1 /*
2 * Copyright (c) 1998, 2019, 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 #ifndef SHARE_OPTO_LOOPNODE_HPP
26 #define SHARE_OPTO_LOOPNODE_HPP
27
28 #include "opto/cfgnode.hpp"
29 #include "opto/multnode.hpp"
30 #include "opto/phaseX.hpp"
31 #include "opto/subnode.hpp"
32 #include "opto/type.hpp"
33
34 class CmpNode;
35 class CountedLoopEndNode;
36 class CountedLoopNode;
37 class IdealLoopTree;
38 class LoopNode;
39 class Node;
40 class OuterStripMinedLoopEndNode;
41 class PathFrequency;
42 class PhaseIdealLoop;
43 class CountedLoopReserveKit;
44 class VectorSet;
45 class Invariance;
46 struct small_cache;
47
48 //
49 // I D E A L I Z E D L O O P S
50 //
51 // Idealized loops are the set of loops I perform more interesting
52 // transformations on, beyond simple hoisting.
53
54 //------------------------------LoopNode---------------------------------------
55 // Simple loop header. Fall in path on left, loop-back path on right.
56 class LoopNode : public RegionNode {
57 // Size is bigger to hold the flags. However, the flags do not change
58 // the semantics so it does not appear in the hash & cmp functions.
59 virtual uint size_of() const { return sizeof(*this); }
60 protected:
61 uint _loop_flags;
62 // Names for flag bitfields
63 enum { Normal=0, Pre=1, Main=2, Post=3, PreMainPostFlagsMask=3,
64 MainHasNoPreLoop=4,
65 HasExactTripCount=8,
66 InnerLoop=16,
67 PartialPeelLoop=32,
68 PartialPeelFailed=64,
69 HasReductions=128,
70 WasSlpAnalyzed=256,
71 PassedSlpAnalysis=512,
72 DoUnrollOnly=1024,
73 VectorizedLoop=2048,
74 HasAtomicPostLoop=4096,
75 HasRangeChecks=8192,
76 IsMultiversioned=16384,
77 StripMined=32768,
78 SubwordLoop=65536,
79 ProfileTripFailed=131072};
80 char _unswitch_count;
81 enum { _unswitch_max=3 };
82 char _postloop_flags;
83 enum { LoopNotRCEChecked = 0, LoopRCEChecked = 1, RCEPostLoop = 2 };
84
85 // Expected trip count from profile data
86 float _profile_trip_cnt;
87
88 public:
89 // Names for edge indices
90 enum { Self=0, EntryControl, LoopBackControl };
91
92 bool is_inner_loop() const { return _loop_flags & InnerLoop; }
93 void set_inner_loop() { _loop_flags |= InnerLoop; }
94
95 bool range_checks_present() const { return _loop_flags & HasRangeChecks; }
96 bool is_multiversioned() const { return _loop_flags & IsMultiversioned; }
97 bool is_vectorized_loop() const { return _loop_flags & VectorizedLoop; }
98 bool is_partial_peel_loop() const { return _loop_flags & PartialPeelLoop; }
99 void set_partial_peel_loop() { _loop_flags |= PartialPeelLoop; }
100 bool partial_peel_has_failed() const { return _loop_flags & PartialPeelFailed; }
101 bool is_strip_mined() const { return _loop_flags & StripMined; }
102 bool is_profile_trip_failed() const { return _loop_flags & ProfileTripFailed; }
103 bool is_subword_loop() const { return _loop_flags & SubwordLoop; }
104
105 void mark_partial_peel_failed() { _loop_flags |= PartialPeelFailed; }
106 void mark_has_reductions() { _loop_flags |= HasReductions; }
107 void mark_was_slp() { _loop_flags |= WasSlpAnalyzed; }
108 void mark_passed_slp() { _loop_flags |= PassedSlpAnalysis; }
109 void mark_do_unroll_only() { _loop_flags |= DoUnrollOnly; }
110 void mark_loop_vectorized() { _loop_flags |= VectorizedLoop; }
111 void mark_has_atomic_post_loop() { _loop_flags |= HasAtomicPostLoop; }
112 void mark_has_range_checks() { _loop_flags |= HasRangeChecks; }
113 void mark_is_multiversioned() { _loop_flags |= IsMultiversioned; }
114 void mark_strip_mined() { _loop_flags |= StripMined; }
115 void clear_strip_mined() { _loop_flags &= ~StripMined; }
116 void mark_profile_trip_failed() { _loop_flags |= ProfileTripFailed; }
117 void mark_subword_loop() { _loop_flags |= SubwordLoop; }
118
119 int unswitch_max() { return _unswitch_max; }
120 int unswitch_count() { return _unswitch_count; }
121
122 int has_been_range_checked() const { return _postloop_flags & LoopRCEChecked; }
123 void set_has_been_range_checked() { _postloop_flags |= LoopRCEChecked; }
124 int is_rce_post_loop() const { return _postloop_flags & RCEPostLoop; }
125 void set_is_rce_post_loop() { _postloop_flags |= RCEPostLoop; }
126
127 void set_unswitch_count(int val) {
128 assert (val <= unswitch_max(), "too many unswitches");
129 _unswitch_count = val;
130 }
131
132 void set_profile_trip_cnt(float ptc) { _profile_trip_cnt = ptc; }
133 float profile_trip_cnt() { return _profile_trip_cnt; }
134
135 LoopNode(Node *entry, Node *backedge)
136 : RegionNode(3), _loop_flags(0), _unswitch_count(0),
137 _postloop_flags(0), _profile_trip_cnt(COUNT_UNKNOWN) {
138 init_class_id(Class_Loop);
139 init_req(EntryControl, entry);
140 init_req(LoopBackControl, backedge);
141 }
142
143 virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);
144 virtual int Opcode() const;
145 bool can_be_counted_loop(PhaseTransform* phase) const {
146 return req() == 3 && in(0) != NULL &&
147 in(1) != NULL && phase->type(in(1)) != Type::TOP &&
148 in(2) != NULL && phase->type(in(2)) != Type::TOP;
149 }
150 bool is_valid_counted_loop() const;
151 #ifndef PRODUCT
152 virtual void dump_spec(outputStream *st) const;
153 #endif
154
155 void verify_strip_mined(int expect_skeleton) const;
156 virtual LoopNode* skip_strip_mined(int expect_skeleton = 1) { return this; }
157 virtual IfTrueNode* outer_loop_tail() const { ShouldNotReachHere(); return NULL; }
158 virtual OuterStripMinedLoopEndNode* outer_loop_end() const { ShouldNotReachHere(); return NULL; }
159 virtual IfFalseNode* outer_loop_exit() const { ShouldNotReachHere(); return NULL; }
160 virtual SafePointNode* outer_safepoint() const { ShouldNotReachHere(); return NULL; }
161 };
162
163 //------------------------------Counted Loops----------------------------------
164 // Counted loops are all trip-counted loops, with exactly 1 trip-counter exit
165 // path (and maybe some other exit paths). The trip-counter exit is always
166 // last in the loop. The trip-counter have to stride by a constant;
167 // the exit value is also loop invariant.
168
169 // CountedLoopNodes and CountedLoopEndNodes come in matched pairs. The
170 // CountedLoopNode has the incoming loop control and the loop-back-control
171 // which is always the IfTrue before the matching CountedLoopEndNode. The
172 // CountedLoopEndNode has an incoming control (possibly not the
173 // CountedLoopNode if there is control flow in the loop), the post-increment
174 // trip-counter value, and the limit. The trip-counter value is always of
175 // the form (Op old-trip-counter stride). The old-trip-counter is produced
176 // by a Phi connected to the CountedLoopNode. The stride is constant.
177 // The Op is any commutable opcode, including Add, Mul, Xor. The
178 // CountedLoopEndNode also takes in the loop-invariant limit value.
179
180 // From a CountedLoopNode I can reach the matching CountedLoopEndNode via the
181 // loop-back control. From CountedLoopEndNodes I can reach CountedLoopNodes
182 // via the old-trip-counter from the Op node.
183
184 //------------------------------CountedLoopNode--------------------------------
185 // CountedLoopNodes head simple counted loops. CountedLoopNodes have as
186 // inputs the incoming loop-start control and the loop-back control, so they
187 // act like RegionNodes. They also take in the initial trip counter, the
188 // loop-invariant stride and the loop-invariant limit value. CountedLoopNodes
189 // produce a loop-body control and the trip counter value. Since
190 // CountedLoopNodes behave like RegionNodes I still have a standard CFG model.
191
192 class CountedLoopNode : public LoopNode {
193 // Size is bigger to hold _main_idx. However, _main_idx does not change
194 // the semantics so it does not appear in the hash & cmp functions.
195 virtual uint size_of() const { return sizeof(*this); }
196
197 // For Pre- and Post-loops during debugging ONLY, this holds the index of
198 // the Main CountedLoop. Used to assert that we understand the graph shape.
199 node_idx_t _main_idx;
200
201 // Known trip count calculated by compute_exact_trip_count()
202 uint _trip_count;
203
204 // Log2 of original loop bodies in unrolled loop
205 int _unrolled_count_log2;
206
207 // Node count prior to last unrolling - used to decide if
208 // unroll,optimize,unroll,optimize,... is making progress
209 int _node_count_before_unroll;
210
211 // If slp analysis is performed we record the maximum
212 // vector mapped unroll factor here
213 int _slp_maximum_unroll_factor;
214
215 public:
216 CountedLoopNode( Node *entry, Node *backedge )
217 : LoopNode(entry, backedge), _main_idx(0), _trip_count(max_juint),
218 _unrolled_count_log2(0), _node_count_before_unroll(0),
219 _slp_maximum_unroll_factor(0) {
220 init_class_id(Class_CountedLoop);
221 // Initialize _trip_count to the largest possible value.
222 // Will be reset (lower) if the loop's trip count is known.
223 }
224
225 virtual int Opcode() const;
226 virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);
227
228 Node *init_control() const { return in(EntryControl); }
229 Node *back_control() const { return in(LoopBackControl); }
230 CountedLoopEndNode *loopexit_or_null() const;
231 CountedLoopEndNode *loopexit() const;
232 Node *init_trip() const;
233 Node *stride() const;
234 int stride_con() const;
235 bool stride_is_con() const;
236 Node *limit() const;
237 Node *incr() const;
238 Node *phi() const;
239
240 // Match increment with optional truncation
241 static Node* match_incr_with_optional_truncation(Node* expr, Node** trunc1, Node** trunc2, const TypeInt** trunc_type);
242
243 // A 'main' loop has a pre-loop and a post-loop. The 'main' loop
244 // can run short a few iterations and may start a few iterations in.
245 // It will be RCE'd and unrolled and aligned.
246
247 // A following 'post' loop will run any remaining iterations. Used
248 // during Range Check Elimination, the 'post' loop will do any final
249 // iterations with full checks. Also used by Loop Unrolling, where
250 // the 'post' loop will do any epilog iterations needed. Basically,
251 // a 'post' loop can not profitably be further unrolled or RCE'd.
252
253 // A preceding 'pre' loop will run at least 1 iteration (to do peeling),
254 // it may do under-flow checks for RCE and may do alignment iterations
255 // so the following main loop 'knows' that it is striding down cache
256 // lines.
257
258 // A 'main' loop that is ONLY unrolled or peeled, never RCE'd or
259 // Aligned, may be missing it's pre-loop.
260 bool is_normal_loop () const { return (_loop_flags&PreMainPostFlagsMask) == Normal; }
261 bool is_pre_loop () const { return (_loop_flags&PreMainPostFlagsMask) == Pre; }
262 bool is_main_loop () const { return (_loop_flags&PreMainPostFlagsMask) == Main; }
263 bool is_post_loop () const { return (_loop_flags&PreMainPostFlagsMask) == Post; }
264 bool is_reduction_loop() const { return (_loop_flags&HasReductions) == HasReductions; }
265 bool was_slp_analyzed () const { return (_loop_flags&WasSlpAnalyzed) == WasSlpAnalyzed; }
266 bool has_passed_slp () const { return (_loop_flags&PassedSlpAnalysis) == PassedSlpAnalysis; }
267 bool is_unroll_only () const { return (_loop_flags&DoUnrollOnly) == DoUnrollOnly; }
268 bool is_main_no_pre_loop() const { return _loop_flags & MainHasNoPreLoop; }
269 bool has_atomic_post_loop () const { return (_loop_flags & HasAtomicPostLoop) == HasAtomicPostLoop; }
270 void set_main_no_pre_loop() { _loop_flags |= MainHasNoPreLoop; }
271
272 int main_idx() const { return _main_idx; }
273
274
275 void set_pre_loop (CountedLoopNode *main) { assert(is_normal_loop(),""); _loop_flags |= Pre ; _main_idx = main->_idx; }
276 void set_main_loop ( ) { assert(is_normal_loop(),""); _loop_flags |= Main; }
277 void set_post_loop (CountedLoopNode *main) { assert(is_normal_loop(),""); _loop_flags |= Post; _main_idx = main->_idx; }
278 void set_normal_loop( ) { _loop_flags &= ~PreMainPostFlagsMask; }
279
280 void set_trip_count(uint tc) { _trip_count = tc; }
281 uint trip_count() { return _trip_count; }
282
283 bool has_exact_trip_count() const { return (_loop_flags & HasExactTripCount) != 0; }
284 void set_exact_trip_count(uint tc) {
285 _trip_count = tc;
286 _loop_flags |= HasExactTripCount;
287 }
288 void set_nonexact_trip_count() {
289 _loop_flags &= ~HasExactTripCount;
290 }
291 void set_notpassed_slp() {
292 _loop_flags &= ~PassedSlpAnalysis;
293 }
294
295 void double_unrolled_count() { _unrolled_count_log2++; }
296 int unrolled_count() { return 1 << MIN2(_unrolled_count_log2, BitsPerInt-3); }
297
298 void set_node_count_before_unroll(int ct) { _node_count_before_unroll = ct; }
299 int node_count_before_unroll() { return _node_count_before_unroll; }
300 void set_slp_max_unroll(int unroll_factor) { _slp_maximum_unroll_factor = unroll_factor; }
301 int slp_max_unroll() const { return _slp_maximum_unroll_factor; }
302
303 virtual LoopNode* skip_strip_mined(int expect_skeleton = 1);
304 OuterStripMinedLoopNode* outer_loop() const;
305 virtual IfTrueNode* outer_loop_tail() const;
306 virtual OuterStripMinedLoopEndNode* outer_loop_end() const;
307 virtual IfFalseNode* outer_loop_exit() const;
308 virtual SafePointNode* outer_safepoint() const;
309
310 // If this is a main loop in a pre/main/post loop nest, walk over
311 // the predicates that were inserted by
312 // duplicate_predicates()/add_range_check_predicate()
313 static Node* skip_predicates_from_entry(Node* ctrl);
314 Node* skip_predicates();
315
316 #ifndef PRODUCT
317 virtual void dump_spec(outputStream *st) const;
318 #endif
319 };
320
321 //------------------------------CountedLoopEndNode-----------------------------
322 // CountedLoopEndNodes end simple trip counted loops. They act much like
323 // IfNodes.
324 class CountedLoopEndNode : public IfNode {
325 public:
326 enum { TestControl, TestValue };
327
328 CountedLoopEndNode( Node *control, Node *test, float prob, float cnt )
329 : IfNode( control, test, prob, cnt) {
330 init_class_id(Class_CountedLoopEnd);
331 }
332 virtual int Opcode() const;
333
334 Node *cmp_node() const { return (in(TestValue)->req() >=2) ? in(TestValue)->in(1) : NULL; }
335 Node *incr() const { Node *tmp = cmp_node(); return (tmp && tmp->req()==3) ? tmp->in(1) : NULL; }
336 Node *limit() const { Node *tmp = cmp_node(); return (tmp && tmp->req()==3) ? tmp->in(2) : NULL; }
337 Node *stride() const { Node *tmp = incr (); return (tmp && tmp->req()==3) ? tmp->in(2) : NULL; }
338 Node *init_trip() const { Node *tmp = phi (); return (tmp && tmp->req()==3) ? tmp->in(1) : NULL; }
339 int stride_con() const;
340 bool stride_is_con() const { Node *tmp = stride (); return (tmp != NULL && tmp->is_Con()); }
341 BoolTest::mask test_trip() const { return in(TestValue)->as_Bool()->_test._test; }
342 PhiNode *phi() const {
343 Node *tmp = incr();
344 if (tmp && tmp->req() == 3) {
345 Node* phi = tmp->in(1);
346 if (phi->is_Phi()) {
347 return phi->as_Phi();
348 }
349 }
350 return NULL;
351 }
352 CountedLoopNode *loopnode() const {
353 // The CountedLoopNode that goes with this CountedLoopEndNode may
354 // have been optimized out by the IGVN so be cautious with the
355 // pattern matching on the graph
356 PhiNode* iv_phi = phi();
357 if (iv_phi == NULL) {
358 return NULL;
359 }
360 Node *ln = iv_phi->in(0);
361 if (ln->is_CountedLoop() && ln->as_CountedLoop()->loopexit_or_null() == this) {
362 return (CountedLoopNode*)ln;
363 }
364 return NULL;
365 }
366
367 #ifndef PRODUCT
368 virtual void dump_spec(outputStream *st) const;
369 #endif
370 };
371
372
373 inline CountedLoopEndNode* CountedLoopNode::loopexit_or_null() const {
374 Node* bctrl = back_control();
375 if (bctrl == NULL) return NULL;
376
377 Node* lexit = bctrl->in(0);
378 return (CountedLoopEndNode*)
379 (lexit->Opcode() == Op_CountedLoopEnd ? lexit : NULL);
380 }
381
382 inline CountedLoopEndNode* CountedLoopNode::loopexit() const {
383 CountedLoopEndNode* cle = loopexit_or_null();
384 assert(cle != NULL, "loopexit is NULL");
385 return cle;
386 }
387
388 inline Node* CountedLoopNode::init_trip() const {
389 CountedLoopEndNode* cle = loopexit_or_null();
390 return cle != NULL ? cle->init_trip() : NULL;
391 }
392 inline Node* CountedLoopNode::stride() const {
393 CountedLoopEndNode* cle = loopexit_or_null();
394 return cle != NULL ? cle->stride() : NULL;
395 }
396 inline int CountedLoopNode::stride_con() const {
397 CountedLoopEndNode* cle = loopexit_or_null();
398 return cle != NULL ? cle->stride_con() : 0;
399 }
400 inline bool CountedLoopNode::stride_is_con() const {
401 CountedLoopEndNode* cle = loopexit_or_null();
402 return cle != NULL && cle->stride_is_con();
403 }
404 inline Node* CountedLoopNode::limit() const {
405 CountedLoopEndNode* cle = loopexit_or_null();
406 return cle != NULL ? cle->limit() : NULL;
407 }
408 inline Node* CountedLoopNode::incr() const {
409 CountedLoopEndNode* cle = loopexit_or_null();
410 return cle != NULL ? cle->incr() : NULL;
411 }
412 inline Node* CountedLoopNode::phi() const {
413 CountedLoopEndNode* cle = loopexit_or_null();
414 return cle != NULL ? cle->phi() : NULL;
415 }
416
417 //------------------------------LoopLimitNode-----------------------------
418 // Counted Loop limit node which represents exact final iterator value:
419 // trip_count = (limit - init_trip + stride - 1)/stride
420 // final_value= trip_count * stride + init_trip.
421 // Use HW instructions to calculate it when it can overflow in integer.
422 // Note, final_value should fit into integer since counted loop has
423 // limit check: limit <= max_int-stride.
424 class LoopLimitNode : public Node {
425 enum { Init=1, Limit=2, Stride=3 };
426 public:
427 LoopLimitNode( Compile* C, Node *init, Node *limit, Node *stride ) : Node(0,init,limit,stride) {
428 // Put it on the Macro nodes list to optimize during macro nodes expansion.
429 init_flags(Flag_is_macro);
430 C->add_macro_node(this);
431 }
432 virtual int Opcode() const;
433 virtual const Type *bottom_type() const { return TypeInt::INT; }
434 virtual uint ideal_reg() const { return Op_RegI; }
435 virtual const Type* Value(PhaseGVN* phase) const;
436 virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);
437 virtual Node* Identity(PhaseGVN* phase);
438 };
439
440 // Support for strip mining
441 class OuterStripMinedLoopNode : public LoopNode {
442 private:
443 CountedLoopNode* inner_loop() const;
444 public:
445 OuterStripMinedLoopNode(Compile* C, Node *entry, Node *backedge)
446 : LoopNode(entry, backedge) {
447 init_class_id(Class_OuterStripMinedLoop);
448 init_flags(Flag_is_macro);
449 C->add_macro_node(this);
450 }
451
452 virtual int Opcode() const;
453
454 virtual IfTrueNode* outer_loop_tail() const;
455 virtual OuterStripMinedLoopEndNode* outer_loop_end() const;
456 virtual IfFalseNode* outer_loop_exit() const;
457 virtual SafePointNode* outer_safepoint() const;
458 void adjust_strip_mined_loop(PhaseIterGVN* igvn);
459 };
460
461 class OuterStripMinedLoopEndNode : public IfNode {
462 public:
463 OuterStripMinedLoopEndNode(Node *control, Node *test, float prob, float cnt)
464 : IfNode(control, test, prob, cnt) {
465 init_class_id(Class_OuterStripMinedLoopEnd);
466 }
467
468 virtual int Opcode() const;
469
470 virtual const Type* Value(PhaseGVN* phase) const;
471 virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);
472 };
473
474 // -----------------------------IdealLoopTree----------------------------------
475 class IdealLoopTree : public ResourceObj {
476 public:
477 IdealLoopTree *_parent; // Parent in loop tree
478 IdealLoopTree *_next; // Next sibling in loop tree
479 IdealLoopTree *_child; // First child in loop tree
480
481 // The head-tail backedge defines the loop.
482 // If a loop has multiple backedges, this is addressed during cleanup where
483 // we peel off the multiple backedges, merging all edges at the bottom and
484 // ensuring that one proper backedge flow into the loop.
485 Node *_head; // Head of loop
486 Node *_tail; // Tail of loop
487 inline Node *tail(); // Handle lazy update of _tail field
488 PhaseIdealLoop* _phase;
489 int _local_loop_unroll_limit;
490 int _local_loop_unroll_factor;
491
492 Node_List _body; // Loop body for inner loops
493
494 uint8_t _nest; // Nesting depth
495 uint8_t _irreducible:1, // True if irreducible
496 _has_call:1, // True if has call safepoint
497 _has_sfpt:1, // True if has non-call safepoint
498 _rce_candidate:1; // True if candidate for range check elimination
499
500 Node_List* _safepts; // List of safepoints in this loop
501 Node_List* _required_safept; // A inner loop cannot delete these safepts;
502 bool _allow_optimizations; // Allow loop optimizations
503
504 IdealLoopTree( PhaseIdealLoop* phase, Node *head, Node *tail )
505 : _parent(0), _next(0), _child(0),
506 _head(head), _tail(tail),
507 _phase(phase),
508 _local_loop_unroll_limit(0), _local_loop_unroll_factor(0),
509 _nest(0), _irreducible(0), _has_call(0), _has_sfpt(0), _rce_candidate(0),
510 _safepts(NULL),
511 _required_safept(NULL),
512 _allow_optimizations(true)
513 {
514 precond(_head != NULL);
515 precond(_tail != NULL);
516 }
517
518 // Is 'l' a member of 'this'?
519 bool is_member(const IdealLoopTree *l) const; // Test for nested membership
520
521 // Set loop nesting depth. Accumulate has_call bits.
522 int set_nest( uint depth );
523
524 // Split out multiple fall-in edges from the loop header. Move them to a
525 // private RegionNode before the loop. This becomes the loop landing pad.
526 void split_fall_in( PhaseIdealLoop *phase, int fall_in_cnt );
527
528 // Split out the outermost loop from this shared header.
529 void split_outer_loop( PhaseIdealLoop *phase );
530
531 // Merge all the backedges from the shared header into a private Region.
532 // Feed that region as the one backedge to this loop.
533 void merge_many_backedges( PhaseIdealLoop *phase );
534
535 // Split shared headers and insert loop landing pads.
536 // Insert a LoopNode to replace the RegionNode.
537 // Returns TRUE if loop tree is structurally changed.
538 bool beautify_loops( PhaseIdealLoop *phase );
539
540 // Perform optimization to use the loop predicates for null checks and range checks.
541 // Applies to any loop level (not just the innermost one)
542 bool loop_predication( PhaseIdealLoop *phase);
543
544 // Perform iteration-splitting on inner loops. Split iterations to
545 // avoid range checks or one-shot null checks. Returns false if the
546 // current round of loop opts should stop.
547 bool iteration_split( PhaseIdealLoop *phase, Node_List &old_new );
548
549 // Driver for various flavors of iteration splitting. Returns false
550 // if the current round of loop opts should stop.
551 bool iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new );
552
553 // Given dominators, try to find loops with calls that must always be
554 // executed (call dominates loop tail). These loops do not need non-call
555 // safepoints (ncsfpt).
556 void check_safepts(VectorSet &visited, Node_List &stack);
557
558 // Allpaths backwards scan from loop tail, terminating each path at first safepoint
559 // encountered.
560 void allpaths_check_safepts(VectorSet &visited, Node_List &stack);
561
562 // Remove safepoints from loop. Optionally keeping one.
563 void remove_safepoints(PhaseIdealLoop* phase, bool keep_one);
564
565 // Convert to counted loops where possible
566 void counted_loop( PhaseIdealLoop *phase );
567
568 // Check for Node being a loop-breaking test
569 Node *is_loop_exit(Node *iff) const;
570
571 // Remove simplistic dead code from loop body
572 void DCE_loop_body();
573
574 // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
575 // Replace with a 1-in-10 exit guess.
576 void adjust_loop_exit_prob( PhaseIdealLoop *phase );
577
578 // Return TRUE or FALSE if the loop should never be RCE'd or aligned.
579 // Useful for unrolling loops with NO array accesses.
580 bool policy_peel_only( PhaseIdealLoop *phase ) const;
581
582 // Return TRUE or FALSE if the loop should be unswitched -- clone
583 // loop with an invariant test
584 bool policy_unswitching( PhaseIdealLoop *phase ) const;
585
586 // Micro-benchmark spamming. Remove empty loops.
587 bool do_remove_empty_loop( PhaseIdealLoop *phase );
588
589 // Convert one iteration loop into normal code.
590 bool do_one_iteration_loop( PhaseIdealLoop *phase );
591
592 // Return TRUE or FALSE if the loop should be peeled or not. Peel if we can
593 // make some loop-invariant test (usually a null-check) happen before the
594 // loop.
595 bool policy_peeling( PhaseIdealLoop *phase ) const;
596
597 // Return TRUE or FALSE if the loop should be maximally unrolled. Stash any
598 // known trip count in the counted loop node.
599 bool policy_maximally_unroll( PhaseIdealLoop *phase ) const;
600
601 // Return TRUE or FALSE if the loop should be unrolled or not. Unroll if
602 // the loop is a CountedLoop and the body is small enough.
603 bool policy_unroll(PhaseIdealLoop *phase);
604
605 // Loop analyses to map to a maximal superword unrolling for vectorization.
606 void policy_unroll_slp_analysis(CountedLoopNode *cl, PhaseIdealLoop *phase, int future_unroll_ct);
607
608 // Return TRUE or FALSE if the loop should be range-check-eliminated.
609 // Gather a list of IF tests that are dominated by iteration splitting;
610 // also gather the end of the first split and the start of the 2nd split.
611 bool policy_range_check( PhaseIdealLoop *phase ) const;
612
613 // Return TRUE or FALSE if the loop should be cache-line aligned.
614 // Gather the expression that does the alignment. Note that only
615 // one array base can be aligned in a loop (unless the VM guarantees
616 // mutual alignment). Note that if we vectorize short memory ops
617 // into longer memory ops, we may want to increase alignment.
618 bool policy_align( PhaseIdealLoop *phase ) const;
619
620 // Return TRUE if "iff" is a range check.
621 bool is_range_check_if(IfNode *iff, PhaseIdealLoop *phase, Invariance& invar) const;
622
623 // Compute loop trip count if possible
624 void compute_trip_count(PhaseIdealLoop* phase);
625
626 // Compute loop trip count from profile data
627 float compute_profile_trip_cnt_helper(Node* n);
628 void compute_profile_trip_cnt( PhaseIdealLoop *phase );
629
630 // Reassociate invariant expressions.
631 void reassociate_invariants(PhaseIdealLoop *phase);
632 // Reassociate invariant add and subtract expressions.
633 Node* reassociate_add_sub(Node* n1, PhaseIdealLoop *phase);
634 // Return nonzero index of invariant operand if invariant and variant
635 // are combined with an Add or Sub. Helper for reassociate_invariants.
636 int is_invariant_addition(Node* n, PhaseIdealLoop *phase);
637
638 // Return true if n is invariant
639 bool is_invariant(Node* n) const;
640
641 // Put loop body on igvn work list
642 void record_for_igvn();
643
644 bool is_root() { return _parent == NULL; }
645 // A proper/reducible loop w/o any (occasional) dead back-edge.
646 bool is_loop() { return !_irreducible && !tail()->is_top(); }
647 bool is_counted() { return is_loop() && _head->is_CountedLoop(); }
648 bool is_innermost() { return is_loop() && _child == NULL; }
649
650 void remove_main_post_loops(CountedLoopNode *cl, PhaseIdealLoop *phase);
651
652 #ifndef PRODUCT
653 void dump_head( ) const; // Dump loop head only
654 void dump() const; // Dump this loop recursively
655 void verify_tree(IdealLoopTree *loop, const IdealLoopTree *parent) const;
656 #endif
657
658 };
659
660 // -----------------------------PhaseIdealLoop---------------------------------
661 // Computes the mapping from Nodes to IdealLoopTrees. Organizes IdealLoopTrees
662 // into a loop tree. Drives the loop-based transformations on the ideal graph.
663 class PhaseIdealLoop : public PhaseTransform {
664 friend class IdealLoopTree;
665 friend class SuperWord;
666 friend class CountedLoopReserveKit;
667 friend class ShenandoahBarrierC2Support;
668 friend class AutoNodeBudget;
669
670 // Pre-computed def-use info
671 PhaseIterGVN &_igvn;
672
673 // Head of loop tree
674 IdealLoopTree *_ltree_root;
675
676 // Array of pre-order numbers, plus post-visited bit.
677 // ZERO for not pre-visited. EVEN for pre-visited but not post-visited.
678 // ODD for post-visited. Other bits are the pre-order number.
679 uint *_preorders;
680 uint _max_preorder;
681
682 const PhaseIdealLoop* _verify_me;
683 bool _verify_only;
684
685 // Allocate _preorders[] array
686 void allocate_preorders() {
687 _max_preorder = C->unique()+8;
688 _preorders = NEW_RESOURCE_ARRAY(uint, _max_preorder);
689 memset(_preorders, 0, sizeof(uint) * _max_preorder);
690 }
691
692 // Allocate _preorders[] array
693 void reallocate_preorders() {
694 if ( _max_preorder < C->unique() ) {
695 _preorders = REALLOC_RESOURCE_ARRAY(uint, _preorders, _max_preorder, C->unique());
696 _max_preorder = C->unique();
697 }
698 memset(_preorders, 0, sizeof(uint) * _max_preorder);
699 }
700
701 // Check to grow _preorders[] array for the case when build_loop_tree_impl()
702 // adds new nodes.
703 void check_grow_preorders( ) {
704 if ( _max_preorder < C->unique() ) {
705 uint newsize = _max_preorder<<1; // double size of array
706 _preorders = REALLOC_RESOURCE_ARRAY(uint, _preorders, _max_preorder, newsize);
707 memset(&_preorders[_max_preorder],0,sizeof(uint)*(newsize-_max_preorder));
708 _max_preorder = newsize;
709 }
710 }
711 // Check for pre-visited. Zero for NOT visited; non-zero for visited.
712 int is_visited( Node *n ) const { return _preorders[n->_idx]; }
713 // Pre-order numbers are written to the Nodes array as low-bit-set values.
714 void set_preorder_visited( Node *n, int pre_order ) {
715 assert( !is_visited( n ), "already set" );
716 _preorders[n->_idx] = (pre_order<<1);
717 };
718 // Return pre-order number.
719 int get_preorder( Node *n ) const { assert( is_visited(n), "" ); return _preorders[n->_idx]>>1; }
720
721 // Check for being post-visited.
722 // Should be previsited already (checked with assert(is_visited(n))).
723 int is_postvisited( Node *n ) const { assert( is_visited(n), "" ); return _preorders[n->_idx]&1; }
724
725 // Mark as post visited
726 void set_postvisited( Node *n ) { assert( !is_postvisited( n ), "" ); _preorders[n->_idx] |= 1; }
727
728 public:
729 // Set/get control node out. Set lower bit to distinguish from IdealLoopTree
730 // Returns true if "n" is a data node, false if it's a control node.
731 bool has_ctrl( Node *n ) const { return ((intptr_t)_nodes[n->_idx]) & 1; }
732
733 private:
734 // clear out dead code after build_loop_late
735 Node_List _deadlist;
736
737 // Support for faster execution of get_late_ctrl()/dom_lca()
738 // when a node has many uses and dominator depth is deep.
739 Node_Array _dom_lca_tags;
740 void init_dom_lca_tags();
741 void clear_dom_lca_tags();
742
743 // Helper for debugging bad dominance relationships
744 bool verify_dominance(Node* n, Node* use, Node* LCA, Node* early);
745
746 Node* compute_lca_of_uses(Node* n, Node* early, bool verify = false);
747
748 // Inline wrapper for frequent cases:
749 // 1) only one use
750 // 2) a use is the same as the current LCA passed as 'n1'
751 Node *dom_lca_for_get_late_ctrl( Node *lca, Node *n, Node *tag ) {
752 assert( n->is_CFG(), "" );
753 // Fast-path NULL lca
754 if( lca != NULL && lca != n ) {
755 assert( lca->is_CFG(), "" );
756 // find LCA of all uses
757 n = dom_lca_for_get_late_ctrl_internal( lca, n, tag );
758 }
759 return find_non_split_ctrl(n);
760 }
761 Node *dom_lca_for_get_late_ctrl_internal( Node *lca, Node *n, Node *tag );
762
763 // Helper function for directing control inputs away from CFG split points.
764 Node *find_non_split_ctrl( Node *ctrl ) const {
765 if (ctrl != NULL) {
766 if (ctrl->is_MultiBranch()) {
767 ctrl = ctrl->in(0);
768 }
769 assert(ctrl->is_CFG(), "CFG");
770 }
771 return ctrl;
772 }
773
774 Node* cast_incr_before_loop(Node* incr, Node* ctrl, Node* loop);
775 void duplicate_predicates_helper(Node* predicate, Node* start, Node* end, IdealLoopTree* outer_loop,
776 LoopNode* outer_main_head, uint dd_main_head);
777 void duplicate_predicates(CountedLoopNode* pre_head, Node* start, Node* end, IdealLoopTree* outer_loop,
778 LoopNode* outer_main_head, uint dd_main_head);
779 Node* clone_skeleton_predicate(Node* iff, Node* value, Node* predicate, Node* uncommon_proj,
780 Node* current_proj, IdealLoopTree* outer_loop, Node* prev_proj);
781 bool skeleton_predicate_has_opaque(IfNode* iff);
782 void update_skeleton_predicates(Node* ctrl, CountedLoopNode* loop_head, Node* init, int stride_con);
783 void insert_loop_limit_check(ProjNode* limit_check_proj, Node* cmp_limit, Node* bol);
784
785 public:
786
787 PhaseIterGVN &igvn() const { return _igvn; }
788
789 static bool is_canonical_loop_entry(CountedLoopNode* cl);
790
791 bool has_node( Node* n ) const {
792 guarantee(n != NULL, "No Node.");
793 return _nodes[n->_idx] != NULL;
794 }
795 // check if transform created new nodes that need _ctrl recorded
796 Node *get_late_ctrl( Node *n, Node *early );
797 Node *get_early_ctrl( Node *n );
798 Node *get_early_ctrl_for_expensive(Node *n, Node* earliest);
799 void set_early_ctrl( Node *n );
800 void set_subtree_ctrl( Node *root );
801 void set_ctrl( Node *n, Node *ctrl ) {
802 assert( !has_node(n) || has_ctrl(n), "" );
803 assert( ctrl->in(0), "cannot set dead control node" );
804 assert( ctrl == find_non_split_ctrl(ctrl), "must set legal crtl" );
805 _nodes.map( n->_idx, (Node*)((intptr_t)ctrl + 1) );
806 }
807 // Set control and update loop membership
808 void set_ctrl_and_loop(Node* n, Node* ctrl) {
809 IdealLoopTree* old_loop = get_loop(get_ctrl(n));
810 IdealLoopTree* new_loop = get_loop(ctrl);
811 if (old_loop != new_loop) {
812 if (old_loop->_child == NULL) old_loop->_body.yank(n);
813 if (new_loop->_child == NULL) new_loop->_body.push(n);
814 }
815 set_ctrl(n, ctrl);
816 }
817 // Control nodes can be replaced or subsumed. During this pass they
818 // get their replacement Node in slot 1. Instead of updating the block
819 // location of all Nodes in the subsumed block, we lazily do it. As we
820 // pull such a subsumed block out of the array, we write back the final
821 // correct block.
822 Node *get_ctrl( Node *i ) {
823 assert(has_node(i), "");
824 Node *n = get_ctrl_no_update(i);
825 _nodes.map( i->_idx, (Node*)((intptr_t)n + 1) );
826 assert(has_node(i) && has_ctrl(i), "");
827 assert(n == find_non_split_ctrl(n), "must return legal ctrl" );
828 return n;
829 }
830 // true if CFG node d dominates CFG node n
831 bool is_dominator(Node *d, Node *n);
832 // return get_ctrl for a data node and self(n) for a CFG node
833 Node* ctrl_or_self(Node* n) {
834 if (has_ctrl(n))
835 return get_ctrl(n);
836 else {
837 assert (n->is_CFG(), "must be a CFG node");
838 return n;
839 }
840 }
841
842 Node *get_ctrl_no_update_helper(Node *i) const {
843 assert(has_ctrl(i), "should be control, not loop");
844 return (Node*)(((intptr_t)_nodes[i->_idx]) & ~1);
845 }
846
847 Node *get_ctrl_no_update(Node *i) const {
848 assert( has_ctrl(i), "" );
849 Node *n = get_ctrl_no_update_helper(i);
850 if (!n->in(0)) {
851 // Skip dead CFG nodes
852 do {
853 n = get_ctrl_no_update_helper(n);
854 } while (!n->in(0));
855 n = find_non_split_ctrl(n);
856 }
857 return n;
858 }
859
860 // Check for loop being set
861 // "n" must be a control node. Returns true if "n" is known to be in a loop.
862 bool has_loop( Node *n ) const {
863 assert(!has_node(n) || !has_ctrl(n), "");
864 return has_node(n);
865 }
866 // Set loop
867 void set_loop( Node *n, IdealLoopTree *loop ) {
868 _nodes.map(n->_idx, (Node*)loop);
869 }
870 // Lazy-dazy update of 'get_ctrl' and 'idom_at' mechanisms. Replace
871 // the 'old_node' with 'new_node'. Kill old-node. Add a reference
872 // from old_node to new_node to support the lazy update. Reference
873 // replaces loop reference, since that is not needed for dead node.
874 void lazy_update(Node *old_node, Node *new_node) {
875 assert(old_node != new_node, "no cycles please");
876 // Re-use the side array slot for this node to provide the
877 // forwarding pointer.
878 _nodes.map(old_node->_idx, (Node*)((intptr_t)new_node + 1));
879 }
880 void lazy_replace(Node *old_node, Node *new_node) {
881 _igvn.replace_node(old_node, new_node);
882 lazy_update(old_node, new_node);
883 }
884
885 private:
886
887 // Place 'n' in some loop nest, where 'n' is a CFG node
888 void build_loop_tree();
889 int build_loop_tree_impl( Node *n, int pre_order );
890 // Insert loop into the existing loop tree. 'innermost' is a leaf of the
891 // loop tree, not the root.
892 IdealLoopTree *sort( IdealLoopTree *loop, IdealLoopTree *innermost );
893
894 // Place Data nodes in some loop nest
895 void build_loop_early( VectorSet &visited, Node_List &worklist, Node_Stack &nstack );
896 void build_loop_late ( VectorSet &visited, Node_List &worklist, Node_Stack &nstack );
897 void build_loop_late_post_work(Node* n, bool pinned);
898 void build_loop_late_post(Node* n);
899 void verify_strip_mined_scheduling(Node *n, Node* least);
900
901 // Array of immediate dominance info for each CFG node indexed by node idx
902 private:
903 uint _idom_size;
904 Node **_idom; // Array of immediate dominators
905 uint *_dom_depth; // Used for fast LCA test
906 GrowableArray<uint>* _dom_stk; // For recomputation of dom depth
907
908 // Perform verification that the graph is valid.
909 PhaseIdealLoop( PhaseIterGVN &igvn) :
910 PhaseTransform(Ideal_Loop),
911 _igvn(igvn),
912 _verify_me(NULL),
913 _verify_only(true),
914 _dom_lca_tags(arena()), // Thread::resource_area
915 _nodes_required(UINT_MAX) {
916 build_and_optimize(LoopOptsVerify);
917 }
918
919 // build the loop tree and perform any requested optimizations
920 void build_and_optimize(LoopOptsMode mode);
921
922 // Dominators for the sea of nodes
923 void Dominators();
924
925 // Compute the Ideal Node to Loop mapping
926 PhaseIdealLoop(PhaseIterGVN &igvn, LoopOptsMode mode) :
927 PhaseTransform(Ideal_Loop),
928 _igvn(igvn),
929 _verify_me(NULL),
930 _verify_only(false),
931 _dom_lca_tags(arena()), // Thread::resource_area
932 _nodes_required(UINT_MAX) {
933 build_and_optimize(mode);
934 }
935
936 // Verify that verify_me made the same decisions as a fresh run.
937 PhaseIdealLoop(PhaseIterGVN &igvn, const PhaseIdealLoop *verify_me) :
938 PhaseTransform(Ideal_Loop),
939 _igvn(igvn),
940 _verify_me(verify_me),
941 _verify_only(false),
942 _dom_lca_tags(arena()), // Thread::resource_area
943 _nodes_required(UINT_MAX) {
944 build_and_optimize(LoopOptsVerify);
945 }
946
947 public:
948 Node* idom_no_update(Node* d) const {
949 return idom_no_update(d->_idx);
950 }
951
952 Node* idom_no_update(uint didx) const {
953 assert(didx < _idom_size, "oob");
954 Node* n = _idom[didx];
955 assert(n != NULL,"Bad immediate dominator info.");
956 while (n->in(0) == NULL) { // Skip dead CFG nodes
957 n = (Node*)(((intptr_t)_nodes[n->_idx]) & ~1);
958 assert(n != NULL,"Bad immediate dominator info.");
959 }
960 return n;
961 }
962
963 Node *idom(Node* d) const {
964 return idom(d->_idx);
965 }
966
967 Node *idom(uint didx) const {
968 Node *n = idom_no_update(didx);
969 _idom[didx] = n; // Lazily remove dead CFG nodes from table.
970 return n;
971 }
972
973 uint dom_depth(Node* d) const {
974 guarantee(d != NULL, "Null dominator info.");
975 guarantee(d->_idx < _idom_size, "");
976 return _dom_depth[d->_idx];
977 }
978 void set_idom(Node* d, Node* n, uint dom_depth);
979 // Locally compute IDOM using dom_lca call
980 Node *compute_idom( Node *region ) const;
981 // Recompute dom_depth
982 void recompute_dom_depth();
983
984 // Is safept not required by an outer loop?
985 bool is_deleteable_safept(Node* sfpt);
986
987 // Replace parallel induction variable (parallel to trip counter)
988 void replace_parallel_iv(IdealLoopTree *loop);
989
990 Node *dom_lca( Node *n1, Node *n2 ) const {
991 return find_non_split_ctrl(dom_lca_internal(n1, n2));
992 }
993 Node *dom_lca_internal( Node *n1, Node *n2 ) const;
994
995 // Build and verify the loop tree without modifying the graph. This
996 // is useful to verify that all inputs properly dominate their uses.
997 static void verify(PhaseIterGVN& igvn) {
998 #ifdef ASSERT
999 ResourceMark rm;
1000 PhaseIdealLoop v(igvn);
1001 #endif
1002 }
1003
1004 // Recommended way to use PhaseIdealLoop.
1005 // Run PhaseIdealLoop in some mode and allocates a local scope for memory allocations.
1006 static void optimize(PhaseIterGVN &igvn, LoopOptsMode mode) {
1007 ResourceMark rm;
1008 PhaseIdealLoop v(igvn, mode);
1009 }
1010
1011 // True if the method has at least 1 irreducible loop
1012 bool _has_irreducible_loops;
1013
1014 // Per-Node transform
1015 virtual Node *transform( Node *a_node ) { return 0; }
1016
1017 bool is_counted_loop(Node* x, IdealLoopTree*& loop);
1018 IdealLoopTree* create_outer_strip_mined_loop(BoolNode *test, Node *cmp, Node *init_control,
1019 IdealLoopTree* loop, float cl_prob, float le_fcnt,
1020 Node*& entry_control, Node*& iffalse);
1021
1022 Node* exact_limit( IdealLoopTree *loop );
1023
1024 // Return a post-walked LoopNode
1025 IdealLoopTree *get_loop( Node *n ) const {
1026 // Dead nodes have no loop, so return the top level loop instead
1027 if (!has_node(n)) return _ltree_root;
1028 assert(!has_ctrl(n), "");
1029 return (IdealLoopTree*)_nodes[n->_idx];
1030 }
1031
1032 IdealLoopTree *ltree_root() const { return _ltree_root; }
1033
1034 // Is 'n' a (nested) member of 'loop'?
1035 int is_member( const IdealLoopTree *loop, Node *n ) const {
1036 return loop->is_member(get_loop(n)); }
1037
1038 // This is the basic building block of the loop optimizations. It clones an
1039 // entire loop body. It makes an old_new loop body mapping; with this
1040 // mapping you can find the new-loop equivalent to an old-loop node. All
1041 // new-loop nodes are exactly equal to their old-loop counterparts, all
1042 // edges are the same. All exits from the old-loop now have a RegionNode
1043 // that merges the equivalent new-loop path. This is true even for the
1044 // normal "loop-exit" condition. All uses of loop-invariant old-loop values
1045 // now come from (one or more) Phis that merge their new-loop equivalents.
1046 // Parameter side_by_side_idom:
1047 // When side_by_size_idom is NULL, the dominator tree is constructed for
1048 // the clone loop to dominate the original. Used in construction of
1049 // pre-main-post loop sequence.
1050 // When nonnull, the clone and original are side-by-side, both are
1051 // dominated by the passed in side_by_side_idom node. Used in
1052 // construction of unswitched loops.
1053 enum CloneLoopMode {
1054 IgnoreStripMined = 0, // Only clone inner strip mined loop
1055 CloneIncludesStripMined = 1, // clone both inner and outer strip mined loops
1056 ControlAroundStripMined = 2 // Only clone inner strip mined loop,
1057 // result control flow branches
1058 // either to inner clone or outer
1059 // strip mined loop.
1060 };
1061 void clone_loop( IdealLoopTree *loop, Node_List &old_new, int dom_depth,
1062 CloneLoopMode mode, Node* side_by_side_idom = NULL);
1063 void clone_loop_handle_data_uses(Node* old, Node_List &old_new,
1064 IdealLoopTree* loop, IdealLoopTree* companion_loop,
1065 Node_List*& split_if_set, Node_List*& split_bool_set,
1066 Node_List*& split_cex_set, Node_List& worklist,
1067 uint new_counter, CloneLoopMode mode);
1068 void clone_outer_loop(LoopNode* head, CloneLoopMode mode, IdealLoopTree *loop,
1069 IdealLoopTree* outer_loop, int dd, Node_List &old_new,
1070 Node_List& extra_data_nodes);
1071
1072 // If we got the effect of peeling, either by actually peeling or by
1073 // making a pre-loop which must execute at least once, we can remove
1074 // all loop-invariant dominated tests in the main body.
1075 void peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new );
1076
1077 // Generate code to do a loop peel for the given loop (and body).
1078 // old_new is a temp array.
1079 void do_peeling( IdealLoopTree *loop, Node_List &old_new );
1080
1081 // Add pre and post loops around the given loop. These loops are used
1082 // during RCE, unrolling and aligning loops.
1083 void insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only );
1084
1085 // Add post loop after the given loop.
1086 Node *insert_post_loop(IdealLoopTree *loop, Node_List &old_new,
1087 CountedLoopNode *main_head, CountedLoopEndNode *main_end,
1088 Node *incr, Node *limit, CountedLoopNode *&post_head);
1089
1090 // Add an RCE'd post loop which we will multi-version adapt for run time test path usage
1091 void insert_scalar_rced_post_loop( IdealLoopTree *loop, Node_List &old_new );
1092
1093 // Add a vector post loop between a vector main loop and the current post loop
1094 void insert_vector_post_loop(IdealLoopTree *loop, Node_List &old_new);
1095 // If Node n lives in the back_ctrl block, we clone a private version of n
1096 // in preheader_ctrl block and return that, otherwise return n.
1097 Node *clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n, VectorSet &visited, Node_Stack &clones );
1098
1099 // Take steps to maximally unroll the loop. Peel any odd iterations, then
1100 // unroll to do double iterations. The next round of major loop transforms
1101 // will repeat till the doubled loop body does all remaining iterations in 1
1102 // pass.
1103 void do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new );
1104
1105 // Unroll the loop body one step - make each trip do 2 iterations.
1106 void do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip );
1107
1108 // Mark vector reduction candidates before loop unrolling
1109 void mark_reductions( IdealLoopTree *loop );
1110
1111 // Return true if exp is a constant times an induction var
1112 bool is_scaled_iv(Node* exp, Node* iv, int* p_scale);
1113
1114 // Return true if exp is a scaled induction var plus (or minus) constant
1115 bool is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth = 0);
1116
1117 // Create a new if above the uncommon_trap_if_pattern for the predicate to be promoted
1118 ProjNode* create_new_if_for_predicate(ProjNode* cont_proj, Node* new_entry,
1119 Deoptimization::DeoptReason reason,
1120 int opcode);
1121 void register_control(Node* n, IdealLoopTree *loop, Node* pred);
1122
1123 // Clone loop predicates to cloned loops (peeled, unswitched)
1124 static ProjNode* clone_predicate(ProjNode* predicate_proj, Node* new_entry,
1125 Deoptimization::DeoptReason reason,
1126 PhaseIdealLoop* loop_phase,
1127 PhaseIterGVN* igvn);
1128
1129 static void clone_loop_predicates_fix_mem(ProjNode* dom_proj , ProjNode* proj,
1130 PhaseIdealLoop* loop_phase,
1131 PhaseIterGVN* igvn);
1132
1133 static Node* clone_loop_predicates(Node* old_entry, Node* new_entry,
1134 bool clone_limit_check,
1135 PhaseIdealLoop* loop_phase,
1136 PhaseIterGVN* igvn);
1137 Node* clone_loop_predicates(Node* old_entry, Node* new_entry, bool clone_limit_check);
1138
1139 static Node* skip_all_loop_predicates(Node* entry);
1140 static Node* skip_loop_predicates(Node* entry);
1141
1142 // Find a good location to insert a predicate
1143 static ProjNode* find_predicate_insertion_point(Node* start_c, Deoptimization::DeoptReason reason);
1144 // Find a predicate
1145 static Node* find_predicate(Node* entry);
1146 // Construct a range check for a predicate if
1147 BoolNode* rc_predicate(IdealLoopTree *loop, Node* ctrl,
1148 int scale, Node* offset,
1149 Node* init, Node* limit, jint stride,
1150 Node* range, bool upper, bool &overflow);
1151
1152 // Implementation of the loop predication to promote checks outside the loop
1153 bool loop_predication_impl(IdealLoopTree *loop);
1154 bool loop_predication_impl_helper(IdealLoopTree *loop, ProjNode* proj, ProjNode *predicate_proj,
1155 CountedLoopNode *cl, ConNode* zero, Invariance& invar,
1156 Deoptimization::DeoptReason reason);
1157 bool loop_predication_should_follow_branches(IdealLoopTree *loop, ProjNode *predicate_proj, float& loop_trip_cnt);
1158 void loop_predication_follow_branches(Node *c, IdealLoopTree *loop, float loop_trip_cnt,
1159 PathFrequency& pf, Node_Stack& stack, VectorSet& seen,
1160 Node_List& if_proj_list);
1161 ProjNode* insert_skeleton_predicate(IfNode* iff, IdealLoopTree *loop,
1162 ProjNode* proj, ProjNode *predicate_proj,
1163 ProjNode* upper_bound_proj,
1164 int scale, Node* offset,
1165 Node* init, Node* limit, jint stride,
1166 Node* rng, bool& overflow,
1167 Deoptimization::DeoptReason reason);
1168 Node* add_range_check_predicate(IdealLoopTree* loop, CountedLoopNode* cl,
1169 Node* predicate_proj, int scale_con, Node* offset,
1170 Node* limit, jint stride_con, Node* value);
1171
1172 // Helper function to collect predicate for eliminating the useless ones
1173 void collect_potentially_useful_predicates(IdealLoopTree *loop, Unique_Node_List &predicate_opaque1);
1174 void eliminate_useless_predicates();
1175
1176 // Change the control input of expensive nodes to allow commoning by
1177 // IGVN when it is guaranteed to not result in a more frequent
1178 // execution of the expensive node. Return true if progress.
1179 bool process_expensive_nodes();
1180
1181 // Check whether node has become unreachable
1182 bool is_node_unreachable(Node *n) const {
1183 return !has_node(n) || n->is_unreachable(_igvn);
1184 }
1185
1186 // Eliminate range-checks and other trip-counter vs loop-invariant tests.
1187 int do_range_check( IdealLoopTree *loop, Node_List &old_new );
1188
1189 // Check to see if do_range_check(...) cleaned the main loop of range-checks
1190 void has_range_checks(IdealLoopTree *loop);
1191
1192 // Process post loops which have range checks and try to build a multi-version
1193 // guard to safely determine if we can execute the post loop which was RCE'd.
1194 bool multi_version_post_loops(IdealLoopTree *rce_loop, IdealLoopTree *legacy_loop);
1195
1196 // Cause the rce'd post loop to optimized away, this happens if we cannot complete multiverioning
1197 void poison_rce_post_loop(IdealLoopTree *rce_loop);
1198
1199 // Create a slow version of the loop by cloning the loop
1200 // and inserting an if to select fast-slow versions.
1201 ProjNode* create_slow_version_of_loop(IdealLoopTree *loop,
1202 Node_List &old_new,
1203 int opcode,
1204 CloneLoopMode mode);
1205
1206 // Clone a loop and return the clone head (clone_loop_head).
1207 // Added nodes include int(1), int(0) - disconnected, If, IfTrue, IfFalse,
1208 // This routine was created for usage in CountedLoopReserveKit.
1209 //
1210 // int(1) -> If -> IfTrue -> original_loop_head
1211 // |
1212 // V
1213 // IfFalse -> clone_loop_head (returned by function pointer)
1214 //
1215 LoopNode* create_reserve_version_of_loop(IdealLoopTree *loop, CountedLoopReserveKit* lk);
1216 // Clone loop with an invariant test (that does not exit) and
1217 // insert a clone of the test that selects which version to
1218 // execute.
1219 void do_unswitching (IdealLoopTree *loop, Node_List &old_new);
1220
1221 // Find candidate "if" for unswitching
1222 IfNode* find_unswitching_candidate(const IdealLoopTree *loop) const;
1223
1224 // Range Check Elimination uses this function!
1225 // Constrain the main loop iterations so the affine function:
1226 // low_limit <= scale_con * I + offset < upper_limit
1227 // always holds true. That is, either increase the number of iterations in
1228 // the pre-loop or the post-loop until the condition holds true in the main
1229 // loop. Scale_con, offset and limit are all loop invariant.
1230 void 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 );
1231 // Helper function for add_constraint().
1232 Node* adjust_limit(int stride_con, Node * scale, Node *offset, Node *rc_limit, Node *loop_limit, Node *pre_ctrl, bool round_up);
1233
1234 // Partially peel loop up through last_peel node.
1235 bool partial_peel( IdealLoopTree *loop, Node_List &old_new );
1236
1237 // Create a scheduled list of nodes control dependent on ctrl set.
1238 void scheduled_nodelist( IdealLoopTree *loop, VectorSet& ctrl, Node_List &sched );
1239 // Has a use in the vector set
1240 bool has_use_in_set( Node* n, VectorSet& vset );
1241 // Has use internal to the vector set (ie. not in a phi at the loop head)
1242 bool has_use_internal_to_set( Node* n, VectorSet& vset, IdealLoopTree *loop );
1243 // clone "n" for uses that are outside of loop
1244 int clone_for_use_outside_loop( IdealLoopTree *loop, Node* n, Node_List& worklist );
1245 // clone "n" for special uses that are in the not_peeled region
1246 void clone_for_special_use_inside_loop( IdealLoopTree *loop, Node* n,
1247 VectorSet& not_peel, Node_List& sink_list, Node_List& worklist );
1248 // Insert phi(lp_entry_val, back_edge_val) at use->in(idx) for loop lp if phi does not already exist
1249 void insert_phi_for_loop( Node* use, uint idx, Node* lp_entry_val, Node* back_edge_val, LoopNode* lp );
1250 #ifdef ASSERT
1251 // Validate the loop partition sets: peel and not_peel
1252 bool is_valid_loop_partition( IdealLoopTree *loop, VectorSet& peel, Node_List& peel_list, VectorSet& not_peel );
1253 // Ensure that uses outside of loop are of the right form
1254 bool is_valid_clone_loop_form( IdealLoopTree *loop, Node_List& peel_list,
1255 uint orig_exit_idx, uint clone_exit_idx);
1256 bool is_valid_clone_loop_exit_use( IdealLoopTree *loop, Node* use, uint exit_idx);
1257 #endif
1258
1259 // Returns nonzero constant stride if-node is a possible iv test (otherwise returns zero.)
1260 int stride_of_possible_iv( Node* iff );
1261 bool is_possible_iv_test( Node* iff ) { return stride_of_possible_iv(iff) != 0; }
1262 // Return the (unique) control output node that's in the loop (if it exists.)
1263 Node* stay_in_loop( Node* n, IdealLoopTree *loop);
1264 // Insert a signed compare loop exit cloned from an unsigned compare.
1265 IfNode* insert_cmpi_loop_exit(IfNode* if_cmpu, IdealLoopTree *loop);
1266 void remove_cmpi_loop_exit(IfNode* if_cmp, IdealLoopTree *loop);
1267 // Utility to register node "n" with PhaseIdealLoop
1268 void register_node(Node* n, IdealLoopTree *loop, Node* pred, int ddepth);
1269 // Utility to create an if-projection
1270 ProjNode* proj_clone(ProjNode* p, IfNode* iff);
1271 // Force the iff control output to be the live_proj
1272 Node* short_circuit_if(IfNode* iff, ProjNode* live_proj);
1273 // Insert a region before an if projection
1274 RegionNode* insert_region_before_proj(ProjNode* proj);
1275 // Insert a new if before an if projection
1276 ProjNode* insert_if_before_proj(Node* left, bool Signed, BoolTest::mask relop, Node* right, ProjNode* proj);
1277
1278 // Passed in a Phi merging (recursively) some nearly equivalent Bool/Cmps.
1279 // "Nearly" because all Nodes have been cloned from the original in the loop,
1280 // but the fall-in edges to the Cmp are different. Clone bool/Cmp pairs
1281 // through the Phi recursively, and return a Bool.
1282 Node *clone_iff( PhiNode *phi, IdealLoopTree *loop );
1283 CmpNode *clone_bool( PhiNode *phi, IdealLoopTree *loop );
1284
1285
1286 // Rework addressing expressions to get the most loop-invariant stuff
1287 // moved out. We'd like to do all associative operators, but it's especially
1288 // important (common) to do address expressions.
1289 Node *remix_address_expressions( Node *n );
1290
1291 // Convert add to muladd to generate MuladdS2I under certain criteria
1292 Node * convert_add_to_muladd(Node * n);
1293
1294 // Attempt to use a conditional move instead of a phi/branch
1295 Node *conditional_move( Node *n );
1296
1297 // Reorganize offset computations to lower register pressure.
1298 // Mostly prevent loop-fallout uses of the pre-incremented trip counter
1299 // (which are then alive with the post-incremented trip counter
1300 // forcing an extra register move)
1301 void reorg_offsets( IdealLoopTree *loop );
1302
1303 // Check for aggressive application of 'split-if' optimization,
1304 // using basic block level info.
1305 void split_if_with_blocks ( VectorSet &visited, Node_Stack &nstack, bool last_round );
1306 Node *split_if_with_blocks_pre ( Node *n );
1307 void split_if_with_blocks_post( Node *n, bool last_round );
1308 Node *has_local_phi_input( Node *n );
1309 // Mark an IfNode as being dominated by a prior test,
1310 // without actually altering the CFG (and hence IDOM info).
1311 void dominated_by( Node *prevdom, Node *iff, bool flip = false, bool exclude_loop_predicate = false );
1312
1313 // Split Node 'n' through merge point
1314 Node *split_thru_region( Node *n, Node *region );
1315 // Split Node 'n' through merge point if there is enough win.
1316 Node *split_thru_phi( Node *n, Node *region, int policy );
1317 // Found an If getting its condition-code input from a Phi in the
1318 // same block. Split thru the Region.
1319 void do_split_if( Node *iff );
1320
1321 // Conversion of fill/copy patterns into intrisic versions
1322 bool do_intrinsify_fill();
1323 bool intrinsify_fill(IdealLoopTree* lpt);
1324 bool match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& store_value,
1325 Node*& shift, Node*& offset);
1326
1327 private:
1328 // Return a type based on condition control flow
1329 const TypeInt* filtered_type( Node *n, Node* n_ctrl);
1330 const TypeInt* filtered_type( Node *n ) { return filtered_type(n, NULL); }
1331 // Helpers for filtered type
1332 const TypeInt* filtered_type_from_dominators( Node* val, Node *val_ctrl);
1333
1334 // Helper functions
1335 Node *spinup( Node *iff, Node *new_false, Node *new_true, Node *region, Node *phi, small_cache *cache );
1336 Node *find_use_block( Node *use, Node *def, Node *old_false, Node *new_false, Node *old_true, Node *new_true );
1337 void handle_use( Node *use, Node *def, small_cache *cache, Node *region_dom, Node *new_false, Node *new_true, Node *old_false, Node *old_true );
1338 bool split_up( Node *n, Node *blk1, Node *blk2 );
1339 void sink_use( Node *use, Node *post_loop );
1340 Node *place_near_use( Node *useblock ) const;
1341 Node* try_move_store_before_loop(Node* n, Node *n_ctrl);
1342 void try_move_store_after_loop(Node* n);
1343 bool identical_backtoback_ifs(Node *n);
1344 bool can_split_if(Node *n_ctrl);
1345
1346 // Determine if a method is too big for a/another round of split-if, based on
1347 // a magic (approximate) ratio derived from the equally magic constant 35000,
1348 // previously used for this purpose (but without relating to the node limit).
1349 bool must_throttle_split_if() {
1350 uint threshold = C->max_node_limit() * 2 / 5;
1351 return C->live_nodes() > threshold;
1352 }
1353
1354 // A simplistic node request tracking mechanism, where
1355 // = UINT_MAX Request not valid or made final.
1356 // < UINT_MAX Nodes currently requested (estimate).
1357 uint _nodes_required;
1358
1359 bool exceeding_node_budget(uint required = 0) {
1360 assert(C->live_nodes() < C->max_node_limit(), "sanity");
1361 uint available = C->max_node_limit() - C->live_nodes();
1362 return available < required + _nodes_required;
1363 }
1364
1365 uint require_nodes(uint require) {
1366 precond(require > 0);
1367 _nodes_required += MAX2(100u, require); // Keep requests at minimum 100.
1368 return _nodes_required;
1369 }
1370
1371 bool may_require_nodes(uint require) {
1372 return !exceeding_node_budget(require) && require_nodes(require) > 0;
1373 }
1374
1375 void require_nodes_begin() {
1376 assert(_nodes_required == UINT_MAX, "Bad state (begin).");
1377 _nodes_required = 0;
1378 }
1379
1380 // Final check that the requested nodes did not exceed the limit and that
1381 // the request was reasonably correct with respect to the number of new
1382 // nodes introduced by any transform since the last 'begin'.
1383 void require_nodes_final_check(uint live_at_begin) {
1384 uint required = _nodes_required;
1385 require_nodes_final();
1386 uint delta = C->live_nodes() - live_at_begin;
1387 // Assert is disabled, see JDK-8223911 and related issues.
1388 assert(true || delta <= 2 * required, "Bad node estimate (actual: %d, request: %d)",
1389 delta, required);
1390 }
1391
1392 void require_nodes_final() {
1393 assert(_nodes_required < UINT_MAX, "Bad state (final).");
1394 assert(!exceeding_node_budget(), "Too many NODES required!");
1395 _nodes_required = UINT_MAX;
1396 }
1397
1398 bool _created_loop_node;
1399
1400 public:
1401 uint nodes_required() const { return _nodes_required; }
1402
1403 void set_created_loop_node() { _created_loop_node = true; }
1404 bool created_loop_node() { return _created_loop_node; }
1405 void register_new_node( Node *n, Node *blk );
1406
1407 #ifdef ASSERT
1408 void dump_bad_graph(const char* msg, Node* n, Node* early, Node* LCA);
1409 #endif
1410
1411 #ifndef PRODUCT
1412 void dump( ) const;
1413 void dump( IdealLoopTree *loop, uint rpo_idx, Node_List &rpo_list ) const;
1414 void verify() const; // Major slow :-)
1415 void verify_compare( Node *n, const PhaseIdealLoop *loop_verify, VectorSet &visited ) const;
1416 IdealLoopTree *get_loop_idx(Node* n) const {
1417 // Dead nodes have no loop, so return the top level loop instead
1418 return _nodes[n->_idx] ? (IdealLoopTree*)_nodes[n->_idx] : _ltree_root;
1419 }
1420 // Print some stats
1421 static void print_statistics();
1422 static int _loop_invokes; // Count of PhaseIdealLoop invokes
1423 static int _loop_work; // Sum of PhaseIdealLoop x _unique
1424 #endif
1425 void rpo( Node *start, Node_Stack &stk, VectorSet &visited, Node_List &rpo_list ) const;
1426 };
1427
1428
1429 class AutoNodeBudget : public StackObj
1430 {
1431 public:
1432 enum budget_check_t { BUDGET_CHECK, NO_BUDGET_CHECK };
1433
1434 AutoNodeBudget(PhaseIdealLoop* phase, budget_check_t chk = BUDGET_CHECK)
1435 : _phase(phase),
1436 _check_at_final(chk == BUDGET_CHECK),
1437 _nodes_at_begin(0)
1438 {
1439 precond(_phase != NULL);
1440
1441 _nodes_at_begin = _phase->C->live_nodes();
1442 _phase->require_nodes_begin();
1443 }
1444
1445 ~AutoNodeBudget() {
1446 if (_check_at_final) {
1447 #ifndef PRODUCT
1448 if (TraceLoopOpts) {
1449 uint request = _phase->nodes_required();
1450
1451 if (request > 0) {
1452 uint delta = _phase->C->live_nodes() - _nodes_at_begin;
1453
1454 if (request < delta) {
1455 tty->print_cr("Exceeding node budget: %d < %d", request, delta);
1456 }
1457 }
1458 }
1459 #endif
1460 _phase->require_nodes_final_check(_nodes_at_begin);
1461 } else {
1462 _phase->require_nodes_final();
1463 }
1464 }
1465
1466 private:
1467 PhaseIdealLoop* _phase;
1468 bool _check_at_final;
1469 uint _nodes_at_begin;
1470 };
1471
1472 // The Estimated Loop Clone Size: CloneFactor * (BodySize + BC) + CC, where BC
1473 // and CC are totally ad-hoc/magic "body" and "clone" constants, respectively,
1474 // used to ensure that node usage estimates made are on the safe side, for the
1475 // most part.
1476 static inline uint est_loop_clone_sz(uint fact, uint size) {
1477 uint const bc = 31;
1478 uint const cc = 41;
1479 uint estimate = fact * (size + bc) + cc;
1480 return (estimate - cc) / fact == size + bc ? estimate : UINT_MAX;
1481 }
1482
1483
1484 // This kit may be used for making of a reserved copy of a loop before this loop
1485 // goes under non-reversible changes.
1486 //
1487 // Function create_reserve() creates a reserved copy (clone) of the loop.
1488 // The reserved copy is created by calling
1489 // PhaseIdealLoop::create_reserve_version_of_loop - see there how
1490 // the original and reserved loops are connected in the outer graph.
1491 // If create_reserve succeeded, it returns 'true' and _has_reserved is set to 'true'.
1492 //
1493 // By default the reserved copy (clone) of the loop is created as dead code - it is
1494 // dominated in the outer loop by this node chain:
1495 // intcon(1)->If->IfFalse->reserved_copy.
1496 // The original loop is dominated by the the same node chain but IfTrue projection:
1497 // intcon(0)->If->IfTrue->original_loop.
1498 //
1499 // In this implementation of CountedLoopReserveKit the ctor includes create_reserve()
1500 // and the dtor, checks _use_new value.
1501 // If _use_new == false, it "switches" control to reserved copy of the loop
1502 // by simple replacing of node intcon(1) with node intcon(0).
1503 //
1504 // Here is a proposed example of usage (see also SuperWord::output in superword.cpp).
1505 //
1506 // void CountedLoopReserveKit_example()
1507 // {
1508 // CountedLoopReserveKit lrk((phase, lpt, DoReserveCopy = true); // create local object
1509 // if (DoReserveCopy && !lrk.has_reserved()) {
1510 // return; //failed to create reserved loop copy
1511 // }
1512 // ...
1513 // //something is wrong, switch to original loop
1514 /// if(something_is_wrong) return; // ~CountedLoopReserveKit makes the switch
1515 // ...
1516 // //everything worked ok, return with the newly modified loop
1517 // lrk.use_new();
1518 // return; // ~CountedLoopReserveKit does nothing once use_new() was called
1519 // }
1520 //
1521 // Keep in mind, that by default if create_reserve() is not followed by use_new()
1522 // the dtor will "switch to the original" loop.
1523 // NOTE. You you modify outside of the original loop this class is no help.
1524 //
1525 class CountedLoopReserveKit {
1526 private:
1527 PhaseIdealLoop* _phase;
1528 IdealLoopTree* _lpt;
1529 LoopNode* _lp;
1530 IfNode* _iff;
1531 LoopNode* _lp_reserved;
1532 bool _has_reserved;
1533 bool _use_new;
1534 const bool _active; //may be set to false in ctor, then the object is dummy
1535
1536 public:
1537 CountedLoopReserveKit(PhaseIdealLoop* phase, IdealLoopTree *loop, bool active);
1538 ~CountedLoopReserveKit();
1539 void use_new() {_use_new = true;}
1540 void set_iff(IfNode* x) {_iff = x;}
1541 bool has_reserved() const { return _active && _has_reserved;}
1542 private:
1543 bool create_reserve();
1544 };// class CountedLoopReserveKit
1545
1546 inline Node* IdealLoopTree::tail() {
1547 // Handle lazy update of _tail field.
1548 if (_tail->in(0) == NULL) {
1549 _tail = _phase->get_ctrl(_tail);
1550 }
1551 return _tail;
1552 }
1553
1554
1555 // Iterate over the loop tree using a preorder, left-to-right traversal.
1556 //
1557 // Example that visits all counted loops from within PhaseIdealLoop
1558 //
1559 // for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
1560 // IdealLoopTree* lpt = iter.current();
1561 // if (!lpt->is_counted()) continue;
1562 // ...
1563 class LoopTreeIterator : public StackObj {
1564 private:
1565 IdealLoopTree* _root;
1566 IdealLoopTree* _curnt;
1567
1568 public:
1569 LoopTreeIterator(IdealLoopTree* root) : _root(root), _curnt(root) {}
1570
1571 bool done() { return _curnt == NULL; } // Finished iterating?
1572
1573 void next(); // Advance to next loop tree
1574
1575 IdealLoopTree* current() { return _curnt; } // Return current value of iterator.
1576 };
1577
1578 #endif // SHARE_OPTO_LOOPNODE_HPP