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comparison src/share/vm/opto/ifnode.cpp @ 0:a61af66fc99e jdk7-b24

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author duke
date Sat, 01 Dec 2007 00:00:00 +0000
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1 /*
2 * Copyright 2000-2006 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
24
25 // Portions of code courtesy of Clifford Click
26
27 // Optimization - Graph Style
28
29 #include "incls/_precompiled.incl"
30 #include "incls/_ifnode.cpp.incl"
31
32
33 extern int explicit_null_checks_elided;
34
35 //=============================================================================
36 //------------------------------Value------------------------------------------
37 // Return a tuple for whichever arm of the IF is reachable
38 const Type *IfNode::Value( PhaseTransform *phase ) const {
39 if( !in(0) ) return Type::TOP;
40 if( phase->type(in(0)) == Type::TOP )
41 return Type::TOP;
42 const Type *t = phase->type(in(1));
43 if( t == Type::TOP ) // data is undefined
44 return TypeTuple::IFNEITHER; // unreachable altogether
45 if( t == TypeInt::ZERO ) // zero, or false
46 return TypeTuple::IFFALSE; // only false branch is reachable
47 if( t == TypeInt::ONE ) // 1, or true
48 return TypeTuple::IFTRUE; // only true branch is reachable
49 assert( t == TypeInt::BOOL, "expected boolean type" );
50
51 return TypeTuple::IFBOTH; // No progress
52 }
53
54 const RegMask &IfNode::out_RegMask() const {
55 return RegMask::Empty;
56 }
57
58 //------------------------------split_if---------------------------------------
59 // Look for places where we merge constants, then test on the merged value.
60 // If the IF test will be constant folded on the path with the constant, we
61 // win by splitting the IF to before the merge point.
62 static Node* split_if(IfNode *iff, PhaseIterGVN *igvn) {
63 // I could be a lot more general here, but I'm trying to squeeze this
64 // in before the Christmas '98 break so I'm gonna be kinda restrictive
65 // on the patterns I accept. CNC
66
67 // Look for a compare of a constant and a merged value
68 Node *i1 = iff->in(1);
69 if( !i1->is_Bool() ) return NULL;
70 BoolNode *b = i1->as_Bool();
71 Node *cmp = b->in(1);
72 if( !cmp->is_Cmp() ) return NULL;
73 i1 = cmp->in(1);
74 if( i1 == NULL || !i1->is_Phi() ) return NULL;
75 PhiNode *phi = i1->as_Phi();
76 if( phi->is_copy() ) return NULL;
77 Node *con2 = cmp->in(2);
78 if( !con2->is_Con() ) return NULL;
79 // See that the merge point contains some constants
80 Node *con1=NULL;
81 uint i4;
82 for( i4 = 1; i4 < phi->req(); i4++ ) {
83 con1 = phi->in(i4);
84 if( !con1 ) return NULL; // Do not optimize partially collaped merges
85 if( con1->is_Con() ) break; // Found a constant
86 // Also allow null-vs-not-null checks
87 const TypePtr *tp = igvn->type(con1)->isa_ptr();
88 if( tp && tp->_ptr == TypePtr::NotNull )
89 break;
90 }
91 if( i4 >= phi->req() ) return NULL; // Found no constants
92
93 igvn->C->set_has_split_ifs(true); // Has chance for split-if
94
95 // Make sure that the compare can be constant folded away
96 Node *cmp2 = cmp->clone();
97 cmp2->set_req(1,con1);
98 cmp2->set_req(2,con2);
99 const Type *t = cmp2->Value(igvn);
100 // This compare is dead, so whack it!
101 igvn->remove_dead_node(cmp2);
102 if( !t->singleton() ) return NULL;
103
104 // No intervening control, like a simple Call
105 Node *r = iff->in(0);
106 if( !r->is_Region() ) return NULL;
107 if( phi->region() != r ) return NULL;
108 // No other users of the cmp/bool
109 if (b->outcnt() != 1 || cmp->outcnt() != 1) {
110 //tty->print_cr("many users of cmp/bool");
111 return NULL;
112 }
113
114 // Make sure we can determine where all the uses of merged values go
115 for (DUIterator_Fast jmax, j = r->fast_outs(jmax); j < jmax; j++) {
116 Node* u = r->fast_out(j);
117 if( u == r ) continue;
118 if( u == iff ) continue;
119 if( u->outcnt() == 0 ) continue; // use is dead & ignorable
120 if( !u->is_Phi() ) {
121 /*
122 if( u->is_Start() ) {
123 tty->print_cr("Region has inlined start use");
124 } else {
125 tty->print_cr("Region has odd use");
126 u->dump(2);
127 }*/
128 return NULL;
129 }
130 if( u != phi ) {
131 // CNC - do not allow any other merged value
132 //tty->print_cr("Merging another value");
133 //u->dump(2);
134 return NULL;
135 }
136 // Make sure we can account for all Phi uses
137 for (DUIterator_Fast kmax, k = u->fast_outs(kmax); k < kmax; k++) {
138 Node* v = u->fast_out(k); // User of the phi
139 // CNC - Allow only really simple patterns.
140 // In particular I disallow AddP of the Phi, a fairly common pattern
141 if( v == cmp ) continue; // The compare is OK
142 if( (v->is_ConstraintCast()) &&
143 v->in(0)->in(0) == iff )
144 continue; // CastPP/II of the IfNode is OK
145 // Disabled following code because I cannot tell if exactly one
146 // path dominates without a real dominator check. CNC 9/9/1999
147 //uint vop = v->Opcode();
148 //if( vop == Op_Phi ) { // Phi from another merge point might be OK
149 // Node *r = v->in(0); // Get controlling point
150 // if( !r ) return NULL; // Degraded to a copy
151 // // Find exactly one path in (either True or False doms, but not IFF)
152 // int cnt = 0;
153 // for( uint i = 1; i < r->req(); i++ )
154 // if( r->in(i) && r->in(i)->in(0) == iff )
155 // cnt++;
156 // if( cnt == 1 ) continue; // Exactly one of True or False guards Phi
157 //}
158 if( !v->is_Call() ) {
159 /*
160 if( v->Opcode() == Op_AddP ) {
161 tty->print_cr("Phi has AddP use");
162 } else if( v->Opcode() == Op_CastPP ) {
163 tty->print_cr("Phi has CastPP use");
164 } else if( v->Opcode() == Op_CastII ) {
165 tty->print_cr("Phi has CastII use");
166 } else {
167 tty->print_cr("Phi has use I cant be bothered with");
168 }
169 */
170 }
171 return NULL;
172
173 /* CNC - Cut out all the fancy acceptance tests
174 // Can we clone this use when doing the transformation?
175 // If all uses are from Phis at this merge or constants, then YES.
176 if( !v->in(0) && v != cmp ) {
177 tty->print_cr("Phi has free-floating use");
178 v->dump(2);
179 return NULL;
180 }
181 for( uint l = 1; l < v->req(); l++ ) {
182 if( (!v->in(l)->is_Phi() || v->in(l)->in(0) != r) &&
183 !v->in(l)->is_Con() ) {
184 tty->print_cr("Phi has use");
185 v->dump(2);
186 return NULL;
187 } // End of if Phi-use input is neither Phi nor Constant
188 } // End of for all inputs to Phi-use
189 */
190 } // End of for all uses of Phi
191 } // End of for all uses of Region
192
193 // Only do this if the IF node is in a sane state
194 if (iff->outcnt() != 2)
195 return NULL;
196
197 // Got a hit! Do the Mondo Hack!
198 //
199 //ABC a1c def ghi B 1 e h A C a c d f g i
200 // R - Phi - Phi - Phi Rc - Phi - Phi - Phi Rx - Phi - Phi - Phi
201 // cmp - 2 cmp - 2 cmp - 2
202 // bool bool_c bool_x
203 // if if_c if_x
204 // T F T F T F
205 // ..s.. ..t .. ..s.. ..t.. ..s.. ..t..
206 //
207 // Split the paths coming into the merge point into 2 seperate groups of
208 // merges. On the left will be all the paths feeding constants into the
209 // Cmp's Phi. On the right will be the remaining paths. The Cmp's Phi
210 // will fold up into a constant; this will let the Cmp fold up as well as
211 // all the control flow. Below the original IF we have 2 control
212 // dependent regions, 's' and 't'. Now we will merge the two paths
213 // just prior to 's' and 't' from the two IFs. At least 1 path (and quite
214 // likely 2 or more) will promptly constant fold away.
215 PhaseGVN *phase = igvn;
216
217 // Make a region merging constants and a region merging the rest
218 uint req_c = 0;
219 for (uint ii = 1; ii < r->req(); ii++) {
220 if( phi->in(ii) == con1 ) {
221 req_c++;
222 }
223 }
224 Node *region_c = new (igvn->C, req_c + 1) RegionNode(req_c + 1);
225 Node *phi_c = con1;
226 uint len = r->req();
227 Node *region_x = new (igvn->C, len - req_c + 1) RegionNode(len - req_c + 1);
228 Node *phi_x = PhiNode::make_blank(region_x, phi);
229 for (uint i = 1, i_c = 1, i_x = 1; i < len; i++) {
230 if( phi->in(i) == con1 ) {
231 region_c->init_req( i_c++, r ->in(i) );
232 } else {
233 region_x->init_req( i_x, r ->in(i) );
234 phi_x ->init_req( i_x++, phi->in(i) );
235 }
236 }
237
238 // Register the new RegionNodes but do not transform them. Cannot
239 // transform until the entire Region/Phi conglerate has been hacked
240 // as a single huge transform.
241 igvn->register_new_node_with_optimizer( region_c );
242 igvn->register_new_node_with_optimizer( region_x );
243 phi_x = phase->transform( phi_x );
244 // Prevent the untimely death of phi_x. Currently he has no uses. He is
245 // about to get one. If this only use goes away, then phi_x will look dead.
246 // However, he will be picking up some more uses down below.
247 Node *hook = new (igvn->C, 4) Node(4);
248 hook->init_req(0, phi_x);
249 hook->init_req(1, phi_c);
250
251 // Make the compare
252 Node *cmp_c = phase->makecon(t);
253 Node *cmp_x = cmp->clone();
254 cmp_x->set_req(1,phi_x);
255 cmp_x->set_req(2,con2);
256 cmp_x = phase->transform(cmp_x);
257 // Make the bool
258 Node *b_c = phase->transform(new (igvn->C, 2) BoolNode(cmp_c,b->_test._test));
259 Node *b_x = phase->transform(new (igvn->C, 2) BoolNode(cmp_x,b->_test._test));
260 // Make the IfNode
261 IfNode *iff_c = new (igvn->C, 2) IfNode(region_c,b_c,iff->_prob,iff->_fcnt);
262 igvn->set_type_bottom(iff_c);
263 igvn->_worklist.push(iff_c);
264 hook->init_req(2, iff_c);
265
266 IfNode *iff_x = new (igvn->C, 2) IfNode(region_x,b_x,iff->_prob, iff->_fcnt);
267 igvn->set_type_bottom(iff_x);
268 igvn->_worklist.push(iff_x);
269 hook->init_req(3, iff_x);
270
271 // Make the true/false arms
272 Node *iff_c_t = phase->transform(new (igvn->C, 1) IfTrueNode (iff_c));
273 Node *iff_c_f = phase->transform(new (igvn->C, 1) IfFalseNode(iff_c));
274 Node *iff_x_t = phase->transform(new (igvn->C, 1) IfTrueNode (iff_x));
275 Node *iff_x_f = phase->transform(new (igvn->C, 1) IfFalseNode(iff_x));
276
277 // Merge the TRUE paths
278 Node *region_s = new (igvn->C, 3) RegionNode(3);
279 igvn->_worklist.push(region_s);
280 region_s->init_req(1, iff_c_t);
281 region_s->init_req(2, iff_x_t);
282 igvn->register_new_node_with_optimizer( region_s );
283
284 // Merge the FALSE paths
285 Node *region_f = new (igvn->C, 3) RegionNode(3);
286 igvn->_worklist.push(region_f);
287 region_f->init_req(1, iff_c_f);
288 region_f->init_req(2, iff_x_f);
289 igvn->register_new_node_with_optimizer( region_f );
290
291 igvn->hash_delete(cmp);// Remove soon-to-be-dead node from hash table.
292 cmp->set_req(1,NULL); // Whack the inputs to cmp because it will be dead
293 cmp->set_req(2,NULL);
294 // Check for all uses of the Phi and give them a new home.
295 // The 'cmp' got cloned, but CastPP/IIs need to be moved.
296 Node *phi_s = NULL; // do not construct unless needed
297 Node *phi_f = NULL; // do not construct unless needed
298 for (DUIterator_Last i2min, i2 = phi->last_outs(i2min); i2 >= i2min; --i2) {
299 Node* v = phi->last_out(i2);// User of the phi
300 igvn->hash_delete(v); // Have to fixup other Phi users
301 igvn->_worklist.push(v);
302 uint vop = v->Opcode();
303 Node *proj = NULL;
304 if( vop == Op_Phi ) { // Remote merge point
305 Node *r = v->in(0);
306 for (uint i3 = 1; i3 < r->req(); i3++)
307 if (r->in(i3) && r->in(i3)->in(0) == iff) {
308 proj = r->in(i3);
309 break;
310 }
311 } else if( v->is_ConstraintCast() ) {
312 proj = v->in(0); // Controlling projection
313 } else {
314 assert( 0, "do not know how to handle this guy" );
315 }
316
317 Node *proj_path_data, *proj_path_ctrl;
318 if( proj->Opcode() == Op_IfTrue ) {
319 if( phi_s == NULL ) {
320 // Only construct phi_s if needed, otherwise provides
321 // interfering use.
322 phi_s = PhiNode::make_blank(region_s,phi);
323 phi_s->init_req( 1, phi_c );
324 phi_s->init_req( 2, phi_x );
325 phi_s = phase->transform(phi_s);
326 }
327 proj_path_data = phi_s;
328 proj_path_ctrl = region_s;
329 } else {
330 if( phi_f == NULL ) {
331 // Only construct phi_f if needed, otherwise provides
332 // interfering use.
333 phi_f = PhiNode::make_blank(region_f,phi);
334 phi_f->init_req( 1, phi_c );
335 phi_f->init_req( 2, phi_x );
336 phi_f = phase->transform(phi_f);
337 }
338 proj_path_data = phi_f;
339 proj_path_ctrl = region_f;
340 }
341
342 // Fixup 'v' for for the split
343 if( vop == Op_Phi ) { // Remote merge point
344 uint i;
345 for( i = 1; i < v->req(); i++ )
346 if( v->in(i) == phi )
347 break;
348 v->set_req(i, proj_path_data );
349 } else if( v->is_ConstraintCast() ) {
350 v->set_req(0, proj_path_ctrl );
351 v->set_req(1, proj_path_data );
352 } else
353 ShouldNotReachHere();
354 }
355
356 // Now replace the original iff's True/False with region_s/region_t.
357 // This makes the original iff go dead.
358 for (DUIterator_Last i3min, i3 = iff->last_outs(i3min); i3 >= i3min; --i3) {
359 Node* p = iff->last_out(i3);
360 assert( p->Opcode() == Op_IfTrue || p->Opcode() == Op_IfFalse, "" );
361 Node *u = (p->Opcode() == Op_IfTrue) ? region_s : region_f;
362 // Replace p with u
363 igvn->add_users_to_worklist(p);
364 for (DUIterator_Last lmin, l = p->last_outs(lmin); l >= lmin;) {
365 Node* x = p->last_out(l);
366 igvn->hash_delete(x);
367 uint uses_found = 0;
368 for( uint j = 0; j < x->req(); j++ ) {
369 if( x->in(j) == p ) {
370 x->set_req(j, u);
371 uses_found++;
372 }
373 }
374 l -= uses_found; // we deleted 1 or more copies of this edge
375 }
376 igvn->remove_dead_node(p);
377 }
378
379 // Force the original merge dead
380 igvn->hash_delete(r);
381 r->set_req_X(0,NULL,igvn);
382
383 // Now remove the bogus extra edges used to keep things alive
384 igvn->remove_dead_node( hook );
385
386 // Must return either the original node (now dead) or a new node
387 // (Do not return a top here, since that would break the uniqueness of top.)
388 return new (igvn->C, 1) ConINode(TypeInt::ZERO);
389 }
390
391 //------------------------------is_range_check---------------------------------
392 // Return 0 if not a range check. Return 1 if a range check and set index and
393 // offset. Return 2 if we had to negate the test. Index is NULL if the check
394 // is versus a constant.
395 int IfNode::is_range_check(Node* &range, Node* &index, jint &offset) {
396 Node* b = in(1);
397 if (b == NULL || !b->is_Bool()) return 0;
398 BoolNode* bn = b->as_Bool();
399 Node* cmp = bn->in(1);
400 if (cmp == NULL) return 0;
401 if (cmp->Opcode() != Op_CmpU) return 0;
402
403 Node* l = cmp->in(1);
404 Node* r = cmp->in(2);
405 int flip_test = 1;
406 if (bn->_test._test == BoolTest::le) {
407 l = cmp->in(2);
408 r = cmp->in(1);
409 flip_test = 2;
410 } else if (bn->_test._test != BoolTest::lt) {
411 return 0;
412 }
413 if (l->is_top()) return 0; // Top input means dead test
414 if (r->Opcode() != Op_LoadRange) return 0;
415
416 // We have recognized one of these forms:
417 // Flip 1: If (Bool[<] CmpU(l, LoadRange)) ...
418 // Flip 2: If (Bool[<=] CmpU(LoadRange, l)) ...
419
420 // Make sure it's a real range check by requiring an uncommon trap
421 // along the OOB path. Otherwise, it's possible that the user wrote
422 // something which optimized to look like a range check but behaves
423 // in some other way.
424 Node* iftrap = proj_out(flip_test == 2 ? true : false);
425 bool found_trap = false;
426 if (iftrap != NULL) {
427 Node* u = iftrap->unique_ctrl_out();
428 if (u != NULL) {
429 // It could be a merge point (Region) for uncommon trap.
430 if (u->is_Region()) {
431 Node* c = u->unique_ctrl_out();
432 if (c != NULL) {
433 iftrap = u;
434 u = c;
435 }
436 }
437 if (u->in(0) == iftrap && u->is_CallStaticJava()) {
438 int req = u->as_CallStaticJava()->uncommon_trap_request();
439 if (Deoptimization::trap_request_reason(req) ==
440 Deoptimization::Reason_range_check) {
441 found_trap = true;
442 }
443 }
444 }
445 }
446 if (!found_trap) return 0; // sorry, no cigar
447
448 // Look for index+offset form
449 Node* ind = l;
450 jint off = 0;
451 if (l->is_top()) {
452 return 0;
453 } else if (l->is_Add()) {
454 if ((off = l->in(1)->find_int_con(0)) != 0) {
455 ind = l->in(2);
456 } else if ((off = l->in(2)->find_int_con(0)) != 0) {
457 ind = l->in(1);
458 }
459 } else if ((off = l->find_int_con(-1)) >= 0) {
460 // constant offset with no variable index
461 ind = NULL;
462 } else {
463 // variable index with no constant offset (or dead negative index)
464 off = 0;
465 }
466
467 // Return all the values:
468 index = ind;
469 offset = off;
470 range = r;
471 return flip_test;
472 }
473
474 //------------------------------adjust_check-----------------------------------
475 // Adjust (widen) a prior range check
476 static void adjust_check(Node* proj, Node* range, Node* index,
477 int flip, jint off_lo, PhaseIterGVN* igvn) {
478 PhaseGVN *gvn = igvn;
479 // Break apart the old check
480 Node *iff = proj->in(0);
481 Node *bol = iff->in(1);
482 if( bol->is_top() ) return; // In case a partially dead range check appears
483 // bail (or bomb[ASSERT/DEBUG]) if NOT projection-->IfNode-->BoolNode
484 DEBUG_ONLY( if( !bol->is_Bool() ) { proj->dump(3); fatal("Expect projection-->IfNode-->BoolNode"); } )
485 if( !bol->is_Bool() ) return;
486
487 Node *cmp = bol->in(1);
488 // Compute a new check
489 Node *new_add = gvn->intcon(off_lo);
490 if( index ) {
491 new_add = off_lo ? gvn->transform(new (gvn->C, 3) AddINode( index, new_add )) : index;
492 }
493 Node *new_cmp = (flip == 1)
494 ? new (gvn->C, 3) CmpUNode( new_add, range )
495 : new (gvn->C, 3) CmpUNode( range, new_add );
496 new_cmp = gvn->transform(new_cmp);
497 // See if no need to adjust the existing check
498 if( new_cmp == cmp ) return;
499 // Else, adjust existing check
500 Node *new_bol = gvn->transform( new (gvn->C, 2) BoolNode( new_cmp, bol->as_Bool()->_test._test ) );
501 igvn->hash_delete( iff );
502 iff->set_req_X( 1, new_bol, igvn );
503 }
504
505 //------------------------------up_one_dom-------------------------------------
506 // Walk up the dominator tree one step. Return NULL at root or true
507 // complex merges. Skips through small diamonds.
508 Node* IfNode::up_one_dom(Node *curr, bool linear_only) {
509 Node *dom = curr->in(0);
510 if( !dom ) // Found a Region degraded to a copy?
511 return curr->nonnull_req(); // Skip thru it
512
513 if( curr != dom ) // Normal walk up one step?
514 return dom;
515
516 // Use linear_only if we are still parsing, since we cannot
517 // trust the regions to be fully filled in.
518 if (linear_only)
519 return NULL;
520
521 // Else hit a Region. Check for a loop header
522 if( dom->is_Loop() )
523 return dom->in(1); // Skip up thru loops
524
525 // Check for small diamonds
526 Node *din1, *din2, *din3, *din4;
527 if( dom->req() == 3 && // 2-path merge point
528 (din1 = dom ->in(1)) && // Left path exists
529 (din2 = dom ->in(2)) && // Right path exists
530 (din3 = din1->in(0)) && // Left path up one
531 (din4 = din2->in(0)) ) { // Right path up one
532 if( din3->is_Call() && // Handle a slow-path call on either arm
533 (din3 = din3->in(0)) )
534 din3 = din3->in(0);
535 if( din4->is_Call() && // Handle a slow-path call on either arm
536 (din4 = din4->in(0)) )
537 din4 = din4->in(0);
538 if( din3 == din4 && din3->is_If() )
539 return din3; // Skip around diamonds
540 }
541
542 // Give up the search at true merges
543 return NULL; // Dead loop? Or hit root?
544 }
545
546 //------------------------------remove_useless_bool----------------------------
547 // Check for people making a useless boolean: things like
548 // if( (x < y ? true : false) ) { ... }
549 // Replace with if( x < y ) { ... }
550 static Node *remove_useless_bool(IfNode *iff, PhaseGVN *phase) {
551 Node *i1 = iff->in(1);
552 if( !i1->is_Bool() ) return NULL;
553 BoolNode *bol = i1->as_Bool();
554
555 Node *cmp = bol->in(1);
556 if( cmp->Opcode() != Op_CmpI ) return NULL;
557
558 // Must be comparing against a bool
559 const Type *cmp2_t = phase->type( cmp->in(2) );
560 if( cmp2_t != TypeInt::ZERO &&
561 cmp2_t != TypeInt::ONE )
562 return NULL;
563
564 // Find a prior merge point merging the boolean
565 i1 = cmp->in(1);
566 if( !i1->is_Phi() ) return NULL;
567 PhiNode *phi = i1->as_Phi();
568 if( phase->type( phi ) != TypeInt::BOOL )
569 return NULL;
570
571 // Check for diamond pattern
572 int true_path = phi->is_diamond_phi();
573 if( true_path == 0 ) return NULL;
574
575 // phi->region->if_proj->ifnode->bool->cmp
576 BoolNode *bol2 = phi->in(0)->in(1)->in(0)->in(1)->as_Bool();
577
578 // Now get the 'sense' of the test correct so we can plug in
579 // either iff2->in(1) or its complement.
580 int flip = 0;
581 if( bol->_test._test == BoolTest::ne ) flip = 1-flip;
582 else if( bol->_test._test != BoolTest::eq ) return NULL;
583 if( cmp2_t == TypeInt::ZERO ) flip = 1-flip;
584
585 const Type *phi1_t = phase->type( phi->in(1) );
586 const Type *phi2_t = phase->type( phi->in(2) );
587 // Check for Phi(0,1) and flip
588 if( phi1_t == TypeInt::ZERO ) {
589 if( phi2_t != TypeInt::ONE ) return NULL;
590 flip = 1-flip;
591 } else {
592 // Check for Phi(1,0)
593 if( phi1_t != TypeInt::ONE ) return NULL;
594 if( phi2_t != TypeInt::ZERO ) return NULL;
595 }
596 if( true_path == 2 ) {
597 flip = 1-flip;
598 }
599
600 Node* new_bol = (flip ? phase->transform( bol2->negate(phase) ) : bol2);
601 iff->set_req(1, new_bol);
602 // Intervening diamond probably goes dead
603 phase->C->set_major_progress();
604 return iff;
605 }
606
607 static IfNode* idealize_test(PhaseGVN* phase, IfNode* iff);
608
609 //------------------------------Ideal------------------------------------------
610 // Return a node which is more "ideal" than the current node. Strip out
611 // control copies
612 Node *IfNode::Ideal(PhaseGVN *phase, bool can_reshape) {
613 if (remove_dead_region(phase, can_reshape)) return this;
614 // No Def-Use info?
615 if (!can_reshape) return NULL;
616 PhaseIterGVN *igvn = phase->is_IterGVN();
617
618 // Don't bother trying to transform a dead if
619 if (in(0)->is_top()) return NULL;
620 // Don't bother trying to transform an if with a dead test
621 if (in(1)->is_top()) return NULL;
622 // Another variation of a dead test
623 if (in(1)->is_Con()) return NULL;
624 // Another variation of a dead if
625 if (outcnt() < 2) return NULL;
626
627 // Canonicalize the test.
628 Node* idt_if = idealize_test(phase, this);
629 if (idt_if != NULL) return idt_if;
630
631 // Try to split the IF
632 Node *s = split_if(this, igvn);
633 if (s != NULL) return s;
634
635 // Check for people making a useless boolean: things like
636 // if( (x < y ? true : false) ) { ... }
637 // Replace with if( x < y ) { ... }
638 Node *bol2 = remove_useless_bool(this, phase);
639 if( bol2 ) return bol2;
640
641 // Setup to scan up the CFG looking for a dominating test
642 Node *dom = in(0);
643 Node *prev_dom = this;
644
645 // Check for range-check vs other kinds of tests
646 Node *index1, *range1;
647 jint offset1;
648 int flip1 = is_range_check(range1, index1, offset1);
649 if( flip1 ) {
650 Node *first_prev_dom = NULL;
651
652 // Try to remove extra range checks. All 'up_one_dom' gives up at merges
653 // so all checks we inspect post-dominate the top-most check we find.
654 // If we are going to fail the current check and we reach the top check
655 // then we are guarenteed to fail, so just start interpreting there.
656 // We 'expand' the top 2 range checks to include all post-dominating
657 // checks.
658
659 // The top 2 range checks seen
660 Node *prev_chk1 = NULL;
661 Node *prev_chk2 = NULL;
662 // Low and high offsets seen so far
663 jint off_lo = offset1;
664 jint off_hi = offset1;
665
666 // Scan for the top 2 checks and collect range of offsets
667 for( int dist = 0; dist < 999; dist++ ) { // Range-Check scan limit
668 if( dom->Opcode() == Op_If && // Not same opcode?
669 prev_dom->in(0) == dom ) { // One path of test does dominate?
670 if( dom == this ) return NULL; // dead loop
671 // See if this is a range check
672 Node *index2, *range2;
673 jint offset2;
674 int flip2 = dom->as_If()->is_range_check(range2, index2, offset2);
675 // See if this is a _matching_ range check, checking against
676 // the same array bounds.
677 if( flip2 == flip1 && range2 == range1 && index2 == index1 &&
678 dom->outcnt() == 2 ) {
679 // Gather expanded bounds
680 off_lo = MIN2(off_lo,offset2);
681 off_hi = MAX2(off_hi,offset2);
682 // Record top 2 range checks
683 prev_chk2 = prev_chk1;
684 prev_chk1 = prev_dom;
685 // If we match the test exactly, then the top test covers
686 // both our lower and upper bounds.
687 if( dom->in(1) == in(1) )
688 prev_chk2 = prev_chk1;
689 }
690 }
691 prev_dom = dom;
692 dom = up_one_dom( dom );
693 if( !dom ) break;
694 }
695
696
697 // Attempt to widen the dominating range check to cover some later
698 // ones. Since range checks "fail" by uncommon-trapping to the
699 // interpreter, widening a check can make us speculative enter the
700 // interpreter. If we see range-check deopt's, do not widen!
701 if (!phase->C->allow_range_check_smearing()) return NULL;
702
703 // Constant indices only need to check the upper bound.
704 // Non-constance indices must check both low and high.
705 if( index1 ) {
706 // Didn't find 2 prior covering checks, so cannot remove anything.
707 if( !prev_chk2 ) return NULL;
708 // 'Widen' the offsets of the 1st and 2nd covering check
709 adjust_check( prev_chk1, range1, index1, flip1, off_lo, igvn );
710 // Do not call adjust_check twice on the same projection
711 // as the first call may have transformed the BoolNode to a ConI
712 if( prev_chk1 != prev_chk2 ) {
713 adjust_check( prev_chk2, range1, index1, flip1, off_hi, igvn );
714 }
715 // Test is now covered by prior checks, dominate it out
716 prev_dom = prev_chk2;
717 } else {
718 // Didn't find prior covering check, so cannot remove anything.
719 if( !prev_chk1 ) return NULL;
720 // 'Widen' the offset of the 1st and only covering check
721 adjust_check( prev_chk1, range1, index1, flip1, off_hi, igvn );
722 // Test is now covered by prior checks, dominate it out
723 prev_dom = prev_chk1;
724 }
725
726
727 } else { // Scan for an equivalent test
728
729 Node *cmp;
730 int dist = 0; // Cutoff limit for search
731 int op = Opcode();
732 if( op == Op_If &&
733 (cmp=in(1)->in(1))->Opcode() == Op_CmpP ) {
734 if( cmp->in(2) != NULL && // make sure cmp is not already dead
735 cmp->in(2)->bottom_type() == TypePtr::NULL_PTR ) {
736 dist = 64; // Limit for null-pointer scans
737 } else {
738 dist = 4; // Do not bother for random pointer tests
739 }
740 } else {
741 dist = 4; // Limit for random junky scans
742 }
743
744 // Normal equivalent-test check.
745 if( !dom ) return NULL; // Dead loop?
746
747 // Search up the dominator tree for an If with an identical test
748 while( dom->Opcode() != op || // Not same opcode?
749 dom->in(1) != in(1) || // Not same input 1?
750 (req() == 3 && dom->in(2) != in(2)) || // Not same input 2?
751 prev_dom->in(0) != dom ) { // One path of test does not dominate?
752 if( dist < 0 ) return NULL;
753
754 dist--;
755 prev_dom = dom;
756 dom = up_one_dom( dom );
757 if( !dom ) return NULL;
758 }
759
760 // Check that we did not follow a loop back to ourselves
761 if( this == dom )
762 return NULL;
763
764 if( dist > 2 ) // Add to count of NULL checks elided
765 explicit_null_checks_elided++;
766
767 } // End of Else scan for an equivalent test
768
769 // Hit! Remove this IF
770 #ifndef PRODUCT
771 if( TraceIterativeGVN ) {
772 tty->print(" Removing IfNode: "); this->dump();
773 }
774 if( VerifyOpto && !phase->allow_progress() ) {
775 // Found an equivalent dominating test,
776 // we can not guarantee reaching a fix-point for these during iterativeGVN
777 // since intervening nodes may not change.
778 return NULL;
779 }
780 #endif
781
782 // Replace dominated IfNode
783 dominated_by( prev_dom, igvn );
784
785 // Must return either the original node (now dead) or a new node
786 // (Do not return a top here, since that would break the uniqueness of top.)
787 return new (phase->C, 1) ConINode(TypeInt::ZERO);
788 }
789
790 //------------------------------dominated_by-----------------------------------
791 void IfNode::dominated_by( Node *prev_dom, PhaseIterGVN *igvn ) {
792 igvn->hash_delete(this); // Remove self to prevent spurious V-N
793 Node *idom = in(0);
794 // Need opcode to decide which way 'this' test goes
795 int prev_op = prev_dom->Opcode();
796 Node *top = igvn->C->top(); // Shortcut to top
797
798 // Now walk the current IfNode's projections.
799 // Loop ends when 'this' has no more uses.
800 for (DUIterator_Last imin, i = last_outs(imin); i >= imin; --i) {
801 Node *ifp = last_out(i); // Get IfTrue/IfFalse
802 igvn->add_users_to_worklist(ifp);
803 // Check which projection it is and set target.
804 // Data-target is either the dominating projection of the same type
805 // or TOP if the dominating projection is of opposite type.
806 // Data-target will be used as the new control edge for the non-CFG
807 // nodes like Casts and Loads.
808 Node *data_target = (ifp->Opcode() == prev_op ) ? prev_dom : top;
809 // Control-target is just the If's immediate dominator or TOP.
810 Node *ctrl_target = (ifp->Opcode() == prev_op ) ? idom : top;
811
812 // For each child of an IfTrue/IfFalse projection, reroute.
813 // Loop ends when projection has no more uses.
814 for (DUIterator_Last jmin, j = ifp->last_outs(jmin); j >= jmin; --j) {
815 Node* s = ifp->last_out(j); // Get child of IfTrue/IfFalse
816 igvn->hash_delete(s); // Yank from hash table before edge hacking
817 if( !s->depends_only_on_test() ) {
818 // Find the control input matching this def-use edge.
819 // For Regions it may not be in slot 0.
820 uint l;
821 for( l = 0; s->in(l) != ifp; l++ ) { }
822 s->set_req(l, ctrl_target);
823 } else { // Else, for control producers,
824 s->set_req(0, data_target); // Move child to data-target
825 }
826 igvn->_worklist.push(s); // Revisit collapsed Phis
827 } // End for each child of a projection
828
829 igvn->remove_dead_node(ifp);
830 } // End for each IfTrue/IfFalse child of If
831
832 // Kill the IfNode
833 igvn->remove_dead_node(this);
834 }
835
836 //------------------------------Identity---------------------------------------
837 // If the test is constant & we match, then we are the input Control
838 Node *IfTrueNode::Identity( PhaseTransform *phase ) {
839 // Can only optimize if cannot go the other way
840 const TypeTuple *t = phase->type(in(0))->is_tuple();
841 return ( t == TypeTuple::IFNEITHER || t == TypeTuple::IFTRUE )
842 ? in(0)->in(0) // IfNode control
843 : this; // no progress
844 }
845
846 //------------------------------dump_spec--------------------------------------
847 #ifndef PRODUCT
848 void IfNode::dump_spec(outputStream *st) const {
849 st->print("P=%f, C=%f",_prob,_fcnt);
850 }
851 #endif
852
853 //------------------------------idealize_test----------------------------------
854 // Try to canonicalize tests better. Peek at the Cmp/Bool/If sequence and
855 // come up with a canonical sequence. Bools getting 'eq', 'gt' and 'ge' forms
856 // converted to 'ne', 'le' and 'lt' forms. IfTrue/IfFalse get swapped as
857 // needed.
858 static IfNode* idealize_test(PhaseGVN* phase, IfNode* iff) {
859 assert(iff->in(0) != NULL, "If must be live");
860
861 if (iff->outcnt() != 2) return NULL; // Malformed projections.
862 Node* old_if_f = iff->proj_out(false);
863 Node* old_if_t = iff->proj_out(true);
864
865 // CountedLoopEnds want the back-control test to be TRUE, irregardless of
866 // whether they are testing a 'gt' or 'lt' condition. The 'gt' condition
867 // happens in count-down loops
868 if (iff->is_CountedLoopEnd()) return NULL;
869 if (!iff->in(1)->is_Bool()) return NULL; // Happens for partially optimized IF tests
870 BoolNode *b = iff->in(1)->as_Bool();
871 BoolTest bt = b->_test;
872 // Test already in good order?
873 if( bt.is_canonical() )
874 return NULL;
875
876 // Flip test to be canonical. Requires flipping the IfFalse/IfTrue and
877 // cloning the IfNode.
878 Node* new_b = phase->transform( new (phase->C, 2) BoolNode(b->in(1), bt.negate()) );
879 if( !new_b->is_Bool() ) return NULL;
880 b = new_b->as_Bool();
881
882 PhaseIterGVN *igvn = phase->is_IterGVN();
883 assert( igvn, "Test is not canonical in parser?" );
884
885 // The IF node never really changes, but it needs to be cloned
886 iff = new (phase->C, 2) IfNode( iff->in(0), b, 1.0-iff->_prob, iff->_fcnt);
887
888 Node *prior = igvn->hash_find_insert(iff);
889 if( prior ) {
890 igvn->remove_dead_node(iff);
891 iff = (IfNode*)prior;
892 } else {
893 // Cannot call transform on it just yet
894 igvn->set_type_bottom(iff);
895 }
896 igvn->_worklist.push(iff);
897
898 // Now handle projections. Cloning not required.
899 Node* new_if_f = (Node*)(new (phase->C, 1) IfFalseNode( iff ));
900 Node* new_if_t = (Node*)(new (phase->C, 1) IfTrueNode ( iff ));
901
902 igvn->register_new_node_with_optimizer(new_if_f);
903 igvn->register_new_node_with_optimizer(new_if_t);
904 igvn->hash_delete(old_if_f);
905 igvn->hash_delete(old_if_t);
906 // Flip test, so flip trailing control
907 igvn->subsume_node(old_if_f, new_if_t);
908 igvn->subsume_node(old_if_t, new_if_f);
909
910 // Progress
911 return iff;
912 }
913
914 //------------------------------Identity---------------------------------------
915 // If the test is constant & we match, then we are the input Control
916 Node *IfFalseNode::Identity( PhaseTransform *phase ) {
917 // Can only optimize if cannot go the other way
918 const TypeTuple *t = phase->type(in(0))->is_tuple();
919 return ( t == TypeTuple::IFNEITHER || t == TypeTuple::IFFALSE )
920 ? in(0)->in(0) // IfNode control
921 : this; // no progress
922 }