DBC: Fix reading locals out of a deopt frame.

runtime/vm/stack_frame_dbc.h

Index: runtime/vm/stack_frame_dbc.h
diff --git a/runtime/vm/stack_frame_dbc.h b/runtime/vm/stack_frame_dbc.h
index a59a417ed883b3b341be303dba46731e3669c626..5d5ee78e3aedac4b83650050fd38494e7ded919a 100644
--- a/runtime/vm/stack_frame_dbc.h
+++ b/runtime/vm/stack_frame_dbc.h
@@ -10,7 +10,7 @@ namespace dart {
 /* DBC Frame Layout
 
 IMPORTANT: On DBC stack is growing upwards which is different from all other
-architectures. This enables effecient addressing for locals via unsigned index.
+architectures. This enables efficient addressing for locals via unsigned index.
 
                |                    | <- TOS
 Callee frame   | ...                |
@@ -56,15 +56,17 @@ static const int kParamEndSlotFromFp = 4;  // One slot past last parameter.
 static const int kFirstLocalSlotFromFp = -1;
 
 
-DART_FORCE_INLINE static uword LocalVarAddress(uword fp, intptr_t index) {
-  ASSERT(index != 0);
-  if (index > 0) {
-     return fp - index * kWordSize;
+DART_FORCE_INLINE static intptr_t LocalVarIndex(intptr_t fp_offset,
+                                                intptr_t var_index) {
+  ASSERT(var_index != 0);
+  if (var_index > 0) {
+    return fp_offset - var_index;
   } else {
-     return fp - (index + 1) * kWordSize;
+    return fp_offset - (var_index + 1);
   }
 }
 
+
 DART_FORCE_INLINE static uword ParamAddress(uword fp, intptr_t reverse_index) {
   return fp - (kDartFrameFixedSize + reverse_index) * kWordSize;
 }