1 /*
2 * Copyright (c) 2000, 2013, 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 "compiler/compileLog.hpp"
27 #include "memory/allocation.inline.hpp"
28 #include "opto/addnode.hpp"
29 #include "opto/callnode.hpp"
30 #include "opto/castnode.hpp"
31 #include "opto/connode.hpp"
32 #include "opto/convertnode.hpp"
33 #include "opto/divnode.hpp"
34 #include "opto/loopnode.hpp"
35 #include "opto/mulnode.hpp"
36 #include "opto/movenode.hpp"
37 #include "opto/opaquenode.hpp"
38 #include "opto/rootnode.hpp"
39 #include "opto/runtime.hpp"
40 #include "opto/subnode.hpp"
41
42 //------------------------------is_loop_exit-----------------------------------
43 // Given an IfNode, return the loop-exiting projection or NULL if both
44 // arms remain in the loop.
45 Node *IdealLoopTree::is_loop_exit(Node *iff) const {
46 if( iff->outcnt() != 2 ) return NULL; // Ignore partially dead tests
47 PhaseIdealLoop *phase = _phase;
48 // Test is an IfNode, has 2 projections. If BOTH are in the loop
49 // we need loop unswitching instead of peeling.
50 if( !is_member(phase->get_loop( iff->raw_out(0) )) )
51 return iff->raw_out(0);
52 if( !is_member(phase->get_loop( iff->raw_out(1) )) )
53 return iff->raw_out(1);
54 return NULL;
55 }
56
57
58 //=============================================================================
59
60
61 //------------------------------record_for_igvn----------------------------
62 // Put loop body on igvn work list
63 void IdealLoopTree::record_for_igvn() {
64 for( uint i = 0; i < _body.size(); i++ ) {
65 Node *n = _body.at(i);
66 _phase->_igvn._worklist.push(n);
67 }
68 }
69
70 //------------------------------compute_exact_trip_count-----------------------
71 // Compute loop exact trip count if possible. Do not recalculate trip count for
72 // split loops (pre-main-post) which have their limits and inits behind Opaque node.
73 void IdealLoopTree::compute_exact_trip_count( PhaseIdealLoop *phase ) {
74 if (!_head->as_Loop()->is_valid_counted_loop()) {
75 return;
76 }
77 CountedLoopNode* cl = _head->as_CountedLoop();
78 // Trip count may become nonexact for iteration split loops since
79 // RCE modifies limits. Note, _trip_count value is not reset since
80 // it is used to limit unrolling of main loop.
81 cl->set_nonexact_trip_count();
82
83 // Loop's test should be part of loop.
84 if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
85 return; // Infinite loop
86
87 #ifdef ASSERT
88 BoolTest::mask bt = cl->loopexit()->test_trip();
89 assert(bt == BoolTest::lt || bt == BoolTest::gt ||
90 bt == BoolTest::ne, "canonical test is expected");
91 #endif
92
93 Node* init_n = cl->init_trip();
94 Node* limit_n = cl->limit();
95 if (init_n != NULL && init_n->is_Con() &&
96 limit_n != NULL && limit_n->is_Con()) {
97 // Use longs to avoid integer overflow.
98 int stride_con = cl->stride_con();
99 jlong init_con = cl->init_trip()->get_int();
100 jlong limit_con = cl->limit()->get_int();
101 int stride_m = stride_con - (stride_con > 0 ? 1 : -1);
102 jlong trip_count = (limit_con - init_con + stride_m)/stride_con;
103 if (trip_count > 0 && (julong)trip_count < (julong)max_juint) {
104 // Set exact trip count.
105 cl->set_exact_trip_count((uint)trip_count);
106 }
107 }
108 }
109
110 //------------------------------compute_profile_trip_cnt----------------------------
111 // Compute loop trip count from profile data as
112 // (backedge_count + loop_exit_count) / loop_exit_count
113 void IdealLoopTree::compute_profile_trip_cnt( PhaseIdealLoop *phase ) {
114 if (!_head->is_CountedLoop()) {
115 return;
116 }
117 CountedLoopNode* head = _head->as_CountedLoop();
118 if (head->profile_trip_cnt() != COUNT_UNKNOWN) {
119 return; // Already computed
120 }
121 float trip_cnt = (float)max_jint; // default is big
122
123 Node* back = head->in(LoopNode::LoopBackControl);
124 while (back != head) {
125 if ((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
126 back->in(0) &&
127 back->in(0)->is_If() &&
128 back->in(0)->as_If()->_fcnt != COUNT_UNKNOWN &&
129 back->in(0)->as_If()->_prob != PROB_UNKNOWN) {
130 break;
131 }
132 back = phase->idom(back);
133 }
134 if (back != head) {
135 assert((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
136 back->in(0), "if-projection exists");
137 IfNode* back_if = back->in(0)->as_If();
138 float loop_back_cnt = back_if->_fcnt * back_if->_prob;
139
140 // Now compute a loop exit count
141 float loop_exit_cnt = 0.0f;
142 for( uint i = 0; i < _body.size(); i++ ) {
143 Node *n = _body[i];
144 if( n->is_If() ) {
145 IfNode *iff = n->as_If();
146 if( iff->_fcnt != COUNT_UNKNOWN && iff->_prob != PROB_UNKNOWN ) {
147 Node *exit = is_loop_exit(iff);
148 if( exit ) {
149 float exit_prob = iff->_prob;
150 if (exit->Opcode() == Op_IfFalse) exit_prob = 1.0 - exit_prob;
151 if (exit_prob > PROB_MIN) {
152 float exit_cnt = iff->_fcnt * exit_prob;
153 loop_exit_cnt += exit_cnt;
154 }
155 }
156 }
157 }
158 }
159 if (loop_exit_cnt > 0.0f) {
160 trip_cnt = (loop_back_cnt + loop_exit_cnt) / loop_exit_cnt;
161 } else {
162 // No exit count so use
163 trip_cnt = loop_back_cnt;
164 }
165 }
166 #ifndef PRODUCT
167 if (TraceProfileTripCount) {
168 tty->print_cr("compute_profile_trip_cnt lp: %d cnt: %f\n", head->_idx, trip_cnt);
169 }
170 #endif
171 head->set_profile_trip_cnt(trip_cnt);
172 }
173
174 //---------------------is_invariant_addition-----------------------------
175 // Return nonzero index of invariant operand for an Add or Sub
176 // of (nonconstant) invariant and variant values. Helper for reassociate_invariants.
177 int IdealLoopTree::is_invariant_addition(Node* n, PhaseIdealLoop *phase) {
178 int op = n->Opcode();
179 if (op == Op_AddI || op == Op_SubI) {
180 bool in1_invar = this->is_invariant(n->in(1));
181 bool in2_invar = this->is_invariant(n->in(2));
182 if (in1_invar && !in2_invar) return 1;
183 if (!in1_invar && in2_invar) return 2;
184 }
185 return 0;
186 }
187
188 //---------------------reassociate_add_sub-----------------------------
189 // Reassociate invariant add and subtract expressions:
190 //
191 // inv1 + (x + inv2) => ( inv1 + inv2) + x
192 // (x + inv2) + inv1 => ( inv1 + inv2) + x
193 // inv1 + (x - inv2) => ( inv1 - inv2) + x
194 // inv1 - (inv2 - x) => ( inv1 - inv2) + x
195 // (x + inv2) - inv1 => (-inv1 + inv2) + x
196 // (x - inv2) + inv1 => ( inv1 - inv2) + x
197 // (x - inv2) - inv1 => (-inv1 - inv2) + x
198 // inv1 + (inv2 - x) => ( inv1 + inv2) - x
199 // inv1 - (x - inv2) => ( inv1 + inv2) - x
200 // (inv2 - x) + inv1 => ( inv1 + inv2) - x
201 // (inv2 - x) - inv1 => (-inv1 + inv2) - x
202 // inv1 - (x + inv2) => ( inv1 - inv2) - x
203 //
204 Node* IdealLoopTree::reassociate_add_sub(Node* n1, PhaseIdealLoop *phase) {
205 if (!n1->is_Add() && !n1->is_Sub() || n1->outcnt() == 0) return NULL;
206 if (is_invariant(n1)) return NULL;
207 int inv1_idx = is_invariant_addition(n1, phase);
208 if (!inv1_idx) return NULL;
209 // Don't mess with add of constant (igvn moves them to expression tree root.)
210 if (n1->is_Add() && n1->in(2)->is_Con()) return NULL;
211 Node* inv1 = n1->in(inv1_idx);
212 Node* n2 = n1->in(3 - inv1_idx);
213 int inv2_idx = is_invariant_addition(n2, phase);
214 if (!inv2_idx) return NULL;
215 Node* x = n2->in(3 - inv2_idx);
216 Node* inv2 = n2->in(inv2_idx);
217
218 bool neg_x = n2->is_Sub() && inv2_idx == 1;
219 bool neg_inv2 = n2->is_Sub() && inv2_idx == 2;
220 bool neg_inv1 = n1->is_Sub() && inv1_idx == 2;
221 if (n1->is_Sub() && inv1_idx == 1) {
222 neg_x = !neg_x;
223 neg_inv2 = !neg_inv2;
224 }
225 Node* inv1_c = phase->get_ctrl(inv1);
226 Node* inv2_c = phase->get_ctrl(inv2);
227 Node* n_inv1;
228 if (neg_inv1) {
229 Node *zero = phase->_igvn.intcon(0);
230 phase->set_ctrl(zero, phase->C->root());
231 n_inv1 = new SubINode(zero, inv1);
232 phase->register_new_node(n_inv1, inv1_c);
233 } else {
234 n_inv1 = inv1;
235 }
236 Node* inv;
237 if (neg_inv2) {
238 inv = new SubINode(n_inv1, inv2);
239 } else {
240 inv = new AddINode(n_inv1, inv2);
241 }
242 phase->register_new_node(inv, phase->get_early_ctrl(inv));
243
244 Node* addx;
245 if (neg_x) {
246 addx = new SubINode(inv, x);
247 } else {
248 addx = new AddINode(x, inv);
249 }
250 phase->register_new_node(addx, phase->get_ctrl(x));
251 phase->_igvn.replace_node(n1, addx);
252 assert(phase->get_loop(phase->get_ctrl(n1)) == this, "");
253 _body.yank(n1);
254 return addx;
255 }
256
257 //---------------------reassociate_invariants-----------------------------
258 // Reassociate invariant expressions:
259 void IdealLoopTree::reassociate_invariants(PhaseIdealLoop *phase) {
260 for (int i = _body.size() - 1; i >= 0; i--) {
261 Node *n = _body.at(i);
262 for (int j = 0; j < 5; j++) {
263 Node* nn = reassociate_add_sub(n, phase);
264 if (nn == NULL) break;
265 n = nn; // again
266 };
267 }
268 }
269
270 //------------------------------policy_peeling---------------------------------
271 // Return TRUE or FALSE if the loop should be peeled or not. Peel if we can
272 // make some loop-invariant test (usually a null-check) happen before the loop.
273 bool IdealLoopTree::policy_peeling( PhaseIdealLoop *phase ) const {
274 Node *test = ((IdealLoopTree*)this)->tail();
275 int body_size = ((IdealLoopTree*)this)->_body.size();
276 int live_node_count = phase->C->live_nodes();
277 // Peeling does loop cloning which can result in O(N^2) node construction
278 if( body_size > 255 /* Prevent overflow for large body_size */
279 || (body_size * body_size + live_node_count > MaxNodeLimit) ) {
280 return false; // too large to safely clone
281 }
282 while( test != _head ) { // Scan till run off top of loop
283 if( test->is_If() ) { // Test?
284 Node *ctrl = phase->get_ctrl(test->in(1));
285 if (ctrl->is_top())
286 return false; // Found dead test on live IF? No peeling!
287 // Standard IF only has one input value to check for loop invariance
288 assert( test->Opcode() == Op_If || test->Opcode() == Op_CountedLoopEnd, "Check this code when new subtype is added");
289 // Condition is not a member of this loop?
290 if( !is_member(phase->get_loop(ctrl)) &&
291 is_loop_exit(test) )
292 return true; // Found reason to peel!
293 }
294 // Walk up dominators to loop _head looking for test which is
295 // executed on every path thru loop.
296 test = phase->idom(test);
297 }
298 return false;
299 }
300
301 //------------------------------peeled_dom_test_elim---------------------------
302 // If we got the effect of peeling, either by actually peeling or by making
303 // a pre-loop which must execute at least once, we can remove all
304 // loop-invariant dominated tests in the main body.
305 void PhaseIdealLoop::peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new ) {
306 bool progress = true;
307 while( progress ) {
308 progress = false; // Reset for next iteration
309 Node *prev = loop->_head->in(LoopNode::LoopBackControl);//loop->tail();
310 Node *test = prev->in(0);
311 while( test != loop->_head ) { // Scan till run off top of loop
312
313 int p_op = prev->Opcode();
314 if( (p_op == Op_IfFalse || p_op == Op_IfTrue) &&
315 test->is_If() && // Test?
316 !test->in(1)->is_Con() && // And not already obvious?
317 // Condition is not a member of this loop?
318 !loop->is_member(get_loop(get_ctrl(test->in(1))))){
319 // Walk loop body looking for instances of this test
320 for( uint i = 0; i < loop->_body.size(); i++ ) {
321 Node *n = loop->_body.at(i);
322 if( n->is_If() && n->in(1) == test->in(1) /*&& n != loop->tail()->in(0)*/ ) {
323 // IfNode was dominated by version in peeled loop body
324 progress = true;
325 dominated_by( old_new[prev->_idx], n );
326 }
327 }
328 }
329 prev = test;
330 test = idom(test);
331 } // End of scan tests in loop
332
333 } // End of while( progress )
334 }
335
336 //------------------------------do_peeling-------------------------------------
337 // Peel the first iteration of the given loop.
338 // Step 1: Clone the loop body. The clone becomes the peeled iteration.
339 // The pre-loop illegally has 2 control users (old & new loops).
340 // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
341 // Do this by making the old-loop fall-in edges act as if they came
342 // around the loopback from the prior iteration (follow the old-loop
343 // backedges) and then map to the new peeled iteration. This leaves
344 // the pre-loop with only 1 user (the new peeled iteration), but the
345 // peeled-loop backedge has 2 users.
346 // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
347 // extra backedge user.
348 //
349 // orig
350 //
351 // stmt1
352 // |
353 // v
354 // loop predicate
355 // |
356 // v
357 // loop<----+
358 // | |
359 // stmt2 |
360 // | |
361 // v |
362 // if ^
363 // / \ |
364 // / \ |
365 // v v |
366 // false true |
367 // / \ |
368 // / ----+
369 // |
370 // v
371 // exit
372 //
373 //
374 // after clone loop
375 //
376 // stmt1
377 // |
378 // v
379 // loop predicate
380 // / \
381 // clone / \ orig
382 // / \
383 // / \
384 // v v
385 // +---->loop clone loop<----+
386 // | | | |
387 // | stmt2 clone stmt2 |
388 // | | | |
389 // | v v |
390 // ^ if clone If ^
391 // | / \ / \ |
392 // | / \ / \ |
393 // | v v v v |
394 // | true false false true |
395 // | / \ / \ |
396 // +---- \ / ----+
397 // \ /
398 // 1v v2
399 // region
400 // |
401 // v
402 // exit
403 //
404 //
405 // after peel and predicate move
406 //
407 // stmt1
408 // /
409 // /
410 // clone / orig
411 // /
412 // / +----------+
413 // / | |
414 // / loop predicate |
415 // / | |
416 // v v |
417 // TOP-->loop clone loop<----+ |
418 // | | | |
419 // stmt2 clone stmt2 | |
420 // | | | ^
421 // v v | |
422 // if clone If ^ |
423 // / \ / \ | |
424 // / \ / \ | |
425 // v v v v | |
426 // true false false true | |
427 // | \ / \ | |
428 // | \ / ----+ ^
429 // | \ / |
430 // | 1v v2 |
431 // v region |
432 // | | |
433 // | v |
434 // | exit |
435 // | |
436 // +--------------->-----------------+
437 //
438 //
439 // final graph
440 //
441 // stmt1
442 // |
443 // v
444 // stmt2 clone
445 // |
446 // v
447 // if clone
448 // / |
449 // / |
450 // v v
451 // false true
452 // | |
453 // | v
454 // | loop predicate
455 // | |
456 // | v
457 // | loop<----+
458 // | | |
459 // | stmt2 |
460 // | | |
461 // | v |
462 // v if ^
463 // | / \ |
464 // | / \ |
465 // | v v |
466 // | false true |
467 // | | \ |
468 // v v --+
469 // region
470 // |
471 // v
472 // exit
473 //
474 void PhaseIdealLoop::do_peeling( IdealLoopTree *loop, Node_List &old_new ) {
475
476 C->set_major_progress();
477 // Peeling a 'main' loop in a pre/main/post situation obfuscates the
478 // 'pre' loop from the main and the 'pre' can no longer have it's
479 // iterations adjusted. Therefore, we need to declare this loop as
480 // no longer a 'main' loop; it will need new pre and post loops before
481 // we can do further RCE.
482 #ifndef PRODUCT
483 if (TraceLoopOpts) {
484 tty->print("Peel ");
485 loop->dump_head();
486 }
487 #endif
488 Node* head = loop->_head;
489 bool counted_loop = head->is_CountedLoop();
490 if (counted_loop) {
491 CountedLoopNode *cl = head->as_CountedLoop();
492 assert(cl->trip_count() > 0, "peeling a fully unrolled loop");
493 cl->set_trip_count(cl->trip_count() - 1);
494 if (cl->is_main_loop()) {
495 cl->set_normal_loop();
496 #ifndef PRODUCT
497 if (PrintOpto && VerifyLoopOptimizations) {
498 tty->print("Peeling a 'main' loop; resetting to 'normal' ");
499 loop->dump_head();
500 }
501 #endif
502 }
503 }
504 Node* entry = head->in(LoopNode::EntryControl);
505
506 // Step 1: Clone the loop body. The clone becomes the peeled iteration.
507 // The pre-loop illegally has 2 control users (old & new loops).
508 clone_loop( loop, old_new, dom_depth(head) );
509
510 // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
511 // Do this by making the old-loop fall-in edges act as if they came
512 // around the loopback from the prior iteration (follow the old-loop
513 // backedges) and then map to the new peeled iteration. This leaves
514 // the pre-loop with only 1 user (the new peeled iteration), but the
515 // peeled-loop backedge has 2 users.
516 Node* new_entry = old_new[head->in(LoopNode::LoopBackControl)->_idx];
517 _igvn.hash_delete(head);
518 head->set_req(LoopNode::EntryControl, new_entry);
519 for (DUIterator_Fast jmax, j = head->fast_outs(jmax); j < jmax; j++) {
520 Node* old = head->fast_out(j);
521 if (old->in(0) == loop->_head && old->req() == 3 && old->is_Phi()) {
522 Node* new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx];
523 if (!new_exit_value ) // Backedge value is ALSO loop invariant?
524 // Then loop body backedge value remains the same.
525 new_exit_value = old->in(LoopNode::LoopBackControl);
526 _igvn.hash_delete(old);
527 old->set_req(LoopNode::EntryControl, new_exit_value);
528 }
529 }
530
531
532 // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
533 // extra backedge user.
534 Node* new_head = old_new[head->_idx];
535 _igvn.hash_delete(new_head);
536 new_head->set_req(LoopNode::LoopBackControl, C->top());
537 for (DUIterator_Fast j2max, j2 = new_head->fast_outs(j2max); j2 < j2max; j2++) {
538 Node* use = new_head->fast_out(j2);
539 if (use->in(0) == new_head && use->req() == 3 && use->is_Phi()) {
540 _igvn.hash_delete(use);
541 use->set_req(LoopNode::LoopBackControl, C->top());
542 }
543 }
544
545
546 // Step 4: Correct dom-depth info. Set to loop-head depth.
547 int dd = dom_depth(head);
548 set_idom(head, head->in(1), dd);
549 for (uint j3 = 0; j3 < loop->_body.size(); j3++) {
550 Node *old = loop->_body.at(j3);
551 Node *nnn = old_new[old->_idx];
552 if (!has_ctrl(nnn))
553 set_idom(nnn, idom(nnn), dd-1);
554 }
555
556 // Now force out all loop-invariant dominating tests. The optimizer
557 // finds some, but we _know_ they are all useless.
558 peeled_dom_test_elim(loop,old_new);
559
560 loop->record_for_igvn();
561 }
562
563 #define EMPTY_LOOP_SIZE 7 // number of nodes in an empty loop
564
565 //------------------------------policy_maximally_unroll------------------------
566 // Calculate exact loop trip count and return true if loop can be maximally
567 // unrolled.
568 bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const {
569 CountedLoopNode *cl = _head->as_CountedLoop();
570 assert(cl->is_normal_loop(), "");
571 if (!cl->is_valid_counted_loop())
572 return false; // Malformed counted loop
573
574 if (!cl->has_exact_trip_count()) {
575 // Trip count is not exact.
576 return false;
577 }
578
579 uint trip_count = cl->trip_count();
580 // Note, max_juint is used to indicate unknown trip count.
581 assert(trip_count > 1, "one iteration loop should be optimized out already");
582 assert(trip_count < max_juint, "exact trip_count should be less than max_uint.");
583
584 // Real policy: if we maximally unroll, does it get too big?
585 // Allow the unrolled mess to get larger than standard loop
586 // size. After all, it will no longer be a loop.
587 uint body_size = _body.size();
588 uint unroll_limit = (uint)LoopUnrollLimit * 4;
589 assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits");
590 if (trip_count > unroll_limit || body_size > unroll_limit) {
591 return false;
592 }
593
594 // Fully unroll a loop with few iterations regardless next
595 // conditions since following loop optimizations will split
596 // such loop anyway (pre-main-post).
597 if (trip_count <= 3)
598 return true;
599
600 // Take into account that after unroll conjoined heads and tails will fold,
601 // otherwise policy_unroll() may allow more unrolling than max unrolling.
602 uint new_body_size = EMPTY_LOOP_SIZE + (body_size - EMPTY_LOOP_SIZE) * trip_count;
603 uint tst_body_size = (new_body_size - EMPTY_LOOP_SIZE) / trip_count + EMPTY_LOOP_SIZE;
604 if (body_size != tst_body_size) // Check for int overflow
605 return false;
606 if (new_body_size > unroll_limit ||
607 // Unrolling can result in a large amount of node construction
608 new_body_size >= MaxNodeLimit - (uint) phase->C->live_nodes()) {
609 return false;
610 }
611
612 // Do not unroll a loop with String intrinsics code.
613 // String intrinsics are large and have loops.
614 for (uint k = 0; k < _body.size(); k++) {
615 Node* n = _body.at(k);
616 switch (n->Opcode()) {
617 case Op_StrComp:
618 case Op_StrEquals:
619 case Op_StrIndexOf:
620 case Op_EncodeISOArray:
621 case Op_AryEq: {
622 return false;
623 }
624 #if INCLUDE_RTM_OPT
625 case Op_FastLock:
626 case Op_FastUnlock: {
627 // Don't unroll RTM locking code because it is large.
628 if (UseRTMLocking) {
629 return false;
630 }
631 }
632 #endif
633 } // switch
634 }
635
636 return true; // Do maximally unroll
637 }
638
639
640 //------------------------------policy_unroll----------------------------------
641 // Return TRUE or FALSE if the loop should be unrolled or not. Unroll if
642 // the loop is a CountedLoop and the body is small enough.
643 bool IdealLoopTree::policy_unroll( PhaseIdealLoop *phase ) const {
644
645 CountedLoopNode *cl = _head->as_CountedLoop();
646 assert(cl->is_normal_loop() || cl->is_main_loop(), "");
647
648 if (!cl->is_valid_counted_loop())
649 return false; // Malformed counted loop
650
651 // Protect against over-unrolling.
652 // After split at least one iteration will be executed in pre-loop.
653 if (cl->trip_count() <= (uint)(cl->is_normal_loop() ? 2 : 1)) return false;
654
655 int future_unroll_ct = cl->unrolled_count() * 2;
656 if (future_unroll_ct > LoopMaxUnroll) return false;
657
658 // Check for initial stride being a small enough constant
659 if (abs(cl->stride_con()) > (1<<2)*future_unroll_ct) return false;
660
661 // Don't unroll if the next round of unrolling would push us
662 // over the expected trip count of the loop. One is subtracted
663 // from the expected trip count because the pre-loop normally
664 // executes 1 iteration.
665 if (UnrollLimitForProfileCheck > 0 &&
666 cl->profile_trip_cnt() != COUNT_UNKNOWN &&
667 future_unroll_ct > UnrollLimitForProfileCheck &&
668 (float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) {
669 return false;
670 }
671
672 // When unroll count is greater than LoopUnrollMin, don't unroll if:
673 // the residual iterations are more than 10% of the trip count
674 // and rounds of "unroll,optimize" are not making significant progress
675 // Progress defined as current size less than 20% larger than previous size.
676 if (UseSuperWord && cl->node_count_before_unroll() > 0 &&
677 future_unroll_ct > LoopUnrollMin &&
678 (future_unroll_ct - 1) * 10.0 > cl->profile_trip_cnt() &&
679 1.2 * cl->node_count_before_unroll() < (double)_body.size()) {
680 return false;
681 }
682
683 Node *init_n = cl->init_trip();
684 Node *limit_n = cl->limit();
685 int stride_con = cl->stride_con();
686 // Non-constant bounds.
687 // Protect against over-unrolling when init or/and limit are not constant
688 // (so that trip_count's init value is maxint) but iv range is known.
689 if (init_n == NULL || !init_n->is_Con() ||
690 limit_n == NULL || !limit_n->is_Con()) {
691 Node* phi = cl->phi();
692 if (phi != NULL) {
693 assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi.");
694 const TypeInt* iv_type = phase->_igvn.type(phi)->is_int();
695 int next_stride = stride_con * 2; // stride after this unroll
696 if (next_stride > 0) {
697 if (iv_type->_lo + next_stride <= iv_type->_lo || // overflow
698 iv_type->_lo + next_stride > iv_type->_hi) {
699 return false; // over-unrolling
700 }
701 } else if (next_stride < 0) {
702 if (iv_type->_hi + next_stride >= iv_type->_hi || // overflow
703 iv_type->_hi + next_stride < iv_type->_lo) {
704 return false; // over-unrolling
705 }
706 }
707 }
708 }
709
710 // After unroll limit will be adjusted: new_limit = limit-stride.
711 // Bailout if adjustment overflow.
712 const TypeInt* limit_type = phase->_igvn.type(limit_n)->is_int();
713 if (stride_con > 0 && ((limit_type->_hi - stride_con) >= limit_type->_hi) ||
714 stride_con < 0 && ((limit_type->_lo - stride_con) <= limit_type->_lo))
715 return false; // overflow
716
717 // Adjust body_size to determine if we unroll or not
718 uint body_size = _body.size();
719 // Key test to unroll loop in CRC32 java code
720 int xors_in_loop = 0;
721 // Also count ModL, DivL and MulL which expand mightly
722 for (uint k = 0; k < _body.size(); k++) {
723 Node* n = _body.at(k);
724 switch (n->Opcode()) {
725 case Op_XorI: xors_in_loop++; break; // CRC32 java code
726 case Op_ModL: body_size += 30; break;
727 case Op_DivL: body_size += 30; break;
728 case Op_MulL: body_size += 10; break;
729 case Op_StrComp:
730 case Op_StrEquals:
731 case Op_StrIndexOf:
732 case Op_EncodeISOArray:
733 case Op_AryEq: {
734 // Do not unroll a loop with String intrinsics code.
735 // String intrinsics are large and have loops.
736 return false;
737 }
738 #if INCLUDE_RTM_OPT
739 case Op_FastLock:
740 case Op_FastUnlock: {
741 // Don't unroll RTM locking code because it is large.
742 if (UseRTMLocking) {
743 return false;
744 }
745 }
746 #endif
747 } // switch
748 }
749
750 // Check for being too big
751 if (body_size > (uint)LoopUnrollLimit) {
752 if (xors_in_loop >= 4 && body_size < (uint)LoopUnrollLimit*4) return true;
753 // Normal case: loop too big
754 return false;
755 }
756
757 // Unroll once! (Each trip will soon do double iterations)
758 return true;
759 }
760
761 //------------------------------policy_align-----------------------------------
762 // Return TRUE or FALSE if the loop should be cache-line aligned. Gather the
763 // expression that does the alignment. Note that only one array base can be
764 // aligned in a loop (unless the VM guarantees mutual alignment). Note that
765 // if we vectorize short memory ops into longer memory ops, we may want to
766 // increase alignment.
767 bool IdealLoopTree::policy_align( PhaseIdealLoop *phase ) const {
768 return false;
769 }
770
771 //------------------------------policy_range_check-----------------------------
772 // Return TRUE or FALSE if the loop should be range-check-eliminated.
773 // Actually we do iteration-splitting, a more powerful form of RCE.
774 bool IdealLoopTree::policy_range_check( PhaseIdealLoop *phase ) const {
775 if (!RangeCheckElimination) return false;
776
777 CountedLoopNode *cl = _head->as_CountedLoop();
778 // If we unrolled with no intention of doing RCE and we later
779 // changed our minds, we got no pre-loop. Either we need to
780 // make a new pre-loop, or we gotta disallow RCE.
781 if (cl->is_main_no_pre_loop()) return false; // Disallowed for now.
782 Node *trip_counter = cl->phi();
783
784 // Check loop body for tests of trip-counter plus loop-invariant vs
785 // loop-invariant.
786 for (uint i = 0; i < _body.size(); i++) {
787 Node *iff = _body[i];
788 if (iff->Opcode() == Op_If) { // Test?
789
790 // Comparing trip+off vs limit
791 Node *bol = iff->in(1);
792 if (bol->req() != 2) continue; // dead constant test
793 if (!bol->is_Bool()) {
794 assert(UseLoopPredicate && bol->Opcode() == Op_Conv2B, "predicate check only");
795 continue;
796 }
797 if (bol->as_Bool()->_test._test == BoolTest::ne)
798 continue; // not RC
799
800 Node *cmp = bol->in(1);
801 Node *rc_exp = cmp->in(1);
802 Node *limit = cmp->in(2);
803
804 Node *limit_c = phase->get_ctrl(limit);
805 if( limit_c == phase->C->top() )
806 return false; // Found dead test on live IF? No RCE!
807 if( is_member(phase->get_loop(limit_c) ) ) {
808 // Compare might have operands swapped; commute them
809 rc_exp = cmp->in(2);
810 limit = cmp->in(1);
811 limit_c = phase->get_ctrl(limit);
812 if( is_member(phase->get_loop(limit_c) ) )
813 continue; // Both inputs are loop varying; cannot RCE
814 }
815
816 if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) {
817 continue;
818 }
819 // Yeah! Found a test like 'trip+off vs limit'
820 // Test is an IfNode, has 2 projections. If BOTH are in the loop
821 // we need loop unswitching instead of iteration splitting.
822 if( is_loop_exit(iff) )
823 return true; // Found reason to split iterations
824 } // End of is IF
825 }
826
827 return false;
828 }
829
830 //------------------------------policy_peel_only-------------------------------
831 // Return TRUE or FALSE if the loop should NEVER be RCE'd or aligned. Useful
832 // for unrolling loops with NO array accesses.
833 bool IdealLoopTree::policy_peel_only( PhaseIdealLoop *phase ) const {
834
835 for( uint i = 0; i < _body.size(); i++ )
836 if( _body[i]->is_Mem() )
837 return false;
838
839 // No memory accesses at all!
840 return true;
841 }
842
843 //------------------------------clone_up_backedge_goo--------------------------
844 // If Node n lives in the back_ctrl block and cannot float, we clone a private
845 // version of n in preheader_ctrl block and return that, otherwise return n.
846 Node *PhaseIdealLoop::clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n, VectorSet &visited, Node_Stack &clones ) {
847 if( get_ctrl(n) != back_ctrl ) return n;
848
849 // Only visit once
850 if (visited.test_set(n->_idx)) {
851 Node *x = clones.find(n->_idx);
852 if (x != NULL)
853 return x;
854 return n;
855 }
856
857 Node *x = NULL; // If required, a clone of 'n'
858 // Check for 'n' being pinned in the backedge.
859 if( n->in(0) && n->in(0) == back_ctrl ) {
860 assert(clones.find(n->_idx) == NULL, "dead loop");
861 x = n->clone(); // Clone a copy of 'n' to preheader
862 clones.push(x, n->_idx);
863 x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader
864 }
865
866 // Recursive fixup any other input edges into x.
867 // If there are no changes we can just return 'n', otherwise
868 // we need to clone a private copy and change it.
869 for( uint i = 1; i < n->req(); i++ ) {
870 Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i), visited, clones );
871 if( g != n->in(i) ) {
872 if( !x ) {
873 assert(clones.find(n->_idx) == NULL, "dead loop");
874 x = n->clone();
875 clones.push(x, n->_idx);
876 }
877 x->set_req(i, g);
878 }
879 }
880 if( x ) { // x can legally float to pre-header location
881 register_new_node( x, preheader_ctrl );
882 return x;
883 } else { // raise n to cover LCA of uses
884 set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) );
885 }
886 return n;
887 }
888
889 bool PhaseIdealLoop::cast_incr_before_loop(Node* incr, Node* ctrl, Node* loop) {
890 Node* castii = new CastIINode(incr, TypeInt::INT, true);
891 castii->set_req(0, ctrl);
892 register_new_node(castii, ctrl);
893 for (DUIterator_Fast imax, i = incr->fast_outs(imax); i < imax; i++) {
894 Node* n = incr->fast_out(i);
895 if (n->is_Phi() && n->in(0) == loop) {
896 int nrep = n->replace_edge(incr, castii);
897 return true;
898 }
899 }
900 return false;
901 }
902
903 //------------------------------insert_pre_post_loops--------------------------
904 // Insert pre and post loops. If peel_only is set, the pre-loop can not have
905 // more iterations added. It acts as a 'peel' only, no lower-bound RCE, no
906 // alignment. Useful to unroll loops that do no array accesses.
907 void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) {
908
909 #ifndef PRODUCT
910 if (TraceLoopOpts) {
911 if (peel_only)
912 tty->print("PeelMainPost ");
913 else
914 tty->print("PreMainPost ");
915 loop->dump_head();
916 }
917 #endif
918 C->set_major_progress();
919
920 // Find common pieces of the loop being guarded with pre & post loops
921 CountedLoopNode *main_head = loop->_head->as_CountedLoop();
922 assert( main_head->is_normal_loop(), "" );
923 CountedLoopEndNode *main_end = main_head->loopexit();
924 guarantee(main_end != NULL, "no loop exit node");
925 assert( main_end->outcnt() == 2, "1 true, 1 false path only" );
926 uint dd_main_head = dom_depth(main_head);
927 uint max = main_head->outcnt();
928
929 Node *pre_header= main_head->in(LoopNode::EntryControl);
930 Node *init = main_head->init_trip();
931 Node *incr = main_end ->incr();
932 Node *limit = main_end ->limit();
933 Node *stride = main_end ->stride();
934 Node *cmp = main_end ->cmp_node();
935 BoolTest::mask b_test = main_end->test_trip();
936
937 // Need only 1 user of 'bol' because I will be hacking the loop bounds.
938 Node *bol = main_end->in(CountedLoopEndNode::TestValue);
939 if( bol->outcnt() != 1 ) {
940 bol = bol->clone();
941 register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl));
942 _igvn.replace_input_of(main_end, CountedLoopEndNode::TestValue, bol);
943 }
944 // Need only 1 user of 'cmp' because I will be hacking the loop bounds.
945 if( cmp->outcnt() != 1 ) {
946 cmp = cmp->clone();
947 register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl));
948 _igvn.replace_input_of(bol, 1, cmp);
949 }
950
951 //------------------------------
952 // Step A: Create Post-Loop.
953 Node* main_exit = main_end->proj_out(false);
954 assert( main_exit->Opcode() == Op_IfFalse, "" );
955 int dd_main_exit = dom_depth(main_exit);
956
957 // Step A1: Clone the loop body. The clone becomes the post-loop. The main
958 // loop pre-header illegally has 2 control users (old & new loops).
959 clone_loop( loop, old_new, dd_main_exit );
960 assert( old_new[main_end ->_idx]->Opcode() == Op_CountedLoopEnd, "" );
961 CountedLoopNode *post_head = old_new[main_head->_idx]->as_CountedLoop();
962 post_head->set_post_loop(main_head);
963
964 // Reduce the post-loop trip count.
965 CountedLoopEndNode* post_end = old_new[main_end ->_idx]->as_CountedLoopEnd();
966 post_end->_prob = PROB_FAIR;
967
968 // Build the main-loop normal exit.
969 IfFalseNode *new_main_exit = new IfFalseNode(main_end);
970 _igvn.register_new_node_with_optimizer( new_main_exit );
971 set_idom(new_main_exit, main_end, dd_main_exit );
972 set_loop(new_main_exit, loop->_parent);
973
974 // Step A2: Build a zero-trip guard for the post-loop. After leaving the
975 // main-loop, the post-loop may not execute at all. We 'opaque' the incr
976 // (the main-loop trip-counter exit value) because we will be changing
977 // the exit value (via unrolling) so we cannot constant-fold away the zero
978 // trip guard until all unrolling is done.
979 Node *zer_opaq = new Opaque1Node(C, incr);
980 Node *zer_cmp = new CmpINode( zer_opaq, limit );
981 Node *zer_bol = new BoolNode( zer_cmp, b_test );
982 register_new_node( zer_opaq, new_main_exit );
983 register_new_node( zer_cmp , new_main_exit );
984 register_new_node( zer_bol , new_main_exit );
985
986 // Build the IfNode
987 IfNode *zer_iff = new IfNode( new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN );
988 _igvn.register_new_node_with_optimizer( zer_iff );
989 set_idom(zer_iff, new_main_exit, dd_main_exit);
990 set_loop(zer_iff, loop->_parent);
991
992 // Plug in the false-path, taken if we need to skip post-loop
993 _igvn.replace_input_of(main_exit, 0, zer_iff);
994 set_idom(main_exit, zer_iff, dd_main_exit);
995 set_idom(main_exit->unique_out(), zer_iff, dd_main_exit);
996 // Make the true-path, must enter the post loop
997 Node *zer_taken = new IfTrueNode( zer_iff );
998 _igvn.register_new_node_with_optimizer( zer_taken );
999 set_idom(zer_taken, zer_iff, dd_main_exit);
1000 set_loop(zer_taken, loop->_parent);
1001 // Plug in the true path
1002 _igvn.hash_delete( post_head );
1003 post_head->set_req(LoopNode::EntryControl, zer_taken);
1004 set_idom(post_head, zer_taken, dd_main_exit);
1005
1006 Arena *a = Thread::current()->resource_area();
1007 VectorSet visited(a);
1008 Node_Stack clones(a, main_head->back_control()->outcnt());
1009 // Step A3: Make the fall-in values to the post-loop come from the
1010 // fall-out values of the main-loop.
1011 for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) {
1012 Node* main_phi = main_head->fast_out(i);
1013 if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0 ) {
1014 Node *post_phi = old_new[main_phi->_idx];
1015 Node *fallmain = clone_up_backedge_goo(main_head->back_control(),
1016 post_head->init_control(),
1017 main_phi->in(LoopNode::LoopBackControl),
1018 visited, clones);
1019 _igvn.hash_delete(post_phi);
1020 post_phi->set_req( LoopNode::EntryControl, fallmain );
1021 }
1022 }
1023
1024 // Update local caches for next stanza
1025 main_exit = new_main_exit;
1026
1027
1028 //------------------------------
1029 // Step B: Create Pre-Loop.
1030
1031 // Step B1: Clone the loop body. The clone becomes the pre-loop. The main
1032 // loop pre-header illegally has 2 control users (old & new loops).
1033 clone_loop( loop, old_new, dd_main_head );
1034 CountedLoopNode* pre_head = old_new[main_head->_idx]->as_CountedLoop();
1035 CountedLoopEndNode* pre_end = old_new[main_end ->_idx]->as_CountedLoopEnd();
1036 pre_head->set_pre_loop(main_head);
1037 Node *pre_incr = old_new[incr->_idx];
1038
1039 // Reduce the pre-loop trip count.
1040 pre_end->_prob = PROB_FAIR;
1041
1042 // Find the pre-loop normal exit.
1043 Node* pre_exit = pre_end->proj_out(false);
1044 assert( pre_exit->Opcode() == Op_IfFalse, "" );
1045 IfFalseNode *new_pre_exit = new IfFalseNode(pre_end);
1046 _igvn.register_new_node_with_optimizer( new_pre_exit );
1047 set_idom(new_pre_exit, pre_end, dd_main_head);
1048 set_loop(new_pre_exit, loop->_parent);
1049
1050 // Step B2: Build a zero-trip guard for the main-loop. After leaving the
1051 // pre-loop, the main-loop may not execute at all. Later in life this
1052 // zero-trip guard will become the minimum-trip guard when we unroll
1053 // the main-loop.
1054 Node *min_opaq = new Opaque1Node(C, limit);
1055 Node *min_cmp = new CmpINode( pre_incr, min_opaq );
1056 Node *min_bol = new BoolNode( min_cmp, b_test );
1057 register_new_node( min_opaq, new_pre_exit );
1058 register_new_node( min_cmp , new_pre_exit );
1059 register_new_node( min_bol , new_pre_exit );
1060
1061 // Build the IfNode (assume the main-loop is executed always).
1062 IfNode *min_iff = new IfNode( new_pre_exit, min_bol, PROB_ALWAYS, COUNT_UNKNOWN );
1063 _igvn.register_new_node_with_optimizer( min_iff );
1064 set_idom(min_iff, new_pre_exit, dd_main_head);
1065 set_loop(min_iff, loop->_parent);
1066
1067 // Plug in the false-path, taken if we need to skip main-loop
1068 _igvn.hash_delete( pre_exit );
1069 pre_exit->set_req(0, min_iff);
1070 set_idom(pre_exit, min_iff, dd_main_head);
1071 set_idom(pre_exit->unique_out(), min_iff, dd_main_head);
1072 // Make the true-path, must enter the main loop
1073 Node *min_taken = new IfTrueNode( min_iff );
1074 _igvn.register_new_node_with_optimizer( min_taken );
1075 set_idom(min_taken, min_iff, dd_main_head);
1076 set_loop(min_taken, loop->_parent);
1077 // Plug in the true path
1078 _igvn.hash_delete( main_head );
1079 main_head->set_req(LoopNode::EntryControl, min_taken);
1080 set_idom(main_head, min_taken, dd_main_head);
1081
1082 visited.Clear();
1083 clones.clear();
1084 // Step B3: Make the fall-in values to the main-loop come from the
1085 // fall-out values of the pre-loop.
1086 for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) {
1087 Node* main_phi = main_head->fast_out(i2);
1088 if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) {
1089 Node *pre_phi = old_new[main_phi->_idx];
1090 Node *fallpre = clone_up_backedge_goo(pre_head->back_control(),
1091 main_head->init_control(),
1092 pre_phi->in(LoopNode::LoopBackControl),
1093 visited, clones);
1094 _igvn.hash_delete(main_phi);
1095 main_phi->set_req( LoopNode::EntryControl, fallpre );
1096 }
1097 }
1098
1099 // Nodes inside the loop may be control dependent on a predicate
1100 // that was moved before the preloop. If the back branch of the main
1101 // or post loops becomes dead, those nodes won't be dependent on the
1102 // test that guards that loop nest anymore which could lead to an
1103 // incorrect array access because it executes independently of the
1104 // test that was guarding the loop nest. We add a special CastII on
1105 // the if branch that enters the loop, between the input induction
1106 // variable value and the induction variable Phi to preserve correct
1107 // dependencies.
1108
1109 // CastII for the post loop:
1110 bool inserted = cast_incr_before_loop(zer_opaq->in(1), zer_taken, post_head);
1111 assert(inserted, "no castII inserted");
1112
1113 // CastII for the main loop:
1114 inserted = cast_incr_before_loop(pre_incr, min_taken, main_head);
1115 assert(inserted, "no castII inserted");
1116
1117 // Step B4: Shorten the pre-loop to run only 1 iteration (for now).
1118 // RCE and alignment may change this later.
1119 Node *cmp_end = pre_end->cmp_node();
1120 assert( cmp_end->in(2) == limit, "" );
1121 Node *pre_limit = new AddINode( init, stride );
1122
1123 // Save the original loop limit in this Opaque1 node for
1124 // use by range check elimination.
1125 Node *pre_opaq = new Opaque1Node(C, pre_limit, limit);
1126
1127 register_new_node( pre_limit, pre_head->in(0) );
1128 register_new_node( pre_opaq , pre_head->in(0) );
1129
1130 // Since no other users of pre-loop compare, I can hack limit directly
1131 assert( cmp_end->outcnt() == 1, "no other users" );
1132 _igvn.hash_delete(cmp_end);
1133 cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq);
1134
1135 // Special case for not-equal loop bounds:
1136 // Change pre loop test, main loop test, and the
1137 // main loop guard test to use lt or gt depending on stride
1138 // direction:
1139 // positive stride use <
1140 // negative stride use >
1141 //
1142 // not-equal test is kept for post loop to handle case
1143 // when init > limit when stride > 0 (and reverse).
1144
1145 if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) {
1146
1147 BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt;
1148 // Modify pre loop end condition
1149 Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool();
1150 BoolNode* new_bol0 = new BoolNode(pre_bol->in(1), new_test);
1151 register_new_node( new_bol0, pre_head->in(0) );
1152 _igvn.replace_input_of(pre_end, CountedLoopEndNode::TestValue, new_bol0);
1153 // Modify main loop guard condition
1154 assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay");
1155 BoolNode* new_bol1 = new BoolNode(min_bol->in(1), new_test);
1156 register_new_node( new_bol1, new_pre_exit );
1157 _igvn.hash_delete(min_iff);
1158 min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1);
1159 // Modify main loop end condition
1160 BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool();
1161 BoolNode* new_bol2 = new BoolNode(main_bol->in(1), new_test);
1162 register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) );
1163 _igvn.replace_input_of(main_end, CountedLoopEndNode::TestValue, new_bol2);
1164 }
1165
1166 // Flag main loop
1167 main_head->set_main_loop();
1168 if( peel_only ) main_head->set_main_no_pre_loop();
1169
1170 // Subtract a trip count for the pre-loop.
1171 main_head->set_trip_count(main_head->trip_count() - 1);
1172
1173 // It's difficult to be precise about the trip-counts
1174 // for the pre/post loops. They are usually very short,
1175 // so guess that 4 trips is a reasonable value.
1176 post_head->set_profile_trip_cnt(4.0);
1177 pre_head->set_profile_trip_cnt(4.0);
1178
1179 // Now force out all loop-invariant dominating tests. The optimizer
1180 // finds some, but we _know_ they are all useless.
1181 peeled_dom_test_elim(loop,old_new);
1182 loop->record_for_igvn();
1183 }
1184
1185 //------------------------------is_invariant-----------------------------
1186 // Return true if n is invariant
1187 bool IdealLoopTree::is_invariant(Node* n) const {
1188 Node *n_c = _phase->has_ctrl(n) ? _phase->get_ctrl(n) : n;
1189 if (n_c->is_top()) return false;
1190 return !is_member(_phase->get_loop(n_c));
1191 }
1192
1193
1194 //------------------------------do_unroll--------------------------------------
1195 // Unroll the loop body one step - make each trip do 2 iterations.
1196 void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) {
1197 assert(LoopUnrollLimit, "");
1198 CountedLoopNode *loop_head = loop->_head->as_CountedLoop();
1199 CountedLoopEndNode *loop_end = loop_head->loopexit();
1200 assert(loop_end, "");
1201 #ifndef PRODUCT
1202 if (PrintOpto && VerifyLoopOptimizations) {
1203 tty->print("Unrolling ");
1204 loop->dump_head();
1205 } else if (TraceLoopOpts) {
1206 if (loop_head->trip_count() < (uint)LoopUnrollLimit) {
1207 tty->print("Unroll %d(%2d) ", loop_head->unrolled_count()*2, loop_head->trip_count());
1208 } else {
1209 tty->print("Unroll %d ", loop_head->unrolled_count()*2);
1210 }
1211 loop->dump_head();
1212 }
1213 #endif
1214
1215 // Remember loop node count before unrolling to detect
1216 // if rounds of unroll,optimize are making progress
1217 loop_head->set_node_count_before_unroll(loop->_body.size());
1218
1219 Node *ctrl = loop_head->in(LoopNode::EntryControl);
1220 Node *limit = loop_head->limit();
1221 Node *init = loop_head->init_trip();
1222 Node *stride = loop_head->stride();
1223
1224 Node *opaq = NULL;
1225 if (adjust_min_trip) { // If not maximally unrolling, need adjustment
1226 // Search for zero-trip guard.
1227 assert( loop_head->is_main_loop(), "" );
1228 assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );
1229 Node *iff = ctrl->in(0);
1230 assert( iff->Opcode() == Op_If, "" );
1231 Node *bol = iff->in(1);
1232 assert( bol->Opcode() == Op_Bool, "" );
1233 Node *cmp = bol->in(1);
1234 assert( cmp->Opcode() == Op_CmpI, "" );
1235 opaq = cmp->in(2);
1236 // Occasionally it's possible for a zero-trip guard Opaque1 node to be
1237 // optimized away and then another round of loop opts attempted.
1238 // We can not optimize this particular loop in that case.
1239 if (opaq->Opcode() != Op_Opaque1)
1240 return; // Cannot find zero-trip guard! Bail out!
1241 // Zero-trip test uses an 'opaque' node which is not shared.
1242 assert(opaq->outcnt() == 1 && opaq->in(1) == limit, "");
1243 }
1244
1245 C->set_major_progress();
1246
1247 Node* new_limit = NULL;
1248 if (UnrollLimitCheck) {
1249 int stride_con = stride->get_int();
1250 int stride_p = (stride_con > 0) ? stride_con : -stride_con;
1251 uint old_trip_count = loop_head->trip_count();
1252 // Verify that unroll policy result is still valid.
1253 assert(old_trip_count > 1 &&
1254 (!adjust_min_trip || stride_p <= (1<<3)*loop_head->unrolled_count()), "sanity");
1255
1256 // Adjust loop limit to keep valid iterations number after unroll.
1257 // Use (limit - stride) instead of (((limit - init)/stride) & (-2))*stride
1258 // which may overflow.
1259 if (!adjust_min_trip) {
1260 assert(old_trip_count > 1 && (old_trip_count & 1) == 0,
1261 "odd trip count for maximally unroll");
1262 // Don't need to adjust limit for maximally unroll since trip count is even.
1263 } else if (loop_head->has_exact_trip_count() && init->is_Con()) {
1264 // Loop's limit is constant. Loop's init could be constant when pre-loop
1265 // become peeled iteration.
1266 jlong init_con = init->get_int();
1267 // We can keep old loop limit if iterations count stays the same:
1268 // old_trip_count == new_trip_count * 2
1269 // Note: since old_trip_count >= 2 then new_trip_count >= 1
1270 // so we also don't need to adjust zero trip test.
1271 jlong limit_con = limit->get_int();
1272 // (stride_con*2) not overflow since stride_con <= 8.
1273 int new_stride_con = stride_con * 2;
1274 int stride_m = new_stride_con - (stride_con > 0 ? 1 : -1);
1275 jlong trip_count = (limit_con - init_con + stride_m)/new_stride_con;
1276 // New trip count should satisfy next conditions.
1277 assert(trip_count > 0 && (julong)trip_count < (julong)max_juint/2, "sanity");
1278 uint new_trip_count = (uint)trip_count;
1279 adjust_min_trip = (old_trip_count != new_trip_count*2);
1280 }
1281
1282 if (adjust_min_trip) {
1283 // Step 2: Adjust the trip limit if it is called for.
1284 // The adjustment amount is -stride. Need to make sure if the
1285 // adjustment underflows or overflows, then the main loop is skipped.
1286 Node* cmp = loop_end->cmp_node();
1287 assert(cmp->in(2) == limit, "sanity");
1288 assert(opaq != NULL && opaq->in(1) == limit, "sanity");
1289
1290 // Verify that policy_unroll result is still valid.
1291 const TypeInt* limit_type = _igvn.type(limit)->is_int();
1292 assert(stride_con > 0 && ((limit_type->_hi - stride_con) < limit_type->_hi) ||
1293 stride_con < 0 && ((limit_type->_lo - stride_con) > limit_type->_lo), "sanity");
1294
1295 if (limit->is_Con()) {
1296 // The check in policy_unroll and the assert above guarantee
1297 // no underflow if limit is constant.
1298 new_limit = _igvn.intcon(limit->get_int() - stride_con);
1299 set_ctrl(new_limit, C->root());
1300 } else {
1301 // Limit is not constant.
1302 if (loop_head->unrolled_count() == 1) { // only for first unroll
1303 // Separate limit by Opaque node in case it is an incremented
1304 // variable from previous loop to avoid using pre-incremented
1305 // value which could increase register pressure.
1306 // Otherwise reorg_offsets() optimization will create a separate
1307 // Opaque node for each use of trip-counter and as result
1308 // zero trip guard limit will be different from loop limit.
1309 assert(has_ctrl(opaq), "should have it");
1310 Node* opaq_ctrl = get_ctrl(opaq);
1311 limit = new Opaque2Node( C, limit );
1312 register_new_node( limit, opaq_ctrl );
1313 }
1314 if (stride_con > 0 && ((limit_type->_lo - stride_con) < limit_type->_lo) ||
1315 stride_con < 0 && ((limit_type->_hi - stride_con) > limit_type->_hi)) {
1316 // No underflow.
1317 new_limit = new SubINode(limit, stride);
1318 } else {
1319 // (limit - stride) may underflow.
1320 // Clamp the adjustment value with MININT or MAXINT:
1321 //
1322 // new_limit = limit-stride
1323 // if (stride > 0)
1324 // new_limit = (limit < new_limit) ? MININT : new_limit;
1325 // else
1326 // new_limit = (limit > new_limit) ? MAXINT : new_limit;
1327 //
1328 BoolTest::mask bt = loop_end->test_trip();
1329 assert(bt == BoolTest::lt || bt == BoolTest::gt, "canonical test is expected");
1330 Node* adj_max = _igvn.intcon((stride_con > 0) ? min_jint : max_jint);
1331 set_ctrl(adj_max, C->root());
1332 Node* old_limit = NULL;
1333 Node* adj_limit = NULL;
1334 Node* bol = limit->is_CMove() ? limit->in(CMoveNode::Condition) : NULL;
1335 if (loop_head->unrolled_count() > 1 &&
1336 limit->is_CMove() && limit->Opcode() == Op_CMoveI &&
1337 limit->in(CMoveNode::IfTrue) == adj_max &&
1338 bol->as_Bool()->_test._test == bt &&
1339 bol->in(1)->Opcode() == Op_CmpI &&
1340 bol->in(1)->in(2) == limit->in(CMoveNode::IfFalse)) {
1341 // Loop was unrolled before.
1342 // Optimize the limit to avoid nested CMove:
1343 // use original limit as old limit.
1344 old_limit = bol->in(1)->in(1);
1345 // Adjust previous adjusted limit.
1346 adj_limit = limit->in(CMoveNode::IfFalse);
1347 adj_limit = new SubINode(adj_limit, stride);
1348 } else {
1349 old_limit = limit;
1350 adj_limit = new SubINode(limit, stride);
1351 }
1352 assert(old_limit != NULL && adj_limit != NULL, "");
1353 register_new_node( adj_limit, ctrl ); // adjust amount
1354 Node* adj_cmp = new CmpINode(old_limit, adj_limit);
1355 register_new_node( adj_cmp, ctrl );
1356 Node* adj_bool = new BoolNode(adj_cmp, bt);
1357 register_new_node( adj_bool, ctrl );
1358 new_limit = new CMoveINode(adj_bool, adj_limit, adj_max, TypeInt::INT);
1359 }
1360 register_new_node(new_limit, ctrl);
1361 }
1362 assert(new_limit != NULL, "");
1363 // Replace in loop test.
1364 assert(loop_end->in(1)->in(1) == cmp, "sanity");
1365 if (cmp->outcnt() == 1 && loop_end->in(1)->outcnt() == 1) {
1366 // Don't need to create new test since only one user.
1367 _igvn.hash_delete(cmp);
1368 cmp->set_req(2, new_limit);
1369 } else {
1370 // Create new test since it is shared.
1371 Node* ctrl2 = loop_end->in(0);
1372 Node* cmp2 = cmp->clone();
1373 cmp2->set_req(2, new_limit);
1374 register_new_node(cmp2, ctrl2);
1375 Node* bol2 = loop_end->in(1)->clone();
1376 bol2->set_req(1, cmp2);
1377 register_new_node(bol2, ctrl2);
1378 _igvn.replace_input_of(loop_end, 1, bol2);
1379 }
1380 // Step 3: Find the min-trip test guaranteed before a 'main' loop.
1381 // Make it a 1-trip test (means at least 2 trips).
1382
1383 // Guard test uses an 'opaque' node which is not shared. Hence I
1384 // can edit it's inputs directly. Hammer in the new limit for the
1385 // minimum-trip guard.
1386 assert(opaq->outcnt() == 1, "");
1387 _igvn.replace_input_of(opaq, 1, new_limit);
1388 }
1389
1390 // Adjust max trip count. The trip count is intentionally rounded
1391 // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
1392 // the main, unrolled, part of the loop will never execute as it is protected
1393 // by the min-trip test. See bug 4834191 for a case where we over-unrolled
1394 // and later determined that part of the unrolled loop was dead.
1395 loop_head->set_trip_count(old_trip_count / 2);
1396
1397 // Double the count of original iterations in the unrolled loop body.
1398 loop_head->double_unrolled_count();
1399
1400 } else { // LoopLimitCheck
1401
1402 // Adjust max trip count. The trip count is intentionally rounded
1403 // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
1404 // the main, unrolled, part of the loop will never execute as it is protected
1405 // by the min-trip test. See bug 4834191 for a case where we over-unrolled
1406 // and later determined that part of the unrolled loop was dead.
1407 loop_head->set_trip_count(loop_head->trip_count() / 2);
1408
1409 // Double the count of original iterations in the unrolled loop body.
1410 loop_head->double_unrolled_count();
1411
1412 // -----------
1413 // Step 2: Cut back the trip counter for an unroll amount of 2.
1414 // Loop will normally trip (limit - init)/stride_con. Since it's a
1415 // CountedLoop this is exact (stride divides limit-init exactly).
1416 // We are going to double the loop body, so we want to knock off any
1417 // odd iteration: (trip_cnt & ~1). Then back compute a new limit.
1418 Node *span = new SubINode( limit, init );
1419 register_new_node( span, ctrl );
1420 Node *trip = new DivINode( 0, span, stride );
1421 register_new_node( trip, ctrl );
1422 Node *mtwo = _igvn.intcon(-2);
1423 set_ctrl(mtwo, C->root());
1424 Node *rond = new AndINode( trip, mtwo );
1425 register_new_node( rond, ctrl );
1426 Node *spn2 = new MulINode( rond, stride );
1427 register_new_node( spn2, ctrl );
1428 new_limit = new AddINode( spn2, init );
1429 register_new_node( new_limit, ctrl );
1430
1431 // Hammer in the new limit
1432 Node *ctrl2 = loop_end->in(0);
1433 Node *cmp2 = new CmpINode( loop_head->incr(), new_limit );
1434 register_new_node( cmp2, ctrl2 );
1435 Node *bol2 = new BoolNode( cmp2, loop_end->test_trip() );
1436 register_new_node( bol2, ctrl2 );
1437 _igvn.replace_input_of(loop_end, CountedLoopEndNode::TestValue, bol2);
1438
1439 // Step 3: Find the min-trip test guaranteed before a 'main' loop.
1440 // Make it a 1-trip test (means at least 2 trips).
1441 if( adjust_min_trip ) {
1442 assert( new_limit != NULL, "" );
1443 // Guard test uses an 'opaque' node which is not shared. Hence I
1444 // can edit it's inputs directly. Hammer in the new limit for the
1445 // minimum-trip guard.
1446 assert( opaq->outcnt() == 1, "" );
1447 _igvn.hash_delete(opaq);
1448 opaq->set_req(1, new_limit);
1449 }
1450 } // LoopLimitCheck
1451
1452 // ---------
1453 // Step 4: Clone the loop body. Move it inside the loop. This loop body
1454 // represents the odd iterations; since the loop trips an even number of
1455 // times its backedge is never taken. Kill the backedge.
1456 uint dd = dom_depth(loop_head);
1457 clone_loop( loop, old_new, dd );
1458
1459 // Make backedges of the clone equal to backedges of the original.
1460 // Make the fall-in from the original come from the fall-out of the clone.
1461 for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) {
1462 Node* phi = loop_head->fast_out(j);
1463 if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) {
1464 Node *newphi = old_new[phi->_idx];
1465 _igvn.hash_delete( phi );
1466 _igvn.hash_delete( newphi );
1467
1468 phi ->set_req(LoopNode:: EntryControl, newphi->in(LoopNode::LoopBackControl));
1469 newphi->set_req(LoopNode::LoopBackControl, phi ->in(LoopNode::LoopBackControl));
1470 phi ->set_req(LoopNode::LoopBackControl, C->top());
1471 }
1472 }
1473 Node *clone_head = old_new[loop_head->_idx];
1474 _igvn.hash_delete( clone_head );
1475 loop_head ->set_req(LoopNode:: EntryControl, clone_head->in(LoopNode::LoopBackControl));
1476 clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl));
1477 loop_head ->set_req(LoopNode::LoopBackControl, C->top());
1478 loop->_head = clone_head; // New loop header
1479
1480 set_idom(loop_head, loop_head ->in(LoopNode::EntryControl), dd);
1481 set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd);
1482
1483 // Kill the clone's backedge
1484 Node *newcle = old_new[loop_end->_idx];
1485 _igvn.hash_delete( newcle );
1486 Node *one = _igvn.intcon(1);
1487 set_ctrl(one, C->root());
1488 newcle->set_req(1, one);
1489 // Force clone into same loop body
1490 uint max = loop->_body.size();
1491 for( uint k = 0; k < max; k++ ) {
1492 Node *old = loop->_body.at(k);
1493 Node *nnn = old_new[old->_idx];
1494 loop->_body.push(nnn);
1495 if (!has_ctrl(old))
1496 set_loop(nnn, loop);
1497 }
1498
1499 loop->record_for_igvn();
1500 }
1501
1502 //------------------------------do_maximally_unroll----------------------------
1503
1504 void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) {
1505 CountedLoopNode *cl = loop->_head->as_CountedLoop();
1506 assert(cl->has_exact_trip_count(), "trip count is not exact");
1507 assert(cl->trip_count() > 0, "");
1508 #ifndef PRODUCT
1509 if (TraceLoopOpts) {
1510 tty->print("MaxUnroll %d ", cl->trip_count());
1511 loop->dump_head();
1512 }
1513 #endif
1514
1515 // If loop is tripping an odd number of times, peel odd iteration
1516 if ((cl->trip_count() & 1) == 1) {
1517 do_peeling(loop, old_new);
1518 }
1519
1520 // Now its tripping an even number of times remaining. Double loop body.
1521 // Do not adjust pre-guards; they are not needed and do not exist.
1522 if (cl->trip_count() > 0) {
1523 assert((cl->trip_count() & 1) == 0, "missed peeling");
1524 do_unroll(loop, old_new, false);
1525 }
1526 }
1527
1528 //------------------------------dominates_backedge---------------------------------
1529 // Returns true if ctrl is executed on every complete iteration
1530 bool IdealLoopTree::dominates_backedge(Node* ctrl) {
1531 assert(ctrl->is_CFG(), "must be control");
1532 Node* backedge = _head->as_Loop()->in(LoopNode::LoopBackControl);
1533 return _phase->dom_lca_internal(ctrl, backedge) == ctrl;
1534 }
1535
1536 //------------------------------adjust_limit-----------------------------------
1537 // Helper function for add_constraint().
1538 Node* PhaseIdealLoop::adjust_limit(int stride_con, Node * scale, Node *offset, Node *rc_limit, Node *loop_limit, Node *pre_ctrl) {
1539 // Compute "I :: (limit-offset)/scale"
1540 Node *con = new SubINode(rc_limit, offset);
1541 register_new_node(con, pre_ctrl);
1542 Node *X = new DivINode(0, con, scale);
1543 register_new_node(X, pre_ctrl);
1544
1545 // Adjust loop limit
1546 loop_limit = (stride_con > 0)
1547 ? (Node*)(new MinINode(loop_limit, X))
1548 : (Node*)(new MaxINode(loop_limit, X));
1549 register_new_node(loop_limit, pre_ctrl);
1550 return loop_limit;
1551 }
1552
1553 //------------------------------add_constraint---------------------------------
1554 // Constrain the main loop iterations so the conditions:
1555 // low_limit <= scale_con * I + offset < upper_limit
1556 // always holds true. That is, either increase the number of iterations in
1557 // the pre-loop or the post-loop until the condition holds true in the main
1558 // loop. Stride, scale, offset and limit are all loop invariant. Further,
1559 // stride and scale are constants (offset and limit often are).
1560 void PhaseIdealLoop::add_constraint( int stride_con, int scale_con, Node *offset, Node *low_limit, Node *upper_limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit ) {
1561 // For positive stride, the pre-loop limit always uses a MAX function
1562 // and the main loop a MIN function. For negative stride these are
1563 // reversed.
1564
1565 // Also for positive stride*scale the affine function is increasing, so the
1566 // pre-loop must check for underflow and the post-loop for overflow.
1567 // Negative stride*scale reverses this; pre-loop checks for overflow and
1568 // post-loop for underflow.
1569
1570 Node *scale = _igvn.intcon(scale_con);
1571 set_ctrl(scale, C->root());
1572
1573 if ((stride_con^scale_con) >= 0) { // Use XOR to avoid overflow
1574 // The overflow limit: scale*I+offset < upper_limit
1575 // For main-loop compute
1576 // ( if (scale > 0) /* and stride > 0 */
1577 // I < (upper_limit-offset)/scale
1578 // else /* scale < 0 and stride < 0 */
1579 // I > (upper_limit-offset)/scale
1580 // )
1581 //
1582 // (upper_limit-offset) may overflow or underflow.
1583 // But it is fine since main loop will either have
1584 // less iterations or will be skipped in such case.
1585 *main_limit = adjust_limit(stride_con, scale, offset, upper_limit, *main_limit, pre_ctrl);
1586
1587 // The underflow limit: low_limit <= scale*I+offset.
1588 // For pre-loop compute
1589 // NOT(scale*I+offset >= low_limit)
1590 // scale*I+offset < low_limit
1591 // ( if (scale > 0) /* and stride > 0 */
1592 // I < (low_limit-offset)/scale
1593 // else /* scale < 0 and stride < 0 */
1594 // I > (low_limit-offset)/scale
1595 // )
1596
1597 if (low_limit->get_int() == -max_jint) {
1598 if (!RangeLimitCheck) return;
1599 // We need this guard when scale*pre_limit+offset >= limit
1600 // due to underflow. So we need execute pre-loop until
1601 // scale*I+offset >= min_int. But (min_int-offset) will
1602 // underflow when offset > 0 and X will be > original_limit
1603 // when stride > 0. To avoid it we replace positive offset with 0.
1604 //
1605 // Also (min_int+1 == -max_int) is used instead of min_int here
1606 // to avoid problem with scale == -1 (min_int/(-1) == min_int).
1607 Node* shift = _igvn.intcon(31);
1608 set_ctrl(shift, C->root());
1609 Node* sign = new RShiftINode(offset, shift);
1610 register_new_node(sign, pre_ctrl);
1611 offset = new AndINode(offset, sign);
1612 register_new_node(offset, pre_ctrl);
1613 } else {
1614 assert(low_limit->get_int() == 0, "wrong low limit for range check");
1615 // The only problem we have here when offset == min_int
1616 // since (0-min_int) == min_int. It may be fine for stride > 0
1617 // but for stride < 0 X will be < original_limit. To avoid it
1618 // max(pre_limit, original_limit) is used in do_range_check().
1619 }
1620 // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);
1621 *pre_limit = adjust_limit((-stride_con), scale, offset, low_limit, *pre_limit, pre_ctrl);
1622
1623 } else { // stride_con*scale_con < 0
1624 // For negative stride*scale pre-loop checks for overflow and
1625 // post-loop for underflow.
1626 //
1627 // The overflow limit: scale*I+offset < upper_limit
1628 // For pre-loop compute
1629 // NOT(scale*I+offset < upper_limit)
1630 // scale*I+offset >= upper_limit
1631 // scale*I+offset+1 > upper_limit
1632 // ( if (scale < 0) /* and stride > 0 */
1633 // I < (upper_limit-(offset+1))/scale
1634 // else /* scale > 0 and stride < 0 */
1635 // I > (upper_limit-(offset+1))/scale
1636 // )
1637 //
1638 // (upper_limit-offset-1) may underflow or overflow.
1639 // To avoid it min(pre_limit, original_limit) is used
1640 // in do_range_check() for stride > 0 and max() for < 0.
1641 Node *one = _igvn.intcon(1);
1642 set_ctrl(one, C->root());
1643
1644 Node *plus_one = new AddINode(offset, one);
1645 register_new_node( plus_one, pre_ctrl );
1646 // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);
1647 *pre_limit = adjust_limit((-stride_con), scale, plus_one, upper_limit, *pre_limit, pre_ctrl);
1648
1649 if (low_limit->get_int() == -max_jint) {
1650 if (!RangeLimitCheck) return;
1651 // We need this guard when scale*main_limit+offset >= limit
1652 // due to underflow. So we need execute main-loop while
1653 // scale*I+offset+1 > min_int. But (min_int-offset-1) will
1654 // underflow when (offset+1) > 0 and X will be < main_limit
1655 // when scale < 0 (and stride > 0). To avoid it we replace
1656 // positive (offset+1) with 0.
1657 //
1658 // Also (min_int+1 == -max_int) is used instead of min_int here
1659 // to avoid problem with scale == -1 (min_int/(-1) == min_int).
1660 Node* shift = _igvn.intcon(31);
1661 set_ctrl(shift, C->root());
1662 Node* sign = new RShiftINode(plus_one, shift);
1663 register_new_node(sign, pre_ctrl);
1664 plus_one = new AndINode(plus_one, sign);
1665 register_new_node(plus_one, pre_ctrl);
1666 } else {
1667 assert(low_limit->get_int() == 0, "wrong low limit for range check");
1668 // The only problem we have here when offset == max_int
1669 // since (max_int+1) == min_int and (0-min_int) == min_int.
1670 // But it is fine since main loop will either have
1671 // less iterations or will be skipped in such case.
1672 }
1673 // The underflow limit: low_limit <= scale*I+offset.
1674 // For main-loop compute
1675 // scale*I+offset+1 > low_limit
1676 // ( if (scale < 0) /* and stride > 0 */
1677 // I < (low_limit-(offset+1))/scale
1678 // else /* scale > 0 and stride < 0 */
1679 // I > (low_limit-(offset+1))/scale
1680 // )
1681
1682 *main_limit = adjust_limit(stride_con, scale, plus_one, low_limit, *main_limit, pre_ctrl);
1683 }
1684 }
1685
1686
1687 //------------------------------is_scaled_iv---------------------------------
1688 // Return true if exp is a constant times an induction var
1689 bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) {
1690 if (exp == iv) {
1691 if (p_scale != NULL) {
1692 *p_scale = 1;
1693 }
1694 return true;
1695 }
1696 int opc = exp->Opcode();
1697 if (opc == Op_MulI) {
1698 if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1699 if (p_scale != NULL) {
1700 *p_scale = exp->in(2)->get_int();
1701 }
1702 return true;
1703 }
1704 if (exp->in(2) == iv && exp->in(1)->is_Con()) {
1705 if (p_scale != NULL) {
1706 *p_scale = exp->in(1)->get_int();
1707 }
1708 return true;
1709 }
1710 } else if (opc == Op_LShiftI) {
1711 if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1712 if (p_scale != NULL) {
1713 *p_scale = 1 << exp->in(2)->get_int();
1714 }
1715 return true;
1716 }
1717 }
1718 return false;
1719 }
1720
1721 //-----------------------------is_scaled_iv_plus_offset------------------------------
1722 // Return true if exp is a simple induction variable expression: k1*iv + (invar + k2)
1723 bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) {
1724 if (is_scaled_iv(exp, iv, p_scale)) {
1725 if (p_offset != NULL) {
1726 Node *zero = _igvn.intcon(0);
1727 set_ctrl(zero, C->root());
1728 *p_offset = zero;
1729 }
1730 return true;
1731 }
1732 int opc = exp->Opcode();
1733 if (opc == Op_AddI) {
1734 if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1735 if (p_offset != NULL) {
1736 *p_offset = exp->in(2);
1737 }
1738 return true;
1739 }
1740 if (exp->in(2)->is_Con()) {
1741 Node* offset2 = NULL;
1742 if (depth < 2 &&
1743 is_scaled_iv_plus_offset(exp->in(1), iv, p_scale,
1744 p_offset != NULL ? &offset2 : NULL, depth+1)) {
1745 if (p_offset != NULL) {
1746 Node *ctrl_off2 = get_ctrl(offset2);
1747 Node* offset = new AddINode(offset2, exp->in(2));
1748 register_new_node(offset, ctrl_off2);
1749 *p_offset = offset;
1750 }
1751 return true;
1752 }
1753 }
1754 } else if (opc == Op_SubI) {
1755 if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1756 if (p_offset != NULL) {
1757 Node *zero = _igvn.intcon(0);
1758 set_ctrl(zero, C->root());
1759 Node *ctrl_off = get_ctrl(exp->in(2));
1760 Node* offset = new SubINode(zero, exp->in(2));
1761 register_new_node(offset, ctrl_off);
1762 *p_offset = offset;
1763 }
1764 return true;
1765 }
1766 if (is_scaled_iv(exp->in(2), iv, p_scale)) {
1767 if (p_offset != NULL) {
1768 *p_scale *= -1;
1769 *p_offset = exp->in(1);
1770 }
1771 return true;
1772 }
1773 }
1774 return false;
1775 }
1776
1777 //------------------------------do_range_check---------------------------------
1778 // Eliminate range-checks and other trip-counter vs loop-invariant tests.
1779 void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
1780 #ifndef PRODUCT
1781 if (PrintOpto && VerifyLoopOptimizations) {
1782 tty->print("Range Check Elimination ");
1783 loop->dump_head();
1784 } else if (TraceLoopOpts) {
1785 tty->print("RangeCheck ");
1786 loop->dump_head();
1787 }
1788 #endif
1789 assert(RangeCheckElimination, "");
1790 CountedLoopNode *cl = loop->_head->as_CountedLoop();
1791 assert(cl->is_main_loop(), "");
1792
1793 // protect against stride not being a constant
1794 if (!cl->stride_is_con())
1795 return;
1796
1797 // Find the trip counter; we are iteration splitting based on it
1798 Node *trip_counter = cl->phi();
1799 // Find the main loop limit; we will trim it's iterations
1800 // to not ever trip end tests
1801 Node *main_limit = cl->limit();
1802
1803 // Need to find the main-loop zero-trip guard
1804 Node *ctrl = cl->in(LoopNode::EntryControl);
1805 assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "");
1806 Node *iffm = ctrl->in(0);
1807 assert(iffm->Opcode() == Op_If, "");
1808 Node *bolzm = iffm->in(1);
1809 assert(bolzm->Opcode() == Op_Bool, "");
1810 Node *cmpzm = bolzm->in(1);
1811 assert(cmpzm->is_Cmp(), "");
1812 Node *opqzm = cmpzm->in(2);
1813 // Can not optimize a loop if zero-trip Opaque1 node is optimized
1814 // away and then another round of loop opts attempted.
1815 if (opqzm->Opcode() != Op_Opaque1)
1816 return;
1817 assert(opqzm->in(1) == main_limit, "do not understand situation");
1818
1819 // Find the pre-loop limit; we will expand it's iterations to
1820 // not ever trip low tests.
1821 Node *p_f = iffm->in(0);
1822 assert(p_f->Opcode() == Op_IfFalse, "");
1823 CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
1824 assert(pre_end->loopnode()->is_pre_loop(), "");
1825 Node *pre_opaq1 = pre_end->limit();
1826 // Occasionally it's possible for a pre-loop Opaque1 node to be
1827 // optimized away and then another round of loop opts attempted.
1828 // We can not optimize this particular loop in that case.
1829 if (pre_opaq1->Opcode() != Op_Opaque1)
1830 return;
1831 Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1;
1832 Node *pre_limit = pre_opaq->in(1);
1833
1834 // Where do we put new limit calculations
1835 Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl);
1836
1837 // Ensure the original loop limit is available from the
1838 // pre-loop Opaque1 node.
1839 Node *orig_limit = pre_opaq->original_loop_limit();
1840 if (orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP)
1841 return;
1842
1843 // Must know if its a count-up or count-down loop
1844
1845 int stride_con = cl->stride_con();
1846 Node *zero = _igvn.intcon(0);
1847 Node *one = _igvn.intcon(1);
1848 // Use symmetrical int range [-max_jint,max_jint]
1849 Node *mini = _igvn.intcon(-max_jint);
1850 set_ctrl(zero, C->root());
1851 set_ctrl(one, C->root());
1852 set_ctrl(mini, C->root());
1853
1854 // Range checks that do not dominate the loop backedge (ie.
1855 // conditionally executed) can lengthen the pre loop limit beyond
1856 // the original loop limit. To prevent this, the pre limit is
1857 // (for stride > 0) MINed with the original loop limit (MAXed
1858 // stride < 0) when some range_check (rc) is conditionally
1859 // executed.
1860 bool conditional_rc = false;
1861
1862 // Check loop body for tests of trip-counter plus loop-invariant vs
1863 // loop-invariant.
1864 for( uint i = 0; i < loop->_body.size(); i++ ) {
1865 Node *iff = loop->_body[i];
1866 if( iff->Opcode() == Op_If ) { // Test?
1867
1868 // Test is an IfNode, has 2 projections. If BOTH are in the loop
1869 // we need loop unswitching instead of iteration splitting.
1870 Node *exit = loop->is_loop_exit(iff);
1871 if( !exit ) continue;
1872 int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0;
1873
1874 // Get boolean condition to test
1875 Node *i1 = iff->in(1);
1876 if( !i1->is_Bool() ) continue;
1877 BoolNode *bol = i1->as_Bool();
1878 BoolTest b_test = bol->_test;
1879 // Flip sense of test if exit condition is flipped
1880 if( flip )
1881 b_test = b_test.negate();
1882
1883 // Get compare
1884 Node *cmp = bol->in(1);
1885
1886 // Look for trip_counter + offset vs limit
1887 Node *rc_exp = cmp->in(1);
1888 Node *limit = cmp->in(2);
1889 jint scale_con= 1; // Assume trip counter not scaled
1890
1891 Node *limit_c = get_ctrl(limit);
1892 if( loop->is_member(get_loop(limit_c) ) ) {
1893 // Compare might have operands swapped; commute them
1894 b_test = b_test.commute();
1895 rc_exp = cmp->in(2);
1896 limit = cmp->in(1);
1897 limit_c = get_ctrl(limit);
1898 if( loop->is_member(get_loop(limit_c) ) )
1899 continue; // Both inputs are loop varying; cannot RCE
1900 }
1901 // Here we know 'limit' is loop invariant
1902
1903 // 'limit' maybe pinned below the zero trip test (probably from a
1904 // previous round of rce), in which case, it can't be used in the
1905 // zero trip test expression which must occur before the zero test's if.
1906 if( limit_c == ctrl ) {
1907 continue; // Don't rce this check but continue looking for other candidates.
1908 }
1909
1910 // Check for scaled induction variable plus an offset
1911 Node *offset = NULL;
1912
1913 if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) {
1914 continue;
1915 }
1916
1917 Node *offset_c = get_ctrl(offset);
1918 if( loop->is_member( get_loop(offset_c) ) )
1919 continue; // Offset is not really loop invariant
1920 // Here we know 'offset' is loop invariant.
1921
1922 // As above for the 'limit', the 'offset' maybe pinned below the
1923 // zero trip test.
1924 if( offset_c == ctrl ) {
1925 continue; // Don't rce this check but continue looking for other candidates.
1926 }
1927 #ifdef ASSERT
1928 if (TraceRangeLimitCheck) {
1929 tty->print_cr("RC bool node%s", flip ? " flipped:" : ":");
1930 bol->dump(2);
1931 }
1932 #endif
1933 // At this point we have the expression as:
1934 // scale_con * trip_counter + offset :: limit
1935 // where scale_con, offset and limit are loop invariant. Trip_counter
1936 // monotonically increases by stride_con, a constant. Both (or either)
1937 // stride_con and scale_con can be negative which will flip about the
1938 // sense of the test.
1939
1940 // Adjust pre and main loop limits to guard the correct iteration set
1941 if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests
1942 if( b_test._test == BoolTest::lt ) { // Range checks always use lt
1943 // The underflow and overflow limits: 0 <= scale*I+offset < limit
1944 add_constraint( stride_con, scale_con, offset, zero, limit, pre_ctrl, &pre_limit, &main_limit );
1945 if (!conditional_rc) {
1946 // (0-offset)/scale could be outside of loop iterations range.
1947 conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck;
1948 }
1949 } else {
1950 #ifndef PRODUCT
1951 if( PrintOpto )
1952 tty->print_cr("missed RCE opportunity");
1953 #endif
1954 continue; // In release mode, ignore it
1955 }
1956 } else { // Otherwise work on normal compares
1957 switch( b_test._test ) {
1958 case BoolTest::gt:
1959 // Fall into GE case
1960 case BoolTest::ge:
1961 // Convert (I*scale+offset) >= Limit to (I*(-scale)+(-offset)) <= -Limit
1962 scale_con = -scale_con;
1963 offset = new SubINode( zero, offset );
1964 register_new_node( offset, pre_ctrl );
1965 limit = new SubINode( zero, limit );
1966 register_new_node( limit, pre_ctrl );
1967 // Fall into LE case
1968 case BoolTest::le:
1969 if (b_test._test != BoolTest::gt) {
1970 // Convert X <= Y to X < Y+1
1971 limit = new AddINode( limit, one );
1972 register_new_node( limit, pre_ctrl );
1973 }
1974 // Fall into LT case
1975 case BoolTest::lt:
1976 // The underflow and overflow limits: MIN_INT <= scale*I+offset < limit
1977 // Note: (MIN_INT+1 == -MAX_INT) is used instead of MIN_INT here
1978 // to avoid problem with scale == -1: MIN_INT/(-1) == MIN_INT.
1979 add_constraint( stride_con, scale_con, offset, mini, limit, pre_ctrl, &pre_limit, &main_limit );
1980 if (!conditional_rc) {
1981 // ((MIN_INT+1)-offset)/scale could be outside of loop iterations range.
1982 // Note: negative offset is replaced with 0 but (MIN_INT+1)/scale could
1983 // still be outside of loop range.
1984 conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck;
1985 }
1986 break;
1987 default:
1988 #ifndef PRODUCT
1989 if( PrintOpto )
1990 tty->print_cr("missed RCE opportunity");
1991 #endif
1992 continue; // Unhandled case
1993 }
1994 }
1995
1996 // Kill the eliminated test
1997 C->set_major_progress();
1998 Node *kill_con = _igvn.intcon( 1-flip );
1999 set_ctrl(kill_con, C->root());
2000 _igvn.replace_input_of(iff, 1, kill_con);
2001 // Find surviving projection
2002 assert(iff->is_If(), "");
2003 ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip);
2004 // Find loads off the surviving projection; remove their control edge
2005 for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) {
2006 Node* cd = dp->fast_out(i); // Control-dependent node
2007 if (cd->is_Load() && cd->depends_only_on_test()) { // Loads can now float around in the loop
2008 // Allow the load to float around in the loop, or before it
2009 // but NOT before the pre-loop.
2010 _igvn.replace_input_of(cd, 0, ctrl); // ctrl, not NULL
2011 --i;
2012 --imax;
2013 }
2014 }
2015
2016 } // End of is IF
2017
2018 }
2019
2020 // Update loop limits
2021 if (conditional_rc) {
2022 pre_limit = (stride_con > 0) ? (Node*)new MinINode(pre_limit, orig_limit)
2023 : (Node*)new MaxINode(pre_limit, orig_limit);
2024 register_new_node(pre_limit, pre_ctrl);
2025 }
2026 _igvn.replace_input_of(pre_opaq, 1, pre_limit);
2027
2028 // Note:: we are making the main loop limit no longer precise;
2029 // need to round up based on stride.
2030 cl->set_nonexact_trip_count();
2031 if (!LoopLimitCheck && stride_con != 1 && stride_con != -1) { // Cutout for common case
2032 // "Standard" round-up logic: ([main_limit-init+(y-1)]/y)*y+init
2033 // Hopefully, compiler will optimize for powers of 2.
2034 Node *ctrl = get_ctrl(main_limit);
2035 Node *stride = cl->stride();
2036 Node *init = cl->init_trip();
2037 Node *span = new SubINode(main_limit,init);
2038 register_new_node(span,ctrl);
2039 Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1));
2040 Node *add = new AddINode(span,rndup);
2041 register_new_node(add,ctrl);
2042 Node *div = new DivINode(0,add,stride);
2043 register_new_node(div,ctrl);
2044 Node *mul = new MulINode(div,stride);
2045 register_new_node(mul,ctrl);
2046 Node *newlim = new AddINode(mul,init);
2047 register_new_node(newlim,ctrl);
2048 main_limit = newlim;
2049 }
2050
2051 Node *main_cle = cl->loopexit();
2052 Node *main_bol = main_cle->in(1);
2053 // Hacking loop bounds; need private copies of exit test
2054 if( main_bol->outcnt() > 1 ) {// BoolNode shared?
2055 main_bol = main_bol->clone();// Clone a private BoolNode
2056 register_new_node( main_bol, main_cle->in(0) );
2057 _igvn.replace_input_of(main_cle, 1, main_bol);
2058 }
2059 Node *main_cmp = main_bol->in(1);
2060 if( main_cmp->outcnt() > 1 ) { // CmpNode shared?
2061 _igvn.hash_delete(main_bol);
2062 main_cmp = main_cmp->clone();// Clone a private CmpNode
2063 register_new_node( main_cmp, main_cle->in(0) );
2064 main_bol->set_req(1,main_cmp);
2065 }
2066 // Hack the now-private loop bounds
2067 _igvn.replace_input_of(main_cmp, 2, main_limit);
2068 // The OpaqueNode is unshared by design
2069 assert( opqzm->outcnt() == 1, "cannot hack shared node" );
2070 _igvn.replace_input_of(opqzm, 1, main_limit);
2071 }
2072
2073 //------------------------------DCE_loop_body----------------------------------
2074 // Remove simplistic dead code from loop body
2075 void IdealLoopTree::DCE_loop_body() {
2076 for( uint i = 0; i < _body.size(); i++ )
2077 if( _body.at(i)->outcnt() == 0 )
2078 _body.map( i--, _body.pop() );
2079 }
2080
2081
2082 //------------------------------adjust_loop_exit_prob--------------------------
2083 // Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage.
2084 // Replace with a 1-in-10 exit guess.
2085 void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) {
2086 Node *test = tail();
2087 while( test != _head ) {
2088 uint top = test->Opcode();
2089 if( top == Op_IfTrue || top == Op_IfFalse ) {
2090 int test_con = ((ProjNode*)test)->_con;
2091 assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity");
2092 IfNode *iff = test->in(0)->as_If();
2093 if( iff->outcnt() == 2 ) { // Ignore dead tests
2094 Node *bol = iff->in(1);
2095 if( bol && bol->req() > 1 && bol->in(1) &&
2096 ((bol->in(1)->Opcode() == Op_StorePConditional ) ||
2097 (bol->in(1)->Opcode() == Op_StoreIConditional ) ||
2098 (bol->in(1)->Opcode() == Op_StoreLConditional ) ||
2099 (bol->in(1)->Opcode() == Op_CompareAndSwapI ) ||
2100 (bol->in(1)->Opcode() == Op_CompareAndSwapL ) ||
2101 (bol->in(1)->Opcode() == Op_CompareAndSwapP ) ||
2102 (bol->in(1)->Opcode() == Op_CompareAndSwapN )))
2103 return; // Allocation loops RARELY take backedge
2104 // Find the OTHER exit path from the IF
2105 Node* ex = iff->proj_out(1-test_con);
2106 float p = iff->_prob;
2107 if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) {
2108 if( top == Op_IfTrue ) {
2109 if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) {
2110 iff->_prob = PROB_STATIC_FREQUENT;
2111 }
2112 } else {
2113 if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) {
2114 iff->_prob = PROB_STATIC_INFREQUENT;
2115 }
2116 }
2117 }
2118 }
2119 }
2120 test = phase->idom(test);
2121 }
2122 }
2123
2124
2125 //------------------------------policy_do_remove_empty_loop--------------------
2126 // Micro-benchmark spamming. Policy is to always remove empty loops.
2127 // The 'DO' part is to replace the trip counter with the value it will
2128 // have on the last iteration. This will break the loop.
2129 bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
2130 // Minimum size must be empty loop
2131 if (_body.size() > EMPTY_LOOP_SIZE)
2132 return false;
2133
2134 if (!_head->is_CountedLoop())
2135 return false; // Dead loop
2136 CountedLoopNode *cl = _head->as_CountedLoop();
2137 if (!cl->is_valid_counted_loop())
2138 return false; // Malformed loop
2139 if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
2140 return false; // Infinite loop
2141
2142 #ifdef ASSERT
2143 // Ensure only one phi which is the iv.
2144 Node* iv = NULL;
2145 for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) {
2146 Node* n = cl->fast_out(i);
2147 if (n->Opcode() == Op_Phi) {
2148 assert(iv == NULL, "Too many phis" );
2149 iv = n;
2150 }
2151 }
2152 assert(iv == cl->phi(), "Wrong phi" );
2153 #endif
2154
2155 // main and post loops have explicitly created zero trip guard
2156 bool needs_guard = !cl->is_main_loop() && !cl->is_post_loop();
2157 if (needs_guard) {
2158 // Skip guard if values not overlap.
2159 const TypeInt* init_t = phase->_igvn.type(cl->init_trip())->is_int();
2160 const TypeInt* limit_t = phase->_igvn.type(cl->limit())->is_int();
2161 int stride_con = cl->stride_con();
2162 if (stride_con > 0) {
2163 needs_guard = (init_t->_hi >= limit_t->_lo);
2164 } else {
2165 needs_guard = (init_t->_lo <= limit_t->_hi);
2166 }
2167 }
2168 if (needs_guard) {
2169 // Check for an obvious zero trip guard.
2170 Node* inctrl = PhaseIdealLoop::skip_loop_predicates(cl->in(LoopNode::EntryControl));
2171 if (inctrl->Opcode() == Op_IfTrue) {
2172 // The test should look like just the backedge of a CountedLoop
2173 Node* iff = inctrl->in(0);
2174 if (iff->is_If()) {
2175 Node* bol = iff->in(1);
2176 if (bol->is_Bool() && bol->as_Bool()->_test._test == cl->loopexit()->test_trip()) {
2177 Node* cmp = bol->in(1);
2178 if (cmp->is_Cmp() && cmp->in(1) == cl->init_trip() && cmp->in(2) == cl->limit()) {
2179 needs_guard = false;
2180 }
2181 }
2182 }
2183 }
2184 }
2185
2186 #ifndef PRODUCT
2187 if (PrintOpto) {
2188 tty->print("Removing empty loop with%s zero trip guard", needs_guard ? "out" : "");
2189 this->dump_head();
2190 } else if (TraceLoopOpts) {
2191 tty->print("Empty with%s zero trip guard ", needs_guard ? "out" : "");
2192 this->dump_head();
2193 }
2194 #endif
2195
2196 if (needs_guard) {
2197 // Peel the loop to ensure there's a zero trip guard
2198 Node_List old_new;
2199 phase->do_peeling(this, old_new);
2200 }
2201
2202 // Replace the phi at loop head with the final value of the last
2203 // iteration. Then the CountedLoopEnd will collapse (backedge never
2204 // taken) and all loop-invariant uses of the exit values will be correct.
2205 Node *phi = cl->phi();
2206 Node *exact_limit = phase->exact_limit(this);
2207 if (exact_limit != cl->limit()) {
2208 // We also need to replace the original limit to collapse loop exit.
2209 Node* cmp = cl->loopexit()->cmp_node();
2210 assert(cl->limit() == cmp->in(2), "sanity");
2211 phase->_igvn._worklist.push(cmp->in(2)); // put limit on worklist
2212 phase->_igvn.replace_input_of(cmp, 2, exact_limit); // put cmp on worklist
2213 }
2214 // Note: the final value after increment should not overflow since
2215 // counted loop has limit check predicate.
2216 Node *final = new SubINode( exact_limit, cl->stride() );
2217 phase->register_new_node(final,cl->in(LoopNode::EntryControl));
2218 phase->_igvn.replace_node(phi,final);
2219 phase->C->set_major_progress();
2220 return true;
2221 }
2222
2223 //------------------------------policy_do_one_iteration_loop-------------------
2224 // Convert one iteration loop into normal code.
2225 bool IdealLoopTree::policy_do_one_iteration_loop( PhaseIdealLoop *phase ) {
2226 if (!_head->as_Loop()->is_valid_counted_loop())
2227 return false; // Only for counted loop
2228
2229 CountedLoopNode *cl = _head->as_CountedLoop();
2230 if (!cl->has_exact_trip_count() || cl->trip_count() != 1) {
2231 return false;
2232 }
2233
2234 #ifndef PRODUCT
2235 if(TraceLoopOpts) {
2236 tty->print("OneIteration ");
2237 this->dump_head();
2238 }
2239 #endif
2240
2241 Node *init_n = cl->init_trip();
2242 #ifdef ASSERT
2243 // Loop boundaries should be constant since trip count is exact.
2244 assert(init_n->get_int() + cl->stride_con() >= cl->limit()->get_int(), "should be one iteration");
2245 #endif
2246 // Replace the phi at loop head with the value of the init_trip.
2247 // Then the CountedLoopEnd will collapse (backedge will not be taken)
2248 // and all loop-invariant uses of the exit values will be correct.
2249 phase->_igvn.replace_node(cl->phi(), cl->init_trip());
2250 phase->C->set_major_progress();
2251 return true;
2252 }
2253
2254 //=============================================================================
2255 //------------------------------iteration_split_impl---------------------------
2256 bool IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) {
2257 // Compute exact loop trip count if possible.
2258 compute_exact_trip_count(phase);
2259
2260 // Convert one iteration loop into normal code.
2261 if (policy_do_one_iteration_loop(phase))
2262 return true;
2263
2264 // Check and remove empty loops (spam micro-benchmarks)
2265 if (policy_do_remove_empty_loop(phase))
2266 return true; // Here we removed an empty loop
2267
2268 bool should_peel = policy_peeling(phase); // Should we peel?
2269
2270 bool should_unswitch = policy_unswitching(phase);
2271
2272 // Non-counted loops may be peeled; exactly 1 iteration is peeled.
2273 // This removes loop-invariant tests (usually null checks).
2274 if (!_head->is_CountedLoop()) { // Non-counted loop
2275 if (PartialPeelLoop && phase->partial_peel(this, old_new)) {
2276 // Partial peel succeeded so terminate this round of loop opts
2277 return false;
2278 }
2279 if (should_peel) { // Should we peel?
2280 #ifndef PRODUCT
2281 if (PrintOpto) tty->print_cr("should_peel");
2282 #endif
2283 phase->do_peeling(this,old_new);
2284 } else if (should_unswitch) {
2285 phase->do_unswitching(this, old_new);
2286 }
2287 return true;
2288 }
2289 CountedLoopNode *cl = _head->as_CountedLoop();
2290
2291 if (!cl->is_valid_counted_loop()) return true; // Ignore various kinds of broken loops
2292
2293 // Do nothing special to pre- and post- loops
2294 if (cl->is_pre_loop() || cl->is_post_loop()) return true;
2295
2296 // Compute loop trip count from profile data
2297 compute_profile_trip_cnt(phase);
2298
2299 // Before attempting fancy unrolling, RCE or alignment, see if we want
2300 // to completely unroll this loop or do loop unswitching.
2301 if (cl->is_normal_loop()) {
2302 if (should_unswitch) {
2303 phase->do_unswitching(this, old_new);
2304 return true;
2305 }
2306 bool should_maximally_unroll = policy_maximally_unroll(phase);
2307 if (should_maximally_unroll) {
2308 // Here we did some unrolling and peeling. Eventually we will
2309 // completely unroll this loop and it will no longer be a loop.
2310 phase->do_maximally_unroll(this,old_new);
2311 return true;
2312 }
2313 }
2314
2315 // Skip next optimizations if running low on nodes. Note that
2316 // policy_unswitching and policy_maximally_unroll have this check.
2317 uint nodes_left = MaxNodeLimit - (uint) phase->C->live_nodes();
2318 if ((2 * _body.size()) > nodes_left) {
2319 return true;
2320 }
2321
2322 // Counted loops may be peeled, may need some iterations run up
2323 // front for RCE, and may want to align loop refs to a cache
2324 // line. Thus we clone a full loop up front whose trip count is
2325 // at least 1 (if peeling), but may be several more.
2326
2327 // The main loop will start cache-line aligned with at least 1
2328 // iteration of the unrolled body (zero-trip test required) and
2329 // will have some range checks removed.
2330
2331 // A post-loop will finish any odd iterations (leftover after
2332 // unrolling), plus any needed for RCE purposes.
2333
2334 bool should_unroll = policy_unroll(phase);
2335
2336 bool should_rce = policy_range_check(phase);
2337
2338 bool should_align = policy_align(phase);
2339
2340 // If not RCE'ing (iteration splitting) or Aligning, then we do not
2341 // need a pre-loop. We may still need to peel an initial iteration but
2342 // we will not be needing an unknown number of pre-iterations.
2343 //
2344 // Basically, if may_rce_align reports FALSE first time through,
2345 // we will not be able to later do RCE or Aligning on this loop.
2346 bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align;
2347
2348 // If we have any of these conditions (RCE, alignment, unrolling) met, then
2349 // we switch to the pre-/main-/post-loop model. This model also covers
2350 // peeling.
2351 if (should_rce || should_align || should_unroll) {
2352 if (cl->is_normal_loop()) // Convert to 'pre/main/post' loops
2353 phase->insert_pre_post_loops(this,old_new, !may_rce_align);
2354
2355 // Adjust the pre- and main-loop limits to let the pre and post loops run
2356 // with full checks, but the main-loop with no checks. Remove said
2357 // checks from the main body.
2358 if (should_rce)
2359 phase->do_range_check(this,old_new);
2360
2361 // Double loop body for unrolling. Adjust the minimum-trip test (will do
2362 // twice as many iterations as before) and the main body limit (only do
2363 // an even number of trips). If we are peeling, we might enable some RCE
2364 // and we'd rather unroll the post-RCE'd loop SO... do not unroll if
2365 // peeling.
2366 if (should_unroll && !should_peel)
2367 phase->do_unroll(this,old_new, true);
2368
2369 // Adjust the pre-loop limits to align the main body
2370 // iterations.
2371 if (should_align)
2372 Unimplemented();
2373
2374 } else { // Else we have an unchanged counted loop
2375 if (should_peel) // Might want to peel but do nothing else
2376 phase->do_peeling(this,old_new);
2377 }
2378 return true;
2379 }
2380
2381
2382 //=============================================================================
2383 //------------------------------iteration_split--------------------------------
2384 bool IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) {
2385 // Recursively iteration split nested loops
2386 if (_child && !_child->iteration_split(phase, old_new))
2387 return false;
2388
2389 // Clean out prior deadwood
2390 DCE_loop_body();
2391
2392
2393 // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
2394 // Replace with a 1-in-10 exit guess.
2395 if (_parent /*not the root loop*/ &&
2396 !_irreducible &&
2397 // Also ignore the occasional dead backedge
2398 !tail()->is_top()) {
2399 adjust_loop_exit_prob(phase);
2400 }
2401
2402 // Gate unrolling, RCE and peeling efforts.
2403 if (!_child && // If not an inner loop, do not split
2404 !_irreducible &&
2405 _allow_optimizations &&
2406 !tail()->is_top()) { // Also ignore the occasional dead backedge
2407 if (!_has_call) {
2408 if (!iteration_split_impl(phase, old_new)) {
2409 return false;
2410 }
2411 } else if (policy_unswitching(phase)) {
2412 phase->do_unswitching(this, old_new);
2413 }
2414 }
2415
2416 // Minor offset re-organization to remove loop-fallout uses of
2417 // trip counter when there was no major reshaping.
2418 phase->reorg_offsets(this);
2419
2420 if (_next && !_next->iteration_split(phase, old_new))
2421 return false;
2422 return true;
2423 }
2424
2425
2426 //=============================================================================
2427 // Process all the loops in the loop tree and replace any fill
2428 // patterns with an intrisc version.
2429 bool PhaseIdealLoop::do_intrinsify_fill() {
2430 bool changed = false;
2431 for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
2432 IdealLoopTree* lpt = iter.current();
2433 changed |= intrinsify_fill(lpt);
2434 }
2435 return changed;
2436 }
2437
2438
2439 // Examine an inner loop looking for a a single store of an invariant
2440 // value in a unit stride loop,
2441 bool PhaseIdealLoop::match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& store_value,
2442 Node*& shift, Node*& con) {
2443 const char* msg = NULL;
2444 Node* msg_node = NULL;
2445
2446 store_value = NULL;
2447 con = NULL;
2448 shift = NULL;
2449
2450 // Process the loop looking for stores. If there are multiple
2451 // stores or extra control flow give at this point.
2452 CountedLoopNode* head = lpt->_head->as_CountedLoop();
2453 for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2454 Node* n = lpt->_body.at(i);
2455 if (n->outcnt() == 0) continue; // Ignore dead
2456 if (n->is_Store()) {
2457 if (store != NULL) {
2458 msg = "multiple stores";
2459 break;
2460 }
2461 int opc = n->Opcode();
2462 if (opc == Op_StoreP || opc == Op_StoreN || opc == Op_StoreNKlass || opc == Op_StoreCM) {
2463 msg = "oop fills not handled";
2464 break;
2465 }
2466 Node* value = n->in(MemNode::ValueIn);
2467 if (!lpt->is_invariant(value)) {
2468 msg = "variant store value";
2469 } else if (!_igvn.type(n->in(MemNode::Address))->isa_aryptr()) {
2470 msg = "not array address";
2471 }
2472 store = n;
2473 store_value = value;
2474 } else if (n->is_If() && n != head->loopexit()) {
2475 msg = "extra control flow";
2476 msg_node = n;
2477 }
2478 }
2479
2480 if (store == NULL) {
2481 // No store in loop
2482 return false;
2483 }
2484
2485 if (msg == NULL && head->stride_con() != 1) {
2486 // could handle negative strides too
2487 if (head->stride_con() < 0) {
2488 msg = "negative stride";
2489 } else {
2490 msg = "non-unit stride";
2491 }
2492 }
2493
2494 if (msg == NULL && !store->in(MemNode::Address)->is_AddP()) {
2495 msg = "can't handle store address";
2496 msg_node = store->in(MemNode::Address);
2497 }
2498
2499 if (msg == NULL &&
2500 (!store->in(MemNode::Memory)->is_Phi() ||
2501 store->in(MemNode::Memory)->in(LoopNode::LoopBackControl) != store)) {
2502 msg = "store memory isn't proper phi";
2503 msg_node = store->in(MemNode::Memory);
2504 }
2505
2506 // Make sure there is an appropriate fill routine
2507 BasicType t = store->as_Mem()->memory_type();
2508 const char* fill_name;
2509 if (msg == NULL &&
2510 StubRoutines::select_fill_function(t, false, fill_name) == NULL) {
2511 msg = "unsupported store";
2512 msg_node = store;
2513 }
2514
2515 if (msg != NULL) {
2516 #ifndef PRODUCT
2517 if (TraceOptimizeFill) {
2518 tty->print_cr("not fill intrinsic candidate: %s", msg);
2519 if (msg_node != NULL) msg_node->dump();
2520 }
2521 #endif
2522 return false;
2523 }
2524
2525 // Make sure the address expression can be handled. It should be
2526 // head->phi * elsize + con. head->phi might have a ConvI2L.
2527 Node* elements[4];
2528 Node* conv = NULL;
2529 bool found_index = false;
2530 int count = store->in(MemNode::Address)->as_AddP()->unpack_offsets(elements, ARRAY_SIZE(elements));
2531 for (int e = 0; e < count; e++) {
2532 Node* n = elements[e];
2533 if (n->is_Con() && con == NULL) {
2534 con = n;
2535 } else if (n->Opcode() == Op_LShiftX && shift == NULL) {
2536 Node* value = n->in(1);
2537 #ifdef _LP64
2538 if (value->Opcode() == Op_ConvI2L) {
2539 conv = value;
2540 value = value->in(1);
2541 }
2542 #endif
2543 if (value != head->phi()) {
2544 msg = "unhandled shift in address";
2545 } else {
2546 if (type2aelembytes(store->as_Mem()->memory_type(), true) != (1 << n->in(2)->get_int())) {
2547 msg = "scale doesn't match";
2548 } else {
2549 found_index = true;
2550 shift = n;
2551 }
2552 }
2553 } else if (n->Opcode() == Op_ConvI2L && conv == NULL) {
2554 if (n->in(1) == head->phi()) {
2555 found_index = true;
2556 conv = n;
2557 } else {
2558 msg = "unhandled input to ConvI2L";
2559 }
2560 } else if (n == head->phi()) {
2561 // no shift, check below for allowed cases
2562 found_index = true;
2563 } else {
2564 msg = "unhandled node in address";
2565 msg_node = n;
2566 }
2567 }
2568
2569 if (count == -1) {
2570 msg = "malformed address expression";
2571 msg_node = store;
2572 }
2573
2574 if (!found_index) {
2575 msg = "missing use of index";
2576 }
2577
2578 // byte sized items won't have a shift
2579 if (msg == NULL && shift == NULL && t != T_BYTE && t != T_BOOLEAN) {
2580 msg = "can't find shift";
2581 msg_node = store;
2582 }
2583
2584 if (msg != NULL) {
2585 #ifndef PRODUCT
2586 if (TraceOptimizeFill) {
2587 tty->print_cr("not fill intrinsic: %s", msg);
2588 if (msg_node != NULL) msg_node->dump();
2589 }
2590 #endif
2591 return false;
2592 }
2593
2594 // No make sure all the other nodes in the loop can be handled
2595 VectorSet ok(Thread::current()->resource_area());
2596
2597 // store related values are ok
2598 ok.set(store->_idx);
2599 ok.set(store->in(MemNode::Memory)->_idx);
2600
2601 CountedLoopEndNode* loop_exit = head->loopexit();
2602 guarantee(loop_exit != NULL, "no loop exit node");
2603
2604 // Loop structure is ok
2605 ok.set(head->_idx);
2606 ok.set(loop_exit->_idx);
2607 ok.set(head->phi()->_idx);
2608 ok.set(head->incr()->_idx);
2609 ok.set(loop_exit->cmp_node()->_idx);
2610 ok.set(loop_exit->in(1)->_idx);
2611
2612 // Address elements are ok
2613 if (con) ok.set(con->_idx);
2614 if (shift) ok.set(shift->_idx);
2615 if (conv) ok.set(conv->_idx);
2616
2617 for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2618 Node* n = lpt->_body.at(i);
2619 if (n->outcnt() == 0) continue; // Ignore dead
2620 if (ok.test(n->_idx)) continue;
2621 // Backedge projection is ok
2622 if (n->is_IfTrue() && n->in(0) == loop_exit) continue;
2623 if (!n->is_AddP()) {
2624 msg = "unhandled node";
2625 msg_node = n;
2626 break;
2627 }
2628 }
2629
2630 // Make sure no unexpected values are used outside the loop
2631 for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2632 Node* n = lpt->_body.at(i);
2633 // These values can be replaced with other nodes if they are used
2634 // outside the loop.
2635 if (n == store || n == loop_exit || n == head->incr() || n == store->in(MemNode::Memory)) continue;
2636 for (SimpleDUIterator iter(n); iter.has_next(); iter.next()) {
2637 Node* use = iter.get();
2638 if (!lpt->_body.contains(use)) {
2639 msg = "node is used outside loop";
2640 // lpt->_body.dump();
2641 msg_node = n;
2642 break;
2643 }
2644 }
2645 }
2646
2647 #ifdef ASSERT
2648 if (TraceOptimizeFill) {
2649 if (msg != NULL) {
2650 tty->print_cr("no fill intrinsic: %s", msg);
2651 if (msg_node != NULL) msg_node->dump();
2652 } else {
2653 tty->print_cr("fill intrinsic for:");
2654 }
2655 store->dump();
2656 if (Verbose) {
2657 lpt->_body.dump();
2658 }
2659 }
2660 #endif
2661
2662 return msg == NULL;
2663 }
2664
2665
2666
2667 bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) {
2668 // Only for counted inner loops
2669 if (!lpt->is_counted() || !lpt->is_inner()) {
2670 return false;
2671 }
2672
2673 // Must have constant stride
2674 CountedLoopNode* head = lpt->_head->as_CountedLoop();
2675 if (!head->is_valid_counted_loop() || !head->is_normal_loop()) {
2676 return false;
2677 }
2678
2679 // Check that the body only contains a store of a loop invariant
2680 // value that is indexed by the loop phi.
2681 Node* store = NULL;
2682 Node* store_value = NULL;
2683 Node* shift = NULL;
2684 Node* offset = NULL;
2685 if (!match_fill_loop(lpt, store, store_value, shift, offset)) {
2686 return false;
2687 }
2688
2689 #ifndef PRODUCT
2690 if (TraceLoopOpts) {
2691 tty->print("ArrayFill ");
2692 lpt->dump_head();
2693 }
2694 #endif
2695
2696 // Now replace the whole loop body by a call to a fill routine that
2697 // covers the same region as the loop.
2698 Node* base = store->in(MemNode::Address)->as_AddP()->in(AddPNode::Base);
2699
2700 // Build an expression for the beginning of the copy region
2701 Node* index = head->init_trip();
2702 #ifdef _LP64
2703 index = new ConvI2LNode(index);
2704 _igvn.register_new_node_with_optimizer(index);
2705 #endif
2706 if (shift != NULL) {
2707 // byte arrays don't require a shift but others do.
2708 index = new LShiftXNode(index, shift->in(2));
2709 _igvn.register_new_node_with_optimizer(index);
2710 }
2711 index = new AddPNode(base, base, index);
2712 _igvn.register_new_node_with_optimizer(index);
2713 Node* from = new AddPNode(base, index, offset);
2714 _igvn.register_new_node_with_optimizer(from);
2715 // Compute the number of elements to copy
2716 Node* len = new SubINode(head->limit(), head->init_trip());
2717 _igvn.register_new_node_with_optimizer(len);
2718
2719 BasicType t = store->as_Mem()->memory_type();
2720 bool aligned = false;
2721 if (offset != NULL && head->init_trip()->is_Con()) {
2722 int element_size = type2aelembytes(t);
2723 aligned = (offset->find_intptr_t_type()->get_con() + head->init_trip()->get_int() * element_size) % HeapWordSize == 0;
2724 }
2725
2726 // Build a call to the fill routine
2727 const char* fill_name;
2728 address fill = StubRoutines::select_fill_function(t, aligned, fill_name);
2729 assert(fill != NULL, "what?");
2730
2731 // Convert float/double to int/long for fill routines
2732 if (t == T_FLOAT) {
2733 store_value = new MoveF2INode(store_value);
2734 _igvn.register_new_node_with_optimizer(store_value);
2735 } else if (t == T_DOUBLE) {
2736 store_value = new MoveD2LNode(store_value);
2737 _igvn.register_new_node_with_optimizer(store_value);
2738 }
2739
2740 if (CCallingConventionRequiresIntsAsLongs &&
2741 // See StubRoutines::select_fill_function for types. FLOAT has been converted to INT.
2742 (t == T_FLOAT || t == T_INT || is_subword_type(t))) {
2743 store_value = new ConvI2LNode(store_value);
2744 _igvn.register_new_node_with_optimizer(store_value);
2745 }
2746
2747 Node* mem_phi = store->in(MemNode::Memory);
2748 Node* result_ctrl;
2749 Node* result_mem;
2750 const TypeFunc* call_type = OptoRuntime::array_fill_Type();
2751 CallLeafNode *call = new CallLeafNoFPNode(call_type, fill,
2752 fill_name, TypeAryPtr::get_array_body_type(t));
2753 uint cnt = 0;
2754 call->init_req(TypeFunc::Parms + cnt++, from);
2755 call->init_req(TypeFunc::Parms + cnt++, store_value);
2756 if (CCallingConventionRequiresIntsAsLongs) {
2757 call->init_req(TypeFunc::Parms + cnt++, C->top());
2758 }
2759 #ifdef _LP64
2760 len = new ConvI2LNode(len);
2761 _igvn.register_new_node_with_optimizer(len);
2762 #endif
2763 call->init_req(TypeFunc::Parms + cnt++, len);
2764 #ifdef _LP64
2765 call->init_req(TypeFunc::Parms + cnt++, C->top());
2766 #endif
2767 call->init_req(TypeFunc::Control, head->init_control());
2768 call->init_req(TypeFunc::I_O, C->top()); // Does no I/O.
2769 call->init_req(TypeFunc::Memory, mem_phi->in(LoopNode::EntryControl));
2770 call->init_req(TypeFunc::ReturnAdr, C->start()->proj_out(TypeFunc::ReturnAdr));
2771 call->init_req(TypeFunc::FramePtr, C->start()->proj_out(TypeFunc::FramePtr));
2772 _igvn.register_new_node_with_optimizer(call);
2773 result_ctrl = new ProjNode(call,TypeFunc::Control);
2774 _igvn.register_new_node_with_optimizer(result_ctrl);
2775 result_mem = new ProjNode(call,TypeFunc::Memory);
2776 _igvn.register_new_node_with_optimizer(result_mem);
2777
2778 /* Disable following optimization until proper fix (add missing checks).
2779
2780 // If this fill is tightly coupled to an allocation and overwrites
2781 // the whole body, allow it to take over the zeroing.
2782 AllocateNode* alloc = AllocateNode::Ideal_allocation(base, this);
2783 if (alloc != NULL && alloc->is_AllocateArray()) {
2784 Node* length = alloc->as_AllocateArray()->Ideal_length();
2785 if (head->limit() == length &&
2786 head->init_trip() == _igvn.intcon(0)) {
2787 if (TraceOptimizeFill) {
2788 tty->print_cr("Eliminated zeroing in allocation");
2789 }
2790 alloc->maybe_set_complete(&_igvn);
2791 } else {
2792 #ifdef ASSERT
2793 if (TraceOptimizeFill) {
2794 tty->print_cr("filling array but bounds don't match");
2795 alloc->dump();
2796 head->init_trip()->dump();
2797 head->limit()->dump();
2798 length->dump();
2799 }
2800 #endif
2801 }
2802 }
2803 */
2804
2805 // Redirect the old control and memory edges that are outside the loop.
2806 Node* exit = head->loopexit()->proj_out(0);
2807 // Sometimes the memory phi of the head is used as the outgoing
2808 // state of the loop. It's safe in this case to replace it with the
2809 // result_mem.
2810 _igvn.replace_node(store->in(MemNode::Memory), result_mem);
2811 _igvn.replace_node(exit, result_ctrl);
2812 _igvn.replace_node(store, result_mem);
2813 // Any uses the increment outside of the loop become the loop limit.
2814 _igvn.replace_node(head->incr(), head->limit());
2815
2816 // Disconnect the head from the loop.
2817 for (uint i = 0; i < lpt->_body.size(); i++) {
2818 Node* n = lpt->_body.at(i);
2819 _igvn.replace_node(n, C->top());
2820 }
2821
2822 return true;
2823 }