loopUnswitch.cpp revision 1472:c18cbe5936b8
1/* 2 * Copyright (c) 2006, 2008, 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 "incls/_precompiled.incl" 26#include "incls/_loopUnswitch.cpp.incl" 27 28//================= Loop Unswitching ===================== 29// 30// orig: transformed: 31// if (invariant-test) then 32// loop loop 33// stmt1 stmt1 34// if (invariant-test) then stmt2 35// stmt2 stmt4 36// else endloop 37// stmt3 else 38// endif loop [clone] 39// stmt4 stmt1 [clone] 40// endloop stmt3 41// stmt4 [clone] 42// endloop 43// endif 44// 45// Note: the "else" clause may be empty 46 47//------------------------------policy_unswitching----------------------------- 48// Return TRUE or FALSE if the loop should be unswitched 49// (ie. clone loop with an invariant test that does not exit the loop) 50bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const { 51 if( !LoopUnswitching ) { 52 return false; 53 } 54 if (!_head->is_Loop()) { 55 return false; 56 } 57 uint nodes_left = MaxNodeLimit - phase->C->unique(); 58 if (2 * _body.size() > nodes_left) { 59 return false; // Too speculative if running low on nodes. 60 } 61 LoopNode* head = _head->as_Loop(); 62 if (head->unswitch_count() + 1 > head->unswitch_max()) { 63 return false; 64 } 65 return phase->find_unswitching_candidate(this) != NULL; 66} 67 68//------------------------------find_unswitching_candidate----------------------------- 69// Find candidate "if" for unswitching 70IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const { 71 72 // Find first invariant test that doesn't exit the loop 73 LoopNode *head = loop->_head->as_Loop(); 74 IfNode* unswitch_iff = NULL; 75 Node* n = head->in(LoopNode::LoopBackControl); 76 while (n != head) { 77 Node* n_dom = idom(n); 78 if (n->is_Region()) { 79 if (n_dom->is_If()) { 80 IfNode* iff = n_dom->as_If(); 81 if (iff->in(1)->is_Bool()) { 82 BoolNode* bol = iff->in(1)->as_Bool(); 83 if (bol->in(1)->is_Cmp()) { 84 // If condition is invariant and not a loop exit, 85 // then found reason to unswitch. 86 if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) { 87 unswitch_iff = iff; 88 } 89 } 90 } 91 } 92 } 93 n = n_dom; 94 } 95 return unswitch_iff; 96} 97 98//------------------------------do_unswitching----------------------------- 99// Clone loop with an invariant test (that does not exit) and 100// insert a clone of the test that selects which version to 101// execute. 102void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) { 103 104 // Find first invariant test that doesn't exit the loop 105 LoopNode *head = loop->_head->as_Loop(); 106 107 IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop); 108 assert(unswitch_iff != NULL, "should be at least one"); 109 110 // Need to revert back to normal loop 111 if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) { 112 head->as_CountedLoop()->set_normal_loop(); 113 } 114 115 ProjNode* proj_true = create_slow_version_of_loop(loop, old_new); 116 117 assert(proj_true->is_IfTrue() && proj_true->unique_ctrl_out() == head, "by construction"); 118 119 // Increment unswitch count 120 LoopNode* head_clone = old_new[head->_idx]->as_Loop(); 121 int nct = head->unswitch_count() + 1; 122 head->set_unswitch_count(nct); 123 head_clone->set_unswitch_count(nct); 124 125 // Add test to new "if" outside of loop 126 IfNode* invar_iff = proj_true->in(0)->as_If(); 127 Node* invar_iff_c = invar_iff->in(0); 128 BoolNode* bol = unswitch_iff->in(1)->as_Bool(); 129 invar_iff->set_req(1, bol); 130 invar_iff->_prob = unswitch_iff->_prob; 131 132 ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj(); 133 134 // Hoist invariant casts out of each loop to the appropriate 135 // control projection. 136 137 Node_List worklist; 138 139 for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) { 140 ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj(); 141 // Copy to a worklist for easier manipulation 142 for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) { 143 Node* use = proj->fast_out(j); 144 if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) { 145 worklist.push(use); 146 } 147 } 148 ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj(); 149 while (worklist.size() > 0) { 150 Node* use = worklist.pop(); 151 Node* nuse = use->clone(); 152 nuse->set_req(0, invar_proj); 153 _igvn.hash_delete(use); 154 use->set_req(1, nuse); 155 _igvn._worklist.push(use); 156 register_new_node(nuse, invar_proj); 157 // Same for the clone 158 Node* use_clone = old_new[use->_idx]; 159 _igvn.hash_delete(use_clone); 160 use_clone->set_req(1, nuse); 161 _igvn._worklist.push(use_clone); 162 } 163 } 164 165 // Hardwire the control paths in the loops into if(true) and if(false) 166 _igvn.hash_delete(unswitch_iff); 167 short_circuit_if(unswitch_iff, proj_true); 168 _igvn._worklist.push(unswitch_iff); 169 170 IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If(); 171 _igvn.hash_delete(unswitch_iff_clone); 172 short_circuit_if(unswitch_iff_clone, proj_false); 173 _igvn._worklist.push(unswitch_iff_clone); 174 175 // Reoptimize loops 176 loop->record_for_igvn(); 177 for(int i = loop->_body.size() - 1; i >= 0 ; i--) { 178 Node *n = loop->_body[i]; 179 Node *n_clone = old_new[n->_idx]; 180 _igvn._worklist.push(n_clone); 181 } 182 183#ifndef PRODUCT 184 if (TraceLoopUnswitching) { 185 tty->print_cr("Loop unswitching orig: %d @ %d new: %d @ %d", 186 head->_idx, unswitch_iff->_idx, 187 old_new[head->_idx]->_idx, unswitch_iff_clone->_idx); 188 } 189#endif 190 191 C->set_major_progress(); 192} 193 194//-------------------------create_slow_version_of_loop------------------------ 195// Create a slow version of the loop by cloning the loop 196// and inserting an if to select fast-slow versions. 197// Return control projection of the entry to the fast version. 198ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop, 199 Node_List &old_new) { 200 LoopNode* head = loop->_head->as_Loop(); 201 Node* entry = head->in(LoopNode::EntryControl); 202 _igvn.hash_delete(entry); 203 _igvn._worklist.push(entry); 204 IdealLoopTree* outer_loop = loop->_parent; 205 206 Node *cont = _igvn.intcon(1); 207 set_ctrl(cont, C->root()); 208 Node* opq = new (C, 2) Opaque1Node(C, cont); 209 register_node(opq, outer_loop, entry, dom_depth(entry)); 210 Node *bol = new (C, 2) Conv2BNode(opq); 211 register_node(bol, outer_loop, entry, dom_depth(entry)); 212 IfNode* iff = new (C, 2) IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN); 213 register_node(iff, outer_loop, entry, dom_depth(entry)); 214 ProjNode* iffast = new (C, 1) IfTrueNode(iff); 215 register_node(iffast, outer_loop, iff, dom_depth(iff)); 216 ProjNode* ifslow = new (C, 1) IfFalseNode(iff); 217 register_node(ifslow, outer_loop, iff, dom_depth(iff)); 218 219 // Clone the loop body. The clone becomes the fast loop. The 220 // original pre-header will (illegally) have 2 control users (old & new loops). 221 clone_loop(loop, old_new, dom_depth(head), iff); 222 assert(old_new[head->_idx]->is_Loop(), "" ); 223 224 // Fast (true) control 225 _igvn.hash_delete(head); 226 head->set_req(LoopNode::EntryControl, iffast); 227 set_idom(head, iffast, dom_depth(head)); 228 _igvn._worklist.push(head); 229 230 // Slow (false) control 231 LoopNode* slow_head = old_new[head->_idx]->as_Loop(); 232 _igvn.hash_delete(slow_head); 233 slow_head->set_req(LoopNode::EntryControl, ifslow); 234 set_idom(slow_head, ifslow, dom_depth(slow_head)); 235 _igvn._worklist.push(slow_head); 236 237 recompute_dom_depth(); 238 239 return iffast; 240} 241