1 /*
2 * Copyright (c) 2006, 2010, 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 // loop loop
36 // stmt1 stmt1
37 // if (invariant-test) then stmt2
38 // stmt2 stmt4
39 // else endloop
40 // stmt3 else
41 // endif loop [clone]
42 // stmt4 stmt1 [clone]
43 // endloop stmt3
44 // stmt4 [clone]
45 // endloop
46 // endif
47 //
48 // Note: the "else" clause may be empty
49
50 //------------------------------policy_unswitching-----------------------------
51 // Return TRUE or FALSE if the loop should be unswitched
52 // (ie. clone loop with an invariant test that does not exit the loop)
53 bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
54 if( !LoopUnswitching ) {
55 return false;
56 }
57 if (!_head->is_Loop()) {
58 return false;
59 }
60 uint nodes_left = MaxNodeLimit - phase->C->unique();
61 if (2 * _body.size() > nodes_left) {
62 return false; // Too speculative if running low on nodes.
63 }
64 LoopNode* head = _head->as_Loop();
65 if (head->unswitch_count() + 1 > head->unswitch_max()) {
66 return false;
67 }
68 return phase->find_unswitching_candidate(this) != NULL;
69 }
70
71 //------------------------------find_unswitching_candidate-----------------------------
72 // Find candidate "if" for unswitching
73 IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
74
75 // Find first invariant test that doesn't exit the loop
76 LoopNode *head = loop->_head->as_Loop();
77 IfNode* unswitch_iff = NULL;
78 Node* n = head->in(LoopNode::LoopBackControl);
79 while (n != head) {
80 Node* n_dom = idom(n);
81 if (n->is_Region()) {
82 if (n_dom->is_If()) {
83 IfNode* iff = n_dom->as_If();
84 if (iff->in(1)->is_Bool()) {
85 BoolNode* bol = iff->in(1)->as_Bool();
86 if (bol->in(1)->is_Cmp()) {
87 // If condition is invariant and not a loop exit,
88 // then found reason to unswitch.
89 if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
90 unswitch_iff = iff;
91 }
92 }
93 }
94 }
95 }
96 n = n_dom;
97 }
98 return unswitch_iff;
99 }
100
101 //------------------------------do_unswitching-----------------------------
102 // Clone loop with an invariant test (that does not exit) and
103 // insert a clone of the test that selects which version to
104 // execute.
105 void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {
106
107 // Find first invariant test that doesn't exit the loop
108 LoopNode *head = loop->_head->as_Loop();
109
110 IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
111 assert(unswitch_iff != NULL, "should be at least one");
112
113 // Need to revert back to normal loop
114 if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
115 head->as_CountedLoop()->set_normal_loop();
116 }
117
118 ProjNode* proj_true = create_slow_version_of_loop(loop, old_new);
119
120 assert(proj_true->is_IfTrue() && proj_true->unique_ctrl_out() == head, "by construction");
121
122 // Increment unswitch count
123 LoopNode* head_clone = old_new[head->_idx]->as_Loop();
124 int nct = head->unswitch_count() + 1;
125 head->set_unswitch_count(nct);
126 head_clone->set_unswitch_count(nct);
127
128 // Add test to new "if" outside of loop
129 IfNode* invar_iff = proj_true->in(0)->as_If();
130 Node* invar_iff_c = invar_iff->in(0);
131 BoolNode* bol = unswitch_iff->in(1)->as_Bool();
132 invar_iff->set_req(1, bol);
133 invar_iff->_prob = unswitch_iff->_prob;
134
135 ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
136
137 // Hoist invariant casts out of each loop to the appropriate
138 // control projection.
139
140 Node_List worklist;
141
142 for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
143 ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
144 // Copy to a worklist for easier manipulation
145 for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
146 Node* use = proj->fast_out(j);
147 if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
148 worklist.push(use);
149 }
150 }
151 ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
152 while (worklist.size() > 0) {
153 Node* use = worklist.pop();
154 Node* nuse = use->clone();
155 nuse->set_req(0, invar_proj);
156 _igvn.hash_delete(use);
157 use->set_req(1, nuse);
158 _igvn._worklist.push(use);
159 register_new_node(nuse, invar_proj);
160 // Same for the clone
161 Node* use_clone = old_new[use->_idx];
162 _igvn.hash_delete(use_clone);
163 use_clone->set_req(1, nuse);
164 _igvn._worklist.push(use_clone);
165 }
166 }
167
168 // Hardwire the control paths in the loops into if(true) and if(false)
169 _igvn.hash_delete(unswitch_iff);
170 short_circuit_if(unswitch_iff, proj_true);
171 _igvn._worklist.push(unswitch_iff);
172
173 IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
174 _igvn.hash_delete(unswitch_iff_clone);
175 short_circuit_if(unswitch_iff_clone, proj_false);
176 _igvn._worklist.push(unswitch_iff_clone);
177
178 // Reoptimize loops
179 loop->record_for_igvn();
180 for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
181 Node *n = loop->_body[i];
182 Node *n_clone = old_new[n->_idx];
183 _igvn._worklist.push(n_clone);
184 }
185
186 #ifndef PRODUCT
187 if (TraceLoopUnswitching) {
188 tty->print_cr("Loop unswitching orig: %d @ %d new: %d @ %d",
189 head->_idx, unswitch_iff->_idx,
190 old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
191 }
192 #endif
193
194 C->set_major_progress();
195 }
196
197 //-------------------------create_slow_version_of_loop------------------------
198 // Create a slow version of the loop by cloning the loop
199 // and inserting an if to select fast-slow versions.
200 // Return control projection of the entry to the fast version.
201 ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
202 Node_List &old_new) {
203 LoopNode* head = loop->_head->as_Loop();
204 Node* entry = head->in(LoopNode::EntryControl);
205 _igvn.hash_delete(entry);
206 _igvn._worklist.push(entry);
207 IdealLoopTree* outer_loop = loop->_parent;
208
209 Node *cont = _igvn.intcon(1);
210 set_ctrl(cont, C->root());
211 Node* opq = new (C, 2) Opaque1Node(C, cont);
212 register_node(opq, outer_loop, entry, dom_depth(entry));
213 Node *bol = new (C, 2) Conv2BNode(opq);
214 register_node(bol, outer_loop, entry, dom_depth(entry));
215 IfNode* iff = new (C, 2) IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN);
216 register_node(iff, outer_loop, entry, dom_depth(entry));
217 ProjNode* iffast = new (C, 1) IfTrueNode(iff);
218 register_node(iffast, outer_loop, iff, dom_depth(iff));
219 ProjNode* ifslow = new (C, 1) IfFalseNode(iff);
220 register_node(ifslow, outer_loop, iff, dom_depth(iff));
221
222 // Clone the loop body. The clone becomes the fast loop. The
223 // original pre-header will (illegally) have 2 control users (old & new loops).
224 clone_loop(loop, old_new, dom_depth(head), iff);
225 assert(old_new[head->_idx]->is_Loop(), "" );
226
227 // Fast (true) control
228 _igvn.hash_delete(head);
229 head->set_req(LoopNode::EntryControl, iffast);
230 set_idom(head, iffast, dom_depth(head));
231 _igvn._worklist.push(head);
232
233 // Slow (false) control
234 LoopNode* slow_head = old_new[head->_idx]->as_Loop();
235 _igvn.hash_delete(slow_head);
236 slow_head->set_req(LoopNode::EntryControl, ifslow);
237 set_idom(slow_head, ifslow, dom_depth(slow_head));
238 _igvn._worklist.push(slow_head);
239
240 recompute_dom_depth();
241
242 return iffast;
243 }