1 #ifdef USE_PRAGMA_IDENT_SRC
2 #pragma ident "@(#)loopUnswitch.cpp 1.6 07/06/29 14:41:32 JVM"
3 #endif
4 /*
5 * Copyright 2006 Sun Microsystems, Inc. All Rights Reserved.
6 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
7 *
8 * This code is free software; you can redistribute it and/or modify it
9 * under the terms of the GNU General Public License version 2 only, as
10 * published by the Free Software Foundation.
11 *
12 * This code is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 * version 2 for more details (a copy is included in the LICENSE file that
16 * accompanied this code).
17 *
18 * You should have received a copy of the GNU General Public License version
19 * 2 along with this work; if not, write to the Free Software Foundation,
20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
21 *
22 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
23 * CA 95054 USA or visit www.sun.com if you need additional information or
24 * have any questions.
25 *
26 */
27
28 #include "incls/_precompiled.incl"
29 #include "incls/_loopUnswitch.cpp.incl"
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 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
70 IfNode* 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.
102 void 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 appropiate
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.
198 ProjNode* 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(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 }