1 /*
   2  * Copyright (c) 2006, 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "memory/allocation.inline.hpp"
  27 #include "opto/connode.hpp"
  28 #include "opto/convertnode.hpp"
  29 #include "opto/loopnode.hpp"
  30 #include "opto/opaquenode.hpp"
  31 #include "opto/rootnode.hpp"
  32 
  33 //================= Loop Unswitching =====================
  34 //
  35 // orig:                       transformed:
  36 //                               if (invariant-test) then
  37 //  predicate                      predicate
  38 //  loop                           loop
  39 //    stmt1                          stmt1
  40 //    if (invariant-test) then       stmt2
  41 //      stmt2                        stmt4
  42 //    else                         endloop
  43 //      stmt3                    else
  44 //    endif                        predicate [clone]
  45 //    stmt4                        loop [clone]
  46 //  endloop                          stmt1 [clone]
  47 //                                   stmt3
  48 //                                   stmt4 [clone]
  49 //                                 endloop
  50 //                               endif
  51 //
  52 // Note: the "else" clause may be empty
  53 
  54 //------------------------------policy_unswitching-----------------------------
  55 // Return TRUE or FALSE if the loop should be unswitched
  56 // (ie. clone loop with an invariant test that does not exit the loop)
  57 bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
  58   if( !LoopUnswitching ) {
  59     return false;
  60   }
  61   if (!_head->is_Loop()) {
  62     return false;
  63   }
  64 
  65   // check for vectorized loops, any unswitching was already applied
  66   if (_head->is_CountedLoop() && _head->as_CountedLoop()->ignore_slp()) {
  67     return false;
  68   }
  69 
  70   int nodes_left = phase->C->max_node_limit() - phase->C->live_nodes();
  71   if ((int)(2 * _body.size()) > nodes_left) {
  72     return false; // Too speculative if running low on nodes.
  73   }
  74   LoopNode* head = _head->as_Loop();
  75   if (head->unswitch_count() + 1 > head->unswitch_max()) {
  76     return false;
  77   }
  78   return phase->find_unswitching_candidate(this) != NULL;
  79 }
  80 
  81 //------------------------------find_unswitching_candidate-----------------------------
  82 // Find candidate "if" for unswitching
  83 IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
  84 
  85   // Find first invariant test that doesn't exit the loop
  86   LoopNode *head = loop->_head->as_Loop();
  87   IfNode* unswitch_iff = NULL;
  88   Node* n = head->in(LoopNode::LoopBackControl);
  89   while (n != head) {
  90     Node* n_dom = idom(n);
  91     if (n->is_Region()) {
  92       if (n_dom->is_If()) {
  93         IfNode* iff = n_dom->as_If();
  94         if (iff->in(1)->is_Bool()) {
  95           BoolNode* bol = iff->in(1)->as_Bool();
  96           if (bol->in(1)->is_Cmp()) {
  97             // If condition is invariant and not a loop exit,
  98             // then found reason to unswitch.
  99             if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
 100               unswitch_iff = iff;
 101             }
 102           }
 103         }
 104       }
 105     }
 106     n = n_dom;
 107   }
 108   return unswitch_iff;
 109 }
 110 
 111 //------------------------------do_unswitching-----------------------------
 112 // Clone loop with an invariant test (that does not exit) and
 113 // insert a clone of the test that selects which version to
 114 // execute.
 115 void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {
 116 
 117   // Find first invariant test that doesn't exit the loop
 118   LoopNode *head = loop->_head->as_Loop();
 119 
 120   IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
 121   assert(unswitch_iff != NULL, "should be at least one");
 122 
 123 #ifndef PRODUCT
 124   if (TraceLoopOpts) {
 125     tty->print("Unswitch   %d ", head->unswitch_count()+1);
 126     loop->dump_head();
 127   }
 128 #endif
 129 
 130   // Need to revert back to normal loop
 131   if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
 132     head->as_CountedLoop()->set_normal_loop();
 133   }
 134 
 135   ProjNode* proj_true = create_slow_version_of_loop(loop, old_new);
 136 
 137 #ifdef ASSERT
 138   Node* uniqc = proj_true->unique_ctrl_out();
 139   Node* entry = head->in(LoopNode::EntryControl);
 140   Node* predicate = find_predicate(entry);
 141   if (predicate != NULL && LoopLimitCheck && UseLoopPredicate) {
 142     // We may have two predicates, find first.
 143     entry = find_predicate(entry->in(0)->in(0));
 144     if (entry != NULL) predicate = entry;
 145   }
 146   if (predicate != NULL) predicate = predicate->in(0);
 147   assert(proj_true->is_IfTrue() &&
 148          (predicate == NULL && uniqc == head ||
 149           predicate != NULL && uniqc == predicate), "by construction");
 150 #endif
 151   // Increment unswitch count
 152   LoopNode* head_clone = old_new[head->_idx]->as_Loop();
 153   int nct = head->unswitch_count() + 1;
 154   head->set_unswitch_count(nct);
 155   head_clone->set_unswitch_count(nct);
 156 
 157   // Add test to new "if" outside of loop
 158   IfNode* invar_iff   = proj_true->in(0)->as_If();
 159   Node* invar_iff_c   = invar_iff->in(0);
 160   BoolNode* bol       = unswitch_iff->in(1)->as_Bool();
 161   invar_iff->set_req(1, bol);
 162   invar_iff->_prob    = unswitch_iff->_prob;
 163 
 164   ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
 165 
 166   // Hoist invariant casts out of each loop to the appropriate
 167   // control projection.
 168 
 169   Node_List worklist;
 170 
 171   for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
 172     ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
 173     // Copy to a worklist for easier manipulation
 174     for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
 175       Node* use = proj->fast_out(j);
 176       if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
 177         worklist.push(use);
 178       }
 179     }
 180     ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
 181     while (worklist.size() > 0) {
 182       Node* use = worklist.pop();
 183       Node* nuse = use->clone();
 184       nuse->set_req(0, invar_proj);
 185       _igvn.replace_input_of(use, 1, nuse);
 186       register_new_node(nuse, invar_proj);
 187       // Same for the clone
 188       Node* use_clone = old_new[use->_idx];
 189       _igvn.replace_input_of(use_clone, 1, nuse);
 190     }
 191   }
 192 
 193   // Hardwire the control paths in the loops into if(true) and if(false)
 194   _igvn.rehash_node_delayed(unswitch_iff);
 195   short_circuit_if(unswitch_iff, proj_true);
 196 
 197   IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
 198   _igvn.rehash_node_delayed(unswitch_iff_clone);
 199   short_circuit_if(unswitch_iff_clone, proj_false);
 200 
 201   // Reoptimize loops
 202   loop->record_for_igvn();
 203   for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
 204     Node *n = loop->_body[i];
 205     Node *n_clone = old_new[n->_idx];
 206     _igvn._worklist.push(n_clone);
 207   }
 208 
 209 #ifndef PRODUCT
 210   if (TraceLoopUnswitching) {
 211     tty->print_cr("Loop unswitching orig: %d @ %d  new: %d @ %d",
 212                   head->_idx,                unswitch_iff->_idx,
 213                   old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
 214   }
 215 #endif
 216 
 217   C->set_major_progress();
 218 }
 219 
 220 //-------------------------create_slow_version_of_loop------------------------
 221 // Create a slow version of the loop by cloning the loop
 222 // and inserting an if to select fast-slow versions.
 223 // Return control projection of the entry to the fast version.
 224 ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
 225                                                       Node_List &old_new) {
 226   LoopNode* head  = loop->_head->as_Loop();
 227   bool counted_loop = head->is_CountedLoop();
 228   Node*     entry = head->in(LoopNode::EntryControl);
 229   _igvn.rehash_node_delayed(entry);
 230   IdealLoopTree* outer_loop = loop->_parent;
 231 
 232   Node *cont      = _igvn.intcon(1);
 233   set_ctrl(cont, C->root());
 234   Node* opq       = new Opaque1Node(C, cont);
 235   register_node(opq, outer_loop, entry, dom_depth(entry));
 236   Node *bol       = new Conv2BNode(opq);
 237   register_node(bol, outer_loop, entry, dom_depth(entry));
 238   IfNode* iff = new IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN);
 239   register_node(iff, outer_loop, entry, dom_depth(entry));
 240   ProjNode* iffast = new IfTrueNode(iff);
 241   register_node(iffast, outer_loop, iff, dom_depth(iff));
 242   ProjNode* ifslow = new IfFalseNode(iff);
 243   register_node(ifslow, outer_loop, iff, dom_depth(iff));
 244 
 245   // Clone the loop body.  The clone becomes the fast loop.  The
 246   // original pre-header will (illegally) have 3 control users
 247   // (old & new loops & new if).
 248   clone_loop(loop, old_new, dom_depth(head), iff);
 249   assert(old_new[head->_idx]->is_Loop(), "" );
 250 
 251   // Fast (true) control
 252   Node* iffast_pred = clone_loop_predicates(entry, iffast, !counted_loop);
 253   _igvn.replace_input_of(head, LoopNode::EntryControl, iffast_pred);
 254   set_idom(head, iffast_pred, dom_depth(head));
 255 
 256   // Slow (false) control
 257   Node* ifslow_pred = clone_loop_predicates(entry, ifslow, !counted_loop);
 258   LoopNode* slow_head = old_new[head->_idx]->as_Loop();
 259   _igvn.replace_input_of(slow_head, LoopNode::EntryControl, ifslow_pred);
 260   set_idom(slow_head, ifslow_pred, dom_depth(slow_head));
 261 
 262   recompute_dom_depth();
 263 
 264   return iffast;
 265 }