1 /*
   2  * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "libadt/vectset.hpp"
  27 #include "memory/allocation.inline.hpp"
  28 #include "opto/block.hpp"
  29 #include "opto/c2compiler.hpp"
  30 #include "opto/callnode.hpp"
  31 #include "opto/cfgnode.hpp"
  32 #include "opto/machnode.hpp"
  33 #include "opto/opcodes.hpp"
  34 #include "opto/phaseX.hpp"
  35 #include "opto/rootnode.hpp"
  36 #include "opto/runtime.hpp"
  37 #include "runtime/deoptimization.hpp"
  38 #if defined AD_MD_HPP
  39 # include AD_MD_HPP
  40 #elif defined TARGET_ARCH_MODEL_x86_32
  41 # include "adfiles/ad_x86_32.hpp"
  42 #elif defined TARGET_ARCH_MODEL_x86_64
  43 # include "adfiles/ad_x86_64.hpp"
  44 #elif defined TARGET_ARCH_MODEL_sparc
  45 # include "adfiles/ad_sparc.hpp"
  46 #elif defined TARGET_ARCH_MODEL_zero
  47 # include "adfiles/ad_zero.hpp"
  48 #elif defined TARGET_ARCH_MODEL_ppc_64
  49 # include "adfiles/ad_ppc_64.hpp"
  50 #endif
  51 
  52 
  53 // Portions of code courtesy of Clifford Click
  54 
  55 // Optimization - Graph Style
  56 
  57 // To avoid float value underflow
  58 #define MIN_BLOCK_FREQUENCY 1.e-35f
  59 
  60 //----------------------------schedule_node_into_block-------------------------
  61 // Insert node n into block b. Look for projections of n and make sure they
  62 // are in b also.
  63 void PhaseCFG::schedule_node_into_block( Node *n, Block *b ) {
  64   // Set basic block of n, Add n to b,
  65   map_node_to_block(n, b);
  66   b->add_inst(n);
  67 
  68   // After Matching, nearly any old Node may have projections trailing it.
  69   // These are usually machine-dependent flags.  In any case, they might
  70   // float to another block below this one.  Move them up.
  71   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
  72     Node*  use  = n->fast_out(i);
  73     if (use->is_Proj()) {
  74       Block* buse = get_block_for_node(use);
  75       if (buse != b) {              // In wrong block?
  76         if (buse != NULL) {
  77           buse->find_remove(use);   // Remove from wrong block
  78         }
  79         map_node_to_block(use, b);
  80         b->add_inst(use);
  81       }
  82     }
  83   }
  84 }
  85 
  86 //----------------------------replace_block_proj_ctrl-------------------------
  87 // Nodes that have is_block_proj() nodes as their control need to use
  88 // the appropriate Region for their actual block as their control since
  89 // the projection will be in a predecessor block.
  90 void PhaseCFG::replace_block_proj_ctrl( Node *n ) {
  91   const Node *in0 = n->in(0);
  92   assert(in0 != NULL, "Only control-dependent");
  93   const Node *p = in0->is_block_proj();
  94   if (p != NULL && p != n) {    // Control from a block projection?
  95     assert(!n->pinned() || n->is_MachConstantBase(), "only pinned MachConstantBase node is expected here");
  96     // Find trailing Region
  97     Block *pb = get_block_for_node(in0); // Block-projection already has basic block
  98     uint j = 0;
  99     if (pb->_num_succs != 1) {  // More then 1 successor?
 100       // Search for successor
 101       uint max = pb->number_of_nodes();
 102       assert( max > 1, "" );
 103       uint start = max - pb->_num_succs;
 104       // Find which output path belongs to projection
 105       for (j = start; j < max; j++) {
 106         if( pb->get_node(j) == in0 )
 107           break;
 108       }
 109       assert( j < max, "must find" );
 110       // Change control to match head of successor basic block
 111       j -= start;
 112     }
 113     n->set_req(0, pb->_succs[j]->head());
 114   }
 115 }
 116 
 117 
 118 //------------------------------schedule_pinned_nodes--------------------------
 119 // Set the basic block for Nodes pinned into blocks
 120 void PhaseCFG::schedule_pinned_nodes(VectorSet &visited) {
 121   // Allocate node stack of size C->live_nodes()+8 to avoid frequent realloc
 122   GrowableArray <Node *> spstack(C->live_nodes() + 8);
 123   spstack.push(_root);
 124   while (spstack.is_nonempty()) {
 125     Node* node = spstack.pop();
 126     if (!visited.test_set(node->_idx)) { // Test node and flag it as visited
 127       if (node->pinned() && !has_block(node)) {  // Pinned?  Nail it down!
 128         assert(node->in(0), "pinned Node must have Control");
 129         // Before setting block replace block_proj control edge
 130         replace_block_proj_ctrl(node);
 131         Node* input = node->in(0);
 132         while (!input->is_block_start()) {
 133           input = input->in(0);
 134         }
 135         Block* block = get_block_for_node(input); // Basic block of controlling input
 136         schedule_node_into_block(node, block);
 137       }
 138 
 139       // process all inputs that are non NULL
 140       for (int i = node->req() - 1; i >= 0; --i) {
 141         if (node->in(i) != NULL) {
 142           spstack.push(node->in(i));
 143         }
 144       }
 145     }
 146   }
 147 }
 148 
 149 #ifdef ASSERT
 150 // Assert that new input b2 is dominated by all previous inputs.
 151 // Check this by by seeing that it is dominated by b1, the deepest
 152 // input observed until b2.
 153 static void assert_dom(Block* b1, Block* b2, Node* n, const PhaseCFG* cfg) {
 154   if (b1 == NULL)  return;
 155   assert(b1->_dom_depth < b2->_dom_depth, "sanity");
 156   Block* tmp = b2;
 157   while (tmp != b1 && tmp != NULL) {
 158     tmp = tmp->_idom;
 159   }
 160   if (tmp != b1) {
 161     // Detected an unschedulable graph.  Print some nice stuff and die.
 162     tty->print_cr("!!! Unschedulable graph !!!");
 163     for (uint j=0; j<n->len(); j++) { // For all inputs
 164       Node* inn = n->in(j); // Get input
 165       if (inn == NULL)  continue;  // Ignore NULL, missing inputs
 166       Block* inb = cfg->get_block_for_node(inn);
 167       tty->print("B%d idom=B%d depth=%2d ",inb->_pre_order,
 168                  inb->_idom ? inb->_idom->_pre_order : 0, inb->_dom_depth);
 169       inn->dump();
 170     }
 171     tty->print("Failing node: ");
 172     n->dump();
 173     assert(false, "unscheduable graph");
 174   }
 175 }
 176 #endif
 177 
 178 static Block* find_deepest_input(Node* n, const PhaseCFG* cfg) {
 179   // Find the last input dominated by all other inputs.
 180   Block* deepb           = NULL;        // Deepest block so far
 181   int    deepb_dom_depth = 0;
 182   for (uint k = 0; k < n->len(); k++) { // For all inputs
 183     Node* inn = n->in(k);               // Get input
 184     if (inn == NULL)  continue;         // Ignore NULL, missing inputs
 185     Block* inb = cfg->get_block_for_node(inn);
 186     assert(inb != NULL, "must already have scheduled this input");
 187     if (deepb_dom_depth < (int) inb->_dom_depth) {
 188       // The new inb must be dominated by the previous deepb.
 189       // The various inputs must be linearly ordered in the dom
 190       // tree, or else there will not be a unique deepest block.
 191       DEBUG_ONLY(assert_dom(deepb, inb, n, cfg));
 192       deepb = inb;                      // Save deepest block
 193       deepb_dom_depth = deepb->_dom_depth;
 194     }
 195   }
 196   assert(deepb != NULL, "must be at least one input to n");
 197   return deepb;
 198 }
 199 
 200 
 201 //------------------------------schedule_early---------------------------------
 202 // Find the earliest Block any instruction can be placed in.  Some instructions
 203 // are pinned into Blocks.  Unpinned instructions can appear in last block in
 204 // which all their inputs occur.
 205 bool PhaseCFG::schedule_early(VectorSet &visited, Node_List &roots) {
 206   // Allocate stack with enough space to avoid frequent realloc
 207   Node_Stack nstack(roots.Size() + 8);
 208   // _root will be processed among C->top() inputs
 209   roots.push(C->top());
 210   visited.set(C->top()->_idx);
 211 
 212   while (roots.size() != 0) {
 213     // Use local variables nstack_top_n & nstack_top_i to cache values
 214     // on stack's top.
 215     Node* parent_node = roots.pop();
 216     uint  input_index = 0;
 217 
 218     while (true) {
 219       if (input_index == 0) {
 220         // Fixup some control.  Constants without control get attached
 221         // to root and nodes that use is_block_proj() nodes should be attached
 222         // to the region that starts their block.
 223         const Node* control_input = parent_node->in(0);
 224         if (control_input != NULL) {
 225           replace_block_proj_ctrl(parent_node);
 226         } else {
 227           // Is a constant with NO inputs?
 228           if (parent_node->req() == 1) {
 229             parent_node->set_req(0, _root);
 230           }
 231         }
 232       }
 233 
 234       // First, visit all inputs and force them to get a block.  If an
 235       // input is already in a block we quit following inputs (to avoid
 236       // cycles). Instead we put that Node on a worklist to be handled
 237       // later (since IT'S inputs may not have a block yet).
 238 
 239       // Assume all n's inputs will be processed
 240       bool done = true;
 241 
 242       while (input_index < parent_node->len()) {
 243         Node* in = parent_node->in(input_index++);
 244         if (in == NULL) {
 245           continue;
 246         }
 247 
 248         int is_visited = visited.test_set(in->_idx);
 249         if (!has_block(in)) {
 250           if (is_visited) {
 251             return false;
 252           }
 253           // Save parent node and next input's index.
 254           nstack.push(parent_node, input_index);
 255           // Process current input now.
 256           parent_node = in;
 257           input_index = 0;
 258           // Not all n's inputs processed.
 259           done = false;
 260           break;
 261         } else if (!is_visited) {
 262           // Visit this guy later, using worklist
 263           roots.push(in);
 264         }
 265       }
 266 
 267       if (done) {
 268         // All of n's inputs have been processed, complete post-processing.
 269 
 270         // Some instructions are pinned into a block.  These include Region,
 271         // Phi, Start, Return, and other control-dependent instructions and
 272         // any projections which depend on them.
 273         if (!parent_node->pinned()) {
 274           // Set earliest legal block.
 275           Block* earliest_block = find_deepest_input(parent_node, this);
 276           map_node_to_block(parent_node, earliest_block);
 277         } else {
 278           assert(get_block_for_node(parent_node) == get_block_for_node(parent_node->in(0)), "Pinned Node should be at the same block as its control edge");
 279         }
 280 
 281         if (nstack.is_empty()) {
 282           // Finished all nodes on stack.
 283           // Process next node on the worklist 'roots'.
 284           break;
 285         }
 286         // Get saved parent node and next input's index.
 287         parent_node = nstack.node();
 288         input_index = nstack.index();
 289         nstack.pop();
 290       }
 291     }
 292   }
 293   return true;
 294 }
 295 
 296 //------------------------------dom_lca----------------------------------------
 297 // Find least common ancestor in dominator tree
 298 // LCA is a current notion of LCA, to be raised above 'this'.
 299 // As a convenient boundary condition, return 'this' if LCA is NULL.
 300 // Find the LCA of those two nodes.
 301 Block* Block::dom_lca(Block* LCA) {
 302   if (LCA == NULL || LCA == this)  return this;
 303 
 304   Block* anc = this;
 305   while (anc->_dom_depth > LCA->_dom_depth)
 306     anc = anc->_idom;           // Walk up till anc is as high as LCA
 307 
 308   while (LCA->_dom_depth > anc->_dom_depth)
 309     LCA = LCA->_idom;           // Walk up till LCA is as high as anc
 310 
 311   while (LCA != anc) {          // Walk both up till they are the same
 312     LCA = LCA->_idom;
 313     anc = anc->_idom;
 314   }
 315 
 316   return LCA;
 317 }
 318 
 319 //--------------------------raise_LCA_above_use--------------------------------
 320 // We are placing a definition, and have been given a def->use edge.
 321 // The definition must dominate the use, so move the LCA upward in the
 322 // dominator tree to dominate the use.  If the use is a phi, adjust
 323 // the LCA only with the phi input paths which actually use this def.
 324 static Block* raise_LCA_above_use(Block* LCA, Node* use, Node* def, const PhaseCFG* cfg) {
 325   Block* buse = cfg->get_block_for_node(use);
 326   if (buse == NULL)    return LCA;   // Unused killing Projs have no use block
 327   if (!use->is_Phi())  return buse->dom_lca(LCA);
 328   uint pmax = use->req();       // Number of Phi inputs
 329   // Why does not this loop just break after finding the matching input to
 330   // the Phi?  Well...it's like this.  I do not have true def-use/use-def
 331   // chains.  Means I cannot distinguish, from the def-use direction, which
 332   // of many use-defs lead from the same use to the same def.  That is, this
 333   // Phi might have several uses of the same def.  Each use appears in a
 334   // different predecessor block.  But when I enter here, I cannot distinguish
 335   // which use-def edge I should find the predecessor block for.  So I find
 336   // them all.  Means I do a little extra work if a Phi uses the same value
 337   // more than once.
 338   for (uint j=1; j<pmax; j++) { // For all inputs
 339     if (use->in(j) == def) {    // Found matching input?
 340       Block* pred = cfg->get_block_for_node(buse->pred(j));
 341       LCA = pred->dom_lca(LCA);
 342     }
 343   }
 344   return LCA;
 345 }
 346 
 347 //----------------------------raise_LCA_above_marks----------------------------
 348 // Return a new LCA that dominates LCA and any of its marked predecessors.
 349 // Search all my parents up to 'early' (exclusive), looking for predecessors
 350 // which are marked with the given index.  Return the LCA (in the dom tree)
 351 // of all marked blocks.  If there are none marked, return the original
 352 // LCA.
 353 static Block* raise_LCA_above_marks(Block* LCA, node_idx_t mark, Block* early, const PhaseCFG* cfg) {
 354   Block_List worklist;
 355   worklist.push(LCA);
 356   while (worklist.size() > 0) {
 357     Block* mid = worklist.pop();
 358     if (mid == early)  continue;  // stop searching here
 359 
 360     // Test and set the visited bit.
 361     if (mid->raise_LCA_visited() == mark)  continue;  // already visited
 362 
 363     // Don't process the current LCA, otherwise the search may terminate early
 364     if (mid != LCA && mid->raise_LCA_mark() == mark) {
 365       // Raise the LCA.
 366       LCA = mid->dom_lca(LCA);
 367       if (LCA == early)  break;   // stop searching everywhere
 368       assert(early->dominates(LCA), "early is high enough");
 369       // Resume searching at that point, skipping intermediate levels.
 370       worklist.push(LCA);
 371       if (LCA == mid)
 372         continue; // Don't mark as visited to avoid early termination.
 373     } else {
 374       // Keep searching through this block's predecessors.
 375       for (uint j = 1, jmax = mid->num_preds(); j < jmax; j++) {
 376         Block* mid_parent = cfg->get_block_for_node(mid->pred(j));
 377         worklist.push(mid_parent);
 378       }
 379     }
 380     mid->set_raise_LCA_visited(mark);
 381   }
 382   return LCA;
 383 }
 384 
 385 //--------------------------memory_early_block--------------------------------
 386 // This is a variation of find_deepest_input, the heart of schedule_early.
 387 // Find the "early" block for a load, if we considered only memory and
 388 // address inputs, that is, if other data inputs were ignored.
 389 //
 390 // Because a subset of edges are considered, the resulting block will
 391 // be earlier (at a shallower dom_depth) than the true schedule_early
 392 // point of the node. We compute this earlier block as a more permissive
 393 // site for anti-dependency insertion, but only if subsume_loads is enabled.
 394 static Block* memory_early_block(Node* load, Block* early, const PhaseCFG* cfg) {
 395   Node* base;
 396   Node* index;
 397   Node* store = load->in(MemNode::Memory);
 398   load->as_Mach()->memory_inputs(base, index);
 399 
 400   assert(base != NodeSentinel && index != NodeSentinel,
 401          "unexpected base/index inputs");
 402 
 403   Node* mem_inputs[4];
 404   int mem_inputs_length = 0;
 405   if (base != NULL)  mem_inputs[mem_inputs_length++] = base;
 406   if (index != NULL) mem_inputs[mem_inputs_length++] = index;
 407   if (store != NULL) mem_inputs[mem_inputs_length++] = store;
 408 
 409   // In the comparision below, add one to account for the control input,
 410   // which may be null, but always takes up a spot in the in array.
 411   if (mem_inputs_length + 1 < (int) load->req()) {
 412     // This "load" has more inputs than just the memory, base and index inputs.
 413     // For purposes of checking anti-dependences, we need to start
 414     // from the early block of only the address portion of the instruction,
 415     // and ignore other blocks that may have factored into the wider
 416     // schedule_early calculation.
 417     if (load->in(0) != NULL) mem_inputs[mem_inputs_length++] = load->in(0);
 418 
 419     Block* deepb           = NULL;        // Deepest block so far
 420     int    deepb_dom_depth = 0;
 421     for (int i = 0; i < mem_inputs_length; i++) {
 422       Block* inb = cfg->get_block_for_node(mem_inputs[i]);
 423       if (deepb_dom_depth < (int) inb->_dom_depth) {
 424         // The new inb must be dominated by the previous deepb.
 425         // The various inputs must be linearly ordered in the dom
 426         // tree, or else there will not be a unique deepest block.
 427         DEBUG_ONLY(assert_dom(deepb, inb, load, cfg));
 428         deepb = inb;                      // Save deepest block
 429         deepb_dom_depth = deepb->_dom_depth;
 430       }
 431     }
 432     early = deepb;
 433   }
 434 
 435   return early;
 436 }
 437 
 438 //--------------------------insert_anti_dependences---------------------------
 439 // A load may need to witness memory that nearby stores can overwrite.
 440 // For each nearby store, either insert an "anti-dependence" edge
 441 // from the load to the store, or else move LCA upward to force the
 442 // load to (eventually) be scheduled in a block above the store.
 443 //
 444 // Do not add edges to stores on distinct control-flow paths;
 445 // only add edges to stores which might interfere.
 446 //
 447 // Return the (updated) LCA.  There will not be any possibly interfering
 448 // store between the load's "early block" and the updated LCA.
 449 // Any stores in the updated LCA will have new precedence edges
 450 // back to the load.  The caller is expected to schedule the load
 451 // in the LCA, in which case the precedence edges will make LCM
 452 // preserve anti-dependences.  The caller may also hoist the load
 453 // above the LCA, if it is not the early block.
 454 Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
 455   assert(load->needs_anti_dependence_check(), "must be a load of some sort");
 456   assert(LCA != NULL, "");
 457   DEBUG_ONLY(Block* LCA_orig = LCA);
 458 
 459   // Compute the alias index.  Loads and stores with different alias indices
 460   // do not need anti-dependence edges.
 461   uint load_alias_idx = C->get_alias_index(load->adr_type());
 462 #ifdef ASSERT
 463   if (load_alias_idx == Compile::AliasIdxBot && C->AliasLevel() > 0 &&
 464       (PrintOpto || VerifyAliases ||
 465        PrintMiscellaneous && (WizardMode || Verbose))) {
 466     // Load nodes should not consume all of memory.
 467     // Reporting a bottom type indicates a bug in adlc.
 468     // If some particular type of node validly consumes all of memory,
 469     // sharpen the preceding "if" to exclude it, so we can catch bugs here.
 470     tty->print_cr("*** Possible Anti-Dependence Bug:  Load consumes all of memory.");
 471     load->dump(2);
 472     if (VerifyAliases)  assert(load_alias_idx != Compile::AliasIdxBot, "");
 473   }
 474 #endif
 475   assert(load_alias_idx || (load->is_Mach() && load->as_Mach()->ideal_Opcode() == Op_StrComp),
 476          "String compare is only known 'load' that does not conflict with any stores");
 477   assert(load_alias_idx || (load->is_Mach() && load->as_Mach()->ideal_Opcode() == Op_StrEquals),
 478          "String equals is a 'load' that does not conflict with any stores");
 479   assert(load_alias_idx || (load->is_Mach() && load->as_Mach()->ideal_Opcode() == Op_StrIndexOf),
 480          "String indexOf is a 'load' that does not conflict with any stores");
 481   assert(load_alias_idx || (load->is_Mach() && load->as_Mach()->ideal_Opcode() == Op_AryEq),
 482          "Arrays equals is a 'load' that do not conflict with any stores");
 483 
 484   if (!C->alias_type(load_alias_idx)->is_rewritable()) {
 485     // It is impossible to spoil this load by putting stores before it,
 486     // because we know that the stores will never update the value
 487     // which 'load' must witness.
 488     return LCA;
 489   }
 490 
 491   node_idx_t load_index = load->_idx;
 492 
 493   // Note the earliest legal placement of 'load', as determined by
 494   // by the unique point in the dom tree where all memory effects
 495   // and other inputs are first available.  (Computed by schedule_early.)
 496   // For normal loads, 'early' is the shallowest place (dom graph wise)
 497   // to look for anti-deps between this load and any store.
 498   Block* early = get_block_for_node(load);
 499 
 500   // If we are subsuming loads, compute an "early" block that only considers
 501   // memory or address inputs. This block may be different than the
 502   // schedule_early block in that it could be at an even shallower depth in the
 503   // dominator tree, and allow for a broader discovery of anti-dependences.
 504   if (C->subsume_loads()) {
 505     early = memory_early_block(load, early, this);
 506   }
 507 
 508   ResourceArea *area = Thread::current()->resource_area();
 509   Node_List worklist_mem(area);     // prior memory state to store
 510   Node_List worklist_store(area);   // possible-def to explore
 511   Node_List worklist_visited(area); // visited mergemem nodes
 512   Node_List non_early_stores(area); // all relevant stores outside of early
 513   bool must_raise_LCA = false;
 514 
 515 #ifdef TRACK_PHI_INPUTS
 516   // %%% This extra checking fails because MergeMem nodes are not GVNed.
 517   // Provide "phi_inputs" to check if every input to a PhiNode is from the
 518   // original memory state.  This indicates a PhiNode for which should not
 519   // prevent the load from sinking.  For such a block, set_raise_LCA_mark
 520   // may be overly conservative.
 521   // Mechanism: count inputs seen for each Phi encountered in worklist_store.
 522   DEBUG_ONLY(GrowableArray<uint> phi_inputs(area, C->unique(),0,0));
 523 #endif
 524 
 525   // 'load' uses some memory state; look for users of the same state.
 526   // Recurse through MergeMem nodes to the stores that use them.
 527 
 528   // Each of these stores is a possible definition of memory
 529   // that 'load' needs to use.  We need to force 'load'
 530   // to occur before each such store.  When the store is in
 531   // the same block as 'load', we insert an anti-dependence
 532   // edge load->store.
 533 
 534   // The relevant stores "nearby" the load consist of a tree rooted
 535   // at initial_mem, with internal nodes of type MergeMem.
 536   // Therefore, the branches visited by the worklist are of this form:
 537   //    initial_mem -> (MergeMem ->)* store
 538   // The anti-dependence constraints apply only to the fringe of this tree.
 539 
 540   Node* initial_mem = load->in(MemNode::Memory);
 541   worklist_store.push(initial_mem);
 542   worklist_visited.push(initial_mem);
 543   worklist_mem.push(NULL);
 544   while (worklist_store.size() > 0) {
 545     // Examine a nearby store to see if it might interfere with our load.
 546     Node* mem   = worklist_mem.pop();
 547     Node* store = worklist_store.pop();
 548     uint op = store->Opcode();
 549 
 550     // MergeMems do not directly have anti-deps.
 551     // Treat them as internal nodes in a forward tree of memory states,
 552     // the leaves of which are each a 'possible-def'.
 553     if (store == initial_mem    // root (exclusive) of tree we are searching
 554         || op == Op_MergeMem    // internal node of tree we are searching
 555         ) {
 556       mem = store;   // It's not a possibly interfering store.
 557       if (store == initial_mem)
 558         initial_mem = NULL;  // only process initial memory once
 559 
 560       for (DUIterator_Fast imax, i = mem->fast_outs(imax); i < imax; i++) {
 561         store = mem->fast_out(i);
 562         if (store->is_MergeMem()) {
 563           // Be sure we don't get into combinatorial problems.
 564           // (Allow phis to be repeated; they can merge two relevant states.)
 565           uint j = worklist_visited.size();
 566           for (; j > 0; j--) {
 567             if (worklist_visited.at(j-1) == store)  break;
 568           }
 569           if (j > 0)  continue; // already on work list; do not repeat
 570           worklist_visited.push(store);
 571         }
 572         worklist_mem.push(mem);
 573         worklist_store.push(store);
 574       }
 575       continue;
 576     }
 577 
 578     if (op == Op_MachProj || op == Op_Catch)   continue;
 579     if (store->needs_anti_dependence_check())  continue;  // not really a store
 580 
 581     // Compute the alias index.  Loads and stores with different alias
 582     // indices do not need anti-dependence edges.  Wide MemBar's are
 583     // anti-dependent on everything (except immutable memories).
 584     const TypePtr* adr_type = store->adr_type();
 585     if (!C->can_alias(adr_type, load_alias_idx))  continue;
 586 
 587     // Most slow-path runtime calls do NOT modify Java memory, but
 588     // they can block and so write Raw memory.
 589     if (store->is_Mach()) {
 590       MachNode* mstore = store->as_Mach();
 591       if (load_alias_idx != Compile::AliasIdxRaw) {
 592         // Check for call into the runtime using the Java calling
 593         // convention (and from there into a wrapper); it has no
 594         // _method.  Can't do this optimization for Native calls because
 595         // they CAN write to Java memory.
 596         if (mstore->ideal_Opcode() == Op_CallStaticJava) {
 597           assert(mstore->is_MachSafePoint(), "");
 598           MachSafePointNode* ms = (MachSafePointNode*) mstore;
 599           assert(ms->is_MachCallJava(), "");
 600           MachCallJavaNode* mcj = (MachCallJavaNode*) ms;
 601           if (mcj->_method == NULL) {
 602             // These runtime calls do not write to Java visible memory
 603             // (other than Raw) and so do not require anti-dependence edges.
 604             continue;
 605           }
 606         }
 607         // Same for SafePoints: they read/write Raw but only read otherwise.
 608         // This is basically a workaround for SafePoints only defining control
 609         // instead of control + memory.
 610         if (mstore->ideal_Opcode() == Op_SafePoint)
 611           continue;
 612       } else {
 613         // Some raw memory, such as the load of "top" at an allocation,
 614         // can be control dependent on the previous safepoint. See
 615         // comments in GraphKit::allocate_heap() about control input.
 616         // Inserting an anti-dep between such a safepoint and a use
 617         // creates a cycle, and will cause a subsequent failure in
 618         // local scheduling.  (BugId 4919904)
 619         // (%%% How can a control input be a safepoint and not a projection??)
 620         if (mstore->ideal_Opcode() == Op_SafePoint && load->in(0) == mstore)
 621           continue;
 622       }
 623     }
 624 
 625     // Identify a block that the current load must be above,
 626     // or else observe that 'store' is all the way up in the
 627     // earliest legal block for 'load'.  In the latter case,
 628     // immediately insert an anti-dependence edge.
 629     Block* store_block = get_block_for_node(store);
 630     assert(store_block != NULL, "unused killing projections skipped above");
 631 
 632     if (store->is_Phi()) {
 633       // 'load' uses memory which is one (or more) of the Phi's inputs.
 634       // It must be scheduled not before the Phi, but rather before
 635       // each of the relevant Phi inputs.
 636       //
 637       // Instead of finding the LCA of all inputs to a Phi that match 'mem',
 638       // we mark each corresponding predecessor block and do a combined
 639       // hoisting operation later (raise_LCA_above_marks).
 640       //
 641       // Do not assert(store_block != early, "Phi merging memory after access")
 642       // PhiNode may be at start of block 'early' with backedge to 'early'
 643       DEBUG_ONLY(bool found_match = false);
 644       for (uint j = PhiNode::Input, jmax = store->req(); j < jmax; j++) {
 645         if (store->in(j) == mem) {   // Found matching input?
 646           DEBUG_ONLY(found_match = true);
 647           Block* pred_block = get_block_for_node(store_block->pred(j));
 648           if (pred_block != early) {
 649             // If any predecessor of the Phi matches the load's "early block",
 650             // we do not need a precedence edge between the Phi and 'load'
 651             // since the load will be forced into a block preceding the Phi.
 652             pred_block->set_raise_LCA_mark(load_index);
 653             assert(!LCA_orig->dominates(pred_block) ||
 654                    early->dominates(pred_block), "early is high enough");
 655             must_raise_LCA = true;
 656           } else {
 657             // anti-dependent upon PHI pinned below 'early', no edge needed
 658             LCA = early;             // but can not schedule below 'early'
 659           }
 660         }
 661       }
 662       assert(found_match, "no worklist bug");
 663 #ifdef TRACK_PHI_INPUTS
 664 #ifdef ASSERT
 665       // This assert asks about correct handling of PhiNodes, which may not
 666       // have all input edges directly from 'mem'. See BugId 4621264
 667       int num_mem_inputs = phi_inputs.at_grow(store->_idx,0) + 1;
 668       // Increment by exactly one even if there are multiple copies of 'mem'
 669       // coming into the phi, because we will run this block several times
 670       // if there are several copies of 'mem'.  (That's how DU iterators work.)
 671       phi_inputs.at_put(store->_idx, num_mem_inputs);
 672       assert(PhiNode::Input + num_mem_inputs < store->req(),
 673              "Expect at least one phi input will not be from original memory state");
 674 #endif //ASSERT
 675 #endif //TRACK_PHI_INPUTS
 676     } else if (store_block != early) {
 677       // 'store' is between the current LCA and earliest possible block.
 678       // Label its block, and decide later on how to raise the LCA
 679       // to include the effect on LCA of this store.
 680       // If this store's block gets chosen as the raised LCA, we
 681       // will find him on the non_early_stores list and stick him
 682       // with a precedence edge.
 683       // (But, don't bother if LCA is already raised all the way.)
 684       if (LCA != early) {
 685         store_block->set_raise_LCA_mark(load_index);
 686         must_raise_LCA = true;
 687         non_early_stores.push(store);
 688       }
 689     } else {
 690       // Found a possibly-interfering store in the load's 'early' block.
 691       // This means 'load' cannot sink at all in the dominator tree.
 692       // Add an anti-dep edge, and squeeze 'load' into the highest block.
 693       assert(store != load->in(0), "dependence cycle found");
 694       if (verify) {
 695         assert(store->find_edge(load) != -1, "missing precedence edge");
 696       } else {
 697         store->add_prec(load);
 698       }
 699       LCA = early;
 700       // This turns off the process of gathering non_early_stores.
 701     }
 702   }
 703   // (Worklist is now empty; all nearby stores have been visited.)
 704 
 705   // Finished if 'load' must be scheduled in its 'early' block.
 706   // If we found any stores there, they have already been given
 707   // precedence edges.
 708   if (LCA == early)  return LCA;
 709 
 710   // We get here only if there are no possibly-interfering stores
 711   // in the load's 'early' block.  Move LCA up above all predecessors
 712   // which contain stores we have noted.
 713   //
 714   // The raised LCA block can be a home to such interfering stores,
 715   // but its predecessors must not contain any such stores.
 716   //
 717   // The raised LCA will be a lower bound for placing the load,
 718   // preventing the load from sinking past any block containing
 719   // a store that may invalidate the memory state required by 'load'.
 720   if (must_raise_LCA)
 721     LCA = raise_LCA_above_marks(LCA, load->_idx, early, this);
 722   if (LCA == early)  return LCA;
 723 
 724   // Insert anti-dependence edges from 'load' to each store
 725   // in the non-early LCA block.
 726   // Mine the non_early_stores list for such stores.
 727   if (LCA->raise_LCA_mark() == load_index) {
 728     while (non_early_stores.size() > 0) {
 729       Node* store = non_early_stores.pop();
 730       Block* store_block = get_block_for_node(store);
 731       if (store_block == LCA) {
 732         // add anti_dependence from store to load in its own block
 733         assert(store != load->in(0), "dependence cycle found");
 734         if (verify) {
 735           assert(store->find_edge(load) != -1, "missing precedence edge");
 736         } else {
 737           store->add_prec(load);
 738         }
 739       } else {
 740         assert(store_block->raise_LCA_mark() == load_index, "block was marked");
 741         // Any other stores we found must be either inside the new LCA
 742         // or else outside the original LCA.  In the latter case, they
 743         // did not interfere with any use of 'load'.
 744         assert(LCA->dominates(store_block)
 745                || !LCA_orig->dominates(store_block), "no stray stores");
 746       }
 747     }
 748   }
 749 
 750   // Return the highest block containing stores; any stores
 751   // within that block have been given anti-dependence edges.
 752   return LCA;
 753 }
 754 
 755 // This class is used to iterate backwards over the nodes in the graph.
 756 
 757 class Node_Backward_Iterator {
 758 
 759 private:
 760   Node_Backward_Iterator();
 761 
 762 public:
 763   // Constructor for the iterator
 764   Node_Backward_Iterator(Node *root, VectorSet &visited, Node_List &stack, PhaseCFG &cfg);
 765 
 766   // Postincrement operator to iterate over the nodes
 767   Node *next();
 768 
 769 private:
 770   VectorSet   &_visited;
 771   Node_List   &_stack;
 772   PhaseCFG &_cfg;
 773 };
 774 
 775 // Constructor for the Node_Backward_Iterator
 776 Node_Backward_Iterator::Node_Backward_Iterator( Node *root, VectorSet &visited, Node_List &stack, PhaseCFG &cfg)
 777   : _visited(visited), _stack(stack), _cfg(cfg) {
 778   // The stack should contain exactly the root
 779   stack.clear();
 780   stack.push(root);
 781 
 782   // Clear the visited bits
 783   visited.Clear();
 784 }
 785 
 786 // Iterator for the Node_Backward_Iterator
 787 Node *Node_Backward_Iterator::next() {
 788 
 789   // If the _stack is empty, then just return NULL: finished.
 790   if ( !_stack.size() )
 791     return NULL;
 792 
 793   // '_stack' is emulating a real _stack.  The 'visit-all-users' loop has been
 794   // made stateless, so I do not need to record the index 'i' on my _stack.
 795   // Instead I visit all users each time, scanning for unvisited users.
 796   // I visit unvisited not-anti-dependence users first, then anti-dependent
 797   // children next.
 798   Node *self = _stack.pop();
 799 
 800   // I cycle here when I am entering a deeper level of recursion.
 801   // The key variable 'self' was set prior to jumping here.
 802   while( 1 ) {
 803 
 804     _visited.set(self->_idx);
 805 
 806     // Now schedule all uses as late as possible.
 807     const Node* src = self->is_Proj() ? self->in(0) : self;
 808     uint src_rpo = _cfg.get_block_for_node(src)->_rpo;
 809 
 810     // Schedule all nodes in a post-order visit
 811     Node *unvisited = NULL;  // Unvisited anti-dependent Node, if any
 812 
 813     // Scan for unvisited nodes
 814     for (DUIterator_Fast imax, i = self->fast_outs(imax); i < imax; i++) {
 815       // For all uses, schedule late
 816       Node* n = self->fast_out(i); // Use
 817 
 818       // Skip already visited children
 819       if ( _visited.test(n->_idx) )
 820         continue;
 821 
 822       // do not traverse backward control edges
 823       Node *use = n->is_Proj() ? n->in(0) : n;
 824       uint use_rpo = _cfg.get_block_for_node(use)->_rpo;
 825 
 826       if ( use_rpo < src_rpo )
 827         continue;
 828 
 829       // Phi nodes always precede uses in a basic block
 830       if ( use_rpo == src_rpo && use->is_Phi() )
 831         continue;
 832 
 833       unvisited = n;      // Found unvisited
 834 
 835       // Check for possible-anti-dependent
 836       if( !n->needs_anti_dependence_check() )
 837         break;            // Not visited, not anti-dep; schedule it NOW
 838     }
 839 
 840     // Did I find an unvisited not-anti-dependent Node?
 841     if ( !unvisited )
 842       break;                  // All done with children; post-visit 'self'
 843 
 844     // Visit the unvisited Node.  Contains the obvious push to
 845     // indicate I'm entering a deeper level of recursion.  I push the
 846     // old state onto the _stack and set a new state and loop (recurse).
 847     _stack.push(self);
 848     self = unvisited;
 849   } // End recursion loop
 850 
 851   return self;
 852 }
 853 
 854 //------------------------------ComputeLatenciesBackwards----------------------
 855 // Compute the latency of all the instructions.
 856 void PhaseCFG::compute_latencies_backwards(VectorSet &visited, Node_List &stack) {
 857 #ifndef PRODUCT
 858   if (trace_opto_pipelining())
 859     tty->print("\n#---- ComputeLatenciesBackwards ----\n");
 860 #endif
 861 
 862   Node_Backward_Iterator iter((Node *)_root, visited, stack, *this);
 863   Node *n;
 864 
 865   // Walk over all the nodes from last to first
 866   while (n = iter.next()) {
 867     // Set the latency for the definitions of this instruction
 868     partial_latency_of_defs(n);
 869   }
 870 } // end ComputeLatenciesBackwards
 871 
 872 //------------------------------partial_latency_of_defs------------------------
 873 // Compute the latency impact of this node on all defs.  This computes
 874 // a number that increases as we approach the beginning of the routine.
 875 void PhaseCFG::partial_latency_of_defs(Node *n) {
 876   // Set the latency for this instruction
 877 #ifndef PRODUCT
 878   if (trace_opto_pipelining()) {
 879     tty->print("# latency_to_inputs: node_latency[%d] = %d for node", n->_idx, get_latency_for_node(n));
 880     dump();
 881   }
 882 #endif
 883 
 884   if (n->is_Proj()) {
 885     n = n->in(0);
 886   }
 887 
 888   if (n->is_Root()) {
 889     return;
 890   }
 891 
 892   uint nlen = n->len();
 893   uint use_latency = get_latency_for_node(n);
 894   uint use_pre_order = get_block_for_node(n)->_pre_order;
 895 
 896   for (uint j = 0; j < nlen; j++) {
 897     Node *def = n->in(j);
 898 
 899     if (!def || def == n) {
 900       continue;
 901     }
 902 
 903     // Walk backwards thru projections
 904     if (def->is_Proj()) {
 905       def = def->in(0);
 906     }
 907 
 908 #ifndef PRODUCT
 909     if (trace_opto_pipelining()) {
 910       tty->print("#    in(%2d): ", j);
 911       def->dump();
 912     }
 913 #endif
 914 
 915     // If the defining block is not known, assume it is ok
 916     Block *def_block = get_block_for_node(def);
 917     uint def_pre_order = def_block ? def_block->_pre_order : 0;
 918 
 919     if ((use_pre_order <  def_pre_order) || (use_pre_order == def_pre_order && n->is_Phi())) {
 920       continue;
 921     }
 922 
 923     uint delta_latency = n->latency(j);
 924     uint current_latency = delta_latency + use_latency;
 925 
 926     if (get_latency_for_node(def) < current_latency) {
 927       set_latency_for_node(def, current_latency);
 928     }
 929 
 930 #ifndef PRODUCT
 931     if (trace_opto_pipelining()) {
 932       tty->print_cr("#      %d + edge_latency(%d) == %d -> %d, node_latency[%d] = %d", use_latency, j, delta_latency, current_latency, def->_idx, get_latency_for_node(def));
 933     }
 934 #endif
 935   }
 936 }
 937 
 938 //------------------------------latency_from_use-------------------------------
 939 // Compute the latency of a specific use
 940 int PhaseCFG::latency_from_use(Node *n, const Node *def, Node *use) {
 941   // If self-reference, return no latency
 942   if (use == n || use->is_Root()) {
 943     return 0;
 944   }
 945 
 946   uint def_pre_order = get_block_for_node(def)->_pre_order;
 947   uint latency = 0;
 948 
 949   // If the use is not a projection, then it is simple...
 950   if (!use->is_Proj()) {
 951 #ifndef PRODUCT
 952     if (trace_opto_pipelining()) {
 953       tty->print("#    out(): ");
 954       use->dump();
 955     }
 956 #endif
 957 
 958     uint use_pre_order = get_block_for_node(use)->_pre_order;
 959 
 960     if (use_pre_order < def_pre_order)
 961       return 0;
 962 
 963     if (use_pre_order == def_pre_order && use->is_Phi())
 964       return 0;
 965 
 966     uint nlen = use->len();
 967     uint nl = get_latency_for_node(use);
 968 
 969     for ( uint j=0; j<nlen; j++ ) {
 970       if (use->in(j) == n) {
 971         // Change this if we want local latencies
 972         uint ul = use->latency(j);
 973         uint  l = ul + nl;
 974         if (latency < l) latency = l;
 975 #ifndef PRODUCT
 976         if (trace_opto_pipelining()) {
 977           tty->print_cr("#      %d + edge_latency(%d) == %d -> %d, latency = %d",
 978                         nl, j, ul, l, latency);
 979         }
 980 #endif
 981       }
 982     }
 983   } else {
 984     // This is a projection, just grab the latency of the use(s)
 985     for (DUIterator_Fast jmax, j = use->fast_outs(jmax); j < jmax; j++) {
 986       uint l = latency_from_use(use, def, use->fast_out(j));
 987       if (latency < l) latency = l;
 988     }
 989   }
 990 
 991   return latency;
 992 }
 993 
 994 //------------------------------latency_from_uses------------------------------
 995 // Compute the latency of this instruction relative to all of it's uses.
 996 // This computes a number that increases as we approach the beginning of the
 997 // routine.
 998 void PhaseCFG::latency_from_uses(Node *n) {
 999   // Set the latency for this instruction
1000 #ifndef PRODUCT
1001   if (trace_opto_pipelining()) {
1002     tty->print("# latency_from_outputs: node_latency[%d] = %d for node", n->_idx, get_latency_for_node(n));
1003     dump();
1004   }
1005 #endif
1006   uint latency=0;
1007   const Node *def = n->is_Proj() ? n->in(0): n;
1008 
1009   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
1010     uint l = latency_from_use(n, def, n->fast_out(i));
1011 
1012     if (latency < l) latency = l;
1013   }
1014 
1015   set_latency_for_node(n, latency);
1016 }
1017 
1018 //------------------------------hoist_to_cheaper_block-------------------------
1019 // Pick a block for node self, between early and LCA, that is a cheaper
1020 // alternative to LCA.
1021 Block* PhaseCFG::hoist_to_cheaper_block(Block* LCA, Block* early, Node* self) {
1022   const double delta = 1+PROB_UNLIKELY_MAG(4);
1023   Block* least       = LCA;
1024   double least_freq  = least->_freq;
1025   uint target        = get_latency_for_node(self);
1026   uint start_latency = get_latency_for_node(LCA->head());
1027   uint end_latency   = get_latency_for_node(LCA->get_node(LCA->end_idx()));
1028   bool in_latency    = (target <= start_latency);
1029   const Block* root_block = get_block_for_node(_root);
1030 
1031   // Turn off latency scheduling if scheduling is just plain off
1032   if (!C->do_scheduling())
1033     in_latency = true;
1034 
1035   // Do not hoist (to cover latency) instructions which target a
1036   // single register.  Hoisting stretches the live range of the
1037   // single register and may force spilling.
1038   MachNode* mach = self->is_Mach() ? self->as_Mach() : NULL;
1039   if (mach && mach->out_RegMask().is_bound1() && mach->out_RegMask().is_NotEmpty())
1040     in_latency = true;
1041 
1042 #ifndef PRODUCT
1043   if (trace_opto_pipelining()) {
1044     tty->print("# Find cheaper block for latency %d: ", get_latency_for_node(self));
1045     self->dump();
1046     tty->print_cr("#   B%d: start latency for [%4d]=%d, end latency for [%4d]=%d, freq=%g",
1047       LCA->_pre_order,
1048       LCA->head()->_idx,
1049       start_latency,
1050       LCA->get_node(LCA->end_idx())->_idx,
1051       end_latency,
1052       least_freq);
1053   }
1054 #endif
1055 
1056   int cand_cnt = 0;  // number of candidates tried
1057 
1058   // Walk up the dominator tree from LCA (Lowest common ancestor) to
1059   // the earliest legal location.  Capture the least execution frequency.
1060   while (LCA != early) {
1061     LCA = LCA->_idom;         // Follow up the dominator tree
1062 
1063     if (LCA == NULL) {
1064       // Bailout without retry
1065       C->record_method_not_compilable("late schedule failed: LCA == NULL");
1066       return least;
1067     }
1068 
1069     // Don't hoist machine instructions to the root basic block
1070     if (mach && LCA == root_block)
1071       break;
1072 
1073     uint start_lat = get_latency_for_node(LCA->head());
1074     uint end_idx   = LCA->end_idx();
1075     uint end_lat   = get_latency_for_node(LCA->get_node(end_idx));
1076     double LCA_freq = LCA->_freq;
1077 #ifndef PRODUCT
1078     if (trace_opto_pipelining()) {
1079       tty->print_cr("#   B%d: start latency for [%4d]=%d, end latency for [%4d]=%d, freq=%g",
1080         LCA->_pre_order, LCA->head()->_idx, start_lat, end_idx, end_lat, LCA_freq);
1081     }
1082 #endif
1083     cand_cnt++;
1084     if (LCA_freq < least_freq              || // Better Frequency
1085         (StressGCM && Compile::randomized_select(cand_cnt)) || // Should be randomly accepted in stress mode
1086          (!StressGCM                    &&    // Otherwise, choose with latency
1087           !in_latency                   &&    // No block containing latency
1088           LCA_freq < least_freq * delta &&    // No worse frequency
1089           target >= end_lat             &&    // within latency range
1090           !self->is_iteratively_computed() )  // But don't hoist IV increments
1091              // because they may end up above other uses of their phi forcing
1092              // their result register to be different from their input.
1093        ) {
1094       least = LCA;            // Found cheaper block
1095       least_freq = LCA_freq;
1096       start_latency = start_lat;
1097       end_latency = end_lat;
1098       if (target <= start_lat)
1099         in_latency = true;
1100     }
1101   }
1102 
1103 #ifndef PRODUCT
1104   if (trace_opto_pipelining()) {
1105     tty->print_cr("#  Choose block B%d with start latency=%d and freq=%g",
1106       least->_pre_order, start_latency, least_freq);
1107   }
1108 #endif
1109 
1110   // See if the latency needs to be updated
1111   if (target < end_latency) {
1112 #ifndef PRODUCT
1113     if (trace_opto_pipelining()) {
1114       tty->print_cr("#  Change latency for [%4d] from %d to %d", self->_idx, target, end_latency);
1115     }
1116 #endif
1117     set_latency_for_node(self, end_latency);
1118     partial_latency_of_defs(self);
1119   }
1120 
1121   return least;
1122 }
1123 
1124 
1125 //------------------------------schedule_late-----------------------------------
1126 // Now schedule all codes as LATE as possible.  This is the LCA in the
1127 // dominator tree of all USES of a value.  Pick the block with the least
1128 // loop nesting depth that is lowest in the dominator tree.
1129 extern const char must_clone[];
1130 void PhaseCFG::schedule_late(VectorSet &visited, Node_List &stack) {
1131 #ifndef PRODUCT
1132   if (trace_opto_pipelining())
1133     tty->print("\n#---- schedule_late ----\n");
1134 #endif
1135 
1136   Node_Backward_Iterator iter((Node *)_root, visited, stack, *this);
1137   Node *self;
1138 
1139   // Walk over all the nodes from last to first
1140   while (self = iter.next()) {
1141     Block* early = get_block_for_node(self); // Earliest legal placement
1142 
1143     if (self->is_top()) {
1144       // Top node goes in bb #2 with other constants.
1145       // It must be special-cased, because it has no out edges.
1146       early->add_inst(self);
1147       continue;
1148     }
1149 
1150     // No uses, just terminate
1151     if (self->outcnt() == 0) {
1152       assert(self->is_MachProj(), "sanity");
1153       continue;                   // Must be a dead machine projection
1154     }
1155 
1156     // If node is pinned in the block, then no scheduling can be done.
1157     if( self->pinned() )          // Pinned in block?
1158       continue;
1159 
1160     MachNode* mach = self->is_Mach() ? self->as_Mach() : NULL;
1161     if (mach) {
1162       switch (mach->ideal_Opcode()) {
1163       case Op_CreateEx:
1164         // Don't move exception creation
1165         early->add_inst(self);
1166         continue;
1167         break;
1168       case Op_CheckCastPP:
1169         // Don't move CheckCastPP nodes away from their input, if the input
1170         // is a rawptr (5071820).
1171         Node *def = self->in(1);
1172         if (def != NULL && def->bottom_type()->base() == Type::RawPtr) {
1173           early->add_inst(self);
1174 #ifdef ASSERT
1175           _raw_oops.push(def);
1176 #endif
1177           continue;
1178         }
1179         break;
1180       }
1181     }
1182 
1183     // Gather LCA of all uses
1184     Block *LCA = NULL;
1185     {
1186       for (DUIterator_Fast imax, i = self->fast_outs(imax); i < imax; i++) {
1187         // For all uses, find LCA
1188         Node* use = self->fast_out(i);
1189         LCA = raise_LCA_above_use(LCA, use, self, this);
1190       }
1191     }  // (Hide defs of imax, i from rest of block.)
1192 
1193     // Place temps in the block of their use.  This isn't a
1194     // requirement for correctness but it reduces useless
1195     // interference between temps and other nodes.
1196     if (mach != NULL && mach->is_MachTemp()) {
1197       map_node_to_block(self, LCA);
1198       LCA->add_inst(self);
1199       continue;
1200     }
1201 
1202     // Check if 'self' could be anti-dependent on memory
1203     if (self->needs_anti_dependence_check()) {
1204       // Hoist LCA above possible-defs and insert anti-dependences to
1205       // defs in new LCA block.
1206       LCA = insert_anti_dependences(LCA, self);
1207     }
1208 
1209     if (early->_dom_depth > LCA->_dom_depth) {
1210       // Somehow the LCA has moved above the earliest legal point.
1211       // (One way this can happen is via memory_early_block.)
1212       if (C->subsume_loads() == true && !C->failing()) {
1213         // Retry with subsume_loads == false
1214         // If this is the first failure, the sentinel string will "stick"
1215         // to the Compile object, and the C2Compiler will see it and retry.
1216         C->record_failure(C2Compiler::retry_no_subsuming_loads());
1217       } else {
1218         // Bailout without retry when (early->_dom_depth > LCA->_dom_depth)
1219         C->record_method_not_compilable("late schedule failed: incorrect graph");
1220       }
1221       return;
1222     }
1223 
1224     // If there is no opportunity to hoist, then we're done.
1225     // In stress mode, try to hoist even the single operations.
1226     bool try_to_hoist = StressGCM || (LCA != early);
1227 
1228     // Must clone guys stay next to use; no hoisting allowed.
1229     // Also cannot hoist guys that alter memory or are otherwise not
1230     // allocatable (hoisting can make a value live longer, leading to
1231     // anti and output dependency problems which are normally resolved
1232     // by the register allocator giving everyone a different register).
1233     if (mach != NULL && must_clone[mach->ideal_Opcode()])
1234       try_to_hoist = false;
1235 
1236     Block* late = NULL;
1237     if (try_to_hoist) {
1238       // Now find the block with the least execution frequency.
1239       // Start at the latest schedule and work up to the earliest schedule
1240       // in the dominator tree.  Thus the Node will dominate all its uses.
1241       late = hoist_to_cheaper_block(LCA, early, self);
1242     } else {
1243       // Just use the LCA of the uses.
1244       late = LCA;
1245     }
1246 
1247     // Put the node into target block
1248     schedule_node_into_block(self, late);
1249 
1250 #ifdef ASSERT
1251     if (self->needs_anti_dependence_check()) {
1252       // since precedence edges are only inserted when we're sure they
1253       // are needed make sure that after placement in a block we don't
1254       // need any new precedence edges.
1255       verify_anti_dependences(late, self);
1256     }
1257 #endif
1258   } // Loop until all nodes have been visited
1259 
1260 } // end ScheduleLate
1261 
1262 //------------------------------GlobalCodeMotion-------------------------------
1263 void PhaseCFG::global_code_motion() {
1264   ResourceMark rm;
1265 
1266 #ifndef PRODUCT
1267   if (trace_opto_pipelining()) {
1268     tty->print("\n---- Start GlobalCodeMotion ----\n");
1269   }
1270 #endif
1271 
1272   // Initialize the node to block mapping for things on the proj_list
1273   for (uint i = 0; i < _matcher.number_of_projections(); i++) {
1274     unmap_node_from_block(_matcher.get_projection(i));
1275   }
1276 
1277   // Set the basic block for Nodes pinned into blocks
1278   Arena* arena = Thread::current()->resource_area();
1279   VectorSet visited(arena);
1280   schedule_pinned_nodes(visited);
1281 
1282   // Find the earliest Block any instruction can be placed in.  Some
1283   // instructions are pinned into Blocks.  Unpinned instructions can
1284   // appear in last block in which all their inputs occur.
1285   visited.Clear();
1286   Node_List stack(arena);
1287   // Pre-grow the list
1288   stack.map((C->live_nodes() >> 1) + 16, NULL);
1289   if (!schedule_early(visited, stack)) {
1290     // Bailout without retry
1291     C->record_method_not_compilable("early schedule failed");
1292     return;
1293   }
1294 
1295   // Build Def-Use edges.
1296   // Compute the latency information (via backwards walk) for all the
1297   // instructions in the graph
1298   _node_latency = new GrowableArray<uint>(); // resource_area allocation
1299 
1300   if (C->do_scheduling()) {
1301     compute_latencies_backwards(visited, stack);
1302   }
1303 
1304   // Now schedule all codes as LATE as possible.  This is the LCA in the
1305   // dominator tree of all USES of a value.  Pick the block with the least
1306   // loop nesting depth that is lowest in the dominator tree.
1307   // ( visited.Clear() called in schedule_late()->Node_Backward_Iterator() )
1308   schedule_late(visited, stack);
1309   if (C->failing()) {
1310     // schedule_late fails only when graph is incorrect.
1311     assert(!VerifyGraphEdges, "verification should have failed");
1312     return;
1313   }
1314 
1315 #ifndef PRODUCT
1316   if (trace_opto_pipelining()) {
1317     tty->print("\n---- Detect implicit null checks ----\n");
1318   }
1319 #endif
1320 
1321   // Detect implicit-null-check opportunities.  Basically, find NULL checks
1322   // with suitable memory ops nearby.  Use the memory op to do the NULL check.
1323   // I can generate a memory op if there is not one nearby.
1324   if (C->is_method_compilation()) {
1325     // By reversing the loop direction we get a very minor gain on mpegaudio.
1326     // Feel free to revert to a forward loop for clarity.
1327     // for( int i=0; i < (int)matcher._null_check_tests.size(); i+=2 ) {
1328     for (int i = _matcher._null_check_tests.size() - 2; i >= 0; i -= 2) {
1329       Node* proj = _matcher._null_check_tests[i];
1330       Node* val  = _matcher._null_check_tests[i + 1];
1331       Block* block = get_block_for_node(proj);
1332       implicit_null_check(block, proj, val, C->allowed_deopt_reasons());
1333       // The implicit_null_check will only perform the transformation
1334       // if the null branch is truly uncommon, *and* it leads to an
1335       // uncommon trap.  Combined with the too_many_traps guards
1336       // above, this prevents SEGV storms reported in 6366351,
1337       // by recompiling offending methods without this optimization.
1338     }
1339   }
1340 
1341 #ifndef PRODUCT
1342   if (trace_opto_pipelining()) {
1343     tty->print("\n---- Start Local Scheduling ----\n");
1344   }
1345 #endif
1346 
1347   // Schedule locally.  Right now a simple topological sort.
1348   // Later, do a real latency aware scheduler.
1349   GrowableArray<int> ready_cnt(C->unique(), C->unique(), -1);
1350   visited.Clear();
1351   for (uint i = 0; i < number_of_blocks(); i++) {
1352     Block* block = get_block(i);
1353     if (!schedule_local(block, ready_cnt, visited)) {
1354       if (!C->failure_reason_is(C2Compiler::retry_no_subsuming_loads())) {
1355         C->record_method_not_compilable("local schedule failed");
1356       }
1357       return;
1358     }
1359   }
1360 
1361   // If we inserted any instructions between a Call and his CatchNode,
1362   // clone the instructions on all paths below the Catch.
1363   for (uint i = 0; i < number_of_blocks(); i++) {
1364     Block* block = get_block(i);
1365     call_catch_cleanup(block);
1366   }
1367 
1368 #ifndef PRODUCT
1369   if (trace_opto_pipelining()) {
1370     tty->print("\n---- After GlobalCodeMotion ----\n");
1371     for (uint i = 0; i < number_of_blocks(); i++) {
1372       Block* block = get_block(i);
1373       block->dump();
1374     }
1375   }
1376 #endif
1377   // Dead.
1378   _node_latency = (GrowableArray<uint> *)((intptr_t)0xdeadbeef);
1379 }
1380 
1381 bool PhaseCFG::do_global_code_motion() {
1382 
1383   build_dominator_tree();
1384   if (C->failing()) {
1385     return false;
1386   }
1387 
1388   NOT_PRODUCT( C->verify_graph_edges(); )
1389 
1390   estimate_block_frequency();
1391 
1392   global_code_motion();
1393 
1394   if (C->failing()) {
1395     return false;
1396   }
1397 
1398   return true;
1399 }
1400 
1401 //------------------------------Estimate_Block_Frequency-----------------------
1402 // Estimate block frequencies based on IfNode probabilities.
1403 void PhaseCFG::estimate_block_frequency() {
1404 
1405   // Force conditional branches leading to uncommon traps to be unlikely,
1406   // not because we get to the uncommon_trap with less relative frequency,
1407   // but because an uncommon_trap typically causes a deopt, so we only get
1408   // there once.
1409   if (C->do_freq_based_layout()) {
1410     Block_List worklist;
1411     Block* root_blk = get_block(0);
1412     for (uint i = 1; i < root_blk->num_preds(); i++) {
1413       Block *pb = get_block_for_node(root_blk->pred(i));
1414       if (pb->has_uncommon_code()) {
1415         worklist.push(pb);
1416       }
1417     }
1418     while (worklist.size() > 0) {
1419       Block* uct = worklist.pop();
1420       if (uct == get_root_block()) {
1421         continue;
1422       }
1423       for (uint i = 1; i < uct->num_preds(); i++) {
1424         Block *pb = get_block_for_node(uct->pred(i));
1425         if (pb->_num_succs == 1) {
1426           worklist.push(pb);
1427         } else if (pb->num_fall_throughs() == 2) {
1428           pb->update_uncommon_branch(uct);
1429         }
1430       }
1431     }
1432   }
1433 
1434   // Create the loop tree and calculate loop depth.
1435   _root_loop = create_loop_tree();
1436   _root_loop->compute_loop_depth(0);
1437 
1438   // Compute block frequency of each block, relative to a single loop entry.
1439   _root_loop->compute_freq();
1440 
1441   // Adjust all frequencies to be relative to a single method entry
1442   _root_loop->_freq = 1.0;
1443   _root_loop->scale_freq();
1444 
1445   // Save outmost loop frequency for LRG frequency threshold
1446   _outer_loop_frequency = _root_loop->outer_loop_freq();
1447 
1448   // force paths ending at uncommon traps to be infrequent
1449   if (!C->do_freq_based_layout()) {
1450     Block_List worklist;
1451     Block* root_blk = get_block(0);
1452     for (uint i = 1; i < root_blk->num_preds(); i++) {
1453       Block *pb = get_block_for_node(root_blk->pred(i));
1454       if (pb->has_uncommon_code()) {
1455         worklist.push(pb);
1456       }
1457     }
1458     while (worklist.size() > 0) {
1459       Block* uct = worklist.pop();
1460       uct->_freq = PROB_MIN;
1461       for (uint i = 1; i < uct->num_preds(); i++) {
1462         Block *pb = get_block_for_node(uct->pred(i));
1463         if (pb->_num_succs == 1 && pb->_freq > PROB_MIN) {
1464           worklist.push(pb);
1465         }
1466       }
1467     }
1468   }
1469 
1470 #ifdef ASSERT
1471   for (uint i = 0; i < number_of_blocks(); i++) {
1472     Block* b = get_block(i);
1473     assert(b->_freq >= MIN_BLOCK_FREQUENCY, "Register Allocator requires meaningful block frequency");
1474   }
1475 #endif
1476 
1477 #ifndef PRODUCT
1478   if (PrintCFGBlockFreq) {
1479     tty->print_cr("CFG Block Frequencies");
1480     _root_loop->dump_tree();
1481     if (Verbose) {
1482       tty->print_cr("PhaseCFG dump");
1483       dump();
1484       tty->print_cr("Node dump");
1485       _root->dump(99999);
1486     }
1487   }
1488 #endif
1489 }
1490 
1491 //----------------------------create_loop_tree--------------------------------
1492 // Create a loop tree from the CFG
1493 CFGLoop* PhaseCFG::create_loop_tree() {
1494 
1495 #ifdef ASSERT
1496   assert(get_block(0) == get_root_block(), "first block should be root block");
1497   for (uint i = 0; i < number_of_blocks(); i++) {
1498     Block* block = get_block(i);
1499     // Check that _loop field are clear...we could clear them if not.
1500     assert(block->_loop == NULL, "clear _loop expected");
1501     // Sanity check that the RPO numbering is reflected in the _blocks array.
1502     // It doesn't have to be for the loop tree to be built, but if it is not,
1503     // then the blocks have been reordered since dom graph building...which
1504     // may question the RPO numbering
1505     assert(block->_rpo == i, "unexpected reverse post order number");
1506   }
1507 #endif
1508 
1509   int idct = 0;
1510   CFGLoop* root_loop = new CFGLoop(idct++);
1511 
1512   Block_List worklist;
1513 
1514   // Assign blocks to loops
1515   for(uint i = number_of_blocks() - 1; i > 0; i-- ) { // skip Root block
1516     Block* block = get_block(i);
1517 
1518     if (block->head()->is_Loop()) {
1519       Block* loop_head = block;
1520       assert(loop_head->num_preds() - 1 == 2, "loop must have 2 predecessors");
1521       Node* tail_n = loop_head->pred(LoopNode::LoopBackControl);
1522       Block* tail = get_block_for_node(tail_n);
1523 
1524       // Defensively filter out Loop nodes for non-single-entry loops.
1525       // For all reasonable loops, the head occurs before the tail in RPO.
1526       if (i <= tail->_rpo) {
1527 
1528         // The tail and (recursive) predecessors of the tail
1529         // are made members of a new loop.
1530 
1531         assert(worklist.size() == 0, "nonempty worklist");
1532         CFGLoop* nloop = new CFGLoop(idct++);
1533         assert(loop_head->_loop == NULL, "just checking");
1534         loop_head->_loop = nloop;
1535         // Add to nloop so push_pred() will skip over inner loops
1536         nloop->add_member(loop_head);
1537         nloop->push_pred(loop_head, LoopNode::LoopBackControl, worklist, this);
1538 
1539         while (worklist.size() > 0) {
1540           Block* member = worklist.pop();
1541           if (member != loop_head) {
1542             for (uint j = 1; j < member->num_preds(); j++) {
1543               nloop->push_pred(member, j, worklist, this);
1544             }
1545           }
1546         }
1547       }
1548     }
1549   }
1550 
1551   // Create a member list for each loop consisting
1552   // of both blocks and (immediate child) loops.
1553   for (uint i = 0; i < number_of_blocks(); i++) {
1554     Block* block = get_block(i);
1555     CFGLoop* lp = block->_loop;
1556     if (lp == NULL) {
1557       // Not assigned to a loop. Add it to the method's pseudo loop.
1558       block->_loop = root_loop;
1559       lp = root_loop;
1560     }
1561     if (lp == root_loop || block != lp->head()) { // loop heads are already members
1562       lp->add_member(block);
1563     }
1564     if (lp != root_loop) {
1565       if (lp->parent() == NULL) {
1566         // Not a nested loop. Make it a child of the method's pseudo loop.
1567         root_loop->add_nested_loop(lp);
1568       }
1569       if (block == lp->head()) {
1570         // Add nested loop to member list of parent loop.
1571         lp->parent()->add_member(lp);
1572       }
1573     }
1574   }
1575 
1576   return root_loop;
1577 }
1578 
1579 //------------------------------push_pred--------------------------------------
1580 void CFGLoop::push_pred(Block* blk, int i, Block_List& worklist, PhaseCFG* cfg) {
1581   Node* pred_n = blk->pred(i);
1582   Block* pred = cfg->get_block_for_node(pred_n);
1583   CFGLoop *pred_loop = pred->_loop;
1584   if (pred_loop == NULL) {
1585     // Filter out blocks for non-single-entry loops.
1586     // For all reasonable loops, the head occurs before the tail in RPO.
1587     if (pred->_rpo > head()->_rpo) {
1588       pred->_loop = this;
1589       worklist.push(pred);
1590     }
1591   } else if (pred_loop != this) {
1592     // Nested loop.
1593     while (pred_loop->_parent != NULL && pred_loop->_parent != this) {
1594       pred_loop = pred_loop->_parent;
1595     }
1596     // Make pred's loop be a child
1597     if (pred_loop->_parent == NULL) {
1598       add_nested_loop(pred_loop);
1599       // Continue with loop entry predecessor.
1600       Block* pred_head = pred_loop->head();
1601       assert(pred_head->num_preds() - 1 == 2, "loop must have 2 predecessors");
1602       assert(pred_head != head(), "loop head in only one loop");
1603       push_pred(pred_head, LoopNode::EntryControl, worklist, cfg);
1604     } else {
1605       assert(pred_loop->_parent == this && _parent == NULL, "just checking");
1606     }
1607   }
1608 }
1609 
1610 //------------------------------add_nested_loop--------------------------------
1611 // Make cl a child of the current loop in the loop tree.
1612 void CFGLoop::add_nested_loop(CFGLoop* cl) {
1613   assert(_parent == NULL, "no parent yet");
1614   assert(cl != this, "not my own parent");
1615   cl->_parent = this;
1616   CFGLoop* ch = _child;
1617   if (ch == NULL) {
1618     _child = cl;
1619   } else {
1620     while (ch->_sibling != NULL) { ch = ch->_sibling; }
1621     ch->_sibling = cl;
1622   }
1623 }
1624 
1625 //------------------------------compute_loop_depth-----------------------------
1626 // Store the loop depth in each CFGLoop object.
1627 // Recursively walk the children to do the same for them.
1628 void CFGLoop::compute_loop_depth(int depth) {
1629   _depth = depth;
1630   CFGLoop* ch = _child;
1631   while (ch != NULL) {
1632     ch->compute_loop_depth(depth + 1);
1633     ch = ch->_sibling;
1634   }
1635 }
1636 
1637 //------------------------------compute_freq-----------------------------------
1638 // Compute the frequency of each block and loop, relative to a single entry
1639 // into the dominating loop head.
1640 void CFGLoop::compute_freq() {
1641   // Bottom up traversal of loop tree (visit inner loops first.)
1642   // Set loop head frequency to 1.0, then transitively
1643   // compute frequency for all successors in the loop,
1644   // as well as for each exit edge.  Inner loops are
1645   // treated as single blocks with loop exit targets
1646   // as the successor blocks.
1647 
1648   // Nested loops first
1649   CFGLoop* ch = _child;
1650   while (ch != NULL) {
1651     ch->compute_freq();
1652     ch = ch->_sibling;
1653   }
1654   assert (_members.length() > 0, "no empty loops");
1655   Block* hd = head();
1656   hd->_freq = 1.0f;
1657   for (int i = 0; i < _members.length(); i++) {
1658     CFGElement* s = _members.at(i);
1659     float freq = s->_freq;
1660     if (s->is_block()) {
1661       Block* b = s->as_Block();
1662       for (uint j = 0; j < b->_num_succs; j++) {
1663         Block* sb = b->_succs[j];
1664         update_succ_freq(sb, freq * b->succ_prob(j));
1665       }
1666     } else {
1667       CFGLoop* lp = s->as_CFGLoop();
1668       assert(lp->_parent == this, "immediate child");
1669       for (int k = 0; k < lp->_exits.length(); k++) {
1670         Block* eb = lp->_exits.at(k).get_target();
1671         float prob = lp->_exits.at(k).get_prob();
1672         update_succ_freq(eb, freq * prob);
1673       }
1674     }
1675   }
1676 
1677   // For all loops other than the outer, "method" loop,
1678   // sum and normalize the exit probability. The "method" loop
1679   // should keep the initial exit probability of 1, so that
1680   // inner blocks do not get erroneously scaled.
1681   if (_depth != 0) {
1682     // Total the exit probabilities for this loop.
1683     float exits_sum = 0.0f;
1684     for (int i = 0; i < _exits.length(); i++) {
1685       exits_sum += _exits.at(i).get_prob();
1686     }
1687 
1688     // Normalize the exit probabilities. Until now, the
1689     // probabilities estimate the possibility of exit per
1690     // a single loop iteration; afterward, they estimate
1691     // the probability of exit per loop entry.
1692     for (int i = 0; i < _exits.length(); i++) {
1693       Block* et = _exits.at(i).get_target();
1694       float new_prob = 0.0f;
1695       if (_exits.at(i).get_prob() > 0.0f) {
1696         new_prob = _exits.at(i).get_prob() / exits_sum;
1697       }
1698       BlockProbPair bpp(et, new_prob);
1699       _exits.at_put(i, bpp);
1700     }
1701 
1702     // Save the total, but guard against unreasonable probability,
1703     // as the value is used to estimate the loop trip count.
1704     // An infinite trip count would blur relative block
1705     // frequencies.
1706     if (exits_sum > 1.0f) exits_sum = 1.0;
1707     if (exits_sum < PROB_MIN) exits_sum = PROB_MIN;
1708     _exit_prob = exits_sum;
1709   }
1710 }
1711 
1712 //------------------------------succ_prob-------------------------------------
1713 // Determine the probability of reaching successor 'i' from the receiver block.
1714 float Block::succ_prob(uint i) {
1715   int eidx = end_idx();
1716   Node *n = get_node(eidx);  // Get ending Node
1717 
1718   int op = n->Opcode();
1719   if (n->is_Mach()) {
1720     if (n->is_MachNullCheck()) {
1721       // Can only reach here if called after lcm. The original Op_If is gone,
1722       // so we attempt to infer the probability from one or both of the
1723       // successor blocks.
1724       assert(_num_succs == 2, "expecting 2 successors of a null check");
1725       // If either successor has only one predecessor, then the
1726       // probability estimate can be derived using the
1727       // relative frequency of the successor and this block.
1728       if (_succs[i]->num_preds() == 2) {
1729         return _succs[i]->_freq / _freq;
1730       } else if (_succs[1-i]->num_preds() == 2) {
1731         return 1 - (_succs[1-i]->_freq / _freq);
1732       } else {
1733         // Estimate using both successor frequencies
1734         float freq = _succs[i]->_freq;
1735         return freq / (freq + _succs[1-i]->_freq);
1736       }
1737     }
1738     op = n->as_Mach()->ideal_Opcode();
1739   }
1740 
1741 
1742   // Switch on branch type
1743   switch( op ) {
1744   case Op_CountedLoopEnd:
1745   case Op_If: {
1746     assert (i < 2, "just checking");
1747     // Conditionals pass on only part of their frequency
1748     float prob  = n->as_MachIf()->_prob;
1749     assert(prob >= 0.0 && prob <= 1.0, "out of range probability");
1750     // If succ[i] is the FALSE branch, invert path info
1751     if( get_node(i + eidx + 1)->Opcode() == Op_IfFalse ) {
1752       return 1.0f - prob; // not taken
1753     } else {
1754       return prob; // taken
1755     }
1756   }
1757 
1758   case Op_Jump:
1759     // Divide the frequency between all successors evenly
1760     return 1.0f/_num_succs;
1761 
1762   case Op_Catch: {
1763     const CatchProjNode *ci = get_node(i + eidx + 1)->as_CatchProj();
1764     if (ci->_con == CatchProjNode::fall_through_index) {
1765       // Fall-thru path gets the lion's share.
1766       return 1.0f - PROB_UNLIKELY_MAG(5)*_num_succs;
1767     } else {
1768       // Presume exceptional paths are equally unlikely
1769       return PROB_UNLIKELY_MAG(5);
1770     }
1771   }
1772 
1773   case Op_Root:
1774   case Op_Goto:
1775     // Pass frequency straight thru to target
1776     return 1.0f;
1777 
1778   case Op_NeverBranch:
1779     return 0.0f;
1780 
1781   case Op_TailCall:
1782   case Op_TailJump:
1783   case Op_Return:
1784   case Op_Halt:
1785   case Op_Rethrow:
1786     // Do not push out freq to root block
1787     return 0.0f;
1788 
1789   default:
1790     ShouldNotReachHere();
1791   }
1792 
1793   return 0.0f;
1794 }
1795 
1796 //------------------------------num_fall_throughs-----------------------------
1797 // Return the number of fall-through candidates for a block
1798 int Block::num_fall_throughs() {
1799   int eidx = end_idx();
1800   Node *n = get_node(eidx);  // Get ending Node
1801 
1802   int op = n->Opcode();
1803   if (n->is_Mach()) {
1804     if (n->is_MachNullCheck()) {
1805       // In theory, either side can fall-thru, for simplicity sake,
1806       // let's say only the false branch can now.
1807       return 1;
1808     }
1809     op = n->as_Mach()->ideal_Opcode();
1810   }
1811 
1812   // Switch on branch type
1813   switch( op ) {
1814   case Op_CountedLoopEnd:
1815   case Op_If:
1816     return 2;
1817 
1818   case Op_Root:
1819   case Op_Goto:
1820     return 1;
1821 
1822   case Op_Catch: {
1823     for (uint i = 0; i < _num_succs; i++) {
1824       const CatchProjNode *ci = get_node(i + eidx + 1)->as_CatchProj();
1825       if (ci->_con == CatchProjNode::fall_through_index) {
1826         return 1;
1827       }
1828     }
1829     return 0;
1830   }
1831 
1832   case Op_Jump:
1833   case Op_NeverBranch:
1834   case Op_TailCall:
1835   case Op_TailJump:
1836   case Op_Return:
1837   case Op_Halt:
1838   case Op_Rethrow:
1839     return 0;
1840 
1841   default:
1842     ShouldNotReachHere();
1843   }
1844 
1845   return 0;
1846 }
1847 
1848 //------------------------------succ_fall_through-----------------------------
1849 // Return true if a specific successor could be fall-through target.
1850 bool Block::succ_fall_through(uint i) {
1851   int eidx = end_idx();
1852   Node *n = get_node(eidx);  // Get ending Node
1853 
1854   int op = n->Opcode();
1855   if (n->is_Mach()) {
1856     if (n->is_MachNullCheck()) {
1857       // In theory, either side can fall-thru, for simplicity sake,
1858       // let's say only the false branch can now.
1859       return get_node(i + eidx + 1)->Opcode() == Op_IfFalse;
1860     }
1861     op = n->as_Mach()->ideal_Opcode();
1862   }
1863 
1864   // Switch on branch type
1865   switch( op ) {
1866   case Op_CountedLoopEnd:
1867   case Op_If:
1868   case Op_Root:
1869   case Op_Goto:
1870     return true;
1871 
1872   case Op_Catch: {
1873     const CatchProjNode *ci = get_node(i + eidx + 1)->as_CatchProj();
1874     return ci->_con == CatchProjNode::fall_through_index;
1875   }
1876 
1877   case Op_Jump:
1878   case Op_NeverBranch:
1879   case Op_TailCall:
1880   case Op_TailJump:
1881   case Op_Return:
1882   case Op_Halt:
1883   case Op_Rethrow:
1884     return false;
1885 
1886   default:
1887     ShouldNotReachHere();
1888   }
1889 
1890   return false;
1891 }
1892 
1893 //------------------------------update_uncommon_branch------------------------
1894 // Update the probability of a two-branch to be uncommon
1895 void Block::update_uncommon_branch(Block* ub) {
1896   int eidx = end_idx();
1897   Node *n = get_node(eidx);  // Get ending Node
1898 
1899   int op = n->as_Mach()->ideal_Opcode();
1900 
1901   assert(op == Op_CountedLoopEnd || op == Op_If, "must be a If");
1902   assert(num_fall_throughs() == 2, "must be a two way branch block");
1903 
1904   // Which successor is ub?
1905   uint s;
1906   for (s = 0; s <_num_succs; s++) {
1907     if (_succs[s] == ub) break;
1908   }
1909   assert(s < 2, "uncommon successor must be found");
1910 
1911   // If ub is the true path, make the proability small, else
1912   // ub is the false path, and make the probability large
1913   bool invert = (get_node(s + eidx + 1)->Opcode() == Op_IfFalse);
1914 
1915   // Get existing probability
1916   float p = n->as_MachIf()->_prob;
1917 
1918   if (invert) p = 1.0 - p;
1919   if (p > PROB_MIN) {
1920     p = PROB_MIN;
1921   }
1922   if (invert) p = 1.0 - p;
1923 
1924   n->as_MachIf()->_prob = p;
1925 }
1926 
1927 //------------------------------update_succ_freq-------------------------------
1928 // Update the appropriate frequency associated with block 'b', a successor of
1929 // a block in this loop.
1930 void CFGLoop::update_succ_freq(Block* b, float freq) {
1931   if (b->_loop == this) {
1932     if (b == head()) {
1933       // back branch within the loop
1934       // Do nothing now, the loop carried frequency will be
1935       // adjust later in scale_freq().
1936     } else {
1937       // simple branch within the loop
1938       b->_freq += freq;
1939     }
1940   } else if (!in_loop_nest(b)) {
1941     // branch is exit from this loop
1942     BlockProbPair bpp(b, freq);
1943     _exits.append(bpp);
1944   } else {
1945     // branch into nested loop
1946     CFGLoop* ch = b->_loop;
1947     ch->_freq += freq;
1948   }
1949 }
1950 
1951 //------------------------------in_loop_nest-----------------------------------
1952 // Determine if block b is in the receiver's loop nest.
1953 bool CFGLoop::in_loop_nest(Block* b) {
1954   int depth = _depth;
1955   CFGLoop* b_loop = b->_loop;
1956   int b_depth = b_loop->_depth;
1957   if (depth == b_depth) {
1958     return true;
1959   }
1960   while (b_depth > depth) {
1961     b_loop = b_loop->_parent;
1962     b_depth = b_loop->_depth;
1963   }
1964   return b_loop == this;
1965 }
1966 
1967 //------------------------------scale_freq-------------------------------------
1968 // Scale frequency of loops and blocks by trip counts from outer loops
1969 // Do a top down traversal of loop tree (visit outer loops first.)
1970 void CFGLoop::scale_freq() {
1971   float loop_freq = _freq * trip_count();
1972   _freq = loop_freq;
1973   for (int i = 0; i < _members.length(); i++) {
1974     CFGElement* s = _members.at(i);
1975     float block_freq = s->_freq * loop_freq;
1976     if (g_isnan(block_freq) || block_freq < MIN_BLOCK_FREQUENCY)
1977       block_freq = MIN_BLOCK_FREQUENCY;
1978     s->_freq = block_freq;
1979   }
1980   CFGLoop* ch = _child;
1981   while (ch != NULL) {
1982     ch->scale_freq();
1983     ch = ch->_sibling;
1984   }
1985 }
1986 
1987 // Frequency of outer loop
1988 float CFGLoop::outer_loop_freq() const {
1989   if (_child != NULL) {
1990     return _child->_freq;
1991   }
1992   return _freq;
1993 }
1994 
1995 #ifndef PRODUCT
1996 //------------------------------dump_tree--------------------------------------
1997 void CFGLoop::dump_tree() const {
1998   dump();
1999   if (_child != NULL)   _child->dump_tree();
2000   if (_sibling != NULL) _sibling->dump_tree();
2001 }
2002 
2003 //------------------------------dump-------------------------------------------
2004 void CFGLoop::dump() const {
2005   for (int i = 0; i < _depth; i++) tty->print("   ");
2006   tty->print("%s: %d  trip_count: %6.0f freq: %6.0f\n",
2007              _depth == 0 ? "Method" : "Loop", _id, trip_count(), _freq);
2008   for (int i = 0; i < _depth; i++) tty->print("   ");
2009   tty->print("         members:");
2010   int k = 0;
2011   for (int i = 0; i < _members.length(); i++) {
2012     if (k++ >= 6) {
2013       tty->print("\n              ");
2014       for (int j = 0; j < _depth+1; j++) tty->print("   ");
2015       k = 0;
2016     }
2017     CFGElement *s = _members.at(i);
2018     if (s->is_block()) {
2019       Block *b = s->as_Block();
2020       tty->print(" B%d(%6.3f)", b->_pre_order, b->_freq);
2021     } else {
2022       CFGLoop* lp = s->as_CFGLoop();
2023       tty->print(" L%d(%6.3f)", lp->_id, lp->_freq);
2024     }
2025   }
2026   tty->print("\n");
2027   for (int i = 0; i < _depth; i++) tty->print("   ");
2028   tty->print("         exits:  ");
2029   k = 0;
2030   for (int i = 0; i < _exits.length(); i++) {
2031     if (k++ >= 7) {
2032       tty->print("\n              ");
2033       for (int j = 0; j < _depth+1; j++) tty->print("   ");
2034       k = 0;
2035     }
2036     Block *blk = _exits.at(i).get_target();
2037     float prob = _exits.at(i).get_prob();
2038     tty->print(" ->%d@%d%%", blk->_pre_order, (int)(prob*100));
2039   }
2040   tty->print("\n");
2041 }
2042 #endif