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 /*

  * Copyright (c) 1997, 2011, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

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  */

 #include "precompiled.hpp"

 #include "libadt/vectset.hpp"

 #include "memory/allocation.inline.hpp"

 #include "opto/block.hpp"

 #include "opto/c2compiler.hpp"

 #include "opto/callnode.hpp"

 #include "opto/cfgnode.hpp"

 #include "opto/machnode.hpp"

 #include "opto/opcodes.hpp"

 #include "opto/phaseX.hpp"

 #include "opto/rootnode.hpp"

 #include "opto/runtime.hpp"

 #include "runtime/deoptimization.hpp"

 #ifdef TARGET_ARCH_MODEL_x86_32

 # include "adfiles/ad_x86_32.hpp"

 #endif

 #ifdef TARGET_ARCH_MODEL_x86_64

 # include "adfiles/ad_x86_64.hpp"

 #endif

 #ifdef TARGET_ARCH_MODEL_sparc

 # include "adfiles/ad_sparc.hpp"

 #endif

 #ifdef TARGET_ARCH_MODEL_zero

 # include "adfiles/ad_zero.hpp"

 #endif

 #ifdef TARGET_ARCH_MODEL_arm

 # include "adfiles/ad_arm.hpp"

 #endif

 #ifdef TARGET_ARCH_MODEL_ppc

 # include "adfiles/ad_ppc.hpp"

 #endif

 // Portions of code courtesy of Clifford Click

 // Optimization - Graph Style

 // To avoid float value underflow

 #define MIN_BLOCK_FREQUENCY 1.e-35f

 //----------------------------schedule_node_into_block-------------------------

 // Insert node n into block b. Look for projections of n and make sure they

 // are in b also.

 void PhaseCFG::schedule_node_into_block( Node *n, Block *b ) {

   // Set basic block of n, Add n to b,

   _bbs.map(n->_idx, b);

   b->add_inst(n);

   // After Matching, nearly any old Node may have projections trailing it.

   // These are usually machine-dependent flags.  In any case, they might

   // float to another block below this one.  Move them up.

   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {

     Node*  use  = n->fast_out(i);

     if (use->is_Proj()) {

       Block* buse = _bbs[use->_idx];

       if (buse != b) {              // In wrong block?

         if (buse != NULL)

           buse->find_remove(use);   // Remove from wrong block

         _bbs.map(use->_idx, b);     // Re-insert in this block

         b->add_inst(use);

       }

     }

   }

 }

 //----------------------------replace_block_proj_ctrl-------------------------

 // Nodes that have is_block_proj() nodes as their control need to use

 // the appropriate Region for their actual block as their control since

 // the projection will be in a predecessor block.

 void PhaseCFG::replace_block_proj_ctrl( Node *n ) {

   const Node *in0 = n->in(0);

   assert(in0 != NULL, "Only control-dependent");

   const Node *p = in0->is_block_proj();

   if (p != NULL && p != n) {    // Control from a block projection?

     assert(!n->pinned() || n->is_MachConstantBase(), "only pinned MachConstantBase node is expected here");

     // Find trailing Region

     Block *pb = _bbs[in0->_idx]; // Block-projection already has basic block

     uint j = 0;

     if (pb->_num_succs != 1) {  // More then 1 successor?

       // Search for successor

       uint max = pb->_nodes.size();

       assert( max > 1, "" );

       uint start = max - pb->_num_succs;

       // Find which output path belongs to projection

       for (j = start; j < max; j++) {

         if( pb->_nodes[j] == in0 )

           break;

       }

       assert( j < max, "must find" );

       // Change control to match head of successor basic block

       j -= start;

     }

     n->set_req(0, pb->_succs[j]->head());

   }

 }

 //------------------------------schedule_pinned_nodes--------------------------

 // Set the basic block for Nodes pinned into blocks

 void PhaseCFG::schedule_pinned_nodes( VectorSet &visited ) {

   // Allocate node stack of size C->unique()+8 to avoid frequent realloc

   GrowableArray <Node *> spstack(C->unique()+8);

   spstack.push(_root);

   while ( spstack.is_nonempty() ) {

     Node *n = spstack.pop();

     if( !visited.test_set(n->_idx) ) { // Test node and flag it as visited

       if( n->pinned() && !_bbs.lookup(n->_idx) ) {  // Pinned?  Nail it down!

         assert( n->in(0), "pinned Node must have Control" );

         // Before setting block replace block_proj control edge

         replace_block_proj_ctrl(n);

         Node *input = n->in(0);

         while( !input->is_block_start() )

           input = input->in(0);

         Block *b = _bbs[input->_idx];  // Basic block of controlling input

         schedule_node_into_block(n, b);

       }

       for( int i = n->req() - 1; i >= 0; --i ) {  // For all inputs

         if( n->in(i) != NULL )

           spstack.push(n->in(i));

       }

     }

   }

 }

 #ifdef ASSERT

 // Assert that new input b2 is dominated by all previous inputs.

 // Check this by by seeing that it is dominated by b1, the deepest

 // input observed until b2.

 static void assert_dom(Block* b1, Block* b2, Node* n, Block_Array &bbs) {

   if (b1 == NULL)  return;

   assert(b1->_dom_depth < b2->_dom_depth, "sanity");

   Block* tmp = b2;

   while (tmp != b1 && tmp != NULL) {

     tmp = tmp->_idom;

   }

   if (tmp != b1) {

     // Detected an unschedulable graph.  Print some nice stuff and die.

     tty->print_cr("!!! Unschedulable graph !!!");

     for (uint j=0; j<n->len(); j++) { // For all inputs

       Node* inn = n->in(j); // Get input

       if (inn == NULL)  continue;  // Ignore NULL, missing inputs

       Block* inb = bbs[inn->_idx];

       tty->print("B%d idom=B%d depth=%2d ",inb->_pre_order,

                  inb->_idom ? inb->_idom->_pre_order : 0, inb->_dom_depth);

       inn->dump();

     }

     tty->print("Failing node: ");

     n->dump();

     assert(false, "unscheduable graph");

   }

 }

 #endif

 static Block* find_deepest_input(Node* n, Block_Array &bbs) {

   // Find the last input dominated by all other inputs.

   Block* deepb           = NULL;        // Deepest block so far

   int    deepb_dom_depth = 0;

   for (uint k = 0; k < n->len(); k++) { // For all inputs

     Node* inn = n->in(k);               // Get input

     if (inn == NULL)  continue;         // Ignore NULL, missing inputs

     Block* inb = bbs[inn->_idx];

     assert(inb != NULL, "must already have scheduled this input");

     if (deepb_dom_depth < (int) inb->_dom_depth) {

       // The new inb must be dominated by the previous deepb.

       // The various inputs must be linearly ordered in the dom

       // tree, or else there will not be a unique deepest block.

       DEBUG_ONLY(assert_dom(deepb, inb, n, bbs));

       deepb = inb;                      // Save deepest block

       deepb_dom_depth = deepb->_dom_depth;

     }

   }

   assert(deepb != NULL, "must be at least one input to n");

   return deepb;

 }

 //------------------------------schedule_early---------------------------------

 // Find the earliest Block any instruction can be placed in.  Some instructions

 // are pinned into Blocks.  Unpinned instructions can appear in last block in

 // which all their inputs occur.

 bool PhaseCFG::schedule_early(VectorSet &visited, Node_List &roots) {

   // Allocate stack with enough space to avoid frequent realloc

   Node_Stack nstack(roots.Size() + 8); // (unique >> 1) + 24 from Java2D stats

   // roots.push(_root); _root will be processed among C->top() inputs

   roots.push(C->top());

   visited.set(C->top()->_idx);

   while (roots.size() != 0) {

     // Use local variables nstack_top_n & nstack_top_i to cache values

     // on stack's top.

     Node *nstack_top_n = roots.pop();

     uint  nstack_top_i = 0;

 //while_nstack_nonempty:

     while (true) {

       // Get parent node and next input's index from stack's top.

       Node *n = nstack_top_n;

       uint  i = nstack_top_i;

       if (i == 0) {

         // Fixup some control.  Constants without control get attached

         // to root and nodes that use is_block_proj() nodes should be attached

         // to the region that starts their block.

         const Node *in0 = n->in(0);

         if (in0 != NULL) {              // Control-dependent?

           replace_block_proj_ctrl(n);

         } else {               // n->in(0) == NULL

           if (n->req() == 1) { // This guy is a constant with NO inputs?

             n->set_req(0, _root);

           }

         }

       }

       // First, visit all inputs and force them to get a block.  If an

       // input is already in a block we quit following inputs (to avoid

       // cycles). Instead we put that Node on a worklist to be handled

       // later (since IT'S inputs may not have a block yet).

       bool done = true;              // Assume all n's inputs will be processed

       while (i < n->len()) {         // For all inputs

         Node *in = n->in(i);         // Get input

         ++i;

         if (in == NULL) continue;    // Ignore NULL, missing inputs

         int is_visited = visited.test_set(in->_idx);

         if (!_bbs.lookup(in->_idx)) { // Missing block selection?

           if (is_visited) {

             // assert( !visited.test(in->_idx), "did not schedule early" );

             return false;

           }

           nstack.push(n, i);         // Save parent node and next input's index.

           nstack_top_n = in;         // Process current input now.

           nstack_top_i = 0;

           done = false;              // Not all n's inputs processed.

           break; // continue while_nstack_nonempty;

         } else if (!is_visited) {    // Input not yet visited?

           roots.push(in);            // Visit this guy later, using worklist

         }

       }

       if (done) {

         // All of n's inputs have been processed, complete post-processing.

         // Some instructions are pinned into a block.  These include Region,

         // Phi, Start, Return, and other control-dependent instructions and

         // any projections which depend on them.

         if (!n->pinned()) {

           // Set earliest legal block.

           _bbs.map(n->_idx, find_deepest_input(n, _bbs));

         } else {

           assert(_bbs[n->_idx] == _bbs[n->in(0)->_idx], "Pinned Node should be at the same block as its control edge");

         }

         if (nstack.is_empty()) {

           // Finished all nodes on stack.

           // Process next node on the worklist 'roots'.

           break;

         }

         // Get saved parent node and next input's index.

         nstack_top_n = nstack.node();

         nstack_top_i = nstack.index();

         nstack.pop();

       } //    if (done)

     }   // while (true)

   }     // while (roots.size() != 0)

   return true;

 }

 //------------------------------dom_lca----------------------------------------

 // Find least common ancestor in dominator tree

 // LCA is a current notion of LCA, to be raised above 'this'.

 // As a convenient boundary condition, return 'this' if LCA is NULL.

 // Find the LCA of those two nodes.

 Block* Block::dom_lca(Block* LCA) {

   if (LCA == NULL || LCA == this)  return this;

   Block* anc = this;

   while (anc->_dom_depth > LCA->_dom_depth)

     anc = anc->_idom;           // Walk up till anc is as high as LCA

   while (LCA->_dom_depth > anc->_dom_depth)

     LCA = LCA->_idom;           // Walk up till LCA is as high as anc

   while (LCA != anc) {          // Walk both up till they are the same

     LCA = LCA->_idom;

     anc = anc->_idom;

   }

   return LCA;

 }

 //--------------------------raise_LCA_above_use--------------------------------

 // We are placing a definition, and have been given a def->use edge.

 // The definition must dominate the use, so move the LCA upward in the

 // dominator tree to dominate the use.  If the use is a phi, adjust

 // the LCA only with the phi input paths which actually use this def.

 static Block* raise_LCA_above_use(Block* LCA, Node* use, Node* def, Block_Array &bbs) {

   Block* buse = bbs[use->_idx];

   if (buse == NULL)    return LCA;   // Unused killing Projs have no use block

   if (!use->is_Phi())  return buse->dom_lca(LCA);

   uint pmax = use->req();       // Number of Phi inputs

   // Why does not this loop just break after finding the matching input to

   // the Phi?  Well...it's like this.  I do not have true def-use/use-def

   // chains.  Means I cannot distinguish, from the def-use direction, which

   // of many use-defs lead from the same use to the same def.  That is, this

   // Phi might have several uses of the same def.  Each use appears in a

   // different predecessor block.  But when I enter here, I cannot distinguish

   // which use-def edge I should find the predecessor block for.  So I find

   // them all.  Means I do a little extra work if a Phi uses the same value

   // more than once.

   for (uint j=1; j<pmax; j++) { // For all inputs

     if (use->in(j) == def) {    // Found matching input?

       Block* pred = bbs[buse->pred(j)->_idx];

       LCA = pred->dom_lca(LCA);

     }

   }

   return LCA;

 }

 //----------------------------raise_LCA_above_marks----------------------------

 // Return a new LCA that dominates LCA and any of its marked predecessors.

 // Search all my parents up to 'early' (exclusive), looking for predecessors

 // which are marked with the given index.  Return the LCA (in the dom tree)

 // of all marked blocks.  If there are none marked, return the original

 // LCA.

 static Block* raise_LCA_above_marks(Block* LCA, node_idx_t mark,

                                     Block* early, Block_Array &bbs) {

   Block_List worklist;

   worklist.push(LCA);

   while (worklist.size() > 0) {

     Block* mid = worklist.pop();

     if (mid == early)  continue;  // stop searching here

     // Test and set the visited bit.

     if (mid->raise_LCA_visited() == mark)  continue;  // already visited

     // Don't process the current LCA, otherwise the search may terminate early

     if (mid != LCA && mid->raise_LCA_mark() == mark) {

       // Raise the LCA.

       LCA = mid->dom_lca(LCA);

       if (LCA == early)  break;   // stop searching everywhere

       assert(early->dominates(LCA), "early is high enough");

       // Resume searching at that point, skipping intermediate levels.

       worklist.push(LCA);

       if (LCA == mid)

         continue; // Don't mark as visited to avoid early termination.

     } else {

       // Keep searching through this block's predecessors.

       for (uint j = 1, jmax = mid->num_preds(); j < jmax; j++) {

         Block* mid_parent = bbs[ mid->pred(j)->_idx ];

         worklist.push(mid_parent);

       }

     }

     mid->set_raise_LCA_visited(mark);

   }

   return LCA;

 }

 //--------------------------memory_early_block--------------------------------

 // This is a variation of find_deepest_input, the heart of schedule_early.

 // Find the "early" block for a load, if we considered only memory and

 // address inputs, that is, if other data inputs were ignored.

 //

 // Because a subset of edges are considered, the resulting block will

 // be earlier (at a shallower dom_depth) than the true schedule_early

 // point of the node. We compute this earlier block as a more permissive

 // site for anti-dependency insertion, but only if subsume_loads is enabled.

 static Block* memory_early_block(Node* load, Block* early, Block_Array &bbs) {

   Node* base;

   Node* index;

   Node* store = load->in(MemNode::Memory);

   load->as_Mach()->memory_inputs(base, index);

   assert(base != NodeSentinel && index != NodeSentinel,

          "unexpected base/index inputs");

   Node* mem_inputs[4];

   int mem_inputs_length = 0;

   if (base != NULL)  mem_inputs[mem_inputs_length++] = base;

   if (index != NULL) mem_inputs[mem_inputs_length++] = index;

   if (store != NULL) mem_inputs[mem_inputs_length++] = store;

   // In the comparision below, add one to account for the control input,

   // which may be null, but always takes up a spot in the in array.

   if (mem_inputs_length + 1 < (int) load->req()) {

     // This "load" has more inputs than just the memory, base and index inputs.

     // For purposes of checking anti-dependences, we need to start

     // from the early block of only the address portion of the instruction,

     // and ignore other blocks that may have factored into the wider

     // schedule_early calculation.

     if (load->in(0) != NULL) mem_inputs[mem_inputs_length++] = load->in(0);

     Block* deepb           = NULL;        // Deepest block so far

     int    deepb_dom_depth = 0;

     for (int i = 0; i < mem_inputs_length; i++) {

       Block* inb = bbs[mem_inputs[i]->_idx];

       if (deepb_dom_depth < (int) inb->_dom_depth) {

         // The new inb must be dominated by the previous deepb.

         // The various inputs must be linearly ordered in the dom

         // tree, or else there will not be a unique deepest block.

         DEBUG_ONLY(assert_dom(deepb, inb, load, bbs));

         deepb = inb;                      // Save deepest block

         deepb_dom_depth = deepb->_dom_depth;

       }

     }

     early = deepb;

   }

   return early;

 }

 //--------------------------insert_anti_dependences---------------------------

 // A load may need to witness memory that nearby stores can overwrite.

 // For each nearby store, either insert an "anti-dependence" edge

 // from the load to the store, or else move LCA upward to force the

 // load to (eventually) be scheduled in a block above the store.

 //

 // Do not add edges to stores on distinct control-flow paths;

 // only add edges to stores which might interfere.

 //

 // Return the (updated) LCA.  There will not be any possibly interfering

 // store between the load's "early block" and the updated LCA.

 // Any stores in the updated LCA will have new precedence edges

 // back to the load.  The caller is expected to schedule the load

 // in the LCA, in which case the precedence edges will make LCM

 // preserve anti-dependences.  The caller may also hoist the load

 // above the LCA, if it is not the early block.

 Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {

   assert(load->needs_anti_dependence_check(), "must be a load of some sort");

   assert(LCA != NULL, "");

   DEBUG_ONLY(Block* LCA_orig = LCA);

   // Compute the alias index.  Loads and stores with different alias indices

   // do not need anti-dependence edges.

   uint load_alias_idx = C->get_alias_index(load->adr_type());

 #ifdef ASSERT

   if (load_alias_idx == Compile::AliasIdxBot && C->AliasLevel() > 0 &&

       (PrintOpto || VerifyAliases ||

        PrintMiscellaneous && (WizardMode || Verbose))) {

     // Load nodes should not consume all of memory.

     // Reporting a bottom type indicates a bug in adlc.

     // If some particular type of node validly consumes all of memory,

     // sharpen the preceding "if" to exclude it, so we can catch bugs here.

     tty->print_cr("*** Possible Anti-Dependence Bug:  Load consumes all of memory.");

     load->dump(2);

     if (VerifyAliases)  assert(load_alias_idx != Compile::AliasIdxBot, "");

   }

 #endif

   assert(load_alias_idx || (load->is_Mach() && load->as_Mach()->ideal_Opcode() == Op_StrComp),

          "String compare is only known 'load' that does not conflict with any stores");

   assert(load_alias_idx || (load->is_Mach() && load->as_Mach()->ideal_Opcode() == Op_StrEquals),

          "String equals is a 'load' that does not conflict with any stores");

   assert(load_alias_idx || (load->is_Mach() && load->as_Mach()->ideal_Opcode() == Op_StrIndexOf),

          "String indexOf is a 'load' that does not conflict with any stores");

   assert(load_alias_idx || (load->is_Mach() && load->as_Mach()->ideal_Opcode() == Op_AryEq),

          "Arrays equals is a 'load' that do not conflict with any stores");

   if (!C->alias_type(load_alias_idx)->is_rewritable()) {

     // It is impossible to spoil this load by putting stores before it,

     // because we know that the stores will never update the value

     // which 'load' must witness.

     return LCA;

   }

   node_idx_t load_index = load->_idx;

   // Note the earliest legal placement of 'load', as determined by

   // by the unique point in the dom tree where all memory effects

   // and other inputs are first available.  (Computed by schedule_early.)

   // For normal loads, 'early' is the shallowest place (dom graph wise)

   // to look for anti-deps between this load and any store.

   Block* early = _bbs[load_index];

   // If we are subsuming loads, compute an "early" block that only considers

   // memory or address inputs. This block may be different than the

   // schedule_early block in that it could be at an even shallower depth in the

   // dominator tree, and allow for a broader discovery of anti-dependences.

   if (C->subsume_loads()) {

     early = memory_early_block(load, early, _bbs);

   }

   ResourceArea *area = Thread::current()->resource_area();

   Node_List worklist_mem(area);     // prior memory state to store

   Node_List worklist_store(area);   // possible-def to explore

   Node_List worklist_visited(area); // visited mergemem nodes

   Node_List non_early_stores(area); // all relevant stores outside of early

   bool must_raise_LCA = false;

 #ifdef TRACK_PHI_INPUTS

   // %%% This extra checking fails because MergeMem nodes are not GVNed.

   // Provide "phi_inputs" to check if every input to a PhiNode is from the

   // original memory state.  This indicates a PhiNode for which should not

   // prevent the load from sinking.  For such a block, set_raise_LCA_mark

   // may be overly conservative.

   // Mechanism: count inputs seen for each Phi encountered in worklist_store.

   DEBUG_ONLY(GrowableArray<uint> phi_inputs(area, C->unique(),0,0));

 #endif

   // 'load' uses some memory state; look for users of the same state.

   // Recurse through MergeMem nodes to the stores that use them.

   // Each of these stores is a possible definition of memory

   // that 'load' needs to use.  We need to force 'load'

   // to occur before each such store.  When the store is in

   // the same block as 'load', we insert an anti-dependence

   // edge load->store.

   // The relevant stores "nearby" the load consist of a tree rooted

   // at initial_mem, with internal nodes of type MergeMem.

   // Therefore, the branches visited by the worklist are of this form:

   //    initial_mem -> (MergeMem ->)* store

   // The anti-dependence constraints apply only to the fringe of this tree.

   Node* initial_mem = load->in(MemNode::Memory);

   worklist_store.push(initial_mem);

   worklist_visited.push(initial_mem);

   worklist_mem.push(NULL);

   while (worklist_store.size() > 0) {

     // Examine a nearby store to see if it might interfere with our load.

     Node* mem   = worklist_mem.pop();

     Node* store = worklist_store.pop();

     uint op = store->Opcode();

     // MergeMems do not directly have anti-deps.

     // Treat them as internal nodes in a forward tree of memory states,

     // the leaves of which are each a 'possible-def'.

     if (store == initial_mem    // root (exclusive) of tree we are searching

         || op == Op_MergeMem    // internal node of tree we are searching

         ) {

       mem = store;   // It's not a possibly interfering store.

       if (store == initial_mem)

         initial_mem = NULL;  // only process initial memory once

       for (DUIterator_Fast imax, i = mem->fast_outs(imax); i < imax; i++) {

         store = mem->fast_out(i);

         if (store->is_MergeMem()) {

           // Be sure we don't get into combinatorial problems.

           // (Allow phis to be repeated; they can merge two relevant states.)

           uint j = worklist_visited.size();

           for (; j > 0; j--) {

             if (worklist_visited.at(j-1) == store)  break;

           }

           if (j > 0)  continue; // already on work list; do not repeat

           worklist_visited.push(store);

         }

         worklist_mem.push(mem);

         worklist_store.push(store);

       }

       continue;

     }

     if (op == Op_MachProj || op == Op_Catch)   continue;

     if (store->needs_anti_dependence_check())  continue;  // not really a store

     // Compute the alias index.  Loads and stores with different alias

     // indices do not need anti-dependence edges.  Wide MemBar's are

     // anti-dependent on everything (except immutable memories).

     const TypePtr* adr_type = store->adr_type();

     if (!C->can_alias(adr_type, load_alias_idx))  continue;

     // Most slow-path runtime calls do NOT modify Java memory, but

     // they can block and so write Raw memory.

     if (store->is_Mach()) {

       MachNode* mstore = store->as_Mach();

       if (load_alias_idx != Compile::AliasIdxRaw) {

         // Check for call into the runtime using the Java calling

         // convention (and from there into a wrapper); it has no

         // _method.  Can't do this optimization for Native calls because

         // they CAN write to Java memory.

         if (mstore->ideal_Opcode() == Op_CallStaticJava) {

           assert(mstore->is_MachSafePoint(), "");

           MachSafePointNode* ms = (MachSafePointNode*) mstore;

           assert(ms->is_MachCallJava(), "");

           MachCallJavaNode* mcj = (MachCallJavaNode*) ms;

           if (mcj->_method == NULL) {

             // These runtime calls do not write to Java visible memory

             // (other than Raw) and so do not require anti-dependence edges.

             continue;

           }

         }

         // Same for SafePoints: they read/write Raw but only read otherwise.

         // This is basically a workaround for SafePoints only defining control

         // instead of control + memory.

         if (mstore->ideal_Opcode() == Op_SafePoint)

           continue;

       } else {

         // Some raw memory, such as the load of "top" at an allocation,

         // can be control dependent on the previous safepoint. See

         // comments in GraphKit::allocate_heap() about control input.

         // Inserting an anti-dep between such a safepoint and a use

         // creates a cycle, and will cause a subsequent failure in

         // local scheduling.  (BugId 4919904)

         // (%%% How can a control input be a safepoint and not a projection??)

         if (mstore->ideal_Opcode() == Op_SafePoint && load->in(0) == mstore)

           continue;

       }

     }

     // Identify a block that the current load must be above,

     // or else observe that 'store' is all the way up in the

     // earliest legal block for 'load'.  In the latter case,

     // immediately insert an anti-dependence edge.

     Block* store_block = _bbs[store->_idx];

     assert(store_block != NULL, "unused killing projections skipped above");

     if (store->is_Phi()) {

       // 'load' uses memory which is one (or more) of the Phi's inputs.

       // It must be scheduled not before the Phi, but rather before

       // each of the relevant Phi inputs.

       //

       // Instead of finding the LCA of all inputs to a Phi that match 'mem',

       // we mark each corresponding predecessor block and do a combined

       // hoisting operation later (raise_LCA_above_marks).

       //

       // Do not assert(store_block != early, "Phi merging memory after access")

       // PhiNode may be at start of block 'early' with backedge to 'early'

       DEBUG_ONLY(bool found_match = false);

       for (uint j = PhiNode::Input, jmax = store->req(); j < jmax; j++) {

         if (store->in(j) == mem) {   // Found matching input?

           DEBUG_ONLY(found_match = true);

           Block* pred_block = _bbs[store_block->pred(j)->_idx];

           if (pred_block != early) {

             // If any predecessor of the Phi matches the load's "early block",

             // we do not need a precedence edge between the Phi and 'load'

             // since the load will be forced into a block preceding the Phi.

             pred_block->set_raise_LCA_mark(load_index);

             assert(!LCA_orig->dominates(pred_block) ||

                    early->dominates(pred_block), "early is high enough");

             must_raise_LCA = true;

           } else {

             // anti-dependent upon PHI pinned below 'early', no edge needed

             LCA = early;             // but can not schedule below 'early'

           }

         }

       }

       assert(found_match, "no worklist bug");

 #ifdef TRACK_PHI_INPUTS

 #ifdef ASSERT

       // This assert asks about correct handling of PhiNodes, which may not

       // have all input edges directly from 'mem'. See BugId 4621264

       int num_mem_inputs = phi_inputs.at_grow(store->_idx,0) + 1;

       // Increment by exactly one even if there are multiple copies of 'mem'

       // coming into the phi, because we will run this block several times

       // if there are several copies of 'mem'.  (That's how DU iterators work.)

       phi_inputs.at_put(store->_idx, num_mem_inputs);

       assert(PhiNode::Input + num_mem_inputs < store->req(),

              "Expect at least one phi input will not be from original memory state");

 #endif //ASSERT

 #endif //TRACK_PHI_INPUTS

     } else if (store_block != early) {

       // 'store' is between the current LCA and earliest possible block.

       // Label its block, and decide later on how to raise the LCA

       // to include the effect on LCA of this store.

       // If this store's block gets chosen as the raised LCA, we

       // will find him on the non_early_stores list and stick him

       // with a precedence edge.

       // (But, don't bother if LCA is already raised all the way.)

       if (LCA != early) {

         store_block->set_raise_LCA_mark(load_index);

         must_raise_LCA = true;

         non_early_stores.push(store);

       }

     } else {

       // Found a possibly-interfering store in the load's 'early' block.

       // This means 'load' cannot sink at all in the dominator tree.

       // Add an anti-dep edge, and squeeze 'load' into the highest block.

       assert(store != load->in(0), "dependence cycle found");

       if (verify) {

         assert(store->find_edge(load) != -1, "missing precedence edge");

       } else {

         store->add_prec(load);

       }

       LCA = early;

       // This turns off the process of gathering non_early_stores.

     }

   }

   // (Worklist is now empty; all nearby stores have been visited.)

   // Finished if 'load' must be scheduled in its 'early' block.

   // If we found any stores there, they have already been given

   // precedence edges.

   if (LCA == early)  return LCA;

   // We get here only if there are no possibly-interfering stores

   // in the load's 'early' block.  Move LCA up above all predecessors

   // which contain stores we have noted.

   //

   // The raised LCA block can be a home to such interfering stores,

   // but its predecessors must not contain any such stores.

   //

   // The raised LCA will be a lower bound for placing the load,

   // preventing the load from sinking past any block containing

   // a store that may invalidate the memory state required by 'load'.

   if (must_raise_LCA)

     LCA = raise_LCA_above_marks(LCA, load->_idx, early, _bbs);

   if (LCA == early)  return LCA;

   // Insert anti-dependence edges from 'load' to each store

   // in the non-early LCA block.

   // Mine the non_early_stores list for such stores.

   if (LCA->raise_LCA_mark() == load_index) {

     while (non_early_stores.size() > 0) {

       Node* store = non_early_stores.pop();

       Block* store_block = _bbs[store->_idx];

       if (store_block == LCA) {

         // add anti_dependence from store to load in its own block

         assert(store != load->in(0), "dependence cycle found");

         if (verify) {

           assert(store->find_edge(load) != -1, "missing precedence edge");

         } else {

           store->add_prec(load);

         }

       } else {

         assert(store_block->raise_LCA_mark() == load_index, "block was marked");

         // Any other stores we found must be either inside the new LCA

         // or else outside the original LCA.  In the latter case, they

         // did not interfere with any use of 'load'.

         assert(LCA->dominates(store_block)

                || !LCA_orig->dominates(store_block), "no stray stores");

       }

     }

   }

   // Return the highest block containing stores; any stores

   // within that block have been given anti-dependence edges.

   return LCA;

 }

 // This class is used to iterate backwards over the nodes in the graph.

 class Node_Backward_Iterator {

 private:

   Node_Backward_Iterator();

 public:

   // Constructor for the iterator

   Node_Backward_Iterator(Node *root, VectorSet &visited, Node_List &stack, Block_Array &bbs);

   // Postincrement operator to iterate over the nodes

   Node *next();

 private:

   VectorSet   &_visited;

   Node_List   &_stack;

   Block_Array &_bbs;

 };

 // Constructor for the Node_Backward_Iterator

 Node_Backward_Iterator::Node_Backward_Iterator( Node *root, VectorSet &visited, Node_List &stack, Block_Array &bbs )

   : _visited(visited), _stack(stack), _bbs(bbs) {

   // The stack should contain exactly the root

   stack.clear();

   stack.push(root);

   // Clear the visited bits

   visited.Clear();

 }

 // Iterator for the Node_Backward_Iterator

 Node *Node_Backward_Iterator::next() {

   // If the _stack is empty, then just return NULL: finished.

   if ( !_stack.size() )

     return NULL;

   // '_stack' is emulating a real _stack.  The 'visit-all-users' loop has been

   // made stateless, so I do not need to record the index 'i' on my _stack.

   // Instead I visit all users each time, scanning for unvisited users.

   // I visit unvisited not-anti-dependence users first, then anti-dependent

   // children next.

   Node *self = _stack.pop();

   // I cycle here when I am entering a deeper level of recursion.

   // The key variable 'self' was set prior to jumping here.

   while( 1 ) {

     _visited.set(self->_idx);

     // Now schedule all uses as late as possible.

     uint src     = self->is_Proj() ? self->in(0)->_idx : self->_idx;

     uint src_rpo = _bbs[src]->_rpo;

     // Schedule all nodes in a post-order visit

     Node *unvisited = NULL;  // Unvisited anti-dependent Node, if any

     // Scan for unvisited nodes

     for (DUIterator_Fast imax, i = self->fast_outs(imax); i < imax; i++) {

       // For all uses, schedule late

       Node* n = self->fast_out(i); // Use

       // Skip already visited children

       if ( _visited.test(n->_idx) )

         continue;

       // do not traverse backward control edges

       Node *use = n->is_Proj() ? n->in(0) : n;

       uint use_rpo = _bbs[use->_idx]->_rpo;

       if ( use_rpo < src_rpo )

         continue;

       // Phi nodes always precede uses in a basic block

       if ( use_rpo == src_rpo && use->is_Phi() )

         continue;

       unvisited = n;      // Found unvisited

       // Check for possible-anti-dependent

       if( !n->needs_anti_dependence_check() )

         break;            // Not visited, not anti-dep; schedule it NOW

     }

     // Did I find an unvisited not-anti-dependent Node?

     if ( !unvisited )

       break;                  // All done with children; post-visit 'self'

     // Visit the unvisited Node.  Contains the obvious push to

     // indicate I'm entering a deeper level of recursion.  I push the

     // old state onto the _stack and set a new state and loop (recurse).

     _stack.push(self);

     self = unvisited;

   } // End recursion loop

   return self;

 }

 //------------------------------ComputeLatenciesBackwards----------------------

 // Compute the latency of all the instructions.

 void PhaseCFG::ComputeLatenciesBackwards(VectorSet &visited, Node_List &stack) {

 #ifndef PRODUCT

   if (trace_opto_pipelining())

     tty->print("\n#---- ComputeLatenciesBackwards ----\n");

 #endif

   Node_Backward_Iterator iter((Node *)_root, visited, stack, _bbs);

   Node *n;

   // Walk over all the nodes from last to first

   while (n = iter.next()) {

     // Set the latency for the definitions of this instruction

     partial_latency_of_defs(n);

   }

 } // end ComputeLatenciesBackwards

 //------------------------------partial_latency_of_defs------------------------

 // Compute the latency impact of this node on all defs.  This computes

 // a number that increases as we approach the beginning of the routine.

 void PhaseCFG::partial_latency_of_defs(Node *n) {

   // Set the latency for this instruction

 #ifndef PRODUCT

   if (trace_opto_pipelining()) {

     tty->print("# latency_to_inputs: node_latency[%d] = %d for node",

                n->_idx, _node_latency->at_grow(n->_idx));

     dump();

   }

 #endif

   if (n->is_Proj())

     n = n->in(0);

   if (n->is_Root())

     return;

   uint nlen = n->len();

   uint use_latency = _node_latency->at_grow(n->_idx);

   uint use_pre_order = _bbs[n->_idx]->_pre_order;

   for ( uint j=0; j<nlen; j++ ) {

     Node *def = n->in(j);

     if (!def || def == n)

       continue;

     // Walk backwards thru projections

     if (def->is_Proj())

       def = def->in(0);

 #ifndef PRODUCT

     if (trace_opto_pipelining()) {

       tty->print("#    in(%2d): ", j);

       def->dump();

     }

 #endif

     // If the defining block is not known, assume it is ok

     Block *def_block = _bbs[def->_idx];

     uint def_pre_order = def_block ? def_block->_pre_order : 0;

     if ( (use_pre_order <  def_pre_order) ||

          (use_pre_order == def_pre_order && n->is_Phi()) )

       continue;

     uint delta_latency = n->latency(j);

     uint current_latency = delta_latency + use_latency;

     if (_node_latency->at_grow(def->_idx) < current_latency) {

       _node_latency->at_put_grow(def->_idx, current_latency);

     }

 #ifndef PRODUCT

     if (trace_opto_pipelining()) {

       tty->print_cr("#      %d + edge_latency(%d) == %d -> %d, node_latency[%d] = %d",

                     use_latency, j, delta_latency, current_latency, def->_idx,

                     _node_latency->at_grow(def->_idx));

     }

 #endif

   }

 }

 //------------------------------latency_from_use-------------------------------

 // Compute the latency of a specific use

 int PhaseCFG::latency_from_use(Node *n, const Node *def, Node *use) {

   // If self-reference, return no latency

   if (use == n || use->is_Root())

     return 0;

   uint def_pre_order = _bbs[def->_idx]->_pre_order;

   uint latency = 0;

   // If the use is not a projection, then it is simple...

   if (!use->is_Proj()) {

 #ifndef PRODUCT

     if (trace_opto_pipelining()) {

       tty->print("#    out(): ");

       use->dump();

     }

 #endif

     uint use_pre_order = _bbs[use->_idx]->_pre_order;

     if (use_pre_order < def_pre_order)

       return 0;

     if (use_pre_order == def_pre_order && use->is_Phi())

       return 0;

     uint nlen = use->len();

     uint nl = _node_latency->at_grow(use->_idx);

     for ( uint j=0; j<nlen; j++ ) {

       if (use->in(j) == n) {

         // Change this if we want local latencies

         uint ul = use->latency(j);

         uint  l = ul + nl;

         if (latency < l) latency = l;

 #ifndef PRODUCT

         if (trace_opto_pipelining()) {

           tty->print_cr("#      %d + edge_latency(%d) == %d -> %d, latency = %d",

                         nl, j, ul, l, latency);

         }

 #endif

       }

     }

   } else {

     // This is a projection, just grab the latency of the use(s)

     for (DUIterator_Fast jmax, j = use->fast_outs(jmax); j < jmax; j++) {

       uint l = latency_from_use(use, def, use->fast_out(j));

       if (latency < l) latency = l;

     }

   }

   return latency;

 }

 //------------------------------latency_from_uses------------------------------

 // Compute the latency of this instruction relative to all of it's uses.

 // This computes a number that increases as we approach the beginning of the

 // routine.

 void PhaseCFG::latency_from_uses(Node *n) {

   // Set the latency for this instruction

 #ifndef PRODUCT

   if (trace_opto_pipelining()) {

     tty->print("# latency_from_outputs: node_latency[%d] = %d for node",

                n->_idx, _node_latency->at_grow(n->_idx));

     dump();

   }

 #endif

   uint latency=0;

   const Node *def = n->is_Proj() ? n->in(0): n;

   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {

     uint l = latency_from_use(n, def, n->fast_out(i));

     if (latency < l) latency = l;

   }

   _node_latency->at_put_grow(n->_idx, latency);

 }

 //------------------------------hoist_to_cheaper_block-------------------------

 // Pick a block for node self, between early and LCA, that is a cheaper

 // alternative to LCA.

 Block* PhaseCFG::hoist_to_cheaper_block(Block* LCA, Block* early, Node* self) {

   const double delta = 1+PROB_UNLIKELY_MAG(4);

   Block* least       = LCA;

   double least_freq  = least->_freq;

   uint target        = _node_latency->at_grow(self->_idx);

   uint start_latency = _node_latency->at_grow(LCA->_nodes[0]->_idx);

   uint end_latency   = _node_latency->at_grow(LCA->_nodes[LCA->end_idx()]->_idx);

   bool in_latency    = (target <= start_latency);

   const Block* root_block = _bbs[_root->_idx];

   // Turn off latency scheduling if scheduling is just plain off

   if (!C->do_scheduling())

     in_latency = true;

   // Do not hoist (to cover latency) instructions which target a

   // single register.  Hoisting stretches the live range of the

   // single register and may force spilling.

   MachNode* mach = self->is_Mach() ? self->as_Mach() : NULL;

   if (mach && mach->out_RegMask().is_bound1() && mach->out_RegMask().is_NotEmpty())

     in_latency = true;

 #ifndef PRODUCT

   if (trace_opto_pipelining()) {

     tty->print("# Find cheaper block for latency %d: ",

       _node_latency->at_grow(self->_idx));

     self->dump();

     tty->print_cr("#   B%d: start latency for [%4d]=%d, end latency for [%4d]=%d, freq=%g",

       LCA->_pre_order,

       LCA->_nodes[0]->_idx,

       start_latency,

       LCA->_nodes[LCA->end_idx()]->_idx,

       end_latency,

       least_freq);

   }

 #endif

   // Walk up the dominator tree from LCA (Lowest common ancestor) to

   // the earliest legal location.  Capture the least execution frequency.

   while (LCA != early) {

     LCA = LCA->_idom;         // Follow up the dominator tree

     if (LCA == NULL) {

       // Bailout without retry

       C->record_method_not_compilable("late schedule failed: LCA == NULL");

       return least;

     }

     // Don't hoist machine instructions to the root basic block

     if (mach && LCA == root_block)

       break;

     uint start_lat = _node_latency->at_grow(LCA->_nodes[0]->_idx);

     uint end_idx   = LCA->end_idx();

     uint end_lat   = _node_latency->at_grow(LCA->_nodes[end_idx]->_idx);

     double LCA_freq = LCA->_freq;

 #ifndef PRODUCT

     if (trace_opto_pipelining()) {

       tty->print_cr("#   B%d: start latency for [%4d]=%d, end latency for [%4d]=%d, freq=%g",

         LCA->_pre_order, LCA->_nodes[0]->_idx, start_lat, end_idx, end_lat, LCA_freq);

     }

 #endif

     if (LCA_freq < least_freq              || // Better Frequency

         ( !in_latency                   &&    // No block containing latency

           LCA_freq < least_freq * delta &&    // No worse frequency

           target >= end_lat             &&    // within latency range

           !self->is_iteratively_computed() )  // But don't hoist IV increments

              // because they may end up above other uses of their phi forcing

              // their result register to be different from their input.

        ) {

       least = LCA;            // Found cheaper block

       least_freq = LCA_freq;

       start_latency = start_lat;

       end_latency = end_lat;

       if (target <= start_lat)

         in_latency = true;

     }

   }

 #ifndef PRODUCT

   if (trace_opto_pipelining()) {

     tty->print_cr("#  Choose block B%d with start latency=%d and freq=%g",

       least->_pre_order, start_latency, least_freq);

   }

 #endif

   // See if the latency needs to be updated

   if (target < end_latency) {

 #ifndef PRODUCT

     if (trace_opto_pipelining()) {

       tty->print_cr("#  Change latency for [%4d] from %d to %d", self->_idx, target, end_latency);

     }

 #endif

     _node_latency->at_put_grow(self->_idx, end_latency);

     partial_latency_of_defs(self);

   }

   return least;

 }

 //------------------------------schedule_late-----------------------------------

 // Now schedule all codes as LATE as possible.  This is the LCA in the

 // dominator tree of all USES of a value.  Pick the block with the least

 // loop nesting depth that is lowest in the dominator tree.

 extern const char must_clone[];

 void PhaseCFG::schedule_late(VectorSet &visited, Node_List &stack) {

 #ifndef PRODUCT

   if (trace_opto_pipelining())

     tty->print("\n#---- schedule_late ----\n");

 #endif

   Node_Backward_Iterator iter((Node *)_root, visited, stack, _bbs);

   Node *self;

   // Walk over all the nodes from last to first

   while (self = iter.next()) {

     Block* early = _bbs[self->_idx];   // Earliest legal placement

     if (self->is_top()) {

       // Top node goes in bb #2 with other constants.

       // It must be special-cased, because it has no out edges.

       early->add_inst(self);

       continue;

     }

     // No uses, just terminate

     if (self->outcnt() == 0) {

       assert(self->is_MachProj(), "sanity");

       continue;                   // Must be a dead machine projection

     }

     // If node is pinned in the block, then no scheduling can be done.

     if( self->pinned() )          // Pinned in block?

       continue;

     MachNode* mach = self->is_Mach() ? self->as_Mach() : NULL;

     if (mach) {

       switch (mach->ideal_Opcode()) {

       case Op_CreateEx:

         // Don't move exception creation

         early->add_inst(self);

         continue;

         break;

       case Op_CheckCastPP:

         // Don't move CheckCastPP nodes away from their input, if the input

         // is a rawptr (5071820).

         Node *def = self->in(1);

         if (def != NULL && def->bottom_type()->base() == Type::RawPtr) {

           early->add_inst(self);

 #ifdef ASSERT

           _raw_oops.push(def);

 #endif

           continue;

         }

         break;

       }

     }

     // Gather LCA of all uses

     Block *LCA = NULL;

     {

       for (DUIterator_Fast imax, i = self->fast_outs(imax); i < imax; i++) {

         // For all uses, find LCA

         Node* use = self->fast_out(i);

         LCA = raise_LCA_above_use(LCA, use, self, _bbs);

       }

     }  // (Hide defs of imax, i from rest of block.)

     // Place temps in the block of their use.  This isn't a

     // requirement for correctness but it reduces useless

     // interference between temps and other nodes.

     if (mach != NULL && mach->is_MachTemp()) {

       _bbs.map(self->_idx, LCA);

       LCA->add_inst(self);

       continue;

     }

     // Check if 'self' could be anti-dependent on memory

     if (self->needs_anti_dependence_check()) {

       // Hoist LCA above possible-defs and insert anti-dependences to

       // defs in new LCA block.

       LCA = insert_anti_dependences(LCA, self);

     }

     if (early->_dom_depth > LCA->_dom_depth) {

       // Somehow the LCA has moved above the earliest legal point.

       // (One way this can happen is via memory_early_block.)

       if (C->subsume_loads() == true && !C->failing()) {

         // Retry with subsume_loads == false

         // If this is the first failure, the sentinel string will "stick"

         // to the Compile object, and the C2Compiler will see it and retry.

         C->record_failure(C2Compiler::retry_no_subsuming_loads());

       } else {

         // Bailout without retry when (early->_dom_depth > LCA->_dom_depth)

         C->record_method_not_compilable("late schedule failed: incorrect graph");

       }

       return;

     }

     // If there is no opportunity to hoist, then we're done.

     bool try_to_hoist = (LCA != early);

     // Must clone guys stay next to use; no hoisting allowed.

     // Also cannot hoist guys that alter memory or are otherwise not

     // allocatable (hoisting can make a value live longer, leading to

     // anti and output dependency problems which are normally resolved

     // by the register allocator giving everyone a different register).

     if (mach != NULL && must_clone[mach->ideal_Opcode()])

       try_to_hoist = false;

     Block* late = NULL;

     if (try_to_hoist) {

       // Now find the block with the least execution frequency.

       // Start at the latest schedule and work up to the earliest schedule

       // in the dominator tree.  Thus the Node will dominate all its uses.

       late = hoist_to_cheaper_block(LCA, early, self);

     } else {

       // Just use the LCA of the uses.

       late = LCA;

     }

     // Put the node into target block

     schedule_node_into_block(self, late);

 #ifdef ASSERT

     if (self->needs_anti_dependence_check()) {

       // since precedence edges are only inserted when we're sure they

       // are needed make sure that after placement in a block we don't

       // need any new precedence edges.

       verify_anti_dependences(late, self);

     }

 #endif

   } // Loop until all nodes have been visited

 } // end ScheduleLate

 //------------------------------GlobalCodeMotion-------------------------------

 void PhaseCFG::GlobalCodeMotion( Matcher &matcher, uint unique, Node_List &proj_list ) {

   ResourceMark rm;

 #ifndef PRODUCT

   if (trace_opto_pipelining()) {

     tty->print("\n---- Start GlobalCodeMotion ----\n");

   }

 #endif

   // Initialize the bbs.map for things on the proj_list

   uint i;

   for( i=0; i < proj_list.size(); i++ )

     _bbs.map(proj_list[i]->_idx, NULL);

   // Set the basic block for Nodes pinned into blocks

   Arena *a = Thread::current()->resource_area();

   VectorSet visited(a);

   schedule_pinned_nodes( visited );

   // Find the earliest Block any instruction can be placed in.  Some

   // instructions are pinned into Blocks.  Unpinned instructions can

   // appear in last block in which all their inputs occur.

   visited.Clear();

   Node_List stack(a);

   stack.map( (unique >> 1) + 16, NULL); // Pre-grow the list

   if (!schedule_early(visited, stack)) {

     // Bailout without retry

     C->record_method_not_compilable("early schedule failed");

     return;

   }

   // Build Def-Use edges.

   proj_list.push(_root);        // Add real root as another root

   proj_list.pop();

   // Compute the latency information (via backwards walk) for all the

   // instructions in the graph

   _node_latency = new GrowableArray<uint>(); // resource_area allocation

   if( C->do_scheduling() )

     ComputeLatenciesBackwards(visited, stack);

   // Now schedule all codes as LATE as possible.  This is the LCA in the

   // dominator tree of all USES of a value.  Pick the block with the least

   // loop nesting depth that is lowest in the dominator tree.

   // ( visited.Clear() called in schedule_late()->Node_Backward_Iterator() )

   schedule_late(visited, stack);

   if( C->failing() ) {

     // schedule_late fails only when graph is incorrect.

     assert(!VerifyGraphEdges, "verification should have failed");

     return;

   }

   unique = C->unique();

 #ifndef PRODUCT

   if (trace_opto_pipelining()) {

     tty->print("\n---- Detect implicit null checks ----\n");

   }

 #endif

   // Detect implicit-null-check opportunities.  Basically, find NULL checks

   // with suitable memory ops nearby.  Use the memory op to do the NULL check.

   // I can generate a memory op if there is not one nearby.

   if (C->is_method_compilation()) {

     // Don't do it for natives, adapters, or runtime stubs

     int allowed_reasons = 0;

     // ...and don't do it when there have been too many traps, globally.

     for (int reason = (int)Deoptimization::Reason_none+1;

          reason < Compile::trapHistLength; reason++) {

       assert(reason < BitsPerInt, "recode bit map");

       if (!C->too_many_traps((Deoptimization::DeoptReason) reason))

         allowed_reasons |= nth_bit(reason);

     }

     // By reversing the loop direction we get a very minor gain on mpegaudio.

     // Feel free to revert to a forward loop for clarity.

     // for( int i=0; i < (int)matcher._null_check_tests.size(); i+=2 ) {

     for( int i= matcher._null_check_tests.size()-2; i>=0; i-=2 ) {

       Node *proj = matcher._null_check_tests[i  ];

       Node *val  = matcher._null_check_tests[i+1];

       _bbs[proj->_idx]->implicit_null_check(this, proj, val, allowed_reasons);

       // The implicit_null_check will only perform the transformation

       // if the null branch is truly uncommon, *and* it leads to an

       // uncommon trap.  Combined with the too_many_traps guards

       // above, this prevents SEGV storms reported in 6366351,

       // by recompiling offending methods without this optimization.

     }

   }

 #ifndef PRODUCT

   if (trace_opto_pipelining()) {

     tty->print("\n---- Start Local Scheduling ----\n");

   }

 #endif

   // Schedule locally.  Right now a simple topological sort.

   // Later, do a real latency aware scheduler.

   uint max_idx = C->unique();

   GrowableArray<int> ready_cnt(max_idx, max_idx, -1);

   visited.Clear();

   for (i = 0; i < _num_blocks; i++) {

     if (!_blocks[i]->schedule_local(this, matcher, ready_cnt, visited)) {

       if (!C->failure_reason_is(C2Compiler::retry_no_subsuming_loads())) {

         C->record_method_not_compilable("local schedule failed");

       }

       return;

     }

   }

   // If we inserted any instructions between a Call and his CatchNode,

   // clone the instructions on all paths below the Catch.

   for( i=0; i < _num_blocks; i++ )

     _blocks[i]->call_catch_cleanup(_bbs);

 #ifndef PRODUCT

   if (trace_opto_pipelining()) {

     tty->print("\n---- After GlobalCodeMotion ----\n");

     for (uint i = 0; i < _num_blocks; i++) {

       _blocks[i]->dump();

     }

   }

 #endif

   // Dead.

   _node_latency = (GrowableArray<uint> *)0xdeadbeef;

 }

 //------------------------------Estimate_Block_Frequency-----------------------

 // Estimate block frequencies based on IfNode probabilities.

 void PhaseCFG::Estimate_Block_Frequency() {

   // Force conditional branches leading to uncommon traps to be unlikely,

   // not because we get to the uncommon_trap with less relative frequency,

   // but because an uncommon_trap typically causes a deopt, so we only get

   // there once.

   if (C->do_freq_based_layout()) {

     Block_List worklist;

     Block* root_blk = _blocks[0];

     for (uint i = 1; i < root_blk->num_preds(); i++) {

       Block *pb = _bbs[root_blk->pred(i)->_idx];

       if (pb->has_uncommon_code()) {

         worklist.push(pb);

       }

     }

     while (worklist.size() > 0) {

       Block* uct = worklist.pop();

       if (uct == _broot) continue;

       for (uint i = 1; i < uct->num_preds(); i++) {

         Block *pb = _bbs[uct->pred(i)->_idx];

         if (pb->_num_succs == 1) {

           worklist.push(pb);

         } else if (pb->num_fall_throughs() == 2) {

           pb->update_uncommon_branch(uct);

         }

       }

     }

   }

   // Create the loop tree and calculate loop depth.

   _root_loop = create_loop_tree();

   _root_loop->compute_loop_depth(0);

   // Compute block frequency of each block, relative to a single loop entry.

   _root_loop->compute_freq();

   // Adjust all frequencies to be relative to a single method entry

   _root_loop->_freq = 1.0;

   _root_loop->scale_freq();

   // Save outmost loop frequency for LRG frequency threshold

   _outer_loop_freq = _root_loop->outer_loop_freq();

   // force paths ending at uncommon traps to be infrequent

   if (!C->do_freq_based_layout()) {

     Block_List worklist;

     Block* root_blk = _blocks[0];

     for (uint i = 1; i < root_blk->num_preds(); i++) {

       Block *pb = _bbs[root_blk->pred(i)->_idx];

       if (pb->has_uncommon_code()) {

         worklist.push(pb);

       }

     }

     while (worklist.size() > 0) {

       Block* uct = worklist.pop();

       uct->_freq = PROB_MIN;

       for (uint i = 1; i < uct->num_preds(); i++) {

         Block *pb = _bbs[uct->pred(i)->_idx];

         if (pb->_num_succs == 1 && pb->_freq > PROB_MIN) {

           worklist.push(pb);

         }

       }

     }

   }

 #ifdef ASSERT

   for (uint i = 0; i < _num_blocks; i++ ) {

     Block *b = _blocks[i];

     assert(b->_freq >= MIN_BLOCK_FREQUENCY, "Register Allocator requires meaningful block frequency");

   }

 #endif

 #ifndef PRODUCT

   if (PrintCFGBlockFreq) {

     tty->print_cr("CFG Block Frequencies");

     _root_loop->dump_tree();

     if (Verbose) {

       tty->print_cr("PhaseCFG dump");

       dump();

       tty->print_cr("Node dump");

       _root->dump(99999);

     }

   }

 #endif

 }

 //----------------------------create_loop_tree--------------------------------

 // Create a loop tree from the CFG

 CFGLoop* PhaseCFG::create_loop_tree() {

 #ifdef ASSERT

   assert( _blocks[0] == _broot, "" );

   for (uint i = 0; i < _num_blocks; i++ ) {

     Block *b = _blocks[i];

     // Check that _loop field are clear...we could clear them if not.

     assert(b->_loop == NULL, "clear _loop expected");

     // Sanity check that the RPO numbering is reflected in the _blocks array.

     // It doesn't have to be for the loop tree to be built, but if it is not,

     // then the blocks have been reordered since dom graph building...which

     // may question the RPO numbering

     assert(b->_rpo == i, "unexpected reverse post order number");

   }

 #endif

   int idct = 0;

   CFGLoop* root_loop = new CFGLoop(idct++);

   Block_List worklist;

   // Assign blocks to loops

   for(uint i = _num_blocks - 1; i > 0; i-- ) { // skip Root block

     Block *b = _blocks[i];

     if (b->head()->is_Loop()) {

       Block* loop_head = b;

       assert(loop_head->num_preds() - 1 == 2, "loop must have 2 predecessors");

       Node* tail_n = loop_head->pred(LoopNode::LoopBackControl);

       Block* tail = _bbs[tail_n->_idx];

       // Defensively filter out Loop nodes for non-single-entry loops.

       // For all reasonable loops, the head occurs before the tail in RPO.

       if (i <= tail->_rpo) {

         // The tail and (recursive) predecessors of the tail

         // are made members of a new loop.

         assert(worklist.size() == 0, "nonempty worklist");

         CFGLoop* nloop = new CFGLoop(idct++);

         assert(loop_head->_loop == NULL, "just checking");

         loop_head->_loop = nloop;

         // Add to nloop so push_pred() will skip over inner loops

         nloop->add_member(loop_head);

         nloop->push_pred(loop_head, LoopNode::LoopBackControl, worklist, _bbs);

         while (worklist.size() > 0) {

           Block* member = worklist.pop();

           if (member != loop_head) {

             for (uint j = 1; j < member->num_preds(); j++) {

               nloop->push_pred(member, j, worklist, _bbs);

             }

           }

         }

       }

     }

   }

   // Create a member list for each loop consisting

   // of both blocks and (immediate child) loops.

   for (uint i = 0; i < _num_blocks; i++) {

     Block *b = _blocks[i];

     CFGLoop* lp = b->_loop;

     if (lp == NULL) {

       // Not assigned to a loop. Add it to the method's pseudo loop.

       b->_loop = root_loop;

       lp = root_loop;

     }

     if (lp == root_loop || b != lp->head()) { // loop heads are already members

       lp->add_member(b);

     }

     if (lp != root_loop) {

       if (lp->parent() == NULL) {

         // Not a nested loop. Make it a child of the method's pseudo loop.

         root_loop->add_nested_loop(lp);

       }

       if (b == lp->head()) {

         // Add nested loop to member list of parent loop.

         lp->parent()->add_member(lp);

       }

     }

   }

   return root_loop;

 }

 //------------------------------push_pred--------------------------------------

 void CFGLoop::push_pred(Block* blk, int i, Block_List& worklist, Block_Array& node_to_blk) {

   Node* pred_n = blk->pred(i);

   Block* pred = node_to_blk[pred_n->_idx];

   CFGLoop *pred_loop = pred->_loop;

   if (pred_loop == NULL) {

     // Filter out blocks for non-single-entry loops.

     // For all reasonable loops, the head occurs before the tail in RPO.

     if (pred->_rpo > head()->_rpo) {

       pred->_loop = this;

       worklist.push(pred);

     }

   } else if (pred_loop != this) {

     // Nested loop.

     while (pred_loop->_parent != NULL && pred_loop->_parent != this) {

       pred_loop = pred_loop->_parent;

     }

     // Make pred's loop be a child

     if (pred_loop->_parent == NULL) {

       add_nested_loop(pred_loop);

       // Continue with loop entry predecessor.

       Block* pred_head = pred_loop->head();

       assert(pred_head->num_preds() - 1 == 2, "loop must have 2 predecessors");

       assert(pred_head != head(), "loop head in only one loop");

       push_pred(pred_head, LoopNode::EntryControl, worklist, node_to_blk);

     } else {

       assert(pred_loop->_parent == this && _parent == NULL, "just checking");

     }

   }

 }

 //------------------------------add_nested_loop--------------------------------

 // Make cl a child of the current loop in the loop tree.

 void CFGLoop::add_nested_loop(CFGLoop* cl) {

   assert(_parent == NULL, "no parent yet");

   assert(cl != this, "not my own parent");

   cl->_parent = this;

   CFGLoop* ch = _child;

   if (ch == NULL) {

     _child = cl;

   } else {

     while (ch->_sibling != NULL) { ch = ch->_sibling; }

     ch->_sibling = cl;

   }

 }

 //------------------------------compute_loop_depth-----------------------------

 // Store the loop depth in each CFGLoop object.

 // Recursively walk the children to do the same for them.

 void CFGLoop::compute_loop_depth(int depth) {

   _depth = depth;

   CFGLoop* ch = _child;

   while (ch != NULL) {

     ch->compute_loop_depth(depth + 1);

     ch = ch->_sibling;

   }

 }

 //------------------------------compute_freq-----------------------------------

 // Compute the frequency of each block and loop, relative to a single entry

 // into the dominating loop head.

 void CFGLoop::compute_freq() {

   // Bottom up traversal of loop tree (visit inner loops first.)

   // Set loop head frequency to 1.0, then transitively

   // compute frequency for all successors in the loop,

   // as well as for each exit edge.  Inner loops are

   // treated as single blocks with loop exit targets

   // as the successor blocks.

   // Nested loops first

   CFGLoop* ch = _child;

   while (ch != NULL) {

     ch->compute_freq();

     ch = ch->_sibling;

   }

   assert (_members.length() > 0, "no empty loops");

   Block* hd = head();

   hd->_freq = 1.0f;

   for (int i = 0; i < _members.length(); i++) {

     CFGElement* s = _members.at(i);

     float freq = s->_freq;

     if (s->is_block()) {

       Block* b = s->as_Block();

       for (uint j = 0; j < b->_num_succs; j++) {

         Block* sb = b->_succs[j];

         update_succ_freq(sb, freq * b->succ_prob(j));

       }

     } else {

       CFGLoop* lp = s->as_CFGLoop();

       assert(lp->_parent == this, "immediate child");

       for (int k = 0; k < lp->_exits.length(); k++) {

         Block* eb = lp->_exits.at(k).get_target();

         float prob = lp->_exits.at(k).get_prob();

         update_succ_freq(eb, freq * prob);

       }

     }

   }

   // For all loops other than the outer, "method" loop,

   // sum and normalize the exit probability. The "method" loop

   // should keep the initial exit probability of 1, so that

   // inner blocks do not get erroneously scaled.

   if (_depth != 0) {

     // Total the exit probabilities for this loop.

     float exits_sum = 0.0f;

     for (int i = 0; i < _exits.length(); i++) {

       exits_sum += _exits.at(i).get_prob();

     }

     // Normalize the exit probabilities. Until now, the

     // probabilities estimate the possibility of exit per

     // a single loop iteration; afterward, they estimate

     // the probability of exit per loop entry.

     for (int i = 0; i < _exits.length(); i++) {

       Block* et = _exits.at(i).get_target();

       float new_prob = 0.0f;

       if (_exits.at(i).get_prob() > 0.0f) {

         new_prob = _exits.at(i).get_prob() / exits_sum;

       }

       BlockProbPair bpp(et, new_prob);

       _exits.at_put(i, bpp);

     }

     // Save the total, but guard against unreasonable probability,

     // as the value is used to estimate the loop trip count.

     // An infinite trip count would blur relative block

     // frequencies.

     if (exits_sum > 1.0f) exits_sum = 1.0;

     if (exits_sum < PROB_MIN) exits_sum = PROB_MIN;

     _exit_prob = exits_sum;

   }

 }

 //------------------------------succ_prob-------------------------------------

 // Determine the probability of reaching successor 'i' from the receiver block.

 float Block::succ_prob(uint i) {

   int eidx = end_idx();

   Node *n = _nodes[eidx];  // Get ending Node

   int op = n->Opcode();

   if (n->is_Mach()) {

     if (n->is_MachNullCheck()) {

       // Can only reach here if called after lcm. The original Op_If is gone,

       // so we attempt to infer the probability from one or both of the

       // successor blocks.

       assert(_num_succs == 2, "expecting 2 successors of a null check");

       // If either successor has only one predecessor, then the

       // probability estimate can be derived using the

       // relative frequency of the successor and this block.

       if (_succs[i]->num_preds() == 2) {

         return _succs[i]->_freq / _freq;

       } else if (_succs[1-i]->num_preds() == 2) {

         return 1 - (_succs[1-i]->_freq / _freq);

       } else {

         // Estimate using both successor frequencies

         float freq = _succs[i]->_freq;

         return freq / (freq + _succs[1-i]->_freq);

       }

     }

     op = n->as_Mach()->ideal_Opcode();

   }

   // Switch on branch type

   switch( op ) {

   case Op_CountedLoopEnd:

   case Op_If: {

     assert (i < 2, "just checking");

     // Conditionals pass on only part of their frequency

     float prob  = n->as_MachIf()->_prob;

     assert(prob >= 0.0 && prob <= 1.0, "out of range probability");

     // If succ[i] is the FALSE branch, invert path info

     if( _nodes[i + eidx + 1]->Opcode() == Op_IfFalse ) {

       return 1.0f - prob; // not taken

     } else {

       return prob; // taken

     }

   }

   case Op_Jump:

     // Divide the frequency between all successors evenly

     return 1.0f/_num_succs;

   case Op_Catch: {

     const CatchProjNode *ci = _nodes[i + eidx + 1]->as_CatchProj();

     if (ci->_con == CatchProjNode::fall_through_index) {

       // Fall-thru path gets the lion's share.

       return 1.0f - PROB_UNLIKELY_MAG(5)*_num_succs;

     } else {

       // Presume exceptional paths are equally unlikely

       return PROB_UNLIKELY_MAG(5);

     }

   }

   case Op_Root:

   case Op_Goto:

     // Pass frequency straight thru to target

     return 1.0f;

   case Op_NeverBranch:

     return 0.0f;

   case Op_TailCall:

   case Op_TailJump:

   case Op_Return:

   case Op_Halt:

   case Op_Rethrow:

     // Do not push out freq to root block

     return 0.0f;

   default:

     ShouldNotReachHere();

   }

   return 0.0f;

 }

 //------------------------------num_fall_throughs-----------------------------

 // Return the number of fall-through candidates for a block

 int Block::num_fall_throughs() {

   int eidx = end_idx();

   Node *n = _nodes[eidx];  // Get ending Node

   int op = n->Opcode();

   if (n->is_Mach()) {

     if (n->is_MachNullCheck()) {

       // In theory, either side can fall-thru, for simplicity sake,

       // let's say only the false branch can now.

       return 1;

     }

     op = n->as_Mach()->ideal_Opcode();

   }

   // Switch on branch type

   switch( op ) {

   case Op_CountedLoopEnd:

   case Op_If:

     return 2;

   case Op_Root:

   case Op_Goto:

     return 1;

   case Op_Catch: {

     for (uint i = 0; i < _num_succs; i++) {

       const CatchProjNode *ci = _nodes[i + eidx + 1]->as_CatchProj();

       if (ci->_con == CatchProjNode::fall_through_index) {

         return 1;

       }

     }

     return 0;

   }

   case Op_Jump:

   case Op_NeverBranch:

   case Op_TailCall:

   case Op_TailJump:

   case Op_Return:

   case Op_Halt:

   case Op_Rethrow:

     return 0;

   default:

     ShouldNotReachHere();

   }

   return 0;

 }

 //------------------------------succ_fall_through-----------------------------

 // Return true if a specific successor could be fall-through target.

 bool Block::succ_fall_through(uint i) {

   int eidx = end_idx();

   Node *n = _nodes[eidx];  // Get ending Node

   int op = n->Opcode();

   if (n->is_Mach()) {

     if (n->is_MachNullCheck()) {

       // In theory, either side can fall-thru, for simplicity sake,

       // let's say only the false branch can now.

       return _nodes[i + eidx + 1]->Opcode() == Op_IfFalse;

     }

     op = n->as_Mach()->ideal_Opcode();

   }

   // Switch on branch type

   switch( op ) {

   case Op_CountedLoopEnd:

   case Op_If:

   case Op_Root:

   case Op_Goto:

     return true;

   case Op_Catch: {

     const CatchProjNode *ci = _nodes[i + eidx + 1]->as_CatchProj();

     return ci->_con == CatchProjNode::fall_through_index;

   }

   case Op_Jump:

   case Op_NeverBranch:

   case Op_TailCall:

   case Op_TailJump:

   case Op_Return:

   case Op_Halt:

   case Op_Rethrow:

     return false;

   default:

     ShouldNotReachHere();

   }

   return false;

 }

 //------------------------------update_uncommon_branch------------------------

 // Update the probability of a two-branch to be uncommon

 void Block::update_uncommon_branch(Block* ub) {

   int eidx = end_idx();

   Node *n = _nodes[eidx];  // Get ending Node

   int op = n->as_Mach()->ideal_Opcode();

   assert(op == Op_CountedLoopEnd || op == Op_If, "must be a If");

   assert(num_fall_throughs() == 2, "must be a two way branch block");

   // Which successor is ub?

   uint s;

   for (s = 0; s <_num_succs; s++) {

     if (_succs[s] == ub) break;

   }

   assert(s < 2, "uncommon successor must be found");

   // If ub is the true path, make the proability small, else

   // ub is the false path, and make the probability large

   bool invert = (_nodes[s + eidx + 1]->Opcode() == Op_IfFalse);

   // Get existing probability

   float p = n->as_MachIf()->_prob;

   if (invert) p = 1.0 - p;

   if (p > PROB_MIN) {

     p = PROB_MIN;

   }

   if (invert) p = 1.0 - p;

   n->as_MachIf()->_prob = p;

 }

 //------------------------------update_succ_freq-------------------------------

 // Update the appropriate frequency associated with block 'b', a successor of

 // a block in this loop.

 void CFGLoop::update_succ_freq(Block* b, float freq) {

   if (b->_loop == this) {

     if (b == head()) {

       // back branch within the loop

       // Do nothing now, the loop carried frequency will be

       // adjust later in scale_freq().

     } else {

       // simple branch within the loop

       b->_freq += freq;

     }

   } else if (!in_loop_nest(b)) {

     // branch is exit from this loop

     BlockProbPair bpp(b, freq);

     _exits.append(bpp);

   } else {

     // branch into nested loop

     CFGLoop* ch = b->_loop;

     ch->_freq += freq;

   }

 }

 //------------------------------in_loop_nest-----------------------------------

 // Determine if block b is in the receiver's loop nest.

 bool CFGLoop::in_loop_nest(Block* b) {

   int depth = _depth;

   CFGLoop* b_loop = b->_loop;

   int b_depth = b_loop->_depth;

   if (depth == b_depth) {

     return true;

   }

   while (b_depth > depth) {

     b_loop = b_loop->_parent;

     b_depth = b_loop->_depth;

   }

   return b_loop == this;

 }

 //------------------------------scale_freq-------------------------------------

 // Scale frequency of loops and blocks by trip counts from outer loops

 // Do a top down traversal of loop tree (visit outer loops first.)

 void CFGLoop::scale_freq() {

   float loop_freq = _freq * trip_count();

   _freq = loop_freq;

   for (int i = 0; i < _members.length(); i++) {

     CFGElement* s = _members.at(i);

     float block_freq = s->_freq * loop_freq;

     if (g_isnan(block_freq) || block_freq < MIN_BLOCK_FREQUENCY)

       block_freq = MIN_BLOCK_FREQUENCY;

     s->_freq = block_freq;

   }

   CFGLoop* ch = _child;

   while (ch != NULL) {

     ch->scale_freq();

     ch = ch->_sibling;

   }

 }

 // Frequency of outer loop

 float CFGLoop::outer_loop_freq() const {

   if (_child != NULL) {

     return _child->_freq;

   }

   return _freq;

 }

 #ifndef PRODUCT

 //------------------------------dump_tree--------------------------------------

 void CFGLoop::dump_tree() const {

   dump();

   if (_child != NULL)   _child->dump_tree();

   if (_sibling != NULL) _sibling->dump_tree();

 }

 //------------------------------dump-------------------------------------------

 void CFGLoop::dump() const {

   for (int i = 0; i < _depth; i++) tty->print("   ");

   tty->print("%s: %d  trip_count: %6.0f freq: %6.0f\n",

              _depth == 0 ? "Method" : "Loop", _id, trip_count(), _freq);

   for (int i = 0; i < _depth; i++) tty->print("   ");

   tty->print("         members:", _id);

   int k = 0;

   for (int i = 0; i < _members.length(); i++) {

     if (k++ >= 6) {

       tty->print("\n              ");

       for (int j = 0; j < _depth+1; j++) tty->print("   ");

       k = 0;

     }

     CFGElement *s = _members.at(i);

     if (s->is_block()) {

       Block *b = s->as_Block();

       tty->print(" B%d(%6.3f)", b->_pre_order, b->_freq);

     } else {

       CFGLoop* lp = s->as_CFGLoop();

       tty->print(" L%d(%6.3f)", lp->_id, lp->_freq);

     }

   }

   tty->print("\n");

   for (int i = 0; i < _depth; i++) tty->print("   ");

   tty->print("         exits:  ");

   k = 0;

   for (int i = 0; i < _exits.length(); i++) {

     if (k++ >= 7) {

       tty->print("\n              ");

       for (int j = 0; j < _depth+1; j++) tty->print("   ");

       k = 0;

     }

     Block *blk = _exits.at(i).get_target();

     float prob = _exits.at(i).get_prob();

     tty->print(" ->%d@%d%%", blk->_pre_order, (int)(prob*100));

   }

   tty->print("\n");

 }

 #endif