Revert of Clean up rewriter.

src/rewriter.cc

 // 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.
 
 #include "src/rewriter.h"
 
 #include "src/ast.h"
 #include "src/parser.h"
 #include "src/scopes.h"
 
 namespace v8 {
 namespace internal {
 
 class Processor: public AstVisitor {
  public:
   Processor(Isolate* isolate, Variable* result,
             AstValueFactory* ast_value_factory)
       : result_(result),
+        result_assigned_(false),
         is_set_(false),
+        in_try_(false),
         factory_(ast_value_factory) {
     InitializeAstVisitor(isolate, ast_value_factory->zone());
   }
 
   virtual ~Processor() { }
 
   void Process(ZoneList<Statement*>* statements);
+  bool result_assigned() const { return result_assigned_; }
 
   AstNodeFactory* factory() { return &factory_; }
 
  private:
   Variable* result_;
 
+  // We are not tracking result usage via the result_'s use
+  // counts (we leave the accurate computation to the
+  // usage analyzer). Instead we simple remember if
+  // there was ever an assignment to result_.
+  bool result_assigned_;
+
   // To avoid storing to .result all the time, we eliminate some of
   // the stores by keeping track of whether or not we're sure .result
   // will be overwritten anyway. This is a bit more tricky than what I
-  // was hoping for.
+  // was hoping for
   bool is_set_;
+  bool in_try_;
 
   AstNodeFactory factory_;
 
   Expression* SetResult(Expression* value) {
+    result_assigned_ = true;
     VariableProxy* result_proxy = factory()->NewVariableProxy(result_);
     return factory()->NewAssignment(
         Token::ASSIGN, result_proxy, value, RelocInfo::kNoPosition);
   }
 
   // Node visitors.
 #define DEF_VISIT(type) virtual void Visit##type(type* node) override;
   AST_NODE_LIST(DEF_VISIT)
 #undef DEF_VISIT
 
@@ skipping 18 matching lines @@
   // a variable declaration with initialization expression is 'undefined'
   // with some JS VMs: For instance, using smjs, print(eval('var x = 7'))
   // returns 'undefined'. To obtain the same behavior with v8, we need
   // to prevent rewriting in that case.
   if (!node->ignore_completion_value()) Process(node->statements());
 }
 
 
 void Processor::VisitExpressionStatement(ExpressionStatement* node) {
   // Rewrite : <x>; -> .result = <x>;
-  if (!is_set_) {
+  if (!is_set_ && !node->expression()->IsThrow()) {
     node->set_expression(SetResult(node->expression()));
-    is_set_ = true;
+    if (!in_try_) is_set_ = true;
   }
 }
 
 
 void Processor::VisitIfStatement(IfStatement* node) {
-  // Rewrite both branches.
-  bool set_after = is_set_;
+  // Rewrite both then and else parts (reversed).
+  bool save = is_set_;
+  Visit(node->else_statement());
+  bool set_after_then = is_set_;
+  is_set_ = save;
   Visit(node->then_statement());
-  bool set_in_then = is_set_;
-  is_set_ = set_after;
-  Visit(node->else_statement());
-  is_set_ = is_set_ && set_in_then;
+  is_set_ = is_set_ && set_after_then;
 }
 
 
 void Processor::VisitIterationStatement(IterationStatement* node) {
   // Rewrite the body.
-  bool set_after = is_set_;
-  is_set_ = false;  // We are in a loop, so we can't rely on [set_after].
+  bool set_after_loop = is_set_;
   Visit(node->body());
-  is_set_ = is_set_ && set_after;
+  is_set_ = is_set_ && set_after_loop;
 }
 
 
 void Processor::VisitDoWhileStatement(DoWhileStatement* node) {
   VisitIterationStatement(node);
 }
 
 
 void Processor::VisitWhileStatement(WhileStatement* node) {
   VisitIterationStatement(node);
 }
 
 
 void Processor::VisitForStatement(ForStatement* node) {
   VisitIterationStatement(node);
 }
 
 
 void Processor::VisitForInStatement(ForInStatement* node) {
   VisitIterationStatement(node);
 }
 
 
 void Processor::VisitForOfStatement(ForOfStatement* node) {
   VisitIterationStatement(node);
 }
 
 
 void Processor::VisitTryCatchStatement(TryCatchStatement* node) {
-  // Rewrite both try and catch block.
-  bool set_after = is_set_;
+  // Rewrite both try and catch blocks (reversed order).
+  bool set_after_catch = is_set_;
+  Visit(node->catch_block());
+  is_set_ = is_set_ && set_after_catch;
+  bool save = in_try_;
+  in_try_ = true;
   Visit(node->try_block());
-  bool set_in_try = is_set_;
-  is_set_ = set_after;
-  Visit(node->catch_block());
-  is_set_ = is_set_ && set_in_try;
+  in_try_ = save;
 }
 
 
 void Processor::VisitTryFinallyStatement(TryFinallyStatement* node) {
-  // Rewrite both try and finally block (in reverse order).
+  // Rewrite both try and finally block (reversed order).
   Visit(node->finally_block());
+  bool save = in_try_;
+  in_try_ = true;
   Visit(node->try_block());
+  in_try_ = save;
 }
 
 
 void Processor::VisitSwitchStatement(SwitchStatement* node) {
-  // Rewrite statements in all case clauses (in reverse order).
+  // Rewrite statements in all case clauses in reversed order.
   ZoneList<CaseClause*>* clauses = node->cases();
-  bool set_after = is_set_;
+  bool set_after_switch = is_set_;
   for (int i = clauses->length() - 1; i >= 0; --i) {
     CaseClause* clause = clauses->at(i);
     Process(clause->statements());
   }
-  is_set_ = is_set_ && set_after;
+  is_set_ = is_set_ && set_after_switch;
 }
 
 
 void Processor::VisitContinueStatement(ContinueStatement* node) {
   is_set_ = false;
 }
 
 
 void Processor::VisitBreakStatement(BreakStatement* node) {
   is_set_ = false;
 }
 
 
 void Processor::VisitWithStatement(WithStatement* node) {
+  bool set_after_body = is_set_;
   Visit(node->statement());
+  is_set_ = is_set_ && set_after_body;
 }
 
 
 void Processor::VisitSloppyBlockFunctionStatement(
     SloppyBlockFunctionStatement* node) {
   Visit(node->statement());
 }
 
 
-void Processor::VisitReturnStatement(ReturnStatement* node) { is_set_ = true; }
-
-
 // Do nothing:
+void Processor::VisitVariableDeclaration(VariableDeclaration* node) {}
+void Processor::VisitFunctionDeclaration(FunctionDeclaration* node) {}
+void Processor::VisitImportDeclaration(ImportDeclaration* node) {}
+void Processor::VisitExportDeclaration(ExportDeclaration* node) {}
 void Processor::VisitEmptyStatement(EmptyStatement* node) {}
+void Processor::VisitReturnStatement(ReturnStatement* node) {}
 void Processor::VisitDebuggerStatement(DebuggerStatement* node) {}
 
 
-// Expressions are never visited.
+// Expressions are never visited yet.
 #define DEF_VISIT(type)                                         \
   void Processor::Visit##type(type* expr) { UNREACHABLE(); }
 EXPRESSION_NODE_LIST(DEF_VISIT)
 #undef DEF_VISIT
 
 
-// Declarations are never visited.
-#define DEF_VISIT(type) \
-  void Processor::Visit##type(type* expr) { UNREACHABLE(); }
-DECLARATION_NODE_LIST(DEF_VISIT)
-#undef DEF_VISIT
-
-
 // Assumes code has been parsed.  Mutates the AST, so the AST should not
 // continue to be used in the case of failure.
 bool Rewriter::Rewrite(ParseInfo* info) {
   FunctionLiteral* function = info->literal();
   DCHECK(function != NULL);
   Scope* scope = function->scope();
   DCHECK(scope != NULL);
   if (!scope->is_script_scope() && !scope->is_eval_scope()) return true;
 
   ZoneList<Statement*>* body = function->body();
   if (!body->is_empty()) {
     Variable* result =
         scope->NewTemporary(info->ast_value_factory()->dot_result_string());
     // The name string must be internalized at this point.
     DCHECK(!result->name().is_null());
     Processor processor(info->isolate(), result, info->ast_value_factory());
     processor.Process(body);
     if (processor.HasStackOverflow()) return false;
 
-    DCHECK(function->end_position() != RelocInfo::kNoPosition);
-    // Set the position of the assignment statement one character past the
-    // source code, such that it definitely is not in the source code range
-    // of an immediate inner scope. For example in
-    //   eval('with ({x:1}) x = 1');
-    // the end position of the function generated for executing the eval code
-    // coincides with the end of the with scope which is the position of '1'.
-    int pos = function->end_position();
-    VariableProxy* result_proxy =
-        processor.factory()->NewVariableProxy(result, pos);
-    Statement* result_statement =
-        processor.factory()->NewReturnStatement(result_proxy, pos);
-    body->Add(result_statement, info->zone());
+    if (processor.result_assigned()) {
+      DCHECK(function->end_position() != RelocInfo::kNoPosition);
+      // Set the position of the assignment statement one character past the
+      // source code, such that it definitely is not in the source code range
+      // of an immediate inner scope. For example in
+      //   eval('with ({x:1}) x = 1');
+      // the end position of the function generated for executing the eval code
+      // coincides with the end of the with scope which is the position of '1'.
+      int pos = function->end_position();
+      VariableProxy* result_proxy =
+          processor.factory()->NewVariableProxy(result, pos);
+      Statement* result_statement =
+          processor.factory()->NewReturnStatement(result_proxy, pos);
+      body->Add(result_statement, info->zone());
+    }
   }
 
   return true;
 }
 
 
 }  // namespace internal
 }  // namespace v8