Generators save and restore stack handlers

This CL adds machinery to unwind stack handlers from the stack and store
them into a generator's operand array.  It also includes routines to
reinstate them.  Together this allows generators to yield within
try/catch and try/finally blocks.

BUG=v8:2355
R=mstarzinger@chromium.org
TEST=mjsunit/harmony/generators-iteration

Review URL: https://codereview.chromium.org/14031028

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14586 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/frames-inl.h

@@ -98,6 +98,12 @@ inline StackHandler::Kind StackHandler::kind() const {
 }
 
 
+inline unsigned StackHandler::index() const {
+  const int offset = StackHandlerConstants::kStateOffset;
+  return IndexField::decode(Memory::unsigned_at(address() + offset));
+}
+
+
 inline Object** StackHandler::context_address() const {
   const int offset = StackHandlerConstants::kContextOffset;
   return reinterpret_cast<Object**>(address() + offset);
@@ -216,8 +222,9 @@ Object* JavaScriptFrame::GetParameter(int index) const {
 inline Address JavaScriptFrame::GetOperandSlot(int index) const {
   Address base = fp() + JavaScriptFrameConstants::kLocal0Offset;
   ASSERT(IsAddressAligned(base, kPointerSize));
-  ASSERT(type() == JAVA_SCRIPT);
-  ASSERT(index < ComputeOperandsCount());
+  ASSERT_EQ(type(), JAVA_SCRIPT);
+  ASSERT_LT(index, ComputeOperandsCount());
+  ASSERT_LE(0, index);
   // Operand stack grows down.
   return base - index * kPointerSize;
 }

src/frames.cc

@@ -840,6 +840,72 @@ void JavaScriptFrame::PrintTop(Isolate* isolate,
 }
 
 
+void JavaScriptFrame::SaveOperandStack(FixedArray* store,
+                                       int* stack_handler_index) const {
+  int operands_count = store->length();
+  ASSERT_LE(operands_count, ComputeOperandsCount());
+
+  // Visit the stack in LIFO order, saving operands and stack handlers into the
+  // array.  The saved stack handlers store a link to the next stack handler,
+  // which will allow RestoreOperandStack to rewind the handlers.
+  StackHandlerIterator it(this, top_handler());
+  int i = operands_count - 1;
+  *stack_handler_index = -1;
+  for (; !it.done(); it.Advance()) {
+    StackHandler* handler = it.handler();
+    // Save operands pushed after the handler was pushed.
+    for (; GetOperandSlot(i) < handler->address(); i--) {
+      store->set(i, GetOperand(i));
+    }
+    ASSERT_GE(i + 1, StackHandlerConstants::kSlotCount);
+    ASSERT_EQ(handler->address(), GetOperandSlot(i));
+    int next_stack_handler_index = i + 1 - StackHandlerConstants::kSlotCount;
+    handler->Unwind(isolate(), store, next_stack_handler_index,
+                    *stack_handler_index);
+    *stack_handler_index = next_stack_handler_index;
+    i -= StackHandlerConstants::kSlotCount;
+  }
+
+  // Save any remaining operands.
+  for (; i >= 0; i--) {
+    store->set(i, GetOperand(i));
+  }
+}
+
+
+void JavaScriptFrame::RestoreOperandStack(FixedArray* store,
+                                          int stack_handler_index) {
+  int operands_count = store->length();
+  ASSERT_LE(operands_count, ComputeOperandsCount());
+  int i = 0;
+  while (i <= stack_handler_index) {
+    if (i < stack_handler_index) {
+      // An operand.
+      ASSERT_EQ(GetOperand(i), isolate()->heap()->the_hole_value());
+      Memory::Object_at(GetOperandSlot(i)) = store->get(i);
+      i++;
+    } else {
+      // A stack handler.
+      ASSERT_EQ(i, stack_handler_index);
+      // The FixedArray store grows up.  The stack grows down.  So the operand
+      // slot for i actually points to the bottom of the top word in the
+      // handler.  The base of the StackHandler* is the address of the bottom
+      // word, which will be the last slot that is in the handler.
+      int handler_slot_index = i + StackHandlerConstants::kSlotCount - 1;
+      StackHandler *handler =
+          StackHandler::FromAddress(GetOperandSlot(handler_slot_index));
+      stack_handler_index = handler->Rewind(isolate(), store, i, fp());
+      i += StackHandlerConstants::kSlotCount;
+    }
+  }
+
+  for (; i < operands_count; i++) {
+    ASSERT_EQ(GetOperand(i), isolate()->heap()->the_hole_value());
+    Memory::Object_at(GetOperandSlot(i)) = store->get(i);
+  }
+}
+
+
 void FrameSummary::Print() {
   PrintF("receiver: ");
   receiver_->ShortPrint();
@@ -1436,6 +1502,60 @@ InnerPointerToCodeCache::InnerPointerToCodeCacheEntry*
 }
 
 
+// -------------------------------------------------------------------------
+
+
+void StackHandler::Unwind(Isolate* isolate,
+                          FixedArray* array,
+                          int offset,
+                          int previous_handler_offset) const {
+  STATIC_ASSERT(StackHandlerConstants::kSlotCount == 5);
+  ASSERT_LE(0, offset);
+  ASSERT_GE(array->length(), offset + 5);
+  // Unwinding a stack handler into an array chains it in the opposite
+  // direction, re-using the "next" slot as a "previous" link, so that stack
+  // handlers can be later re-wound in the correct order.  Decode the "state"
+  // slot into "index" and "kind" and store them separately, using the fp slot.
+  array->set(offset, Smi::FromInt(previous_handler_offset));        // next
+  array->set(offset + 1, *code_address());                          // code
+  array->set(offset + 2, Smi::FromInt(static_cast<int>(index())));  // state
+  array->set(offset + 3, *context_address());                       // context
+  array->set(offset + 4, Smi::FromInt(static_cast<int>(kind())));   // fp
+
+  *isolate->handler_address() = next()->address();
+}
+
+
+int StackHandler::Rewind(Isolate* isolate,
+                         FixedArray* array,
+                         int offset,
+                         Address fp) {
+  STATIC_ASSERT(StackHandlerConstants::kSlotCount == 5);
+  ASSERT_LE(0, offset);
+  ASSERT_GE(array->length(), offset + 5);
+  Smi* prev_handler_offset = Smi::cast(array->get(offset));
+  Code* code = Code::cast(array->get(offset + 1));
+  Smi* smi_index = Smi::cast(array->get(offset + 2));
+  Object* context = array->get(offset + 3);
+  Smi* smi_kind = Smi::cast(array->get(offset + 4));
+
+  unsigned state = KindField::encode(static_cast<Kind>(smi_kind->value())) |
+      IndexField::encode(static_cast<unsigned>(smi_index->value()));
+
+  Memory::Address_at(address() + StackHandlerConstants::kNextOffset) =
+      *isolate->handler_address();
+  Memory::Object_at(address() + StackHandlerConstants::kCodeOffset) = code;
+  Memory::uintptr_at(address() + StackHandlerConstants::kStateOffset) = state;
+  Memory::Object_at(address() + StackHandlerConstants::kContextOffset) =
+      context;
+  Memory::Address_at(address() + StackHandlerConstants::kFPOffset) = fp;
+
+  *isolate->handler_address() = address();
+
+  return prev_handler_offset->value();
+}
+
+
 // -------------------------------------------------------------------------
 
 int NumRegs(RegList reglist) {

src/frames.h

@@ -93,6 +93,7 @@ class StackHandlerConstants : public AllStatic {
   static const int kFPOffset       = 4 * kPointerSize;
 
   static const int kSize = kFPOffset + kPointerSize;
+  static const int kSlotCount = kSize >> kPointerSizeLog2;
 };
 
 
@@ -131,9 +132,15 @@ class StackHandler BASE_EMBEDDED {
   inline bool is_catch() const;
   inline bool is_finally() const;
 
+  // Generator support to preserve stack handlers.
+  void Unwind(Isolate* isolate, FixedArray* array, int offset,
+              int previous_handler_offset) const;
+  int Rewind(Isolate* isolate, FixedArray* array, int offset, Address fp);
+
  private:
   // Accessors.
   inline Kind kind() const;
+  inline unsigned index() const;
 
   inline Object** context_address() const;
   inline Object** code_address() const;
@@ -541,6 +548,10 @@ class JavaScriptFrame: public StandardFrame {
   inline Object* GetOperand(int index) const;
   inline int ComputeOperandsCount() const;
 
+  // Generator support to preserve operand stack and stack handlers.
+  void SaveOperandStack(FixedArray* store, int* stack_handler_index) const;
+  void RestoreOperandStack(FixedArray* store, int stack_handler_index);
+
   // Debugger access.
   void SetParameterValue(int index, Object* value) const;
 

src/objects-debug.cc

@@ -415,6 +415,7 @@ void JSGeneratorObject::JSGeneratorObjectVerify() {
   VerifyObjectField(kReceiverOffset);
   VerifyObjectField(kOperandStackOffset);
   VerifyObjectField(kContinuationOffset);
+  VerifyObjectField(kStackHandlerIndexOffset);
 }
 
 

src/objects-inl.h

@@ -5108,6 +5108,7 @@ ACCESSORS(JSGeneratorObject, context, Context, kContextOffset)
 ACCESSORS(JSGeneratorObject, receiver, Object, kReceiverOffset)
 SMI_ACCESSORS(JSGeneratorObject, continuation, kContinuationOffset)
 ACCESSORS(JSGeneratorObject, operand_stack, FixedArray, kOperandStackOffset)
+SMI_ACCESSORS(JSGeneratorObject, stack_handler_index, kStackHandlerIndexOffset)
 
 
 JSGeneratorObject* JSGeneratorObject::cast(Object* obj) {

src/objects.h

@@ -6410,9 +6410,14 @@ class JSGeneratorObject: public JSObject {
   inline int continuation();
   inline void set_continuation(int continuation);
 
-  // [operands]: Saved operand stack.
+  // [operand_stack]: Saved operand stack.
   DECL_ACCESSORS(operand_stack, FixedArray)
 
+  // [stack_handler_index]: Index of first stack handler in operand_stack, or -1
+  // if the captured activation had no stack handler.
+  inline int stack_handler_index();
+  inline void set_stack_handler_index(int stack_handler_index);
+
   // Casting.
   static inline JSGeneratorObject* cast(Object* obj);
 
@@ -6430,7 +6435,9 @@ class JSGeneratorObject: public JSObject {
   static const int kReceiverOffset = kContextOffset + kPointerSize;
   static const int kContinuationOffset = kReceiverOffset + kPointerSize;
   static const int kOperandStackOffset = kContinuationOffset + kPointerSize;
-  static const int kSize = kOperandStackOffset + kPointerSize;
+  static const int kStackHandlerIndexOffset =
+      kOperandStackOffset + kPointerSize;
+  static const int kSize = kStackHandlerIndexOffset + kPointerSize;
 
   // Resume mode, for use by runtime functions.
   enum ResumeMode { SEND, THROW };

src/runtime.cc

@@ -2577,6 +2577,7 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateJSGeneratorObject) {
   generator->set_receiver(frame->receiver());
   generator->set_continuation(0);
   generator->set_operand_stack(isolate->heap()->empty_fixed_array());
+  generator->set_stack_handler_index(-1);
 
   return generator;
 }
@@ -2603,23 +2604,18 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_SuspendJSGeneratorObject) {
   if (operands_count == 0) {
     ASSERT_EQ(generator_object->operand_stack(),
               isolate->heap()->empty_fixed_array());
+    ASSERT_EQ(generator_object->stack_handler_index(), -1);
     // If there are no operands on the stack, there shouldn't be a handler
     // active either.
     ASSERT(!frame->HasHandler());
   } else {
-    if (frame->HasHandler()) {
-      // TODO(wingo): Unwind the stack handlers.
-      UNIMPLEMENTED();
-    }
-
-    FixedArray* operand_stack;
+    int stack_handler_index = -1;
     MaybeObject* alloc = isolate->heap()->AllocateFixedArray(operands_count);
+    FixedArray* operand_stack;
     if (!alloc->To(&operand_stack)) return alloc;
-
-    for (int i = 0; i < operands_count; i++) {
-      operand_stack->set(i, frame->GetOperand(i));
-    }
+    frame->SaveOperandStack(operand_stack, &stack_handler_index);
     generator_object->set_operand_stack(operand_stack);
+    generator_object->set_stack_handler_index(stack_handler_index);
   }
 
   // Set continuation down here to avoid side effects if the operand stack
@@ -2669,14 +2665,10 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_ResumeJSGeneratorObject) {
   FixedArray* operand_stack = generator_object->operand_stack();
   int operands_count = operand_stack->length();
   if (operands_count != 0) {
-    // TODO(wingo): Rewind stack handlers.  However until
-    // SuspendJSGeneratorObject unwinds them, we won't see frames with stack
-    // handlers here.
-    for (int i = 0; i < operands_count; i++) {
-      ASSERT_EQ(frame->GetOperand(i), isolate->heap()->the_hole_value());
-      Memory::Object_at(frame->GetOperandSlot(i)) = operand_stack->get(i);
-    }
+    frame->RestoreOperandStack(operand_stack,
+                               generator_object->stack_handler_index());
     generator_object->set_operand_stack(isolate->heap()->empty_fixed_array());
+    generator_object->set_stack_handler_index(-1);
   }
 
   JSGeneratorObject::ResumeMode resume_mode =

src/v8memory.h

@@ -64,6 +64,14 @@ class Memory {
     return *reinterpret_cast<unsigned*>(addr);
   }
 
+  static intptr_t& intptr_at(Address addr)  {
+    return *reinterpret_cast<intptr_t*>(addr);
+  }
+
+  static uintptr_t& uintptr_at(Address addr) {
+    return *reinterpret_cast<uintptr_t*>(addr);
+  }
+
   static double& double_at(Address addr)  {
     return *reinterpret_cast<double*>(addr);
   }