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comparison src/share/vm/opto/loopUnswitch.cpp @ 0:a61af66fc99e jdk7-b24

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author duke
date Sat, 01 Dec 2007 00:00:00 +0000
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1 /*
2 * Copyright 2006 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any 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)
50 bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
51 if( !LoopUnswitching ) {
52 return false;
53 }
54 uint nodes_left = MaxNodeLimit - phase->C->unique();
55 if (2 * _body.size() > nodes_left) {
56 return false; // Too speculative if running low on nodes.
57 }
58 LoopNode* head = _head->as_Loop();
59 if (head->unswitch_count() + 1 > head->unswitch_max()) {
60 return false;
61 }
62 return phase->find_unswitching_candidate(this) != NULL;
63 }
64
65 //------------------------------find_unswitching_candidate-----------------------------
66 // Find candidate "if" for unswitching
67 IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
68
69 // Find first invariant test that doesn't exit the loop
70 LoopNode *head = loop->_head->as_Loop();
71 IfNode* unswitch_iff = NULL;
72 Node* n = head->in(LoopNode::LoopBackControl);
73 while (n != head) {
74 Node* n_dom = idom(n);
75 if (n->is_Region()) {
76 if (n_dom->is_If()) {
77 IfNode* iff = n_dom->as_If();
78 if (iff->in(1)->is_Bool()) {
79 BoolNode* bol = iff->in(1)->as_Bool();
80 if (bol->in(1)->is_Cmp()) {
81 // If condition is invariant and not a loop exit,
82 // then found reason to unswitch.
83 if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
84 unswitch_iff = iff;
85 }
86 }
87 }
88 }
89 }
90 n = n_dom;
91 }
92 return unswitch_iff;
93 }
94
95 //------------------------------do_unswitching-----------------------------
96 // Clone loop with an invariant test (that does not exit) and
97 // insert a clone of the test that selects which version to
98 // execute.
99 void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {
100
101 // Find first invariant test that doesn't exit the loop
102 LoopNode *head = loop->_head->as_Loop();
103
104 IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
105 assert(unswitch_iff != NULL, "should be at least one");
106
107 // Need to revert back to normal loop
108 if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
109 head->as_CountedLoop()->set_normal_loop();
110 }
111
112 ProjNode* proj_true = create_slow_version_of_loop(loop, old_new);
113
114 assert(proj_true->is_IfTrue() && proj_true->unique_ctrl_out() == head, "by construction");
115
116 // Increment unswitch count
117 LoopNode* head_clone = old_new[head->_idx]->as_Loop();
118 int nct = head->unswitch_count() + 1;
119 head->set_unswitch_count(nct);
120 head_clone->set_unswitch_count(nct);
121
122 // Add test to new "if" outside of loop
123 IfNode* invar_iff = proj_true->in(0)->as_If();
124 Node* invar_iff_c = invar_iff->in(0);
125 BoolNode* bol = unswitch_iff->in(1)->as_Bool();
126 invar_iff->set_req(1, bol);
127 invar_iff->_prob = unswitch_iff->_prob;
128
129 ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
130
131 // Hoist invariant casts out of each loop to the appropiate
132 // control projection.
133
134 Node_List worklist;
135
136 for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
137 ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
138 // Copy to a worklist for easier manipulation
139 for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
140 Node* use = proj->fast_out(j);
141 if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
142 worklist.push(use);
143 }
144 }
145 ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
146 while (worklist.size() > 0) {
147 Node* use = worklist.pop();
148 Node* nuse = use->clone();
149 nuse->set_req(0, invar_proj);
150 _igvn.hash_delete(use);
151 use->set_req(1, nuse);
152 _igvn._worklist.push(use);
153 register_new_node(nuse, invar_proj);
154 // Same for the clone
155 Node* use_clone = old_new[use->_idx];
156 _igvn.hash_delete(use_clone);
157 use_clone->set_req(1, nuse);
158 _igvn._worklist.push(use_clone);
159 }
160 }
161
162 // Hardwire the control paths in the loops into if(true) and if(false)
163 _igvn.hash_delete(unswitch_iff);
164 short_circuit_if(unswitch_iff, proj_true);
165 _igvn._worklist.push(unswitch_iff);
166
167 IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
168 _igvn.hash_delete(unswitch_iff_clone);
169 short_circuit_if(unswitch_iff_clone, proj_false);
170 _igvn._worklist.push(unswitch_iff_clone);
171
172 // Reoptimize loops
173 loop->record_for_igvn();
174 for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
175 Node *n = loop->_body[i];
176 Node *n_clone = old_new[n->_idx];
177 _igvn._worklist.push(n_clone);
178 }
179
180 #ifndef PRODUCT
181 if (TraceLoopUnswitching) {
182 tty->print_cr("Loop unswitching orig: %d @ %d new: %d @ %d",
183 head->_idx, unswitch_iff->_idx,
184 old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
185 }
186 #endif
187
188 C->set_major_progress();
189 }
190
191 //-------------------------create_slow_version_of_loop------------------------
192 // Create a slow version of the loop by cloning the loop
193 // and inserting an if to select fast-slow versions.
194 // Return control projection of the entry to the fast version.
195 ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
196 Node_List &old_new) {
197 LoopNode* head = loop->_head->as_Loop();
198 Node* entry = head->in(LoopNode::EntryControl);
199 _igvn.hash_delete(entry);
200 _igvn._worklist.push(entry);
201 IdealLoopTree* outer_loop = loop->_parent;
202
203 Node *cont = _igvn.intcon(1);
204 set_ctrl(cont, C->root());
205 Node* opq = new (C, 2) Opaque1Node(cont);
206 register_node(opq, outer_loop, entry, dom_depth(entry));
207 Node *bol = new (C, 2) Conv2BNode(opq);
208 register_node(bol, outer_loop, entry, dom_depth(entry));
209 IfNode* iff = new (C, 2) IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN);
210 register_node(iff, outer_loop, entry, dom_depth(entry));
211 ProjNode* iffast = new (C, 1) IfTrueNode(iff);
212 register_node(iffast, outer_loop, iff, dom_depth(iff));
213 ProjNode* ifslow = new (C, 1) IfFalseNode(iff);
214 register_node(ifslow, outer_loop, iff, dom_depth(iff));
215
216 // Clone the loop body. The clone becomes the fast loop. The
217 // original pre-header will (illegally) have 2 control users (old & new loops).
218 clone_loop(loop, old_new, dom_depth(head), iff);
219 assert(old_new[head->_idx]->is_Loop(), "" );
220
221 // Fast (true) control
222 _igvn.hash_delete(head);
223 head->set_req(LoopNode::EntryControl, iffast);
224 set_idom(head, iffast, dom_depth(head));
225 _igvn._worklist.push(head);
226
227 // Slow (false) control
228 LoopNode* slow_head = old_new[head->_idx]->as_Loop();
229 _igvn.hash_delete(slow_head);
230 slow_head->set_req(LoopNode::EntryControl, ifslow);
231 set_idom(slow_head, ifslow, dom_depth(slow_head));
232 _igvn._worklist.push(slow_head);
233
234 recompute_dom_depth();
235
236 return iffast;
237 }