1 /*
  2  * Copyright (c) 1999, 2018, Oracle and/or its affiliates. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 12  * version 2 for more details (a copy is included in the LICENSE file that
 13  * accompanied this code).
 14  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #include "precompiled.hpp"
 26 #include "memory/allocation.inline.hpp"
 27 #include "opto/callnode.hpp"
 28 #include "opto/inlinetypenode.hpp"
 29 #include "opto/loopnode.hpp"
 30 #include "opto/movenode.hpp"
 31 
 32 
 33 //------------------------------split_thru_region------------------------------
 34 // Split Node 'n' through merge point.
 35 RegionNode* PhaseIdealLoop::split_thru_region(Node* n, RegionNode* region) {
 36   assert(n->is_CFG(), "");
 37   RegionNode* r = new RegionNode(region->req());
 38   IdealLoopTree* loop = get_loop(n);
 39   for (uint i = 1; i < region->req(); i++) {
 40     Node* x = n->clone();
 41     Node* in0 = n->in(0);
 42     if (in0->in(0) == region) x->set_req(0, in0->in(i));
 43     for (uint j = 1; j < n->req(); j++) {
 44       Node* in = n->in(j);
 45       if (get_ctrl(in) == region) {
 46         x->set_req(j, in->in(i));
 47       }
 48     }
 49     _igvn.register_new_node_with_optimizer(x);
 50     set_loop(x, loop);
 51     set_idom(x, x->in(0), dom_depth(x->in(0))+1);
 52     r->init_req(i, x);
 53   }
 54 
 55   // Record region
 56   r->set_req(0,region);         // Not a TRUE RegionNode
 57   _igvn.register_new_node_with_optimizer(r);
 58   set_loop(r, loop);
 59   if (!loop->_child) {
 60     loop->_body.push(r);
 61   }
 62   return r;
 63 }
 64 
 65 //------------------------------split_up---------------------------------------
 66 // Split block-local op up through the phis to empty the current block
 67 bool PhaseIdealLoop::split_up( Node *n, Node *blk1, Node *blk2 ) {
 68   if( n->is_CFG() ) {
 69     assert( n->in(0) != blk1, "Lousy candidate for split-if" );
 70     return false;
 71   }
 72   if( get_ctrl(n) != blk1 && get_ctrl(n) != blk2 )
 73     return false;               // Not block local
 74   if( n->is_Phi() ) return false; // Local PHIs are expected
 75 
 76   // Recursively split-up inputs
 77   for (uint i = 1; i < n->req(); i++) {
 78     if( split_up( n->in(i), blk1, blk2 ) ) {
 79       // Got split recursively and self went dead?
 80       if (n->outcnt() == 0)
 81         _igvn.remove_dead_node(n);
 82       return true;
 83     }
 84   }
 85 
 86   // Check for needing to clone-up a compare.  Can't do that, it forces
 87   // another (nested) split-if transform.  Instead, clone it "down".
 88   if( n->is_Cmp() ) {
 89     assert(get_ctrl(n) == blk2 || get_ctrl(n) == blk1, "must be in block with IF");
 90     // Check for simple Cmp/Bool/CMove which we can clone-up.  Cmp/Bool/CMove
 91     // sequence can have no other users and it must all reside in the split-if
 92     // block.  Non-simple Cmp/Bool/CMove sequences are 'cloned-down' below -
 93     // private, per-use versions of the Cmp and Bool are made.  These sink to
 94     // the CMove block.  If the CMove is in the split-if block, then in the
 95     // next iteration this will become a simple Cmp/Bool/CMove set to clone-up.
 96     Node *bol, *cmov;
 97     if( !(n->outcnt() == 1 && n->unique_out()->is_Bool() &&
 98           (bol = n->unique_out()->as_Bool()) &&
 99           (get_ctrl(bol) == blk1 ||
100            get_ctrl(bol) == blk2) &&
101           bol->outcnt() == 1 &&
102           bol->unique_out()->is_CMove() &&
103           (cmov = bol->unique_out()->as_CMove()) &&
104           (get_ctrl(cmov) == blk1 ||
105            get_ctrl(cmov) == blk2) ) ) {
106 
107       // Must clone down
108 #ifndef PRODUCT
109       if( PrintOpto && VerifyLoopOptimizations ) {
110         tty->print("Cloning down: ");
111         n->dump();
112       }
113 #endif
114       if (!n->is_FastLock()) {
115         // Clone down any block-local BoolNode uses of this CmpNode
116         for (DUIterator i = n->outs(); n->has_out(i); i++) {
117           Node* bol = n->out(i);
118           assert( bol->is_Bool(), "" );
119           if (bol->outcnt() == 1) {
120             Node* use = bol->unique_out();
121             if (use->Opcode() == Op_Opaque4) {
122               if (use->outcnt() == 1) {
123                 Node* iff = use->unique_out();
124                 assert(iff->is_If(), "unexpected node type");
125                 Node *use_c = iff->in(0);
126                 if (use_c == blk1 || use_c == blk2) {
127                   continue;
128                 }
129               }
130             } else {
131               // We might see an Opaque1 from a loop limit check here
132               assert(use->is_If() || use->is_CMove() || use->Opcode() == Op_Opaque1, "unexpected node type");
133               Node *use_c = use->is_If() ? use->in(0) : get_ctrl(use);
134               if (use_c == blk1 || use_c == blk2) {
135                 assert(use->is_CMove(), "unexpected node type");
136                 continue;
137               }
138             }
139           }
140           if (get_ctrl(bol) == blk1 || get_ctrl(bol) == blk2) {
141             // Recursively sink any BoolNode
142 #ifndef PRODUCT
143             if( PrintOpto && VerifyLoopOptimizations ) {
144               tty->print("Cloning down: ");
145               bol->dump();
146             }
147 #endif
148             for (DUIterator j = bol->outs(); bol->has_out(j); j++) {
149               Node* u = bol->out(j);
150               // Uses are either IfNodes, CMoves or Opaque4
151               if (u->Opcode() == Op_Opaque4) {
152                 assert(u->in(1) == bol, "bad input");
153                 for (DUIterator_Last kmin, k = u->last_outs(kmin); k >= kmin; --k) {
154                   Node* iff = u->last_out(k);
155                   assert(iff->is_If() || iff->is_CMove(), "unexpected node type");
156                   assert( iff->in(1) == u, "" );
157                   // Get control block of either the CMove or the If input
158                   Node *iff_ctrl = iff->is_If() ? iff->in(0) : get_ctrl(iff);
159                   Node *x1 = bol->clone();
160                   Node *x2 = u->clone();
161                   register_new_node(x1, iff_ctrl);
162                   register_new_node(x2, iff_ctrl);
163                   _igvn.replace_input_of(x2, 1, x1);
164                   _igvn.replace_input_of(iff, 1, x2);
165                 }
166                 _igvn.remove_dead_node(u);
167                 --j;
168               } else {
169                 // We might see an Opaque1 from a loop limit check here
170                 assert(u->is_If() || u->is_CMove() || u->Opcode() == Op_Opaque1, "unexpected node type");
171                 assert(u->in(1) == bol, "");
172                 // Get control block of either the CMove or the If input
173                 Node *u_ctrl = u->is_If() ? u->in(0) : get_ctrl(u);
174                 assert((u_ctrl != blk1 && u_ctrl != blk2) || u->is_CMove(), "won't converge");
175                 Node *x = bol->clone();
176                 register_new_node(x, u_ctrl);
177                 _igvn.replace_input_of(u, 1, x);
178                 --j;
179               }
180             }
181             _igvn.remove_dead_node(bol);
182             --i;
183           }
184         }
185       }
186       // Clone down this CmpNode
187       for (DUIterator_Last jmin, j = n->last_outs(jmin); j >= jmin; --j) {
188         Node* use = n->last_out(j);
189         uint pos = 1;
190         if (n->is_FastLock()) {
191           pos = TypeFunc::Parms + 2;
192           assert(use->is_Lock(), "FastLock only used by LockNode");
193         }
194         assert(use->in(pos) == n, "" );
195         Node *x = n->clone();
196         register_new_node(x, ctrl_or_self(use));
197         _igvn.replace_input_of(use, pos, x);
198       }
199       _igvn.remove_dead_node( n );
200 
201       return true;
202     }
203   }
204   if (subgraph_has_opaque(n)) {
205     Unique_Node_List wq;
206     wq.push(n);
207     for (uint i = 0; i < wq.size(); i++) {
208       Node* m = wq.at(i);
209       if (m->is_If()) {
210         assert(skeleton_predicate_has_opaque(m->as_If()), "opaque node not reachable from if?");
211         Node* bol = clone_skeleton_predicate_bool(m, NULL, NULL, m->in(0));
212         _igvn.replace_input_of(m, 1, bol);
213       } else {
214         assert(!m->is_CFG(), "not CFG expected");
215         for (DUIterator_Fast jmax, j = m->fast_outs(jmax); j < jmax; j++) {
216           Node* u = m->fast_out(j);
217           wq.push(u);
218         }
219       }
220     }
221   }
222 
223   // See if splitting-up a Store.  Any anti-dep loads must go up as
224   // well.  An anti-dep load might be in the wrong block, because in
225   // this particular layout/schedule we ignored anti-deps and allow
226   // memory to be alive twice.  This only works if we do the same
227   // operations on anti-dep loads as we do their killing stores.
228   if( n->is_Store() && n->in(MemNode::Memory)->in(0) == n->in(0) ) {
229     // Get store's memory slice
230     int alias_idx = C->get_alias_index(_igvn.type(n->in(MemNode::Address))->is_ptr());
231 
232     // Get memory-phi anti-dep loads will be using
233     Node *memphi = n->in(MemNode::Memory);
234     assert( memphi->is_Phi(), "" );
235     // Hoist any anti-dep load to the splitting block;
236     // it will then "split-up".
237     for (DUIterator_Fast imax,i = memphi->fast_outs(imax); i < imax; i++) {
238       Node *load = memphi->fast_out(i);
239       if( load->is_Load() && alias_idx == C->get_alias_index(_igvn.type(load->in(MemNode::Address))->is_ptr()) )
240         set_ctrl(load,blk1);
241     }
242   }
243 
244   // Found some other Node; must clone it up
245 #ifndef PRODUCT
246   if( PrintOpto && VerifyLoopOptimizations ) {
247     tty->print("Cloning up: ");
248     n->dump();
249   }
250 #endif
251 
252   // ConvI2L may have type information on it which becomes invalid if
253   // it moves up in the graph so change any clones so widen the type
254   // to TypeLong::INT when pushing it up.
255   const Type* rtype = NULL;
256   if (n->Opcode() == Op_ConvI2L && n->bottom_type() != TypeLong::INT) {
257     rtype = TypeLong::INT;
258   }
259 
260   // Now actually split-up this guy.  One copy per control path merging.
261   Node *phi = PhiNode::make_blank(blk1, n);
262   for( uint j = 1; j < blk1->req(); j++ ) {
263     Node *x = n->clone();
264     // Widen the type of the ConvI2L when pushing up.
265     if (rtype != NULL) x->as_Type()->set_type(rtype);
266     if( n->in(0) && n->in(0) == blk1 )
267       x->set_req( 0, blk1->in(j) );
268     for( uint i = 1; i < n->req(); i++ ) {
269       Node *m = n->in(i);
270       if( get_ctrl(m) == blk1 ) {
271         assert( m->in(0) == blk1, "" );
272         x->set_req( i, m->in(j) );
273       }
274     }
275     register_new_node( x, blk1->in(j) );
276     phi->init_req( j, x );
277   }
278   // Announce phi to optimizer
279   register_new_node(phi, blk1);
280 
281   // Remove cloned-up value from optimizer; use phi instead
282   _igvn.replace_node( n, phi );
283 
284   // (There used to be a self-recursive call to split_up() here,
285   // but it is not needed.  All necessary forward walking is done
286   // by do_split_if() below.)
287 
288   return true;
289 }
290 
291 //------------------------------register_new_node------------------------------
292 void PhaseIdealLoop::register_new_node( Node *n, Node *blk ) {
293   assert(!n->is_CFG(), "must be data node");
294   _igvn.register_new_node_with_optimizer(n);
295   set_ctrl(n, blk);
296   IdealLoopTree *loop = get_loop(blk);
297   if( !loop->_child )
298     loop->_body.push(n);
299 }
300 
301 //------------------------------small_cache------------------------------------
302 struct small_cache : public Dict {
303 
304   small_cache() : Dict( cmpkey, hashptr ) {}
305   Node *probe( Node *use_blk ) { return (Node*)((*this)[use_blk]); }
306   void lru_insert( Node *use_blk, Node *new_def ) { Insert(use_blk,new_def); }
307 };
308 
309 //------------------------------spinup-----------------------------------------
310 // "Spin up" the dominator tree, starting at the use site and stopping when we
311 // find the post-dominating point.
312 
313 // We must be at the merge point which post-dominates 'new_false' and
314 // 'new_true'.  Figure out which edges into the RegionNode eventually lead up
315 // to false and which to true.  Put in a PhiNode to merge values; plug in
316 // the appropriate false-arm or true-arm values.  If some path leads to the
317 // original IF, then insert a Phi recursively.
318 Node *PhaseIdealLoop::spinup( Node *iff_dom, Node *new_false, Node *new_true, Node *use_blk, Node *def, small_cache *cache ) {
319   if (use_blk->is_top())        // Handle dead uses
320     return use_blk;
321   Node *prior_n = (Node*)((intptr_t)0xdeadbeef);
322   Node *n = use_blk;            // Get path input
323   assert( use_blk != iff_dom, "" );
324   // Here's the "spinup" the dominator tree loop.  Do a cache-check
325   // along the way, in case we've come this way before.
326   while( n != iff_dom ) {       // Found post-dominating point?
327     prior_n = n;
328     n = idom(n);                // Search higher
329     Node *s = cache->probe( prior_n ); // Check cache
330     if( s ) return s;           // Cache hit!
331   }
332 
333   Node *phi_post;
334   if( prior_n == new_false || prior_n == new_true ) {
335     phi_post = def->clone();
336     phi_post->set_req(0, prior_n );
337     register_new_node(phi_post, prior_n);
338   } else {
339     // This method handles both control uses (looking for Regions) or data
340     // uses (looking for Phis).  If looking for a control use, then we need
341     // to insert a Region instead of a Phi; however Regions always exist
342     // previously (the hash_find_insert below would always hit) so we can
343     // return the existing Region.
344     if( def->is_CFG() ) {
345       phi_post = prior_n;       // If looking for CFG, return prior
346     } else {
347       assert( def->is_Phi(), "" );
348       assert( prior_n->is_Region(), "must be a post-dominating merge point" );
349 
350       // Need a Phi here
351       phi_post = PhiNode::make_blank(prior_n, def);
352       // Search for both true and false on all paths till find one.
353       for( uint i = 1; i < phi_post->req(); i++ ) // For all paths
354         phi_post->init_req( i, spinup( iff_dom, new_false, new_true, prior_n->in(i), def, cache ) );
355       Node *t = _igvn.hash_find_insert(phi_post);
356       if( t ) {                 // See if we already have this one
357         // phi_post will not be used, so kill it
358         _igvn.remove_dead_node(phi_post);
359         phi_post->destruct(&_igvn);
360         phi_post = t;
361       } else {
362         register_new_node( phi_post, prior_n );
363       }
364     }
365   }
366 
367   // Update cache everywhere
368   prior_n = (Node*)((intptr_t)0xdeadbeef);  // Reset IDOM walk
369   n = use_blk;                  // Get path input
370   // Spin-up the idom tree again, basically doing path-compression.
371   // Insert cache entries along the way, so that if we ever hit this
372   // point in the IDOM tree again we'll stop immediately on a cache hit.
373   while( n != iff_dom ) {       // Found post-dominating point?
374     prior_n = n;
375     n = idom(n);                // Search higher
376     cache->lru_insert( prior_n, phi_post ); // Fill cache
377   } // End of while not gone high enough
378 
379   return phi_post;
380 }
381 
382 //------------------------------find_use_block---------------------------------
383 // Find the block a USE is in.  Normally USE's are in the same block as the
384 // using instruction.  For Phi-USE's, the USE is in the predecessor block
385 // along the corresponding path.
386 Node *PhaseIdealLoop::find_use_block( Node *use, Node *def, Node *old_false, Node *new_false, Node *old_true, Node *new_true ) {
387   // CFG uses are their own block
388   if( use->is_CFG() )
389     return use;
390 
391   if( use->is_Phi() ) {         // Phi uses in prior block
392     // Grab the first Phi use; there may be many.
393     // Each will be handled as a separate iteration of
394     // the "while( phi->outcnt() )" loop.
395     uint j;
396     for( j = 1; j < use->req(); j++ )
397       if( use->in(j) == def )
398         break;
399     assert( j < use->req(), "def should be among use's inputs" );
400     return use->in(0)->in(j);
401   }
402   // Normal (non-phi) use
403   Node *use_blk = get_ctrl(use);
404   // Some uses are directly attached to the old (and going away)
405   // false and true branches.
406   if( use_blk == old_false ) {
407     use_blk = new_false;
408     set_ctrl(use, new_false);
409   }
410   if( use_blk == old_true ) {
411     use_blk = new_true;
412     set_ctrl(use, new_true);
413   }
414 
415   if (use_blk == NULL) {        // He's dead, Jim
416     _igvn.replace_node(use, C->top());
417   }
418 
419   return use_blk;
420 }
421 
422 //------------------------------handle_use-------------------------------------
423 // Handle uses of the merge point.  Basically, split-if makes the merge point
424 // go away so all uses of the merge point must go away as well.  Most block
425 // local uses have already been split-up, through the merge point.  Uses from
426 // far below the merge point can't always be split up (e.g., phi-uses are
427 // pinned) and it makes too much stuff live.  Instead we use a path-based
428 // solution to move uses down.
429 //
430 // If the use is along the pre-split-CFG true branch, then the new use will
431 // be from the post-split-CFG true merge point.  Vice-versa for the false
432 // path.  Some uses will be along both paths; then we sink the use to the
433 // post-dominating location; we may need to insert a Phi there.
434 void PhaseIdealLoop::handle_use( Node *use, Node *def, small_cache *cache, Node *region_dom, Node *new_false, Node *new_true, Node *old_false, Node *old_true ) {
435 
436   Node *use_blk = find_use_block(use,def,old_false,new_false,old_true,new_true);
437   if( !use_blk ) return;        // He's dead, Jim
438 
439   // Walk up the dominator tree until I hit either the old IfFalse, the old
440   // IfTrue or the old If.  Insert Phis where needed.
441   Node *new_def = spinup( region_dom, new_false, new_true, use_blk, def, cache );
442 
443   // Found where this USE goes.  Re-point him.
444   uint i;
445   for( i = 0; i < use->req(); i++ )
446     if( use->in(i) == def )
447       break;
448   assert( i < use->req(), "def should be among use's inputs" );
449   _igvn.replace_input_of(use, i, new_def);
450 }
451 
452 //------------------------------do_split_if------------------------------------
453 // Found an If getting its condition-code input from a Phi in the same block.
454 // Split thru the Region.
455 void PhaseIdealLoop::do_split_if(Node* iff, RegionNode** new_false_region, RegionNode** new_true_region) {
456   if (PrintOpto && VerifyLoopOptimizations) {
457     tty->print_cr("Split-if");
458   }
459   if (TraceLoopOpts) {
460     tty->print_cr("SplitIf");
461   }
462 
463   C->set_major_progress();
464   RegionNode *region = iff->in(0)->as_Region();
465   Node *region_dom = idom(region);
466 
467   // We are going to clone this test (and the control flow with it) up through
468   // the incoming merge point.  We need to empty the current basic block.
469   // Clone any instructions which must be in this block up through the merge
470   // point.
471   DUIterator i, j;
472   bool progress = true;
473   while (progress) {
474     progress = false;
475     for (i = region->outs(); region->has_out(i); i++) {
476       Node* n = region->out(i);
477       if( n == region ) continue;
478       // The IF to be split is OK.
479       if( n == iff ) continue;
480       if( !n->is_Phi() ) {      // Found pinned memory op or such
481         if (split_up(n, region, iff)) {
482           i = region->refresh_out_pos(i);
483           progress = true;
484         }
485         continue;
486       }
487       assert( n->in(0) == region, "" );
488 
489       // Recursively split up all users of a Phi
490       for (j = n->outs(); n->has_out(j); j++) {
491         Node* m = n->out(j);
492         // If m is dead, throw it away, and declare progress
493         if (_nodes[m->_idx] == NULL) {
494           _igvn.remove_dead_node(m);
495           // fall through
496         } else if (m != iff && split_up(m, region, iff)) {
497           // fall through
498         } else {
499           continue;
500         }
501         // Something unpredictable changed.
502         // Tell the iterators to refresh themselves, and rerun the loop.
503         i = region->refresh_out_pos(i);
504         j = region->refresh_out_pos(j);
505         progress = true;
506       }
507     }
508   }
509 
510   // Now we have no instructions in the block containing the IF.
511   // Split the IF.
512   RegionNode *new_iff = split_thru_region(iff, region);
513 
514   // Replace both uses of 'new_iff' with Regions merging True/False
515   // paths.  This makes 'new_iff' go dead.
516   Node *old_false = NULL, *old_true = NULL;
517   RegionNode* new_false = NULL;
518   RegionNode* new_true = NULL;
519   for (DUIterator_Last j2min, j2 = iff->last_outs(j2min); j2 >= j2min; --j2) {
520     Node *ifp = iff->last_out(j2);
521     assert( ifp->Opcode() == Op_IfFalse || ifp->Opcode() == Op_IfTrue, "" );
522     ifp->set_req(0, new_iff);
523     RegionNode* ifpx = split_thru_region(ifp, region);
524 
525     // Replace 'If' projection of a Region with a Region of
526     // 'If' projections.
527     ifpx->set_req(0, ifpx);       // A TRUE RegionNode
528 
529     // Setup dominator info
530     set_idom(ifpx, region_dom, dom_depth(region_dom) + 1);
531 
532     // Check for splitting loop tails
533     if( get_loop(iff)->tail() == ifp )
534       get_loop(iff)->_tail = ifpx;
535 
536     // Replace in the graph with lazy-update mechanism
537     new_iff->set_req(0, new_iff); // hook self so it does not go dead
538     lazy_replace(ifp, ifpx);
539     new_iff->set_req(0, region);
540 
541     // Record bits for later xforms
542     if( ifp->Opcode() == Op_IfFalse ) {
543       old_false = ifp;
544       new_false = ifpx;
545     } else {
546       old_true = ifp;
547       new_true = ifpx;
548     }
549   }
550   _igvn.remove_dead_node(new_iff);
551   // Lazy replace IDOM info with the region's dominator
552   lazy_replace(iff, region_dom);
553   lazy_update(region, region_dom); // idom must be update before handle_uses
554   region->set_req(0, NULL);        // Break the self-cycle. Required for lazy_update to work on region
555 
556   // Now make the original merge point go dead, by handling all its uses.
557   small_cache region_cache;
558   // Preload some control flow in region-cache
559   region_cache.lru_insert( new_false, new_false );
560   region_cache.lru_insert( new_true , new_true  );
561   // Now handle all uses of the splitting block
562   for (DUIterator k = region->outs(); region->has_out(k); k++) {
563     Node* phi = region->out(k);
564     if (!phi->in(0)) {         // Dead phi?  Remove it
565       _igvn.remove_dead_node(phi);
566     } else if (phi == region) { // Found the self-reference
567       continue;                 // No roll-back of DUIterator
568     } else if (phi->is_Phi()) { // Expected common case: Phi hanging off of Region
569       assert(phi->in(0) == region, "Inconsistent graph");
570       // Need a per-def cache.  Phi represents a def, so make a cache
571       small_cache phi_cache;
572 
573       // Inspect all Phi uses to make the Phi go dead
574       for (DUIterator_Last lmin, l = phi->last_outs(lmin); l >= lmin; --l) {
575         Node* use = phi->last_out(l);
576         // Compute the new DEF for this USE.  New DEF depends on the path
577         // taken from the original DEF to the USE.  The new DEF may be some
578         // collection of PHI's merging values from different paths.  The Phis
579         // inserted depend only on the location of the USE.  We use a
580         // 2-element cache to handle multiple uses from the same block.
581         handle_use(use, phi, &phi_cache, region_dom, new_false, new_true, old_false, old_true);
582       } // End of while phi has uses
583       // Remove the dead Phi
584       _igvn.remove_dead_node( phi );
585     } else {
586       assert(phi->in(0) == region, "Inconsistent graph");
587       // Random memory op guarded by Region.  Compute new DEF for USE.
588       handle_use(phi, region, &region_cache, region_dom, new_false, new_true, old_false, old_true);
589     }
590     // Every path above deletes a use of the region, except for the region
591     // self-cycle (which is needed by handle_use calling find_use_block
592     // calling get_ctrl calling get_ctrl_no_update looking for dead
593     // regions).  So roll back the DUIterator innards.
594     --k;
595   } // End of while merge point has phis
596 
597   _igvn.remove_dead_node(region);
598 
599   if (new_false_region != NULL) {
600     *new_false_region = new_false;
601   }
602   if (new_true_region != NULL) {
603     *new_true_region = new_true;
604   }
605 
606 #ifndef PRODUCT
607   if( VerifyLoopOptimizations ) verify();
608 #endif
609 }