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/loopnode.hpp"
29 #include "opto/rootnode.hpp"
30
31 //================= Loop Unswitching =====================
32 //
33 // orig: transformed:
34 // if (invariant-test) then
35 // predicate predicate
36 // loop loop
37 // stmt1 stmt1
38 // if (invariant-test) then stmt2
39 // stmt2 stmt4
40 // else endloop
41 // stmt3 else
42 // endif predicate [clone]
43 // stmt4 loop [clone]
44 // endloop stmt1 [clone]
45 // stmt3
46 // stmt4 [clone]
47 // endloop
48 // endif
49 //
50 // Note: the "else" clause may be empty
51
52 //------------------------------policy_unswitching-----------------------------
53 // Return TRUE or FALSE if the loop should be unswitched
54 // (ie. clone loop with an invariant test that does not exit the loop)
55 bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
56 if( !LoopUnswitching ) {
57 return false;
58 }
59 if (!_head->is_Loop()) {
60 return false;
61 }
62 uint nodes_left = MaxNodeLimit - phase->C->live_nodes();
63 if (2 * _body.size() > nodes_left) {
64 return false; // Too speculative if running low on nodes.
65 }
66 LoopNode* head = _head->as_Loop();
67 if (head->unswitch_count() + 1 > head->unswitch_max()) {
68 return false;
69 }
70 return phase->find_unswitching_candidate(this) != NULL;
71 }
72
73 //------------------------------find_unswitching_candidate-----------------------------
74 // Find candidate "if" for unswitching
75 IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
76
77 // Find first invariant test that doesn't exit the loop
78 LoopNode *head = loop->_head->as_Loop();
79 IfNode* unswitch_iff = NULL;
80 Node* n = head->in(LoopNode::LoopBackControl);
81 while (n != head) {
82 Node* n_dom = idom(n);
83 if (n->is_Region()) {
84 if (n_dom->is_If()) {
85 IfNode* iff = n_dom->as_If();
86 if (iff->in(1)->is_Bool()) {
87 BoolNode* bol = iff->in(1)->as_Bool();
88 if (bol->in(1)->is_Cmp()) {
89 // If condition is invariant and not a loop exit,
90 // then found reason to unswitch.
91 if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
92 unswitch_iff = iff;
93 }
94 }
95 }
96 }
97 }
98 n = n_dom;
99 }
100 return unswitch_iff;
101 }
102
103 //------------------------------do_unswitching-----------------------------
104 // Clone loop with an invariant test (that does not exit) and
105 // insert a clone of the test that selects which version to
106 // execute.
107 void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {
108
109 // Find first invariant test that doesn't exit the loop
110 LoopNode *head = loop->_head->as_Loop();
111
112 IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
113 assert(unswitch_iff != NULL, "should be at least one");
114
115 #ifndef PRODUCT
116 if (TraceLoopOpts) {
117 tty->print("Unswitch %d ", head->unswitch_count()+1);
118 loop->dump_head();
119 }
120 #endif
121
122 // Need to revert back to normal loop
123 if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
124 head->as_CountedLoop()->set_normal_loop();
125 }
126
127 ProjNode* proj_true = create_slow_version_of_loop(loop, old_new);
128
129 #ifdef ASSERT
130 Node* uniqc = proj_true->unique_ctrl_out();
131 Node* entry = head->in(LoopNode::EntryControl);
132 Node* predicate = find_predicate(entry);
133 if (predicate != NULL && LoopLimitCheck && UseLoopPredicate) {
134 // We may have two predicates, find first.
135 entry = find_predicate(entry->in(0)->in(0));
136 if (entry != NULL) predicate = entry;
137 }
138 if (predicate != NULL) predicate = predicate->in(0);
139 assert(proj_true->is_IfTrue() &&
140 (predicate == NULL && uniqc == head ||
141 predicate != NULL && uniqc == predicate), "by construction");
142 #endif
143 // Increment unswitch count
144 LoopNode* head_clone = old_new[head->_idx]->as_Loop();
145 int nct = head->unswitch_count() + 1;
146 head->set_unswitch_count(nct);
147 head_clone->set_unswitch_count(nct);
148
149 // Add test to new "if" outside of loop
150 IfNode* invar_iff = proj_true->in(0)->as_If();
151 Node* invar_iff_c = invar_iff->in(0);
152 BoolNode* bol = unswitch_iff->in(1)->as_Bool();
153 invar_iff->set_req(1, bol);
154 invar_iff->_prob = unswitch_iff->_prob;
155
156 ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
157
158 // Hoist invariant casts out of each loop to the appropriate
159 // control projection.
160
161 Node_List worklist;
162
163 for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
164 ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
165 // Copy to a worklist for easier manipulation
166 for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
167 Node* use = proj->fast_out(j);
168 if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
169 worklist.push(use);
170 }
171 }
172 ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
173 while (worklist.size() > 0) {
174 Node* use = worklist.pop();
175 Node* nuse = use->clone();
176 nuse->set_req(0, invar_proj);
177 _igvn.replace_input_of(use, 1, nuse);
178 register_new_node(nuse, invar_proj);
179 // Same for the clone
180 Node* use_clone = old_new[use->_idx];
181 _igvn.replace_input_of(use_clone, 1, nuse);
182 }
183 }
184
185 // Hardwire the control paths in the loops into if(true) and if(false)
186 _igvn.rehash_node_delayed(unswitch_iff);
187 short_circuit_if(unswitch_iff, proj_true);
188
189 IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
190 _igvn.rehash_node_delayed(unswitch_iff_clone);
191 short_circuit_if(unswitch_iff_clone, proj_false);
192
193 // Reoptimize loops
194 loop->record_for_igvn();
195 for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
196 Node *n = loop->_body[i];
197 Node *n_clone = old_new[n->_idx];
198 _igvn._worklist.push(n_clone);
199 }
200
201 #ifndef PRODUCT
202 if (TraceLoopUnswitching) {
203 tty->print_cr("Loop unswitching orig: %d @ %d new: %d @ %d",
204 head->_idx, unswitch_iff->_idx,
205 old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
206 }
207 #endif
208
209 C->set_major_progress();
210 }
211
212 //-------------------------create_slow_version_of_loop------------------------
213 // Create a slow version of the loop by cloning the loop
214 // and inserting an if to select fast-slow versions.
215 // Return control projection of the entry to the fast version.
216 ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
217 Node_List &old_new) {
218 LoopNode* head = loop->_head->as_Loop();
219 bool counted_loop = head->is_CountedLoop();
220 Node* entry = head->in(LoopNode::EntryControl);
221 _igvn.rehash_node_delayed(entry);
222 IdealLoopTree* outer_loop = loop->_parent;
223
224 Node *cont = _igvn.intcon(1);
225 set_ctrl(cont, C->root());
226 Node* opq = new (C) Opaque1Node(C, cont);
227 register_node(opq, outer_loop, entry, dom_depth(entry));
228 Node *bol = new (C) Conv2BNode(opq);
229 register_node(bol, outer_loop, entry, dom_depth(entry));
230 IfNode* iff = new (C) IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN);
231 register_node(iff, outer_loop, entry, dom_depth(entry));
232 ProjNode* iffast = new (C) IfTrueNode(iff);
233 register_node(iffast, outer_loop, iff, dom_depth(iff));
234 ProjNode* ifslow = new (C) IfFalseNode(iff);
235 register_node(ifslow, outer_loop, iff, dom_depth(iff));
236
237 // Clone the loop body. The clone becomes the fast loop. The
238 // original pre-header will (illegally) have 3 control users
239 // (old & new loops & new if).
240 clone_loop(loop, old_new, dom_depth(head), iff);
241 assert(old_new[head->_idx]->is_Loop(), "" );
242
243 // Fast (true) control
244 Node* iffast_pred = clone_loop_predicates(entry, iffast, !counted_loop);
245 _igvn.replace_input_of(head, LoopNode::EntryControl, iffast_pred);
246 set_idom(head, iffast_pred, dom_depth(head));
247
248 // Slow (false) control
249 Node* ifslow_pred = clone_loop_predicates(entry, ifslow, !counted_loop);
250 LoopNode* slow_head = old_new[head->_idx]->as_Loop();
251 _igvn.replace_input_of(slow_head, LoopNode::EntryControl, ifslow_pred);
252 set_idom(slow_head, ifslow_pred, dom_depth(slow_head));
253
254 recompute_dom_depth();
255
256 return iffast;
257 }