1 /*
2 * Copyright (c) 2006, 2023, 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/predicates.hpp"
32 #include "opto/rootnode.hpp"
33
34 //================= Loop Unswitching =====================
35 //
36 // orig: transformed:
37 // if (invariant-test) then
38 // predicates predicates
39 // loop loop
40 // stmt1 stmt1
41 // if (invariant-test) then stmt2
42 // stmt2 stmt4
43 // else endloop
44 // stmt3 else
45 // endif predicates [clone]
46 // stmt4 loop [clone]
47 // endloop stmt1 [clone]
48 // stmt3
49 // stmt4 [clone]
50 // endloop
51 // endif
52 //
53 // Note: the "else" clause may be empty
54
55 //------------------------------policy_unswitching-----------------------------
56 // Return TRUE or FALSE if the loop should be unswitched
57 // (ie. clone loop with an invariant test that does not exit the loop)
58 bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
59 if (!LoopUnswitching) {
60 return false;
61 }
62 if (!_head->is_Loop()) {
63 return false;
64 }
65
66 // If nodes are depleted, some transform has miscalculated its needs.
67 assert(!phase->exceeding_node_budget(), "sanity");
68
69 // check for vectorized loops, any unswitching was already applied
70 if (_head->is_CountedLoop() && _head->as_CountedLoop()->is_unroll_only()) {
71 return false;
72 }
73
74 LoopNode* head = _head->as_Loop();
75 if (head->unswitch_count() + 1 > head->unswitch_max()) {
76 return false;
77 }
78 if (phase->find_unswitching_candidate(this) == nullptr) {
79 return false;
80 }
81
82 // Too speculative if running low on nodes.
83 return phase->may_require_nodes(est_loop_clone_sz(2));
84 }
85
86 //------------------------------find_unswitching_candidate-----------------------------
87 // Find candidate "if" for unswitching
88 IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
89
90 // Find first invariant test that doesn't exit the loop
91 LoopNode *head = loop->_head->as_Loop();
92 IfNode* unswitch_iff = nullptr;
93 Node* n = head->in(LoopNode::LoopBackControl);
94 while (n != head) {
95 Node* n_dom = idom(n);
96 if (n->is_Region()) {
97 if (n_dom->is_If()) {
98 IfNode* iff = n_dom->as_If();
99 if (iff->in(1)->is_Bool()) {
100 BoolNode* bol = iff->in(1)->as_Bool();
101 if (bol->in(1)->is_Cmp()) {
102 // If condition is invariant and not a loop exit,
103 // then found reason to unswitch.
104 if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
105 unswitch_iff = iff;
106 }
107 }
108 }
109 }
110 }
111 n = n_dom;
112 }
113 return unswitch_iff;
114 }
115
116 //------------------------------do_unswitching-----------------------------
117 // Clone loop with an invariant test (that does not exit) and
118 // insert a clone of the test that selects which version to
119 // execute.
120 void PhaseIdealLoop::do_unswitching(IdealLoopTree *loop, Node_List &old_new) {
121 LoopNode* head = loop->_head->as_Loop();
122 if (has_control_dependencies_from_predicates(head)) {
123 return;
124 }
125
126 // Find first invariant test that doesn't exit the loop
127 IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
128 assert(unswitch_iff != nullptr, "should be at least one");
129
130 #ifndef PRODUCT
131 if (TraceLoopOpts) {
132 tty->print("Unswitch %d ", head->unswitch_count()+1);
133 loop->dump_head();
134 }
135 #endif
136
137 C->print_method(PHASE_BEFORE_LOOP_UNSWITCHING, 4, head);
138
139 // Need to revert back to normal loop
140 if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
141 head->as_CountedLoop()->set_normal_loop();
142 }
143
144 IfNode* invar_iff = create_slow_version_of_loop(loop, old_new, unswitch_iff, CloneIncludesStripMined);
145 ProjNode* proj_true = invar_iff->proj_out(1);
146 verify_fast_loop(head, proj_true);
147
148 // Increment unswitch count
149 LoopNode* head_clone = old_new[head->_idx]->as_Loop();
150 int nct = head->unswitch_count() + 1;
151 head->set_unswitch_count(nct);
152 head_clone->set_unswitch_count(nct);
153
154 // Hoist invariant casts out of each loop to the appropriate
155 // control projection.
156
157 Node_List worklist;
158 for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
159 ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
160 // Copy to a worklist for easier manipulation
161 for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
162 Node* use = proj->fast_out(j);
163 if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
164 worklist.push(use);
165 }
166 }
167 ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
168 while (worklist.size() > 0) {
169 Node* use = worklist.pop();
170 Node* nuse = use->clone();
171 nuse->set_req(0, invar_proj);
172 _igvn.replace_input_of(use, 1, nuse);
173 register_new_node(nuse, invar_proj);
174 // Same for the clone
175 Node* use_clone = old_new[use->_idx];
176 _igvn.replace_input_of(use_clone, 1, nuse);
177 }
178 }
179
180 // Hardwire the control paths in the loops into if(true) and if(false)
181 _igvn.rehash_node_delayed(unswitch_iff);
182 dominated_by(proj_true->as_IfProj(), unswitch_iff);
183
184 IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
185 _igvn.rehash_node_delayed(unswitch_iff_clone);
186 ProjNode* proj_false = invar_iff->proj_out(0);
187 dominated_by(proj_false->as_IfProj(), unswitch_iff_clone);
188
189 // Reoptimize loops
190 loop->record_for_igvn();
191 for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
192 Node *n = loop->_body[i];
193 Node *n_clone = old_new[n->_idx];
194 _igvn._worklist.push(n_clone);
195 }
196
197 #ifndef PRODUCT
198 if (TraceLoopUnswitching) {
199 tty->print_cr("Loop unswitching orig: %d @ %d new: %d @ %d",
200 head->_idx, unswitch_iff->_idx,
201 old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
202 }
203 #endif
204
205 C->print_method(PHASE_AFTER_LOOP_UNSWITCHING, 4, head_clone);
206
207 C->set_major_progress();
208 }
209
210 bool PhaseIdealLoop::has_control_dependencies_from_predicates(LoopNode* head) const {
211 Node* entry = head->skip_strip_mined()->in(LoopNode::EntryControl);
212 Predicates predicates(entry);
213 if (predicates.has_any()) {
214 assert(entry->is_IfProj(), "sanity - must be ifProj since there is at least one predicate");
215 if (entry->outcnt() > 1) {
216 // Bailout if there are predicates from which there are additional control dependencies (i.e. from loop
217 // entry 'entry') to previously partially peeled statements since this case is not handled and can lead
218 // to a wrong execution. Remove this bailout, once this is fixed.
219 return true;
220 }
221 }
222 return false;
223 }
224
225 //-------------------------create_slow_version_of_loop------------------------
226 // Create a slow version of the loop by cloning the loop
227 // and inserting an if to select fast-slow versions.
228 // Return the inserted if.
229 IfNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
230 Node_List &old_new,
231 IfNode* unswitch_iff,
232 CloneLoopMode mode) {
233 LoopNode* head = loop->_head->as_Loop();
234 Node* entry = head->skip_strip_mined()->in(LoopNode::EntryControl);
235 _igvn.rehash_node_delayed(entry);
236 IdealLoopTree* outer_loop = loop->_parent;
237
238 head->verify_strip_mined(1);
239
240 // Add test to new "if" outside of loop
241 Node *bol = unswitch_iff->in(1)->as_Bool();
242 IfNode* iff = (unswitch_iff->Opcode() == Op_RangeCheck) ? new RangeCheckNode(entry, bol, unswitch_iff->_prob, unswitch_iff->_fcnt) :
243 new IfNode(entry, bol, unswitch_iff->_prob, unswitch_iff->_fcnt);
244 register_node(iff, outer_loop, entry, dom_depth(entry));
245 IfProjNode* iffast = new IfTrueNode(iff);
246 register_node(iffast, outer_loop, iff, dom_depth(iff));
247 IfProjNode* ifslow = new IfFalseNode(iff);
248 register_node(ifslow, outer_loop, iff, dom_depth(iff));
249
250 // Clone the loop body. The clone becomes the slow loop. The
251 // original pre-header will (illegally) have 3 control users
252 // (old & new loops & new if).
253 clone_loop(loop, old_new, dom_depth(head->skip_strip_mined()), mode, iff);
254 assert(old_new[head->_idx]->is_Loop(), "" );
255
256 // Fast (true) and Slow (false) control
257 IfProjNode* iffast_pred = iffast;
258 IfProjNode* ifslow_pred = ifslow;
259 clone_parse_and_assertion_predicates_to_unswitched_loop(loop, old_new, iffast_pred, ifslow_pred);
260
261 Node* l = head->skip_strip_mined();
262 _igvn.replace_input_of(l, LoopNode::EntryControl, iffast_pred);
263 set_idom(l, iffast_pred, dom_depth(l));
264 LoopNode* slow_l = old_new[head->_idx]->as_Loop()->skip_strip_mined();
265 _igvn.replace_input_of(slow_l, LoopNode::EntryControl, ifslow_pred);
266 set_idom(slow_l, ifslow_pred, dom_depth(l));
267
268 recompute_dom_depth();
269
270 return iff;
271 }
272
273 #ifdef ASSERT
274 void PhaseIdealLoop::verify_fast_loop(LoopNode* head, const ProjNode* proj_true) const {
275 assert(proj_true->is_IfTrue(), "must be true projection");
276 Node* entry = head->skip_strip_mined()->in(LoopNode::EntryControl);
277 Predicates predicates(entry);
278 if (!predicates.has_any()) {
279 // No Parse Predicate.
280 Node* uniqc = proj_true->unique_ctrl_out();
281 assert((uniqc == head && !head->is_strip_mined()) || (uniqc == head->in(LoopNode::EntryControl)
282 && head->is_strip_mined()), "must hold by construction if no predicates");
283 } else {
284 // There is at least one Parse Predicate. When skipping all predicates/predicate blocks, we should end up
285 // at 'proj_true'.
286 assert(proj_true == predicates.entry(), "must hold by construction if at least one Parse Predicate");
287 }
288 }
289 #endif // ASSERT
290