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 Node *PhaseIdealLoop::split_thru_region( Node *n, Node *region ) {
 36   uint wins = 0;
 37   assert( n->is_CFG(), "" );
 38   assert( region->is_Region(), "" );
 39   Node *r = new RegionNode( region->req() );
 40   IdealLoopTree *loop = get_loop( n );
 41   for( uint i = 1; i < region->req(); i++ ) {
 42     Node *x = n->clone();
 43     Node *in0 = n->in(0);
 44     if( in0->in(0) == region ) x->set_req( 0, in0->in(i) );
 45     for( uint j = 1; j < n->req(); j++ ) {
 46       Node *in = n->in(j);
 47       if( get_ctrl(in) == region )
 48         x->set_req( j, in->in(i) );
 49     }
 50     _igvn.register_new_node_with_optimizer(x);
 51     set_loop(x, loop);
 52     set_idom(x, x->in(0), dom_depth(x->in(0))+1);
 53     r->init_req(i, x);
 54   }
 55 
 56   // Record region
 57   r->set_req(0,region);         // Not a TRUE RegionNode
 58   _igvn.register_new_node_with_optimizer(r);
 59   set_loop(r, loop);
 60   if( !loop->_child )
 61     loop->_body.push(r);
 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 
205   // See if splitting-up a Store.  Any anti-dep loads must go up as
206   // well.  An anti-dep load might be in the wrong block, because in
207   // this particular layout/schedule we ignored anti-deps and allow
208   // memory to be alive twice.  This only works if we do the same
209   // operations on anti-dep loads as we do their killing stores.
210   if( n->is_Store() && n->in(MemNode::Memory)->in(0) == n->in(0) ) {
211     // Get store's memory slice
212     int alias_idx = C->get_alias_index(_igvn.type(n->in(MemNode::Address))->is_ptr());
213 
214     // Get memory-phi anti-dep loads will be using
215     Node *memphi = n->in(MemNode::Memory);
216     assert( memphi->is_Phi(), "" );
217     // Hoist any anti-dep load to the splitting block;
218     // it will then "split-up".
219     for (DUIterator_Fast imax,i = memphi->fast_outs(imax); i < imax; i++) {
220       Node *load = memphi->fast_out(i);
221       if( load->is_Load() && alias_idx == C->get_alias_index(_igvn.type(load->in(MemNode::Address))->is_ptr()) )
222         set_ctrl(load,blk1);
223     }
224   }
225 
226   // Found some other Node; must clone it up
227 #ifndef PRODUCT
228   if( PrintOpto && VerifyLoopOptimizations ) {
229     tty->print("Cloning up: ");
230     n->dump();
231   }
232 #endif
233 
234   // ConvI2L may have type information on it which becomes invalid if
235   // it moves up in the graph so change any clones so widen the type
236   // to TypeLong::INT when pushing it up.
237   const Type* rtype = NULL;
238   if (n->Opcode() == Op_ConvI2L && n->bottom_type() != TypeLong::INT) {
239     rtype = TypeLong::INT;
240   }
241 
242   // Now actually split-up this guy.  One copy per control path merging.
243   Node *phi = PhiNode::make_blank(blk1, n);
244   for( uint j = 1; j < blk1->req(); j++ ) {
245     Node *x = n->clone();
246     // Widen the type of the ConvI2L when pushing up.
247     if (rtype != NULL) x->as_Type()->set_type(rtype);
248     if( n->in(0) && n->in(0) == blk1 )
249       x->set_req( 0, blk1->in(j) );
250     for( uint i = 1; i < n->req(); i++ ) {
251       Node *m = n->in(i);
252       if( get_ctrl(m) == blk1 ) {
253         assert( m->in(0) == blk1, "" );
254         x->set_req( i, m->in(j) );
255       }
256     }
257     register_new_node( x, blk1->in(j) );
258     phi->init_req( j, x );
259   }
260   // Announce phi to optimizer
261   register_new_node(phi, blk1);
262 
263   // Remove cloned-up value from optimizer; use phi instead
264   _igvn.replace_node( n, phi );
265 
266   // (There used to be a self-recursive call to split_up() here,
267   // but it is not needed.  All necessary forward walking is done
268   // by do_split_if() below.)
269 
270   return true;
271 }
272 
273 //------------------------------register_new_node------------------------------
274 void PhaseIdealLoop::register_new_node( Node *n, Node *blk ) {
275   assert(!n->is_CFG(), "must be data node");
276   _igvn.register_new_node_with_optimizer(n);
277   set_ctrl(n, blk);
278   IdealLoopTree *loop = get_loop(blk);
279   if( !loop->_child )
280     loop->_body.push(n);
281 }
282 
283 //------------------------------small_cache------------------------------------
284 struct small_cache : public Dict {
285 
286   small_cache() : Dict( cmpkey, hashptr ) {}
287   Node *probe( Node *use_blk ) { return (Node*)((*this)[use_blk]); }
288   void lru_insert( Node *use_blk, Node *new_def ) { Insert(use_blk,new_def); }
289 };
290 
291 //------------------------------spinup-----------------------------------------
292 // "Spin up" the dominator tree, starting at the use site and stopping when we
293 // find the post-dominating point.
294 
295 // We must be at the merge point which post-dominates 'new_false' and
296 // 'new_true'.  Figure out which edges into the RegionNode eventually lead up
297 // to false and which to true.  Put in a PhiNode to merge values; plug in
298 // the appropriate false-arm or true-arm values.  If some path leads to the
299 // original IF, then insert a Phi recursively.
300 Node *PhaseIdealLoop::spinup( Node *iff_dom, Node *new_false, Node *new_true, Node *use_blk, Node *def, small_cache *cache ) {
301   if (use_blk->is_top())        // Handle dead uses
302     return use_blk;
303   Node *prior_n = (Node*)((intptr_t)0xdeadbeef);
304   Node *n = use_blk;            // Get path input
305   assert( use_blk != iff_dom, "" );
306   // Here's the "spinup" the dominator tree loop.  Do a cache-check
307   // along the way, in case we've come this way before.
308   while( n != iff_dom ) {       // Found post-dominating point?
309     prior_n = n;
310     n = idom(n);                // Search higher
311     Node *s = cache->probe( prior_n ); // Check cache
312     if( s ) return s;           // Cache hit!
313   }
314 
315   Node *phi_post;
316   if( prior_n == new_false || prior_n == new_true ) {
317     phi_post = def->clone();
318     phi_post->set_req(0, prior_n );
319     register_new_node(phi_post, prior_n);
320   } else {
321     // This method handles both control uses (looking for Regions) or data
322     // uses (looking for Phis).  If looking for a control use, then we need
323     // to insert a Region instead of a Phi; however Regions always exist
324     // previously (the hash_find_insert below would always hit) so we can
325     // return the existing Region.
326     if( def->is_CFG() ) {
327       phi_post = prior_n;       // If looking for CFG, return prior
328     } else {
329       assert( def->is_Phi(), "" );
330       assert( prior_n->is_Region(), "must be a post-dominating merge point" );
331 
332       // Need a Phi here
333       phi_post = PhiNode::make_blank(prior_n, def);
334       // Search for both true and false on all paths till find one.
335       for( uint i = 1; i < phi_post->req(); i++ ) // For all paths
336         phi_post->init_req( i, spinup( iff_dom, new_false, new_true, prior_n->in(i), def, cache ) );
337       Node *t = _igvn.hash_find_insert(phi_post);
338       if( t ) {                 // See if we already have this one
339         // phi_post will not be used, so kill it
340         _igvn.remove_dead_node(phi_post);
341         phi_post->destruct(&_igvn);
342         phi_post = t;
343       } else {
344         register_new_node( phi_post, prior_n );
345       }
346     }
347   }
348 
349   // Update cache everywhere
350   prior_n = (Node*)((intptr_t)0xdeadbeef);  // Reset IDOM walk
351   n = use_blk;                  // Get path input
352   // Spin-up the idom tree again, basically doing path-compression.
353   // Insert cache entries along the way, so that if we ever hit this
354   // point in the IDOM tree again we'll stop immediately on a cache hit.
355   while( n != iff_dom ) {       // Found post-dominating point?
356     prior_n = n;
357     n = idom(n);                // Search higher
358     cache->lru_insert( prior_n, phi_post ); // Fill cache
359   } // End of while not gone high enough
360 
361   return phi_post;
362 }
363 
364 //------------------------------find_use_block---------------------------------
365 // Find the block a USE is in.  Normally USE's are in the same block as the
366 // using instruction.  For Phi-USE's, the USE is in the predecessor block
367 // along the corresponding path.
368 Node *PhaseIdealLoop::find_use_block( Node *use, Node *def, Node *old_false, Node *new_false, Node *old_true, Node *new_true ) {
369   // CFG uses are their own block
370   if( use->is_CFG() )
371     return use;
372 
373   if( use->is_Phi() ) {         // Phi uses in prior block
374     // Grab the first Phi use; there may be many.
375     // Each will be handled as a separate iteration of
376     // the "while( phi->outcnt() )" loop.
377     uint j;
378     for( j = 1; j < use->req(); j++ )
379       if( use->in(j) == def )
380         break;
381     assert( j < use->req(), "def should be among use's inputs" );
382     return use->in(0)->in(j);
383   }
384   // Normal (non-phi) use
385   Node *use_blk = get_ctrl(use);
386   // Some uses are directly attached to the old (and going away)
387   // false and true branches.
388   if( use_blk == old_false ) {
389     use_blk = new_false;
390     set_ctrl(use, new_false);
391   }
392   if( use_blk == old_true ) {
393     use_blk = new_true;
394     set_ctrl(use, new_true);
395   }
396 
397   if (use_blk == NULL) {        // He's dead, Jim
398     _igvn.replace_node(use, C->top());
399   }
400 
401   return use_blk;
402 }
403 
404 //------------------------------handle_use-------------------------------------
405 // Handle uses of the merge point.  Basically, split-if makes the merge point
406 // go away so all uses of the merge point must go away as well.  Most block
407 // local uses have already been split-up, through the merge point.  Uses from
408 // far below the merge point can't always be split up (e.g., phi-uses are
409 // pinned) and it makes too much stuff live.  Instead we use a path-based
410 // solution to move uses down.
411 //
412 // If the use is along the pre-split-CFG true branch, then the new use will
413 // be from the post-split-CFG true merge point.  Vice-versa for the false
414 // path.  Some uses will be along both paths; then we sink the use to the
415 // post-dominating location; we may need to insert a Phi there.
416 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 ) {
417 
418   Node *use_blk = find_use_block(use,def,old_false,new_false,old_true,new_true);
419   if( !use_blk ) return;        // He's dead, Jim
420 
421   // Walk up the dominator tree until I hit either the old IfFalse, the old
422   // IfTrue or the old If.  Insert Phis where needed.
423   Node *new_def = spinup( region_dom, new_false, new_true, use_blk, def, cache );
424 
425   // Found where this USE goes.  Re-point him.
426   uint i;
427   for( i = 0; i < use->req(); i++ )
428     if( use->in(i) == def )
429       break;
430   assert( i < use->req(), "def should be among use's inputs" );
431   _igvn.replace_input_of(use, i, new_def);
432 }
433 
434 //------------------------------do_split_if------------------------------------
435 // Found an If getting its condition-code input from a Phi in the same block.
436 // Split thru the Region.
437 void PhaseIdealLoop::do_split_if( Node *iff ) {
438   if (PrintOpto && VerifyLoopOptimizations) {
439     tty->print_cr("Split-if");
440   }
441   if (TraceLoopOpts) {
442     tty->print_cr("SplitIf");
443   }
444 
445   C->set_major_progress();
446   Node *region = iff->in(0);
447   Node *region_dom = idom(region);
448 
449   // We are going to clone this test (and the control flow with it) up through
450   // the incoming merge point.  We need to empty the current basic block.
451   // Clone any instructions which must be in this block up through the merge
452   // point.
453   DUIterator i, j;
454   bool progress = true;
455   while (progress) {
456     progress = false;
457     for (i = region->outs(); region->has_out(i); i++) {
458       Node* n = region->out(i);
459       if( n == region ) continue;
460       // The IF to be split is OK.
461       if( n == iff ) continue;
462       if( !n->is_Phi() ) {      // Found pinned memory op or such
463         if (split_up(n, region, iff)) {
464           i = region->refresh_out_pos(i);
465           progress = true;
466         }
467         continue;
468       }
469       assert( n->in(0) == region, "" );
470 
471       // Recursively split up all users of a Phi
472       for (j = n->outs(); n->has_out(j); j++) {
473         Node* m = n->out(j);
474         // If m is dead, throw it away, and declare progress
475         if (_nodes[m->_idx] == NULL) {
476           _igvn.remove_dead_node(m);
477           // fall through
478         } else if (m != iff && split_up(m, region, iff)) {

479           // fall through
480         } else {
481           continue;
482         }
483         // Something unpredictable changed.
484         // Tell the iterators to refresh themselves, and rerun the loop.
485         i = region->refresh_out_pos(i);
486         j = region->refresh_out_pos(j);
487         progress = true;
488       }
489     }
490   }
491 
492   // Now we have no instructions in the block containing the IF.
493   // Split the IF.
494   Node *new_iff = split_thru_region( iff, region );
495 
496   // Replace both uses of 'new_iff' with Regions merging True/False
497   // paths.  This makes 'new_iff' go dead.
498   Node *old_false = NULL, *old_true = NULL;
499   Node *new_false = NULL, *new_true = NULL;
500   for (DUIterator_Last j2min, j2 = iff->last_outs(j2min); j2 >= j2min; --j2) {
501     Node *ifp = iff->last_out(j2);
502     assert( ifp->Opcode() == Op_IfFalse || ifp->Opcode() == Op_IfTrue, "" );
503     ifp->set_req(0, new_iff);
504     Node *ifpx = split_thru_region( ifp, region );
505 
506     // Replace 'If' projection of a Region with a Region of
507     // 'If' projections.
508     ifpx->set_req(0, ifpx);       // A TRUE RegionNode
509 
510     // Setup dominator info
511     set_idom(ifpx, region_dom, dom_depth(region_dom) + 1);
512 
513     // Check for splitting loop tails
514     if( get_loop(iff)->tail() == ifp )
515       get_loop(iff)->_tail = ifpx;
516 
517     // Replace in the graph with lazy-update mechanism
518     new_iff->set_req(0, new_iff); // hook self so it does not go dead
519     lazy_replace(ifp, ifpx);
520     new_iff->set_req(0, region);
521 
522     // Record bits for later xforms
523     if( ifp->Opcode() == Op_IfFalse ) {
524       old_false = ifp;
525       new_false = ifpx;
526     } else {
527       old_true = ifp;
528       new_true = ifpx;
529     }
530   }
531   _igvn.remove_dead_node(new_iff);
532   // Lazy replace IDOM info with the region's dominator
533   lazy_replace(iff, region_dom);
534   lazy_update(region, region_dom); // idom must be update before handle_uses
535   region->set_req(0, NULL);        // Break the self-cycle. Required for lazy_update to work on region
536 
537   // Now make the original merge point go dead, by handling all its uses.
538   small_cache region_cache;
539   // Preload some control flow in region-cache
540   region_cache.lru_insert( new_false, new_false );
541   region_cache.lru_insert( new_true , new_true  );
542   // Now handle all uses of the splitting block
543   for (DUIterator k = region->outs(); region->has_out(k); k++) {
544     Node* phi = region->out(k);
545     if (!phi->in(0)) {         // Dead phi?  Remove it
546       _igvn.remove_dead_node(phi);
547     } else if (phi == region) { // Found the self-reference
548       continue;                 // No roll-back of DUIterator
549     } else if (phi->is_Phi()) { // Expected common case: Phi hanging off of Region
550       assert(phi->in(0) == region, "Inconsistent graph");
551       // Need a per-def cache.  Phi represents a def, so make a cache
552       small_cache phi_cache;
553 
554       // Inspect all Phi uses to make the Phi go dead
555       for (DUIterator_Last lmin, l = phi->last_outs(lmin); l >= lmin; --l) {
556         Node* use = phi->last_out(l);
557         // Compute the new DEF for this USE.  New DEF depends on the path
558         // taken from the original DEF to the USE.  The new DEF may be some
559         // collection of PHI's merging values from different paths.  The Phis
560         // inserted depend only on the location of the USE.  We use a
561         // 2-element cache to handle multiple uses from the same block.
562         handle_use(use, phi, &phi_cache, region_dom, new_false, new_true, old_false, old_true);
563       } // End of while phi has uses
564       // Remove the dead Phi
565       _igvn.remove_dead_node( phi );
566     } else {
567       assert(phi->in(0) == region, "Inconsistent graph");
568       // Random memory op guarded by Region.  Compute new DEF for USE.
569       handle_use(phi, region, &region_cache, region_dom, new_false, new_true, old_false, old_true);
570     }
571     // Every path above deletes a use of the region, except for the region
572     // self-cycle (which is needed by handle_use calling find_use_block
573     // calling get_ctrl calling get_ctrl_no_update looking for dead
574     // regions).  So roll back the DUIterator innards.
575     --k;
576   } // End of while merge point has phis
577 
578   _igvn.remove_dead_node(region);
579 
580 #ifndef PRODUCT
581   if( VerifyLoopOptimizations ) verify();
582 #endif
583 }
--- EOF ---