1 /*
   2  * Copyright (c) 1997, 2013, 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 "classfile/systemDictionary.hpp"
  27 #include "memory/allocation.inline.hpp"
  28 #include "oops/objArrayKlass.hpp"
  29 #include "opto/addnode.hpp"
  30 #include "opto/cfgnode.hpp"
  31 #include "opto/connode.hpp"
  32 #include "opto/loopnode.hpp"
  33 #include "opto/machnode.hpp"
  34 #include "opto/mulnode.hpp"
  35 #include "opto/phaseX.hpp"
  36 #include "opto/regmask.hpp"
  37 #include "opto/runtime.hpp"
  38 #include "opto/subnode.hpp"
  39 #if INCLUDE_ALL_GCS
  40 #include "gc_implementation/shenandoah/c2/shenandoahBarrierSetC2.hpp"
  41 #include "gc_implementation/shenandoah/c2/shenandoahSupport.hpp"
  42 #endif
  43 
  44 // Portions of code courtesy of Clifford Click
  45 
  46 // Optimization - Graph Style
  47 
  48 //=============================================================================
  49 //------------------------------Value------------------------------------------
  50 // Compute the type of the RegionNode.
  51 const Type *RegionNode::Value( PhaseTransform *phase ) const {
  52   for( uint i=1; i<req(); ++i ) {       // For all paths in
  53     Node *n = in(i);            // Get Control source
  54     if( !n ) continue;          // Missing inputs are TOP
  55     if( phase->type(n) == Type::CONTROL )
  56       return Type::CONTROL;
  57   }
  58   return Type::TOP;             // All paths dead?  Then so are we
  59 }
  60 
  61 //------------------------------Identity---------------------------------------
  62 // Check for Region being Identity.
  63 Node *RegionNode::Identity( PhaseTransform *phase ) {
  64   // Cannot have Region be an identity, even if it has only 1 input.
  65   // Phi users cannot have their Region input folded away for them,
  66   // since they need to select the proper data input
  67   return this;
  68 }
  69 
  70 //------------------------------merge_region-----------------------------------
  71 // If a Region flows into a Region, merge into one big happy merge.  This is
  72 // hard to do if there is stuff that has to happen
  73 static Node *merge_region(RegionNode *region, PhaseGVN *phase) {
  74   if( region->Opcode() != Op_Region ) // Do not do to LoopNodes
  75     return NULL;
  76   Node *progress = NULL;        // Progress flag
  77   PhaseIterGVN *igvn = phase->is_IterGVN();
  78 
  79   uint rreq = region->req();
  80   for( uint i = 1; i < rreq; i++ ) {
  81     Node *r = region->in(i);
  82     if( r && r->Opcode() == Op_Region && // Found a region?
  83         r->in(0) == r &&        // Not already collapsed?
  84         r != region &&          // Avoid stupid situations
  85         r->outcnt() == 2 ) {    // Self user and 'region' user only?
  86       assert(!r->as_Region()->has_phi(), "no phi users");
  87       if( !progress ) {         // No progress
  88         if (region->has_phi()) {
  89           return NULL;        // Only flatten if no Phi users
  90           // igvn->hash_delete( phi );
  91         }
  92         igvn->hash_delete( region );
  93         progress = region;      // Making progress
  94       }
  95       igvn->hash_delete( r );
  96 
  97       // Append inputs to 'r' onto 'region'
  98       for( uint j = 1; j < r->req(); j++ ) {
  99         // Move an input from 'r' to 'region'
 100         region->add_req(r->in(j));
 101         r->set_req(j, phase->C->top());
 102         // Update phis of 'region'
 103         //for( uint k = 0; k < max; k++ ) {
 104         //  Node *phi = region->out(k);
 105         //  if( phi->is_Phi() ) {
 106         //    phi->add_req(phi->in(i));
 107         //  }
 108         //}
 109 
 110         rreq++;                 // One more input to Region
 111       } // Found a region to merge into Region
 112       // Clobber pointer to the now dead 'r'
 113       region->set_req(i, phase->C->top());
 114     }
 115   }
 116 
 117   return progress;
 118 }
 119 
 120 
 121 
 122 //--------------------------------has_phi--------------------------------------
 123 // Helper function: Return any PhiNode that uses this region or NULL
 124 PhiNode* RegionNode::has_phi() const {
 125   for (DUIterator_Fast imax, i = fast_outs(imax); i < imax; i++) {
 126     Node* phi = fast_out(i);
 127     if (phi->is_Phi()) {   // Check for Phi users
 128       assert(phi->in(0) == (Node*)this, "phi uses region only via in(0)");
 129       return phi->as_Phi();  // this one is good enough
 130     }
 131   }
 132 
 133   return NULL;
 134 }
 135 
 136 
 137 //-----------------------------has_unique_phi----------------------------------
 138 // Helper function: Return the only PhiNode that uses this region or NULL
 139 PhiNode* RegionNode::has_unique_phi() const {
 140   // Check that only one use is a Phi
 141   PhiNode* only_phi = NULL;
 142   for (DUIterator_Fast imax, i = fast_outs(imax); i < imax; i++) {
 143     Node* phi = fast_out(i);
 144     if (phi->is_Phi()) {   // Check for Phi users
 145       assert(phi->in(0) == (Node*)this, "phi uses region only via in(0)");
 146       if (only_phi == NULL) {
 147         only_phi = phi->as_Phi();
 148       } else {
 149         return NULL;  // multiple phis
 150       }
 151     }
 152   }
 153 
 154   return only_phi;
 155 }
 156 
 157 
 158 //------------------------------check_phi_clipping-----------------------------
 159 // Helper function for RegionNode's identification of FP clipping
 160 // Check inputs to the Phi
 161 static bool check_phi_clipping( PhiNode *phi, ConNode * &min, uint &min_idx, ConNode * &max, uint &max_idx, Node * &val, uint &val_idx ) {
 162   min     = NULL;
 163   max     = NULL;
 164   val     = NULL;
 165   min_idx = 0;
 166   max_idx = 0;
 167   val_idx = 0;
 168   uint  phi_max = phi->req();
 169   if( phi_max == 4 ) {
 170     for( uint j = 1; j < phi_max; ++j ) {
 171       Node *n = phi->in(j);
 172       int opcode = n->Opcode();
 173       switch( opcode ) {
 174       case Op_ConI:
 175         {
 176           if( min == NULL ) {
 177             min     = n->Opcode() == Op_ConI ? (ConNode*)n : NULL;
 178             min_idx = j;
 179           } else {
 180             max     = n->Opcode() == Op_ConI ? (ConNode*)n : NULL;
 181             max_idx = j;
 182             if( min->get_int() > max->get_int() ) {
 183               // Swap min and max
 184               ConNode *temp;
 185               uint     temp_idx;
 186               temp     = min;     min     = max;     max     = temp;
 187               temp_idx = min_idx; min_idx = max_idx; max_idx = temp_idx;
 188             }
 189           }
 190         }
 191         break;
 192       default:
 193         {
 194           val = n;
 195           val_idx = j;
 196         }
 197         break;
 198       }
 199     }
 200   }
 201   return ( min && max && val && (min->get_int() <= 0) && (max->get_int() >=0) );
 202 }
 203 
 204 
 205 //------------------------------check_if_clipping------------------------------
 206 // Helper function for RegionNode's identification of FP clipping
 207 // Check that inputs to Region come from two IfNodes,
 208 //
 209 //            If
 210 //      False    True
 211 //       If        |
 212 //  False  True    |
 213 //    |      |     |
 214 //  RegionNode_inputs
 215 //
 216 static bool check_if_clipping( const RegionNode *region, IfNode * &bot_if, IfNode * &top_if ) {
 217   top_if = NULL;
 218   bot_if = NULL;
 219 
 220   // Check control structure above RegionNode for (if  ( if  ) )
 221   Node *in1 = region->in(1);
 222   Node *in2 = region->in(2);
 223   Node *in3 = region->in(3);
 224   // Check that all inputs are projections
 225   if( in1->is_Proj() && in2->is_Proj() && in3->is_Proj() ) {
 226     Node *in10 = in1->in(0);
 227     Node *in20 = in2->in(0);
 228     Node *in30 = in3->in(0);
 229     // Check that #1 and #2 are ifTrue and ifFalse from same If
 230     if( in10 != NULL && in10->is_If() &&
 231         in20 != NULL && in20->is_If() &&
 232         in30 != NULL && in30->is_If() && in10 == in20 &&
 233         (in1->Opcode() != in2->Opcode()) ) {
 234       Node  *in100 = in10->in(0);
 235       Node *in1000 = (in100 != NULL && in100->is_Proj()) ? in100->in(0) : NULL;
 236       // Check that control for in10 comes from other branch of IF from in3
 237       if( in1000 != NULL && in1000->is_If() &&
 238           in30 == in1000 && (in3->Opcode() != in100->Opcode()) ) {
 239         // Control pattern checks
 240         top_if = (IfNode*)in1000;
 241         bot_if = (IfNode*)in10;
 242       }
 243     }
 244   }
 245 
 246   return (top_if != NULL);
 247 }
 248 
 249 
 250 //------------------------------check_convf2i_clipping-------------------------
 251 // Helper function for RegionNode's identification of FP clipping
 252 // Verify that the value input to the phi comes from "ConvF2I; LShift; RShift"
 253 static bool check_convf2i_clipping( PhiNode *phi, uint idx, ConvF2INode * &convf2i, Node *min, Node *max) {
 254   convf2i = NULL;
 255 
 256   // Check for the RShiftNode
 257   Node *rshift = phi->in(idx);
 258   assert( rshift, "Previous checks ensure phi input is present");
 259   if( rshift->Opcode() != Op_RShiftI )  { return false; }
 260 
 261   // Check for the LShiftNode
 262   Node *lshift = rshift->in(1);
 263   assert( lshift, "Previous checks ensure phi input is present");
 264   if( lshift->Opcode() != Op_LShiftI )  { return false; }
 265 
 266   // Check for the ConvF2INode
 267   Node *conv = lshift->in(1);
 268   if( conv->Opcode() != Op_ConvF2I ) { return false; }
 269 
 270   // Check that shift amounts are only to get sign bits set after F2I
 271   jint max_cutoff     = max->get_int();
 272   jint min_cutoff     = min->get_int();
 273   jint left_shift     = lshift->in(2)->get_int();
 274   jint right_shift    = rshift->in(2)->get_int();
 275   jint max_post_shift = nth_bit(BitsPerJavaInteger - left_shift - 1);
 276   if( left_shift != right_shift ||
 277       0 > left_shift || left_shift >= BitsPerJavaInteger ||
 278       max_post_shift < max_cutoff ||
 279       max_post_shift < -min_cutoff ) {
 280     // Shifts are necessary but current transformation eliminates them
 281     return false;
 282   }
 283 
 284   // OK to return the result of ConvF2I without shifting
 285   convf2i = (ConvF2INode*)conv;
 286   return true;
 287 }
 288 
 289 
 290 //------------------------------check_compare_clipping-------------------------
 291 // Helper function for RegionNode's identification of FP clipping
 292 static bool check_compare_clipping( bool less_than, IfNode *iff, ConNode *limit, Node * & input ) {
 293   Node *i1 = iff->in(1);
 294   if ( !i1->is_Bool() ) { return false; }
 295   BoolNode *bool1 = i1->as_Bool();
 296   if(       less_than && bool1->_test._test != BoolTest::le ) { return false; }
 297   else if( !less_than && bool1->_test._test != BoolTest::lt ) { return false; }
 298   const Node *cmpF = bool1->in(1);
 299   if( cmpF->Opcode() != Op_CmpF )      { return false; }
 300   // Test that the float value being compared against
 301   // is equivalent to the int value used as a limit
 302   Node *nodef = cmpF->in(2);
 303   if( nodef->Opcode() != Op_ConF ) { return false; }
 304   jfloat conf = nodef->getf();
 305   jint   coni = limit->get_int();
 306   if( ((int)conf) != coni )        { return false; }
 307   input = cmpF->in(1);
 308   return true;
 309 }
 310 
 311 //------------------------------is_unreachable_region--------------------------
 312 // Find if the Region node is reachable from the root.
 313 bool RegionNode::is_unreachable_region(PhaseGVN *phase) const {
 314   assert(req() == 2, "");
 315 
 316   // First, cut the simple case of fallthrough region when NONE of
 317   // region's phis references itself directly or through a data node.
 318   uint max = outcnt();
 319   uint i;
 320   for (i = 0; i < max; i++) {
 321     Node* phi = raw_out(i);
 322     if (phi != NULL && phi->is_Phi()) {
 323       assert(phase->eqv(phi->in(0), this) && phi->req() == 2, "");
 324       if (phi->outcnt() == 0)
 325         continue; // Safe case - no loops
 326       if (phi->outcnt() == 1) {
 327         Node* u = phi->raw_out(0);
 328         // Skip if only one use is an other Phi or Call or Uncommon trap.
 329         // It is safe to consider this case as fallthrough.
 330         if (u != NULL && (u->is_Phi() || u->is_CFG()))
 331           continue;
 332       }
 333       // Check when phi references itself directly or through an other node.
 334       if (phi->as_Phi()->simple_data_loop_check(phi->in(1)) >= PhiNode::Unsafe)
 335         break; // Found possible unsafe data loop.
 336     }
 337   }
 338   if (i >= max)
 339     return false; // An unsafe case was NOT found - don't need graph walk.
 340 
 341   // Unsafe case - check if the Region node is reachable from root.
 342   ResourceMark rm;
 343 
 344   Arena *a = Thread::current()->resource_area();
 345   Node_List nstack(a);
 346   VectorSet visited(a);
 347 
 348   // Mark all control nodes reachable from root outputs
 349   Node *n = (Node*)phase->C->root();
 350   nstack.push(n);
 351   visited.set(n->_idx);
 352   while (nstack.size() != 0) {
 353     n = nstack.pop();
 354     uint max = n->outcnt();
 355     for (uint i = 0; i < max; i++) {
 356       Node* m = n->raw_out(i);
 357       if (m != NULL && m->is_CFG()) {
 358         if (phase->eqv(m, this)) {
 359           return false; // We reached the Region node - it is not dead.
 360         }
 361         if (!visited.test_set(m->_idx))
 362           nstack.push(m);
 363       }
 364     }
 365   }
 366 
 367   return true; // The Region node is unreachable - it is dead.
 368 }
 369 
 370 bool RegionNode::try_clean_mem_phi(PhaseGVN *phase) {
 371   // Incremental inlining + PhaseStringOpts sometimes produce:
 372   //
 373   // cmpP with 1 top input
 374   //           |
 375   //          If
 376   //         /  \
 377   //   IfFalse  IfTrue  /- Some Node
 378   //         \  /      /    /
 379   //        Region    / /-MergeMem
 380   //             \---Phi
 381   //
 382   //
 383   // It's expected by PhaseStringOpts that the Region goes away and is
 384   // replaced by If's control input but because there's still a Phi,
 385   // the Region stays in the graph. The top input from the cmpP is
 386   // propagated forward and a subgraph that is useful goes away. The
 387   // code below replaces the Phi with the MergeMem so that the Region
 388   // is simplified.
 389 
 390   PhiNode* phi = has_unique_phi();
 391   if (phi && phi->type() == Type::MEMORY && req() == 3 && phi->is_diamond_phi(true)) {
 392     MergeMemNode* m = NULL;
 393     assert(phi->req() == 3, "same as region");
 394     for (uint i = 1; i < 3; ++i) {
 395       Node *mem = phi->in(i);
 396       if (mem && mem->is_MergeMem() && in(i)->outcnt() == 1) {
 397         // Nothing is control-dependent on path #i except the region itself.
 398         m = mem->as_MergeMem();
 399         uint j = 3 - i;
 400         Node* other = phi->in(j);
 401         if (other && other == m->base_memory()) {
 402           // m is a successor memory to other, and is not pinned inside the diamond, so push it out.
 403           // This will allow the diamond to collapse completely.
 404           phase->is_IterGVN()->replace_node(phi, m);
 405           return true;
 406         }
 407       }
 408     }
 409   }
 410   return false;
 411 }
 412 
 413 //------------------------------Ideal------------------------------------------
 414 // Return a node which is more "ideal" than the current node.  Must preserve
 415 // the CFG, but we can still strip out dead paths.
 416 Node *RegionNode::Ideal(PhaseGVN *phase, bool can_reshape) {
 417   if( !can_reshape && !in(0) ) return NULL;     // Already degraded to a Copy
 418   assert(!in(0) || !in(0)->is_Root(), "not a specially hidden merge");
 419 
 420   // Check for RegionNode with no Phi users and both inputs come from either
 421   // arm of the same IF.  If found, then the control-flow split is useless.
 422   bool has_phis = false;
 423   if (can_reshape) {            // Need DU info to check for Phi users
 424     has_phis = (has_phi() != NULL);       // Cache result
 425     if (has_phis && try_clean_mem_phi(phase)) {
 426       has_phis = false;
 427     }
 428 
 429     if (!has_phis) {            // No Phi users?  Nothing merging?
 430       for (uint i = 1; i < req()-1; i++) {
 431         Node *if1 = in(i);
 432         if( !if1 ) continue;
 433         Node *iff = if1->in(0);
 434         if( !iff || !iff->is_If() ) continue;
 435         for( uint j=i+1; j<req(); j++ ) {
 436           if( in(j) && in(j)->in(0) == iff &&
 437               if1->Opcode() != in(j)->Opcode() ) {
 438             // Add the IF Projections to the worklist. They (and the IF itself)
 439             // will be eliminated if dead.
 440             phase->is_IterGVN()->add_users_to_worklist(iff);
 441             set_req(i, iff->in(0));// Skip around the useless IF diamond
 442             set_req(j, NULL);
 443             return this;      // Record progress
 444           }
 445         }
 446       }
 447     }
 448   }
 449 
 450   // Remove TOP or NULL input paths. If only 1 input path remains, this Region
 451   // degrades to a copy.
 452   bool add_to_worklist = false;
 453   int cnt = 0;                  // Count of values merging
 454   DEBUG_ONLY( int cnt_orig = req(); ) // Save original inputs count
 455   int del_it = 0;               // The last input path we delete
 456   // For all inputs...
 457   for( uint i=1; i<req(); ++i ){// For all paths in
 458     Node *n = in(i);            // Get the input
 459     if( n != NULL ) {
 460       // Remove useless control copy inputs
 461       if( n->is_Region() && n->as_Region()->is_copy() ) {
 462         set_req(i, n->nonnull_req());
 463         i--;
 464         continue;
 465       }
 466       if( n->is_Proj() ) {      // Remove useless rethrows
 467         Node *call = n->in(0);
 468         if (call->is_Call() && call->as_Call()->entry_point() == OptoRuntime::rethrow_stub()) {
 469           set_req(i, call->in(0));
 470           i--;
 471           continue;
 472         }
 473       }
 474       if( phase->type(n) == Type::TOP ) {
 475         set_req(i, NULL);       // Ignore TOP inputs
 476         i--;
 477         continue;
 478       }
 479       cnt++;                    // One more value merging
 480 
 481     } else if (can_reshape) {   // Else found dead path with DU info
 482       PhaseIterGVN *igvn = phase->is_IterGVN();
 483       del_req(i);               // Yank path from self
 484       del_it = i;
 485       uint max = outcnt();
 486       DUIterator j;
 487       bool progress = true;
 488       while(progress) {         // Need to establish property over all users
 489         progress = false;
 490         for (j = outs(); has_out(j); j++) {
 491           Node *n = out(j);
 492           if( n->req() != req() && n->is_Phi() ) {
 493             assert( n->in(0) == this, "" );
 494             igvn->hash_delete(n); // Yank from hash before hacking edges
 495             n->set_req_X(i,NULL,igvn);// Correct DU info
 496             n->del_req(i);        // Yank path from Phis
 497             if( max != outcnt() ) {
 498               progress = true;
 499               j = refresh_out_pos(j);
 500               max = outcnt();
 501             }
 502           }
 503         }
 504       }
 505       add_to_worklist = true;
 506       i--;
 507     }
 508   }
 509 
 510   if (can_reshape && cnt == 1) {
 511     // Is it dead loop?
 512     // If it is LoopNopde it had 2 (+1 itself) inputs and
 513     // one of them was cut. The loop is dead if it was EntryContol.
 514     // Loop node may have only one input because entry path
 515     // is removed in PhaseIdealLoop::Dominators().
 516     assert(!this->is_Loop() || cnt_orig <= 3, "Loop node should have 3 or less inputs");
 517     if (this->is_Loop() && (del_it == LoopNode::EntryControl ||
 518                             del_it == 0 && is_unreachable_region(phase)) ||
 519        !this->is_Loop() && has_phis && is_unreachable_region(phase)) {
 520       // Yes,  the region will be removed during the next step below.
 521       // Cut the backedge input and remove phis since no data paths left.
 522       // We don't cut outputs to other nodes here since we need to put them
 523       // on the worklist.
 524       del_req(1);
 525       cnt = 0;
 526       assert( req() == 1, "no more inputs expected" );
 527       uint max = outcnt();
 528       bool progress = true;
 529       Node *top = phase->C->top();
 530       PhaseIterGVN *igvn = phase->is_IterGVN();
 531       DUIterator j;
 532       while(progress) {
 533         progress = false;
 534         for (j = outs(); has_out(j); j++) {
 535           Node *n = out(j);
 536           if( n->is_Phi() ) {
 537             assert( igvn->eqv(n->in(0), this), "" );
 538             assert( n->req() == 2 &&  n->in(1) != NULL, "Only one data input expected" );
 539             // Break dead loop data path.
 540             // Eagerly replace phis with top to avoid phis copies generation.
 541             igvn->replace_node(n, top);
 542             if( max != outcnt() ) {
 543               progress = true;
 544               j = refresh_out_pos(j);
 545               max = outcnt();
 546             }
 547           }
 548         }
 549       }
 550       add_to_worklist = true;
 551     }
 552   }
 553   if (add_to_worklist) {
 554     phase->is_IterGVN()->add_users_to_worklist(this); // Revisit collapsed Phis
 555   }
 556 
 557   if( cnt <= 1 ) {              // Only 1 path in?
 558     set_req(0, NULL);           // Null control input for region copy
 559     if( cnt == 0 && !can_reshape) { // Parse phase - leave the node as it is.
 560       // No inputs or all inputs are NULL.
 561       return NULL;
 562     } else if (can_reshape) {   // Optimization phase - remove the node
 563       PhaseIterGVN *igvn = phase->is_IterGVN();
 564       Node *parent_ctrl;
 565       if( cnt == 0 ) {
 566         assert( req() == 1, "no inputs expected" );
 567         // During IGVN phase such region will be subsumed by TOP node
 568         // so region's phis will have TOP as control node.
 569         // Kill phis here to avoid it. PhiNode::is_copy() will be always false.
 570         // Also set other user's input to top.
 571         parent_ctrl = phase->C->top();
 572       } else {
 573         // The fallthrough case since we already checked dead loops above.
 574         parent_ctrl = in(1);
 575         assert(parent_ctrl != NULL, "Region is a copy of some non-null control");
 576         assert(!igvn->eqv(parent_ctrl, this), "Close dead loop");
 577       }
 578       if (!add_to_worklist)
 579         igvn->add_users_to_worklist(this); // Check for further allowed opts
 580       for (DUIterator_Last imin, i = last_outs(imin); i >= imin; --i) {
 581         Node* n = last_out(i);
 582         igvn->hash_delete(n); // Remove from worklist before modifying edges
 583         if( n->is_Phi() ) {   // Collapse all Phis
 584           // Eagerly replace phis to avoid copies generation.
 585           Node* in;
 586           if( cnt == 0 ) {
 587             assert( n->req() == 1, "No data inputs expected" );
 588             in = parent_ctrl; // replaced by top
 589           } else {
 590             assert( n->req() == 2 &&  n->in(1) != NULL, "Only one data input expected" );
 591             in = n->in(1);               // replaced by unique input
 592             if( n->as_Phi()->is_unsafe_data_reference(in) )
 593               in = phase->C->top();      // replaced by top
 594           }
 595           if (n->outcnt() == 0) {
 596             in = phase->C->top();
 597           }
 598           igvn->replace_node(n, in);
 599         }
 600         else if( n->is_Region() ) { // Update all incoming edges
 601           assert( !igvn->eqv(n, this), "Must be removed from DefUse edges");
 602           uint uses_found = 0;
 603           for( uint k=1; k < n->req(); k++ ) {
 604             if( n->in(k) == this ) {
 605               n->set_req(k, parent_ctrl);
 606               uses_found++;
 607             }
 608           }
 609           if( uses_found > 1 ) { // (--i) done at the end of the loop.
 610             i -= (uses_found - 1);
 611           }
 612         }
 613         else {
 614           assert( igvn->eqv(n->in(0), this), "Expect RegionNode to be control parent");
 615           n->set_req(0, parent_ctrl);
 616         }
 617 #ifdef ASSERT
 618         for( uint k=0; k < n->req(); k++ ) {
 619           assert( !igvn->eqv(n->in(k), this), "All uses of RegionNode should be gone");
 620         }
 621 #endif
 622       }
 623       // Remove the RegionNode itself from DefUse info
 624       igvn->remove_dead_node(this);
 625       return NULL;
 626     }
 627     return this;                // Record progress
 628   }
 629 
 630 
 631   // If a Region flows into a Region, merge into one big happy merge.
 632   if (can_reshape) {
 633     Node *m = merge_region(this, phase);
 634     if (m != NULL)  return m;
 635   }
 636 
 637   // Check if this region is the root of a clipping idiom on floats
 638   if( ConvertFloat2IntClipping && can_reshape && req() == 4 ) {
 639     // Check that only one use is a Phi and that it simplifies to two constants +
 640     PhiNode* phi = has_unique_phi();
 641     if (phi != NULL) {          // One Phi user
 642       // Check inputs to the Phi
 643       ConNode *min;
 644       ConNode *max;
 645       Node    *val;
 646       uint     min_idx;
 647       uint     max_idx;
 648       uint     val_idx;
 649       if( check_phi_clipping( phi, min, min_idx, max, max_idx, val, val_idx )  ) {
 650         IfNode *top_if;
 651         IfNode *bot_if;
 652         if( check_if_clipping( this, bot_if, top_if ) ) {
 653           // Control pattern checks, now verify compares
 654           Node   *top_in = NULL;   // value being compared against
 655           Node   *bot_in = NULL;
 656           if( check_compare_clipping( true,  bot_if, min, bot_in ) &&
 657               check_compare_clipping( false, top_if, max, top_in ) ) {
 658             if( bot_in == top_in ) {
 659               PhaseIterGVN *gvn = phase->is_IterGVN();
 660               assert( gvn != NULL, "Only had DefUse info in IterGVN");
 661               // Only remaining check is that bot_in == top_in == (Phi's val + mods)
 662 
 663               // Check for the ConvF2INode
 664               ConvF2INode *convf2i;
 665               if( check_convf2i_clipping( phi, val_idx, convf2i, min, max ) &&
 666                 convf2i->in(1) == bot_in ) {
 667                 // Matched pattern, including LShiftI; RShiftI, replace with integer compares
 668                 // max test
 669                 Node *cmp   = gvn->register_new_node_with_optimizer(new (phase->C) CmpINode( convf2i, min ));
 670                 Node *boo   = gvn->register_new_node_with_optimizer(new (phase->C) BoolNode( cmp, BoolTest::lt ));
 671                 IfNode *iff = (IfNode*)gvn->register_new_node_with_optimizer(new (phase->C) IfNode( top_if->in(0), boo, PROB_UNLIKELY_MAG(5), top_if->_fcnt ));
 672                 Node *if_min= gvn->register_new_node_with_optimizer(new (phase->C) IfTrueNode (iff));
 673                 Node *ifF   = gvn->register_new_node_with_optimizer(new (phase->C) IfFalseNode(iff));
 674                 // min test
 675                 cmp         = gvn->register_new_node_with_optimizer(new (phase->C) CmpINode( convf2i, max ));
 676                 boo         = gvn->register_new_node_with_optimizer(new (phase->C) BoolNode( cmp, BoolTest::gt ));
 677                 iff         = (IfNode*)gvn->register_new_node_with_optimizer(new (phase->C) IfNode( ifF, boo, PROB_UNLIKELY_MAG(5), bot_if->_fcnt ));
 678                 Node *if_max= gvn->register_new_node_with_optimizer(new (phase->C) IfTrueNode (iff));
 679                 ifF         = gvn->register_new_node_with_optimizer(new (phase->C) IfFalseNode(iff));
 680                 // update input edges to region node
 681                 set_req_X( min_idx, if_min, gvn );
 682                 set_req_X( max_idx, if_max, gvn );
 683                 set_req_X( val_idx, ifF,    gvn );
 684                 // remove unnecessary 'LShiftI; RShiftI' idiom
 685                 gvn->hash_delete(phi);
 686                 phi->set_req_X( val_idx, convf2i, gvn );
 687                 gvn->hash_find_insert(phi);
 688                 // Return transformed region node
 689                 return this;
 690               }
 691             }
 692           }
 693         }
 694       }
 695     }
 696   }
 697 
 698   return NULL;
 699 }
 700 
 701 
 702 
 703 const RegMask &RegionNode::out_RegMask() const {
 704   return RegMask::Empty;
 705 }
 706 
 707 // Find the one non-null required input.  RegionNode only
 708 Node *Node::nonnull_req() const {
 709   assert( is_Region(), "" );
 710   for( uint i = 1; i < _cnt; i++ )
 711     if( in(i) )
 712       return in(i);
 713   ShouldNotReachHere();
 714   return NULL;
 715 }
 716 
 717 
 718 //=============================================================================
 719 // note that these functions assume that the _adr_type field is flattened
 720 uint PhiNode::hash() const {
 721   const Type* at = _adr_type;
 722   return TypeNode::hash() + (at ? at->hash() : 0);
 723 }
 724 uint PhiNode::cmp( const Node &n ) const {
 725   return TypeNode::cmp(n) && _adr_type == ((PhiNode&)n)._adr_type;
 726 }
 727 static inline
 728 const TypePtr* flatten_phi_adr_type(const TypePtr* at) {
 729   if (at == NULL || at == TypePtr::BOTTOM)  return at;
 730   return Compile::current()->alias_type(at)->adr_type();
 731 }
 732 
 733 //----------------------------make---------------------------------------------
 734 // create a new phi with edges matching r and set (initially) to x
 735 PhiNode* PhiNode::make(Node* r, Node* x, const Type *t, const TypePtr* at) {
 736   uint preds = r->req();   // Number of predecessor paths
 737   assert(t != Type::MEMORY || at == flatten_phi_adr_type(at), "flatten at");
 738   PhiNode* p = new (Compile::current()) PhiNode(r, t, at);
 739   for (uint j = 1; j < preds; j++) {
 740     // Fill in all inputs, except those which the region does not yet have
 741     if (r->in(j) != NULL)
 742       p->init_req(j, x);
 743   }
 744   return p;
 745 }
 746 PhiNode* PhiNode::make(Node* r, Node* x) {
 747   const Type*    t  = x->bottom_type();
 748   const TypePtr* at = NULL;
 749   if (t == Type::MEMORY)  at = flatten_phi_adr_type(x->adr_type());
 750   return make(r, x, t, at);
 751 }
 752 PhiNode* PhiNode::make_blank(Node* r, Node* x) {
 753   const Type*    t  = x->bottom_type();
 754   const TypePtr* at = NULL;
 755   if (t == Type::MEMORY)  at = flatten_phi_adr_type(x->adr_type());
 756   return new (Compile::current()) PhiNode(r, t, at);
 757 }
 758 
 759 
 760 //------------------------slice_memory-----------------------------------------
 761 // create a new phi with narrowed memory type
 762 PhiNode* PhiNode::slice_memory(const TypePtr* adr_type) const {
 763   PhiNode* mem = (PhiNode*) clone();
 764   *(const TypePtr**)&mem->_adr_type = adr_type;
 765   // convert self-loops, or else we get a bad graph
 766   for (uint i = 1; i < req(); i++) {
 767     if ((const Node*)in(i) == this)  mem->set_req(i, mem);
 768   }
 769   mem->verify_adr_type();
 770   return mem;
 771 }
 772 
 773 //------------------------split_out_instance-----------------------------------
 774 // Split out an instance type from a bottom phi.
 775 PhiNode* PhiNode::split_out_instance(const TypePtr* at, PhaseIterGVN *igvn) const {
 776   const TypeOopPtr *t_oop = at->isa_oopptr();
 777   assert(t_oop != NULL && t_oop->is_known_instance(), "expecting instance oopptr");
 778   const TypePtr *t = adr_type();
 779   assert(type() == Type::MEMORY &&
 780          (t == TypePtr::BOTTOM || t == TypeRawPtr::BOTTOM ||
 781           t->isa_oopptr() && !t->is_oopptr()->is_known_instance() &&
 782           t->is_oopptr()->cast_to_exactness(true)
 783            ->is_oopptr()->cast_to_ptr_type(t_oop->ptr())
 784            ->is_oopptr()->cast_to_instance_id(t_oop->instance_id()) == t_oop),
 785          "bottom or raw memory required");
 786 
 787   // Check if an appropriate node already exists.
 788   Node *region = in(0);
 789   for (DUIterator_Fast kmax, k = region->fast_outs(kmax); k < kmax; k++) {
 790     Node* use = region->fast_out(k);
 791     if( use->is_Phi()) {
 792       PhiNode *phi2 = use->as_Phi();
 793       if (phi2->type() == Type::MEMORY && phi2->adr_type() == at) {
 794         return phi2;
 795       }
 796     }
 797   }
 798   Compile *C = igvn->C;
 799   Arena *a = Thread::current()->resource_area();
 800   Node_Array node_map = new Node_Array(a);
 801   Node_Stack stack(a, C->live_nodes() >> 4);
 802   PhiNode *nphi = slice_memory(at);
 803   igvn->register_new_node_with_optimizer( nphi );
 804   node_map.map(_idx, nphi);
 805   stack.push((Node *)this, 1);
 806   while(!stack.is_empty()) {
 807     PhiNode *ophi = stack.node()->as_Phi();
 808     uint i = stack.index();
 809     assert(i >= 1, "not control edge");
 810     stack.pop();
 811     nphi = node_map[ophi->_idx]->as_Phi();
 812     for (; i < ophi->req(); i++) {
 813       Node *in = ophi->in(i);
 814       if (in == NULL || igvn->type(in) == Type::TOP)
 815         continue;
 816       Node *opt = MemNode::optimize_simple_memory_chain(in, t_oop, NULL, igvn);
 817       PhiNode *optphi = opt->is_Phi() ? opt->as_Phi() : NULL;
 818       if (optphi != NULL && optphi->adr_type() == TypePtr::BOTTOM) {
 819         opt = node_map[optphi->_idx];
 820         if (opt == NULL) {
 821           stack.push(ophi, i);
 822           nphi = optphi->slice_memory(at);
 823           igvn->register_new_node_with_optimizer( nphi );
 824           node_map.map(optphi->_idx, nphi);
 825           ophi = optphi;
 826           i = 0; // will get incremented at top of loop
 827           continue;
 828         }
 829       }
 830       nphi->set_req(i, opt);
 831     }
 832   }
 833   return nphi;
 834 }
 835 
 836 //------------------------verify_adr_type--------------------------------------
 837 #ifdef ASSERT
 838 void PhiNode::verify_adr_type(VectorSet& visited, const TypePtr* at) const {
 839   if (visited.test_set(_idx))  return;  //already visited
 840 
 841   // recheck constructor invariants:
 842   verify_adr_type(false);
 843 
 844   // recheck local phi/phi consistency:
 845   assert(_adr_type == at || _adr_type == TypePtr::BOTTOM,
 846          "adr_type must be consistent across phi nest");
 847 
 848   // walk around
 849   for (uint i = 1; i < req(); i++) {
 850     Node* n = in(i);
 851     if (n == NULL)  continue;
 852     const Node* np = in(i);
 853     if (np->is_Phi()) {
 854       np->as_Phi()->verify_adr_type(visited, at);
 855     } else if (n->bottom_type() == Type::TOP
 856                || (n->is_Mem() && n->in(MemNode::Address)->bottom_type() == Type::TOP)) {
 857       // ignore top inputs
 858     } else {
 859       const TypePtr* nat = flatten_phi_adr_type(n->adr_type());
 860       // recheck phi/non-phi consistency at leaves:
 861       assert((nat != NULL) == (at != NULL), "");
 862       assert(nat == at || nat == TypePtr::BOTTOM,
 863              "adr_type must be consistent at leaves of phi nest");
 864     }
 865   }
 866 }
 867 
 868 // Verify a whole nest of phis rooted at this one.
 869 void PhiNode::verify_adr_type(bool recursive) const {
 870   if (is_error_reported())  return;  // muzzle asserts when debugging an error
 871   if (Node::in_dump())      return;  // muzzle asserts when printing
 872 
 873   assert((_type == Type::MEMORY) == (_adr_type != NULL), "adr_type for memory phis only");
 874 
 875   if (!VerifyAliases)       return;  // verify thoroughly only if requested
 876 
 877   assert(_adr_type == flatten_phi_adr_type(_adr_type),
 878          "Phi::adr_type must be pre-normalized");
 879 
 880   if (recursive) {
 881     VectorSet visited(Thread::current()->resource_area());
 882     verify_adr_type(visited, _adr_type);
 883   }
 884 }
 885 #endif
 886 
 887 
 888 //------------------------------Value------------------------------------------
 889 // Compute the type of the PhiNode
 890 const Type *PhiNode::Value( PhaseTransform *phase ) const {
 891   Node *r = in(0);              // RegionNode
 892   if( !r )                      // Copy or dead
 893     return in(1) ? phase->type(in(1)) : Type::TOP;
 894 
 895   // Note: During parsing, phis are often transformed before their regions.
 896   // This means we have to use type_or_null to defend against untyped regions.
 897   if( phase->type_or_null(r) == Type::TOP )  // Dead code?
 898     return Type::TOP;
 899 
 900   // Check for trip-counted loop.  If so, be smarter.
 901   CountedLoopNode *l = r->is_CountedLoop() ? r->as_CountedLoop() : NULL;
 902   if( l && l->can_be_counted_loop(phase) &&
 903       ((const Node*)l->phi() == this) ) { // Trip counted loop!
 904     // protect against init_trip() or limit() returning NULL
 905     const Node *init   = l->init_trip();
 906     const Node *limit  = l->limit();
 907     if( init != NULL && limit != NULL && l->stride_is_con() ) {
 908       const TypeInt *lo = init ->bottom_type()->isa_int();
 909       const TypeInt *hi = limit->bottom_type()->isa_int();
 910       if( lo && hi ) {            // Dying loops might have TOP here
 911         int stride = l->stride_con();
 912         if( stride < 0 ) {          // Down-counter loop
 913           const TypeInt *tmp = lo; lo = hi; hi = tmp;
 914           stride = -stride;
 915         }
 916         if( lo->_hi < hi->_lo )     // Reversed endpoints are well defined :-(
 917           return TypeInt::make(lo->_lo,hi->_hi,3);
 918       }
 919     }
 920   }
 921 
 922   // Until we have harmony between classes and interfaces in the type
 923   // lattice, we must tread carefully around phis which implicitly
 924   // convert the one to the other.
 925   const TypePtr* ttp = _type->make_ptr();
 926   const TypeInstPtr* ttip = (ttp != NULL) ? ttp->isa_instptr() : NULL;
 927   const TypeKlassPtr* ttkp = (ttp != NULL) ? ttp->isa_klassptr() : NULL;
 928   bool is_intf = false;
 929   if (ttip != NULL) {
 930     ciKlass* k = ttip->klass();
 931     if (k->is_loaded() && k->is_interface())
 932       is_intf = true;
 933   }
 934   if (ttkp != NULL) {
 935     ciKlass* k = ttkp->klass();
 936     if (k->is_loaded() && k->is_interface())
 937       is_intf = true;
 938   }
 939 
 940   // Default case: merge all inputs
 941   const Type *t = Type::TOP;        // Merged type starting value
 942   for (uint i = 1; i < req(); ++i) {// For all paths in
 943     // Reachable control path?
 944     if (r->in(i) && phase->type(r->in(i)) == Type::CONTROL) {
 945       const Type* ti = phase->type(in(i));
 946       // We assume that each input of an interface-valued Phi is a true
 947       // subtype of that interface.  This might not be true of the meet
 948       // of all the input types.  The lattice is not distributive in
 949       // such cases.  Ward off asserts in type.cpp by refusing to do
 950       // meets between interfaces and proper classes.
 951       const TypePtr* tip = ti->make_ptr();
 952       const TypeInstPtr* tiip = (tip != NULL) ? tip->isa_instptr() : NULL;
 953       if (tiip) {
 954         bool ti_is_intf = false;
 955         ciKlass* k = tiip->klass();
 956         if (k->is_loaded() && k->is_interface())
 957           ti_is_intf = true;
 958         if (is_intf != ti_is_intf)
 959           { t = _type; break; }
 960       }
 961       t = t->meet_speculative(ti);
 962     }
 963   }
 964 
 965   // The worst-case type (from ciTypeFlow) should be consistent with "t".
 966   // That is, we expect that "t->higher_equal(_type)" holds true.
 967   // There are various exceptions:
 968   // - Inputs which are phis might in fact be widened unnecessarily.
 969   //   For example, an input might be a widened int while the phi is a short.
 970   // - Inputs might be BotPtrs but this phi is dependent on a null check,
 971   //   and postCCP has removed the cast which encodes the result of the check.
 972   // - The type of this phi is an interface, and the inputs are classes.
 973   // - Value calls on inputs might produce fuzzy results.
 974   //   (Occurrences of this case suggest improvements to Value methods.)
 975   //
 976   // It is not possible to see Type::BOTTOM values as phi inputs,
 977   // because the ciTypeFlow pre-pass produces verifier-quality types.
 978   const Type* ft = t->filter_speculative(_type);  // Worst case type
 979 
 980 #ifdef ASSERT
 981   // The following logic has been moved into TypeOopPtr::filter.
 982   const Type* jt = t->join_speculative(_type);
 983   if (jt->empty()) {           // Emptied out???
 984 
 985     // Check for evil case of 't' being a class and '_type' expecting an
 986     // interface.  This can happen because the bytecodes do not contain
 987     // enough type info to distinguish a Java-level interface variable
 988     // from a Java-level object variable.  If we meet 2 classes which
 989     // both implement interface I, but their meet is at 'j/l/O' which
 990     // doesn't implement I, we have no way to tell if the result should
 991     // be 'I' or 'j/l/O'.  Thus we'll pick 'j/l/O'.  If this then flows
 992     // into a Phi which "knows" it's an Interface type we'll have to
 993     // uplift the type.
 994     if (!t->empty() && ttip && ttip->is_loaded() && ttip->klass()->is_interface()) {
 995       assert(ft == _type, ""); // Uplift to interface
 996     } else if (!t->empty() && ttkp && ttkp->is_loaded() && ttkp->klass()->is_interface()) {
 997       assert(ft == _type, ""); // Uplift to interface
 998     } else {
 999       // We also have to handle 'evil cases' of interface- vs. class-arrays
1000       Type::get_arrays_base_elements(jt, _type, NULL, &ttip);
1001       if (!t->empty() && ttip != NULL && ttip->is_loaded() && ttip->klass()->is_interface()) {
1002           assert(ft == _type, "");   // Uplift to array of interface
1003       } else {
1004         // Otherwise it's something stupid like non-overlapping int ranges
1005         // found on dying counted loops.
1006         assert(ft == Type::TOP, ""); // Canonical empty value
1007       }
1008     }
1009   }
1010 
1011   else {
1012 
1013     // If we have an interface-typed Phi and we narrow to a class type, the join
1014     // should report back the class.  However, if we have a J/L/Object
1015     // class-typed Phi and an interface flows in, it's possible that the meet &
1016     // join report an interface back out.  This isn't possible but happens
1017     // because the type system doesn't interact well with interfaces.
1018     const TypePtr *jtp = jt->make_ptr();
1019     const TypeInstPtr *jtip = (jtp != NULL) ? jtp->isa_instptr() : NULL;
1020     const TypeKlassPtr *jtkp = (jtp != NULL) ? jtp->isa_klassptr() : NULL;
1021     if( jtip && ttip ) {
1022       if( jtip->is_loaded() &&  jtip->klass()->is_interface() &&
1023           ttip->is_loaded() && !ttip->klass()->is_interface() ) {
1024         // Happens in a CTW of rt.jar, 320-341, no extra flags
1025         assert(ft == ttip->cast_to_ptr_type(jtip->ptr()) ||
1026                ft->isa_narrowoop() && ft->make_ptr() == ttip->cast_to_ptr_type(jtip->ptr()), "");
1027         jt = ft;
1028       }
1029     }
1030     if( jtkp && ttkp ) {
1031       if( jtkp->is_loaded() &&  jtkp->klass()->is_interface() &&
1032           !jtkp->klass_is_exact() && // Keep exact interface klass (6894807)
1033           ttkp->is_loaded() && !ttkp->klass()->is_interface() ) {
1034         assert(ft == ttkp->cast_to_ptr_type(jtkp->ptr()) ||
1035                ft->isa_narrowklass() && ft->make_ptr() == ttkp->cast_to_ptr_type(jtkp->ptr()), "");
1036         jt = ft;
1037       }
1038     }
1039     if (jt != ft && jt->base() == ft->base()) {
1040       if (jt->isa_int() &&
1041           jt->is_int()->_lo == ft->is_int()->_lo &&
1042           jt->is_int()->_hi == ft->is_int()->_hi)
1043         jt = ft;
1044       if (jt->isa_long() &&
1045           jt->is_long()->_lo == ft->is_long()->_lo &&
1046           jt->is_long()->_hi == ft->is_long()->_hi)
1047         jt = ft;
1048     }
1049     if (jt != ft) {
1050       tty->print("merge type:  "); t->dump(); tty->cr();
1051       tty->print("kill type:   "); _type->dump(); tty->cr();
1052       tty->print("join type:   "); jt->dump(); tty->cr();
1053       tty->print("filter type: "); ft->dump(); tty->cr();
1054     }
1055     assert(jt == ft, "");
1056   }
1057 #endif //ASSERT
1058 
1059   // Deal with conversion problems found in data loops.
1060   ft = phase->saturate(ft, phase->type_or_null(this), _type);
1061 
1062   return ft;
1063 }
1064 
1065 
1066 //------------------------------is_diamond_phi---------------------------------
1067 // Does this Phi represent a simple well-shaped diamond merge?  Return the
1068 // index of the true path or 0 otherwise.
1069 // If check_control_only is true, do not inspect the If node at the
1070 // top, and return -1 (not an edge number) on success.
1071 int PhiNode::is_diamond_phi(bool check_control_only) const {
1072   // Check for a 2-path merge
1073   Node *region = in(0);
1074   if( !region ) return 0;
1075   if( region->req() != 3 ) return 0;
1076   if(         req() != 3 ) return 0;
1077   // Check that both paths come from the same If
1078   Node *ifp1 = region->in(1);
1079   Node *ifp2 = region->in(2);
1080   if( !ifp1 || !ifp2 ) return 0;
1081   Node *iff = ifp1->in(0);
1082   if( !iff || !iff->is_If() ) return 0;
1083   if( iff != ifp2->in(0) ) return 0;
1084   if (check_control_only)  return -1;
1085   // Check for a proper bool/cmp
1086   const Node *b = iff->in(1);
1087   if( !b->is_Bool() ) return 0;
1088   const Node *cmp = b->in(1);
1089   if( !cmp->is_Cmp() ) return 0;
1090 
1091   // Check for branching opposite expected
1092   if( ifp2->Opcode() == Op_IfTrue ) {
1093     assert( ifp1->Opcode() == Op_IfFalse, "" );
1094     return 2;
1095   } else {
1096     assert( ifp1->Opcode() == Op_IfTrue, "" );
1097     return 1;
1098   }
1099 }
1100 
1101 //----------------------------check_cmove_id-----------------------------------
1102 // Check for CMove'ing a constant after comparing against the constant.
1103 // Happens all the time now, since if we compare equality vs a constant in
1104 // the parser, we "know" the variable is constant on one path and we force
1105 // it.  Thus code like "if( x==0 ) {/*EMPTY*/}" ends up inserting a
1106 // conditional move: "x = (x==0)?0:x;".  Yucko.  This fix is slightly more
1107 // general in that we don't need constants.  Since CMove's are only inserted
1108 // in very special circumstances, we do it here on generic Phi's.
1109 Node* PhiNode::is_cmove_id(PhaseTransform* phase, int true_path) {
1110   assert(true_path !=0, "only diamond shape graph expected");
1111 
1112   // is_diamond_phi() has guaranteed the correctness of the nodes sequence:
1113   // phi->region->if_proj->ifnode->bool->cmp
1114   Node*     region = in(0);
1115   Node*     iff    = region->in(1)->in(0);
1116   BoolNode* b      = iff->in(1)->as_Bool();
1117   Node*     cmp    = b->in(1);
1118   Node*     tval   = in(true_path);
1119   Node*     fval   = in(3-true_path);
1120   Node*     id     = CMoveNode::is_cmove_id(phase, cmp, tval, fval, b);
1121   if (id == NULL)
1122     return NULL;
1123 
1124   // Either value might be a cast that depends on a branch of 'iff'.
1125   // Since the 'id' value will float free of the diamond, either
1126   // decast or return failure.
1127   Node* ctl = id->in(0);
1128   if (ctl != NULL && ctl->in(0) == iff) {
1129     if (id->is_ConstraintCast()) {
1130       return id->in(1);
1131     } else {
1132       // Don't know how to disentangle this value.
1133       return NULL;
1134     }
1135   }
1136 
1137   return id;
1138 }
1139 
1140 //------------------------------Identity---------------------------------------
1141 // Check for Region being Identity.
1142 Node *PhiNode::Identity( PhaseTransform *phase ) {
1143   // Check for no merging going on
1144   // (There used to be special-case code here when this->region->is_Loop.
1145   // It would check for a tributary phi on the backedge that the main phi
1146   // trivially, perhaps with a single cast.  The unique_input method
1147   // does all this and more, by reducing such tributaries to 'this'.)
1148   Node* uin = unique_input(phase);
1149   if (uin != NULL) {
1150     return uin;
1151   }
1152 
1153   int true_path = is_diamond_phi();
1154   if (true_path != 0) {
1155     Node* id = is_cmove_id(phase, true_path);
1156     if (id != NULL)  return id;
1157   }
1158 
1159   return this;                     // No identity
1160 }
1161 
1162 //-----------------------------unique_input------------------------------------
1163 // Find the unique value, discounting top, self-loops, and casts.
1164 // Return top if there are no inputs, and self if there are multiple.
1165 Node* PhiNode::unique_input(PhaseTransform* phase) {
1166   //  1) One unique direct input, or
1167   //  2) some of the inputs have an intervening ConstraintCast and
1168   //     the type of input is the same or sharper (more specific)
1169   //     than the phi's type.
1170   //  3) an input is a self loop
1171   //
1172   //  1) input   or   2) input     or   3) input __
1173   //     /   \           /   \               \  /  \
1174   //     \   /          |    cast             phi  cast
1175   //      phi            \   /               /  \  /
1176   //                      phi               /    --
1177 
1178   Node* r = in(0);                      // RegionNode
1179   if (r == NULL)  return in(1);         // Already degraded to a Copy
1180   Node* uncasted_input = NULL; // The unique uncasted input (ConstraintCasts removed)
1181   Node* direct_input   = NULL; // The unique direct input
1182 
1183   for (uint i = 1, cnt = req(); i < cnt; ++i) {
1184     Node* rc = r->in(i);
1185     if (rc == NULL || phase->type(rc) == Type::TOP)
1186       continue;                 // ignore unreachable control path
1187     Node* n = in(i);
1188     if (n == NULL)
1189       continue;
1190     Node* un = n->uncast();
1191     if (un == NULL || un == this || phase->type(un) == Type::TOP) {
1192       continue; // ignore if top, or in(i) and "this" are in a data cycle
1193     }
1194     // Check for a unique uncasted input
1195     if (uncasted_input == NULL) {
1196       uncasted_input = un;
1197     } else if (uncasted_input != un) {
1198       uncasted_input = NodeSentinel; // no unique uncasted input
1199     }
1200     // Check for a unique direct input
1201     if (direct_input == NULL) {
1202       direct_input = n;
1203     } else if (direct_input != n) {
1204       direct_input = NodeSentinel; // no unique direct input
1205     }
1206   }
1207   if (direct_input == NULL) {
1208     return phase->C->top();        // no inputs
1209   }
1210   assert(uncasted_input != NULL,"");
1211 
1212   if (direct_input != NodeSentinel) {
1213     return direct_input;           // one unique direct input
1214   }
1215   if (uncasted_input != NodeSentinel &&
1216       phase->type(uncasted_input)->higher_equal(type())) {
1217     return uncasted_input;         // one unique uncasted input
1218   }
1219 
1220   // Nothing.
1221   return NULL;
1222 }
1223 
1224 //------------------------------is_x2logic-------------------------------------
1225 // Check for simple convert-to-boolean pattern
1226 // If:(C Bool) Region:(IfF IfT) Phi:(Region 0 1)
1227 // Convert Phi to an ConvIB.
1228 static Node *is_x2logic( PhaseGVN *phase, PhiNode *phi, int true_path ) {
1229   assert(true_path !=0, "only diamond shape graph expected");
1230   // Convert the true/false index into an expected 0/1 return.
1231   // Map 2->0 and 1->1.
1232   int flipped = 2-true_path;
1233 
1234   // is_diamond_phi() has guaranteed the correctness of the nodes sequence:
1235   // phi->region->if_proj->ifnode->bool->cmp
1236   Node *region = phi->in(0);
1237   Node *iff = region->in(1)->in(0);
1238   BoolNode *b = (BoolNode*)iff->in(1);
1239   const CmpNode *cmp = (CmpNode*)b->in(1);
1240 
1241   Node *zero = phi->in(1);
1242   Node *one  = phi->in(2);
1243   const Type *tzero = phase->type( zero );
1244   const Type *tone  = phase->type( one  );
1245 
1246   // Check for compare vs 0
1247   const Type *tcmp = phase->type(cmp->in(2));
1248   if( tcmp != TypeInt::ZERO && tcmp != TypePtr::NULL_PTR ) {
1249     // Allow cmp-vs-1 if the other input is bounded by 0-1
1250     if( !(tcmp == TypeInt::ONE && phase->type(cmp->in(1)) == TypeInt::BOOL) )
1251       return NULL;
1252     flipped = 1-flipped;        // Test is vs 1 instead of 0!
1253   }
1254 
1255   // Check for setting zero/one opposite expected
1256   if( tzero == TypeInt::ZERO ) {
1257     if( tone == TypeInt::ONE ) {
1258     } else return NULL;
1259   } else if( tzero == TypeInt::ONE ) {
1260     if( tone == TypeInt::ZERO ) {
1261       flipped = 1-flipped;
1262     } else return NULL;
1263   } else return NULL;
1264 
1265   // Check for boolean test backwards
1266   if( b->_test._test == BoolTest::ne ) {
1267   } else if( b->_test._test == BoolTest::eq ) {
1268     flipped = 1-flipped;
1269   } else return NULL;
1270 
1271   // Build int->bool conversion
1272   Node *n = new (phase->C) Conv2BNode(cmp->in(1));
1273   if( flipped )
1274     n = new (phase->C) XorINode( phase->transform(n), phase->intcon(1) );
1275 
1276   return n;
1277 }
1278 
1279 //------------------------------is_cond_add------------------------------------
1280 // Check for simple conditional add pattern:  "(P < Q) ? X+Y : X;"
1281 // To be profitable the control flow has to disappear; there can be no other
1282 // values merging here.  We replace the test-and-branch with:
1283 // "(sgn(P-Q))&Y) + X".  Basically, convert "(P < Q)" into 0 or -1 by
1284 // moving the carry bit from (P-Q) into a register with 'sbb EAX,EAX'.
1285 // Then convert Y to 0-or-Y and finally add.
1286 // This is a key transform for SpecJava _201_compress.
1287 static Node* is_cond_add(PhaseGVN *phase, PhiNode *phi, int true_path) {
1288   assert(true_path !=0, "only diamond shape graph expected");
1289 
1290   // is_diamond_phi() has guaranteed the correctness of the nodes sequence:
1291   // phi->region->if_proj->ifnode->bool->cmp
1292   RegionNode *region = (RegionNode*)phi->in(0);
1293   Node *iff = region->in(1)->in(0);
1294   BoolNode* b = iff->in(1)->as_Bool();
1295   const CmpNode *cmp = (CmpNode*)b->in(1);
1296 
1297   // Make sure only merging this one phi here
1298   if (region->has_unique_phi() != phi)  return NULL;
1299 
1300   // Make sure each arm of the diamond has exactly one output, which we assume
1301   // is the region.  Otherwise, the control flow won't disappear.
1302   if (region->in(1)->outcnt() != 1) return NULL;
1303   if (region->in(2)->outcnt() != 1) return NULL;
1304 
1305   // Check for "(P < Q)" of type signed int
1306   if (b->_test._test != BoolTest::lt)  return NULL;
1307   if (cmp->Opcode() != Op_CmpI)        return NULL;
1308 
1309   Node *p = cmp->in(1);
1310   Node *q = cmp->in(2);
1311   Node *n1 = phi->in(  true_path);
1312   Node *n2 = phi->in(3-true_path);
1313 
1314   int op = n1->Opcode();
1315   if( op != Op_AddI           // Need zero as additive identity
1316       /*&&op != Op_SubI &&
1317       op != Op_AddP &&
1318       op != Op_XorI &&
1319       op != Op_OrI*/ )
1320     return NULL;
1321 
1322   Node *x = n2;
1323   Node *y = NULL;
1324   if( x == n1->in(1) ) {
1325     y = n1->in(2);
1326   } else if( x == n1->in(2) ) {
1327     y = n1->in(1);
1328   } else return NULL;
1329 
1330   // Not so profitable if compare and add are constants
1331   if( q->is_Con() && phase->type(q) != TypeInt::ZERO && y->is_Con() )
1332     return NULL;
1333 
1334   Node *cmplt = phase->transform( new (phase->C) CmpLTMaskNode(p,q) );
1335   Node *j_and   = phase->transform( new (phase->C) AndINode(cmplt,y) );
1336   return new (phase->C) AddINode(j_and,x);
1337 }
1338 
1339 //------------------------------is_absolute------------------------------------
1340 // Check for absolute value.
1341 static Node* is_absolute( PhaseGVN *phase, PhiNode *phi_root, int true_path) {
1342   assert(true_path !=0, "only diamond shape graph expected");
1343 
1344   int  cmp_zero_idx = 0;        // Index of compare input where to look for zero
1345   int  phi_x_idx = 0;           // Index of phi input where to find naked x
1346 
1347   // ABS ends with the merge of 2 control flow paths.
1348   // Find the false path from the true path. With only 2 inputs, 3 - x works nicely.
1349   int false_path = 3 - true_path;
1350 
1351   // is_diamond_phi() has guaranteed the correctness of the nodes sequence:
1352   // phi->region->if_proj->ifnode->bool->cmp
1353   BoolNode *bol = phi_root->in(0)->in(1)->in(0)->in(1)->as_Bool();
1354 
1355   // Check bool sense
1356   switch( bol->_test._test ) {
1357   case BoolTest::lt: cmp_zero_idx = 1; phi_x_idx = true_path;  break;
1358   case BoolTest::le: cmp_zero_idx = 2; phi_x_idx = false_path; break;
1359   case BoolTest::gt: cmp_zero_idx = 2; phi_x_idx = true_path;  break;
1360   case BoolTest::ge: cmp_zero_idx = 1; phi_x_idx = false_path; break;
1361   default:           return NULL;                              break;
1362   }
1363 
1364   // Test is next
1365   Node *cmp = bol->in(1);
1366   const Type *tzero = NULL;
1367   switch( cmp->Opcode() ) {
1368   case Op_CmpF:    tzero = TypeF::ZERO; break; // Float ABS
1369   case Op_CmpD:    tzero = TypeD::ZERO; break; // Double ABS
1370   default: return NULL;
1371   }
1372 
1373   // Find zero input of compare; the other input is being abs'd
1374   Node *x = NULL;
1375   bool flip = false;
1376   if( phase->type(cmp->in(cmp_zero_idx)) == tzero ) {
1377     x = cmp->in(3 - cmp_zero_idx);
1378   } else if( phase->type(cmp->in(3 - cmp_zero_idx)) == tzero ) {
1379     // The test is inverted, we should invert the result...
1380     x = cmp->in(cmp_zero_idx);
1381     flip = true;
1382   } else {
1383     return NULL;
1384   }
1385 
1386   // Next get the 2 pieces being selected, one is the original value
1387   // and the other is the negated value.
1388   if( phi_root->in(phi_x_idx) != x ) return NULL;
1389 
1390   // Check other phi input for subtract node
1391   Node *sub = phi_root->in(3 - phi_x_idx);
1392 
1393   // Allow only Sub(0,X) and fail out for all others; Neg is not OK
1394   if( tzero == TypeF::ZERO ) {
1395     if( sub->Opcode() != Op_SubF ||
1396         sub->in(2) != x ||
1397         phase->type(sub->in(1)) != tzero ) return NULL;
1398     x = new (phase->C) AbsFNode(x);
1399     if (flip) {
1400       x = new (phase->C) SubFNode(sub->in(1), phase->transform(x));
1401     }
1402   } else {
1403     if( sub->Opcode() != Op_SubD ||
1404         sub->in(2) != x ||
1405         phase->type(sub->in(1)) != tzero ) return NULL;
1406     x = new (phase->C) AbsDNode(x);
1407     if (flip) {
1408       x = new (phase->C) SubDNode(sub->in(1), phase->transform(x));
1409     }
1410   }
1411 
1412   return x;
1413 }
1414 
1415 //------------------------------split_once-------------------------------------
1416 // Helper for split_flow_path
1417 static void split_once(PhaseIterGVN *igvn, Node *phi, Node *val, Node *n, Node *newn) {
1418   igvn->hash_delete(n);         // Remove from hash before hacking edges
1419 
1420   uint j = 1;
1421   for (uint i = phi->req()-1; i > 0; i--) {
1422     if (phi->in(i) == val) {   // Found a path with val?
1423       // Add to NEW Region/Phi, no DU info
1424       newn->set_req( j++, n->in(i) );
1425       // Remove from OLD Region/Phi
1426       n->del_req(i);
1427     }
1428   }
1429 
1430   // Register the new node but do not transform it.  Cannot transform until the
1431   // entire Region/Phi conglomerate has been hacked as a single huge transform.
1432   igvn->register_new_node_with_optimizer( newn );
1433 
1434   // Now I can point to the new node.
1435   n->add_req(newn);
1436   igvn->_worklist.push(n);
1437 }
1438 
1439 //------------------------------split_flow_path--------------------------------
1440 // Check for merging identical values and split flow paths
1441 static Node* split_flow_path(PhaseGVN *phase, PhiNode *phi) {
1442   BasicType bt = phi->type()->basic_type();
1443   if( bt == T_ILLEGAL || type2size[bt] <= 0 )
1444     return NULL;                // Bail out on funny non-value stuff
1445   if( phi->req() <= 3 )         // Need at least 2 matched inputs and a
1446     return NULL;                // third unequal input to be worth doing
1447 
1448   // Scan for a constant
1449   uint i;
1450   for( i = 1; i < phi->req()-1; i++ ) {
1451     Node *n = phi->in(i);
1452     if( !n ) return NULL;
1453     if( phase->type(n) == Type::TOP ) return NULL;
1454     if( n->Opcode() == Op_ConP || n->Opcode() == Op_ConN || n->Opcode() == Op_ConNKlass )
1455       break;
1456   }
1457   if( i >= phi->req() )         // Only split for constants
1458     return NULL;
1459 
1460   Node *val = phi->in(i);       // Constant to split for
1461   uint hit = 0;                 // Number of times it occurs
1462   Node *r = phi->region();
1463 
1464   for( ; i < phi->req(); i++ ){ // Count occurrences of constant
1465     Node *n = phi->in(i);
1466     if( !n ) return NULL;
1467     if( phase->type(n) == Type::TOP ) return NULL;
1468     if( phi->in(i) == val ) {
1469       hit++;
1470       if (PhaseIdealLoop::find_predicate(r->in(i)) != NULL) {
1471         return NULL;            // don't split loop entry path
1472       }
1473     }
1474   }
1475 
1476   if( hit <= 1 ||               // Make sure we find 2 or more
1477       hit == phi->req()-1 )     // and not ALL the same value
1478     return NULL;
1479 
1480   // Now start splitting out the flow paths that merge the same value.
1481   // Split first the RegionNode.
1482   PhaseIterGVN *igvn = phase->is_IterGVN();
1483   RegionNode *newr = new (phase->C) RegionNode(hit+1);
1484   split_once(igvn, phi, val, r, newr);
1485 
1486   // Now split all other Phis than this one
1487   for (DUIterator_Fast kmax, k = r->fast_outs(kmax); k < kmax; k++) {
1488     Node* phi2 = r->fast_out(k);
1489     if( phi2->is_Phi() && phi2->as_Phi() != phi ) {
1490       PhiNode *newphi = PhiNode::make_blank(newr, phi2);
1491       split_once(igvn, phi, val, phi2, newphi);
1492     }
1493   }
1494 
1495   // Clean up this guy
1496   igvn->hash_delete(phi);
1497   for( i = phi->req()-1; i > 0; i-- ) {
1498     if( phi->in(i) == val ) {
1499       phi->del_req(i);
1500     }
1501   }
1502   phi->add_req(val);
1503 
1504   return phi;
1505 }
1506 
1507 //=============================================================================
1508 //------------------------------simple_data_loop_check-------------------------
1509 //  Try to determining if the phi node in a simple safe/unsafe data loop.
1510 //  Returns:
1511 // enum LoopSafety { Safe = 0, Unsafe, UnsafeLoop };
1512 // Safe       - safe case when the phi and it's inputs reference only safe data
1513 //              nodes;
1514 // Unsafe     - the phi and it's inputs reference unsafe data nodes but there
1515 //              is no reference back to the phi - need a graph walk
1516 //              to determine if it is in a loop;
1517 // UnsafeLoop - unsafe case when the phi references itself directly or through
1518 //              unsafe data node.
1519 //  Note: a safe data node is a node which could/never reference itself during
1520 //  GVN transformations. For now it is Con, Proj, Phi, CastPP, CheckCastPP.
1521 //  I mark Phi nodes as safe node not only because they can reference itself
1522 //  but also to prevent mistaking the fallthrough case inside an outer loop
1523 //  as dead loop when the phi references itselfs through an other phi.
1524 PhiNode::LoopSafety PhiNode::simple_data_loop_check(Node *in) const {
1525   // It is unsafe loop if the phi node references itself directly.
1526   if (in == (Node*)this)
1527     return UnsafeLoop; // Unsafe loop
1528   // Unsafe loop if the phi node references itself through an unsafe data node.
1529   // Exclude cases with null inputs or data nodes which could reference
1530   // itself (safe for dead loops).
1531   if (in != NULL && !in->is_dead_loop_safe()) {
1532     // Check inputs of phi's inputs also.
1533     // It is much less expensive then full graph walk.
1534     uint cnt = in->req();
1535     uint i = (in->is_Proj() && !in->is_CFG())  ? 0 : 1;
1536     for (; i < cnt; ++i) {
1537       Node* m = in->in(i);
1538       if (m == (Node*)this)
1539         return UnsafeLoop; // Unsafe loop
1540       if (m != NULL && !m->is_dead_loop_safe()) {
1541         // Check the most common case (about 30% of all cases):
1542         // phi->Load/Store->AddP->(ConP ConP Con)/(Parm Parm Con).
1543         Node *m1 = (m->is_AddP() && m->req() > 3) ? m->in(1) : NULL;
1544         if (m1 == (Node*)this)
1545           return UnsafeLoop; // Unsafe loop
1546         if (m1 != NULL && m1 == m->in(2) &&
1547             m1->is_dead_loop_safe() && m->in(3)->is_Con()) {
1548           continue; // Safe case
1549         }
1550         // The phi references an unsafe node - need full analysis.
1551         return Unsafe;
1552       }
1553     }
1554   }
1555   return Safe; // Safe case - we can optimize the phi node.
1556 }
1557 
1558 //------------------------------is_unsafe_data_reference-----------------------
1559 // If phi can be reached through the data input - it is data loop.
1560 bool PhiNode::is_unsafe_data_reference(Node *in) const {
1561   assert(req() > 1, "");
1562   // First, check simple cases when phi references itself directly or
1563   // through an other node.
1564   LoopSafety safety = simple_data_loop_check(in);
1565   if (safety == UnsafeLoop)
1566     return true;  // phi references itself - unsafe loop
1567   else if (safety == Safe)
1568     return false; // Safe case - phi could be replaced with the unique input.
1569 
1570   // Unsafe case when we should go through data graph to determine
1571   // if the phi references itself.
1572 
1573   ResourceMark rm;
1574 
1575   Arena *a = Thread::current()->resource_area();
1576   Node_List nstack(a);
1577   VectorSet visited(a);
1578 
1579   nstack.push(in); // Start with unique input.
1580   visited.set(in->_idx);
1581   while (nstack.size() != 0) {
1582     Node* n = nstack.pop();
1583     uint cnt = n->req();
1584     uint i = (n->is_Proj() && !n->is_CFG()) ? 0 : 1;
1585     for (; i < cnt; i++) {
1586       Node* m = n->in(i);
1587       if (m == (Node*)this) {
1588         return true;    // Data loop
1589       }
1590       if (m != NULL && !m->is_dead_loop_safe()) { // Only look for unsafe cases.
1591         if (!visited.test_set(m->_idx))
1592           nstack.push(m);
1593       }
1594     }
1595   }
1596   return false; // The phi is not reachable from its inputs
1597 }
1598 
1599 
1600 //------------------------------Ideal------------------------------------------
1601 // Return a node which is more "ideal" than the current node.  Must preserve
1602 // the CFG, but we can still strip out dead paths.
1603 Node *PhiNode::Ideal(PhaseGVN *phase, bool can_reshape) {
1604   // The next should never happen after 6297035 fix.
1605   if( is_copy() )               // Already degraded to a Copy ?
1606     return NULL;                // No change
1607 
1608   Node *r = in(0);              // RegionNode
1609   assert(r->in(0) == NULL || !r->in(0)->is_Root(), "not a specially hidden merge");
1610 
1611   // Note: During parsing, phis are often transformed before their regions.
1612   // This means we have to use type_or_null to defend against untyped regions.
1613   if( phase->type_or_null(r) == Type::TOP ) // Dead code?
1614     return NULL;                // No change
1615 
1616   Node *top = phase->C->top();
1617   bool new_phi = (outcnt() == 0); // transforming new Phi
1618   // No change for igvn if new phi is not hooked
1619   if (new_phi && can_reshape)
1620     return NULL;
1621 
1622   // The are 2 situations when only one valid phi's input is left
1623   // (in addition to Region input).
1624   // One: region is not loop - replace phi with this input.
1625   // Two: region is loop - replace phi with top since this data path is dead
1626   //                       and we need to break the dead data loop.
1627   Node* progress = NULL;        // Record if any progress made
1628   for( uint j = 1; j < req(); ++j ){ // For all paths in
1629     // Check unreachable control paths
1630     Node* rc = r->in(j);
1631     Node* n = in(j);            // Get the input
1632     if (rc == NULL || phase->type(rc) == Type::TOP) {
1633       if (n != top) {           // Not already top?
1634         PhaseIterGVN *igvn = phase->is_IterGVN();
1635         if (can_reshape && igvn != NULL) {
1636           igvn->_worklist.push(r);
1637         }
1638         // Nuke it down
1639         if (can_reshape) {
1640           set_req_X(j, top, igvn);
1641         } else {
1642           set_req(j, top);
1643         }
1644         progress = this;        // Record progress
1645       }
1646     }
1647   }
1648 
1649   if (can_reshape && outcnt() == 0) {
1650     // set_req() above may kill outputs if Phi is referenced
1651     // only by itself on the dead (top) control path.
1652     return top;
1653   }
1654 
1655   Node* uin = unique_input(phase);
1656   if (uin == top) {             // Simplest case: no alive inputs.
1657     if (can_reshape)            // IGVN transformation
1658       return top;
1659     else
1660       return NULL;              // Identity will return TOP
1661   } else if (uin != NULL) {
1662     // Only one not-NULL unique input path is left.
1663     // Determine if this input is backedge of a loop.
1664     // (Skip new phis which have no uses and dead regions).
1665     if (outcnt() > 0 && r->in(0) != NULL) {
1666       // First, take the short cut when we know it is a loop and
1667       // the EntryControl data path is dead.
1668       // Loop node may have only one input because entry path
1669       // is removed in PhaseIdealLoop::Dominators().
1670       assert(!r->is_Loop() || r->req() <= 3, "Loop node should have 3 or less inputs");
1671       bool is_loop = (r->is_Loop() && r->req() == 3);
1672       // Then, check if there is a data loop when phi references itself directly
1673       // or through other data nodes.
1674       if (is_loop && !uin->eqv_uncast(in(LoopNode::EntryControl)) ||
1675          !is_loop && is_unsafe_data_reference(uin)) {
1676         // Break this data loop to avoid creation of a dead loop.
1677         if (can_reshape) {
1678           return top;
1679         } else {
1680           // We can't return top if we are in Parse phase - cut inputs only
1681           // let Identity to handle the case.
1682           replace_edge(uin, top);
1683           return NULL;
1684         }
1685       }
1686     }
1687 
1688     // One unique input.
1689     debug_only(Node* ident = Identity(phase));
1690     // The unique input must eventually be detected by the Identity call.
1691 #ifdef ASSERT
1692     if (ident != uin && !ident->is_top()) {
1693       // print this output before failing assert
1694       r->dump(3);
1695       this->dump(3);
1696       ident->dump();
1697       uin->dump();
1698     }
1699 #endif
1700     assert(ident == uin || ident->is_top(), "Identity must clean this up");
1701     return NULL;
1702   }
1703 
1704 
1705   Node* opt = NULL;
1706   int true_path = is_diamond_phi();
1707   if( true_path != 0 ) {
1708     // Check for CMove'ing identity. If it would be unsafe,
1709     // handle it here. In the safe case, let Identity handle it.
1710     Node* unsafe_id = is_cmove_id(phase, true_path);
1711     if( unsafe_id != NULL && is_unsafe_data_reference(unsafe_id) )
1712       opt = unsafe_id;
1713 
1714     // Check for simple convert-to-boolean pattern
1715     if( opt == NULL )
1716       opt = is_x2logic(phase, this, true_path);
1717 
1718     // Check for absolute value
1719     if( opt == NULL )
1720       opt = is_absolute(phase, this, true_path);
1721 
1722     // Check for conditional add
1723     if( opt == NULL && can_reshape )
1724       opt = is_cond_add(phase, this, true_path);
1725 
1726     // These 4 optimizations could subsume the phi:
1727     // have to check for a dead data loop creation.
1728     if( opt != NULL ) {
1729       if( opt == unsafe_id || is_unsafe_data_reference(opt) ) {
1730         // Found dead loop.
1731         if( can_reshape )
1732           return top;
1733         // We can't return top if we are in Parse phase - cut inputs only
1734         // to stop further optimizations for this phi. Identity will return TOP.
1735         assert(req() == 3, "only diamond merge phi here");
1736         set_req(1, top);
1737         set_req(2, top);
1738         return NULL;
1739       } else {
1740         return opt;
1741       }
1742     }
1743   }
1744 
1745   // Check for merging identical values and split flow paths
1746   if (can_reshape) {
1747     opt = split_flow_path(phase, this);
1748     // This optimization only modifies phi - don't need to check for dead loop.
1749     assert(opt == NULL || phase->eqv(opt, this), "do not elide phi");
1750     if (opt != NULL)  return opt;
1751   }
1752 
1753   if (in(1) != NULL && in(1)->Opcode() == Op_AddP && can_reshape) {
1754     // Try to undo Phi of AddP:
1755     // (Phi (AddP base base y) (AddP base2 base2 y))
1756     // becomes:
1757     // newbase := (Phi base base2)
1758     // (AddP newbase newbase y)
1759     //
1760     // This occurs as a result of unsuccessful split_thru_phi and
1761     // interferes with taking advantage of addressing modes. See the
1762     // clone_shift_expressions code in matcher.cpp
1763     Node* addp = in(1);
1764     const Type* type = addp->in(AddPNode::Base)->bottom_type();
1765     Node* y = addp->in(AddPNode::Offset);
1766     if (y != NULL && addp->in(AddPNode::Base) == addp->in(AddPNode::Address)) {
1767       // make sure that all the inputs are similar to the first one,
1768       // i.e. AddP with base == address and same offset as first AddP
1769       bool doit = true;
1770       for (uint i = 2; i < req(); i++) {
1771         if (in(i) == NULL ||
1772             in(i)->Opcode() != Op_AddP ||
1773             in(i)->in(AddPNode::Base) != in(i)->in(AddPNode::Address) ||
1774             in(i)->in(AddPNode::Offset) != y) {
1775           doit = false;
1776           break;
1777         }
1778         // Accumulate type for resulting Phi
1779         type = type->meet_speculative(in(i)->in(AddPNode::Base)->bottom_type());
1780       }
1781       Node* base = NULL;
1782       if (doit) {
1783         // Check for neighboring AddP nodes in a tree.
1784         // If they have a base, use that it.
1785         for (DUIterator_Fast kmax, k = this->fast_outs(kmax); k < kmax; k++) {
1786           Node* u = this->fast_out(k);
1787           if (u->is_AddP()) {
1788             Node* base2 = u->in(AddPNode::Base);
1789             if (base2 != NULL && !base2->is_top()) {
1790               if (base == NULL)
1791                 base = base2;
1792               else if (base != base2)
1793                 { doit = false; break; }
1794             }
1795           }
1796         }
1797       }
1798       if (doit) {
1799         if (base == NULL) {
1800           base = new (phase->C) PhiNode(in(0), type, NULL);
1801           for (uint i = 1; i < req(); i++) {
1802             base->init_req(i, in(i)->in(AddPNode::Base));
1803           }
1804           phase->is_IterGVN()->register_new_node_with_optimizer(base);
1805         }
1806         return new (phase->C) AddPNode(base, base, y);
1807       }
1808     }
1809   }
1810 
1811   // Split phis through memory merges, so that the memory merges will go away.
1812   // Piggy-back this transformation on the search for a unique input....
1813   // It will be as if the merged memory is the unique value of the phi.
1814   // (Do not attempt this optimization unless parsing is complete.
1815   // It would make the parser's memory-merge logic sick.)
1816   // (MergeMemNode is not dead_loop_safe - need to check for dead loop.)
1817   if (progress == NULL && can_reshape && type() == Type::MEMORY) {
1818     // see if this phi should be sliced
1819     uint merge_width = 0;
1820     bool saw_self = false;
1821     for( uint i=1; i<req(); ++i ) {// For all paths in
1822       Node *ii = in(i);
1823       if (ii->is_MergeMem()) {
1824         MergeMemNode* n = ii->as_MergeMem();
1825         merge_width = MAX2(merge_width, n->req());
1826         saw_self = saw_self || phase->eqv(n->base_memory(), this);
1827       }
1828     }
1829 
1830     // This restriction is temporarily necessary to ensure termination:
1831     if (!saw_self && adr_type() == TypePtr::BOTTOM)  merge_width = 0;
1832 
1833     if (merge_width > Compile::AliasIdxRaw) {
1834       // found at least one non-empty MergeMem
1835       const TypePtr* at = adr_type();
1836       if (at != TypePtr::BOTTOM) {
1837         // Patch the existing phi to select an input from the merge:
1838         // Phi:AT1(...MergeMem(m0, m1, m2)...) into
1839         //     Phi:AT1(...m1...)
1840         int alias_idx = phase->C->get_alias_index(at);
1841         for (uint i=1; i<req(); ++i) {
1842           Node *ii = in(i);
1843           if (ii->is_MergeMem()) {
1844             MergeMemNode* n = ii->as_MergeMem();
1845             // compress paths and change unreachable cycles to TOP
1846             // If not, we can update the input infinitely along a MergeMem cycle
1847             // Equivalent code is in MemNode::Ideal_common
1848             Node *m  = phase->transform(n);
1849             if (outcnt() == 0) {  // Above transform() may kill us!
1850               return top;
1851             }
1852             // If transformed to a MergeMem, get the desired slice
1853             // Otherwise the returned node represents memory for every slice
1854             Node *new_mem = (m->is_MergeMem()) ?
1855                              m->as_MergeMem()->memory_at(alias_idx) : m;
1856             // Update input if it is progress over what we have now
1857             if (new_mem != ii) {
1858               set_req(i, new_mem);
1859               progress = this;
1860             }
1861           }
1862         }
1863       } else {
1864         // We know that at least one MergeMem->base_memory() == this
1865         // (saw_self == true). If all other inputs also references this phi
1866         // (directly or through data nodes) - it is dead loop.
1867         bool saw_safe_input = false;
1868         for (uint j = 1; j < req(); ++j) {
1869           Node *n = in(j);
1870           if (n->is_MergeMem() && n->as_MergeMem()->base_memory() == this)
1871             continue;              // skip known cases
1872           if (!is_unsafe_data_reference(n)) {
1873             saw_safe_input = true; // found safe input
1874             break;
1875           }
1876         }
1877         if (!saw_safe_input)
1878           return top; // all inputs reference back to this phi - dead loop
1879 
1880         // Phi(...MergeMem(m0, m1:AT1, m2:AT2)...) into
1881         //     MergeMem(Phi(...m0...), Phi:AT1(...m1...), Phi:AT2(...m2...))
1882         PhaseIterGVN *igvn = phase->is_IterGVN();
1883         Node* hook = new (phase->C) Node(1);
1884         PhiNode* new_base = (PhiNode*) clone();
1885         // Must eagerly register phis, since they participate in loops.
1886         if (igvn) {
1887           igvn->register_new_node_with_optimizer(new_base);
1888           hook->add_req(new_base);
1889         }
1890         MergeMemNode* result = MergeMemNode::make(phase->C, new_base);
1891         for (uint i = 1; i < req(); ++i) {
1892           Node *ii = in(i);
1893           if (ii->is_MergeMem()) {
1894             MergeMemNode* n = ii->as_MergeMem();
1895             for (MergeMemStream mms(result, n); mms.next_non_empty2(); ) {
1896               // If we have not seen this slice yet, make a phi for it.
1897               bool made_new_phi = false;
1898               if (mms.is_empty()) {
1899                 Node* new_phi = new_base->slice_memory(mms.adr_type(phase->C));
1900                 made_new_phi = true;
1901                 if (igvn) {
1902                   igvn->register_new_node_with_optimizer(new_phi);
1903                   hook->add_req(new_phi);
1904                 }
1905                 mms.set_memory(new_phi);
1906               }
1907               Node* phi = mms.memory();
1908               assert(made_new_phi || phi->in(i) == n, "replace the i-th merge by a slice");
1909               phi->set_req(i, mms.memory2());
1910             }
1911           }
1912         }
1913         // Distribute all self-loops.
1914         { // (Extra braces to hide mms.)
1915           for (MergeMemStream mms(result); mms.next_non_empty(); ) {
1916             Node* phi = mms.memory();
1917             for (uint i = 1; i < req(); ++i) {
1918               if (phi->in(i) == this)  phi->set_req(i, phi);
1919             }
1920           }
1921         }
1922         // now transform the new nodes, and return the mergemem
1923         for (MergeMemStream mms(result); mms.next_non_empty(); ) {
1924           Node* phi = mms.memory();
1925           mms.set_memory(phase->transform(phi));
1926         }
1927         if (igvn) { // Unhook.
1928           igvn->hash_delete(hook);
1929           for (uint i = 1; i < hook->req(); i++) {
1930             hook->set_req(i, NULL);
1931           }
1932         }
1933         // Replace self with the result.
1934         return result;
1935       }
1936     }
1937     //
1938     // Other optimizations on the memory chain
1939     //
1940     const TypePtr* at = adr_type();
1941     for( uint i=1; i<req(); ++i ) {// For all paths in
1942       Node *ii = in(i);
1943       Node *new_in = MemNode::optimize_memory_chain(ii, at, NULL, phase);
1944       if (ii != new_in ) {
1945         set_req(i, new_in);
1946         progress = this;
1947       }
1948     }
1949   }
1950 
1951 #ifdef _LP64
1952   // Push DecodeN/DecodeNKlass down through phi.
1953   // The rest of phi graph will transform by split EncodeP node though phis up.
1954   if ((UseCompressedOops || UseCompressedClassPointers) && can_reshape && progress == NULL) {
1955     bool may_push = true;
1956     bool has_decodeN = false;
1957     bool is_decodeN = false;
1958     for (uint i=1; i<req(); ++i) {// For all paths in
1959       Node *ii = in(i);
1960       if (ii->is_DecodeNarrowPtr() && ii->bottom_type() == bottom_type()) {
1961         // Do optimization if a non dead path exist.
1962         if (ii->in(1)->bottom_type() != Type::TOP) {
1963           has_decodeN = true;
1964           is_decodeN = ii->is_DecodeN();
1965         }
1966       } else if (!ii->is_Phi()) {
1967         may_push = false;
1968       }
1969     }
1970 
1971     if (has_decodeN && may_push) {
1972       PhaseIterGVN *igvn = phase->is_IterGVN();
1973       // Make narrow type for new phi.
1974       const Type* narrow_t;
1975       if (is_decodeN) {
1976         narrow_t = TypeNarrowOop::make(this->bottom_type()->is_ptr());
1977       } else {
1978         narrow_t = TypeNarrowKlass::make(this->bottom_type()->is_ptr());
1979       }
1980       PhiNode* new_phi = new (phase->C) PhiNode(r, narrow_t);
1981       uint orig_cnt = req();
1982       for (uint i=1; i<req(); ++i) {// For all paths in
1983         Node *ii = in(i);
1984         Node* new_ii = NULL;
1985         if (ii->is_DecodeNarrowPtr()) {
1986           assert(ii->bottom_type() == bottom_type(), "sanity");
1987           new_ii = ii->in(1);
1988         } else {
1989           assert(ii->is_Phi(), "sanity");
1990           if (ii->as_Phi() == this) {
1991             new_ii = new_phi;
1992           } else {
1993             if (is_decodeN) {
1994               new_ii = new (phase->C) EncodePNode(ii, narrow_t);
1995             } else {
1996               new_ii = new (phase->C) EncodePKlassNode(ii, narrow_t);
1997             }
1998             igvn->register_new_node_with_optimizer(new_ii);
1999           }
2000         }
2001         new_phi->set_req(i, new_ii);
2002       }
2003       igvn->register_new_node_with_optimizer(new_phi, this);
2004       if (is_decodeN) {
2005         progress = new (phase->C) DecodeNNode(new_phi, bottom_type());
2006       } else {
2007         progress = new (phase->C) DecodeNKlassNode(new_phi, bottom_type());
2008       }
2009     }
2010   }
2011 #endif
2012 
2013   return progress;              // Return any progress
2014 }
2015 
2016 //------------------------------is_tripcount-----------------------------------
2017 bool PhiNode::is_tripcount() const {
2018   return (in(0) != NULL && in(0)->is_CountedLoop() &&
2019           in(0)->as_CountedLoop()->phi() == this);
2020 }
2021 
2022 //------------------------------out_RegMask------------------------------------
2023 const RegMask &PhiNode::in_RegMask(uint i) const {
2024   return i ? out_RegMask() : RegMask::Empty;
2025 }
2026 
2027 const RegMask &PhiNode::out_RegMask() const {
2028   uint ideal_reg = _type->ideal_reg();
2029   assert( ideal_reg != Node::NotAMachineReg, "invalid type at Phi" );
2030   if( ideal_reg == 0 ) return RegMask::Empty;
2031   assert(ideal_reg != Op_RegFlags, "flags register is not spillable");
2032   return *(Compile::current()->matcher()->idealreg2spillmask[ideal_reg]);
2033 }
2034 
2035 #ifndef PRODUCT
2036 void PhiNode::dump_spec(outputStream *st) const {
2037   TypeNode::dump_spec(st);
2038   if (is_tripcount()) {
2039     st->print(" #tripcount");
2040   }
2041 }
2042 #endif
2043 
2044 
2045 //=============================================================================
2046 const Type *GotoNode::Value( PhaseTransform *phase ) const {
2047   // If the input is reachable, then we are executed.
2048   // If the input is not reachable, then we are not executed.
2049   return phase->type(in(0));
2050 }
2051 
2052 Node *GotoNode::Identity( PhaseTransform *phase ) {
2053   return in(0);                // Simple copy of incoming control
2054 }
2055 
2056 const RegMask &GotoNode::out_RegMask() const {
2057   return RegMask::Empty;
2058 }
2059 
2060 //=============================================================================
2061 const RegMask &JumpNode::out_RegMask() const {
2062   return RegMask::Empty;
2063 }
2064 
2065 //=============================================================================
2066 const RegMask &JProjNode::out_RegMask() const {
2067   return RegMask::Empty;
2068 }
2069 
2070 //=============================================================================
2071 const RegMask &CProjNode::out_RegMask() const {
2072   return RegMask::Empty;
2073 }
2074 
2075 
2076 
2077 //=============================================================================
2078 
2079 uint PCTableNode::hash() const { return Node::hash() + _size; }
2080 uint PCTableNode::cmp( const Node &n ) const
2081 { return _size == ((PCTableNode&)n)._size; }
2082 
2083 const Type *PCTableNode::bottom_type() const {
2084   const Type** f = TypeTuple::fields(_size);
2085   for( uint i = 0; i < _size; i++ ) f[i] = Type::CONTROL;
2086   return TypeTuple::make(_size, f);
2087 }
2088 
2089 //------------------------------Value------------------------------------------
2090 // Compute the type of the PCTableNode.  If reachable it is a tuple of
2091 // Control, otherwise the table targets are not reachable
2092 const Type *PCTableNode::Value( PhaseTransform *phase ) const {
2093   if( phase->type(in(0)) == Type::CONTROL )
2094     return bottom_type();
2095   return Type::TOP;             // All paths dead?  Then so are we
2096 }
2097 
2098 //------------------------------Ideal------------------------------------------
2099 // Return a node which is more "ideal" than the current node.  Strip out
2100 // control copies
2101 Node *PCTableNode::Ideal(PhaseGVN *phase, bool can_reshape) {
2102   return remove_dead_region(phase, can_reshape) ? this : NULL;
2103 }
2104 
2105 //=============================================================================
2106 uint JumpProjNode::hash() const {
2107   return Node::hash() + _dest_bci;
2108 }
2109 
2110 uint JumpProjNode::cmp( const Node &n ) const {
2111   return ProjNode::cmp(n) &&
2112     _dest_bci == ((JumpProjNode&)n)._dest_bci;
2113 }
2114 
2115 #ifndef PRODUCT
2116 void JumpProjNode::dump_spec(outputStream *st) const {
2117   ProjNode::dump_spec(st);
2118    st->print("@bci %d ",_dest_bci);
2119 }
2120 #endif
2121 
2122 //=============================================================================
2123 //------------------------------Value------------------------------------------
2124 // Check for being unreachable, or for coming from a Rethrow.  Rethrow's cannot
2125 // have the default "fall_through_index" path.
2126 const Type *CatchNode::Value( PhaseTransform *phase ) const {
2127   // Unreachable?  Then so are all paths from here.
2128   if( phase->type(in(0)) == Type::TOP ) return Type::TOP;
2129   // First assume all paths are reachable
2130   const Type** f = TypeTuple::fields(_size);
2131   for( uint i = 0; i < _size; i++ ) f[i] = Type::CONTROL;
2132   // Identify cases that will always throw an exception
2133   // () rethrow call
2134   // () virtual or interface call with NULL receiver
2135   // () call is a check cast with incompatible arguments
2136   if( in(1)->is_Proj() ) {
2137     Node *i10 = in(1)->in(0);
2138     if( i10->is_Call() ) {
2139       CallNode *call = i10->as_Call();
2140       // Rethrows always throw exceptions, never return
2141       if (call->entry_point() == OptoRuntime::rethrow_stub()) {
2142         f[CatchProjNode::fall_through_index] = Type::TOP;
2143       } else if( call->req() > TypeFunc::Parms ) {
2144         const Type *arg0 = phase->type( call->in(TypeFunc::Parms) );
2145         // Check for null receiver to virtual or interface calls
2146         if( call->is_CallDynamicJava() &&
2147             arg0->higher_equal(TypePtr::NULL_PTR) ) {
2148           f[CatchProjNode::fall_through_index] = Type::TOP;
2149         }
2150       } // End of if not a runtime stub
2151     } // End of if have call above me
2152   } // End of slot 1 is not a projection
2153   return TypeTuple::make(_size, f);
2154 }
2155 
2156 //=============================================================================
2157 uint CatchProjNode::hash() const {
2158   return Node::hash() + _handler_bci;
2159 }
2160 
2161 
2162 uint CatchProjNode::cmp( const Node &n ) const {
2163   return ProjNode::cmp(n) &&
2164     _handler_bci == ((CatchProjNode&)n)._handler_bci;
2165 }
2166 
2167 
2168 //------------------------------Identity---------------------------------------
2169 // If only 1 target is possible, choose it if it is the main control
2170 Node *CatchProjNode::Identity( PhaseTransform *phase ) {
2171   // If my value is control and no other value is, then treat as ID
2172   const TypeTuple *t = phase->type(in(0))->is_tuple();
2173   if (t->field_at(_con) != Type::CONTROL)  return this;
2174   // If we remove the last CatchProj and elide the Catch/CatchProj, then we
2175   // also remove any exception table entry.  Thus we must know the call
2176   // feeding the Catch will not really throw an exception.  This is ok for
2177   // the main fall-thru control (happens when we know a call can never throw
2178   // an exception) or for "rethrow", because a further optimization will
2179   // yank the rethrow (happens when we inline a function that can throw an
2180   // exception and the caller has no handler).  Not legal, e.g., for passing
2181   // a NULL receiver to a v-call, or passing bad types to a slow-check-cast.
2182   // These cases MUST throw an exception via the runtime system, so the VM
2183   // will be looking for a table entry.
2184   Node *proj = in(0)->in(1);    // Expect a proj feeding CatchNode
2185   CallNode *call;
2186   if (_con != TypeFunc::Control && // Bail out if not the main control.
2187       !(proj->is_Proj() &&      // AND NOT a rethrow
2188         proj->in(0)->is_Call() &&
2189         (call = proj->in(0)->as_Call()) &&
2190         call->entry_point() == OptoRuntime::rethrow_stub()))
2191     return this;
2192 
2193   // Search for any other path being control
2194   for (uint i = 0; i < t->cnt(); i++) {
2195     if (i != _con && t->field_at(i) == Type::CONTROL)
2196       return this;
2197   }
2198   // Only my path is possible; I am identity on control to the jump
2199   return in(0)->in(0);
2200 }
2201 
2202 
2203 #ifndef PRODUCT
2204 void CatchProjNode::dump_spec(outputStream *st) const {
2205   ProjNode::dump_spec(st);
2206   st->print("@bci %d ",_handler_bci);
2207 }
2208 #endif
2209 
2210 //=============================================================================
2211 //------------------------------Identity---------------------------------------
2212 // Check for CreateEx being Identity.
2213 Node *CreateExNode::Identity( PhaseTransform *phase ) {
2214   if( phase->type(in(1)) == Type::TOP ) return in(1);
2215   if( phase->type(in(0)) == Type::TOP ) return in(0);
2216   // We only come from CatchProj, unless the CatchProj goes away.
2217   // If the CatchProj is optimized away, then we just carry the
2218   // exception oop through.
2219   CallNode *call = in(1)->in(0)->as_Call();
2220 
2221   return ( in(0)->is_CatchProj() && in(0)->in(0)->in(1) == in(1) )
2222     ? this
2223     : call->in(TypeFunc::Parms);
2224 }
2225 
2226 //=============================================================================
2227 //------------------------------Value------------------------------------------
2228 // Check for being unreachable.
2229 const Type *NeverBranchNode::Value( PhaseTransform *phase ) const {
2230   if (!in(0) || in(0)->is_top()) return Type::TOP;
2231   return bottom_type();
2232 }
2233 
2234 //------------------------------Ideal------------------------------------------
2235 // Check for no longer being part of a loop
2236 Node *NeverBranchNode::Ideal(PhaseGVN *phase, bool can_reshape) {
2237   if (can_reshape && !in(0)->is_Loop()) {
2238     // Dead code elimination can sometimes delete this projection so
2239     // if it's not there, there's nothing to do.
2240     Node* fallthru = proj_out(0);
2241     if (fallthru != NULL) {
2242       phase->is_IterGVN()->replace_node(fallthru, in(0));
2243     }
2244     return phase->C->top();
2245   }
2246   return NULL;
2247 }
2248 
2249 #ifndef PRODUCT
2250 void NeverBranchNode::format( PhaseRegAlloc *ra_, outputStream *st) const {
2251   st->print("%s", Name());
2252 }
2253 #endif