Generators save and restore stack handlers

src/frames.cc

Index: src/frames.cc
diff --git a/src/frames.cc b/src/frames.cc
index aaf8c79e23256a12d4d3a7fe7bce939f9f604ff8..aff389532da15768571b8d3cfa9a1fea74fe1092 100644
--- a/src/frames.cc
+++ b/src/frames.cc
@@ -840,6 +840,77 @@ 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());
+  const int kStackHandlerSlotCount =

[Michael Starzinger, 2013/05/07 09:55:44]

Move the "kStackHandlerSlotCount" constant into the StackHandlerConstants class
(e.g. StackHandlerConstants::kSlotCount).

+    (StackHandlerConstants::kSize >> kPointerSizeLog2);
+  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, kStackHandlerSlotCount);
+    ASSERT_EQ(handler->address(), GetOperandSlot(i));
+    int next_stack_handler_index = i + 1 - kStackHandlerSlotCount;
+    handler->Unwind(isolate(), store, next_stack_handler_index,
+                    Smi::FromInt(*stack_handler_index));
+    *stack_handler_index = next_stack_handler_index;
+    i -= kStackHandlerSlotCount;
+  }
+
+  // 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;
+  const int kStackHandlerSlotCount =

[Michael Starzinger, 2013/05/07 09:55:44]

Likewise.

+    (StackHandlerConstants::kSize >> kPointerSizeLog2);
+  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 + kStackHandlerSlotCount - 1;
+      StackHandler *handler =
+          StackHandler::FromAddress(GetOperandSlot(handler_slot_index));
+      Object *data = handler->Rewind(isolate(), store, i, fp());
+      stack_handler_index = Smi::cast(data)->value();
+      i += kStackHandlerSlotCount;
+    }
+  }
+
+  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();
@@ -1438,6 +1509,59 @@ InnerPointerToCodeCache::InnerPointerToCodeCacheEntry*
 
 // -------------------------------------------------------------------------
 
+
+void StackHandler::Unwind(Isolate* isolate, FixedArray* array, int offset,

[Michael Starzinger, 2013/05/07 09:55:44]

style: Better put each argument on a single line, makes it easier to read (see
e.g. StackFrame::IteratePc).

+                          Object* data) const {
+  STATIC_ASSERT(StackHandlerConstants::kSize == 5 * kPointerSize);
+  ASSERT_LE(0, offset);
+  ASSERT_GE(array->length(), offset + 5);
+  array->set(offset, data);                    // next
+  array->set(offset + 1, *code_address());     // code
+  uintptr_t state =
+      Memory::uintptr_at(address() + StackHandlerConstants::kStateOffset);
+  // Convert state to 31-bit signed integer, so it fits in a Smi.
+  ASSERT(state < (1U << (32 - kSmiTagSize)));
+  int int_state = static_cast<int>(state << kSmiTagSize) >> kSmiTagSize;
+  Smi *smi_state = Smi::FromInt(int_state);
+  array->set(offset + 2, smi_state);           // state
+  array->set(offset + 3, *context_address());  // context
+  array->set(offset + 4, Smi::FromInt(0));     // fp
+
+  *isolate->handler_address() = next()->address();
+}
+
+
+Object* StackHandler::Rewind(Isolate* isolate, FixedArray* array, int offset,

[Michael Starzinger, 2013/05/07 09:55:44]

style: Likewise.

+                             Address fp) {
+  STATIC_ASSERT(StackHandlerConstants::kSize == 5 * kPointerSize);
+  ASSERT_LE(0, offset);
+  ASSERT_GE(array->length(), offset + 5);
+  Object *data = array->get(offset);
+  Code *code = Code::cast(array->get(offset + 1));
+  Smi *smi_state = Smi::cast(array->get(offset + 2));
+  int int_state = smi_state->value();
+  // Convert saved state from Smi to 31-bit unsigned integer.
+  unsigned state =
+      static_cast<unsigned>(int_state << kSmiTagSize) >> kSmiTagSize;

[Michael Starzinger, 2013/05/07 09:55:44]

I think this conversion is broken on 64-bit systems. In general this conversion
(and the one above) scare me a bit. Can we rewrite this using just static casts?

+  Object *context = array->get(offset + 3);
+  ASSERT_EQ(Smi::FromInt(0), array->get(offset + 4));
+
+  Memory::Address_at(address() + StackHandlerConstants::kNextOffset) =
+    *isolate->handler_address();

[Michael Starzinger, 2013/05/07 09:55:44]

nit: Indentation is off.

+  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 data;
+}
+
+
+// -------------------------------------------------------------------------
+
 int NumRegs(RegList reglist) {
   return CompilerIntrinsics::CountSetBits(reglist);
 }