Enable visitor in rewriter to replace statements.

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),
+        replacement_(nullptr),
         is_set_(false),
         factory_(ast_value_factory) {
     InitializeAstVisitor(isolate, ast_value_factory->zone());
   }
 
   virtual ~Processor() { }
 
   void Process(ZoneList<Statement*>* statements);
 
   AstNodeFactory* factory() { return &factory_; }
 
  private:
   Variable* result_;
 
+  // When visiting a node, we "return" a replacement for that node in
+  // [replacement_].  In many cases this will just be the original node.
+  Statement* replacement_;
+
   // 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.
   bool is_set_;
 
   AstNodeFactory factory_;
 
   Expression* SetResult(Expression* value) {
     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
 
   void VisitIterationStatement(IterationStatement* stmt);
 
   DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
 };
 
 
 void Processor::Process(ZoneList<Statement*>* statements) {
   for (int i = statements->length() - 1; i >= 0; --i) {
     Visit(statements->at(i));
+    statements->Set(i, replacement_);

[rossberg, 2015/09/28 11:42:15]

How about treating replacement_ as an option and changing the logic here (and in
the other places that set a subnode) to

  if (replacement_ != nullptr) {
    statements->Set(...);
    replacement_ = nullptr;
  }

Then you only need to assign something to replacement_ in the few visit methods
where you actually need to change the node.

   }
 }
 
 
 void Processor::VisitBlock(Block* node) {
   // An initializer block is the rewritten form of a variable declaration
   // with initialization expressions. The initializer block contains the
   // list of assignments corresponding to the initialization expressions.
   // While unclear from the spec (ECMA-262, 3rd., 12.2), the value of
   // 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());
+  replacement_ = node;
 }
 
 
 void Processor::VisitExpressionStatement(ExpressionStatement* node) {
   // Rewrite : <x>; -> .result = <x>;
   if (!is_set_ && !node->expression()->IsThrow()) {
     node->set_expression(SetResult(node->expression()));
     is_set_ = true;
   }
+  replacement_ = node;
 }
 
 
 void Processor::VisitIfStatement(IfStatement* node) {
   // Rewrite both branches.
   bool set_after = is_set_;
   Visit(node->then_statement());
+  node->set_then_statement(replacement_);
   bool set_in_then = is_set_;
   is_set_ = set_after;
   Visit(node->else_statement());
+  node->set_else_statement(replacement_);
   is_set_ = is_set_ && set_in_then;
+  replacement_ = node;
 }
 
 
 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].
   Visit(node->body());
+  node->set_body(replacement_);
   is_set_ = is_set_ && set_after;
+  replacement_ = node;
 }
 
 
 void Processor::VisitDoWhileStatement(DoWhileStatement* node) {
   VisitIterationStatement(node);
 }
 
 
 void Processor::VisitWhileStatement(WhileStatement* node) {
   VisitIterationStatement(node);
@@ skipping 12 matching lines @@
 
 void Processor::VisitForOfStatement(ForOfStatement* node) {
   VisitIterationStatement(node);
 }
 
 
 void Processor::VisitTryCatchStatement(TryCatchStatement* node) {
   // Rewrite both try and catch block.
   bool set_after = is_set_;
   Visit(node->try_block());
+  node->set_try_block(static_cast<Block*>(replacement_));
   bool set_in_try = is_set_;
   is_set_ = set_after;
   Visit(node->catch_block());
+  node->set_catch_block(static_cast<Block*>(replacement_));
   is_set_ = is_set_ && set_in_try;
+  replacement_ = node;
 }
 
 
 void Processor::VisitTryFinallyStatement(TryFinallyStatement* node) {
   // Rewrite both try and finally block (in reverse order).
   Visit(node->finally_block());
-  Visit(node->try_block());
+  node->set_finally_block(static_cast<Block*>(replacement_));
+  Visit(node->try_block());  // Exception will not be caught.
+  node->set_try_block(static_cast<Block*>(replacement_));
+  replacement_ = node;
 }
 
 
 void Processor::VisitSwitchStatement(SwitchStatement* node) {
   // Rewrite statements in all case clauses (in reverse order).
   ZoneList<CaseClause*>* clauses = node->cases();
   bool set_after = 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;
+  replacement_ = node;
 }
 
 
 void Processor::VisitContinueStatement(ContinueStatement* node) {
   is_set_ = false;
+  replacement_ = node;
 }
 
 
 void Processor::VisitBreakStatement(BreakStatement* node) {
   is_set_ = false;
+  replacement_ = node;
 }
 
 
 void Processor::VisitWithStatement(WithStatement* node) {
   Visit(node->statement());
+  node->set_statement(replacement_);
+  replacement_ = node;
 }
 
 
 void Processor::VisitSloppyBlockFunctionStatement(
     SloppyBlockFunctionStatement* node) {
   Visit(node->statement());
+  node->set_statement(replacement_);
+  replacement_ = node;
 }
 
 
-void Processor::VisitReturnStatement(ReturnStatement* node) { is_set_ = true; }
+void Processor::VisitEmptyStatement(EmptyStatement* node) {
+  replacement_ = node;
+}
 
 
-// Do nothing:
-void Processor::VisitEmptyStatement(EmptyStatement* node) {}
-void Processor::VisitDebuggerStatement(DebuggerStatement* node) {}
+void Processor::VisitReturnStatement(ReturnStatement* node) {
+  is_set_ = true;
+  replacement_ = node;
+}
+
+
+void Processor::VisitDebuggerStatement(DebuggerStatement* node) {
+  replacement_ = node;
+}
 
 
 // Expressions are never visited.
 #define DEF_VISIT(type)                                         \
   void Processor::Visit##type(type* expr) { UNREACHABLE(); }
 EXPRESSION_NODE_LIST(DEF_VISIT)
 #undef DEF_VISIT
 
 
 // Declarations are never visited.
@@ skipping 36 matching lines @@
         processor.factory()->NewReturnStatement(result_proxy, pos);
     body->Add(result_statement, info->zone());
   }
 
   return true;
 }
 
 
 }  // namespace internal
 }  // namespace v8