1 #ifdef USE_PRAGMA_IDENT_SRC
2 #pragma ident "@(#)loopTransform.cpp 1.116 07/06/01 11:35:03 JVM"
3 #endif
4 /*
5 * Copyright 2000-2007 Sun Microsystems, Inc. All Rights Reserved.
6 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
7 *
8 * This code is free software; you can redistribute it and/or modify it
9 * under the terms of the GNU General Public License version 2 only, as
10 * published by the Free Software Foundation.
11 *
12 * This code is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 * version 2 for more details (a copy is included in the LICENSE file that
16 * accompanied this code).
17 *
18 * You should have received a copy of the GNU General Public License version
19 * 2 along with this work; if not, write to the Free Software Foundation,
20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
21 *
22 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
23 * CA 95054 USA or visit www.sun.com if you need additional information or
24 * have any questions.
25 *
26 */
27
28 #include "incls/_precompiled.incl"
29 #include "incls/_loopTransform.cpp.incl"
30
31 //------------------------------is_loop_exit-----------------------------------
32 // Given an IfNode, return the loop-exiting projection or NULL if both
33 // arms remain in the loop.
34 Node *IdealLoopTree::is_loop_exit(Node *iff) const {
35 if( iff->outcnt() != 2 ) return NULL; // Ignore partially dead tests
36 PhaseIdealLoop *phase = _phase;
37 // Test is an IfNode, has 2 projections. If BOTH are in the loop
38 // we need loop unswitching instead of peeling.
39 if( !is_member(phase->get_loop( iff->raw_out(0) )) )
40 return iff->raw_out(0);
41 if( !is_member(phase->get_loop( iff->raw_out(1) )) )
42 return iff->raw_out(1);
43 return NULL;
44 }
45
46
47 //=============================================================================
48
49
50 //------------------------------record_for_igvn----------------------------
51 // Put loop body on igvn work list
52 void IdealLoopTree::record_for_igvn() {
53 for( uint i = 0; i < _body.size(); i++ ) {
54 Node *n = _body.at(i);
55 _phase->_igvn._worklist.push(n);
56 }
57 }
58
59 //------------------------------compute_profile_trip_cnt----------------------------
60 // Compute loop trip count from profile data as
61 // (backedge_count + loop_exit_count) / loop_exit_count
62 void IdealLoopTree::compute_profile_trip_cnt( PhaseIdealLoop *phase ) {
63 if (!_head->is_CountedLoop()) {
64 return;
65 }
66 CountedLoopNode* head = _head->as_CountedLoop();
67 if (head->profile_trip_cnt() != COUNT_UNKNOWN) {
68 return; // Already computed
69 }
70 float trip_cnt = (float)max_jint; // default is big
71
72 Node* back = head->in(LoopNode::LoopBackControl);
73 while (back != head) {
74 if ((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
75 back->in(0) &&
76 back->in(0)->is_If() &&
77 back->in(0)->as_If()->_fcnt != COUNT_UNKNOWN &&
78 back->in(0)->as_If()->_prob != PROB_UNKNOWN) {
79 break;
80 }
81 back = phase->idom(back);
82 }
83 if (back != head) {
84 assert((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
85 back->in(0), "if-projection exists");
86 IfNode* back_if = back->in(0)->as_If();
87 float loop_back_cnt = back_if->_fcnt * back_if->_prob;
88
89 // Now compute a loop exit count
90 float loop_exit_cnt = 0.0f;
91 for( uint i = 0; i < _body.size(); i++ ) {
92 Node *n = _body[i];
93 if( n->is_If() ) {
94 IfNode *iff = n->as_If();
95 if( iff->_fcnt != COUNT_UNKNOWN && iff->_prob != PROB_UNKNOWN ) {
96 Node *exit = is_loop_exit(iff);
97 if( exit ) {
98 float exit_prob = iff->_prob;
99 if (exit->Opcode() == Op_IfFalse) exit_prob = 1.0 - exit_prob;
100 if (exit_prob > PROB_MIN) {
101 float exit_cnt = iff->_fcnt * exit_prob;
102 loop_exit_cnt += exit_cnt;
103 }
104 }
105 }
106 }
107 }
108 if (loop_exit_cnt > 0.0f) {
109 trip_cnt = (loop_back_cnt + loop_exit_cnt) / loop_exit_cnt;
110 } else {
111 // No exit count so use
112 trip_cnt = loop_back_cnt;
113 }
114 }
115 #ifndef PRODUCT
116 if (TraceProfileTripCount) {
117 tty->print_cr("compute_profile_trip_cnt lp: %d cnt: %f\n", head->_idx, trip_cnt);
118 }
119 #endif
120 head->set_profile_trip_cnt(trip_cnt);
121 }
122
123 //---------------------is_invariant_addition-----------------------------
124 // Return nonzero index of invariant operand for an Add or Sub
125 // of (nonconstant) invariant and variant values. Helper for reassoicate_invariants.
126 int IdealLoopTree::is_invariant_addition(Node* n, PhaseIdealLoop *phase) {
127 int op = n->Opcode();
128 if (op == Op_AddI || op == Op_SubI) {
129 bool in1_invar = this->is_invariant(n->in(1));
130 bool in2_invar = this->is_invariant(n->in(2));
131 if (in1_invar && !in2_invar) return 1;
132 if (!in1_invar && in2_invar) return 2;
133 }
134 return 0;
135 }
136
137 //---------------------reassociate_add_sub-----------------------------
138 // Reassociate invariant add and subtract expressions:
139 //
140 // inv1 + (x + inv2) => ( inv1 + inv2) + x
141 // (x + inv2) + inv1 => ( inv1 + inv2) + x
142 // inv1 + (x - inv2) => ( inv1 - inv2) + x
143 // inv1 - (inv2 - x) => ( inv1 - inv2) + x
144 // (x + inv2) - inv1 => (-inv1 + inv2) + x
145 // (x - inv2) + inv1 => ( inv1 - inv2) + x
146 // (x - inv2) - inv1 => (-inv1 - inv2) + x
147 // inv1 + (inv2 - x) => ( inv1 + inv2) - x
148 // inv1 - (x - inv2) => ( inv1 + inv2) - x
149 // (inv2 - x) + inv1 => ( inv1 + inv2) - x
150 // (inv2 - x) - inv1 => (-inv1 + inv2) - x
151 // inv1 - (x + inv2) => ( inv1 - inv2) - x
152 //
153 Node* IdealLoopTree::reassociate_add_sub(Node* n1, PhaseIdealLoop *phase) {
154 if (!n1->is_Add() && !n1->is_Sub() || n1->outcnt() == 0) return NULL;
155 if (is_invariant(n1)) return NULL;
156 int inv1_idx = is_invariant_addition(n1, phase);
157 if (!inv1_idx) return NULL;
158 // Don't mess with add of constant (igvn moves them to expression tree root.)
159 if (n1->is_Add() && n1->in(2)->is_Con()) return NULL;
160 Node* inv1 = n1->in(inv1_idx);
161 Node* n2 = n1->in(3 - inv1_idx);
162 int inv2_idx = is_invariant_addition(n2, phase);
163 if (!inv2_idx) return NULL;
164 Node* x = n2->in(3 - inv2_idx);
165 Node* inv2 = n2->in(inv2_idx);
166
167 bool neg_x = n2->is_Sub() && inv2_idx == 1;
168 bool neg_inv2 = n2->is_Sub() && inv2_idx == 2;
169 bool neg_inv1 = n1->is_Sub() && inv1_idx == 2;
170 if (n1->is_Sub() && inv1_idx == 1) {
171 neg_x = !neg_x;
172 neg_inv2 = !neg_inv2;
173 }
174 Node* inv1_c = phase->get_ctrl(inv1);
175 Node* inv2_c = phase->get_ctrl(inv2);
176 Node* n_inv1;
177 if (neg_inv1) {
178 Node *zero = phase->_igvn.intcon(0);
179 phase->set_ctrl(zero, phase->C->root());
180 n_inv1 = new (phase->C, 3) SubINode(zero, inv1);
181 phase->register_new_node(n_inv1, inv1_c);
182 } else {
183 n_inv1 = inv1;
184 }
185 Node* inv;
186 if (neg_inv2) {
187 inv = new (phase->C, 3) SubINode(n_inv1, inv2);
188 } else {
189 inv = new (phase->C, 3) AddINode(n_inv1, inv2);
190 }
191 phase->register_new_node(inv, phase->get_early_ctrl(inv));
192
193 Node* addx;
194 if (neg_x) {
195 addx = new (phase->C, 3) SubINode(inv, x);
196 } else {
197 addx = new (phase->C, 3) AddINode(x, inv);
198 }
199 phase->register_new_node(addx, phase->get_ctrl(x));
200 phase->_igvn.hash_delete(n1);
201 phase->_igvn.subsume_node(n1, addx);
202 return addx;
203 }
204
205 //---------------------reassociate_invariants-----------------------------
206 // Reassociate invariant expressions:
207 void IdealLoopTree::reassociate_invariants(PhaseIdealLoop *phase) {
208 for (int i = _body.size() - 1; i >= 0; i--) {
209 Node *n = _body.at(i);
210 for (int j = 0; j < 5; j++) {
211 Node* nn = reassociate_add_sub(n, phase);
212 if (nn == NULL) break;
213 n = nn; // again
214 };
215 }
216 }
217
218 //------------------------------policy_peeling---------------------------------
219 // Return TRUE or FALSE if the loop should be peeled or not. Peel if we can
220 // make some loop-invariant test (usually a null-check) happen before the loop.
221 bool IdealLoopTree::policy_peeling( PhaseIdealLoop *phase ) const {
222 Node *test = ((IdealLoopTree*)this)->tail();
223 int body_size = ((IdealLoopTree*)this)->_body.size();
224 int uniq = phase->C->unique();
225 // Peeling does loop cloning which can result in O(N^2) node construction
226 if( body_size > 255 /* Prevent overflow for large body_size */
227 || (body_size * body_size + uniq > MaxNodeLimit) ) {
228 return false; // too large to safely clone
229 }
230 while( test != _head ) { // Scan till run off top of loop
231 if( test->is_If() ) { // Test?
232 Node *ctrl = phase->get_ctrl(test->in(1));
233 if (ctrl->is_top())
234 return false; // Found dead test on live IF? No peeling!
235 // Standard IF only has one input value to check for loop invariance
236 assert( test->Opcode() == Op_If || test->Opcode() == Op_CountedLoopEnd, "Check this code when new subtype is added");
237 // Condition is not a member of this loop?
238 if( !is_member(phase->get_loop(ctrl)) &&
239 is_loop_exit(test) )
240 return true; // Found reason to peel!
241 }
242 // Walk up dominators to loop _head looking for test which is
243 // executed on every path thru loop.
244 test = phase->idom(test);
245 }
246 return false;
247 }
248
249 //------------------------------peeled_dom_test_elim---------------------------
250 // If we got the effect of peeling, either by actually peeling or by making
251 // a pre-loop which must execute at least once, we can remove all
252 // loop-invariant dominated tests in the main body.
253 void PhaseIdealLoop::peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new ) {
254 bool progress = true;
255 while( progress ) {
256 progress = false; // Reset for next iteration
257 Node *prev = loop->_head->in(LoopNode::LoopBackControl);//loop->tail();
258 Node *test = prev->in(0);
259 while( test != loop->_head ) { // Scan till run off top of loop
260
261 int p_op = prev->Opcode();
262 if( (p_op == Op_IfFalse || p_op == Op_IfTrue) &&
263 test->is_If() && // Test?
264 !test->in(1)->is_Con() && // And not already obvious?
265 // Condition is not a member of this loop?
266 !loop->is_member(get_loop(get_ctrl(test->in(1))))){
267 // Walk loop body looking for instances of this test
268 for( uint i = 0; i < loop->_body.size(); i++ ) {
269 Node *n = loop->_body.at(i);
270 if( n->is_If() && n->in(1) == test->in(1) /*&& n != loop->tail()->in(0)*/ ) {
271 // IfNode was dominated by version in peeled loop body
272 progress = true;
273 dominated_by( old_new[prev->_idx], n );
274 }
275 }
276 }
277 prev = test;
278 test = idom(test);
279 } // End of scan tests in loop
280
281 } // End of while( progress )
282 }
283
284 //------------------------------do_peeling-------------------------------------
285 // Peel the first iteration of the given loop.
286 // Step 1: Clone the loop body. The clone becomes the peeled iteration.
287 // The pre-loop illegally has 2 control users (old & new loops).
288 // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
289 // Do this by making the old-loop fall-in edges act as if they came
290 // around the loopback from the prior iteration (follow the old-loop
291 // backedges) and then map to the new peeled iteration. This leaves
292 // the pre-loop with only 1 user (the new peeled iteration), but the
293 // peeled-loop backedge has 2 users.
294 // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
295 // extra backedge user.
296 void PhaseIdealLoop::do_peeling( IdealLoopTree *loop, Node_List &old_new ) {
297
298 C->set_major_progress();
299 // Peeling a 'main' loop in a pre/main/post situation obfuscates the
300 // 'pre' loop from the main and the 'pre' can no longer have it's
301 // iterations adjusted. Therefore, we need to declare this loop as
302 // no longer a 'main' loop; it will need new pre and post loops before
303 // we can do further RCE.
304 Node *h = loop->_head;
305 if( h->is_CountedLoop() ) {
306 CountedLoopNode *cl = h->as_CountedLoop();
307 assert(cl->trip_count() > 0, "peeling a fully unrolled loop");
308 cl->set_trip_count(cl->trip_count() - 1);
309 if( cl->is_main_loop() ) {
310 cl->set_normal_loop();
311 #ifndef PRODUCT
312 if( PrintOpto && VerifyLoopOptimizations ) {
313 tty->print("Peeling a 'main' loop; resetting to 'normal' ");
314 loop->dump_head();
315 }
316 #endif
317 }
318 }
319
320 // Step 1: Clone the loop body. The clone becomes the peeled iteration.
321 // The pre-loop illegally has 2 control users (old & new loops).
322 clone_loop( loop, old_new, dom_depth(loop->_head) );
323
324
325 // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
326 // Do this by making the old-loop fall-in edges act as if they came
327 // around the loopback from the prior iteration (follow the old-loop
328 // backedges) and then map to the new peeled iteration. This leaves
329 // the pre-loop with only 1 user (the new peeled iteration), but the
330 // peeled-loop backedge has 2 users.
331 for (DUIterator_Fast jmax, j = loop->_head->fast_outs(jmax); j < jmax; j++) {
332 Node* old = loop->_head->fast_out(j);
333 if( old->in(0) == loop->_head && old->req() == 3 &&
334 (old->is_Loop() || old->is_Phi()) ) {
335 Node *new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx];
336 if( !new_exit_value ) // Backedge value is ALSO loop invariant?
337 // Then loop body backedge value remains the same.
338 new_exit_value = old->in(LoopNode::LoopBackControl);
339 _igvn.hash_delete(old);
340 old->set_req(LoopNode::EntryControl, new_exit_value);
341 }
342 }
343
344
345 // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
346 // extra backedge user.
347 Node *nnn = old_new[loop->_head->_idx];
348 _igvn.hash_delete(nnn);
349 nnn->set_req(LoopNode::LoopBackControl, C->top());
350 for (DUIterator_Fast j2max, j2 = nnn->fast_outs(j2max); j2 < j2max; j2++) {
351 Node* use = nnn->fast_out(j2);
352 if( use->in(0) == nnn && use->req() == 3 && use->is_Phi() ) {
353 _igvn.hash_delete(use);
354 use->set_req(LoopNode::LoopBackControl, C->top());
355 }
356 }
357
358
359 // Step 4: Correct dom-depth info. Set to loop-head depth.
360 int dd = dom_depth(loop->_head);
361 set_idom(loop->_head, loop->_head->in(1), dd);
362 for (uint j3 = 0; j3 < loop->_body.size(); j3++) {
363 Node *old = loop->_body.at(j3);
364 Node *nnn = old_new[old->_idx];
365 if (!has_ctrl(nnn))
366 set_idom(nnn, idom(nnn), dd-1);
367 // While we're at it, remove any SafePoints from the peeled code
368 if( old->Opcode() == Op_SafePoint ) {
369 Node *nnn = old_new[old->_idx];
370 lazy_replace(nnn,nnn->in(TypeFunc::Control));
371 }
372 }
373
374 // Now force out all loop-invariant dominating tests. The optimizer
375 // finds some, but we _know_ they are all useless.
376 peeled_dom_test_elim(loop,old_new);
377
378 loop->record_for_igvn();
379 }
380
381 //------------------------------policy_maximally_unroll------------------------
382 // Return exact loop trip count, or 0 if not maximally unrolling
383 bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const {
384 CountedLoopNode *cl = _head->as_CountedLoop();
385 assert( cl->is_normal_loop(), "" );
386
387 Node *init_n = cl->init_trip();
388 Node *limit_n = cl->limit();
389
390 // Non-constant bounds
391 if( init_n == NULL || !init_n->is_Con() ||
392 limit_n == NULL || !limit_n->is_Con() ||
393 // protect against stride not being a constant
394 !cl->stride_is_con() ) {
395 return false;
396 }
397 int init = init_n->get_int();
398 int limit = limit_n->get_int();
399 int span = limit - init;
400 int stride = cl->stride_con();
401
402 if (init >= limit || stride > span) {
403 // return a false (no maximally unroll) and the regular unroll/peel
404 // route will make a small mess which CCP will fold away.
405 return false;
406 }
407 uint trip_count = span/stride; // trip_count can be greater than 2 Gig.
408 assert( (int)trip_count*stride == span, "must divide evenly" );
409
410 // Real policy: if we maximally unroll, does it get too big?
411 // Allow the unrolled mess to get larger than standard loop
412 // size. After all, it will no longer be a loop.
413 uint body_size = _body.size();
414 uint unroll_limit = (uint)LoopUnrollLimit * 4;
415 assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits");
416 cl->set_trip_count(trip_count);
417 if( trip_count <= unroll_limit && body_size <= unroll_limit ) {
418 uint new_body_size = body_size * trip_count;
419 if (new_body_size <= unroll_limit &&
420 body_size == new_body_size / trip_count &&
421 // Unrolling can result in a large amount of node construction
422 new_body_size < MaxNodeLimit - phase->C->unique()) {
423 return true; // maximally unroll
424 }
425 }
426
427 return false; // Do not maximally unroll
428 }
429
430
431 //------------------------------policy_unroll----------------------------------
432 // Return TRUE or FALSE if the loop should be unrolled or not. Unroll if
433 // the loop is a CountedLoop and the body is small enough.
434 bool IdealLoopTree::policy_unroll( PhaseIdealLoop *phase ) const {
435
436 CountedLoopNode *cl = _head->as_CountedLoop();
437 assert( cl->is_normal_loop() || cl->is_main_loop(), "" );
438
439 // protect against stride not being a constant
440 if( !cl->stride_is_con() ) return false;
441
442 // protect against over-unrolling
443 if( cl->trip_count() <= 1 ) return false;
444
445 int future_unroll_ct = cl->unrolled_count() * 2;
446
447 // Don't unroll if the next round of unrolling would push us
448 // over the expected trip count of the loop. One is subtracted
449 // from the expected trip count because the pre-loop normally
450 // executes 1 iteration.
451 if (UnrollLimitForProfileCheck > 0 &&
452 cl->profile_trip_cnt() != COUNT_UNKNOWN &&
453 future_unroll_ct > UnrollLimitForProfileCheck &&
454 (float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) {
455 return false;
456 }
457
458 // When unroll count is greater than LoopUnrollMin, don't unroll if:
459 // the residual iterations are more than 10% of the trip count
460 // and rounds of "unroll,optimize" are not making significant progress
461 // Progress defined as current size less than 20% larger than previous size.
462 if (UseSuperWord && cl->node_count_before_unroll() > 0 &&
463 future_unroll_ct > LoopUnrollMin &&
464 (future_unroll_ct - 1) * 10.0 > cl->profile_trip_cnt() &&
465 1.2 * cl->node_count_before_unroll() < (double)_body.size()) {
466 return false;
467 }
468
469 Node *init_n = cl->init_trip();
470 Node *limit_n = cl->limit();
471 // Non-constant bounds.
472 // Protect against over-unrolling when init or/and limit are not constant
473 // (so that trip_count's init value is maxint) but iv range is known.
474 if( init_n == NULL || !init_n->is_Con() ||
475 limit_n == NULL || !limit_n->is_Con() ) {
476 Node* phi = cl->phi();
477 if( phi != NULL ) {
478 assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi.");
479 const TypeInt* iv_type = phase->_igvn.type(phi)->is_int();
480 int next_stride = cl->stride_con() * 2; // stride after this unroll
481 if( next_stride > 0 ) {
482 if( iv_type->_lo + next_stride <= iv_type->_lo || // overflow
483 iv_type->_lo + next_stride > iv_type->_hi ) {
484 return false; // over-unrolling
485 }
486 } else if( next_stride < 0 ) {
487 if( iv_type->_hi + next_stride >= iv_type->_hi || // overflow
488 iv_type->_hi + next_stride < iv_type->_lo ) {
489 return false; // over-unrolling
490 }
491 }
492 }
493 }
494
495 // Adjust body_size to determine if we unroll or not
496 uint body_size = _body.size();
497 // Key test to unroll CaffeineMark's Logic test
498 int xors_in_loop = 0;
499 // Also count ModL, DivL and MulL which expand mightly
500 for( uint k = 0; k < _body.size(); k++ ) {
501 switch( _body.at(k)->Opcode() ) {
502 case Op_XorI: xors_in_loop++; break; // CaffeineMark's Logic test
503 case Op_ModL: body_size += 30; break;
504 case Op_DivL: body_size += 30; break;
505 case Op_MulL: body_size += 10; break;
506 }
507 }
508
509 // Check for being too big
510 if( body_size > (uint)LoopUnrollLimit ) {
511 if( xors_in_loop >= 4 && body_size < (uint)LoopUnrollLimit*4) return true;
512 // Normal case: loop too big
513 return false;
514 }
515
516 // Check for stride being a small enough constant
517 if( abs(cl->stride_con()) > (1<<3) ) return false;
518
519 // Unroll once! (Each trip will soon do double iterations)
520 return true;
521 }
522
523 //------------------------------policy_align-----------------------------------
524 // Return TRUE or FALSE if the loop should be cache-line aligned. Gather the
525 // expression that does the alignment. Note that only one array base can be
526 // aligned in a loop (unless the VM guarentees mutual alignment). Note that
527 // if we vectorize short memory ops into longer memory ops, we may want to
528 // increase alignment.
529 bool IdealLoopTree::policy_align( PhaseIdealLoop *phase ) const {
530 return false;
531 }
532
533 //------------------------------policy_range_check-----------------------------
534 // Return TRUE or FALSE if the loop should be range-check-eliminated.
535 // Actually we do iteration-splitting, a more powerful form of RCE.
536 bool IdealLoopTree::policy_range_check( PhaseIdealLoop *phase ) const {
537 if( !RangeCheckElimination ) return false;
538
539 CountedLoopNode *cl = _head->as_CountedLoop();
540 // If we unrolled with no intention of doing RCE and we later
541 // changed our minds, we got no pre-loop. Either we need to
542 // make a new pre-loop, or we gotta disallow RCE.
543 if( cl->is_main_no_pre_loop() ) return false; // Disallowed for now.
544 Node *trip_counter = cl->phi();
545
546 // Check loop body for tests of trip-counter plus loop-invariant vs
547 // loop-invariant.
548 for( uint i = 0; i < _body.size(); i++ ) {
549 Node *iff = _body[i];
550 if( iff->Opcode() == Op_If ) { // Test?
551
552 // Comparing trip+off vs limit
553 Node *bol = iff->in(1);
554 if( bol->req() != 2 ) continue; // dead constant test
555 Node *cmp = bol->in(1);
556
557 Node *rc_exp = cmp->in(1);
558 Node *limit = cmp->in(2);
559
560 Node *limit_c = phase->get_ctrl(limit);
561 if( limit_c == phase->C->top() )
562 return false; // Found dead test on live IF? No RCE!
563 if( is_member(phase->get_loop(limit_c) ) ) {
564 // Compare might have operands swapped; commute them
565 rc_exp = cmp->in(2);
566 limit = cmp->in(1);
567 limit_c = phase->get_ctrl(limit);
568 if( is_member(phase->get_loop(limit_c) ) )
569 continue; // Both inputs are loop varying; cannot RCE
570 }
571
572 if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) {
573 continue;
574 }
575 // Yeah! Found a test like 'trip+off vs limit'
576 // Test is an IfNode, has 2 projections. If BOTH are in the loop
577 // we need loop unswitching instead of iteration splitting.
578 if( is_loop_exit(iff) )
579 return true; // Found reason to split iterations
580 } // End of is IF
581 }
582
583 return false;
584 }
585
586 //------------------------------policy_peel_only-------------------------------
587 // Return TRUE or FALSE if the loop should NEVER be RCE'd or aligned. Useful
588 // for unrolling loops with NO array accesses.
589 bool IdealLoopTree::policy_peel_only( PhaseIdealLoop *phase ) const {
590
591 for( uint i = 0; i < _body.size(); i++ )
592 if( _body[i]->is_Mem() )
593 return false;
594
595 // No memory accesses at all!
596 return true;
597 }
598
599 //------------------------------clone_up_backedge_goo--------------------------
600 // If Node n lives in the back_ctrl block and cannot float, we clone a private
601 // version of n in preheader_ctrl block and return that, otherwise return n.
602 Node *PhaseIdealLoop::clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n ) {
603 if( get_ctrl(n) != back_ctrl ) return n;
604
605 Node *x = NULL; // If required, a clone of 'n'
606 // Check for 'n' being pinned in the backedge.
607 if( n->in(0) && n->in(0) == back_ctrl ) {
608 x = n->clone(); // Clone a copy of 'n' to preheader
609 x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader
610 }
611
612 // Recursive fixup any other input edges into x.
613 // If there are no changes we can just return 'n', otherwise
614 // we need to clone a private copy and change it.
615 for( uint i = 1; i < n->req(); i++ ) {
616 Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i) );
617 if( g != n->in(i) ) {
618 if( !x )
619 x = n->clone();
620 x->set_req(i, g);
621 }
622 }
623 if( x ) { // x can legally float to pre-header location
624 register_new_node( x, preheader_ctrl );
625 return x;
626 } else { // raise n to cover LCA of uses
627 set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) );
628 }
629 return n;
630 }
631
632 //------------------------------insert_pre_post_loops--------------------------
633 // Insert pre and post loops. If peel_only is set, the pre-loop can not have
634 // more iterations added. It acts as a 'peel' only, no lower-bound RCE, no
635 // alignment. Useful to unroll loops that do no array accesses.
636 void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) {
637
638 C->set_major_progress();
639
640 // Find common pieces of the loop being guarded with pre & post loops
641 CountedLoopNode *main_head = loop->_head->as_CountedLoop();
642 assert( main_head->is_normal_loop(), "" );
643 CountedLoopEndNode *main_end = main_head->loopexit();
644 assert( main_end->outcnt() == 2, "1 true, 1 false path only" );
645 uint dd_main_head = dom_depth(main_head);
646 uint max = main_head->outcnt();
647
648 Node *pre_header= main_head->in(LoopNode::EntryControl);
649 Node *init = main_head->init_trip();
650 Node *incr = main_end ->incr();
651 Node *limit = main_end ->limit();
652 Node *stride = main_end ->stride();
653 Node *cmp = main_end ->cmp_node();
654 BoolTest::mask b_test = main_end->test_trip();
655
656 // Need only 1 user of 'bol' because I will be hacking the loop bounds.
657 Node *bol = main_end->in(CountedLoopEndNode::TestValue);
658 if( bol->outcnt() != 1 ) {
659 bol = bol->clone();
660 register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl));
661 _igvn.hash_delete(main_end);
662 main_end->set_req(CountedLoopEndNode::TestValue, bol);
663 }
664 // Need only 1 user of 'cmp' because I will be hacking the loop bounds.
665 if( cmp->outcnt() != 1 ) {
666 cmp = cmp->clone();
667 register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl));
668 _igvn.hash_delete(bol);
669 bol->set_req(1, cmp);
670 }
671
672 //------------------------------
673 // Step A: Create Post-Loop.
674 Node* main_exit = main_end->proj_out(false);
675 assert( main_exit->Opcode() == Op_IfFalse, "" );
676 int dd_main_exit = dom_depth(main_exit);
677
678 // Step A1: Clone the loop body. The clone becomes the post-loop. The main
679 // loop pre-header illegally has 2 control users (old & new loops).
680 clone_loop( loop, old_new, dd_main_exit );
681 assert( old_new[main_end ->_idx]->Opcode() == Op_CountedLoopEnd, "" );
682 CountedLoopNode *post_head = old_new[main_head->_idx]->as_CountedLoop();
683 post_head->set_post_loop(main_head);
684
685 // Build the main-loop normal exit.
686 IfFalseNode *new_main_exit = new (C, 1) IfFalseNode(main_end);
687 _igvn.register_new_node_with_optimizer( new_main_exit );
688 set_idom(new_main_exit, main_end, dd_main_exit );
689 set_loop(new_main_exit, loop->_parent);
690
691 // Step A2: Build a zero-trip guard for the post-loop. After leaving the
692 // main-loop, the post-loop may not execute at all. We 'opaque' the incr
693 // (the main-loop trip-counter exit value) because we will be changing
694 // the exit value (via unrolling) so we cannot constant-fold away the zero
695 // trip guard until all unrolling is done.
696 Node *zer_opaq = new (C, 2) Opaque1Node(incr);
697 Node *zer_cmp = new (C, 3) CmpINode( zer_opaq, limit );
698 Node *zer_bol = new (C, 2) BoolNode( zer_cmp, b_test );
699 register_new_node( zer_opaq, new_main_exit );
700 register_new_node( zer_cmp , new_main_exit );
701 register_new_node( zer_bol , new_main_exit );
702
703 // Build the IfNode
704 IfNode *zer_iff = new (C, 2) IfNode( new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN );
705 _igvn.register_new_node_with_optimizer( zer_iff );
706 set_idom(zer_iff, new_main_exit, dd_main_exit);
707 set_loop(zer_iff, loop->_parent);
708
709 // Plug in the false-path, taken if we need to skip post-loop
710 _igvn.hash_delete( main_exit );
711 main_exit->set_req(0, zer_iff);
712 _igvn._worklist.push(main_exit);
713 set_idom(main_exit, zer_iff, dd_main_exit);
714 set_idom(main_exit->unique_out(), zer_iff, dd_main_exit);
715 // Make the true-path, must enter the post loop
716 Node *zer_taken = new (C, 1) IfTrueNode( zer_iff );
717 _igvn.register_new_node_with_optimizer( zer_taken );
718 set_idom(zer_taken, zer_iff, dd_main_exit);
719 set_loop(zer_taken, loop->_parent);
720 // Plug in the true path
721 _igvn.hash_delete( post_head );
722 post_head->set_req(LoopNode::EntryControl, zer_taken);
723 set_idom(post_head, zer_taken, dd_main_exit);
724
725 // Step A3: Make the fall-in values to the post-loop come from the
726 // fall-out values of the main-loop.
727 for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) {
728 Node* main_phi = main_head->fast_out(i);
729 if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0 ) {
730 Node *post_phi = old_new[main_phi->_idx];
731 Node *fallmain = clone_up_backedge_goo(main_head->back_control(),
732 post_head->init_control(),
733 main_phi->in(LoopNode::LoopBackControl));
734 _igvn.hash_delete(post_phi);
735 post_phi->set_req( LoopNode::EntryControl, fallmain );
736 }
737 }
738
739 // Update local caches for next stanza
740 main_exit = new_main_exit;
741
742
743 //------------------------------
744 // Step B: Create Pre-Loop.
745
746 // Step B1: Clone the loop body. The clone becomes the pre-loop. The main
747 // loop pre-header illegally has 2 control users (old & new loops).
748 clone_loop( loop, old_new, dd_main_head );
749 CountedLoopNode* pre_head = old_new[main_head->_idx]->as_CountedLoop();
750 CountedLoopEndNode* pre_end = old_new[main_end ->_idx]->as_CountedLoopEnd();
751 pre_head->set_pre_loop(main_head);
752 Node *pre_incr = old_new[incr->_idx];
753
754 // Find the pre-loop normal exit.
755 Node* pre_exit = pre_end->proj_out(false);
756 assert( pre_exit->Opcode() == Op_IfFalse, "" );
757 IfFalseNode *new_pre_exit = new (C, 1) IfFalseNode(pre_end);
758 _igvn.register_new_node_with_optimizer( new_pre_exit );
759 set_idom(new_pre_exit, pre_end, dd_main_head);
760 set_loop(new_pre_exit, loop->_parent);
761
762 // Step B2: Build a zero-trip guard for the main-loop. After leaving the
763 // pre-loop, the main-loop may not execute at all. Later in life this
764 // zero-trip guard will become the minimum-trip guard when we unroll
765 // the main-loop.
766 Node *min_opaq = new (C, 2) Opaque1Node(limit);
767 Node *min_cmp = new (C, 3) CmpINode( pre_incr, min_opaq );
768 Node *min_bol = new (C, 2) BoolNode( min_cmp, b_test );
769 register_new_node( min_opaq, new_pre_exit );
770 register_new_node( min_cmp , new_pre_exit );
771 register_new_node( min_bol , new_pre_exit );
772
773 // Build the IfNode
774 IfNode *min_iff = new (C, 2) IfNode( new_pre_exit, min_bol, PROB_FAIR, COUNT_UNKNOWN );
775 _igvn.register_new_node_with_optimizer( min_iff );
776 set_idom(min_iff, new_pre_exit, dd_main_head);
777 set_loop(min_iff, loop->_parent);
778
779 // Plug in the false-path, taken if we need to skip main-loop
780 _igvn.hash_delete( pre_exit );
781 pre_exit->set_req(0, min_iff);
782 set_idom(pre_exit, min_iff, dd_main_head);
783 set_idom(pre_exit->unique_out(), min_iff, dd_main_head);
784 // Make the true-path, must enter the main loop
785 Node *min_taken = new (C, 1) IfTrueNode( min_iff );
786 _igvn.register_new_node_with_optimizer( min_taken );
787 set_idom(min_taken, min_iff, dd_main_head);
788 set_loop(min_taken, loop->_parent);
789 // Plug in the true path
790 _igvn.hash_delete( main_head );
791 main_head->set_req(LoopNode::EntryControl, min_taken);
792 set_idom(main_head, min_taken, dd_main_head);
793
794 // Step B3: Make the fall-in values to the main-loop come from the
795 // fall-out values of the pre-loop.
796 for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) {
797 Node* main_phi = main_head->fast_out(i2);
798 if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) {
799 Node *pre_phi = old_new[main_phi->_idx];
800 Node *fallpre = clone_up_backedge_goo(pre_head->back_control(),
801 main_head->init_control(),
802 pre_phi->in(LoopNode::LoopBackControl));
803 _igvn.hash_delete(main_phi);
804 main_phi->set_req( LoopNode::EntryControl, fallpre );
805 }
806 }
807
808 // Step B4: Shorten the pre-loop to run only 1 iteration (for now).
809 // RCE and alignment may change this later.
810 Node *cmp_end = pre_end->cmp_node();
811 assert( cmp_end->in(2) == limit, "" );
812 Node *pre_limit = new (C, 3) AddINode( init, stride );
813
814 // Save the original loop limit in this Opaque1 node for
815 // use by range check elimination.
816 Node *pre_opaq = new (C, 3) Opaque1Node(pre_limit, limit);
817
818 register_new_node( pre_limit, pre_head->in(0) );
819 register_new_node( pre_opaq , pre_head->in(0) );
820
821 // Since no other users of pre-loop compare, I can hack limit directly
822 assert( cmp_end->outcnt() == 1, "no other users" );
823 _igvn.hash_delete(cmp_end);
824 cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq);
825
826 // Special case for not-equal loop bounds:
827 // Change pre loop test, main loop test, and the
828 // main loop guard test to use lt or gt depending on stride
829 // direction:
830 // positive stride use <
831 // negative stride use >
832
833 if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) {
834
835 BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt;
836 // Modify pre loop end condition
837 Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool();
838 BoolNode* new_bol0 = new (C, 2) BoolNode(pre_bol->in(1), new_test);
839 register_new_node( new_bol0, pre_head->in(0) );
840 _igvn.hash_delete(pre_end);
841 pre_end->set_req(CountedLoopEndNode::TestValue, new_bol0);
842 // Modify main loop guard condition
843 assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay");
844 BoolNode* new_bol1 = new (C, 2) BoolNode(min_bol->in(1), new_test);
845 register_new_node( new_bol1, new_pre_exit );
846 _igvn.hash_delete(min_iff);
847 min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1);
848 // Modify main loop end condition
849 BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool();
850 BoolNode* new_bol2 = new (C, 2) BoolNode(main_bol->in(1), new_test);
851 register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) );
852 _igvn.hash_delete(main_end);
853 main_end->set_req(CountedLoopEndNode::TestValue, new_bol2);
854 }
855
856 // Flag main loop
857 main_head->set_main_loop();
858 if( peel_only ) main_head->set_main_no_pre_loop();
859
860 // It's difficult to be precise about the trip-counts
861 // for the pre/post loops. They are usually very short,
862 // so guess that 4 trips is a reasonable value.
863 post_head->set_profile_trip_cnt(4.0);
864 pre_head->set_profile_trip_cnt(4.0);
865
866 // Now force out all loop-invariant dominating tests. The optimizer
867 // finds some, but we _know_ they are all useless.
868 peeled_dom_test_elim(loop,old_new);
869 }
870
871 //------------------------------is_invariant-----------------------------
872 // Return true if n is invariant
873 bool IdealLoopTree::is_invariant(Node* n) const {
874 Node *n_c = _phase->get_ctrl(n);
875 if (n_c->is_top()) return false;
876 return !is_member(_phase->get_loop(n_c));
877 }
878
879
880 //------------------------------do_unroll--------------------------------------
881 // Unroll the loop body one step - make each trip do 2 iterations.
882 void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) {
883 assert( LoopUnrollLimit, "" );
884 #ifndef PRODUCT
885 if( PrintOpto && VerifyLoopOptimizations ) {
886 tty->print("Unrolling ");
887 loop->dump_head();
888 }
889 #endif
890 CountedLoopNode *loop_head = loop->_head->as_CountedLoop();
891 CountedLoopEndNode *loop_end = loop_head->loopexit();
892 assert( loop_end, "" );
893
894 // Remember loop node count before unrolling to detect
895 // if rounds of unroll,optimize are making progress
896 loop_head->set_node_count_before_unroll(loop->_body.size());
897
898 Node *ctrl = loop_head->in(LoopNode::EntryControl);
899 Node *limit = loop_head->limit();
900 Node *init = loop_head->init_trip();
901 Node *strid = loop_head->stride();
902
903 Node *opaq = NULL;
904 if( adjust_min_trip ) { // If not maximally unrolling, need adjustment
905 assert( loop_head->is_main_loop(), "" );
906 assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );
907 Node *iff = ctrl->in(0);
908 assert( iff->Opcode() == Op_If, "" );
909 Node *bol = iff->in(1);
910 assert( bol->Opcode() == Op_Bool, "" );
911 Node *cmp = bol->in(1);
912 assert( cmp->Opcode() == Op_CmpI, "" );
913 opaq = cmp->in(2);
914 // Occasionally it's possible for a pre-loop Opaque1 node to be
915 // optimized away and then another round of loop opts attempted.
916 // We can not optimize this particular loop in that case.
917 if( opaq->Opcode() != Op_Opaque1 )
918 return; // Cannot find pre-loop! Bail out!
919 }
920
921 C->set_major_progress();
922
923 // Adjust max trip count. The trip count is intentionally rounded
924 // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
925 // the main, unrolled, part of the loop will never execute as it is protected
926 // by the min-trip test. See bug 4834191 for a case where we over-unrolled
927 // and later determined that part of the unrolled loop was dead.
928 loop_head->set_trip_count(loop_head->trip_count() / 2);
929
930 // Double the count of original iterations in the unrolled loop body.
931 loop_head->double_unrolled_count();
932
933 // -----------
934 // Step 2: Cut back the trip counter for an unroll amount of 2.
935 // Loop will normally trip (limit - init)/stride_con. Since it's a
936 // CountedLoop this is exact (stride divides limit-init exactly).
937 // We are going to double the loop body, so we want to knock off any
938 // odd iteration: (trip_cnt & ~1). Then back compute a new limit.
939 Node *span = new (C, 3) SubINode( limit, init );
940 register_new_node( span, ctrl );
941 Node *trip = new (C, 3) DivINode( 0, span, strid );
942 register_new_node( trip, ctrl );
943 Node *mtwo = _igvn.intcon(-2);
944 set_ctrl(mtwo, C->root());
945 Node *rond = new (C, 3) AndINode( trip, mtwo );
946 register_new_node( rond, ctrl );
947 Node *spn2 = new (C, 3) MulINode( rond, strid );
948 register_new_node( spn2, ctrl );
949 Node *lim2 = new (C, 3) AddINode( spn2, init );
950 register_new_node( lim2, ctrl );
951
952 // Hammer in the new limit
953 Node *ctrl2 = loop_end->in(0);
954 Node *cmp2 = new (C, 3) CmpINode( loop_head->incr(), lim2 );
955 register_new_node( cmp2, ctrl2 );
956 Node *bol2 = new (C, 2) BoolNode( cmp2, loop_end->test_trip() );
957 register_new_node( bol2, ctrl2 );
958 _igvn.hash_delete(loop_end);
959 loop_end->set_req(CountedLoopEndNode::TestValue, bol2);
960
961 // Step 3: Find the min-trip test guaranteed before a 'main' loop.
962 // Make it a 1-trip test (means at least 2 trips).
963 if( adjust_min_trip ) {
964 // Guard test uses an 'opaque' node which is not shared. Hence I
965 // can edit it's inputs directly. Hammer in the new limit for the
966 // minimum-trip guard.
967 assert( opaq->outcnt() == 1, "" );
968 _igvn.hash_delete(opaq);
969 opaq->set_req(1, lim2);
970 }
971
972 // ---------
973 // Step 4: Clone the loop body. Move it inside the loop. This loop body
974 // represents the odd iterations; since the loop trips an even number of
975 // times its backedge is never taken. Kill the backedge.
976 uint dd = dom_depth(loop_head);
977 clone_loop( loop, old_new, dd );
978
979 // Make backedges of the clone equal to backedges of the original.
980 // Make the fall-in from the original come from the fall-out of the clone.
981 for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) {
982 Node* phi = loop_head->fast_out(j);
983 if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) {
984 Node *newphi = old_new[phi->_idx];
985 _igvn.hash_delete( phi );
986 _igvn.hash_delete( newphi );
987
988 phi ->set_req(LoopNode:: EntryControl, newphi->in(LoopNode::LoopBackControl));
989 newphi->set_req(LoopNode::LoopBackControl, phi ->in(LoopNode::LoopBackControl));
990 phi ->set_req(LoopNode::LoopBackControl, C->top());
991 }
992 }
993 Node *clone_head = old_new[loop_head->_idx];
994 _igvn.hash_delete( clone_head );
995 loop_head ->set_req(LoopNode:: EntryControl, clone_head->in(LoopNode::LoopBackControl));
996 clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl));
997 loop_head ->set_req(LoopNode::LoopBackControl, C->top());
998 loop->_head = clone_head; // New loop header
999
1000 set_idom(loop_head, loop_head ->in(LoopNode::EntryControl), dd);
1001 set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd);
1002
1003 // Kill the clone's backedge
1004 Node *newcle = old_new[loop_end->_idx];
1005 _igvn.hash_delete( newcle );
1006 Node *one = _igvn.intcon(1);
1007 set_ctrl(one, C->root());
1008 newcle->set_req(1, one);
1009 // Force clone into same loop body
1010 uint max = loop->_body.size();
1011 for( uint k = 0; k < max; k++ ) {
1012 Node *old = loop->_body.at(k);
1013 Node *nnn = old_new[old->_idx];
1014 loop->_body.push(nnn);
1015 if (!has_ctrl(old))
1016 set_loop(nnn, loop);
1017 }
1018 }
1019
1020 //------------------------------do_maximally_unroll----------------------------
1021
1022 void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) {
1023 CountedLoopNode *cl = loop->_head->as_CountedLoop();
1024 assert( cl->trip_count() > 0, "");
1025
1026 // If loop is tripping an odd number of times, peel odd iteration
1027 if( (cl->trip_count() & 1) == 1 ) {
1028 do_peeling( loop, old_new );
1029 }
1030
1031 // Now its tripping an even number of times remaining. Double loop body.
1032 // Do not adjust pre-guards; they are not needed and do not exist.
1033 if( cl->trip_count() > 0 ) {
1034 do_unroll( loop, old_new, false );
1035 }
1036 }
1037
1038 //------------------------------dominates_backedge---------------------------------
1039 // Returns true if ctrl is executed on every complete iteration
1040 bool IdealLoopTree::dominates_backedge(Node* ctrl) {
1041 assert(ctrl->is_CFG(), "must be control");
1042 Node* backedge = _head->as_Loop()->in(LoopNode::LoopBackControl);
1043 return _phase->dom_lca_internal(ctrl, backedge) == ctrl;
1044 }
1045
1046 //------------------------------add_constraint---------------------------------
1047 // Constrain the main loop iterations so the condition:
1048 // scale_con * I + offset < limit
1049 // always holds true. That is, either increase the number of iterations in
1050 // the pre-loop or the post-loop until the condition holds true in the main
1051 // loop. Stride, scale, offset and limit are all loop invariant. Further,
1052 // stride and scale are constants (offset and limit often are).
1053 void PhaseIdealLoop::add_constraint( int stride_con, int scale_con, Node *offset, Node *limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit ) {
1054
1055 // Compute "I :: (limit-offset)/scale_con"
1056 Node *con = new (C, 3) SubINode( limit, offset );
1057 register_new_node( con, pre_ctrl );
1058 Node *scale = _igvn.intcon(scale_con);
1059 set_ctrl(scale, C->root());
1060 Node *X = new (C, 3) DivINode( 0, con, scale );
1061 register_new_node( X, pre_ctrl );
1062
1063 // For positive stride, the pre-loop limit always uses a MAX function
1064 // and the main loop a MIN function. For negative stride these are
1065 // reversed.
1066
1067 // Also for positive stride*scale the affine function is increasing, so the
1068 // pre-loop must check for underflow and the post-loop for overflow.
1069 // Negative stride*scale reverses this; pre-loop checks for overflow and
1070 // post-loop for underflow.
1071 if( stride_con*scale_con > 0 ) {
1072 // Compute I < (limit-offset)/scale_con
1073 // Adjust main-loop last iteration to be MIN/MAX(main_loop,X)
1074 *main_limit = (stride_con > 0)
1075 ? (Node*)(new (C, 3) MinINode( *main_limit, X ))
1076 : (Node*)(new (C, 3) MaxINode( *main_limit, X ));
1077 register_new_node( *main_limit, pre_ctrl );
1078
1079 } else {
1080 // Compute (limit-offset)/scale_con + SGN(-scale_con) <= I
1081 // Add the negation of the main-loop constraint to the pre-loop.
1082 // See footnote [++] below for a derivation of the limit expression.
1083 Node *incr = _igvn.intcon(scale_con > 0 ? -1 : 1);
1084 set_ctrl(incr, C->root());
1085 Node *adj = new (C, 3) AddINode( X, incr );
1086 register_new_node( adj, pre_ctrl );
1087 *pre_limit = (scale_con > 0)
1088 ? (Node*)new (C, 3) MinINode( *pre_limit, adj )
1089 : (Node*)new (C, 3) MaxINode( *pre_limit, adj );
1090 register_new_node( *pre_limit, pre_ctrl );
1091
1092 // [++] Here's the algebra that justifies the pre-loop limit expression:
1093 //
1094 // NOT( scale_con * I + offset < limit )
1095 // ==
1096 // scale_con * I + offset >= limit
1097 // ==
1098 // SGN(scale_con) * I >= (limit-offset)/|scale_con|
1099 // ==
1100 // (limit-offset)/|scale_con| <= I * SGN(scale_con)
1101 // ==
1102 // (limit-offset)/|scale_con|-1 < I * SGN(scale_con)
1103 // ==
1104 // ( if (scale_con > 0) /*common case*/
1105 // (limit-offset)/scale_con - 1 < I
1106 // else
1107 // (limit-offset)/scale_con + 1 > I
1108 // )
1109 // ( if (scale_con > 0) /*common case*/
1110 // (limit-offset)/scale_con + SGN(-scale_con) < I
1111 // else
1112 // (limit-offset)/scale_con + SGN(-scale_con) > I
1113 }
1114 }
1115
1116
1117 //------------------------------is_scaled_iv---------------------------------
1118 // Return true if exp is a constant times an induction var
1119 bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) {
1120 if (exp == iv) {
1121 if (p_scale != NULL) {
1122 *p_scale = 1;
1123 }
1124 return true;
1125 }
1126 int opc = exp->Opcode();
1127 if (opc == Op_MulI) {
1128 if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1129 if (p_scale != NULL) {
1130 *p_scale = exp->in(2)->get_int();
1131 }
1132 return true;
1133 }
1134 if (exp->in(2) == iv && exp->in(1)->is_Con()) {
1135 if (p_scale != NULL) {
1136 *p_scale = exp->in(1)->get_int();
1137 }
1138 return true;
1139 }
1140 } else if (opc == Op_LShiftI) {
1141 if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1142 if (p_scale != NULL) {
1143 *p_scale = 1 << exp->in(2)->get_int();
1144 }
1145 return true;
1146 }
1147 }
1148 return false;
1149 }
1150
1151 //-----------------------------is_scaled_iv_plus_offset------------------------------
1152 // Return true if exp is a simple induction variable expression: k1*iv + (invar + k2)
1153 bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) {
1154 if (is_scaled_iv(exp, iv, p_scale)) {
1155 if (p_offset != NULL) {
1156 Node *zero = _igvn.intcon(0);
1157 set_ctrl(zero, C->root());
1158 *p_offset = zero;
1159 }
1160 return true;
1161 }
1162 int opc = exp->Opcode();
1163 if (opc == Op_AddI) {
1164 if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1165 if (p_offset != NULL) {
1166 *p_offset = exp->in(2);
1167 }
1168 return true;
1169 }
1170 if (exp->in(2)->is_Con()) {
1171 Node* offset2 = NULL;
1172 if (depth < 2 &&
1173 is_scaled_iv_plus_offset(exp->in(1), iv, p_scale,
1174 p_offset != NULL ? &offset2 : NULL, depth+1)) {
1175 if (p_offset != NULL) {
1176 Node *ctrl_off2 = get_ctrl(offset2);
1177 Node* offset = new (C, 3) AddINode(offset2, exp->in(2));
1178 register_new_node(offset, ctrl_off2);
1179 *p_offset = offset;
1180 }
1181 return true;
1182 }
1183 }
1184 } else if (opc == Op_SubI) {
1185 if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1186 if (p_offset != NULL) {
1187 Node *zero = _igvn.intcon(0);
1188 set_ctrl(zero, C->root());
1189 Node *ctrl_off = get_ctrl(exp->in(2));
1190 Node* offset = new (C, 3) SubINode(zero, exp->in(2));
1191 register_new_node(offset, ctrl_off);
1192 *p_offset = offset;
1193 }
1194 return true;
1195 }
1196 if (is_scaled_iv(exp->in(2), iv, p_scale)) {
1197 if (p_offset != NULL) {
1198 *p_scale *= -1;
1199 *p_offset = exp->in(1);
1200 }
1201 return true;
1202 }
1203 }
1204 return false;
1205 }
1206
1207 //------------------------------do_range_check---------------------------------
1208 // Eliminate range-checks and other trip-counter vs loop-invariant tests.
1209 void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
1210 #ifndef PRODUCT
1211 if( PrintOpto && VerifyLoopOptimizations ) {
1212 tty->print("Range Check Elimination ");
1213 loop->dump_head();
1214 }
1215 #endif
1216 assert( RangeCheckElimination, "" );
1217 CountedLoopNode *cl = loop->_head->as_CountedLoop();
1218 assert( cl->is_main_loop(), "" );
1219
1220 // Find the trip counter; we are iteration splitting based on it
1221 Node *trip_counter = cl->phi();
1222 // Find the main loop limit; we will trim it's iterations
1223 // to not ever trip end tests
1224 Node *main_limit = cl->limit();
1225 // Find the pre-loop limit; we will expand it's iterations to
1226 // not ever trip low tests.
1227 Node *ctrl = cl->in(LoopNode::EntryControl);
1228 assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );
1229 Node *iffm = ctrl->in(0);
1230 assert( iffm->Opcode() == Op_If, "" );
1231 Node *p_f = iffm->in(0);
1232 assert( p_f->Opcode() == Op_IfFalse, "" );
1233 CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
1234 assert( pre_end->loopnode()->is_pre_loop(), "" );
1235 Node *pre_opaq1 = pre_end->limit();
1236 // Occasionally it's possible for a pre-loop Opaque1 node to be
1237 // optimized away and then another round of loop opts attempted.
1238 // We can not optimize this particular loop in that case.
1239 if( pre_opaq1->Opcode() != Op_Opaque1 )
1240 return;
1241 Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1;
1242 Node *pre_limit = pre_opaq->in(1);
1243
1244 // Where do we put new limit calculations
1245 Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl);
1246
1247 // Ensure the original loop limit is available from the
1248 // pre-loop Opaque1 node.
1249 Node *orig_limit = pre_opaq->original_loop_limit();
1250 if( orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP )
1251 return;
1252
1253 // Need to find the main-loop zero-trip guard
1254 Node *bolzm = iffm->in(1);
1255 assert( bolzm->Opcode() == Op_Bool, "" );
1256 Node *cmpzm = bolzm->in(1);
1257 assert( cmpzm->is_Cmp(), "" );
1258 Node *opqzm = cmpzm->in(2);
1259 if( opqzm->Opcode() != Op_Opaque1 )
1260 return;
1261 assert( opqzm->in(1) == main_limit, "do not understand situation" );
1262
1263 // Must know if its a count-up or count-down loop
1264
1265 // protect against stride not being a constant
1266 if ( !cl->stride_is_con() ) {
1267 return;
1268 }
1269 int stride_con = cl->stride_con();
1270 Node *zero = _igvn.intcon(0);
1271 Node *one = _igvn.intcon(1);
1272 set_ctrl(zero, C->root());
1273 set_ctrl(one, C->root());
1274
1275 // Range checks that do not dominate the loop backedge (ie.
1276 // conditionally executed) can lengthen the pre loop limit beyond
1277 // the original loop limit. To prevent this, the pre limit is
1278 // (for stride > 0) MINed with the original loop limit (MAXed
1279 // stride < 0) when some range_check (rc) is conditionally
1280 // executed.
1281 bool conditional_rc = false;
1282
1283 // Check loop body for tests of trip-counter plus loop-invariant vs
1284 // loop-invariant.
1285 for( uint i = 0; i < loop->_body.size(); i++ ) {
1286 Node *iff = loop->_body[i];
1287 if( iff->Opcode() == Op_If ) { // Test?
1288
1289 // Test is an IfNode, has 2 projections. If BOTH are in the loop
1290 // we need loop unswitching instead of iteration splitting.
1291 Node *exit = loop->is_loop_exit(iff);
1292 if( !exit ) continue;
1293 int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0;
1294
1295 // Get boolean condition to test
1296 Node *i1 = iff->in(1);
1297 if( !i1->is_Bool() ) continue;
1298 BoolNode *bol = i1->as_Bool();
1299 BoolTest b_test = bol->_test;
1300 // Flip sense of test if exit condition is flipped
1301 if( flip )
1302 b_test = b_test.negate();
1303
1304 // Get compare
1305 Node *cmp = bol->in(1);
1306
1307 // Look for trip_counter + offset vs limit
1308 Node *rc_exp = cmp->in(1);
1309 Node *limit = cmp->in(2);
1310 jint scale_con= 1; // Assume trip counter not scaled
1311
1312 Node *limit_c = get_ctrl(limit);
1313 if( loop->is_member(get_loop(limit_c) ) ) {
1314 // Compare might have operands swapped; commute them
1315 b_test = b_test.commute();
1316 rc_exp = cmp->in(2);
1317 limit = cmp->in(1);
1318 limit_c = get_ctrl(limit);
1319 if( loop->is_member(get_loop(limit_c) ) )
1320 continue; // Both inputs are loop varying; cannot RCE
1321 }
1322 // Here we know 'limit' is loop invariant
1323
1324 // 'limit' maybe pinned below the zero trip test (probably from a
1325 // previous round of rce), in which case, it can't be used in the
1326 // zero trip test expression which must occur before the zero test's if.
1327 if( limit_c == ctrl ) {
1328 continue; // Don't rce this check but continue looking for other candidates.
1329 }
1330
1331 // Check for scaled induction variable plus an offset
1332 Node *offset = NULL;
1333
1334 if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) {
1335 continue;
1336 }
1337
1338 Node *offset_c = get_ctrl(offset);
1339 if( loop->is_member( get_loop(offset_c) ) )
1340 continue; // Offset is not really loop invariant
1341 // Here we know 'offset' is loop invariant.
1342
1343 // As above for the 'limit', the 'offset' maybe pinned below the
1344 // zero trip test.
1345 if( offset_c == ctrl ) {
1346 continue; // Don't rce this check but continue looking for other candidates.
1347 }
1348
1349 // At this point we have the expression as:
1350 // scale_con * trip_counter + offset :: limit
1351 // where scale_con, offset and limit are loop invariant. Trip_counter
1352 // monotonically increases by stride_con, a constant. Both (or either)
1353 // stride_con and scale_con can be negative which will flip about the
1354 // sense of the test.
1355
1356 // Adjust pre and main loop limits to guard the correct iteration set
1357 if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests
1358 if( b_test._test == BoolTest::lt ) { // Range checks always use lt
1359 // The overflow limit: scale*I+offset < limit
1360 add_constraint( stride_con, scale_con, offset, limit, pre_ctrl, &pre_limit, &main_limit );
1361 // The underflow limit: 0 <= scale*I+offset.
1362 // Some math yields: -scale*I-(offset+1) < 0
1363 Node *plus_one = new (C, 3) AddINode( offset, one );
1364 register_new_node( plus_one, pre_ctrl );
1365 Node *neg_offset = new (C, 3) SubINode( zero, plus_one );
1366 register_new_node( neg_offset, pre_ctrl );
1367 add_constraint( stride_con, -scale_con, neg_offset, zero, pre_ctrl, &pre_limit, &main_limit );
1368 if (!conditional_rc) {
1369 conditional_rc = !loop->dominates_backedge(iff);
1370 }
1371 } else {
1372 #ifndef PRODUCT
1373 if( PrintOpto )
1374 tty->print_cr("missed RCE opportunity");
1375 #endif
1376 continue; // In release mode, ignore it
1377 }
1378 } else { // Otherwise work on normal compares
1379 switch( b_test._test ) {
1380 case BoolTest::ge: // Convert X >= Y to -X <= -Y
1381 scale_con = -scale_con;
1382 offset = new (C, 3) SubINode( zero, offset );
1383 register_new_node( offset, pre_ctrl );
1384 limit = new (C, 3) SubINode( zero, limit );
1385 register_new_node( limit, pre_ctrl );
1386 // Fall into LE case
1387 case BoolTest::le: // Convert X <= Y to X < Y+1
1388 limit = new (C, 3) AddINode( limit, one );
1389 register_new_node( limit, pre_ctrl );
1390 // Fall into LT case
1391 case BoolTest::lt:
1392 add_constraint( stride_con, scale_con, offset, limit, pre_ctrl, &pre_limit, &main_limit );
1393 if (!conditional_rc) {
1394 conditional_rc = !loop->dominates_backedge(iff);
1395 }
1396 break;
1397 default:
1398 #ifndef PRODUCT
1399 if( PrintOpto )
1400 tty->print_cr("missed RCE opportunity");
1401 #endif
1402 continue; // Unhandled case
1403 }
1404 }
1405
1406 // Kill the eliminated test
1407 C->set_major_progress();
1408 Node *kill_con = _igvn.intcon( 1-flip );
1409 set_ctrl(kill_con, C->root());
1410 _igvn.hash_delete(iff);
1411 iff->set_req(1, kill_con);
1412 _igvn._worklist.push(iff);
1413 // Find surviving projection
1414 assert(iff->is_If(), "");
1415 ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip);
1416 // Find loads off the surviving projection; remove their control edge
1417 for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) {
1418 Node* cd = dp->fast_out(i); // Control-dependent node
1419 if( cd->is_Load() ) { // Loads can now float around in the loop
1420 _igvn.hash_delete(cd);
1421 // Allow the load to float around in the loop, or before it
1422 // but NOT before the pre-loop.
1423 cd->set_req(0, ctrl); // ctrl, not NULL
1424 _igvn._worklist.push(cd);
1425 --i;
1426 --imax;
1427 }
1428 }
1429
1430 } // End of is IF
1431
1432 }
1433
1434 // Update loop limits
1435 if (conditional_rc) {
1436 pre_limit = (stride_con > 0) ? (Node*)new (C,3) MinINode(pre_limit, orig_limit)
1437 : (Node*)new (C,3) MaxINode(pre_limit, orig_limit);
1438 register_new_node(pre_limit, pre_ctrl);
1439 }
1440 _igvn.hash_delete(pre_opaq);
1441 pre_opaq->set_req(1, pre_limit);
1442
1443 // Note:: we are making the main loop limit no longer precise;
1444 // need to round up based on stride.
1445 if( stride_con != 1 && stride_con != -1 ) { // Cutout for common case
1446 // "Standard" round-up logic: ([main_limit-init+(y-1)]/y)*y+init
1447 // Hopefully, compiler will optimize for powers of 2.
1448 Node *ctrl = get_ctrl(main_limit);
1449 Node *stride = cl->stride();
1450 Node *init = cl->init_trip();
1451 Node *span = new (C, 3) SubINode(main_limit,init);
1452 register_new_node(span,ctrl);
1453 Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1));
1454 Node *add = new (C, 3) AddINode(span,rndup);
1455 register_new_node(add,ctrl);
1456 Node *div = new (C, 3) DivINode(0,add,stride);
1457 register_new_node(div,ctrl);
1458 Node *mul = new (C, 3) MulINode(div,stride);
1459 register_new_node(mul,ctrl);
1460 Node *newlim = new (C, 3) AddINode(mul,init);
1461 register_new_node(newlim,ctrl);
1462 main_limit = newlim;
1463 }
1464
1465 Node *main_cle = cl->loopexit();
1466 Node *main_bol = main_cle->in(1);
1467 // Hacking loop bounds; need private copies of exit test
1468 if( main_bol->outcnt() > 1 ) {// BoolNode shared?
1469 _igvn.hash_delete(main_cle);
1470 main_bol = main_bol->clone();// Clone a private BoolNode
1471 register_new_node( main_bol, main_cle->in(0) );
1472 main_cle->set_req(1,main_bol);
1473 }
1474 Node *main_cmp = main_bol->in(1);
1475 if( main_cmp->outcnt() > 1 ) { // CmpNode shared?
1476 _igvn.hash_delete(main_bol);
1477 main_cmp = main_cmp->clone();// Clone a private CmpNode
1478 register_new_node( main_cmp, main_cle->in(0) );
1479 main_bol->set_req(1,main_cmp);
1480 }
1481 // Hack the now-private loop bounds
1482 _igvn.hash_delete(main_cmp);
1483 main_cmp->set_req(2, main_limit);
1484 _igvn._worklist.push(main_cmp);
1485 // The OpaqueNode is unshared by design
1486 _igvn.hash_delete(opqzm);
1487 assert( opqzm->outcnt() == 1, "cannot hack shared node" );
1488 opqzm->set_req(1,main_limit);
1489 _igvn._worklist.push(opqzm);
1490 }
1491
1492 //------------------------------DCE_loop_body----------------------------------
1493 // Remove simplistic dead code from loop body
1494 void IdealLoopTree::DCE_loop_body() {
1495 for( uint i = 0; i < _body.size(); i++ )
1496 if( _body.at(i)->outcnt() == 0 )
1497 _body.map( i--, _body.pop() );
1498 }
1499
1500
1501 //------------------------------adjust_loop_exit_prob--------------------------
1502 // Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage.
1503 // Replace with a 1-in-10 exit guess.
1504 void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) {
1505 Node *test = tail();
1506 while( test != _head ) {
1507 uint top = test->Opcode();
1508 if( top == Op_IfTrue || top == Op_IfFalse ) {
1509 int test_con = ((ProjNode*)test)->_con;
1510 assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity");
1511 IfNode *iff = test->in(0)->as_If();
1512 if( iff->outcnt() == 2 ) { // Ignore dead tests
1513 Node *bol = iff->in(1);
1514 if( bol && bol->req() > 1 && bol->in(1) &&
1515 ((bol->in(1)->Opcode() == Op_StorePConditional ) ||
1516 (bol->in(1)->Opcode() == Op_StoreLConditional ) ||
1517 (bol->in(1)->Opcode() == Op_CompareAndSwapI ) ||
1518 (bol->in(1)->Opcode() == Op_CompareAndSwapL ) ||
1519 (bol->in(1)->Opcode() == Op_CompareAndSwapP )))
1520 return; // Allocation loops RARELY take backedge
1521 // Find the OTHER exit path from the IF
1522 Node* ex = iff->proj_out(1-test_con);
1523 float p = iff->_prob;
1524 if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) {
1525 if( top == Op_IfTrue ) {
1526 if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) {
1527 iff->_prob = PROB_STATIC_FREQUENT;
1528 }
1529 } else {
1530 if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) {
1531 iff->_prob = PROB_STATIC_INFREQUENT;
1532 }
1533 }
1534 }
1535 }
1536 }
1537 test = phase->idom(test);
1538 }
1539 }
1540
1541
1542 //------------------------------policy_do_remove_empty_loop--------------------
1543 // Micro-benchmark spamming. Policy is to always remove empty loops.
1544 // The 'DO' part is to replace the trip counter with the value it will
1545 // have on the last iteration. This will break the loop.
1546 bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
1547 // Minimum size must be empty loop
1548 if( _body.size() > 7/*number of nodes in an empty loop*/ ) return false;
1549
1550 if( !_head->is_CountedLoop() ) return false; // Dead loop
1551 CountedLoopNode *cl = _head->as_CountedLoop();
1552 if( !cl->loopexit() ) return false; // Malformed loop
1553 if( !phase->is_member(this,phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue)) ) )
1554 return false; // Infinite loop
1555 #ifndef PRODUCT
1556 if( PrintOpto )
1557 tty->print_cr("Removing empty loop");
1558 #endif
1559 #ifdef ASSERT
1560 // Ensure only one phi which is the iv.
1561 Node* iv = NULL;
1562 for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) {
1563 Node* n = cl->fast_out(i);
1564 if (n->Opcode() == Op_Phi) {
1565 assert(iv == NULL, "Too many phis" );
1566 iv = n;
1567 }
1568 }
1569 assert(iv == cl->phi(), "Wrong phi" );
1570 #endif
1571 // Replace the phi at loop head with the final value of the last
1572 // iteration. Then the CountedLoopEnd will collapse (backedge never
1573 // taken) and all loop-invariant uses of the exit values will be correct.
1574 Node *phi = cl->phi();
1575 Node *final = new (phase->C, 3) SubINode( cl->limit(), cl->stride() );
1576 phase->register_new_node(final,cl->in(LoopNode::EntryControl));
1577 phase->_igvn.hash_delete(phi);
1578 phase->_igvn.subsume_node(phi,final);
1579 phase->C->set_major_progress();
1580 return true;
1581 }
1582
1583
1584 //=============================================================================
1585 //------------------------------iteration_split_impl---------------------------
1586 void IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) {
1587 // Check and remove empty loops (spam micro-benchmarks)
1588 if( policy_do_remove_empty_loop(phase) )
1589 return; // Here we removed an empty loop
1590
1591 bool should_peel = policy_peeling(phase); // Should we peel?
1592
1593 bool should_unswitch = policy_unswitching(phase);
1594
1595 // Non-counted loops may be peeled; exactly 1 iteration is peeled.
1596 // This removes loop-invariant tests (usually null checks).
1597 if( !_head->is_CountedLoop() ) { // Non-counted loop
1598 if (PartialPeelLoop && phase->partial_peel(this, old_new)) {
1599 return;
1600 }
1601 if( should_peel ) { // Should we peel?
1602 #ifndef PRODUCT
1603 if (PrintOpto) tty->print_cr("should_peel");
1604 #endif
1605 phase->do_peeling(this,old_new);
1606 } else if( should_unswitch ) {
1607 phase->do_unswitching(this, old_new);
1608 }
1609 return;
1610 }
1611 CountedLoopNode *cl = _head->as_CountedLoop();
1612
1613 if( !cl->loopexit() ) return; // Ignore various kinds of broken loops
1614
1615 // Do nothing special to pre- and post- loops
1616 if( cl->is_pre_loop() || cl->is_post_loop() ) return;
1617
1618 // Compute loop trip count from profile data
1619 compute_profile_trip_cnt(phase);
1620
1621 // Before attempting fancy unrolling, RCE or alignment, see if we want
1622 // to completely unroll this loop or do loop unswitching.
1623 if( cl->is_normal_loop() ) {
1624 bool should_maximally_unroll = policy_maximally_unroll(phase);
1625 if( should_maximally_unroll ) {
1626 // Here we did some unrolling and peeling. Eventually we will
1627 // completely unroll this loop and it will no longer be a loop.
1628 phase->do_maximally_unroll(this,old_new);
1629 return;
1630 }
1631 if (should_unswitch) {
1632 phase->do_unswitching(this, old_new);
1633 return;
1634 }
1635 }
1636
1637
1638 // Counted loops may be peeled, may need some iterations run up
1639 // front for RCE, and may want to align loop refs to a cache
1640 // line. Thus we clone a full loop up front whose trip count is
1641 // at least 1 (if peeling), but may be several more.
1642
1643 // The main loop will start cache-line aligned with at least 1
1644 // iteration of the unrolled body (zero-trip test required) and
1645 // will have some range checks removed.
1646
1647 // A post-loop will finish any odd iterations (leftover after
1648 // unrolling), plus any needed for RCE purposes.
1649
1650 bool should_unroll = policy_unroll(phase);
1651
1652 bool should_rce = policy_range_check(phase);
1653
1654 bool should_align = policy_align(phase);
1655
1656 // If not RCE'ing (iteration splitting) or Aligning, then we do not
1657 // need a pre-loop. We may still need to peel an initial iteration but
1658 // we will not be needing an unknown number of pre-iterations.
1659 //
1660 // Basically, if may_rce_align reports FALSE first time through,
1661 // we will not be able to later do RCE or Aligning on this loop.
1662 bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align;
1663
1664 // If we have any of these conditions (RCE, alignment, unrolling) met, then
1665 // we switch to the pre-/main-/post-loop model. This model also covers
1666 // peeling.
1667 if( should_rce || should_align || should_unroll ) {
1668 if( cl->is_normal_loop() ) // Convert to 'pre/main/post' loops
1669 phase->insert_pre_post_loops(this,old_new, !may_rce_align);
1670
1671 // Adjust the pre- and main-loop limits to let the pre and post loops run
1672 // with full checks, but the main-loop with no checks. Remove said
1673 // checks from the main body.
1674 if( should_rce )
1675 phase->do_range_check(this,old_new);
1676
1677 // Double loop body for unrolling. Adjust the minimum-trip test (will do
1678 // twice as many iterations as before) and the main body limit (only do
1679 // an even number of trips). If we are peeling, we might enable some RCE
1680 // and we'd rather unroll the post-RCE'd loop SO... do not unroll if
1681 // peeling.
1682 if( should_unroll && !should_peel )
1683 phase->do_unroll(this,old_new, true);
1684
1685 // Adjust the pre-loop limits to align the main body
1686 // iterations.
1687 if( should_align )
1688 Unimplemented();
1689
1690 } else { // Else we have an unchanged counted loop
1691 if( should_peel ) // Might want to peel but do nothing else
1692 phase->do_peeling(this,old_new);
1693 }
1694 }
1695
1696
1697 //=============================================================================
1698 //------------------------------iteration_split--------------------------------
1699 void IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) {
1700 // Recursively iteration split nested loops
1701 if( _child ) _child->iteration_split( phase, old_new );
1702
1703 // Clean out prior deadwood
1704 DCE_loop_body();
1705
1706
1707 // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
1708 // Replace with a 1-in-10 exit guess.
1709 if( _parent /*not the root loop*/ &&
1710 !_irreducible &&
1711 // Also ignore the occasional dead backedge
1712 !tail()->is_top() ) {
1713 adjust_loop_exit_prob(phase);
1714 }
1715
1716
1717 // Gate unrolling, RCE and peeling efforts.
1718 if( !_child && // If not an inner loop, do not split
1719 !_irreducible &&
1720 !tail()->is_top() ) { // Also ignore the occasional dead backedge
1721 if (!_has_call) {
1722 iteration_split_impl( phase, old_new );
1723 } else if (policy_unswitching(phase)) {
1724 phase->do_unswitching(this, old_new);
1725 }
1726 }
1727
1728 // Minor offset re-organization to remove loop-fallout uses of
1729 // trip counter.
1730 if( _head->is_CountedLoop() ) phase->reorg_offsets( this );
1731 if( _next ) _next->iteration_split( phase, old_new );
1732 }