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1 /*
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2 * Copyright 2006 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 #include "incls/_precompiled.incl"
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26 #include "incls/_loopUnswitch.cpp.incl"
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27
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28 //================= Loop Unswitching =====================
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29 //
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30 // orig: transformed:
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31 // if (invariant-test) then
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32 // loop loop
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33 // stmt1 stmt1
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34 // if (invariant-test) then stmt2
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35 // stmt2 stmt4
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36 // else endloop
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37 // stmt3 else
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38 // endif loop [clone]
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39 // stmt4 stmt1 [clone]
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40 // endloop stmt3
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41 // stmt4 [clone]
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42 // endloop
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43 // endif
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44 //
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45 // Note: the "else" clause may be empty
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46
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47 //------------------------------policy_unswitching-----------------------------
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48 // Return TRUE or FALSE if the loop should be unswitched
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49 // (ie. clone loop with an invariant test that does not exit the loop)
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50 bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
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51 if( !LoopUnswitching ) {
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52 return false;
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53 }
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54 uint nodes_left = MaxNodeLimit - phase->C->unique();
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55 if (2 * _body.size() > nodes_left) {
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56 return false; // Too speculative if running low on nodes.
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57 }
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58 LoopNode* head = _head->as_Loop();
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59 if (head->unswitch_count() + 1 > head->unswitch_max()) {
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60 return false;
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61 }
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62 return phase->find_unswitching_candidate(this) != NULL;
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63 }
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64
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65 //------------------------------find_unswitching_candidate-----------------------------
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66 // Find candidate "if" for unswitching
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67 IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
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68
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69 // Find first invariant test that doesn't exit the loop
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70 LoopNode *head = loop->_head->as_Loop();
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71 IfNode* unswitch_iff = NULL;
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72 Node* n = head->in(LoopNode::LoopBackControl);
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73 while (n != head) {
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74 Node* n_dom = idom(n);
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75 if (n->is_Region()) {
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76 if (n_dom->is_If()) {
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77 IfNode* iff = n_dom->as_If();
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78 if (iff->in(1)->is_Bool()) {
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79 BoolNode* bol = iff->in(1)->as_Bool();
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80 if (bol->in(1)->is_Cmp()) {
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81 // If condition is invariant and not a loop exit,
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82 // then found reason to unswitch.
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83 if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
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84 unswitch_iff = iff;
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85 }
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86 }
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87 }
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88 }
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89 }
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90 n = n_dom;
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91 }
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92 return unswitch_iff;
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93 }
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94
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95 //------------------------------do_unswitching-----------------------------
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96 // Clone loop with an invariant test (that does not exit) and
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97 // insert a clone of the test that selects which version to
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98 // execute.
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99 void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {
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100
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101 // Find first invariant test that doesn't exit the loop
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102 LoopNode *head = loop->_head->as_Loop();
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103
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104 IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
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105 assert(unswitch_iff != NULL, "should be at least one");
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106
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107 // Need to revert back to normal loop
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108 if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
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109 head->as_CountedLoop()->set_normal_loop();
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110 }
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111
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112 ProjNode* proj_true = create_slow_version_of_loop(loop, old_new);
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113
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114 assert(proj_true->is_IfTrue() && proj_true->unique_ctrl_out() == head, "by construction");
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115
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116 // Increment unswitch count
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117 LoopNode* head_clone = old_new[head->_idx]->as_Loop();
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118 int nct = head->unswitch_count() + 1;
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119 head->set_unswitch_count(nct);
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120 head_clone->set_unswitch_count(nct);
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121
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122 // Add test to new "if" outside of loop
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123 IfNode* invar_iff = proj_true->in(0)->as_If();
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124 Node* invar_iff_c = invar_iff->in(0);
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125 BoolNode* bol = unswitch_iff->in(1)->as_Bool();
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126 invar_iff->set_req(1, bol);
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127 invar_iff->_prob = unswitch_iff->_prob;
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128
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129 ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
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130
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131 // Hoist invariant casts out of each loop to the appropiate
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132 // control projection.
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133
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134 Node_List worklist;
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135
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136 for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
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137 ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
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138 // Copy to a worklist for easier manipulation
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139 for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
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140 Node* use = proj->fast_out(j);
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141 if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
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142 worklist.push(use);
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143 }
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144 }
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145 ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
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146 while (worklist.size() > 0) {
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147 Node* use = worklist.pop();
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148 Node* nuse = use->clone();
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149 nuse->set_req(0, invar_proj);
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150 _igvn.hash_delete(use);
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151 use->set_req(1, nuse);
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152 _igvn._worklist.push(use);
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153 register_new_node(nuse, invar_proj);
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154 // Same for the clone
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155 Node* use_clone = old_new[use->_idx];
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156 _igvn.hash_delete(use_clone);
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157 use_clone->set_req(1, nuse);
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158 _igvn._worklist.push(use_clone);
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159 }
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160 }
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161
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162 // Hardwire the control paths in the loops into if(true) and if(false)
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163 _igvn.hash_delete(unswitch_iff);
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164 short_circuit_if(unswitch_iff, proj_true);
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165 _igvn._worklist.push(unswitch_iff);
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166
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167 IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
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168 _igvn.hash_delete(unswitch_iff_clone);
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169 short_circuit_if(unswitch_iff_clone, proj_false);
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170 _igvn._worklist.push(unswitch_iff_clone);
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171
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172 // Reoptimize loops
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173 loop->record_for_igvn();
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174 for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
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175 Node *n = loop->_body[i];
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176 Node *n_clone = old_new[n->_idx];
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177 _igvn._worklist.push(n_clone);
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178 }
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179
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180 #ifndef PRODUCT
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181 if (TraceLoopUnswitching) {
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182 tty->print_cr("Loop unswitching orig: %d @ %d new: %d @ %d",
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183 head->_idx, unswitch_iff->_idx,
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184 old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
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185 }
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186 #endif
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187
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188 C->set_major_progress();
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189 }
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190
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191 //-------------------------create_slow_version_of_loop------------------------
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192 // Create a slow version of the loop by cloning the loop
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193 // and inserting an if to select fast-slow versions.
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194 // Return control projection of the entry to the fast version.
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195 ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
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196 Node_List &old_new) {
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197 LoopNode* head = loop->_head->as_Loop();
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198 Node* entry = head->in(LoopNode::EntryControl);
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199 _igvn.hash_delete(entry);
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200 _igvn._worklist.push(entry);
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201 IdealLoopTree* outer_loop = loop->_parent;
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202
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203 Node *cont = _igvn.intcon(1);
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204 set_ctrl(cont, C->root());
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205 Node* opq = new (C, 2) Opaque1Node(cont);
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206 register_node(opq, outer_loop, entry, dom_depth(entry));
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207 Node *bol = new (C, 2) Conv2BNode(opq);
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208 register_node(bol, outer_loop, entry, dom_depth(entry));
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209 IfNode* iff = new (C, 2) IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN);
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210 register_node(iff, outer_loop, entry, dom_depth(entry));
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211 ProjNode* iffast = new (C, 1) IfTrueNode(iff);
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212 register_node(iffast, outer_loop, iff, dom_depth(iff));
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213 ProjNode* ifslow = new (C, 1) IfFalseNode(iff);
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214 register_node(ifslow, outer_loop, iff, dom_depth(iff));
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215
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216 // Clone the loop body. The clone becomes the fast loop. The
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217 // original pre-header will (illegally) have 2 control users (old & new loops).
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218 clone_loop(loop, old_new, dom_depth(head), iff);
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219 assert(old_new[head->_idx]->is_Loop(), "" );
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220
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221 // Fast (true) control
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222 _igvn.hash_delete(head);
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223 head->set_req(LoopNode::EntryControl, iffast);
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224 set_idom(head, iffast, dom_depth(head));
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225 _igvn._worklist.push(head);
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226
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227 // Slow (false) control
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228 LoopNode* slow_head = old_new[head->_idx]->as_Loop();
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229 _igvn.hash_delete(slow_head);
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230 slow_head->set_req(LoopNode::EntryControl, ifslow);
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231 set_idom(slow_head, ifslow, dom_depth(slow_head));
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232 _igvn._worklist.push(slow_head);
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233
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234 recompute_dom_depth();
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235
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236 return iffast;
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237 }
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