--- a/src/share/vm/c1/c1_LinearScan.cpp	Sat Dec 18 01:15:01 2010 -0800
+++ b/src/share/vm/c1/c1_LinearScan.cpp	Sat Dec 18 08:38:07 2010 -0800
@@ -90,6 +90,7 @@
  , _intervals(0)   // initialized later with correct length
  , _new_intervals_from_allocation(new IntervalList())
  , _sorted_intervals(NULL)
+ , _needs_full_resort(false)
  , _lir_ops(0)     // initialized later with correct length
  , _block_of_op(0) // initialized later with correct length
  , _has_info(0)
@@ -1520,6 +1521,14 @@
 void LinearScan::sort_intervals_before_allocation() {
   TIME_LINEAR_SCAN(timer_sort_intervals_before);
 
+  if (_needs_full_resort) {
+    // There is no known reason why this should occur but just in case...
+    assert(false, "should never occur");
+    // Re-sort existing interval list because an Interval::from() has changed
+    _sorted_intervals->sort(interval_cmp);
+    _needs_full_resort = false;
+  }
+
   IntervalList* unsorted_list = &_intervals;
   int unsorted_len = unsorted_list->length();
   int sorted_len = 0;
@@ -1559,11 +1568,18 @@
     }
   }
   _sorted_intervals = sorted_list;
+  assert(is_sorted(_sorted_intervals), "intervals unsorted");
 }
 
 void LinearScan::sort_intervals_after_allocation() {
   TIME_LINEAR_SCAN(timer_sort_intervals_after);
 
+  if (_needs_full_resort) {
+    // Re-sort existing interval list because an Interval::from() has changed
+    _sorted_intervals->sort(interval_cmp);
+    _needs_full_resort = false;
+  }
+
   IntervalArray* old_list      = _sorted_intervals;
   IntervalList*  new_list      = _new_intervals_from_allocation;
   int old_len = old_list->length();
@@ -1571,6 +1587,7 @@
 
   if (new_len == 0) {
     // no intervals have been added during allocation, so sorted list is already up to date
+    assert(is_sorted(_sorted_intervals), "intervals unsorted");
     return;
   }
 
@@ -1593,6 +1610,7 @@
   }
 
   _sorted_intervals = combined_list;
+  assert(is_sorted(_sorted_intervals), "intervals unsorted");
 }
 
 
@@ -1825,6 +1843,8 @@
       interval = interval->split(from_op_id);
       interval->assign_reg(reg, regHi);
       append_interval(interval);
+    } else {
+      _needs_full_resort = true;
     }
     assert(interval->from() == from_op_id, "must be true now");
 
@@ -4492,7 +4512,8 @@
     }
   } else {
     type_name = type2name(type());
-    if (assigned_reg() != -1) {
+    if (assigned_reg() != -1 &&
+        (LinearScan::num_physical_regs(type()) == 1 || assigned_regHi() != -1)) {
       opr = LinearScan::calc_operand_for_interval(this);
     }
   }

--- a/src/share/vm/c1/c1_LinearScan.hpp	Sat Dec 18 01:15:01 2010 -0800
+++ b/src/share/vm/c1/c1_LinearScan.hpp	Sat Dec 18 08:38:07 2010 -0800
@@ -148,6 +148,7 @@
   IntervalList              _intervals;         // mapping from register number to interval
   IntervalList*             _new_intervals_from_allocation; // list with all intervals created during allocation when an existing interval is split
   IntervalArray*            _sorted_intervals;  // intervals sorted by Interval::from()
+  bool                      _needs_full_resort; // set to true if an Interval::from() is changed and _sorted_intervals must be resorted
 
   LIR_OpArray               _lir_ops;           // mapping from LIR_Op id to LIR_Op node
   BlockBeginArray           _block_of_op;       // mapping from LIR_Op id to the BlockBegin containing this instruction

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/compiler/6579789/Test6579789.java	Sat Dec 18 08:38:07 2010 -0800
@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2010, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+/**
+ * @test
+ * @bug 6579789
+ * @summary Internal error "c1_LinearScan.cpp:1429 Error: assert(false,"")" in debuggee with fastdebug VM
+ * @run main/othervm -Xcomp -XX:UseSSE=0 -XX:CompileOnly=Test6579789.bug Test6579789
+ */
+
+public class Test6579789 {
+    public static void main(String[] args) {
+        bug(4);
+    }
+    public static void bug(int n) {
+        float f = 1;
+        int i = 1;
+        try {
+            int x = 1 / n; // instruction that can trap
+            f = 2;
+            i = 2;
+            int y = 2 / n; // instruction that can trap
+        } catch (Exception ex) {
+            f++;
+            i++;
+        }
+    }
+}