Make stackmaps store their actual length.

runtime/vm/stack_frame.cc

Index: runtime/vm/stack_frame.cc
diff --git a/runtime/vm/stack_frame.cc b/runtime/vm/stack_frame.cc
index 53e66170e0d6b5909ed37a2dc0b807047082b8cf..01a67359e704d6a986aeebdec790a61575a57144 100644
--- a/runtime/vm/stack_frame.cc
+++ b/runtime/vm/stack_frame.cc
@@ -54,8 +54,8 @@ void StackFrame::VisitObjectPointers(ObjectPointerVisitor* visitor) {
   ASSERT(visitor != NULL);
   NoGCScope no_gc;
   RawObject** start_addr = reinterpret_cast<RawObject**>(sp());
-  RawObject** end_addr = reinterpret_cast<RawObject**>(
-      fp() + (ParsedFunction::kFirstLocalSlotIndex * kWordSize));
+  RawObject** end_addr = reinterpret_cast<RawObject**>(fp()) +
+      ParsedFunction::kFirstLocalSlotIndex;
   Code code;
   code = LookupDartCode();
   if (!code.IsNull()) {
@@ -66,24 +66,18 @@ void StackFrame::VisitObjectPointers(ObjectPointerVisitor* visitor) {
     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 end_bit_index = map.MaximumBitIndex();
-      // It's possible that no bits are set.
-      if (end_bit_index != Stackmap::kNoMaximum) {
-        intptr_t bit_index = map.MinimumBitIndex();
-        ASSERT(bit_index != Stackmap::kNoMinimum);
-        ASSERT(bit_index <= end_bit_index);
-        ASSERT(end_bit_index <= (end_addr - start_addr));
-        while (bit_index <= end_bit_index) {
-          if (map.IsObject(bit_index)) {
-            visitor->VisitPointer(end_addr - bit_index);
-          }
-          ++bit_index;
+      intptr_t length = map.Length();
+      for (intptr_t bit_index = 0; bit_index < length; ++bit_index) {
+        if (map.IsObject(bit_index)) {
+          visitor->VisitPointer(end_addr - bit_index);
         }
       }
       // The stack slots that are not spill slots (i.e., outgoing arguments)
       // are tagged objects.
-      end_addr = end_addr - (code.spill_slot_count() - 1);
-      ASSERT(end_addr >= start_addr);
+      end_addr -= length;
+      // The end address can be one slot (but not more) past the start
+      // address in the case that all slots were covered by the stack map.
+      ASSERT((end_addr + 1) >= start_addr);
     }
   }
   // Each slot between the start and end address are tagged objects.