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 int nodes_left = phase->C->max_node_limit() - phase->C->live_nodes();
65 if ((int)(2 * _body.size()) > nodes_left) {
66 return false; // Too speculative if running low on nodes.
67 }
68 LoopNode* head = _head->as_Loop();
69 if (head->unswitch_count() + 1 > head->unswitch_max()) {
70 return false;
71 }
72 return phase->find_unswitching_candidate(this) != NULL;
73 }
74
75 //------------------------------find_unswitching_candidate-----------------------------
76 // Find candidate "if" for unswitching
77 IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
78
79 // Find first invariant test that doesn't exit the loop
80 LoopNode *head = loop->_head->as_Loop();
81 IfNode* unswitch_iff = NULL;
82 Node* n = head->in(LoopNode::LoopBackControl);
83 while (n != head) {
84 Node* n_dom = idom(n);
85 if (n->is_Region()) {
86 if (n_dom->is_If()) {
87 IfNode* iff = n_dom->as_If();
88 if (iff->in(1)->is_Bool()) {
89 BoolNode* bol = iff->in(1)->as_Bool();
90 if (bol->in(1)->is_Cmp()) {
91 // If condition is invariant and not a loop exit,
92 // then found reason to unswitch.
93 if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
94 unswitch_iff = iff;
95 }
96 }
97 }
98 }
99 }
100 n = n_dom;
101 }
102 return unswitch_iff;
103 }
104
105 //------------------------------do_unswitching-----------------------------
106 // Clone loop with an invariant test (that does not exit) and
107 // insert a clone of the test that selects which version to
108 // execute.
109 void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {
110
111 // Find first invariant test that doesn't exit the loop
112 LoopNode *head = loop->_head->as_Loop();
113
114 IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
115 assert(unswitch_iff != NULL, "should be at least one");
116
117 #ifndef PRODUCT
118 if (TraceLoopOpts) {
119 tty->print("Unswitch %d ", head->unswitch_count()+1);
120 loop->dump_head();
121 }
122 #endif
123
124 // Need to revert back to normal loop
125 if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
126 head->as_CountedLoop()->set_normal_loop();
127 }
128
129 ProjNode* proj_true = create_slow_version_of_loop(loop, old_new);
130
131 #ifdef ASSERT
132 Node* uniqc = proj_true->unique_ctrl_out();
133 Node* entry = head->in(LoopNode::EntryControl);
134 Node* predicate = find_predicate(entry);
135 if (predicate != NULL && LoopLimitCheck && UseLoopPredicate) {
136 // We may have two predicates, find first.
137 entry = find_predicate(entry->in(0)->in(0));
138 if (entry != NULL) predicate = entry;
139 }
140 if (predicate != NULL) predicate = predicate->in(0);
141 assert(proj_true->is_IfTrue() &&
142 (predicate == NULL && uniqc == head ||
143 predicate != NULL && uniqc == predicate), "by construction");
144 #endif
145 // Increment unswitch count
146 LoopNode* head_clone = old_new[head->_idx]->as_Loop();
147 int nct = head->unswitch_count() + 1;
148 head->set_unswitch_count(nct);
149 head_clone->set_unswitch_count(nct);
150
151 // Add test to new "if" outside of loop
152 IfNode* invar_iff = proj_true->in(0)->as_If();
153 Node* invar_iff_c = invar_iff->in(0);
154 BoolNode* bol = unswitch_iff->in(1)->as_Bool();
155 invar_iff->set_req(1, bol);
156 invar_iff->_prob = unswitch_iff->_prob;
157
158 ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
159
160 // Hoist invariant casts out of each loop to the appropriate
161 // control projection.
162
163 Node_List worklist;
164
165 for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
166 ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
167 // Copy to a worklist for easier manipulation
168 for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
169 Node* use = proj->fast_out(j);
170 if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
171 worklist.push(use);
172 }
173 }
174 ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
175 while (worklist.size() > 0) {
176 Node* use = worklist.pop();
177 Node* nuse = use->clone();
178 nuse->set_req(0, invar_proj);
179 _igvn.replace_input_of(use, 1, nuse);
180 register_new_node(nuse, invar_proj);
181 // Same for the clone
182 Node* use_clone = old_new[use->_idx];
183 _igvn.replace_input_of(use_clone, 1, nuse);
184 }
185 }
186
187 // Hardwire the control paths in the loops into if(true) and if(false)
188 _igvn.rehash_node_delayed(unswitch_iff);
189 short_circuit_if(unswitch_iff, proj_true);
190
191 IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
192 _igvn.rehash_node_delayed(unswitch_iff_clone);
193 short_circuit_if(unswitch_iff_clone, proj_false);
194
195 // Reoptimize loops
196 loop->record_for_igvn();
197 for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
198 Node *n = loop->_body[i];
199 Node *n_clone = old_new[n->_idx];
200 _igvn._worklist.push(n_clone);
201 }
202
203 #ifndef PRODUCT
204 if (TraceLoopUnswitching) {
205 tty->print_cr("Loop unswitching orig: %d @ %d new: %d @ %d",
206 head->_idx, unswitch_iff->_idx,
207 old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
208 }
209 #endif
210
211 C->set_major_progress();
212 }
213
214 //-------------------------create_slow_version_of_loop------------------------
215 // Create a slow version of the loop by cloning the loop
216 // and inserting an if to select fast-slow versions.
217 // Return control projection of the entry to the fast version.
218 ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
219 Node_List &old_new) {
220 LoopNode* head = loop->_head->as_Loop();
221 bool counted_loop = head->is_CountedLoop();
222 Node* entry = head->in(LoopNode::EntryControl);
223 _igvn.rehash_node_delayed(entry);
224 IdealLoopTree* outer_loop = loop->_parent;
225
226 Node *cont = _igvn.intcon(1);
227 set_ctrl(cont, C->root());
228 Node* opq = new Opaque1Node(C, cont);
229 register_node(opq, outer_loop, entry, dom_depth(entry));
230 Node *bol = new Conv2BNode(opq);
231 register_node(bol, outer_loop, entry, dom_depth(entry));
232 IfNode* iff = new IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN);
233 register_node(iff, outer_loop, entry, dom_depth(entry));
234 ProjNode* iffast = new IfTrueNode(iff);
235 register_node(iffast, outer_loop, iff, dom_depth(iff));
236 ProjNode* ifslow = new IfFalseNode(iff);
237 register_node(ifslow, outer_loop, iff, dom_depth(iff));
238
239 // Clone the loop body. The clone becomes the fast loop. The
240 // original pre-header will (illegally) have 3 control users
241 // (old & new loops & new if).
242 clone_loop(loop, old_new, dom_depth(head), iff);
243 assert(old_new[head->_idx]->is_Loop(), "" );
244
245 // Fast (true) control
246 Node* iffast_pred = clone_loop_predicates(entry, iffast, !counted_loop);
247 _igvn.replace_input_of(head, LoopNode::EntryControl, iffast_pred);
248 set_idom(head, iffast_pred, dom_depth(head));
249
250 // Slow (false) control
251 Node* ifslow_pred = clone_loop_predicates(entry, ifslow, !counted_loop);
252 LoopNode* slow_head = old_new[head->_idx]->as_Loop();
253 _igvn.replace_input_of(slow_head, LoopNode::EntryControl, ifslow_pred);
254 set_idom(slow_head, ifslow_pred, dom_depth(slow_head));
255
256 recompute_dom_depth();
257
258 return iffast;
259 }