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Java example source code file (stringopts.cpp)

This example Java source code file (stringopts.cpp) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

addi, c\-, callstaticjavanode, iffalse, ifnode, iftrue, node, null, printoptimizestringconcat, product, regionnode, typeint\:\:int

The stringopts.cpp Java example source code

/*
 * Copyright (c) 2009, 2013, 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
 * questions.
 *
 */

#include "precompiled.hpp"
#include "compiler/compileLog.hpp"
#include "opto/addnode.hpp"
#include "opto/callGenerator.hpp"
#include "opto/callnode.hpp"
#include "opto/divnode.hpp"
#include "opto/graphKit.hpp"
#include "opto/idealKit.hpp"
#include "opto/rootnode.hpp"
#include "opto/runtime.hpp"
#include "opto/stringopts.hpp"
#include "opto/subnode.hpp"

#define __ kit.

class StringConcat : public ResourceObj {
 private:
  PhaseStringOpts*    _stringopts;
  Node*               _string_alloc;
  AllocateNode*       _begin;          // The allocation the begins the pattern
  CallStaticJavaNode* _end;            // The final call of the pattern.  Will either be
                                       // SB.toString or or String.<init>(SB.toString)
  bool                _multiple;       // indicates this is a fusion of two or more
                                       // separate StringBuilders

  Node*               _arguments;      // The list of arguments to be concatenated
  GrowableArray<int>  _mode;           // into a String along with a mode flag
                                       // indicating how to treat the value.
  Node_List           _constructors;   // List of constructors (many in case of stacked concat)
  Node_List           _control;        // List of control nodes that will be deleted
  Node_List           _uncommon_traps; // Uncommon traps that needs to be rewritten
                                       // to restart at the initial JVMState.

 public:
  // Mode for converting arguments to Strings
  enum {
    StringMode,
    IntMode,
    CharMode,
    StringNullCheckMode
  };

  StringConcat(PhaseStringOpts* stringopts, CallStaticJavaNode* end):
    _end(end),
    _begin(NULL),
    _multiple(false),
    _string_alloc(NULL),
    _stringopts(stringopts) {
    _arguments = new (_stringopts->C) Node(1);
    _arguments->del_req(0);
  }

  bool validate_mem_flow();
  bool validate_control_flow();

  void merge_add() {
#if 0
    // XXX This is place holder code for reusing an existing String
    // allocation but the logic for checking the state safety is
    // probably inadequate at the moment.
    CallProjections endprojs;
    sc->end()->extract_projections(&endprojs, false);
    if (endprojs.resproj != NULL) {
      for (SimpleDUIterator i(endprojs.resproj); i.has_next(); i.next()) {
        CallStaticJavaNode *use = i.get()->isa_CallStaticJava();
        if (use != NULL && use->method() != NULL &&
            use->method()->intrinsic_id() == vmIntrinsics::_String_String &&
            use->in(TypeFunc::Parms + 1) == endprojs.resproj) {
          // Found useless new String(sb.toString()) so reuse the newly allocated String
          // when creating the result instead of allocating a new one.
          sc->set_string_alloc(use->in(TypeFunc::Parms));
          sc->set_end(use);
        }
      }
    }
#endif
  }

  StringConcat* merge(StringConcat* other, Node* arg);

  void set_allocation(AllocateNode* alloc) {
    _begin = alloc;
  }

  void append(Node* value, int mode) {
    _arguments->add_req(value);
    _mode.append(mode);
  }
  void push(Node* value, int mode) {
    _arguments->ins_req(0, value);
    _mode.insert_before(0, mode);
  }

  void push_string(Node* value) {
    push(value, StringMode);
  }
  void push_string_null_check(Node* value) {
    push(value, StringNullCheckMode);
  }
  void push_int(Node* value) {
    push(value, IntMode);
  }
  void push_char(Node* value) {
    push(value, CharMode);
  }

  static bool is_SB_toString(Node* call) {
    if (call->is_CallStaticJava()) {
      CallStaticJavaNode* csj = call->as_CallStaticJava();
      ciMethod* m = csj->method();
      if (m != NULL &&
          (m->intrinsic_id() == vmIntrinsics::_StringBuilder_toString ||
           m->intrinsic_id() == vmIntrinsics::_StringBuffer_toString)) {
        return true;
      }
    }
    return false;
  }

  static Node* skip_string_null_check(Node* value) {
    // Look for a diamond shaped Null check of toString() result
    // (could be code from String.valueOf()):
    // (Proj == NULL) ? "null":"CastPP(Proj)#NotNULL
    if (value->is_Phi()) {
      int true_path = value->as_Phi()->is_diamond_phi();
      if (true_path != 0) {
        // phi->region->if_proj->ifnode->bool
        BoolNode* b = value->in(0)->in(1)->in(0)->in(1)->as_Bool();
        Node* cmp = b->in(1);
        Node* v1 = cmp->in(1);
        Node* v2 = cmp->in(2);
        // Null check of the return of toString which can simply be skipped.
        if (b->_test._test == BoolTest::ne &&
            v2->bottom_type() == TypePtr::NULL_PTR &&
            value->in(true_path)->Opcode() == Op_CastPP &&
            value->in(true_path)->in(1) == v1 &&
            v1->is_Proj() && is_SB_toString(v1->in(0))) {
          return v1;
        }
      }
    }
    return value;
  }

  Node* argument(int i) {
    return _arguments->in(i);
  }
  Node* argument_uncast(int i) {
    Node* arg = argument(i);
    int amode = mode(i);
    if (amode == StringConcat::StringMode ||
        amode == StringConcat::StringNullCheckMode) {
      arg = skip_string_null_check(arg);
    }
    return arg;
  }
  void set_argument(int i, Node* value) {
    _arguments->set_req(i, value);
  }
  int num_arguments() {
    return _mode.length();
  }
  int mode(int i) {
    return _mode.at(i);
  }
  void add_control(Node* ctrl) {
    assert(!_control.contains(ctrl), "only push once");
    _control.push(ctrl);
  }
  void add_constructor(Node* init) {
    assert(!_constructors.contains(init), "only push once");
    _constructors.push(init);
  }
  CallStaticJavaNode* end() { return _end; }
  AllocateNode* begin() { return _begin; }
  Node* string_alloc() { return _string_alloc; }

  void eliminate_unneeded_control();
  void eliminate_initialize(InitializeNode* init);
  void eliminate_call(CallNode* call);

  void maybe_log_transform() {
    CompileLog* log = _stringopts->C->log();
    if (log != NULL) {
      log->head("replace_string_concat arguments='%d' string_alloc='%d' multiple='%d'",
                num_arguments(),
                _string_alloc != NULL,
                _multiple);
      JVMState* p = _begin->jvms();
      while (p != NULL) {
        log->elem("jvms bci='%d' method='%d'", p->bci(), log->identify(p->method()));
        p = p->caller();
      }
      log->tail("replace_string_concat");
    }
  }

  void convert_uncommon_traps(GraphKit& kit, const JVMState* jvms) {
    for (uint u = 0; u < _uncommon_traps.size(); u++) {
      Node* uct = _uncommon_traps.at(u);

      // Build a new call using the jvms state of the allocate
      address call_addr = SharedRuntime::uncommon_trap_blob()->entry_point();
      const TypeFunc* call_type = OptoRuntime::uncommon_trap_Type();
      const TypePtr* no_memory_effects = NULL;
      Compile* C = _stringopts->C;
      CallStaticJavaNode* call = new (C) CallStaticJavaNode(call_type, call_addr, "uncommon_trap",
                                                            jvms->bci(), no_memory_effects);
      for (int e = 0; e < TypeFunc::Parms; e++) {
        call->init_req(e, uct->in(e));
      }
      // Set the trap request to record intrinsic failure if this trap
      // is taken too many times.  Ideally we would handle then traps by
      // doing the original bookkeeping in the MDO so that if it caused
      // the code to be thrown out we could still recompile and use the
      // optimization.  Failing the uncommon traps doesn't really mean
      // that the optimization is a bad idea but there's no other way to
      // do the MDO updates currently.
      int trap_request = Deoptimization::make_trap_request(Deoptimization::Reason_intrinsic,
                                                           Deoptimization::Action_make_not_entrant);
      call->init_req(TypeFunc::Parms, __ intcon(trap_request));
      kit.add_safepoint_edges(call);

      _stringopts->gvn()->transform(call);
      C->gvn_replace_by(uct, call);
      uct->disconnect_inputs(NULL, C);
    }
  }

  void cleanup() {
    // disconnect the hook node
    _arguments->disconnect_inputs(NULL, _stringopts->C);
  }
};


void StringConcat::eliminate_unneeded_control() {
  for (uint i = 0; i < _control.size(); i++) {
    Node* n = _control.at(i);
    if (n->is_Allocate()) {
      eliminate_initialize(n->as_Allocate()->initialization());
    }
    if (n->is_Call()) {
      if (n != _end) {
        eliminate_call(n->as_Call());
      }
    } else if (n->is_IfTrue()) {
      Compile* C = _stringopts->C;
      C->gvn_replace_by(n, n->in(0)->in(0));
      // get rid of the other projection
      C->gvn_replace_by(n->in(0)->as_If()->proj_out(false), C->top());
    }
  }
}


StringConcat* StringConcat::merge(StringConcat* other, Node* arg) {
  StringConcat* result = new StringConcat(_stringopts, _end);
  for (uint x = 0; x < _control.size(); x++) {
    Node* n = _control.at(x);
    if (n->is_Call()) {
      result->_control.push(n);
    }
  }
  for (uint x = 0; x < other->_control.size(); x++) {
    Node* n = other->_control.at(x);
    if (n->is_Call()) {
      result->_control.push(n);
    }
  }
  assert(result->_control.contains(other->_end), "what?");
  assert(result->_control.contains(_begin), "what?");
  for (int x = 0; x < num_arguments(); x++) {
    Node* argx = argument_uncast(x);
    if (argx == arg) {
      // replace the toString result with the all the arguments that
      // made up the other StringConcat
      for (int y = 0; y < other->num_arguments(); y++) {
        result->append(other->argument(y), other->mode(y));
      }
    } else {
      result->append(argx, mode(x));
    }
  }
  result->set_allocation(other->_begin);
  for (uint i = 0; i < _constructors.size(); i++) {
    result->add_constructor(_constructors.at(i));
  }
  for (uint i = 0; i < other->_constructors.size(); i++) {
    result->add_constructor(other->_constructors.at(i));
  }
  result->_multiple = true;
  return result;
}


void StringConcat::eliminate_call(CallNode* call) {
  Compile* C = _stringopts->C;
  CallProjections projs;
  call->extract_projections(&projs, false);
  if (projs.fallthrough_catchproj != NULL) {
    C->gvn_replace_by(projs.fallthrough_catchproj, call->in(TypeFunc::Control));
  }
  if (projs.fallthrough_memproj != NULL) {
    C->gvn_replace_by(projs.fallthrough_memproj, call->in(TypeFunc::Memory));
  }
  if (projs.catchall_memproj != NULL) {
    C->gvn_replace_by(projs.catchall_memproj, C->top());
  }
  if (projs.fallthrough_ioproj != NULL) {
    C->gvn_replace_by(projs.fallthrough_ioproj, call->in(TypeFunc::I_O));
  }
  if (projs.catchall_ioproj != NULL) {
    C->gvn_replace_by(projs.catchall_ioproj, C->top());
  }
  if (projs.catchall_catchproj != NULL) {
    // EA can't cope with the partially collapsed graph this
    // creates so put it on the worklist to be collapsed later.
    for (SimpleDUIterator i(projs.catchall_catchproj); i.has_next(); i.next()) {
      Node *use = i.get();
      int opc = use->Opcode();
      if (opc == Op_CreateEx || opc == Op_Region) {
        _stringopts->record_dead_node(use);
      }
    }
    C->gvn_replace_by(projs.catchall_catchproj, C->top());
  }
  if (projs.resproj != NULL) {
    C->gvn_replace_by(projs.resproj, C->top());
  }
  C->gvn_replace_by(call, C->top());
}

void StringConcat::eliminate_initialize(InitializeNode* init) {
  Compile* C = _stringopts->C;

  // Eliminate Initialize node.
  assert(init->outcnt() <= 2, "only a control and memory projection expected");
  assert(init->req() <= InitializeNode::RawStores, "no pending inits");
  Node *ctrl_proj = init->proj_out(TypeFunc::Control);
  if (ctrl_proj != NULL) {
    C->gvn_replace_by(ctrl_proj, init->in(TypeFunc::Control));
  }
  Node *mem_proj = init->proj_out(TypeFunc::Memory);
  if (mem_proj != NULL) {
    Node *mem = init->in(TypeFunc::Memory);
    C->gvn_replace_by(mem_proj, mem);
  }
  C->gvn_replace_by(init, C->top());
  init->disconnect_inputs(NULL, C);
}

Node_List PhaseStringOpts::collect_toString_calls() {
  Node_List string_calls;
  Node_List worklist;

  _visited.Clear();

  // Prime the worklist
  for (uint i = 1; i < C->root()->len(); i++) {
    Node* n = C->root()->in(i);
    if (n != NULL && !_visited.test_set(n->_idx)) {
      worklist.push(n);
    }
  }

  while (worklist.size() > 0) {
    Node* ctrl = worklist.pop();
    if (StringConcat::is_SB_toString(ctrl)) {
      CallStaticJavaNode* csj = ctrl->as_CallStaticJava();
      string_calls.push(csj);
    }
    if (ctrl->in(0) != NULL && !_visited.test_set(ctrl->in(0)->_idx)) {
      worklist.push(ctrl->in(0));
    }
    if (ctrl->is_Region()) {
      for (uint i = 1; i < ctrl->len(); i++) {
        if (ctrl->in(i) != NULL && !_visited.test_set(ctrl->in(i)->_idx)) {
          worklist.push(ctrl->in(i));
        }
      }
    }
  }
  return string_calls;
}


StringConcat* PhaseStringOpts::build_candidate(CallStaticJavaNode* call) {
  ciMethod* m = call->method();
  ciSymbol* string_sig;
  ciSymbol* int_sig;
  ciSymbol* char_sig;
  if (m->holder() == C->env()->StringBuilder_klass()) {
    string_sig = ciSymbol::String_StringBuilder_signature();
    int_sig = ciSymbol::int_StringBuilder_signature();
    char_sig = ciSymbol::char_StringBuilder_signature();
  } else if (m->holder() == C->env()->StringBuffer_klass()) {
    string_sig = ciSymbol::String_StringBuffer_signature();
    int_sig = ciSymbol::int_StringBuffer_signature();
    char_sig = ciSymbol::char_StringBuffer_signature();
  } else {
    return NULL;
  }
#ifndef PRODUCT
  if (PrintOptimizeStringConcat) {
    tty->print("considering toString call in ");
    call->jvms()->dump_spec(tty); tty->cr();
  }
#endif

  StringConcat* sc = new StringConcat(this, call);

  AllocateNode* alloc = NULL;
  InitializeNode* init = NULL;

  // possible opportunity for StringBuilder fusion
  CallStaticJavaNode* cnode = call;
  while (cnode) {
    Node* recv = cnode->in(TypeFunc::Parms)->uncast();
    if (recv->is_Proj()) {
      recv = recv->in(0);
    }
    cnode = recv->isa_CallStaticJava();
    if (cnode == NULL) {
      alloc = recv->isa_Allocate();
      if (alloc == NULL) {
        break;
      }
      // Find the constructor call
      Node* result = alloc->result_cast();
      if (result == NULL || !result->is_CheckCastPP() || alloc->in(TypeFunc::Memory)->is_top()) {
        // strange looking allocation
#ifndef PRODUCT
        if (PrintOptimizeStringConcat) {
          tty->print("giving up because allocation looks strange ");
          alloc->jvms()->dump_spec(tty); tty->cr();
        }
#endif
        break;
      }
      Node* constructor = NULL;
      for (SimpleDUIterator i(result); i.has_next(); i.next()) {
        CallStaticJavaNode *use = i.get()->isa_CallStaticJava();
        if (use != NULL &&
            use->method() != NULL &&
            !use->method()->is_static() &&
            use->method()->name() == ciSymbol::object_initializer_name() &&
            use->method()->holder() == m->holder()) {
          // Matched the constructor.
          ciSymbol* sig = use->method()->signature()->as_symbol();
          if (sig == ciSymbol::void_method_signature() ||
              sig == ciSymbol::int_void_signature() ||
              sig == ciSymbol::string_void_signature()) {
            if (sig == ciSymbol::string_void_signature()) {
              // StringBuilder(String) so pick this up as the first argument
              assert(use->in(TypeFunc::Parms + 1) != NULL, "what?");
              const Type* type = _gvn->type(use->in(TypeFunc::Parms + 1));
              if (type == TypePtr::NULL_PTR) {
                // StringBuilder(null) throws exception.
#ifndef PRODUCT
                if (PrintOptimizeStringConcat) {
                  tty->print("giving up because StringBuilder(null) throws exception");
                  alloc->jvms()->dump_spec(tty); tty->cr();
                }
#endif
                return NULL;
              }
              // StringBuilder(str) argument needs null check.
              sc->push_string_null_check(use->in(TypeFunc::Parms + 1));
            }
            // The int variant takes an initial size for the backing
            // array so just treat it like the void version.
            constructor = use;
          } else {
#ifndef PRODUCT
            if (PrintOptimizeStringConcat) {
              tty->print("unexpected constructor signature: %s", sig->as_utf8());
            }
#endif
          }
          break;
        }
      }
      if (constructor == NULL) {
        // couldn't find constructor
#ifndef PRODUCT
        if (PrintOptimizeStringConcat) {
          tty->print("giving up because couldn't find constructor ");
          alloc->jvms()->dump_spec(tty); tty->cr();
        }
#endif
        break;
      }

      // Walked all the way back and found the constructor call so see
      // if this call converted into a direct string concatenation.
      sc->add_control(call);
      sc->add_control(constructor);
      sc->add_control(alloc);
      sc->set_allocation(alloc);
      sc->add_constructor(constructor);
      if (sc->validate_control_flow() && sc->validate_mem_flow()) {
        return sc;
      } else {
        return NULL;
      }
    } else if (cnode->method() == NULL) {
      break;
    } else if (!cnode->method()->is_static() &&
               cnode->method()->holder() == m->holder() &&
               cnode->method()->name() == ciSymbol::append_name() &&
               (cnode->method()->signature()->as_symbol() == string_sig ||
                cnode->method()->signature()->as_symbol() == char_sig ||
                cnode->method()->signature()->as_symbol() == int_sig)) {
      sc->add_control(cnode);
      Node* arg = cnode->in(TypeFunc::Parms + 1);
      if (cnode->method()->signature()->as_symbol() == int_sig) {
        sc->push_int(arg);
      } else if (cnode->method()->signature()->as_symbol() == char_sig) {
        sc->push_char(arg);
      } else {
        if (arg->is_Proj() && arg->in(0)->is_CallStaticJava()) {
          CallStaticJavaNode* csj = arg->in(0)->as_CallStaticJava();
          if (csj->method() != NULL &&
              csj->method()->intrinsic_id() == vmIntrinsics::_Integer_toString &&
              arg->outcnt() == 1) {
            // _control is the list of StringBuilder calls nodes which
            // will be replaced by new String code after this optimization.
            // Integer::toString() call is not part of StringBuilder calls
            // chain. It could be eliminated only if its result is used
            // only by this SB calls chain.
            // Another limitation: it should be used only once because
            // it is unknown that it is used only by this SB calls chain
            // until all related SB calls nodes are collected.
            assert(arg->unique_out() == cnode, "sanity");
            sc->add_control(csj);
            sc->push_int(csj->in(TypeFunc::Parms));
            continue;
          }
        }
        sc->push_string(arg);
      }
      continue;
    } else {
      // some unhandled signature
#ifndef PRODUCT
      if (PrintOptimizeStringConcat) {
        tty->print("giving up because encountered unexpected signature ");
        cnode->tf()->dump(); tty->cr();
        cnode->in(TypeFunc::Parms + 1)->dump();
      }
#endif
      break;
    }
  }
  return NULL;
}


PhaseStringOpts::PhaseStringOpts(PhaseGVN* gvn, Unique_Node_List*):
  Phase(StringOpts),
  _gvn(gvn),
  _visited(Thread::current()->resource_area()) {

  assert(OptimizeStringConcat, "shouldn't be here");

  size_table_field = C->env()->Integer_klass()->get_field_by_name(ciSymbol::make("sizeTable"),
                                                                  ciSymbol::make("[I"), true);
  if (size_table_field == NULL) {
    // Something wrong so give up.
    assert(false, "why can't we find Integer.sizeTable?");
    return;
  }

  // Collect the types needed to talk about the various slices of memory
  char_adr_idx = C->get_alias_index(TypeAryPtr::CHARS);

  // For each locally allocated StringBuffer see if the usages can be
  // collapsed into a single String construction.

  // Run through the list of allocation looking for SB.toString to see
  // if it's possible to fuse the usage of the SB into a single String
  // construction.
  GrowableArray<StringConcat*> concats;
  Node_List toStrings = collect_toString_calls();
  while (toStrings.size() > 0) {
    StringConcat* sc = build_candidate(toStrings.pop()->as_CallStaticJava());
    if (sc != NULL) {
      concats.push(sc);
    }
  }

  // try to coalesce separate concats
 restart:
  for (int c = 0; c < concats.length(); c++) {
    StringConcat* sc = concats.at(c);
    for (int i = 0; i < sc->num_arguments(); i++) {
      Node* arg = sc->argument_uncast(i);
      if (arg->is_Proj() && StringConcat::is_SB_toString(arg->in(0))) {
        CallStaticJavaNode* csj = arg->in(0)->as_CallStaticJava();
        for (int o = 0; o < concats.length(); o++) {
          if (c == o) continue;
          StringConcat* other = concats.at(o);
          if (other->end() == csj) {
#ifndef PRODUCT
            if (PrintOptimizeStringConcat) {
              tty->print_cr("considering stacked concats");
            }
#endif

            StringConcat* merged = sc->merge(other, arg);
            if (merged->validate_control_flow() && merged->validate_mem_flow()) {
#ifndef PRODUCT
              if (PrintOptimizeStringConcat) {
                tty->print_cr("stacking would succeed");
              }
#endif
              if (c < o) {
                concats.remove_at(o);
                concats.at_put(c, merged);
              } else {
                concats.remove_at(c);
                concats.at_put(o, merged);
              }
              goto restart;
            } else {
#ifndef PRODUCT
              if (PrintOptimizeStringConcat) {
                tty->print_cr("stacking would fail");
              }
#endif
            }
          }
        }
      }
    }
  }


  for (int c = 0; c < concats.length(); c++) {
    StringConcat* sc = concats.at(c);
    replace_string_concat(sc);
  }

  remove_dead_nodes();
}

void PhaseStringOpts::record_dead_node(Node* dead) {
  dead_worklist.push(dead);
}

void PhaseStringOpts::remove_dead_nodes() {
  // Delete any dead nodes to make things clean enough that escape
  // analysis doesn't get unhappy.
  while (dead_worklist.size() > 0) {
    Node* use = dead_worklist.pop();
    int opc = use->Opcode();
    switch (opc) {
      case Op_Region: {
        uint i = 1;
        for (i = 1; i < use->req(); i++) {
          if (use->in(i) != C->top()) {
            break;
          }
        }
        if (i >= use->req()) {
          for (SimpleDUIterator i(use); i.has_next(); i.next()) {
            Node* m = i.get();
            if (m->is_Phi()) {
              dead_worklist.push(m);
            }
          }
          C->gvn_replace_by(use, C->top());
        }
        break;
      }
      case Op_AddP:
      case Op_CreateEx: {
        // Recurisvely clean up references to CreateEx so EA doesn't
        // get unhappy about the partially collapsed graph.
        for (SimpleDUIterator i(use); i.has_next(); i.next()) {
          Node* m = i.get();
          if (m->is_AddP()) {
            dead_worklist.push(m);
          }
        }
        C->gvn_replace_by(use, C->top());
        break;
      }
      case Op_Phi:
        if (use->in(0) == C->top()) {
          C->gvn_replace_by(use, C->top());
        }
        break;
    }
  }
}


bool StringConcat::validate_mem_flow() {
  Compile* C = _stringopts->C;

  for (uint i = 0; i < _control.size(); i++) {
#ifndef PRODUCT
    Node_List path;
#endif
    Node* curr = _control.at(i);
    if (curr->is_Call() && curr != _begin) { // For all calls except the first allocation
      // Now here's the main invariant in our case:
      // For memory between the constructor, and appends, and toString we should only see bottom memory,
      // produced by the previous call we know about.
      if (!_constructors.contains(curr)) {
        NOT_PRODUCT(path.push(curr);)
        Node* mem = curr->in(TypeFunc::Memory);
        assert(mem != NULL, "calls should have memory edge");
        assert(!mem->is_Phi(), "should be handled by control flow validation");
        NOT_PRODUCT(path.push(mem);)
        while (mem->is_MergeMem()) {
          for (uint i = 1; i < mem->req(); i++) {
            if (i != Compile::AliasIdxBot && mem->in(i) != C->top()) {
#ifndef PRODUCT
              if (PrintOptimizeStringConcat) {
                tty->print("fusion has incorrect memory flow (side effects) for ");
                _begin->jvms()->dump_spec(tty); tty->cr();
                path.dump();
              }
#endif
              return false;
            }
          }
          // skip through a potential MergeMem chain, linked through Bot
          mem = mem->in(Compile::AliasIdxBot);
          NOT_PRODUCT(path.push(mem);)
        }
        // now let it fall through, and see if we have a projection
        if (mem->is_Proj()) {
          // Should point to a previous known call
          Node *prev = mem->in(0);
          NOT_PRODUCT(path.push(prev);)
          if (!prev->is_Call() || !_control.contains(prev)) {
#ifndef PRODUCT
            if (PrintOptimizeStringConcat) {
              tty->print("fusion has incorrect memory flow (unknown call) for ");
              _begin->jvms()->dump_spec(tty); tty->cr();
              path.dump();
            }
#endif
            return false;
          }
        } else {
          assert(mem->is_Store() || mem->is_LoadStore(), err_msg_res("unexpected node type: %s", mem->Name()));
#ifndef PRODUCT
          if (PrintOptimizeStringConcat) {
            tty->print("fusion has incorrect memory flow (unexpected source) for ");
            _begin->jvms()->dump_spec(tty); tty->cr();
            path.dump();
          }
#endif
          return false;
        }
      } else {
        // For memory that feeds into constructors it's more complicated.
        // However the advantage is that any side effect that happens between the Allocate/Initialize and
        // the constructor will have to be control-dependent on Initialize.
        // So we actually don't have to do anything, since it's going to be caught by the control flow
        // analysis.
#ifdef ASSERT
        // Do a quick verification of the control pattern between the constructor and the initialize node
        assert(curr->is_Call(), "constructor should be a call");
        // Go up the control starting from the constructor call
        Node* ctrl = curr->in(0);
        IfNode* iff = NULL;
        RegionNode* copy = NULL;

        while (true) {
          // skip known check patterns
          if (ctrl->is_Region()) {
            if (ctrl->as_Region()->is_copy()) {
              copy = ctrl->as_Region();
              ctrl = copy->is_copy();
            } else { // a cast
              assert(ctrl->req() == 3 &&
                     ctrl->in(1) != NULL && ctrl->in(1)->is_Proj() &&
                     ctrl->in(2) != NULL && ctrl->in(2)->is_Proj() &&
                     ctrl->in(1)->in(0) == ctrl->in(2)->in(0) &&
                     ctrl->in(1)->in(0) != NULL && ctrl->in(1)->in(0)->is_If(),
                     "must be a simple diamond");
              Node* true_proj = ctrl->in(1)->is_IfTrue() ? ctrl->in(1) : ctrl->in(2);
              for (SimpleDUIterator i(true_proj); i.has_next(); i.next()) {
                Node* use = i.get();
                assert(use == ctrl || use->is_ConstraintCast(),
                       err_msg_res("unexpected user: %s", use->Name()));
              }

              iff = ctrl->in(1)->in(0)->as_If();
              ctrl = iff->in(0);
            }
          } else if (ctrl->is_IfTrue()) { // null checks, class checks
            iff = ctrl->in(0)->as_If();
            assert(iff->is_If(), "must be if");
            // Verify that the other arm is an uncommon trap
            Node* otherproj = iff->proj_out(1 - ctrl->as_Proj()->_con);
            CallStaticJavaNode* call = otherproj->unique_out()->isa_CallStaticJava();
            assert(strcmp(call->_name, "uncommon_trap") == 0, "must be uncommond trap");
            ctrl = iff->in(0);
          } else {
            break;
          }
        }

        assert(ctrl->is_Proj(), "must be a projection");
        assert(ctrl->in(0)->is_Initialize(), "should be initialize");
        for (SimpleDUIterator i(ctrl); i.has_next(); i.next()) {
          Node* use = i.get();
          assert(use == copy || use == iff || use == curr || use->is_CheckCastPP() || use->is_Load(),
                 err_msg_res("unexpected user: %s", use->Name()));
        }
#endif // ASSERT
      }
    }
  }

#ifndef PRODUCT
  if (PrintOptimizeStringConcat) {
    tty->print("fusion has correct memory flow for ");
    _begin->jvms()->dump_spec(tty); tty->cr();
    tty->cr();
  }
#endif
  return true;
}

bool StringConcat::validate_control_flow() {
  // We found all the calls and arguments now lets see if it's
  // safe to transform the graph as we would expect.

  // Check to see if this resulted in too many uncommon traps previously
  if (Compile::current()->too_many_traps(_begin->jvms()->method(), _begin->jvms()->bci(),
                        Deoptimization::Reason_intrinsic)) {
    return false;
  }

  // Walk backwards over the control flow from toString to the
  // allocation and make sure all the control flow is ok.  This
  // means it's either going to be eliminated once the calls are
  // removed or it can safely be transformed into an uncommon
  // trap.

  int null_check_count = 0;
  Unique_Node_List ctrl_path;

  assert(_control.contains(_begin), "missing");
  assert(_control.contains(_end), "missing");

  // Collect the nodes that we know about and will eliminate into ctrl_path
  for (uint i = 0; i < _control.size(); i++) {
    // Push the call and it's control projection
    Node* n = _control.at(i);
    if (n->is_Allocate()) {
      AllocateNode* an = n->as_Allocate();
      InitializeNode* init = an->initialization();
      ctrl_path.push(init);
      ctrl_path.push(init->as_Multi()->proj_out(0));
    }
    if (n->is_Call()) {
      CallNode* cn = n->as_Call();
      ctrl_path.push(cn);
      ctrl_path.push(cn->proj_out(0));
      ctrl_path.push(cn->proj_out(0)->unique_out());
      if (cn->proj_out(0)->unique_out()->as_Catch()->proj_out(0) != NULL) {
        ctrl_path.push(cn->proj_out(0)->unique_out()->as_Catch()->proj_out(0));
      }
    } else {
      ShouldNotReachHere();
    }
  }

  // Skip backwards through the control checking for unexpected control flow
  Node* ptr = _end;
  bool fail = false;
  while (ptr != _begin) {
    if (ptr->is_Call() && ctrl_path.member(ptr)) {
      ptr = ptr->in(0);
    } else if (ptr->is_CatchProj() && ctrl_path.member(ptr)) {
      ptr = ptr->in(0)->in(0)->in(0);
      assert(ctrl_path.member(ptr), "should be a known piece of control");
    } else if (ptr->is_IfTrue()) {
      IfNode* iff = ptr->in(0)->as_If();
      BoolNode* b = iff->in(1)->isa_Bool();

      if (b == NULL) {
        fail = true;
        break;
      }

      Node* cmp = b->in(1);
      Node* v1 = cmp->in(1);
      Node* v2 = cmp->in(2);
      Node* otherproj = iff->proj_out(1 - ptr->as_Proj()->_con);

      // Null check of the return of append which can simply be eliminated
      if (b->_test._test == BoolTest::ne &&
          v2->bottom_type() == TypePtr::NULL_PTR &&
          v1->is_Proj() && ctrl_path.member(v1->in(0))) {
        // NULL check of the return value of the append
        null_check_count++;
        if (otherproj->outcnt() == 1) {
          CallStaticJavaNode* call = otherproj->unique_out()->isa_CallStaticJava();
          if (call != NULL && call->_name != NULL && strcmp(call->_name, "uncommon_trap") == 0) {
            ctrl_path.push(call);
          }
        }
        _control.push(ptr);
        ptr = ptr->in(0)->in(0);
        continue;
      }

      // A test which leads to an uncommon trap which should be safe.
      // Later this trap will be converted into a trap that restarts
      // at the beginning.
      if (otherproj->outcnt() == 1) {
        CallStaticJavaNode* call = otherproj->unique_out()->isa_CallStaticJava();
        if (call != NULL && call->_name != NULL && strcmp(call->_name, "uncommon_trap") == 0) {
          // control flow leads to uct so should be ok
          _uncommon_traps.push(call);
          ctrl_path.push(call);
          ptr = ptr->in(0)->in(0);
          continue;
        }
      }

#ifndef PRODUCT
      // Some unexpected control flow we don't know how to handle.
      if (PrintOptimizeStringConcat) {
        tty->print_cr("failing with unknown test");
        b->dump();
        cmp->dump();
        v1->dump();
        v2->dump();
        tty->cr();
      }
#endif
      fail = true;
      break;
    } else if (ptr->is_Proj() && ptr->in(0)->is_Initialize()) {
      ptr = ptr->in(0)->in(0);
    } else if (ptr->is_Region()) {
      Node* copy = ptr->as_Region()->is_copy();
      if (copy != NULL) {
        ptr = copy;
        continue;
      }
      if (ptr->req() == 3 &&
          ptr->in(1) != NULL && ptr->in(1)->is_Proj() &&
          ptr->in(2) != NULL && ptr->in(2)->is_Proj() &&
          ptr->in(1)->in(0) == ptr->in(2)->in(0) &&
          ptr->in(1)->in(0) != NULL && ptr->in(1)->in(0)->is_If()) {
        // Simple diamond.
        // XXX should check for possibly merging stores.  simple data merges are ok.
        // The IGVN will make this simple diamond go away when it
        // transforms the Region. Make sure it sees it.
        Compile::current()->record_for_igvn(ptr);
        ptr = ptr->in(1)->in(0)->in(0);
        continue;
      }
#ifndef PRODUCT
      if (PrintOptimizeStringConcat) {
        tty->print_cr("fusion would fail for region");
        _begin->dump();
        ptr->dump(2);
      }
#endif
      fail = true;
      break;
    } else {
      // other unknown control
      if (!fail) {
#ifndef PRODUCT
        if (PrintOptimizeStringConcat) {
          tty->print_cr("fusion would fail for");
          _begin->dump();
        }
#endif
        fail = true;
      }
#ifndef PRODUCT
      if (PrintOptimizeStringConcat) {
        ptr->dump();
      }
#endif
      ptr = ptr->in(0);
    }
  }
#ifndef PRODUCT
  if (PrintOptimizeStringConcat && fail) {
    tty->cr();
  }
#endif
  if (fail) return !fail;

  // Validate that all these results produced are contained within
  // this cluster of objects.  First collect all the results produced
  // by calls in the region.
  _stringopts->_visited.Clear();
  Node_List worklist;
  Node* final_result = _end->proj_out(TypeFunc::Parms);
  for (uint i = 0; i < _control.size(); i++) {
    CallNode* cnode = _control.at(i)->isa_Call();
    if (cnode != NULL) {
      _stringopts->_visited.test_set(cnode->_idx);
    }
    Node* result = cnode != NULL ? cnode->proj_out(TypeFunc::Parms) : NULL;
    if (result != NULL && result != final_result) {
      worklist.push(result);
    }
  }

  Node* last_result = NULL;
  while (worklist.size() > 0) {
    Node* result = worklist.pop();
    if (_stringopts->_visited.test_set(result->_idx))
      continue;
    for (SimpleDUIterator i(result); i.has_next(); i.next()) {
      Node *use = i.get();
      if (ctrl_path.member(use)) {
        // already checked this
        continue;
      }
      int opc = use->Opcode();
      if (opc == Op_CmpP || opc == Op_Node) {
        ctrl_path.push(use);
        continue;
      }
      if (opc == Op_CastPP || opc == Op_CheckCastPP) {
        for (SimpleDUIterator j(use); j.has_next(); j.next()) {
          worklist.push(j.get());
        }
        worklist.push(use->in(1));
        ctrl_path.push(use);
        continue;
      }
#ifndef PRODUCT
      if (PrintOptimizeStringConcat) {
        if (result != last_result) {
          last_result = result;
          tty->print_cr("extra uses for result:");
          last_result->dump();
        }
        use->dump();
      }
#endif
      fail = true;
      break;
    }
  }

#ifndef PRODUCT
  if (PrintOptimizeStringConcat && !fail) {
    ttyLocker ttyl;
    tty->cr();
    tty->print("fusion has correct control flow (%d %d) for ", null_check_count, _uncommon_traps.size());
    _begin->jvms()->dump_spec(tty); tty->cr();
    for (int i = 0; i < num_arguments(); i++) {
      argument(i)->dump();
    }
    _control.dump();
    tty->cr();
  }
#endif

  return !fail;
}

Node* PhaseStringOpts::fetch_static_field(GraphKit& kit, ciField* field) {
  const TypeInstPtr* mirror_type = TypeInstPtr::make(field->holder()->java_mirror());
  Node* klass_node = __ makecon(mirror_type);
  BasicType bt = field->layout_type();
  ciType* field_klass = field->type();

  const Type *type;
  if( bt == T_OBJECT ) {
    if (!field->type()->is_loaded()) {
      type = TypeInstPtr::BOTTOM;
    } else if (field->is_constant()) {
      // This can happen if the constant oop is non-perm.
      ciObject* con = field->constant_value().as_object();
      // Do not "join" in the previous type; it doesn't add value,
      // and may yield a vacuous result if the field is of interface type.
      type = TypeOopPtr::make_from_constant(con, true)->isa_oopptr();
      assert(type != NULL, "field singleton type must be consistent");
      return __ makecon(type);
    } else {
      type = TypeOopPtr::make_from_klass(field_klass->as_klass());
    }
  } else {
    type = Type::get_const_basic_type(bt);
  }

  return kit.make_load(NULL, kit.basic_plus_adr(klass_node, field->offset_in_bytes()),
                       type, T_OBJECT,
                       C->get_alias_index(mirror_type->add_offset(field->offset_in_bytes())));
}

Node* PhaseStringOpts::int_stringSize(GraphKit& kit, Node* arg) {
  RegionNode *final_merge = new (C) RegionNode(3);
  kit.gvn().set_type(final_merge, Type::CONTROL);
  Node* final_size = new (C) PhiNode(final_merge, TypeInt::INT);
  kit.gvn().set_type(final_size, TypeInt::INT);

  IfNode* iff = kit.create_and_map_if(kit.control(),
                                      __ Bool(__ CmpI(arg, __ intcon(0x80000000)), BoolTest::ne),
                                      PROB_FAIR, COUNT_UNKNOWN);
  Node* is_min = __ IfFalse(iff);
  final_merge->init_req(1, is_min);
  final_size->init_req(1, __ intcon(11));

  kit.set_control(__ IfTrue(iff));
  if (kit.stopped()) {
    final_merge->init_req(2, C->top());
    final_size->init_req(2, C->top());
  } else {

    // int size = (i < 0) ? stringSize(-i) + 1 : stringSize(i);
    RegionNode *r = new (C) RegionNode(3);
    kit.gvn().set_type(r, Type::CONTROL);
    Node *phi = new (C) PhiNode(r, TypeInt::INT);
    kit.gvn().set_type(phi, TypeInt::INT);
    Node *size = new (C) PhiNode(r, TypeInt::INT);
    kit.gvn().set_type(size, TypeInt::INT);
    Node* chk = __ CmpI(arg, __ intcon(0));
    Node* p = __ Bool(chk, BoolTest::lt);
    IfNode* iff = kit.create_and_map_if(kit.control(), p, PROB_FAIR, COUNT_UNKNOWN);
    Node* lessthan = __ IfTrue(iff);
    Node* greaterequal = __ IfFalse(iff);
    r->init_req(1, lessthan);
    phi->init_req(1, __ SubI(__ intcon(0), arg));
    size->init_req(1, __ intcon(1));
    r->init_req(2, greaterequal);
    phi->init_req(2, arg);
    size->init_req(2, __ intcon(0));
    kit.set_control(r);
    C->record_for_igvn(r);
    C->record_for_igvn(phi);
    C->record_for_igvn(size);

    // for (int i=0; ; i++)
    //   if (x <= sizeTable[i])
    //     return i+1;

    // Add loop predicate first.
    kit.add_predicate();

    RegionNode *loop = new (C) RegionNode(3);
    loop->init_req(1, kit.control());
    kit.gvn().set_type(loop, Type::CONTROL);

    Node *index = new (C) PhiNode(loop, TypeInt::INT);
    index->init_req(1, __ intcon(0));
    kit.gvn().set_type(index, TypeInt::INT);
    kit.set_control(loop);
    Node* sizeTable = fetch_static_field(kit, size_table_field);

    Node* value = kit.load_array_element(NULL, sizeTable, index, TypeAryPtr::INTS);
    C->record_for_igvn(value);
    Node* limit = __ CmpI(phi, value);
    Node* limitb = __ Bool(limit, BoolTest::le);
    IfNode* iff2 = kit.create_and_map_if(kit.control(), limitb, PROB_MIN, COUNT_UNKNOWN);
    Node* lessEqual = __ IfTrue(iff2);
    Node* greater = __ IfFalse(iff2);

    loop->init_req(2, greater);
    index->init_req(2, __ AddI(index, __ intcon(1)));

    kit.set_control(lessEqual);
    C->record_for_igvn(loop);
    C->record_for_igvn(index);

    final_merge->init_req(2, kit.control());
    final_size->init_req(2, __ AddI(__ AddI(index, size), __ intcon(1)));
  }

  kit.set_control(final_merge);
  C->record_for_igvn(final_merge);
  C->record_for_igvn(final_size);

  return final_size;
}

void PhaseStringOpts::int_getChars(GraphKit& kit, Node* arg, Node* char_array, Node* start, Node* end) {
  RegionNode *final_merge = new (C) RegionNode(4);
  kit.gvn().set_type(final_merge, Type::CONTROL);
  Node *final_mem = PhiNode::make(final_merge, kit.memory(char_adr_idx), Type::MEMORY, TypeAryPtr::CHARS);
  kit.gvn().set_type(final_mem, Type::MEMORY);

  // need to handle Integer.MIN_VALUE specially because negating doesn't make it positive
  {
    // i == MIN_VALUE
    IfNode* iff = kit.create_and_map_if(kit.control(),
                                        __ Bool(__ CmpI(arg, __ intcon(0x80000000)), BoolTest::ne),
                                        PROB_FAIR, COUNT_UNKNOWN);

    Node* old_mem = kit.memory(char_adr_idx);

    kit.set_control(__ IfFalse(iff));
    if (kit.stopped()) {
      // Statically not equal to MIN_VALUE so this path is dead
      final_merge->init_req(3, kit.control());
    } else {
      copy_string(kit, __ makecon(TypeInstPtr::make(C->env()->the_min_jint_string())),
                  char_array, start);
      final_merge->init_req(3, kit.control());
      final_mem->init_req(3, kit.memory(char_adr_idx));
    }

    kit.set_control(__ IfTrue(iff));
    kit.set_memory(old_mem, char_adr_idx);
  }


  // Simplified version of Integer.getChars

  // int q, r;
  // int charPos = index;
  Node* charPos = end;

  // char sign = 0;

  Node* i = arg;
  Node* sign = __ intcon(0);

  // if (i < 0) {
  //     sign = '-';
  //     i = -i;
  // }
  {
    IfNode* iff = kit.create_and_map_if(kit.control(),
                                        __ Bool(__ CmpI(arg, __ intcon(0)), BoolTest::lt),
                                        PROB_FAIR, COUNT_UNKNOWN);

    RegionNode *merge = new (C) RegionNode(3);
    kit.gvn().set_type(merge, Type::CONTROL);
    i = new (C) PhiNode(merge, TypeInt::INT);
    kit.gvn().set_type(i, TypeInt::INT);
    sign = new (C) PhiNode(merge, TypeInt::INT);
    kit.gvn().set_type(sign, TypeInt::INT);

    merge->init_req(1, __ IfTrue(iff));
    i->init_req(1, __ SubI(__ intcon(0), arg));
    sign->init_req(1, __ intcon('-'));
    merge->init_req(2, __ IfFalse(iff));
    i->init_req(2, arg);
    sign->init_req(2, __ intcon(0));

    kit.set_control(merge);

    C->record_for_igvn(merge);
    C->record_for_igvn(i);
    C->record_for_igvn(sign);
  }

  // for (;;) {
  //     q = i / 10;
  //     r = i - ((q << 3) + (q << 1));  // r = i-(q*10) ...
  //     buf [--charPos] = digits [r];
  //     i = q;
  //     if (i == 0) break;
  // }

  {
    // Add loop predicate first.
    kit.add_predicate();

    RegionNode *head = new (C) RegionNode(3);
    head->init_req(1, kit.control());
    kit.gvn().set_type(head, Type::CONTROL);
    Node *i_phi = new (C) PhiNode(head, TypeInt::INT);
    i_phi->init_req(1, i);
    kit.gvn().set_type(i_phi, TypeInt::INT);
    charPos = PhiNode::make(head, charPos);
    kit.gvn().set_type(charPos, TypeInt::INT);
    Node *mem = PhiNode::make(head, kit.memory(char_adr_idx), Type::MEMORY, TypeAryPtr::CHARS);
    kit.gvn().set_type(mem, Type::MEMORY);
    kit.set_control(head);
    kit.set_memory(mem, char_adr_idx);

    Node* q = __ DivI(NULL, i_phi, __ intcon(10));
    Node* r = __ SubI(i_phi, __ AddI(__ LShiftI(q, __ intcon(3)),
                                     __ LShiftI(q, __ intcon(1))));
    Node* m1 = __ SubI(charPos, __ intcon(1));
    Node* ch = __ AddI(r, __ intcon('0'));

    Node* st = __ store_to_memory(kit.control(), kit.array_element_address(char_array, m1, T_CHAR),
                                  ch, T_CHAR, char_adr_idx);


    IfNode* iff = kit.create_and_map_if(head, __ Bool(__ CmpI(q, __ intcon(0)), BoolTest::ne),
                                        PROB_FAIR, COUNT_UNKNOWN);
    Node* ne = __ IfTrue(iff);
    Node* eq = __ IfFalse(iff);

    head->init_req(2, ne);
    mem->init_req(2, st);
    i_phi->init_req(2, q);
    charPos->init_req(2, m1);

    charPos = m1;

    kit.set_control(eq);
    kit.set_memory(st, char_adr_idx);

    C->record_for_igvn(head);
    C->record_for_igvn(mem);
    C->record_for_igvn(i_phi);
    C->record_for_igvn(charPos);
  }

  {
    // if (sign != 0) {
    //     buf [--charPos] = sign;
    // }
    IfNode* iff = kit.create_and_map_if(kit.control(),
                                        __ Bool(__ CmpI(sign, __ intcon(0)), BoolTest::ne),
                                        PROB_FAIR, COUNT_UNKNOWN);

    final_merge->init_req(2, __ IfFalse(iff));
    final_mem->init_req(2, kit.memory(char_adr_idx));

    kit.set_control(__ IfTrue(iff));
    if (kit.stopped()) {
      final_merge->init_req(1, C->top());
      final_mem->init_req(1, C->top());
    } else {
      Node* m1 = __ SubI(charPos, __ intcon(1));
      Node* st = __ store_to_memory(kit.control(), kit.array_element_address(char_array, m1, T_CHAR),
                                    sign, T_CHAR, char_adr_idx);

      final_merge->init_req(1, kit.control());
      final_mem->init_req(1, st);
    }

    kit.set_control(final_merge);
    kit.set_memory(final_mem, char_adr_idx);

    C->record_for_igvn(final_merge);
    C->record_for_igvn(final_mem);
  }
}


Node* PhaseStringOpts::copy_string(GraphKit& kit, Node* str, Node* char_array, Node* start) {
  Node* string = str;
  Node* offset = kit.load_String_offset(kit.control(), string);
  Node* count  = kit.load_String_length(kit.control(), string);
  Node* value  = kit.load_String_value (kit.control(), string);

  // copy the contents
  if (offset->is_Con() && count->is_Con() && value->is_Con() && count->get_int() < unroll_string_copy_length) {
    // For small constant strings just emit individual stores.
    // A length of 6 seems like a good space/speed tradeof.
    int c = count->get_int();
    int o = offset->get_int();
    const TypeOopPtr* t = kit.gvn().type(value)->isa_oopptr();
    ciTypeArray* value_array = t->const_oop()->as_type_array();
    for (int e = 0; e < c; e++) {
      __ store_to_memory(kit.control(), kit.array_element_address(char_array, start, T_CHAR),
                         __ intcon(value_array->char_at(o + e)), T_CHAR, char_adr_idx);
      start = __ AddI(start, __ intcon(1));
    }
  } else {
    Node* src_ptr = kit.array_element_address(value, offset, T_CHAR);
    Node* dst_ptr = kit.array_element_address(char_array, start, T_CHAR);
    Node* c = count;
    Node* extra = NULL;
#ifdef _LP64
    c = __ ConvI2L(c);
    extra = C->top();
#endif
    Node* call = kit.make_runtime_call(GraphKit::RC_LEAF|GraphKit::RC_NO_FP,
                                       OptoRuntime::fast_arraycopy_Type(),
                                       CAST_FROM_FN_PTR(address, StubRoutines::jshort_disjoint_arraycopy()),
                                       "jshort_disjoint_arraycopy", TypeAryPtr::CHARS,
                                       src_ptr, dst_ptr, c, extra);
    start = __ AddI(start, count);
  }
  return start;
}


void PhaseStringOpts::replace_string_concat(StringConcat* sc) {
  // Log a little info about the transformation
  sc->maybe_log_transform();

  // pull the JVMState of the allocation into a SafePointNode to serve as
  // as a shim for the insertion of the new code.
  JVMState* jvms     = sc->begin()->jvms()->clone_shallow(C);
  uint size = sc->begin()->req();
  SafePointNode* map = new (C) SafePointNode(size, jvms);

  // copy the control and memory state from the final call into our
  // new starting state.  This allows any preceeding tests to feed
  // into the new section of code.
  for (uint i1 = 0; i1 < TypeFunc::Parms; i1++) {
    map->init_req(i1, sc->end()->in(i1));
  }
  // blow away old allocation arguments
  for (uint i1 = TypeFunc::Parms; i1 < jvms->debug_start(); i1++) {
    map->init_req(i1, C->top());
  }
  // Copy the rest of the inputs for the JVMState
  for (uint i1 = jvms->debug_start(); i1 < sc->begin()->req(); i1++) {
    map->init_req(i1, sc->begin()->in(i1));
  }
  // Make sure the memory state is a MergeMem for parsing.
  if (!map->in(TypeFunc::Memory)->is_MergeMem()) {
    map->set_req(TypeFunc::Memory, MergeMemNode::make(C, map->in(TypeFunc::Memory)));
  }

  jvms->set_map(map);
  map->ensure_stack(jvms, jvms->method()->max_stack());


  // disconnect all the old StringBuilder calls from the graph
  sc->eliminate_unneeded_control();

  // At this point all the old work has been completely removed from
  // the graph and the saved JVMState exists at the point where the
  // final toString call used to be.
  GraphKit kit(jvms);

  // There may be uncommon traps which are still using the
  // intermediate states and these need to be rewritten to point at
  // the JVMState at the beginning of the transformation.
  sc->convert_uncommon_traps(kit, jvms);

  // Now insert the logic to compute the size of the string followed
  // by all the logic to construct array and resulting string.

  Node* null_string = __ makecon(TypeInstPtr::make(C->env()->the_null_string()));

  // Create a region for the overflow checks to merge into.
  int args = MAX2(sc->num_arguments(), 1);
  RegionNode* overflow = new (C) RegionNode(args);
  kit.gvn().set_type(overflow, Type::CONTROL);

  // Create a hook node to hold onto the individual sizes since they
  // are need for the copying phase.
  Node* string_sizes = new (C) Node(args);

  Node* length = __ intcon(0);
  for (int argi = 0; argi < sc->num_arguments(); argi++) {
    Node* arg = sc->argument(argi);
    switch (sc->mode(argi)) {
      case StringConcat::IntMode: {
        Node* string_size = int_stringSize(kit, arg);

        // accumulate total
        length = __ AddI(length, string_size);

        // Cache this value for the use by int_toString
        string_sizes->init_req(argi, string_size);
        break;
      }
      case StringConcat::StringNullCheckMode: {
        const Type* type = kit.gvn().type(arg);
        assert(type != TypePtr::NULL_PTR, "missing check");
        if (!type->higher_equal(TypeInstPtr::NOTNULL)) {
          // Null check with uncommont trap since
          // StringBuilder(null) throws exception.
          // Use special uncommon trap instead of
          // calling normal do_null_check().
          Node* p = __ Bool(__ CmpP(arg, kit.null()), BoolTest::ne);
          IfNode* iff = kit.create_and_map_if(kit.control(), p, PROB_MIN, COUNT_UNKNOWN);
          overflow->add_req(__ IfFalse(iff));
          Node* notnull = __ IfTrue(iff);
          kit.set_control(notnull); // set control for the cast_not_null
          arg = kit.cast_not_null(arg, false);
          sc->set_argument(argi, arg);
        }
        assert(kit.gvn().type(arg)->higher_equal(TypeInstPtr::NOTNULL), "sanity");
        // Fallthrough to add string length.
      }
      case StringConcat::StringMode: {
        const Type* type = kit.gvn().type(arg);
        if (type == TypePtr::NULL_PTR) {
          // replace the argument with the null checked version
          arg = null_string;
          sc->set_argument(argi, arg);
        } else if (!type->higher_equal(TypeInstPtr::NOTNULL)) {
          // s = s != null ? s : "null";
          // length = length + (s.count - s.offset);
          RegionNode *r = new (C) RegionNode(3);
          kit.gvn().set_type(r, Type::CONTROL);
          Node *phi = new (C) PhiNode(r, type);
          kit.gvn().set_type(phi, phi->bottom_type());
          Node* p = __ Bool(__ CmpP(arg, kit.null()), BoolTest::ne);
          IfNode* iff = kit.create_and_map_if(kit.control(), p, PROB_MIN, COUNT_UNKNOWN);
          Node* notnull = __ IfTrue(iff);
          Node* isnull =  __ IfFalse(iff);
          kit.set_control(notnull); // set control for the cast_not_null
          r->init_req(1, notnull);
          phi->init_req(1, kit.cast_not_null(arg, false));
          r->init_req(2, isnull);
          phi->init_req(2, null_string);
          kit.set_control(r);
          C->record_for_igvn(r);
          C->record_for_igvn(phi);
          // replace the argument with the null checked version
          arg = phi;
          sc->set_argument(argi, arg);
        }

        Node* count = kit.load_String_length(kit.control(), arg);

        length = __ AddI(length, count);
        string_sizes->init_req(argi, NULL);
        break;
      }
      case StringConcat::CharMode: {
        // one character only
        length = __ AddI(length, __ intcon(1));
        break;
      }
      default:
        ShouldNotReachHere();
    }
    if (argi > 0) {
      // Check that the sum hasn't overflowed
      IfNode* iff = kit.create_and_map_if(kit.control(),
                                          __ Bool(__ CmpI(length, __ intcon(0)), BoolTest::lt),
                                          PROB_MIN, COUNT_UNKNOWN);
      kit.set_control(__ IfFalse(iff));
      overflow->set_req(argi, __ IfTrue(iff));
    }
  }

  {
    // Hook
    PreserveJVMState pjvms(&kit);
    kit.set_control(overflow);
    C->record_for_igvn(overflow);
    kit.uncommon_trap(Deoptimization::Reason_intrinsic,
                      Deoptimization::Action_make_not_entrant);
  }

  Node* result;
  if (!kit.stopped()) {

    // length now contains the number of characters needed for the
    // char[] so create a new AllocateArray for the char[]
    Node* char_array = NULL;
    {
      PreserveReexecuteState preexecs(&kit);
      // The original jvms is for an allocation of either a String or
      // StringBuffer so no stack adjustment is necessary for proper
      // reexecution.  If we deoptimize in the slow path the bytecode
      // will be reexecuted and the char[] allocation will be thrown away.
      kit.jvms()->set_should_reexecute(true);
      char_array = kit.new_array(__ makecon(TypeKlassPtr::make(ciTypeArrayKlass::make(T_CHAR))),
                                 length, 1);
    }

    // Mark the allocation so that zeroing is skipped since the code
    // below will overwrite the entire array
    AllocateArrayNode* char_alloc = AllocateArrayNode::Ideal_array_allocation(char_array, _gvn);
    char_alloc->maybe_set_complete(_gvn);

    // Now copy the string representations into the final char[]
    Node* start = __ intcon(0);
    for (int argi = 0; argi < sc->num_arguments(); argi++) {
      Node* arg = sc->argument(argi);
      switch (sc->mode(argi)) {
        case StringConcat::IntMode: {
          Node* end = __ AddI(start, string_sizes->in(argi));
          // getChars words backwards so pass the ending point as well as the start
          int_getChars(kit, arg, char_array, start, end);
          start = end;
          break;
        }
        case StringConcat::StringNullCheckMode:
        case StringConcat::StringMode: {
          start = copy_string(kit, arg, char_array, start);
          break;
        }
        case StringConcat::CharMode: {
          __ store_to_memory(kit.control(), kit.array_element_address(char_array, start, T_CHAR),
                             arg, T_CHAR, char_adr_idx);
          start = __ AddI(start, __ intcon(1));
          break;
        }
        default:
          ShouldNotReachHere();
      }
    }

    // If we're not reusing an existing String allocation then allocate one here.
    result = sc->string_alloc();
    if (result == NULL) {
      PreserveReexecuteState preexecs(&kit);
      // The original jvms is for an allocation of either a String or
      // StringBuffer so no stack adjustment is necessary for proper
      // reexecution.
      kit.jvms()->set_should_reexecute(true);
      result = kit.new_instance(__ makecon(TypeKlassPtr::make(C->env()->String_klass())));
    }

    // Intialize the string
    if (java_lang_String::has_offset_field()) {
      kit.store_String_offset(kit.control(), result, __ intcon(0));
      kit.store_String_length(kit.control(), result, length);
    }
    kit.store_String_value(kit.control(), result, char_array);
  } else {
    result = C->top();
  }
  // hook up the outgoing control and result
  kit.replace_call(sc->end(), result);

  // Unhook any hook nodes
  string_sizes->disconnect_inputs(NULL, C);
  sc->cleanup();
}

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