Fix issue 265 by handling extra statement state on the frame based on...

src/virtual-frame.cc

 // Copyright 2009 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 111 matching lines @@
 }
 
 
 // Modify the state of the virtual frame to match the actual frame by
 // removing elements from the top of the virtual frame.  The elements will
 // be externally popped from the actual frame (eg, by a runtime call).  No
 // code is emitted.
 void VirtualFrame::Forget(int count) {
   ASSERT(count >= 0);
   ASSERT(stack_pointer_ == elements_.length() - 1);
+
+  stack_pointer_ -= count;
+  ForgetElements(count);
+}
+
+
+void VirtualFrame::ForgetElements(int count) {
+  ASSERT(count >= 0);
   ASSERT(elements_.length() >= count);
 
-  stack_pointer_ -= count;
   for (int i = 0; i < count; i++) {
     FrameElement last = elements_.RemoveLast();
     if (last.is_register()) {
-      Unuse(last.reg());
+      // A hack to properly count register references for the code
+      // generator's current frame and also for other frames.  The
+      // same code appears in PrepareMergeTo.
+      if (cgen_->frame() == this) {
+        Unuse(last.reg());
+      } else {
+        frame_registers_.Unuse(last.reg());
+      }
     }
   }
 }
 
 
 void VirtualFrame::Use(Register reg) {
   frame_registers_.Use(reg);
   cgen_->allocator()->Use(reg);
 }
 
@@ skipping 168 matching lines @@
     if (elements_[i].is_register()) {
       cgen_->allocator()->Use(elements_[i].reg());
     }
   }
 }
 
 
 void VirtualFrame::PrepareForReturn() {
   // Spill all locals. This is necessary to make sure all locals have
   // the right value when breaking at the return site in the debugger.
+  //
+  // TODO(203): It is also necessary to ensure that merging at the
+  // return site does not generate code to overwrite eax, where the
+  // return value is kept in a non-refcounted register reference.
   for (int i = 0; i < expression_base_index(); i++) SpillElementAt(i);
-
-  // Drop all non-local stack elements.
-  Drop(height());
-
-  // Validate state: The expression stack should be empty and the
-  // stack pointer should have been updated to reflect this.
-  ASSERT(height() == 0);
-  ASSERT(stack_pointer_ == expression_base_index() - 1);
 }
 
 
 void VirtualFrame::SetElementAt(int index, Result* value) {
   int frame_index = elements_.length() - index - 1;
   ASSERT(frame_index >= 0);
   ASSERT(frame_index < elements_.length());
   ASSERT(value->is_valid());
   FrameElement original = elements_[frame_index];
 
@@ skipping 199 matching lines @@
   for (int i = 0; i < kNumRegisters; i++) {
     if (frame_registers_.count(i) != other->frame_registers_.count(i)) {
       return false;
     }
   }
 
   return true;
 }
 
 } }  // namespace v8::internal