--- old/src/share/vm/gc/g1/g1BlockOffsetTable.cpp	2017-02-22 14:36:06.338757002 +0100
+++ new/src/share/vm/gc/g1/g1BlockOffsetTable.cpp	2017-02-22 14:36:06.214752180 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -78,9 +78,10 @@
   _bot(array),
   _space(gsp),
   _next_offset_threshold(NULL),
-  _next_offset_index(0),
-  _object_can_span(false)
-{ }
+  _next_offset_index(0)
+{
+  debug_only(_object_can_span = false;)
+}
 
 // The arguments follow the normal convention of denoting
 // a right-open interval: [start, end)
@@ -366,6 +367,10 @@
 }
 
 #ifndef PRODUCT
+void G1BlockOffsetTablePart::set_object_can_span(bool can_span) {
+  _object_can_span = can_span;
+}
+
 void
 G1BlockOffsetTablePart::print_on(outputStream* out) {
   size_t from_index = _bot->index_for(_space->bottom());
@@ -420,7 +425,3 @@
     alloc_block(obj_top, fill_size);
   }
 }
-
-void G1BlockOffsetTablePart::set_continues_humongous(bool is_humongous) {
-  _object_can_span = is_humongous;
-}
--- old/src/share/vm/gc/g1/g1BlockOffsetTable.hpp	2017-02-22 14:36:06.990782354 +0100
+++ new/src/share/vm/gc/g1/g1BlockOffsetTable.hpp	2017-02-22 14:36:06.858777221 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -116,7 +116,9 @@
   // allocation boundary at which offset array must be updated
   HeapWord* _next_offset_threshold;
   size_t    _next_offset_index;      // index corresponding to that boundary
-  bool      _object_can_span;        // Set for continues humongous
+
+  // Indicates if an object can span into this G1BlockOffsetTablePart.
+  debug_only(bool _object_can_span;)
 
   // This is the global BlockOffsetTable.
   G1BlockOffsetTable* _bot;
@@ -225,7 +227,7 @@
   }
 
   void set_for_starts_humongous(HeapWord* obj_top, size_t fill_size);
-  void set_continues_humongous(bool is_humongous);
+  void set_object_can_span(bool can_span) PRODUCT_RETURN;
 
   void print_on(outputStream* out) PRODUCT_RETURN;
 };
--- old/src/share/vm/gc/g1/g1BlockOffsetTable.inline.hpp	2017-02-22 14:36:07.658808329 +0100
+++ new/src/share/vm/gc/g1/g1BlockOffsetTable.inline.hpp	2017-02-22 14:36:07.534803507 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -108,7 +108,8 @@
                                                                bool has_max_index,
                                                                size_t max_index) const {
   assert(_object_can_span || _bot->offset_array(_bot->index_for(_space->bottom())) == 0,
-         "normal objects can't cross region boundaries");
+         "Object crossed region boundary, found offset %u instead of 0",
+         (uint) _bot->offset_array(_bot->index_for(_space->bottom())));
   size_t index = _bot->index_for(addr);
   // We must make sure that the offset table entry we use is valid.  If
   // "addr" is past the end, start at the last known one and go forward.
--- old/src/share/vm/gc/g1/heapRegion.cpp	2017-02-22 14:36:08.314833837 +0100
+++ new/src/share/vm/gc/g1/heapRegion.cpp	2017-02-22 14:36:08.178828549 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -268,7 +268,7 @@
   _type.set_continues_humongous();
   _humongous_start_region = first_hr;
 
-  _bot_part.set_continues_humongous(true);
+  _bot_part.set_object_can_span(true);
 }
 
 void HeapRegion::clear_humongous() {
@@ -277,7 +277,7 @@
   assert(capacity() == HeapRegion::GrainBytes, "pre-condition");
   _humongous_start_region = NULL;
 
-  _bot_part.set_continues_humongous(false);
+  _bot_part.set_object_can_span(false);
 }
 
 HeapRegion::HeapRegion(uint hrm_index,