/1216013002

Cr-Commit-Position: refs/heads/master@{#29354}

src/parser.cc

@@ -4036,9 +4036,9 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
 
     // 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_->AllowsLazyCompilation() &&
-                             !parenthesized_function_);
+    bool is_lazily_parsed = mode() == PARSE_LAZILY &&
+                            scope_->AllowsLazyParsing() &&
+                            !parenthesized_function_;
     parenthesized_function_ = false;  // The bit was set for this function only.
 
     // Eager or lazy parse?
@@ -4048,11 +4048,6 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
     // try to lazy parse in the first place, we'll have to parse eagerly.
     Scanner::BookmarkScope bookmark(scanner());
     if (is_lazily_parsed) {
-      for (Scope* s = scope_->outer_scope();
-           s != nullptr && (s != s->DeclarationScope()); s = s->outer_scope()) {
-        s->ForceContextAllocation();
-      }
-
       Scanner::BookmarkScope* maybe_bookmark =
           bookmark.Set() ? &bookmark : nullptr;
       SkipLazyFunctionBody(&materialized_literal_count,

src/preparser.h

@@ -152,15 +152,14 @@ class ParserBase : public Traits {
   class BlockState BASE_EMBEDDED {
    public:
     BlockState(Scope** scope_stack, Scope* scope)
-        : scope_stack_(scope_stack), outer_scope_(*scope_stack), scope_(scope) {
-      *scope_stack_ = scope_;
+        : scope_stack_(scope_stack), outer_scope_(*scope_stack) {
+      *scope_stack_ = scope;
     }
     ~BlockState() { *scope_stack_ = outer_scope_; }
 
    private:
     Scope** scope_stack_;
     Scope* outer_scope_;
-    Scope* scope_;
   };
 
   class FunctionState BASE_EMBEDDED {

src/scopes.cc

@@ -734,6 +734,17 @@ bool Scope::HasLazyCompilableOuterContext() const {
 }
 
 
+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.
+  for (const Scope* scope = this; scope != NULL; scope = scope->outer_scope_) {
+    if (scope->is_block_scope()) return false;
+  }
+  return AllowsLazyCompilation();
+}
+
+
 bool Scope::AllowsLazyCompilation() const {
   return !force_eager_compilation_ && HasLazyCompilableOuterContext();
 }

src/scopes.h

@@ -470,6 +470,9 @@ class Scope: public ZoneObject {
   // Make sure this scope and all outer scopes are eagerly compiled.
   void ForceEagerCompilation()  { force_eager_compilation_ = true; }
 
+  // Determine if we can parse a function literal in this scope lazily.
+  bool AllowsLazyParsing() const;
+
   // Determine if we can use lazy compilation for this scope.
   bool AllowsLazyCompilation() const;
 

test/mjsunit/regress/regress-4255-1.js

+// Copyright 2015 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.
+
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+
+'use strict';
+{
+  let x = function() {};
+  // Trigger OSR.
+  for (var i = 0; i < 1000000; i++);
+}

test/mjsunit/regress/regress-4255-2.js

+// Copyright 2015 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.
+
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+
+'use strict';
+for (let i = function f() {}; !i;);
+  // Trigger OSR.
+for (var i = 0; i < 1000000; i++);

test/mjsunit/regress/regress-4255-3.js

+// Copyright 2015 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.
+
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+
+'use strict';
+for (let i in [1, 2, 3]) { function f() {} }
+// Trigger OSR.
+for (var i = 0; i < 1000000; i++);

test/mjsunit/regress/regress-4255-4.js

+// Copyright 2015 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.
+
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+// comments to trigger lazy compilation comments to trigger lazy compilation
+
+'use strict';
+class C { constructor() {} }
+// Trigger OSR
+for (var i = 0; i < 1000000; i++);