Enable visitor in rewriter to replace statements.

src/rewriter.cc

Index: src/rewriter.cc
diff --git a/src/rewriter.cc b/src/rewriter.cc
index 110a6ccdf98b99ea7928592582c518978463cb95..2de25407e3fe608bb95857be826023be69b83ac4 100644
--- a/src/rewriter.cc
+++ b/src/rewriter.cc
@@ -16,6 +16,7 @@ class Processor: public AstVisitor {
   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());
@@ -30,6 +31,10 @@ class Processor: public AstVisitor {
  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
@@ -58,6 +63,7 @@ class Processor: public AstVisitor {
 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.

   }
 }
 
@@ -72,6 +78,7 @@ void Processor::VisitBlock(Block* node) {
   // 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;
 }
 
 
@@ -81,6 +88,7 @@ void Processor::VisitExpressionStatement(ExpressionStatement* node) {
     node->set_expression(SetResult(node->expression()));
     is_set_ = true;
   }
+  replacement_ = node;
 }
 
 
@@ -88,10 +96,13 @@ 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;
 }
 
 
@@ -100,7 +111,9 @@ void Processor::VisitIterationStatement(IterationStatement* node) {
   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;
 }
 
 
@@ -133,17 +146,23 @@ 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;
 }
 
 
@@ -156,36 +175,51 @@ void Processor::VisitSwitchStatement(SwitchStatement* node) {
     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.