Scope tree serialization and ScopeIterator cleanup.

src/runtime.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 10907 matching lines @@
                                         serialized_scope_info, scope_info,
                                         context, block_scope)) {
       return Handle<JSObject>();
     }
   }
 
   return block_scope;
 }
 
 
-// Iterate over the actual scopes visible from a stack frame. All scopes are
+// Iterate over the actual scopes visible from a stack frame. The iteration
+// proceeds from the innermost visible nested scope outwards. All scopes are
 // backed by an actual context except the local scope, which is inserted
-// "artifically" in the context chain.
+// "artificially" in the context chain.
 class ScopeIterator {
  public:
   enum ScopeType {

[Kevin Millikin (Chromium), 2011/10/05 08:43:36]

Can this be the same as Scope::Type?

[Steven, 2011/10/06 19:09:27]

Almost. The ScopeIterator so far makes a difference about the innermost function
scope (ScopeTypeLocal) and outer function scopes (ScopeTypeClosure). This would
have to be unified if you want to use Scope::Type. What do you think?

On 2011/10/05 08:43:36, Kevin Millikin wrote:

     ScopeTypeGlobal = 0,
     ScopeTypeLocal,
     ScopeTypeWith,
     ScopeTypeClosure,
     ScopeTypeCatch,
     ScopeTypeBlock
   };
 
   ScopeIterator(Isolate* isolate,
                 JavaScriptFrame* frame,
                 int inlined_frame_index)
     : isolate_(isolate),
       frame_(frame),
       inlined_frame_index_(inlined_frame_index),
       function_(JSFunction::cast(frame->function())),
       context_(Context::cast(frame->context())),
-      local_done_(false),
-      at_local_(false) {
+      nested_scope_chain_(4) {
 
-    // Check whether the first scope is actually a local scope.
-    // If there is a stack slot for .result then this local scope has been
-    // created for evaluating top level code and it is not a real local scope.
-    // Checking for the existence of .result seems fragile, but the scope info
-    // saved with the code object does not otherwise have that information.
-    int index = function_->shared()->scope_info()->
-        StackSlotIndex(isolate_->heap()->result_symbol());
-    if (index >= 0) {
-      local_done_ = true;
-    } else if (context_->IsGlobalContext() ||
-               context_->IsFunctionContext()) {
-      at_local_ = true;
-    } else if (context_->closure() != *function_) {
-      // The context_ is a block or with or catch block from the outer function.
-      ASSERT(context_->IsWithContext() ||
-             context_->IsCatchContext() ||
-             context_->IsBlockContext());
-      at_local_ = true;
-    }
+    Handle<SerializedScopeInfo> scope_info(function_->shared()->scope_info());
+    int statement_position =
+        function_->shared()->code()->SourceStatementPosition(frame_->pc());
+    scope_info->GetNestedScopeChain(&nested_scope_chain_, statement_position);
   }
 
   // More scopes?
   bool Done() { return context_.is_null(); }
 
   // Move to the next scope.
   void Next() {
-    // If at a local scope mark the local scope as passed.
-    if (at_local_) {
-      at_local_ = false;
-      local_done_ = true;
-
-      // If the current context is not associated with the local scope the
-      // current context is the next real scope, so don't move to the next
-      // context in this case.
-      if (context_->closure() != *function_) {
-        return;
-      }
-    }
-
-    // The global scope is always the last in the chain.
-    if (context_->IsGlobalContext()) {
+    ScopeType scope_type = Type();
+    if (scope_type == ScopeTypeGlobal) {
+      // The global scope is always the last in the chain.
+      ASSERT(context_->IsGlobalContext());
       context_ = Handle<Context>();
       return;
     }
-
-    // Move to the next context.
-    context_ = Handle<Context>(context_->previous(), isolate_);
-
-    // If passing the local scope indicate that the current scope is now the
-    // local scope.
-    if (!local_done_ &&
-        (context_->IsGlobalContext() || context_->IsFunctionContext())) {
-      at_local_ = true;
+    if (nested_scope_chain_.is_empty()) {
+      context_ = Handle<Context>(context_->previous(), isolate_);
+    } else {
+      if (nested_scope_chain_.last()->HasContext()) {
+        context_ = Handle<Context>(context_->previous(), isolate_);
+      }
+      nested_scope_chain_.RemoveLast();
     }
   }
 
   // Return the type of the current scope.
   ScopeType Type() {
-    if (at_local_) {
-      return ScopeTypeLocal;
+    if (!nested_scope_chain_.is_empty()) {
+      Handle<SerializedScopeInfo> scope_info = nested_scope_chain_.last();
+      switch (scope_info->ScopeType()) {
+        case Scope::FUNCTION_SCOPE:
+          ASSERT(context_->IsFunctionContext() ||
+                 !scope_info->HasContext());
+          return ScopeTypeLocal;
+        case Scope::GLOBAL_SCOPE:
+          ASSERT(context_->IsGlobalContext());
+          return ScopeTypeGlobal;
+        case Scope::WITH_SCOPE:
+          ASSERT(context_->IsWithContext());
+          return ScopeTypeWith;
+        case Scope::CATCH_SCOPE:
+          ASSERT(context_->IsCatchContext());
+          return ScopeTypeCatch;
+        case Scope::BLOCK_SCOPE:
+          ASSERT(!scope_info->HasContext() ||
+                 context_->IsBlockContext());
+          return ScopeTypeBlock;
+        case Scope::EVAL_SCOPE:
+          UNREACHABLE();
+      }
     }
     if (context_->IsGlobalContext()) {
       ASSERT(context_->global()->IsGlobalObject());
       return ScopeTypeGlobal;
     }
     if (context_->IsFunctionContext()) {
       return ScopeTypeClosure;
     }
     if (context_->IsCatchContext()) {
       return ScopeTypeCatch;
     }
     if (context_->IsBlockContext()) {
       return ScopeTypeBlock;
     }
     ASSERT(context_->IsWithContext());
     return ScopeTypeWith;
   }
 
   // Return the JavaScript object with the content of the current scope.
   Handle<JSObject> ScopeObject() {
     switch (Type()) {
       case ScopeIterator::ScopeTypeGlobal:
         return Handle<JSObject>(CurrentContext()->global());
       case ScopeIterator::ScopeTypeLocal:
         // Materialize the content of the local scope into a JSObject.
+        ASSERT(nested_scope_chain_.length() == 1);
         return MaterializeLocalScope(isolate_, frame_, inlined_frame_index_);
       case ScopeIterator::ScopeTypeWith:
         // Return the with object.
         return Handle<JSObject>(JSObject::cast(CurrentContext()->extension()));
       case ScopeIterator::ScopeTypeCatch:
         return MaterializeCatchScope(isolate_, CurrentContext());
       case ScopeIterator::ScopeTypeClosure:
         // Materialize the content of the closure scope into a JSObject.
         return MaterializeClosure(isolate_, CurrentContext());
       case ScopeIterator::ScopeTypeBlock:
         return MaterializeBlockScope(isolate_, CurrentContext());
     }
     UNREACHABLE();
     return Handle<JSObject>();
   }
 
+  Handle<SerializedScopeInfo> CurrentScopeInfo() {
+    if (!nested_scope_chain_.is_empty()) {
+      return nested_scope_chain_.last();
+    } else if (context_->IsBlockContext()) {
+      return Handle<SerializedScopeInfo>(
+          SerializedScopeInfo::cast(context_->extension()));
+    } else if (context_->IsFunctionContext()) {
+      return Handle<SerializedScopeInfo>(
+          context_->closure()->shared()->scope_info());
+    }
+    return Handle<SerializedScopeInfo>::null();
+  }
+
   // Return the context for this scope. For the local context there might not
   // be an actual context.
   Handle<Context> CurrentContext() {
-    if (at_local_ && context_->closure() != *function_) {
+    if (Type() == ScopeTypeGlobal ||
+        nested_scope_chain_.is_empty()) {
+      return context_;
+    } else if (nested_scope_chain_.last()->HasContext()) {
+      return context_;
+    } else {
       return Handle<Context>();
     }
-    return context_;
   }
 
 #ifdef DEBUG
   // Debug print of the content of the current scope.
   void DebugPrint() {
     switch (Type()) {
       case ScopeIterator::ScopeTypeGlobal:
         PrintF("Global:\n");
         CurrentContext()->Print();
         break;
@@ skipping 42 matching lines @@
     PrintF("\n");
   }
 #endif
 
  private:
   Isolate* isolate_;
   JavaScriptFrame* frame_;
   int inlined_frame_index_;
   Handle<JSFunction> function_;
   Handle<Context> context_;
-  bool local_done_;
-  bool at_local_;
+  List<Handle<SerializedScopeInfo> > nested_scope_chain_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(ScopeIterator);
 };
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_GetScopeCount) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 2);
 
   // Check arguments.
@@ skipping 442 matching lines @@
 RUNTIME_FUNCTION(MaybeObject*, Runtime_ClearStepping) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 0);
   isolate->debug()->ClearStepping();
   return isolate->heap()->undefined_value();
 }
 
 
 // Creates a copy of the with context chain. The copy of the context chain is
 // is linked to the function context supplied.
-static Handle<Context> CopyWithContextChain(Isolate* isolate,
-                                            Handle<JSFunction> function,
-                                            Handle<Context> current,
-                                            Handle<Context> base) {
-  // At the end of the chain. Return the base context to link to.
-  if (current->IsFunctionContext() || current->IsGlobalContext()) {
-    return base;
+static Handle<Context> CopyNestedScopeContextChain(Isolate* isolate,
+                                                   Handle<JSFunction> function,
+                                                   Handle<Context> base,
+                                                   JavaScriptFrame* frame,
+                                                   int inlined_frame_index) {
+  HandleScope scope(isolate);
+  List<Handle<SerializedScopeInfo> > scope_chain;
+  List<Handle<Context> > context_chain;
+
+  ScopeIterator it(isolate, frame, inlined_frame_index);
+  for (; it.Type() != ScopeIterator::ScopeTypeGlobal &&
+         it.Type() != ScopeIterator::ScopeTypeLocal ; it.Next()) {
+    ASSERT(!it.Done());
+    scope_chain.Add(it.CurrentScopeInfo());
+    context_chain.Add(it.CurrentContext());
   }
 
-  // Recursively copy the with and catch contexts.
-  HandleScope scope(isolate);
-  Handle<Context> previous(current->previous());
-  Handle<Context> new_previous =
-      CopyWithContextChain(isolate, function, previous, base);
-  Handle<Context> new_current;
-  if (current->IsCatchContext()) {
-    Handle<String> name(String::cast(current->extension()));
-    Handle<Object> thrown_object(current->get(Context::THROWN_OBJECT_INDEX));
-    new_current =
-        isolate->factory()->NewCatchContext(function,
-                                            new_previous,
-                                            name,
-                                            thrown_object);
-  } else if (current->IsBlockContext()) {
-    Handle<SerializedScopeInfo> scope_info(
-        SerializedScopeInfo::cast(current->extension()));
-    new_current =
-        isolate->factory()->NewBlockContext(function, new_previous, scope_info);
-    // Copy context slots.
-    int num_context_slots = scope_info->NumberOfContextSlots();
-    for (int i = Context::MIN_CONTEXT_SLOTS; i < num_context_slots; ++i) {
-      new_current->set(i, current->get(i));
+  // At the end of the chain. Return the base context to link to.
+  Handle<Context> context = base;
+
+  // Iteratively copy and or materialize the nested contexts.
+  while (!scope_chain.is_empty()) {
+    Handle<SerializedScopeInfo> scope_info = scope_chain.RemoveLast();
+    Handle<Context> current = context_chain.RemoveLast();
+    ASSERT(!(scope_info->HasContext() & current.is_null()));
+
+    if (scope_info->ScopeType() == Scope::CATCH_SCOPE) {
+      Handle<String> name(String::cast(current->extension()));
+      Handle<Object> thrown_object(current->get(Context::THROWN_OBJECT_INDEX));
+      context =
+          isolate->factory()->NewCatchContext(function,
+                                              context,
+                                              name,
+                                              thrown_object);
+    } else if (scope_info->ScopeType() == Scope::BLOCK_SCOPE) {
+      // Materialize the contents of the block scope into a JSObject.
+      Handle<JSObject> block_scope_object =
+          MaterializeBlockScope(isolate, current);
+      if (block_scope_object.is_null()) {
+        return Handle<Context>::null();
+      }
+      // Allocate a new function context for the debug evaluation and set the
+      // extension object.
+      Handle<Context> new_context =
+          isolate->factory()->NewFunctionContext(Context::MIN_CONTEXT_SLOTS,
+                                                 function);
+      new_context->set_extension(*block_scope_object);
+      new_context->set_previous(*context);
+      context = new_context;
+    } else {
+      ASSERT(scope_info->ScopeType() == Scope::WITH_SCOPE);
+      ASSERT(current->IsWithContext());
+      Handle<JSObject> extension(JSObject::cast(current->extension()));
+      context =
+          isolate->factory()->NewWithContext(function, context, extension);
     }
-  } else {
-    ASSERT(current->IsWithContext());
-    Handle<JSObject> extension(JSObject::cast(current->extension()));
-    new_current =
-        isolate->factory()->NewWithContext(function, new_previous, extension);
   }
-  return scope.CloseAndEscape(new_current);
+
+  return scope.CloseAndEscape(context);
 }
 
 
 // Helper function to find or create the arguments object for
 // Runtime_DebugEvaluate.
 static Handle<Object> GetArgumentsObject(Isolate* isolate,
                                          JavaScriptFrame* frame,
                                          int inlined_frame_index,
                                          Handle<JSFunction> function,
                                          Handle<SerializedScopeInfo> scope_info,
@@ skipping 117 matching lines @@
       isolate->factory()->NewFunctionContext(Context::MIN_CONTEXT_SLOTS,
                                              go_between);
   context->set_extension(*local_scope);
   // Copy any with contexts present and chain them in front of this context.
   Handle<Context> frame_context(Context::cast(frame->context()));
   Handle<Context> function_context;
   // Get the function's context if it has one.
   if (scope_info->HasHeapAllocatedLocals()) {
     function_context = Handle<Context>(frame_context->declaration_context());
   }
-  context = CopyWithContextChain(isolate, go_between, frame_context, context);
+  context = CopyNestedScopeContextChain(isolate,
+                                        go_between,
+                                        context,
+                                        frame,
+                                        inlined_frame_index);
 
   if (additional_context->IsJSObject()) {
     Handle<JSObject> extension = Handle<JSObject>::cast(additional_context);
     context =
         isolate->factory()->NewWithContext(go_between, context, extension);
   }
 
   // Wrap the evaluation statement in a new function compiled in the newly
   // created context. The function has one parameter which has to be called
   // 'arguments'. This it to have access to what would have been 'arguments' in
@@ skipping 1421 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags);
   }
 }
 
 
 } }  // namespace v8::internal