Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * 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())),

                        MemNode::unordered);

 }

 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, MemNode::unordered);

     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, MemNode::unordered);

       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,

                          MemNode::unordered);

       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, MemNode::unordered);

           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();

 }