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 * 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

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 */

//================= Loop Unswitching =====================

//

// orig:                       transformed:

//                               if (invariant-test) then

//  loop                           loop

//    stmt1                          stmt1

//    if (invariant-test) then       stmt2

//      stmt2                        stmt4

//    else                         endloop

//      stmt3                    else

//    endif                        loop [clone]

//    stmt4                          stmt1 [clone]

//  endloop                          stmt3

//                                   stmt4 [clone]

//                                 endloop

//                               endif

//

// Note: the "else" clause may be empty

//------------------------------policy_unswitching-----------------------------

// Return TRUE or FALSE if the loop should be unswitched

// (ie. clone loop with an invariant test that does not exit the loop)

bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {

  if( !LoopUnswitching ) {

    return false;

  }

  if (!_head->is_Loop()) {

    return false;

  }

  uint nodes_left = MaxNodeLimit - phase->C->unique();

  if (2 * _body.size() > nodes_left) {

    return false; // Too speculative if running low on nodes.

  }

  LoopNode* head = _head->as_Loop();

  if (head->unswitch_count() + 1 > head->unswitch_max()) {

    return false;

  }

  return phase->find_unswitching_candidate(this) != NULL;

}

//------------------------------find_unswitching_candidate-----------------------------

// Find candidate "if" for unswitching

IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {

  // Find first invariant test that doesn't exit the loop

  LoopNode *head = loop->_head->as_Loop();

  IfNode* unswitch_iff = NULL;

  Node* n = head->in(LoopNode::LoopBackControl);

  while (n != head) {

    Node* n_dom = idom(n);

    if (n->is_Region()) {

      if (n_dom->is_If()) {

        IfNode* iff = n_dom->as_If();

        if (iff->in(1)->is_Bool()) {

          BoolNode* bol = iff->in(1)->as_Bool();

          if (bol->in(1)->is_Cmp()) {

            // If condition is invariant and not a loop exit,

            // then found reason to unswitch.

            if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {

              unswitch_iff = iff;

            }

          }

        }

      }

    }

    n = n_dom;

  }

  return unswitch_iff;

}

//------------------------------do_unswitching-----------------------------

// Clone loop with an invariant test (that does not exit) and

// insert a clone of the test that selects which version to

// execute.

void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {

  // Find first invariant test that doesn't exit the loop

  LoopNode *head = loop->_head->as_Loop();

  IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);

  assert(unswitch_iff != NULL, "should be at least one");

  // Need to revert back to normal loop

  if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {

    head->as_CountedLoop()->set_normal_loop();

  }

  ProjNode* proj_true = create_slow_version_of_loop(loop, old_new);

  assert(proj_true->is_IfTrue() && proj_true->unique_ctrl_out() == head, "by construction");

  // Increment unswitch count

  LoopNode* head_clone = old_new[head->_idx]->as_Loop();

  int nct = head->unswitch_count() + 1;

  head->set_unswitch_count(nct);

  head_clone->set_unswitch_count(nct);

  // Add test to new "if" outside of loop

  IfNode* invar_iff   = proj_true->in(0)->as_If();

  Node* invar_iff_c   = invar_iff->in(0);

  BoolNode* bol       = unswitch_iff->in(1)->as_Bool();

  invar_iff->set_req(1, bol);

  invar_iff->_prob    = unswitch_iff->_prob;

  ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();

  // Hoist invariant casts out of each loop to the appropriate

  // control projection.

  Node_List worklist;

  for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {

    ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();

    // Copy to a worklist for easier manipulation

    for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {

      Node* use = proj->fast_out(j);

      if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {

        worklist.push(use);

      }

    }

    ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();

    while (worklist.size() > 0) {

      Node* use = worklist.pop();

      Node* nuse = use->clone();

      nuse->set_req(0, invar_proj);

      _igvn.hash_delete(use);

      use->set_req(1, nuse);

      _igvn._worklist.push(use);

      register_new_node(nuse, invar_proj);

      // Same for the clone

      Node* use_clone = old_new[use->_idx];

      _igvn.hash_delete(use_clone);

      use_clone->set_req(1, nuse);

      _igvn._worklist.push(use_clone);

    }

  }

  // Hardwire the control paths in the loops into if(true) and if(false)

  _igvn.hash_delete(unswitch_iff);

  short_circuit_if(unswitch_iff, proj_true);

  _igvn._worklist.push(unswitch_iff);

  IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();

  _igvn.hash_delete(unswitch_iff_clone);

  short_circuit_if(unswitch_iff_clone, proj_false);

  _igvn._worklist.push(unswitch_iff_clone);

  // Reoptimize loops

  loop->record_for_igvn();

  for(int i = loop->_body.size() - 1; i >= 0 ; i--) {

    Node *n = loop->_body[i];

    Node *n_clone = old_new[n->_idx];

    _igvn._worklist.push(n_clone);

  }

#ifndef PRODUCT

  if (TraceLoopUnswitching) {

    tty->print_cr("Loop unswitching orig: %d @ %d  new: %d @ %d",

                  head->_idx,                unswitch_iff->_idx,

                  old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);

  }

#endif

  C->set_major_progress();

}

//-------------------------create_slow_version_of_loop------------------------

// Create a slow version of the loop by cloning the loop

// and inserting an if to select fast-slow versions.

// Return control projection of the entry to the fast version.

ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,

                                                      Node_List &old_new) {

  LoopNode* head  = loop->_head->as_Loop();

  Node*     entry = head->in(LoopNode::EntryControl);

  _igvn.hash_delete(entry);

  _igvn._worklist.push(entry);

  IdealLoopTree* outer_loop = loop->_parent;

  Node *cont      = _igvn.intcon(1);

  set_ctrl(cont, C->root());

  Node* opq       = new (C, 2) Opaque1Node(C, cont);

  register_node(opq, outer_loop, entry, dom_depth(entry));

  Node *bol       = new (C, 2) Conv2BNode(opq);

  register_node(bol, outer_loop, entry, dom_depth(entry));

  IfNode* iff = new (C, 2) IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN);

  register_node(iff, outer_loop, entry, dom_depth(entry));

  ProjNode* iffast = new (C, 1) IfTrueNode(iff);

  register_node(iffast, outer_loop, iff, dom_depth(iff));

  ProjNode* ifslow = new (C, 1) 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 2 control users (old & new loops).

  clone_loop(loop, old_new, dom_depth(head), iff);

  assert(old_new[head->_idx]->is_Loop(), "" );

  // Fast (true) control

  _igvn.hash_delete(head);

  head->set_req(LoopNode::EntryControl, iffast);

  set_idom(head, iffast, dom_depth(head));

  _igvn._worklist.push(head);

  // Slow (false) control

  LoopNode* slow_head = old_new[head->_idx]->as_Loop();

  _igvn.hash_delete(slow_head);

  slow_head->set_req(LoopNode::EntryControl, ifslow);

  set_idom(slow_head, ifslow, dom_depth(slow_head));

  _igvn._worklist.push(slow_head);

  recompute_dom_depth();

  return iffast;

}