--- old/src/hotspot/share/gc/g1/survRateGroup.cpp	2019-06-04 13:17:07.732651051 -0700
+++ new/src/hotspot/share/gc/g1/survRateGroup.cpp	2019-06-04 13:17:07.472651060 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2019, 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
@@ -37,7 +37,8 @@
   _surv_rate_pred(NULL),
   _all_regions_allocated(0),
   _region_num(0),
-  _setup_seq_num(0)
+  _setup_seq_num(0),
+  _retained_region_num(0)
 {
   reset();
   start_adding_regions();
@@ -49,6 +50,7 @@
   _last_pred             = 0.0;
   // the following will set up the arrays with length 1
   _region_num            = 1;
+  _retained_region_num   = 0;
 
   // The call to stop_adding_regions() will use "new" to refill
   // the _surv_rate_pred array, so we need to make sure to call
@@ -72,7 +74,9 @@
 
 void SurvRateGroup::start_adding_regions() {
   _setup_seq_num   = _stats_arrays_length;
-  _region_num      = 0;
+  // Retained region number should be reflected to address actual reused case.
+  _region_num      = _retained_region_num;
+  _retained_region_num = 0;
 }
 
 void SurvRateGroup::stop_adding_regions() {
@@ -90,7 +94,8 @@
 
 void SurvRateGroup::record_surviving_words(int age_in_group, size_t surv_words) {
   guarantee( 0 <= age_in_group && (size_t) age_in_group < _region_num,
-             "pre-condition" );
+             "Age in group (" PTR_FORMAT ") should be [0, " SIZE_FORMAT "), but it is %d",
+             p2i(this), _region_num, age_in_group);
 
   double surv_rate = (double) surv_words / (double) HeapRegion::GrainWords;
   _surv_rate_pred[age_in_group]->add(surv_rate);