[Interpreter] Ensure context is popped when we break or continue

src/interpreter/bytecode-generator.cc

 // 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.
 
 #include "src/interpreter/bytecode-generator.h"
 
 #include "src/ast/scopes.h"
 #include "src/compiler.h"
 #include "src/interpreter/bytecode-register-allocator.h"
 #include "src/interpreter/control-flow-builders.h"
@@ skipping 63 matching lines @@
   int depth_;
   bool should_pop_context_;
 };
 
 
 // Scoped class for tracking control statements entered by the
 // visitor. The pattern derives AstGraphBuilder::ControlScope.
 class BytecodeGenerator::ControlScope BASE_EMBEDDED {
  public:
   explicit ControlScope(BytecodeGenerator* generator)
-      : generator_(generator), outer_(generator->execution_control()) {
+      : generator_(generator), outer_(generator->execution_control()),
+        context_(generator->execution_context()) {
     generator_->set_execution_control(this);
   }
   virtual ~ControlScope() { generator_->set_execution_control(outer()); }
 
   void Break(Statement* stmt) { PerformCommand(CMD_BREAK, stmt); }
   void Continue(Statement* stmt) { PerformCommand(CMD_CONTINUE, stmt); }
 
  protected:
   enum Command { CMD_BREAK, CMD_CONTINUE };
   void PerformCommand(Command command, Statement* statement);
-  virtual bool Execute(Command command, Statement* statement) = 0;
+  virtual bool ShouldExecute(Command command, Statement* statement) = 0;
+  virtual void Execute(Command command) = 0;
 
   BytecodeGenerator* generator() const { return generator_; }
   ControlScope* outer() const { return outer_; }
+  ContextScope* context() const { return context_; }
 
  private:
   BytecodeGenerator* generator_;
   ControlScope* outer_;
+  ContextScope* context_;
 
   DISALLOW_COPY_AND_ASSIGN(ControlScope);
 };
 
 
 // Scoped class for enabling break inside blocks and switch blocks.
 class BytecodeGenerator::ControlScopeForBreakable final
     : public BytecodeGenerator::ControlScope {
  public:
   ControlScopeForBreakable(BytecodeGenerator* generator,
                            BreakableStatement* statement,
                            BreakableControlFlowBuilder* control_builder)
       : ControlScope(generator),
         statement_(statement),
         control_builder_(control_builder) {}
 
  protected:
-  virtual bool Execute(Command command, Statement* statement) {
+  bool ShouldExecute(Command command, Statement* statement) override {
     if (statement != statement_) return false;
+    return command == CMD_BREAK;
+  }
+
+  void Execute(Command command) override {
     switch (command) {
       case CMD_BREAK:
         control_builder_->Break();
-        return true;
+        break;
       case CMD_CONTINUE:
+        UNREACHABLE();
         break;
     }
-    return false;
   }
 
  private:
   Statement* statement_;
   BreakableControlFlowBuilder* control_builder_;
 };
 
 
 // Scoped class for enabling 'break' and 'continue' in iteration
 // constructs, e.g. do...while, while..., for...
 class BytecodeGenerator::ControlScopeForIteration final
     : public BytecodeGenerator::ControlScope {
  public:
   ControlScopeForIteration(BytecodeGenerator* generator,
                            IterationStatement* statement,
                            LoopBuilder* loop_builder)
       : ControlScope(generator),
         statement_(statement),
         loop_builder_(loop_builder) {}
 
  protected:
-  virtual bool Execute(Command command, Statement* statement) {
+  bool ShouldExecute(Command command, Statement* statement) override {
     if (statement != statement_) return false;
+    return command == CMD_BREAK || command == CMD_CONTINUE;
+  }
+
+  void Execute(Command command) override {
     switch (command) {
       case CMD_BREAK:
         loop_builder_->Break();
-        return true;
+        break;
       case CMD_CONTINUE:
         loop_builder_->Continue();
-        return true;
+        break;
     }
-    return false;
   }
 
  private:
   Statement* statement_;
   LoopBuilder* loop_builder_;
 };
 
 
 void BytecodeGenerator::ControlScope::PerformCommand(Command command,
                                                      Statement* statement) {
   ControlScope* current = this;
   do {
-    if (current->Execute(command, statement)) return;
+    if (current->ShouldExecute(command, statement)) {

[Michael Starzinger, 2016/01/21 13:25:20]

As discussed offline: How would you feel about going for the sub-optimal
solution of potential popping a context for every control scope first? That way
the implementation of the various control scopes stays simple while we hack on
them. We can certainly leave a TODO in that regard. Once we got them all done we
can revisit how to optimize away the redundant pops. WDYT?

[rmcilroy, 2016/01/22 11:46:08]

Done.

+      if (current->context() != this->context()) {
+        // Pop context to the expected depth.
+        generator()->builder()->PopContext(current->context()->reg());
+      }
+      current->Execute(command);
+      return;
+    }
     current = current->outer();
   } while (current != nullptr);
   UNREACHABLE();
 }
 
 
 class BytecodeGenerator::RegisterAllocationScope {
  public:
   explicit RegisterAllocationScope(BytecodeGenerator* generator)
       : generator_(generator),
@@ skipping 2028 matching lines @@
 }
 
 
 int BytecodeGenerator::feedback_index(FeedbackVectorSlot slot) const {
   return info()->feedback_vector()->GetIndex(slot);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8