Fix an off-by-one error in the stack frame iteration.

runtime/vm/stack_frame.cc

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/stack_frame.h"
 
 #include "vm/assembler_macros.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/os.h"
@@ skipping 43 matching lines @@
   Code code;
   code = LookupDartCode();
   if (!code.IsNull()) {
     Array maps;
     maps = Array::null();
     Stackmap map;
     map = code.GetStackmap(pc(), &maps, &map);
     if (!map.IsNull()) {
       // A stack map is present in the code object, use the stack map to visit
       // frame slots which are marked as having objects.
-      intptr_t bit_offset = map.MinimumBitOffset();
-      intptr_t end_bit_offset = map.MaximumBitOffset();
-      while (bit_offset <= end_bit_offset) {
-        uword addr = (fp() - ((bit_offset + 1) * kWordSize));
+      intptr_t bit_index = map.MinimumBitOffset();

[Vyacheslav Egorov (Google), 2012/07/30 13:00:38]

s/MinimumBitOffset/MinimumBitIndex/

[Kevin Millikin (Google), 2012/07/30 13:41:03]

OK, but that caused a cascade of offset -> index renames.

+      intptr_t end_bit_index = map.MaximumBitOffset();
+      uword base_addr =
+          fp() + (ParsedFunction::kFirstLocalSlotIndex * kWordSize);
+      while (bit_index <= end_bit_index) {
+        uword addr = base_addr - (bit_index * kWordSize);
         ASSERT(addr >= sp());
-        if (map.IsObject(bit_offset)) {
+        if (map.IsObject(bit_index)) {
           visitor->VisitPointer(reinterpret_cast<RawObject**>(addr));
         }
-        bit_offset += 1;
+        ++bit_index;
       }
       return;
     }
   }
   // No stack maps are present in the code object which means this
   // frame relies on tagged pointers and hence we visit each entry
   // on the frame between SP and FP.
   ASSERT(visitor != NULL);
   RawObject** start = reinterpret_cast<RawObject**>(sp());

[Vyacheslav Egorov (Google), 2012/07/30 13:00:38]

I find it a bit suspicious that we don't visit code object entry slot on the
stack, but apparently code never dies.

   RawObject** end = reinterpret_cast<RawObject**>(
       fp() + (ParsedFunction::kFirstLocalSlotIndex * kWordSize));
   visitor->VisitPointers(start, end);
 }
 
 
 RawFunction* StackFrame::LookupDartFunction() const {
   const Code& code = Code::Handle(LookupDartCode());
   if (!code.IsNull()) {
     return code.function();
@@ skipping 150 matching lines @@
 EntryFrame* StackFrameIterator::NextEntryFrame() {
   ASSERT(!frames_.HasNext());
   entry_.sp_ = frames_.sp_;
   entry_.fp_ = frames_.fp_;
   SetupNextExitFrameData();  // Setup data for next exit frame in chain.
   ASSERT(entry_.IsValid());
   return &entry_;
 }
 
 }  // namespace dart