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