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/mulnode.hpp"
28 #include "opto/addnode.hpp"
29 #include "opto/connode.hpp"
30 #include "opto/convertnode.hpp"
31 #include "opto/loopnode.hpp"
32 #include "opto/opaquenode.hpp"
33 #include "opto/predicates.hpp"
34 #include "opto/rootnode.hpp"
35
36 //================= Loop Unswitching =====================
37 //
38 // orig: transformed:
39 // if (invariant-test) then
40 // predicates predicates
41 // loop loop
42 // stmt1 stmt1
43 // if (invariant-test) then stmt2
44 // stmt2 stmt4
45 // else endloop
46 // stmt3 else
47 // endif predicates [clone]
48 // stmt4 loop [clone]
49 // endloop stmt1 [clone]
50 // stmt3
51 // stmt4 [clone]
52 // endloop
53 // endif
54 //
55 // Note: the "else" clause may be empty
56
57
58 //------------------------------policy_unswitching-----------------------------
59 // Return TRUE or FALSE if the loop should be unswitched
60 // (ie. clone loop with an invariant test that does not exit the loop)
61 bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
62 if (!LoopUnswitching) {
63 return false;
64 }
65 if (!_head->is_Loop()) {
66 return false;
67 }
68
69 // If nodes are depleted, some transform has miscalculated its needs.
70 assert(!phase->exceeding_node_budget(), "sanity");
71
72 // check for vectorized loops, any unswitching was already applied
73 if (_head->is_CountedLoop() && _head->as_CountedLoop()->is_unroll_only()) {
74 return false;
75 }
76
77 LoopNode* head = _head->as_Loop();
78 if (head->unswitch_count() + 1 > head->unswitch_max()) {
79 return false;
80 }
81
82 if (head->is_flat_arrays()) {
83 return false;
84 }
85
86 Node_List unswitch_iffs;
87 if (phase->find_unswitching_candidate(this, unswitch_iffs) == nullptr) {
88 return false;
89 }
90
91 // Too speculative if running low on nodes.
92 return phase->may_require_nodes(est_loop_clone_sz(2));
93 }
94
95 //------------------------------find_unswitching_candidate-----------------------------
96 // Find candidate "if" for unswitching
97 IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop, Node_List& unswitch_iffs) const {
98
99 // Find first invariant test that doesn't exit the loop
100 LoopNode *head = loop->_head->as_Loop();
101 IfNode* unswitch_iff = nullptr;
102 Node* n = head->in(LoopNode::LoopBackControl);
103 while (n != head) {
104 Node* n_dom = idom(n);
105 if (n->is_Region()) {
106 if (n_dom->is_If()) {
107 IfNode* iff = n_dom->as_If();
108 if (iff->in(1)->is_Bool()) {
109 BoolNode* bol = iff->in(1)->as_Bool();
110 if (bol->in(1)->is_Cmp()) {
111 // If condition is invariant and not a loop exit,
112 // then found reason to unswitch.
113 if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
114 unswitch_iff = iff;
115 }
116 }
117 }
118 }
119 }
120 n = n_dom;
121 }
122 if (unswitch_iff != nullptr) {
123 unswitch_iffs.push(unswitch_iff);
124 }
125
126 // Collect all non-flat array checks for unswitching to create a fast loop
127 // without checks (only non-flat array accesses) and a slow loop with checks.
128 if (unswitch_iff == nullptr || unswitch_iff->is_flat_array_check(&_igvn)) {
129 for (uint i = 0; i < loop->_body.size(); i++) {
130 IfNode* n = loop->_body.at(i)->isa_If();
131 if (n != nullptr && n != unswitch_iff && n->is_flat_array_check(&_igvn) &&
132 loop->is_invariant(n->in(1)) && !loop->is_loop_exit(n)) {
133 unswitch_iffs.push(n);
134 if (unswitch_iff == nullptr) {
135 unswitch_iff = n;
136 }
137 }
138 }
139 }
140 return unswitch_iff;
141 }
142
143 //------------------------------do_unswitching-----------------------------
144 // Clone loop with an invariant test (that does not exit) and
145 // insert a clone of the test that selects which version to
146 // execute.
147 void PhaseIdealLoop::do_unswitching(IdealLoopTree *loop, Node_List &old_new) {
148 LoopNode* head = loop->_head->as_Loop();
149 if (has_control_dependencies_from_predicates(head)) {
150 return;
151 }
152
153 // Find first invariant test that doesn't exit the loop
154 Node_List unswitch_iffs;
155 IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop, unswitch_iffs);
156 assert(unswitch_iff != nullptr && unswitch_iff == unswitch_iffs.at(0), "should be at least one");
157 bool flat_array_checks = unswitch_iffs.size() > 1;
158
159 #ifndef PRODUCT
160 if (TraceLoopOpts) {
161 tty->print("Unswitch %d ", head->unswitch_count()+1);
162 loop->dump_head();
163 for (uint i = 0; i < unswitch_iffs.size(); i++) {
164 unswitch_iffs.at(i)->dump(3);
165 tty->cr();
166 }
167 }
168 #endif
169
170 // Need to revert back to normal loop
171 if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
172 head->as_CountedLoop()->set_normal_loop();
173 }
174
175 IfNode* invar_iff = create_slow_version_of_loop(loop, old_new, unswitch_iffs, CloneIncludesStripMined);
176 ProjNode* proj_true = invar_iff->proj_out(1);
177 verify_fast_loop(head, proj_true);
178
179 // Increment unswitch count
180 LoopNode* head_clone = old_new[head->_idx]->as_Loop();
181 int nct = head->unswitch_count() + 1;
182 head->set_unswitch_count(nct);
183 head_clone->set_unswitch_count(nct);
184
185 // Hoist invariant casts out of each loop to the appropriate control projection.
186 Node_List worklist;
187 for (uint i = 0; i < unswitch_iffs.size(); i++) {
188 IfNode* iff = unswitch_iffs.at(i)->as_If();
189 for (DUIterator_Fast imax, i = iff->fast_outs(imax); i < imax; i++) {
190 ProjNode* proj = iff->fast_out(i)->as_Proj();
191 // Copy to a worklist for easier manipulation
192 for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
193 Node* use = proj->fast_out(j);
194 if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
195 worklist.push(use);
196 }
197 }
198 ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
199 while (worklist.size() > 0) {
200 Node* use = worklist.pop();
201 Node* nuse = use->clone();
202 nuse->set_req(0, invar_proj);
203 _igvn.replace_input_of(use, 1, nuse);
204 register_new_node(nuse, invar_proj);
205 // Same for the clone if we are removing checks from the slow loop
206 if (!flat_array_checks) {
207 Node* use_clone = old_new[use->_idx];
208 _igvn.replace_input_of(use_clone, 1, nuse);
209 }
210 }
211 }
212 }
213
214 // Hardwire the control paths in the loops into if(true) and if(false)
215 for (uint i = 0; i < unswitch_iffs.size(); i++) {
216 IfNode* iff = unswitch_iffs.at(i)->as_If();
217 _igvn.rehash_node_delayed(iff);
218 dominated_by(proj_true->as_IfProj(), iff);
219 }
220 IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
221 if (!flat_array_checks) {
222 ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
223 _igvn.rehash_node_delayed(unswitch_iff_clone);
224 dominated_by(proj_false->as_IfProj(), unswitch_iff_clone);
225 } else {
226 // Leave the flat array checks in the slow loop and
227 // prevent it from being unswitched again based on these checks.
228 head_clone->mark_flat_arrays();
229 }
230
231 // Reoptimize loops
232 loop->record_for_igvn();
233 for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
234 Node *n = loop->_body[i];
235 Node *n_clone = old_new[n->_idx];
236 _igvn._worklist.push(n_clone);
237 }
238
239 #ifndef PRODUCT
240 if (TraceLoopUnswitching) {
241 for (uint i = 0; i < unswitch_iffs.size(); i++) {
242 tty->print_cr("Loop unswitching orig: %d @ %d new: %d @ %d",
243 head->_idx, unswitch_iffs.at(i)->_idx,
244 old_new[head->_idx]->_idx, old_new[unswitch_iffs.at(i)->_idx]->_idx);
245 }
246 }
247 #endif
248
249 C->set_major_progress();
250 }
251
252 bool PhaseIdealLoop::has_control_dependencies_from_predicates(LoopNode* head) const {
253 Node* entry = head->skip_strip_mined()->in(LoopNode::EntryControl);
254 Predicates predicates(entry);
255 if (predicates.has_any()) {
256 assert(entry->is_IfProj(), "sanity - must be ifProj since there is at least one predicate");
257 if (entry->outcnt() > 1) {
258 // Bailout if there are predicates from which there are additional control dependencies (i.e. from loop
259 // entry 'entry') to previously partially peeled statements since this case is not handled and can lead
260 // to a wrong execution. Remove this bailout, once this is fixed.
261 return true;
262 }
263 }
264 return false;
265 }
266
267 //-------------------------create_slow_version_of_loop------------------------
268 // Create a slow version of the loop by cloning the loop
269 // and inserting an if to select fast-slow versions.
270 // Return the inserted if.
271 IfNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
272 Node_List &old_new,
273 Node_List &unswitch_iffs,
274 CloneLoopMode mode) {
275 LoopNode* head = loop->_head->as_Loop();
276 bool counted_loop = head->is_CountedLoop();
277 Node* entry = head->skip_strip_mined()->in(LoopNode::EntryControl);
278 _igvn.rehash_node_delayed(entry);
279 IdealLoopTree* outer_loop = loop->_parent;
280
281 head->verify_strip_mined(1);
282
283 // Add test to new "if" outside of loop
284 IfNode* unswitch_iff = unswitch_iffs.at(0)->as_If();
285 BoolNode* bol = unswitch_iff->in(1)->as_Bool();
286 if (unswitch_iffs.size() > 1) {
287 // Flat array checks are used on array access to switch between
288 // a legacy object array access and a flat inline type array
289 // access. We want the performance impact on legacy accesses to be
290 // as small as possible so we make two copies of the loop: a fast
291 // one where all accesses are known to be legacy, a slow one where
292 // some accesses are to flat arrays. Flat array checks
293 // can be removed from the fast loop (true proj) but not from the
294 // slow loop (false proj) as it can have a mix of flat/legacy accesses.
295 assert(bol->_test._test == BoolTest::ne, "IfTrue proj must point to flat array");
296 bol = bol->clone()->as_Bool();
297 register_new_node(bol, entry);
298 FlatArrayCheckNode* cmp = bol->in(1)->clone()->as_FlatArrayCheck();
299 register_new_node(cmp, entry);
300 bol->set_req(1, cmp);
301 // Combine all checks into a single one that fails if one array is a flat array
302 assert(cmp->req() == 3, "unexpected number of inputs for FlatArrayCheck");
303 cmp->add_req_batch(C->top(), unswitch_iffs.size() - 1);
304 for (uint i = 0; i < unswitch_iffs.size(); i++) {
305 Node* array = unswitch_iffs.at(i)->in(1)->in(1)->in(FlatArrayCheckNode::ArrayOrKlass);
306 cmp->set_req(FlatArrayCheckNode::ArrayOrKlass + i, array);
307 }
308 }
309
310 IfNode* iff = (unswitch_iff->Opcode() == Op_RangeCheck) ? new RangeCheckNode(entry, bol, unswitch_iff->_prob, unswitch_iff->_fcnt) :
311 new IfNode(entry, bol, unswitch_iff->_prob, unswitch_iff->_fcnt);
312 register_node(iff, outer_loop, entry, dom_depth(entry));
313 IfProjNode* iffast = new IfTrueNode(iff);
314 register_node(iffast, outer_loop, iff, dom_depth(iff));
315 IfProjNode* ifslow = new IfFalseNode(iff);
316 register_node(ifslow, outer_loop, iff, dom_depth(iff));
317
318 // Clone the loop body. The clone becomes the slow loop. The
319 // original pre-header will (illegally) have 3 control users
320 // (old & new loops & new if).
321 clone_loop(loop, old_new, dom_depth(head->skip_strip_mined()), mode, iff);
322 assert(old_new[head->_idx]->is_Loop(), "" );
323
324 // Fast (true) and Slow (false) control
325 IfProjNode* iffast_pred = iffast;
326 IfProjNode* ifslow_pred = ifslow;
327 clone_parse_and_assertion_predicates_to_unswitched_loop(loop, old_new, iffast_pred, ifslow_pred);
328
329 Node* l = head->skip_strip_mined();
330 _igvn.replace_input_of(l, LoopNode::EntryControl, iffast_pred);
331 set_idom(l, iffast_pred, dom_depth(l));
332 LoopNode* slow_l = old_new[head->_idx]->as_Loop()->skip_strip_mined();
333 _igvn.replace_input_of(slow_l, LoopNode::EntryControl, ifslow_pred);
334 set_idom(slow_l, ifslow_pred, dom_depth(l));
335
336 recompute_dom_depth();
337
338 return iff;
339 }
340
341 #ifdef ASSERT
342 void PhaseIdealLoop::verify_fast_loop(LoopNode* head, const ProjNode* proj_true) const {
343 assert(proj_true->is_IfTrue(), "must be true projection");
344 Node* entry = head->skip_strip_mined()->in(LoopNode::EntryControl);
345 Predicates predicates(entry);
346 if (!predicates.has_any()) {
347 // No Parse Predicate.
348 Node* uniqc = proj_true->unique_ctrl_out();
349 assert((uniqc == head && !head->is_strip_mined()) || (uniqc == head->in(LoopNode::EntryControl)
350 && head->is_strip_mined()), "must hold by construction if no predicates");
351 } else {
352 // There is at least one Parse Predicate. When skipping all predicates/predicate blocks, we should end up
353 // at 'proj_true'.
354 assert(proj_true == predicates.entry(), "must hold by construction if at least one Parse Predicate");
355 }
356 }
357 #endif // ASSERT
358