--- a/hotspot/src/share/vm/opto/c2_globals.hpp	Fri Oct 09 15:00:17 2015 +0200
+++ b/hotspot/src/share/vm/opto/c2_globals.hpp	Fri Oct 09 12:17:58 2015 -0700
@@ -342,6 +342,9 @@
   product(bool, SuperWordReductions, true,                                  \
           "Enable reductions support in superword.")                        \
                                                                             \
+  product(bool, DoReserveCopyInSuperWord, true,                             \
+          "Create reserve copy of graph in SuperWord.")                     \
+                                                                            \
   notproduct(bool, TraceSuperWord, false,                                   \
           "Trace superword transforms")                                     \
                                                                             \

--- a/hotspot/src/share/vm/opto/loopUnswitch.cpp	Fri Oct 09 15:00:17 2015 +0200
+++ b/hotspot/src/share/vm/opto/loopUnswitch.cpp	Fri Oct 09 12:17:58 2015 -0700
@@ -263,3 +263,136 @@
 
   return iffast;
 }
+
+LoopNode* PhaseIdealLoop::create_reserve_version_of_loop(IdealLoopTree *loop, CountedLoopReserveKit* lk) {
+  Node_List old_new;
+  LoopNode* head  = loop->_head->as_Loop();
+  bool counted_loop = head->is_CountedLoop();
+  Node*     entry = head->in(LoopNode::EntryControl);
+  _igvn.rehash_node_delayed(entry);
+  IdealLoopTree* outer_loop = loop->_parent;
+
+  ConINode* const_1 = _igvn.intcon(1);
+  set_ctrl(const_1, C->root());
+  IfNode* iff = new IfNode(entry, const_1, PROB_MAX, COUNT_UNKNOWN);
+  register_node(iff, outer_loop, entry, dom_depth(entry));
+  ProjNode* iffast = new IfTrueNode(iff);
+  register_node(iffast, outer_loop, iff, dom_depth(iff));
+  ProjNode* ifslow = new IfFalseNode(iff);
+  register_node(ifslow, outer_loop, iff, dom_depth(iff));
+
+  // Clone the loop body.  The clone becomes the fast loop.  The
+  // original pre-header will (illegally) have 3 control users
+  // (old & new loops & new if).
+  clone_loop(loop, old_new, dom_depth(head), iff);
+  assert(old_new[head->_idx]->is_Loop(), "" );
+
+  LoopNode* slow_head = old_new[head->_idx]->as_Loop();
+
+#ifndef PRODUCT
+  if (TraceLoopOpts) {
+    tty->print_cr("PhaseIdealLoop::create_reserve_version_of_loop:");
+    tty->print("\t iff = %d, ", iff->_idx); iff->dump();
+    tty->print("\t iffast = %d, ", iffast->_idx); iffast->dump();
+    tty->print("\t ifslow = %d, ", ifslow->_idx); ifslow->dump();
+    tty->print("\t before replace_input_of: head = %d, ", head->_idx); head->dump();
+    tty->print("\t before replace_input_of: slow_head = %d, ", slow_head->_idx); slow_head->dump();
+  }
+#endif
+
+  // Fast (true) control
+  _igvn.replace_input_of(head, LoopNode::EntryControl, iffast);
+  // Slow (false) control
+  _igvn.replace_input_of(slow_head, LoopNode::EntryControl, ifslow);
+
+  recompute_dom_depth();
+
+  lk->set_iff(iff);
+
+#ifndef PRODUCT
+  if (TraceLoopOpts ) {
+    tty->print("\t after  replace_input_of: head = %d, ", head->_idx); head->dump();
+    tty->print("\t after  replace_input_of: slow_head = %d, ", slow_head->_idx); slow_head->dump();
+  }
+#endif
+
+  return slow_head->as_Loop();
+}
+
+CountedLoopReserveKit::CountedLoopReserveKit(PhaseIdealLoop* phase, IdealLoopTree *loop, bool active = true) :
+  _phase(phase),
+  _lpt(loop),
+  _lp(NULL),
+  _iff(NULL),
+  _lp_reserved(NULL),
+  _has_reserved(false),
+  _use_new(false),
+  _active(active)
+  {
+    create_reserve();
+  };
+
+CountedLoopReserveKit::~CountedLoopReserveKit() {
+  if (!_active) {
+    return;
+  }
+
+  if (_has_reserved && !_use_new) {
+    // intcon(0)->iff-node reverts CF to the reserved copy
+    ConINode* const_0 = _phase->_igvn.intcon(0);
+    _phase->set_ctrl(const_0, _phase->C->root());
+    _iff->set_req(1, const_0);
+
+    #ifndef PRODUCT
+      if (TraceLoopOpts) {
+        tty->print_cr("CountedLoopReserveKit::~CountedLoopReserveKit()");
+        tty->print("\t discard loop %d and revert to the reserved loop clone %d: ", _lp->_idx, _lp_reserved->_idx);
+        _lp_reserved->dump();
+      }
+    #endif
+  }
+}
+
+bool CountedLoopReserveKit::create_reserve() {
+  if (!_active) {
+    return false;
+  }
+
+  if(!_lpt->_head->is_CountedLoop()) {
+    NOT_PRODUCT(if(TraceLoopOpts) {tty->print_cr("CountedLoopReserveKit::create_reserve: %d not counted loop", _lpt->_head->_idx);})
+    return false;
+  }
+  CountedLoopNode *cl = _lpt->_head->as_CountedLoop();
+  if (!cl->is_valid_counted_loop()) {
+    NOT_PRODUCT(if(TraceLoopOpts) {tty->print_cr("CountedLoopReserveKit::create_reserve: %d not valid counted loop", cl->_idx);})
+    return false; // skip malformed counted loop
+  }
+  if (!cl->is_main_loop()) {
+    NOT_PRODUCT(if(TraceLoopOpts) {tty->print_cr("CountedLoopReserveKit::create_reserve: %d not main loop", cl->_idx);})
+    return false; // skip normal, pre, and post loops
+  }
+
+  _lp = _lpt->_head->as_Loop();
+  _lp_reserved = _phase->create_reserve_version_of_loop(_lpt, this);
+
+  if (!_lp_reserved->is_CountedLoop()) {
+    return false;
+  }
+
+  Node* ifslow_pred = _lp_reserved->as_CountedLoop()->in(LoopNode::EntryControl);
+
+  if (!ifslow_pred->is_IfFalse()) {
+    return false;
+  }
+
+  Node* iff = ifslow_pred->in(0);
+  if (!iff->is_If() || iff != _iff) {
+    return false;
+  }
+
+  if (iff->in(1)->Opcode() != Op_ConI) {
+    return false;
+  }
+
+  return _has_reserved = true;
+}

--- a/hotspot/src/share/vm/opto/loopnode.hpp	Fri Oct 09 15:00:17 2015 +0200
+++ b/hotspot/src/share/vm/opto/loopnode.hpp	Fri Oct 09 12:17:58 2015 -0700
@@ -38,6 +38,7 @@
 class LoopNode;
 class Node;
 class PhaseIdealLoop;
+class CountedLoopReserveKit;
 class VectorSet;
 class Invariance;
 struct small_cache;
@@ -529,6 +530,8 @@
 class PhaseIdealLoop : public PhaseTransform {
   friend class IdealLoopTree;
   friend class SuperWord;
+  friend class CountedLoopReserveKit;
+
   // Pre-computed def-use info
   PhaseIterGVN &_igvn;
 
@@ -965,6 +968,16 @@
   ProjNode* create_slow_version_of_loop(IdealLoopTree *loop,
                                         Node_List &old_new);
 
+  // Clone a loop and return the clone head (clone_loop_head).
+  // Added nodes include int(1), int(0) - disconnected, If, IfTrue, IfFalse,
+  // This routine was created for usage in CountedLoopReserveKit.
+  //
+  //    int(1) -> If -> IfTrue -> original_loop_head
+  //              |
+  //              V
+  //           IfFalse -> clone_loop_head (returned by function pointer)
+  //
+  LoopNode* create_reserve_version_of_loop(IdealLoopTree *loop, CountedLoopReserveKit* lk);
   // Clone loop with an invariant test (that does not exit) and
   // insert a clone of the test that selects which version to
   // execute.
@@ -1117,6 +1130,68 @@
 #endif
 };
 
+// This kit may be used for making of a reserved copy of a loop before this loop
+//  goes under non-reversible changes.
+//
+// Function create_reserve() creates a reserved copy (clone) of the loop.
+// The reserved copy is created by calling
+// PhaseIdealLoop::create_reserve_version_of_loop - see there how
+// the original and reserved loops are connected in the outer graph.
+// If create_reserve succeeded, it returns 'true' and _has_reserved is set to 'true'.
+//
+// By default the reserved copy (clone) of the loop is created as dead code - it is
+// dominated in the outer loop by this node chain:
+//   intcon(1)->If->IfFalse->reserved_copy.
+// The original loop is dominated by the the same node chain but IfTrue projection:
+//   intcon(1)->If->IfTrue->original_loop.
+//
+// In this implementation of CountedLoopReserveKit the ctor includes create_reserve()
+// and the dtor, checks _use_new value.
+// If _use_new == false, it "switches" control to reserved copy of the loop
+// by simple replacing of node intcon(1) with node intcon(0).
+//
+// Here is a proposed example of usage (see also SuperWord::output in superword.cpp).
+//
+// void CountedLoopReserveKit_example()
+// {
+//    CountedLoopReserveKit lrk((phase, lpt, DoReserveCopy = true); // create local object
+//    if (DoReserveCopy && !lrk.has_reserved()) {
+//      return; //failed to create reserved loop copy
+//    }
+//    ...
+//    //something is wrong, switch to original loop
+///   if(something_is_wrong) return; // ~CountedLoopReserveKit makes the switch
+//    ...
+//    //everything worked ok, return with the newly modified loop
+//    lrk.use_new();
+//    return; // ~CountedLoopReserveKit does nothing once use_new() was called
+//  }
+//
+// Keep in mind, that by default if create_reserve() is not followed by use_new()
+// the dtor will "switch to the original" loop.
+// NOTE. You you modify outside of the original loop this class is no help.
+//
+class CountedLoopReserveKit {
+  private:
+    PhaseIdealLoop* _phase;
+    IdealLoopTree*  _lpt;
+    LoopNode*       _lp;
+    IfNode*         _iff;
+    LoopNode*       _lp_reserved;
+    bool            _has_reserved;
+    bool            _use_new;
+    const bool      _active; //may be set to false in ctor, then the object is dummy
+
+  public:
+    CountedLoopReserveKit(PhaseIdealLoop* phase, IdealLoopTree *loop, bool active);
+    ~CountedLoopReserveKit();
+    void use_new()                {_use_new = true;}
+    void set_iff(IfNode* x)       {_iff = x;}
+    bool has_reserved()     const { return _active && _has_reserved;}
+  private:
+    bool create_reserve();
+};// class CountedLoopReserveKit
+
 inline Node* IdealLoopTree::tail() {
 // Handle lazy update of _tail field
   Node *n = _tail;

--- a/hotspot/src/share/vm/opto/superword.cpp	Fri Oct 09 15:00:17 2015 +0200
+++ b/hotspot/src/share/vm/opto/superword.cpp	Fri Oct 09 12:17:58 2015 -0700
@@ -81,6 +81,10 @@
   if (_phase->C->method() != NULL) {
     _phase->C->method()->has_option_value("VectorizeDebug", _vector_loop_debug);
   }
+  _CountedLoopReserveKit_debug = 0;
+  if (_phase->C->method() != NULL) {
+    _phase->C->method()->has_option_value("DoReserveCopyInSuperWordDebug", _CountedLoopReserveKit_debug);
+  }
 #endif
 }
 
@@ -1763,6 +1767,22 @@
   }
 }
 
+#ifndef PRODUCT
+void SuperWord::print_loop(bool whole) {
+  Node_Stack stack(_arena, _phase->C->unique() >> 2);
+  Node_List rpo_list;
+  VectorSet visited(_arena);
+  visited.set(lpt()->_head->_idx);
+  _phase->rpo(lpt()->_head, stack, visited, rpo_list);
+  _phase->dump(lpt(), rpo_list.size(), rpo_list );
+  if(whole) {
+    tty->print_cr("\n Whole loop tree");
+    _phase->dump();
+    tty->print_cr(" End of whole loop tree\n");
+  }
+}
+#endif
+
 //------------------------------output---------------------------
 // Convert packs into vector node operations
 void SuperWord::output() {
@@ -1770,7 +1790,7 @@
 
 #ifndef PRODUCT
   if (TraceLoopOpts) {
-    tty->print("SuperWord    ");
+    tty->print("SuperWord::output    ");
     lpt()->dump_head();
   }
 #endif
@@ -1789,6 +1809,18 @@
   CountedLoopNode *cl = lpt()->_head->as_CountedLoop();
   uint max_vlen_in_bytes = 0;
   uint max_vlen = 0;
+
+  NOT_PRODUCT(if(_CountedLoopReserveKit_debug > 0) {tty->print_cr("SWPointer::output: print loop before create_reserve_version_of_loop"); print_loop(true);})
+
+  CountedLoopReserveKit make_reversable(_phase, _lpt, DoReserveCopyInSuperWord);
+
+  NOT_PRODUCT(if(_CountedLoopReserveKit_debug > 0) {tty->print_cr("SWPointer::output: print loop after create_reserve_version_of_loop"); print_loop(true);})
+
+  if (DoReserveCopyInSuperWord && !make_reversable.has_reserved()) {
+    NOT_PRODUCT({tty->print_cr("SWPointer::output: loop was not reserved correctly, exiting SuperWord");})
+    return;
+  }
+
   for (int i = 0; i < _block.length(); i++) {
     Node* n = _block.at(i);
     Node_List* p = my_pack(n);
@@ -1888,6 +1920,7 @@
     }
   }
   C->set_max_vector_size(max_vlen_in_bytes);
+
   if (SuperWordLoopUnrollAnalysis) {
     if (cl->has_passed_slp()) {
       uint slp_max_unroll_factor = cl->slp_max_unroll();
@@ -1900,6 +1933,12 @@
       }
     }
   }
+
+  if (DoReserveCopyInSuperWord) {
+    make_reversable.use_new();
+  }
+  NOT_PRODUCT(if(_CountedLoopReserveKit_debug > 0) {tty->print_cr("\n Final loop after SuperWord"); print_loop(true);})
+  return;
 }
 
 //------------------------------vector_opd---------------------------

--- a/hotspot/src/share/vm/opto/superword.hpp	Fri Oct 09 15:00:17 2015 +0200
+++ b/hotspot/src/share/vm/opto/superword.hpp	Fri Oct 09 12:17:58 2015 -0700
@@ -299,6 +299,7 @@
   GrowableArray<int> _ii_order;
 #ifndef PRODUCT
   uintx          _vector_loop_debug; // provide more printing in debug mode
+  uintx          _CountedLoopReserveKit_debug; // for debugging CountedLoopReserveKit
 #endif
 
   // Accessors
@@ -375,6 +376,7 @@
   // Tracing support
   #ifndef PRODUCT
   void find_adjacent_refs_trace_1(Node* best_align_to_mem_ref, int best_iv_adjustment);
+  void print_loop(bool whole);
   #endif
   // Find a memory reference to align the loop induction variable to.
   MemNode* find_align_to_ref(Node_List &memops);