1 /*
   2  * Copyright (c) 1998, 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 "memory/allocation.inline.hpp"
  27 #include "opto/block.hpp"
  28 #include "opto/c2compiler.hpp"
  29 #include "opto/callnode.hpp"
  30 #include "opto/cfgnode.hpp"
  31 #include "opto/machnode.hpp"
  32 #include "opto/runtime.hpp"
  33 #ifdef TARGET_ARCH_MODEL_x86_32
  34 # include "adfiles/ad_x86_32.hpp"
  35 #endif
  36 #ifdef TARGET_ARCH_MODEL_x86_64
  37 # include "adfiles/ad_x86_64.hpp"
  38 #endif
  39 #ifdef TARGET_ARCH_MODEL_sparc
  40 # include "adfiles/ad_sparc.hpp"
  41 #endif
  42 #ifdef TARGET_ARCH_MODEL_zero
  43 # include "adfiles/ad_zero.hpp"
  44 #endif
  45 #ifdef TARGET_ARCH_MODEL_arm
  46 # include "adfiles/ad_arm.hpp"
  47 #endif
  48 #ifdef TARGET_ARCH_MODEL_ppc_32
  49 # include "adfiles/ad_ppc_32.hpp"
  50 #endif
  51 #ifdef TARGET_ARCH_MODEL_ppc_64
  52 # include "adfiles/ad_ppc_64.hpp"
  53 #endif
  54 
  55 // Optimization - Graph Style
  56 
  57 // Check whether val is not-null-decoded compressed oop,
  58 // i.e. will grab into the base of the heap if it represents NULL.
  59 static bool accesses_heap_base_zone(Node *val) {
  60   if (Universe::narrow_oop_base() > 0) { // Implies UseCompressedOops.
  61     if (val && val->is_Mach()) {
  62       if (val->as_Mach()->ideal_Opcode() == Op_DecodeN) {
  63         // This assumes all Decodes with TypePtr::NotNull are matched to nodes that
  64         // decode NULL to point to the heap base (Decode_NN).
  65         if (val->bottom_type()->is_oopptr()->ptr() == TypePtr::NotNull) {
  66           return true;
  67         }
  68       }
  69       // Must recognize load operation with Decode matched in memory operand.
  70       // We should not reach here exept for PPC/AIX, as os::zero_page_read_protected()
  71       // returns true everywhere else. On PPC, no such memory operands
  72       // exist, therefore we did not yet implement a check for such operands.
  73       NOT_AIX(Unimplemented());
  74     }
  75   }
  76   return false;
  77 }
  78 
  79 static bool needs_explicit_null_check_for_read(Node *val) {
  80   // On some OSes (AIX) the page at address 0 is only write protected.
  81   // If so, only Store operations will trap.
  82   if (os::zero_page_read_protected()) {
  83     return false;  // Implicit null check will work.
  84   }
  85   // Also a read accessing the base of a heap-based compressed heap will trap.
  86   if (accesses_heap_base_zone(val) &&                    // Hits the base zone page.
  87       Universe::narrow_oop_use_implicit_null_checks()) { // Base zone page is protected.
  88     return false;
  89   }
  90 
  91   return true;
  92 }
  93 
  94 //------------------------------implicit_null_check----------------------------
  95 // Detect implicit-null-check opportunities.  Basically, find NULL checks
  96 // with suitable memory ops nearby.  Use the memory op to do the NULL check.
  97 // I can generate a memory op if there is not one nearby.
  98 // The proj is the control projection for the not-null case.
  99 // The val is the pointer being checked for nullness or
 100 // decodeHeapOop_not_null node if it did not fold into address.
 101 void PhaseCFG::implicit_null_check(Block* block, Node *proj, Node *val, int allowed_reasons) {
 102   // Assume if null check need for 0 offset then always needed
 103   // Intel solaris doesn't support any null checks yet and no
 104   // mechanism exists (yet) to set the switches at an os_cpu level
 105   if( !ImplicitNullChecks || MacroAssembler::needs_explicit_null_check(0)) return;
 106 
 107   // Make sure the ptr-is-null path appears to be uncommon!
 108   float f = block->end()->as_MachIf()->_prob;
 109   if( proj->Opcode() == Op_IfTrue ) f = 1.0f - f;
 110   if( f > PROB_UNLIKELY_MAG(4) ) return;
 111 
 112   uint bidx = 0;                // Capture index of value into memop
 113   bool was_store;               // Memory op is a store op
 114 
 115   // Get the successor block for if the test ptr is non-null
 116   Block* not_null_block;  // this one goes with the proj
 117   Block* null_block;
 118   if (block->get_node(block->number_of_nodes()-1) == proj) {
 119     null_block     = block->_succs[0];
 120     not_null_block = block->_succs[1];
 121   } else {
 122     assert(block->get_node(block->number_of_nodes()-2) == proj, "proj is one or the other");
 123     not_null_block = block->_succs[0];
 124     null_block     = block->_succs[1];
 125   }
 126   while (null_block->is_Empty() == Block::empty_with_goto) {
 127     null_block     = null_block->_succs[0];
 128   }
 129 
 130   // Search the exception block for an uncommon trap.
 131   // (See Parse::do_if and Parse::do_ifnull for the reason
 132   // we need an uncommon trap.  Briefly, we need a way to
 133   // detect failure of this optimization, as in 6366351.)
 134   {
 135     bool found_trap = false;
 136     for (uint i1 = 0; i1 < null_block->number_of_nodes(); i1++) {
 137       Node* nn = null_block->get_node(i1);
 138       if (nn->is_MachCall() &&
 139           nn->as_MachCall()->entry_point() == SharedRuntime::uncommon_trap_blob()->entry_point()) {
 140         const Type* trtype = nn->in(TypeFunc::Parms)->bottom_type();
 141         if (trtype->isa_int() && trtype->is_int()->is_con()) {
 142           jint tr_con = trtype->is_int()->get_con();
 143           Deoptimization::DeoptReason reason = Deoptimization::trap_request_reason(tr_con);
 144           Deoptimization::DeoptAction action = Deoptimization::trap_request_action(tr_con);
 145           assert((int)reason < (int)BitsPerInt, "recode bit map");
 146           if (is_set_nth_bit(allowed_reasons, (int) reason)
 147               && action != Deoptimization::Action_none) {
 148             // This uncommon trap is sure to recompile, eventually.
 149             // When that happens, C->too_many_traps will prevent
 150             // this transformation from happening again.
 151             found_trap = true;
 152           }
 153         }
 154         break;
 155       }
 156     }
 157     if (!found_trap) {
 158       // We did not find an uncommon trap.
 159       return;
 160     }
 161   }
 162 
 163   // Check for decodeHeapOop_not_null node which did not fold into address
 164   bool is_decoden = ((intptr_t)val) & 1;
 165   val = (Node*)(((intptr_t)val) & ~1);
 166 
 167   assert(!is_decoden || (val->in(0) == NULL) && val->is_Mach() &&
 168          (val->as_Mach()->ideal_Opcode() == Op_DecodeN), "sanity");
 169 
 170   // Search the successor block for a load or store who's base value is also
 171   // the tested value.  There may be several.
 172   Node_List *out = new Node_List(Thread::current()->resource_area());
 173   MachNode *best = NULL;        // Best found so far
 174   for (DUIterator i = val->outs(); val->has_out(i); i++) {
 175     Node *m = val->out(i);
 176     if( !m->is_Mach() ) continue;
 177     MachNode *mach = m->as_Mach();
 178     was_store = false;
 179     int iop = mach->ideal_Opcode();
 180     switch( iop ) {
 181     case Op_LoadB:
 182     case Op_LoadUB:
 183     case Op_LoadUS:
 184     case Op_LoadD:
 185     case Op_LoadF:
 186     case Op_LoadI:
 187     case Op_LoadL:
 188     case Op_LoadP:
 189     case Op_LoadN:
 190     case Op_LoadS:
 191     case Op_LoadKlass:
 192     case Op_LoadNKlass:
 193     case Op_LoadRange:
 194     case Op_LoadD_unaligned:
 195     case Op_LoadL_unaligned:
 196       assert(mach->in(2) == val, "should be address");
 197       break;
 198     case Op_StoreB:
 199     case Op_StoreC:
 200     case Op_StoreCM:
 201     case Op_StoreD:
 202     case Op_StoreF:
 203     case Op_StoreI:
 204     case Op_StoreL:
 205     case Op_StoreP:
 206     case Op_StoreN:
 207     case Op_StoreNKlass:
 208       was_store = true;         // Memory op is a store op
 209       // Stores will have their address in slot 2 (memory in slot 1).
 210       // If the value being nul-checked is in another slot, it means we
 211       // are storing the checked value, which does NOT check the value!
 212       if( mach->in(2) != val ) continue;
 213       break;                    // Found a memory op?
 214     case Op_StrComp:
 215     case Op_StrEquals:
 216     case Op_StrIndexOf:
 217     case Op_AryEq:
 218     case Op_EncodeISOArray:
 219       // Not a legit memory op for implicit null check regardless of
 220       // embedded loads
 221       continue;
 222     default:                    // Also check for embedded loads
 223       if( !mach->needs_anti_dependence_check() )
 224         continue;               // Not an memory op; skip it
 225       if( must_clone[iop] ) {
 226         // Do not move nodes which produce flags because
 227         // RA will try to clone it to place near branch and
 228         // it will cause recompilation, see clone_node().
 229         continue;
 230       }
 231       {
 232         // Check that value is used in memory address in
 233         // instructions with embedded load (CmpP val1,(val2+off)).
 234         Node* base;
 235         Node* index;
 236         const MachOper* oper = mach->memory_inputs(base, index);
 237         if (oper == NULL || oper == (MachOper*)-1) {
 238           continue;             // Not an memory op; skip it
 239         }
 240         if (val == base ||
 241             val == index && val->bottom_type()->isa_narrowoop()) {
 242           break;                // Found it
 243         } else {
 244           continue;             // Skip it
 245         }
 246       }
 247       break;
 248     }
 249 
 250     // On some OSes (AIX) the page at address 0 is only write protected.
 251     // If so, only Store operations will trap.
 252     // But a read accessing the base of a heap-based compressed heap will trap.
 253     if (!was_store && needs_explicit_null_check_for_read(val)) {
 254       continue;
 255     }
 256 
 257     // check if the offset is not too high for implicit exception
 258     {
 259       intptr_t offset = 0;
 260       const TypePtr *adr_type = NULL;  // Do not need this return value here
 261       const Node* base = mach->get_base_and_disp(offset, adr_type);
 262       if (base == NULL || base == NodeSentinel) {
 263         // Narrow oop address doesn't have base, only index
 264         if( val->bottom_type()->isa_narrowoop() &&
 265             MacroAssembler::needs_explicit_null_check(offset) )
 266           continue;             // Give up if offset is beyond page size
 267         // cannot reason about it; is probably not implicit null exception
 268       } else {
 269         const TypePtr* tptr;
 270         if (UseCompressedOops && (Universe::narrow_oop_shift() == 0 ||
 271                                   Universe::narrow_klass_shift() == 0)) {
 272           // 32-bits narrow oop can be the base of address expressions
 273           tptr = base->get_ptr_type();
 274         } else {
 275           // only regular oops are expected here
 276           tptr = base->bottom_type()->is_ptr();
 277         }
 278         // Give up if offset is not a compile-time constant
 279         if( offset == Type::OffsetBot || tptr->_offset == Type::OffsetBot )
 280           continue;
 281         offset += tptr->_offset; // correct if base is offseted
 282         if( MacroAssembler::needs_explicit_null_check(offset) )
 283           continue;             // Give up is reference is beyond 4K page size
 284       }
 285     }
 286 
 287     // Check ctrl input to see if the null-check dominates the memory op
 288     Block *cb = get_block_for_node(mach);
 289     cb = cb->_idom;             // Always hoist at least 1 block
 290     if( !was_store ) {          // Stores can be hoisted only one block
 291       while( cb->_dom_depth > (block->_dom_depth + 1))
 292         cb = cb->_idom;         // Hoist loads as far as we want
 293       // The non-null-block should dominate the memory op, too. Live
 294       // range spilling will insert a spill in the non-null-block if it is
 295       // needs to spill the memory op for an implicit null check.
 296       if (cb->_dom_depth == (block->_dom_depth + 1)) {
 297         if (cb != not_null_block) continue;
 298         cb = cb->_idom;
 299       }
 300     }
 301     if( cb != block ) continue;
 302 
 303     // Found a memory user; see if it can be hoisted to check-block
 304     uint vidx = 0;              // Capture index of value into memop
 305     uint j;
 306     for( j = mach->req()-1; j > 0; j-- ) {
 307       if( mach->in(j) == val ) {
 308         vidx = j;
 309         // Ignore DecodeN val which could be hoisted to where needed.
 310         if( is_decoden ) continue;
 311       }
 312       // Block of memory-op input
 313       Block *inb = get_block_for_node(mach->in(j));
 314       Block *b = block;          // Start from nul check
 315       while( b != inb && b->_dom_depth > inb->_dom_depth )
 316         b = b->_idom;           // search upwards for input
 317       // See if input dominates null check
 318       if( b != inb )
 319         break;
 320     }
 321     if( j > 0 )
 322       continue;
 323     Block *mb = get_block_for_node(mach);
 324     // Hoisting stores requires more checks for the anti-dependence case.
 325     // Give up hoisting if we have to move the store past any load.
 326     if( was_store ) {
 327       Block *b = mb;            // Start searching here for a local load
 328       // mach use (faulting) trying to hoist
 329       // n might be blocker to hoisting
 330       while( b != block ) {
 331         uint k;
 332         for( k = 1; k < b->number_of_nodes(); k++ ) {
 333           Node *n = b->get_node(k);
 334           if( n->needs_anti_dependence_check() &&
 335               n->in(LoadNode::Memory) == mach->in(StoreNode::Memory) )
 336             break;              // Found anti-dependent load
 337         }
 338         if( k < b->number_of_nodes() )
 339           break;                // Found anti-dependent load
 340         // Make sure control does not do a merge (would have to check allpaths)
 341         if( b->num_preds() != 2 ) break;
 342         b = get_block_for_node(b->pred(1)); // Move up to predecessor block
 343       }
 344       if( b != block ) continue;
 345     }
 346 
 347     // Make sure this memory op is not already being used for a NullCheck
 348     Node *e = mb->end();
 349     if( e->is_MachNullCheck() && e->in(1) == mach )
 350       continue;                 // Already being used as a NULL check
 351 
 352     // Found a candidate!  Pick one with least dom depth - the highest
 353     // in the dom tree should be closest to the null check.
 354     if (best == NULL || get_block_for_node(mach)->_dom_depth < get_block_for_node(best)->_dom_depth) {
 355       best = mach;
 356       bidx = vidx;
 357     }
 358   }
 359   // No candidate!
 360   if (best == NULL) {
 361     return;
 362   }
 363 
 364   // ---- Found an implicit null check
 365   extern int implicit_null_checks;
 366   implicit_null_checks++;
 367 
 368   if( is_decoden ) {
 369     // Check if we need to hoist decodeHeapOop_not_null first.
 370     Block *valb = get_block_for_node(val);
 371     if( block != valb && block->_dom_depth < valb->_dom_depth ) {
 372       // Hoist it up to the end of the test block.
 373       valb->find_remove(val);
 374       block->add_inst(val);
 375       map_node_to_block(val, block);
 376       // DecodeN on x86 may kill flags. Check for flag-killing projections
 377       // that also need to be hoisted.
 378       for (DUIterator_Fast jmax, j = val->fast_outs(jmax); j < jmax; j++) {
 379         Node* n = val->fast_out(j);
 380         if( n->is_MachProj() ) {
 381           get_block_for_node(n)->find_remove(n);
 382           block->add_inst(n);
 383           map_node_to_block(n, block);
 384         }
 385       }
 386     }
 387   }
 388   // Hoist the memory candidate up to the end of the test block.
 389   Block *old_block = get_block_for_node(best);
 390   old_block->find_remove(best);
 391   block->add_inst(best);
 392   map_node_to_block(best, block);
 393 
 394   // Move the control dependence
 395   if (best->in(0) && best->in(0) == old_block->head())
 396     best->set_req(0, block->head());
 397 
 398   // Check for flag-killing projections that also need to be hoisted
 399   // Should be DU safe because no edge updates.
 400   for (DUIterator_Fast jmax, j = best->fast_outs(jmax); j < jmax; j++) {
 401     Node* n = best->fast_out(j);
 402     if( n->is_MachProj() ) {
 403       get_block_for_node(n)->find_remove(n);
 404       block->add_inst(n);
 405       map_node_to_block(n, block);
 406     }
 407   }
 408 
 409   // proj==Op_True --> ne test; proj==Op_False --> eq test.
 410   // One of two graph shapes got matched:
 411   //   (IfTrue  (If (Bool NE (CmpP ptr NULL))))
 412   //   (IfFalse (If (Bool EQ (CmpP ptr NULL))))
 413   // NULL checks are always branch-if-eq.  If we see a IfTrue projection
 414   // then we are replacing a 'ne' test with a 'eq' NULL check test.
 415   // We need to flip the projections to keep the same semantics.
 416   if( proj->Opcode() == Op_IfTrue ) {
 417     // Swap order of projections in basic block to swap branch targets
 418     Node *tmp1 = block->get_node(block->end_idx()+1);
 419     Node *tmp2 = block->get_node(block->end_idx()+2);
 420     block->map_node(tmp2, block->end_idx()+1);
 421     block->map_node(tmp1, block->end_idx()+2);
 422     Node *tmp = new (C) Node(C->top()); // Use not NULL input
 423     tmp1->replace_by(tmp);
 424     tmp2->replace_by(tmp1);
 425     tmp->replace_by(tmp2);
 426     tmp->destruct();
 427   }
 428 
 429   // Remove the existing null check; use a new implicit null check instead.
 430   // Since schedule-local needs precise def-use info, we need to correct
 431   // it as well.
 432   Node *old_tst = proj->in(0);
 433   MachNode *nul_chk = new (C) MachNullCheckNode(old_tst->in(0),best,bidx);
 434   block->map_node(nul_chk, block->end_idx());
 435   map_node_to_block(nul_chk, block);
 436   // Redirect users of old_test to nul_chk
 437   for (DUIterator_Last i2min, i2 = old_tst->last_outs(i2min); i2 >= i2min; --i2)
 438     old_tst->last_out(i2)->set_req(0, nul_chk);
 439   // Clean-up any dead code
 440   for (uint i3 = 0; i3 < old_tst->req(); i3++)
 441     old_tst->set_req(i3, NULL);
 442 
 443   latency_from_uses(nul_chk);
 444   latency_from_uses(best);
 445 }
 446 
 447 
 448 //------------------------------select-----------------------------------------
 449 // Select a nice fellow from the worklist to schedule next. If there is only
 450 // one choice, then use it. Projections take top priority for correctness
 451 // reasons - if I see a projection, then it is next.  There are a number of
 452 // other special cases, for instructions that consume condition codes, et al.
 453 // These are chosen immediately. Some instructions are required to immediately
 454 // precede the last instruction in the block, and these are taken last. Of the
 455 // remaining cases (most), choose the instruction with the greatest latency
 456 // (that is, the most number of pseudo-cycles required to the end of the
 457 // routine). If there is a tie, choose the instruction with the most inputs.
 458 Node* PhaseCFG::select(Block* block, Node_List &worklist, GrowableArray<int> &ready_cnt, VectorSet &next_call, uint sched_slot) {
 459 
 460   // If only a single entry on the stack, use it
 461   uint cnt = worklist.size();
 462   if (cnt == 1) {
 463     Node *n = worklist[0];
 464     worklist.map(0,worklist.pop());
 465     return n;
 466   }
 467 
 468   uint choice  = 0; // Bigger is most important
 469   uint latency = 0; // Bigger is scheduled first
 470   uint score   = 0; // Bigger is better
 471   int idx = -1;     // Index in worklist
 472   int cand_cnt = 0; // Candidate count
 473 
 474   for( uint i=0; i<cnt; i++ ) { // Inspect entire worklist
 475     // Order in worklist is used to break ties.
 476     // See caller for how this is used to delay scheduling
 477     // of induction variable increments to after the other
 478     // uses of the phi are scheduled.
 479     Node *n = worklist[i];      // Get Node on worklist
 480 
 481     int iop = n->is_Mach() ? n->as_Mach()->ideal_Opcode() : 0;
 482     if( n->is_Proj() ||         // Projections always win
 483         n->Opcode()== Op_Con || // So does constant 'Top'
 484         iop == Op_CreateEx ||   // Create-exception must start block
 485         iop == Op_CheckCastPP
 486         ) {
 487       // select the node n
 488       // remove n from worklist and retain the order of remaining nodes
 489       worklist.remove((uint)i);
 490       return n;
 491     }
 492 
 493     // Final call in a block must be adjacent to 'catch'
 494     Node *e = block->end();
 495     if( e->is_Catch() && e->in(0)->in(0) == n )
 496       continue;
 497 
 498     // Memory op for an implicit null check has to be at the end of the block
 499     if( e->is_MachNullCheck() && e->in(1) == n )
 500       continue;
 501 
 502     // Schedule IV increment last.
 503     if (e->is_Mach() && e->as_Mach()->ideal_Opcode() == Op_CountedLoopEnd &&
 504         e->in(1)->in(1) == n && n->is_iteratively_computed())
 505       continue;
 506 
 507     uint n_choice  = 2;
 508 
 509     // See if this instruction is consumed by a branch. If so, then (as the
 510     // branch is the last instruction in the basic block) force it to the
 511     // end of the basic block
 512     if ( must_clone[iop] ) {
 513       // See if any use is a branch
 514       bool found_machif = false;
 515 
 516       for (DUIterator_Fast jmax, j = n->fast_outs(jmax); j < jmax; j++) {
 517         Node* use = n->fast_out(j);
 518 
 519         // The use is a conditional branch, make them adjacent
 520         if (use->is_MachIf() && get_block_for_node(use) == block) {
 521           found_machif = true;
 522           break;
 523         }
 524 
 525         // More than this instruction pending for successor to be ready,
 526         // don't choose this if other opportunities are ready
 527         if (ready_cnt.at(use->_idx) > 1)
 528           n_choice = 1;
 529       }
 530 
 531       // loop terminated, prefer not to use this instruction
 532       if (found_machif)
 533         continue;
 534     }
 535 
 536     // See if this has a predecessor that is "must_clone", i.e. sets the
 537     // condition code. If so, choose this first
 538     for (uint j = 0; j < n->req() ; j++) {
 539       Node *inn = n->in(j);
 540       if (inn) {
 541         if (inn->is_Mach() && must_clone[inn->as_Mach()->ideal_Opcode()] ) {
 542           n_choice = 3;
 543           break;
 544         }
 545       }
 546     }
 547 
 548     // MachTemps should be scheduled last so they are near their uses
 549     if (n->is_MachTemp()) {
 550       n_choice = 1;
 551     }
 552 
 553     uint n_latency = get_latency_for_node(n);
 554     uint n_score   = n->req();   // Many inputs get high score to break ties
 555 
 556     // Keep best latency found
 557     cand_cnt++;
 558     if (choice < n_choice ||
 559         (choice == n_choice &&
 560          ((StressLCM && Compile::randomized_select(cand_cnt)) ||
 561           (!StressLCM &&
 562            (latency < n_latency ||
 563             (latency == n_latency &&
 564              (score < n_score))))))) {
 565       choice  = n_choice;
 566       latency = n_latency;
 567       score   = n_score;
 568       idx     = i;               // Also keep index in worklist
 569     }
 570   } // End of for all ready nodes in worklist
 571 
 572   assert(idx >= 0, "index should be set");
 573   Node *n = worklist[(uint)idx];      // Get the winner
 574 
 575   // select the node n
 576   // remove n from worklist and retain the order of remaining nodes
 577   worklist.remove((uint)idx);
 578   return n;
 579 }
 580 
 581 
 582 //------------------------------set_next_call----------------------------------
 583 void PhaseCFG::set_next_call(Block* block, Node* n, VectorSet& next_call) {
 584   if( next_call.test_set(n->_idx) ) return;
 585   for( uint i=0; i<n->len(); i++ ) {
 586     Node *m = n->in(i);
 587     if( !m ) continue;  // must see all nodes in block that precede call
 588     if (get_block_for_node(m) == block) {
 589       set_next_call(block, m, next_call);
 590     }
 591   }
 592 }
 593 
 594 //------------------------------needed_for_next_call---------------------------
 595 // Set the flag 'next_call' for each Node that is needed for the next call to
 596 // be scheduled.  This flag lets me bias scheduling so Nodes needed for the
 597 // next subroutine call get priority - basically it moves things NOT needed
 598 // for the next call till after the call.  This prevents me from trying to
 599 // carry lots of stuff live across a call.
 600 void PhaseCFG::needed_for_next_call(Block* block, Node* this_call, VectorSet& next_call) {
 601   // Find the next control-defining Node in this block
 602   Node* call = NULL;
 603   for (DUIterator_Fast imax, i = this_call->fast_outs(imax); i < imax; i++) {
 604     Node* m = this_call->fast_out(i);
 605     if (get_block_for_node(m) == block && // Local-block user
 606         m != this_call &&       // Not self-start node
 607         m->is_MachCall()) {
 608       call = m;
 609       break;
 610     }
 611   }
 612   if (call == NULL)  return;    // No next call (e.g., block end is near)
 613   // Set next-call for all inputs to this call
 614   set_next_call(block, call, next_call);
 615 }
 616 
 617 //------------------------------add_call_kills-------------------------------------
 618 // helper function that adds caller save registers to MachProjNode
 619 static void add_call_kills(MachProjNode *proj, RegMask& regs, const char* save_policy, bool exclude_soe) {
 620   // Fill in the kill mask for the call
 621   for( OptoReg::Name r = OptoReg::Name(0); r < _last_Mach_Reg; r=OptoReg::add(r,1) ) {
 622     if( !regs.Member(r) ) {     // Not already defined by the call
 623       // Save-on-call register?
 624       if ((save_policy[r] == 'C') ||
 625           (save_policy[r] == 'A') ||
 626           ((save_policy[r] == 'E') && exclude_soe)) {
 627         proj->_rout.Insert(r);
 628       }
 629     }
 630   }
 631 }
 632 
 633 
 634 //------------------------------sched_call-------------------------------------
 635 uint PhaseCFG::sched_call(Block* block, uint node_cnt, Node_List& worklist, GrowableArray<int>& ready_cnt, MachCallNode* mcall, VectorSet& next_call) {
 636   RegMask regs;
 637 
 638   // Schedule all the users of the call right now.  All the users are
 639   // projection Nodes, so they must be scheduled next to the call.
 640   // Collect all the defined registers.
 641   for (DUIterator_Fast imax, i = mcall->fast_outs(imax); i < imax; i++) {
 642     Node* n = mcall->fast_out(i);
 643     assert( n->is_MachProj(), "" );
 644     int n_cnt = ready_cnt.at(n->_idx)-1;
 645     ready_cnt.at_put(n->_idx, n_cnt);
 646     assert( n_cnt == 0, "" );
 647     // Schedule next to call
 648     block->map_node(n, node_cnt++);
 649     // Collect defined registers
 650     regs.OR(n->out_RegMask());
 651     // Check for scheduling the next control-definer
 652     if( n->bottom_type() == Type::CONTROL )
 653       // Warm up next pile of heuristic bits
 654       needed_for_next_call(block, n, next_call);
 655 
 656     // Children of projections are now all ready
 657     for (DUIterator_Fast jmax, j = n->fast_outs(jmax); j < jmax; j++) {
 658       Node* m = n->fast_out(j); // Get user
 659       if(get_block_for_node(m) != block) {
 660         continue;
 661       }
 662       if( m->is_Phi() ) continue;
 663       int m_cnt = ready_cnt.at(m->_idx)-1;
 664       ready_cnt.at_put(m->_idx, m_cnt);
 665       if( m_cnt == 0 )
 666         worklist.push(m);
 667     }
 668 
 669   }
 670 
 671   // Act as if the call defines the Frame Pointer.
 672   // Certainly the FP is alive and well after the call.
 673   regs.Insert(_matcher.c_frame_pointer());
 674 
 675   // Set all registers killed and not already defined by the call.
 676   uint r_cnt = mcall->tf()->range()->cnt();
 677   int op = mcall->ideal_Opcode();
 678   MachProjNode *proj = new (C) MachProjNode( mcall, r_cnt+1, RegMask::Empty, MachProjNode::fat_proj );
 679   map_node_to_block(proj, block);
 680   block->insert_node(proj, node_cnt++);
 681 
 682   // Select the right register save policy.
 683   const char * save_policy;
 684   switch (op) {
 685     case Op_CallRuntime:
 686     case Op_CallLeaf:
 687     case Op_CallLeafNoFP:
 688       // Calling C code so use C calling convention
 689       save_policy = _matcher._c_reg_save_policy;
 690       break;
 691 
 692     case Op_CallStaticJava:
 693     case Op_CallDynamicJava:
 694       // Calling Java code so use Java calling convention
 695       save_policy = _matcher._register_save_policy;
 696       break;
 697 
 698     default:
 699       ShouldNotReachHere();
 700   }
 701 
 702   // When using CallRuntime mark SOE registers as killed by the call
 703   // so values that could show up in the RegisterMap aren't live in a
 704   // callee saved register since the register wouldn't know where to
 705   // find them.  CallLeaf and CallLeafNoFP are ok because they can't
 706   // have debug info on them.  Strictly speaking this only needs to be
 707   // done for oops since idealreg2debugmask takes care of debug info
 708   // references but there no way to handle oops differently than other
 709   // pointers as far as the kill mask goes.
 710   bool exclude_soe = op == Op_CallRuntime;
 711 
 712   // If the call is a MethodHandle invoke, we need to exclude the
 713   // register which is used to save the SP value over MH invokes from
 714   // the mask.  Otherwise this register could be used for
 715   // deoptimization information.
 716   if (op == Op_CallStaticJava) {
 717     MachCallStaticJavaNode* mcallstaticjava = (MachCallStaticJavaNode*) mcall;
 718     if (mcallstaticjava->_method_handle_invoke)
 719       proj->_rout.OR(Matcher::method_handle_invoke_SP_save_mask());
 720   }
 721 
 722   add_call_kills(proj, regs, save_policy, exclude_soe);
 723 
 724   return node_cnt;
 725 }
 726 
 727 
 728 //------------------------------schedule_local---------------------------------
 729 // Topological sort within a block.  Someday become a real scheduler.
 730 bool PhaseCFG::schedule_local(Block* block, GrowableArray<int>& ready_cnt, VectorSet& next_call) {
 731   // Already "sorted" are the block start Node (as the first entry), and
 732   // the block-ending Node and any trailing control projections.  We leave
 733   // these alone.  PhiNodes and ParmNodes are made to follow the block start
 734   // Node.  Everything else gets topo-sorted.
 735 
 736 #ifndef PRODUCT
 737     if (trace_opto_pipelining()) {
 738       tty->print_cr("# --- schedule_local B%d, before: ---", block->_pre_order);
 739       for (uint i = 0;i < block->number_of_nodes(); i++) {
 740         tty->print("# ");
 741         block->get_node(i)->fast_dump();
 742       }
 743       tty->print_cr("#");
 744     }
 745 #endif
 746 
 747   // RootNode is already sorted
 748   if (block->number_of_nodes() == 1) {
 749     return true;
 750   }
 751 
 752   // Move PhiNodes and ParmNodes from 1 to cnt up to the start
 753   uint node_cnt = block->end_idx();
 754   uint phi_cnt = 1;
 755   uint i;
 756   for( i = 1; i<node_cnt; i++ ) { // Scan for Phi
 757     Node *n = block->get_node(i);
 758     if( n->is_Phi() ||          // Found a PhiNode or ParmNode
 759         (n->is_Proj()  && n->in(0) == block->head()) ) {
 760       // Move guy at 'phi_cnt' to the end; makes a hole at phi_cnt
 761       block->map_node(block->get_node(phi_cnt), i);
 762       block->map_node(n, phi_cnt++);  // swap Phi/Parm up front
 763     } else {                    // All others
 764       // Count block-local inputs to 'n'
 765       uint cnt = n->len();      // Input count
 766       uint local = 0;
 767       for( uint j=0; j<cnt; j++ ) {
 768         Node *m = n->in(j);
 769         if( m && get_block_for_node(m) == block && !m->is_top() )
 770           local++;              // One more block-local input
 771       }
 772       ready_cnt.at_put(n->_idx, local); // Count em up
 773 
 774 #ifdef ASSERT
 775       if( UseConcMarkSweepGC || UseG1GC ) {
 776         if( n->is_Mach() && n->as_Mach()->ideal_Opcode() == Op_StoreCM ) {
 777           // Check the precedence edges
 778           for (uint prec = n->req(); prec < n->len(); prec++) {
 779             Node* oop_store = n->in(prec);
 780             if (oop_store != NULL) {
 781               assert(get_block_for_node(oop_store)->_dom_depth <= block->_dom_depth, "oop_store must dominate card-mark");
 782             }
 783           }
 784         }
 785       }
 786 #endif
 787 
 788       // A few node types require changing a required edge to a precedence edge
 789       // before allocation.
 790       if( n->is_Mach() && n->req() > TypeFunc::Parms &&
 791           (n->as_Mach()->ideal_Opcode() == Op_MemBarAcquire ||
 792            n->as_Mach()->ideal_Opcode() == Op_MemBarVolatile) ) {
 793         // MemBarAcquire could be created without Precedent edge.
 794         // del_req() replaces the specified edge with the last input edge
 795         // and then removes the last edge. If the specified edge > number of
 796         // edges the last edge will be moved outside of the input edges array
 797         // and the edge will be lost. This is why this code should be
 798         // executed only when Precedent (== TypeFunc::Parms) edge is present.
 799         Node *x = n->in(TypeFunc::Parms);
 800         n->del_req(TypeFunc::Parms);
 801         n->add_prec(x);
 802       }
 803     }
 804   }
 805   for(uint i2=i; i2< block->number_of_nodes(); i2++ ) // Trailing guys get zapped count
 806     ready_cnt.at_put(block->get_node(i2)->_idx, 0);
 807 
 808   // All the prescheduled guys do not hold back internal nodes
 809   uint i3;
 810   for(i3 = 0; i3<phi_cnt; i3++ ) {  // For all pre-scheduled
 811     Node *n = block->get_node(i3);       // Get pre-scheduled
 812     for (DUIterator_Fast jmax, j = n->fast_outs(jmax); j < jmax; j++) {
 813       Node* m = n->fast_out(j);
 814       if (get_block_for_node(m) == block) { // Local-block user
 815         int m_cnt = ready_cnt.at(m->_idx)-1;
 816         ready_cnt.at_put(m->_idx, m_cnt);   // Fix ready count
 817       }
 818     }
 819   }
 820 
 821   Node_List delay;
 822   // Make a worklist
 823   Node_List worklist;
 824   for(uint i4=i3; i4<node_cnt; i4++ ) {    // Put ready guys on worklist
 825     Node *m = block->get_node(i4);
 826     if( !ready_cnt.at(m->_idx) ) {   // Zero ready count?
 827       if (m->is_iteratively_computed()) {
 828         // Push induction variable increments last to allow other uses
 829         // of the phi to be scheduled first. The select() method breaks
 830         // ties in scheduling by worklist order.
 831         delay.push(m);
 832       } else if (m->is_Mach() && m->as_Mach()->ideal_Opcode() == Op_CreateEx) {
 833         // Force the CreateEx to the top of the list so it's processed
 834         // first and ends up at the start of the block.
 835         worklist.insert(0, m);
 836       } else {
 837         worklist.push(m);         // Then on to worklist!
 838       }
 839     }
 840   }
 841   while (delay.size()) {
 842     Node* d = delay.pop();
 843     worklist.push(d);
 844   }
 845 
 846   // Warm up the 'next_call' heuristic bits
 847   needed_for_next_call(block, block->head(), next_call);
 848 
 849 #ifndef PRODUCT
 850     if (trace_opto_pipelining()) {
 851       for (uint j=0; j< block->number_of_nodes(); j++) {
 852         Node     *n = block->get_node(j);
 853         int     idx = n->_idx;
 854         tty->print("#   ready cnt:%3d  ", ready_cnt.at(idx));
 855         tty->print("latency:%3d  ", get_latency_for_node(n));
 856         tty->print("%4d: %s\n", idx, n->Name());
 857       }
 858     }
 859 #endif
 860 
 861   uint max_idx = (uint)ready_cnt.length();
 862   // Pull from worklist and schedule
 863   while( worklist.size() ) {    // Worklist is not ready
 864 
 865 #ifndef PRODUCT
 866     if (trace_opto_pipelining()) {
 867       tty->print("#   ready list:");
 868       for( uint i=0; i<worklist.size(); i++ ) { // Inspect entire worklist
 869         Node *n = worklist[i];      // Get Node on worklist
 870         tty->print(" %d", n->_idx);
 871       }
 872       tty->cr();
 873     }
 874 #endif
 875 
 876     // Select and pop a ready guy from worklist
 877     Node* n = select(block, worklist, ready_cnt, next_call, phi_cnt);
 878     block->map_node(n, phi_cnt++);    // Schedule him next
 879 
 880 #ifndef PRODUCT
 881     if (trace_opto_pipelining()) {
 882       tty->print("#    select %d: %s", n->_idx, n->Name());
 883       tty->print(", latency:%d", get_latency_for_node(n));
 884       n->dump();
 885       if (Verbose) {
 886         tty->print("#   ready list:");
 887         for( uint i=0; i<worklist.size(); i++ ) { // Inspect entire worklist
 888           Node *n = worklist[i];      // Get Node on worklist
 889           tty->print(" %d", n->_idx);
 890         }
 891         tty->cr();
 892       }
 893     }
 894 
 895 #endif
 896     if( n->is_MachCall() ) {
 897       MachCallNode *mcall = n->as_MachCall();
 898       phi_cnt = sched_call(block, phi_cnt, worklist, ready_cnt, mcall, next_call);
 899       continue;
 900     }
 901 
 902     if (n->is_Mach() && n->as_Mach()->has_call()) {
 903       RegMask regs;
 904       regs.Insert(_matcher.c_frame_pointer());
 905       regs.OR(n->out_RegMask());
 906 
 907       MachProjNode *proj = new (C) MachProjNode( n, 1, RegMask::Empty, MachProjNode::fat_proj );
 908       map_node_to_block(proj, block);
 909       block->insert_node(proj, phi_cnt++);
 910 
 911       add_call_kills(proj, regs, _matcher._c_reg_save_policy, false);
 912     }
 913 
 914     // Children are now all ready
 915     for (DUIterator_Fast i5max, i5 = n->fast_outs(i5max); i5 < i5max; i5++) {
 916       Node* m = n->fast_out(i5); // Get user
 917       if (get_block_for_node(m) != block) {
 918         continue;
 919       }
 920       if( m->is_Phi() ) continue;
 921       if (m->_idx >= max_idx) { // new node, skip it
 922         assert(m->is_MachProj() && n->is_Mach() && n->as_Mach()->has_call(), "unexpected node types");
 923         continue;
 924       }
 925       int m_cnt = ready_cnt.at(m->_idx)-1;
 926       ready_cnt.at_put(m->_idx, m_cnt);
 927       if( m_cnt == 0 )
 928         worklist.push(m);
 929     }
 930   }
 931 
 932   if( phi_cnt != block->end_idx() ) {
 933     // did not schedule all.  Retry, Bailout, or Die
 934     if (C->subsume_loads() == true && !C->failing()) {
 935       // Retry with subsume_loads == false
 936       // If this is the first failure, the sentinel string will "stick"
 937       // to the Compile object, and the C2Compiler will see it and retry.
 938       C->record_failure(C2Compiler::retry_no_subsuming_loads());
 939     }
 940     // assert( phi_cnt == end_idx(), "did not schedule all" );
 941     return false;
 942   }
 943 
 944 #ifndef PRODUCT
 945   if (trace_opto_pipelining()) {
 946     tty->print_cr("#");
 947     tty->print_cr("# after schedule_local");
 948     for (uint i = 0;i < block->number_of_nodes();i++) {
 949       tty->print("# ");
 950       block->get_node(i)->fast_dump();
 951     }
 952     tty->cr();
 953   }
 954 #endif
 955 
 956 
 957   return true;
 958 }
 959 
 960 //--------------------------catch_cleanup_fix_all_inputs-----------------------
 961 static void catch_cleanup_fix_all_inputs(Node *use, Node *old_def, Node *new_def) {
 962   for (uint l = 0; l < use->len(); l++) {
 963     if (use->in(l) == old_def) {
 964       if (l < use->req()) {
 965         use->set_req(l, new_def);
 966       } else {
 967         use->rm_prec(l);
 968         use->add_prec(new_def);
 969         l--;
 970       }
 971     }
 972   }
 973 }
 974 
 975 //------------------------------catch_cleanup_find_cloned_def------------------
 976 Node* PhaseCFG::catch_cleanup_find_cloned_def(Block *use_blk, Node *def, Block *def_blk, int n_clone_idx) {
 977   assert( use_blk != def_blk, "Inter-block cleanup only");
 978 
 979   // The use is some block below the Catch.  Find and return the clone of the def
 980   // that dominates the use. If there is no clone in a dominating block, then
 981   // create a phi for the def in a dominating block.
 982 
 983   // Find which successor block dominates this use.  The successor
 984   // blocks must all be single-entry (from the Catch only; I will have
 985   // split blocks to make this so), hence they all dominate.
 986   while( use_blk->_dom_depth > def_blk->_dom_depth+1 )
 987     use_blk = use_blk->_idom;
 988 
 989   // Find the successor
 990   Node *fixup = NULL;
 991 
 992   uint j;
 993   for( j = 0; j < def_blk->_num_succs; j++ )
 994     if( use_blk == def_blk->_succs[j] )
 995       break;
 996 
 997   if( j == def_blk->_num_succs ) {
 998     // Block at same level in dom-tree is not a successor.  It needs a
 999     // PhiNode, the PhiNode uses from the def and IT's uses need fixup.
1000     Node_Array inputs = new Node_List(Thread::current()->resource_area());
1001     for(uint k = 1; k < use_blk->num_preds(); k++) {
1002       Block* block = get_block_for_node(use_blk->pred(k));
1003       inputs.map(k, catch_cleanup_find_cloned_def(block, def, def_blk, n_clone_idx));
1004     }
1005 
1006     // Check to see if the use_blk already has an identical phi inserted.
1007     // If it exists, it will be at the first position since all uses of a
1008     // def are processed together.
1009     Node *phi = use_blk->get_node(1);
1010     if( phi->is_Phi() ) {
1011       fixup = phi;
1012       for (uint k = 1; k < use_blk->num_preds(); k++) {
1013         if (phi->in(k) != inputs[k]) {
1014           // Not a match
1015           fixup = NULL;
1016           break;
1017         }
1018       }
1019     }
1020 
1021     // If an existing PhiNode was not found, make a new one.
1022     if (fixup == NULL) {
1023       Node *new_phi = PhiNode::make(use_blk->head(), def);
1024       use_blk->insert_node(new_phi, 1);
1025       map_node_to_block(new_phi, use_blk);
1026       for (uint k = 1; k < use_blk->num_preds(); k++) {
1027         new_phi->set_req(k, inputs[k]);
1028       }
1029       fixup = new_phi;
1030     }
1031 
1032   } else {
1033     // Found the use just below the Catch.  Make it use the clone.
1034     fixup = use_blk->get_node(n_clone_idx);
1035   }
1036 
1037   return fixup;
1038 }
1039 
1040 //--------------------------catch_cleanup_intra_block--------------------------
1041 // Fix all input edges in use that reference "def".  The use is in the same
1042 // block as the def and both have been cloned in each successor block.
1043 static void catch_cleanup_intra_block(Node *use, Node *def, Block *blk, int beg, int n_clone_idx) {
1044 
1045   // Both the use and def have been cloned. For each successor block,
1046   // get the clone of the use, and make its input the clone of the def
1047   // found in that block.
1048 
1049   uint use_idx = blk->find_node(use);
1050   uint offset_idx = use_idx - beg;
1051   for( uint k = 0; k < blk->_num_succs; k++ ) {
1052     // Get clone in each successor block
1053     Block *sb = blk->_succs[k];
1054     Node *clone = sb->get_node(offset_idx+1);
1055     assert( clone->Opcode() == use->Opcode(), "" );
1056 
1057     // Make use-clone reference the def-clone
1058     catch_cleanup_fix_all_inputs(clone, def, sb->get_node(n_clone_idx));
1059   }
1060 }
1061 
1062 //------------------------------catch_cleanup_inter_block---------------------
1063 // Fix all input edges in use that reference "def".  The use is in a different
1064 // block than the def.
1065 void PhaseCFG::catch_cleanup_inter_block(Node *use, Block *use_blk, Node *def, Block *def_blk, int n_clone_idx) {
1066   if( !use_blk ) return;        // Can happen if the use is a precedence edge
1067 
1068   Node *new_def = catch_cleanup_find_cloned_def(use_blk, def, def_blk, n_clone_idx);
1069   catch_cleanup_fix_all_inputs(use, def, new_def);
1070 }
1071 
1072 //------------------------------call_catch_cleanup-----------------------------
1073 // If we inserted any instructions between a Call and his CatchNode,
1074 // clone the instructions on all paths below the Catch.
1075 void PhaseCFG::call_catch_cleanup(Block* block) {
1076 
1077   // End of region to clone
1078   uint end = block->end_idx();
1079   if( !block->get_node(end)->is_Catch() ) return;
1080   // Start of region to clone
1081   uint beg = end;
1082   while(!block->get_node(beg-1)->is_MachProj() ||
1083         !block->get_node(beg-1)->in(0)->is_MachCall() ) {
1084     beg--;
1085     assert(beg > 0,"Catch cleanup walking beyond block boundary");
1086   }
1087   // Range of inserted instructions is [beg, end)
1088   if( beg == end ) return;
1089 
1090   // Clone along all Catch output paths.  Clone area between the 'beg' and
1091   // 'end' indices.
1092   for( uint i = 0; i < block->_num_succs; i++ ) {
1093     Block *sb = block->_succs[i];
1094     // Clone the entire area; ignoring the edge fixup for now.
1095     for( uint j = end; j > beg; j-- ) {
1096       // It is safe here to clone a node with anti_dependence
1097       // since clones dominate on each path.
1098       Node *clone = block->get_node(j-1)->clone();
1099       sb->insert_node(clone, 1);
1100       map_node_to_block(clone, sb);
1101     }
1102   }
1103 
1104 
1105   // Fixup edges.  Check the def-use info per cloned Node
1106   for(uint i2 = beg; i2 < end; i2++ ) {
1107     uint n_clone_idx = i2-beg+1; // Index of clone of n in each successor block
1108     Node *n = block->get_node(i2);        // Node that got cloned
1109     // Need DU safe iterator because of edge manipulation in calls.
1110     Unique_Node_List *out = new Unique_Node_List(Thread::current()->resource_area());
1111     for (DUIterator_Fast j1max, j1 = n->fast_outs(j1max); j1 < j1max; j1++) {
1112       out->push(n->fast_out(j1));
1113     }
1114     uint max = out->size();
1115     for (uint j = 0; j < max; j++) {// For all users
1116       Node *use = out->pop();
1117       Block *buse = get_block_for_node(use);
1118       if( use->is_Phi() ) {
1119         for( uint k = 1; k < use->req(); k++ )
1120           if( use->in(k) == n ) {
1121             Block* b = get_block_for_node(buse->pred(k));
1122             Node *fixup = catch_cleanup_find_cloned_def(b, n, block, n_clone_idx);
1123             use->set_req(k, fixup);
1124           }
1125       } else {
1126         if (block == buse) {
1127           catch_cleanup_intra_block(use, n, block, beg, n_clone_idx);
1128         } else {
1129           catch_cleanup_inter_block(use, buse, n, block, n_clone_idx);
1130         }
1131       }
1132     } // End for all users
1133 
1134   } // End of for all Nodes in cloned area
1135 
1136   // Remove the now-dead cloned ops
1137   for(uint i3 = beg; i3 < end; i3++ ) {
1138     block->get_node(beg)->disconnect_inputs(NULL, C);
1139     block->remove_node(beg);
1140   }
1141 
1142   // If the successor blocks have a CreateEx node, move it back to the top
1143   for(uint i4 = 0; i4 < block->_num_succs; i4++ ) {
1144     Block *sb = block->_succs[i4];
1145     uint new_cnt = end - beg;
1146     // Remove any newly created, but dead, nodes.
1147     for( uint j = new_cnt; j > 0; j-- ) {
1148       Node *n = sb->get_node(j);
1149       if (n->outcnt() == 0 &&
1150           (!n->is_Proj() || n->as_Proj()->in(0)->outcnt() == 1) ){
1151         n->disconnect_inputs(NULL, C);
1152         sb->remove_node(j);
1153         new_cnt--;
1154       }
1155     }
1156     // If any newly created nodes remain, move the CreateEx node to the top
1157     if (new_cnt > 0) {
1158       Node *cex = sb->get_node(1+new_cnt);
1159       if( cex->is_Mach() && cex->as_Mach()->ideal_Opcode() == Op_CreateEx ) {
1160         sb->remove_node(1+new_cnt);
1161         sb->insert_node(cex, 1);
1162       }
1163     }
1164   }
1165 }