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

 /*

  * Copyright (c) 1999, 2011, Oracle and/or its affiliates. All rights reserved.

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

  *

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

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

  * published by the Free Software Foundation.

  *

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

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

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

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

  * accompanied this code).

  *

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

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

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

  *

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

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

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  */

 #include "precompiled.hpp"

 #include "c1/c1_Canonicalizer.hpp"

 #include "c1/c1_Optimizer.hpp"

 #include "c1/c1_ValueMap.hpp"

 #include "c1/c1_ValueSet.hpp"

 #include "c1/c1_ValueStack.hpp"

 #include "utilities/bitMap.inline.hpp"

 #include "compiler/compileLog.hpp"

 define_array(ValueSetArray, ValueSet*);

 define_stack(ValueSetList, ValueSetArray);

 Optimizer::Optimizer(IR* ir) {

   assert(ir->is_valid(), "IR must be valid");

   _ir = ir;

 }

 class CE_Eliminator: public BlockClosure {

  private:

   IR* _hir;

   int _cee_count;                                // the number of CEs successfully eliminated

   int _ifop_count;                               // the number of IfOps successfully simplified

   int _has_substitution;

  public:

   CE_Eliminator(IR* hir) : _cee_count(0), _ifop_count(0), _hir(hir) {

     _has_substitution = false;

     _hir->iterate_preorder(this);

     if (_has_substitution) {

       // substituted some ifops/phis, so resolve the substitution

       SubstitutionResolver sr(_hir);

     }

     CompileLog* log = _hir->compilation()->log();

     if (log != NULL)

       log->set_context("optimize name='cee'");

   }

   ~CE_Eliminator() {

     CompileLog* log = _hir->compilation()->log();

     if (log != NULL)

       log->clear_context(); // skip marker if nothing was printed

   }

   int cee_count() const                          { return _cee_count; }

   int ifop_count() const                         { return _ifop_count; }

   void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {

     int e = sux->number_of_exception_handlers();

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

       BlockBegin* xhandler = sux->exception_handler_at(i);

       block->add_exception_handler(xhandler);

       assert(xhandler->is_predecessor(sux), "missing predecessor");

       if (sux->number_of_preds() == 0) {

         // sux is disconnected from graph so disconnect from exception handlers

         xhandler->remove_predecessor(sux);

       }

       if (!xhandler->is_predecessor(block)) {

         xhandler->add_predecessor(block);

       }

     }

   }

   virtual void block_do(BlockBegin* block);

  private:

   Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval);

 };

 void CE_Eliminator::block_do(BlockBegin* block) {

   // 1) find conditional expression

   // check if block ends with an If

   If* if_ = block->end()->as_If();

   if (if_ == NULL) return;

   // check if If works on int or object types

   // (we cannot handle If's working on long, float or doubles yet,

   // since IfOp doesn't support them - these If's show up if cmp

   // operations followed by If's are eliminated)

   ValueType* if_type = if_->x()->type();

   if (!if_type->is_int() && !if_type->is_object()) return;

   BlockBegin* t_block = if_->tsux();

   BlockBegin* f_block = if_->fsux();

   Instruction* t_cur = t_block->next();

   Instruction* f_cur = f_block->next();

   // one Constant may be present between BlockBegin and BlockEnd

   Value t_const = NULL;

   Value f_const = NULL;

   if (t_cur->as_Constant() != NULL && !t_cur->can_trap()) {

     t_const = t_cur;

     t_cur = t_cur->next();

   }

   if (f_cur->as_Constant() != NULL && !f_cur->can_trap()) {

     f_const = f_cur;

     f_cur = f_cur->next();

   }

   // check if both branches end with a goto

   Goto* t_goto = t_cur->as_Goto();

   if (t_goto == NULL) return;

   Goto* f_goto = f_cur->as_Goto();

   if (f_goto == NULL) return;

   // check if both gotos merge into the same block

   BlockBegin* sux = t_goto->default_sux();

   if (sux != f_goto->default_sux()) return;

   // check if at least one word was pushed on sux_state

   // inlining depths must match

   ValueStack* if_state = if_->state();

   ValueStack* sux_state = sux->state();

   if (if_state->scope()->level() > sux_state->scope()->level()) {

     while (sux_state->scope() != if_state->scope()) {

       if_state = if_state->caller_state();

       assert(if_state != NULL, "states do not match up");

     }

   } else if (if_state->scope()->level() < sux_state->scope()->level()) {

     while (sux_state->scope() != if_state->scope()) {

       sux_state = sux_state->caller_state();

       assert(sux_state != NULL, "states do not match up");

     }

   }

   if (sux_state->stack_size() <= if_state->stack_size()) return;

   // check if phi function is present at end of successor stack and that

   // only this phi was pushed on the stack

   Value sux_phi = sux_state->stack_at(if_state->stack_size());

   if (sux_phi == NULL || sux_phi->as_Phi() == NULL || sux_phi->as_Phi()->block() != sux) return;

   if (sux_phi->type()->size() != sux_state->stack_size() - if_state->stack_size()) return;

   // get the values that were pushed in the true- and false-branch

   Value t_value = t_goto->state()->stack_at(if_state->stack_size());

   Value f_value = f_goto->state()->stack_at(if_state->stack_size());

   // backend does not support floats

   assert(t_value->type()->base() == f_value->type()->base(), "incompatible types");

   if (t_value->type()->is_float_kind()) return;

   // check that successor has no other phi functions but sux_phi

   // this can happen when t_block or f_block contained additonal stores to local variables

   // that are no longer represented by explicit instructions

   for_each_phi_fun(sux, phi,

                    if (phi != sux_phi) return;

                    );

   // true and false blocks can't have phis

   for_each_phi_fun(t_block, phi, return; );

   for_each_phi_fun(f_block, phi, return; );

   // 2) substitute conditional expression

   //    with an IfOp followed by a Goto

   // cut if_ away and get node before

   Instruction* cur_end = if_->prev(block);

   // append constants of true- and false-block if necessary

   // clone constants because original block must not be destroyed

   assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");

   if (t_value == t_const) {

     t_value = new Constant(t_const->type());

     NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));

     cur_end = cur_end->set_next(t_value);

   }

   if (f_value == f_const) {

     f_value = new Constant(f_const->type());

     NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));

     cur_end = cur_end->set_next(f_value);

   }

   Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value);

   assert(result != NULL, "make_ifop must return a non-null instruction");

   if (!result->is_linked() && result->can_be_linked()) {

     NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));

     cur_end = cur_end->set_next(result);

   }

   // append Goto to successor

   ValueStack* state_before = if_->is_safepoint() ? if_->state_before() : NULL;

   Goto* goto_ = new Goto(sux, state_before, if_->is_safepoint() || t_goto->is_safepoint() || f_goto->is_safepoint());

   // prepare state for Goto

   ValueStack* goto_state = if_state;

   goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());

   goto_state->push(result->type(), result);

   assert(goto_state->is_same(sux_state), "states must match now");

   goto_->set_state(goto_state);

   cur_end = cur_end->set_next(goto_, goto_state->bci());

   // Adjust control flow graph

   BlockBegin::disconnect_edge(block, t_block);

   BlockBegin::disconnect_edge(block, f_block);

   if (t_block->number_of_preds() == 0) {

     BlockBegin::disconnect_edge(t_block, sux);

   }

   adjust_exception_edges(block, t_block);

   if (f_block->number_of_preds() == 0) {

     BlockBegin::disconnect_edge(f_block, sux);

   }

   adjust_exception_edges(block, f_block);

   // update block end

   block->set_end(goto_);

   // substitute the phi if possible

   if (sux_phi->as_Phi()->operand_count() == 1) {

     assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");

     sux_phi->set_subst(result);

     _has_substitution = true;

   }

   // 3) successfully eliminated a conditional expression

   _cee_count++;

   if (PrintCEE) {

     tty->print_cr("%d. CEE in B%d (B%d B%d)", cee_count(), block->block_id(), t_block->block_id(), f_block->block_id());

     tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());

   }

   _hir->verify();

 }

 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval) {

   if (!OptimizeIfOps) {

     return new IfOp(x, cond, y, tval, fval);

   }

   tval = tval->subst();

   fval = fval->subst();

   if (tval == fval) {

     _ifop_count++;

     return tval;

   }

   x = x->subst();

   y = y->subst();

   Constant* y_const = y->as_Constant();

   if (y_const != NULL) {

     IfOp* x_ifop = x->as_IfOp();

     if (x_ifop != NULL) {                 // x is an ifop, y is a constant

       Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();

       Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();

       if (x_tval_const != NULL && x_fval_const != NULL) {

         Instruction::Condition x_ifop_cond = x_ifop->cond();

         Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);

         Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);

         // not_comparable here is a valid return in case we're comparing unloaded oop constants

         if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {

           Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;

           Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;

           _ifop_count++;

           if (new_tval == new_fval) {

             return new_tval;

           } else {

             return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);

           }

         }

       }

     } else {

       Constant* x_const = x->as_Constant();

       if (x_const != NULL) {         // x and y are constants

         Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);

         // not_comparable here is a valid return in case we're comparing unloaded oop constants

         if (x_compare_res != Constant::not_comparable) {

           _ifop_count++;

           return x_compare_res == Constant::cond_true ? tval : fval;

         }

       }

     }

   }

   return new IfOp(x, cond, y, tval, fval);

 }

 void Optimizer::eliminate_conditional_expressions() {

   // find conditional expressions & replace them with IfOps

   CE_Eliminator ce(ir());

 }

 class BlockMerger: public BlockClosure {

  private:

   IR* _hir;

   int _merge_count;              // the number of block pairs successfully merged

  public:

   BlockMerger(IR* hir)

   : _hir(hir)

   , _merge_count(0)

   {

     _hir->iterate_preorder(this);

     CompileLog* log = _hir->compilation()->log();

     if (log != NULL)

       log->set_context("optimize name='eliminate_blocks'");

   }

   ~BlockMerger() {

     CompileLog* log = _hir->compilation()->log();

     if (log != NULL)

       log->clear_context(); // skip marker if nothing was printed

   }

   bool try_merge(BlockBegin* block) {

     BlockEnd* end = block->end();

     if (end->as_Goto() != NULL) {

       assert(end->number_of_sux() == 1, "end must have exactly one successor");

       // Note: It would be sufficient to check for the number of successors (= 1)

       //       in order to decide if this block can be merged potentially. That

       //       would then also include switch statements w/ only a default case.

       //       However, in that case we would need to make sure the switch tag

       //       expression is executed if it can produce observable side effects.

       //       We should probably have the canonicalizer simplifying such switch

       //       statements and then we are sure we don't miss these merge opportunities

       //       here (was bug - gri 7/7/99).

       BlockBegin* sux = end->default_sux();

       if (sux->number_of_preds() == 1 && !sux->is_entry_block() && !end->is_safepoint()) {

         // merge the two blocks

 #ifdef ASSERT

         // verify that state at the end of block and at the beginning of sux are equal

         // no phi functions must be present at beginning of sux

         ValueStack* sux_state = sux->state();

         ValueStack* end_state = end->state();

         assert(end_state->scope() == sux_state->scope(), "scopes must match");

         assert(end_state->stack_size() == sux_state->stack_size(), "stack not equal");

         assert(end_state->locals_size() == sux_state->locals_size(), "locals not equal");

         int index;

         Value sux_value;

         for_each_stack_value(sux_state, index, sux_value) {

           assert(sux_value == end_state->stack_at(index), "stack not equal");

         }

         for_each_local_value(sux_state, index, sux_value) {

           assert(sux_value == end_state->local_at(index), "locals not equal");

         }

         assert(sux_state->caller_state() == end_state->caller_state(), "caller not equal");

 #endif

         // find instruction before end & append first instruction of sux block

         Instruction* prev = end->prev(block);

         Instruction* next = sux->next();

         assert(prev->as_BlockEnd() == NULL, "must not be a BlockEnd");

         prev->set_next(next);

         sux->disconnect_from_graph();

         block->set_end(sux->end());

         // add exception handlers of deleted block, if any

         for (int k = 0; k < sux->number_of_exception_handlers(); k++) {

           BlockBegin* xhandler = sux->exception_handler_at(k);

           block->add_exception_handler(xhandler);

           // also substitute predecessor of exception handler

           assert(xhandler->is_predecessor(sux), "missing predecessor");

           xhandler->remove_predecessor(sux);

           if (!xhandler->is_predecessor(block)) {

             xhandler->add_predecessor(block);

           }

         }

         // debugging output

         _merge_count++;

         if (PrintBlockElimination) {

           tty->print_cr("%d. merged B%d & B%d (stack size = %d)",

                         _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());

         }

         _hir->verify();

         If* if_ = block->end()->as_If();

         if (if_) {

           IfOp* ifop    = if_->x()->as_IfOp();

           Constant* con = if_->y()->as_Constant();

           bool swapped = false;

           if (!con || !ifop) {

             ifop = if_->y()->as_IfOp();

             con  = if_->x()->as_Constant();

             swapped = true;

           }

           if (con && ifop) {

             Constant* tval = ifop->tval()->as_Constant();

             Constant* fval = ifop->fval()->as_Constant();

             if (tval && fval) {

               // Find the instruction before if_, starting with ifop.

               // When if_ and ifop are not in the same block, prev

               // becomes NULL In such (rare) cases it is not

               // profitable to perform the optimization.

               Value prev = ifop;

               while (prev != NULL && prev->next() != if_) {

                 prev = prev->next();

               }

               if (prev != NULL) {

                 Instruction::Condition cond = if_->cond();

                 BlockBegin* tsux = if_->tsux();

                 BlockBegin* fsux = if_->fsux();

                 if (swapped) {

                   cond = Instruction::mirror(cond);

                 }

                 BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);

                 BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);

                 if (tblock != fblock && !if_->is_safepoint()) {

                   If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),

                                      tblock, fblock, if_->state_before(), if_->is_safepoint());

                   newif->set_state(if_->state()->copy());

                   assert(prev->next() == if_, "must be guaranteed by above search");

                   NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));

                   prev->set_next(newif);

                   block->set_end(newif);

                   _merge_count++;

                   if (PrintBlockElimination) {

                     tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());

                   }

                   _hir->verify();

                 }

               }

             }

           }

         }

         return true;

       }

     }

     return false;

   }

   virtual void block_do(BlockBegin* block) {

     _hir->verify();

     // repeat since the same block may merge again

     while (try_merge(block)) {

       _hir->verify();

     }

   }

 };

 void Optimizer::eliminate_blocks() {

   // merge blocks if possible

   BlockMerger bm(ir());

 }

 class NullCheckEliminator;

 class NullCheckVisitor: public InstructionVisitor {

 private:

   NullCheckEliminator* _nce;

   NullCheckEliminator* nce() { return _nce; }

 public:

   NullCheckVisitor() {}

   void set_eliminator(NullCheckEliminator* nce) { _nce = nce; }

   void do_Phi            (Phi*             x);

   void do_Local          (Local*           x);

   void do_Constant       (Constant*        x);

   void do_LoadField      (LoadField*       x);

   void do_StoreField     (StoreField*      x);

   void do_ArrayLength    (ArrayLength*     x);

   void do_LoadIndexed    (LoadIndexed*     x);

   void do_StoreIndexed   (StoreIndexed*    x);

   void do_NegateOp       (NegateOp*        x);

   void do_ArithmeticOp   (ArithmeticOp*    x);

   void do_ShiftOp        (ShiftOp*         x);

   void do_LogicOp        (LogicOp*         x);

   void do_CompareOp      (CompareOp*       x);

   void do_IfOp           (IfOp*            x);

   void do_Convert        (Convert*         x);

   void do_NullCheck      (NullCheck*       x);

   void do_TypeCast       (TypeCast*        x);

   void do_Invoke         (Invoke*          x);

   void do_NewInstance    (NewInstance*     x);

   void do_NewTypeArray   (NewTypeArray*    x);

   void do_NewObjectArray (NewObjectArray*  x);

   void do_NewMultiArray  (NewMultiArray*   x);

   void do_CheckCast      (CheckCast*       x);

   void do_InstanceOf     (InstanceOf*      x);

   void do_MonitorEnter   (MonitorEnter*    x);

   void do_MonitorExit    (MonitorExit*     x);

   void do_Intrinsic      (Intrinsic*       x);

   void do_BlockBegin     (BlockBegin*      x);

   void do_Goto           (Goto*            x);

   void do_If             (If*              x);

   void do_IfInstanceOf   (IfInstanceOf*    x);

   void do_TableSwitch    (TableSwitch*     x);

   void do_LookupSwitch   (LookupSwitch*    x);

   void do_Return         (Return*          x);

   void do_Throw          (Throw*           x);

   void do_Base           (Base*            x);

   void do_OsrEntry       (OsrEntry*        x);

   void do_ExceptionObject(ExceptionObject* x);

   void do_RoundFP        (RoundFP*         x);

   void do_UnsafeGetRaw   (UnsafeGetRaw*    x);

   void do_UnsafePutRaw   (UnsafePutRaw*    x);

   void do_UnsafeGetObject(UnsafeGetObject* x);

   void do_UnsafePutObject(UnsafePutObject* x);

   void do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x);

   void do_UnsafePrefetchRead (UnsafePrefetchRead*  x);

   void do_UnsafePrefetchWrite(UnsafePrefetchWrite* x);

   void do_ProfileCall    (ProfileCall*     x);

   void do_ProfileInvoke  (ProfileInvoke*   x);

   void do_RuntimeCall    (RuntimeCall*     x);

   void do_MemBar         (MemBar*          x);

 };

 // Because of a static contained within (for the purpose of iteration

 // over instructions), it is only valid to have one of these active at

 // a time

 class NullCheckEliminator: public ValueVisitor {

  private:

   Optimizer*        _opt;

   ValueSet*         _visitable_instructions;        // Visit each instruction only once per basic block

   BlockList*        _work_list;                   // Basic blocks to visit

   bool visitable(Value x) {

     assert(_visitable_instructions != NULL, "check");

     return _visitable_instructions->contains(x);

   }

   void mark_visited(Value x) {

     assert(_visitable_instructions != NULL, "check");

     _visitable_instructions->remove(x);

   }

   void mark_visitable(Value x) {

     assert(_visitable_instructions != NULL, "check");

     _visitable_instructions->put(x);

   }

   void clear_visitable_state() {

     assert(_visitable_instructions != NULL, "check");

     _visitable_instructions->clear();

   }

   ValueSet*         _set;                         // current state, propagated to subsequent BlockBegins

   ValueSetList      _block_states;                // BlockBegin null-check states for all processed blocks

   NullCheckVisitor  _visitor;

   NullCheck*        _last_explicit_null_check;

   bool set_contains(Value x)                      { assert(_set != NULL, "check"); return _set->contains(x); }

   void set_put     (Value x)                      { assert(_set != NULL, "check"); _set->put(x); }

   void set_remove  (Value x)                      { assert(_set != NULL, "check"); _set->remove(x); }

   BlockList* work_list()                          { return _work_list; }

   void iterate_all();

   void iterate_one(BlockBegin* block);

   ValueSet* state()                               { return _set; }

   void      set_state_from (ValueSet* state)      { _set->set_from(state); }

   ValueSet* state_for      (BlockBegin* block)    { return _block_states[block->block_id()]; }

   void      set_state_for  (BlockBegin* block, ValueSet* stack) { _block_states[block->block_id()] = stack; }

   // Returns true if caused a change in the block's state.

   bool      merge_state_for(BlockBegin* block,

                             ValueSet*   incoming_state);

  public:

   // constructor

   NullCheckEliminator(Optimizer* opt)

     : _opt(opt)

     , _set(new ValueSet())

     , _last_explicit_null_check(NULL)

     , _block_states(BlockBegin::number_of_blocks(), NULL)

     , _work_list(new BlockList()) {

     _visitable_instructions = new ValueSet();

     _visitor.set_eliminator(this);

     CompileLog* log = _opt->ir()->compilation()->log();

     if (log != NULL)

       log->set_context("optimize name='null_check_elimination'");

   }

   ~NullCheckEliminator() {

     CompileLog* log = _opt->ir()->compilation()->log();

     if (log != NULL)

       log->clear_context(); // skip marker if nothing was printed

   }

   Optimizer*  opt()                               { return _opt; }

   IR*         ir ()                               { return opt()->ir(); }

   // Process a graph

   void iterate(BlockBegin* root);

   void visit(Value* f);

   // In some situations (like NullCheck(x); getfield(x)) the debug

   // information from the explicit NullCheck can be used to populate

   // the getfield, even if the two instructions are in different

   // scopes; this allows implicit null checks to be used but the

   // correct exception information to be generated. We must clear the

   // last-traversed NullCheck when we reach a potentially-exception-

   // throwing instruction, as well as in some other cases.

   void        set_last_explicit_null_check(NullCheck* check) { _last_explicit_null_check = check; }

   NullCheck*  last_explicit_null_check()                     { return _last_explicit_null_check; }

   Value       last_explicit_null_check_obj()                 { return (_last_explicit_null_check

                                                                          ? _last_explicit_null_check->obj()

                                                                          : NULL); }

   NullCheck*  consume_last_explicit_null_check() {

     _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);

     _last_explicit_null_check->set_can_trap(false);

     return _last_explicit_null_check;

   }

   void        clear_last_explicit_null_check()               { _last_explicit_null_check = NULL; }

   // Handlers for relevant instructions

   // (separated out from NullCheckVisitor for clarity)

   // The basic contract is that these must leave the instruction in

   // the desired state; must not assume anything about the state of

   // the instruction. We make multiple passes over some basic blocks

   // and the last pass is the only one whose result is valid.

   void handle_AccessField     (AccessField* x);

   void handle_ArrayLength     (ArrayLength* x);

   void handle_LoadIndexed     (LoadIndexed* x);

   void handle_StoreIndexed    (StoreIndexed* x);

   void handle_NullCheck       (NullCheck* x);

   void handle_Invoke          (Invoke* x);

   void handle_NewInstance     (NewInstance* x);

   void handle_NewArray        (NewArray* x);

   void handle_AccessMonitor   (AccessMonitor* x);

   void handle_Intrinsic       (Intrinsic* x);

   void handle_ExceptionObject (ExceptionObject* x);

   void handle_Phi             (Phi* x);

 };

 // NEEDS_CLEANUP

 // There may be other instructions which need to clear the last

 // explicit null check. Anything across which we can not hoist the

 // debug information for a NullCheck instruction must clear it. It

 // might be safer to pattern match "NullCheck ; {AccessField,

 // ArrayLength, LoadIndexed}" but it is more easily structured this way.

 // Should test to see performance hit of clearing it for all handlers

 // with empty bodies below. If it is negligible then we should leave

 // that in for safety, otherwise should think more about it.

 void NullCheckVisitor::do_Phi            (Phi*             x) { nce()->handle_Phi(x);      }

 void NullCheckVisitor::do_Local          (Local*           x) {}

 void NullCheckVisitor::do_Constant       (Constant*        x) { /* FIXME: handle object constants */ }

 void NullCheckVisitor::do_LoadField      (LoadField*       x) { nce()->handle_AccessField(x); }

 void NullCheckVisitor::do_StoreField     (StoreField*      x) { nce()->handle_AccessField(x); }

 void NullCheckVisitor::do_ArrayLength    (ArrayLength*     x) { nce()->handle_ArrayLength(x); }

 void NullCheckVisitor::do_LoadIndexed    (LoadIndexed*     x) { nce()->handle_LoadIndexed(x); }

 void NullCheckVisitor::do_StoreIndexed   (StoreIndexed*    x) { nce()->handle_StoreIndexed(x); }

 void NullCheckVisitor::do_NegateOp       (NegateOp*        x) {}

 void NullCheckVisitor::do_ArithmeticOp   (ArithmeticOp*    x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }

 void NullCheckVisitor::do_ShiftOp        (ShiftOp*         x) {}

 void NullCheckVisitor::do_LogicOp        (LogicOp*         x) {}

 void NullCheckVisitor::do_CompareOp      (CompareOp*       x) {}

 void NullCheckVisitor::do_IfOp           (IfOp*            x) {}

 void NullCheckVisitor::do_Convert        (Convert*         x) {}

 void NullCheckVisitor::do_NullCheck      (NullCheck*       x) { nce()->handle_NullCheck(x); }

 void NullCheckVisitor::do_TypeCast       (TypeCast*        x) {}

 void NullCheckVisitor::do_Invoke         (Invoke*          x) { nce()->handle_Invoke(x); }

 void NullCheckVisitor::do_NewInstance    (NewInstance*     x) { nce()->handle_NewInstance(x); }

 void NullCheckVisitor::do_NewTypeArray   (NewTypeArray*    x) { nce()->handle_NewArray(x); }

 void NullCheckVisitor::do_NewObjectArray (NewObjectArray*  x) { nce()->handle_NewArray(x); }

 void NullCheckVisitor::do_NewMultiArray  (NewMultiArray*   x) { nce()->handle_NewArray(x); }

 void NullCheckVisitor::do_CheckCast      (CheckCast*       x) { nce()->clear_last_explicit_null_check(); }

 void NullCheckVisitor::do_InstanceOf     (InstanceOf*      x) {}

 void NullCheckVisitor::do_MonitorEnter   (MonitorEnter*    x) { nce()->handle_AccessMonitor(x); }

 void NullCheckVisitor::do_MonitorExit    (MonitorExit*     x) { nce()->handle_AccessMonitor(x); }

 void NullCheckVisitor::do_Intrinsic      (Intrinsic*       x) { nce()->handle_Intrinsic(x);     }

 void NullCheckVisitor::do_BlockBegin     (BlockBegin*      x) {}

 void NullCheckVisitor::do_Goto           (Goto*            x) {}

 void NullCheckVisitor::do_If             (If*              x) {}

 void NullCheckVisitor::do_IfInstanceOf   (IfInstanceOf*    x) {}

 void NullCheckVisitor::do_TableSwitch    (TableSwitch*     x) {}

 void NullCheckVisitor::do_LookupSwitch   (LookupSwitch*    x) {}

 void NullCheckVisitor::do_Return         (Return*          x) {}

 void NullCheckVisitor::do_Throw          (Throw*           x) { nce()->clear_last_explicit_null_check(); }

 void NullCheckVisitor::do_Base           (Base*            x) {}

 void NullCheckVisitor::do_OsrEntry       (OsrEntry*        x) {}

 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }

 void NullCheckVisitor::do_RoundFP        (RoundFP*         x) {}

 void NullCheckVisitor::do_UnsafeGetRaw   (UnsafeGetRaw*    x) {}

 void NullCheckVisitor::do_UnsafePutRaw   (UnsafePutRaw*    x) {}

 void NullCheckVisitor::do_UnsafeGetObject(UnsafeGetObject* x) {}

 void NullCheckVisitor::do_UnsafePutObject(UnsafePutObject* x) {}

 void NullCheckVisitor::do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x) {}

 void NullCheckVisitor::do_UnsafePrefetchRead (UnsafePrefetchRead*  x) {}

 void NullCheckVisitor::do_UnsafePrefetchWrite(UnsafePrefetchWrite* x) {}

 void NullCheckVisitor::do_ProfileCall    (ProfileCall*     x) { nce()->clear_last_explicit_null_check(); }

 void NullCheckVisitor::do_ProfileInvoke  (ProfileInvoke*   x) {}

 void NullCheckVisitor::do_RuntimeCall    (RuntimeCall*     x) {}

 void NullCheckVisitor::do_MemBar         (MemBar*          x) {}

 void NullCheckEliminator::visit(Value* p) {

   assert(*p != NULL, "should not find NULL instructions");

   if (visitable(*p)) {

     mark_visited(*p);

     (*p)->visit(&_visitor);

   }

 }

 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {

   ValueSet* state = state_for(block);

   if (state == NULL) {

     state = incoming_state->copy();

     set_state_for(block, state);

     return true;

   } else {

     bool changed = state->set_intersect(incoming_state);

     if (PrintNullCheckElimination && changed) {

       tty->print_cr("Block %d's null check state changed", block->block_id());

     }

     return changed;

   }

 }

 void NullCheckEliminator::iterate_all() {

   while (work_list()->length() > 0) {

     iterate_one(work_list()->pop());

   }

 }

 void NullCheckEliminator::iterate_one(BlockBegin* block) {

   clear_visitable_state();

   // clear out an old explicit null checks

   set_last_explicit_null_check(NULL);

   if (PrintNullCheckElimination) {

     tty->print_cr(" ...iterating block %d in null check elimination for %s::%s%s",

                   block->block_id(),

                   ir()->method()->holder()->name()->as_utf8(),

                   ir()->method()->name()->as_utf8(),

                   ir()->method()->signature()->as_symbol()->as_utf8());

   }

   // Create new state if none present (only happens at root)

   if (state_for(block) == NULL) {

     ValueSet* tmp_state = new ValueSet();

     set_state_for(block, tmp_state);

     // Initial state is that local 0 (receiver) is non-null for

     // non-static methods

     ValueStack* stack  = block->state();

     IRScope*    scope  = stack->scope();

     ciMethod*   method = scope->method();

     if (!method->is_static()) {

       Local* local0 = stack->local_at(0)->as_Local();

       assert(local0 != NULL, "must be");

       assert(local0->type() == objectType, "invalid type of receiver");

       if (local0 != NULL) {

         // Local 0 is used in this scope

         tmp_state->put(local0);

         if (PrintNullCheckElimination) {

           tty->print_cr("Local 0 (value %d) proven non-null upon entry", local0->id());

         }

       }

     }

   }

   // Must copy block's state to avoid mutating it during iteration

   // through the block -- otherwise "not-null" states can accidentally

   // propagate "up" through the block during processing of backward

   // branches and algorithm is incorrect (and does not converge)

   set_state_from(state_for(block));

   // allow visiting of Phis belonging to this block

   for_each_phi_fun(block, phi,

                    mark_visitable(phi);

                    );

   BlockEnd* e = block->end();

   assert(e != NULL, "incomplete graph");

   int i;

   // Propagate the state before this block into the exception

   // handlers.  They aren't true successors since we aren't guaranteed

   // to execute the whole block before executing them.  Also putting

   // them on first seems to help reduce the amount of iteration to

   // reach a fixed point.

   for (i = 0; i < block->number_of_exception_handlers(); i++) {

     BlockBegin* next = block->exception_handler_at(i);

     if (merge_state_for(next, state())) {

       if (!work_list()->contains(next)) {

         work_list()->push(next);

       }

     }

   }

   // Iterate through block, updating state.

   for (Instruction* instr = block; instr != NULL; instr = instr->next()) {

     // Mark instructions in this block as visitable as they are seen

     // in the instruction list.  This keeps the iteration from

     // visiting instructions which are references in other blocks or

     // visiting instructions more than once.

     mark_visitable(instr);

     if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != NULL)) {

       mark_visited(instr);

       instr->input_values_do(this);

       instr->visit(&_visitor);

     }

   }

   // Propagate state to successors if necessary

   for (i = 0; i < e->number_of_sux(); i++) {

     BlockBegin* next = e->sux_at(i);

     if (merge_state_for(next, state())) {

       if (!work_list()->contains(next)) {

         work_list()->push(next);

       }

     }

   }

 }

 void NullCheckEliminator::iterate(BlockBegin* block) {

   work_list()->push(block);

   iterate_all();

 }

 void NullCheckEliminator::handle_AccessField(AccessField* x) {

   if (x->is_static()) {

     if (x->as_LoadField() != NULL) {

       // If the field is a non-null static final object field (as is

       // often the case for sun.misc.Unsafe), put this LoadField into

       // the non-null map

       ciField* field = x->field();

       if (field->is_constant()) {

         ciConstant field_val = field->constant_value();

         BasicType field_type = field_val.basic_type();

         if (field_type == T_OBJECT || field_type == T_ARRAY) {

           ciObject* obj_val = field_val.as_object();

           if (!obj_val->is_null_object()) {

             if (PrintNullCheckElimination) {

               tty->print_cr("AccessField %d proven non-null by static final non-null oop check",

                             x->id());

             }

             set_put(x);

           }

         }

       }

     }

     // Be conservative

     clear_last_explicit_null_check();

     return;

   }

   Value obj = x->obj();

   if (set_contains(obj)) {

     // Value is non-null => update AccessField

     if (last_explicit_null_check_obj() == obj && !x->needs_patching()) {

       x->set_explicit_null_check(consume_last_explicit_null_check());

       x->set_needs_null_check(true);

       if (PrintNullCheckElimination) {

         tty->print_cr("Folded NullCheck %d into AccessField %d's null check for value %d",

                       x->explicit_null_check()->id(), x->id(), obj->id());

       }

     } else {

       x->set_explicit_null_check(NULL);

       x->set_needs_null_check(false);

       if (PrintNullCheckElimination) {

         tty->print_cr("Eliminated AccessField %d's null check for value %d", x->id(), obj->id());

       }

     }

   } else {

     set_put(obj);

     if (PrintNullCheckElimination) {

       tty->print_cr("AccessField %d of value %d proves value to be non-null", x->id(), obj->id());

     }

     // Ensure previous passes do not cause wrong state

     x->set_needs_null_check(true);

     x->set_explicit_null_check(NULL);

   }

   clear_last_explicit_null_check();

 }

 void NullCheckEliminator::handle_ArrayLength(ArrayLength* x) {

   Value array = x->array();

   if (set_contains(array)) {

     // Value is non-null => update AccessArray

     if (last_explicit_null_check_obj() == array) {

       x->set_explicit_null_check(consume_last_explicit_null_check());

       x->set_needs_null_check(true);

       if (PrintNullCheckElimination) {

         tty->print_cr("Folded NullCheck %d into ArrayLength %d's null check for value %d",

                       x->explicit_null_check()->id(), x->id(), array->id());

       }

     } else {

       x->set_explicit_null_check(NULL);

       x->set_needs_null_check(false);

       if (PrintNullCheckElimination) {

         tty->print_cr("Eliminated ArrayLength %d's null check for value %d", x->id(), array->id());

       }

     }

   } else {

     set_put(array);

     if (PrintNullCheckElimination) {

       tty->print_cr("ArrayLength %d of value %d proves value to be non-null", x->id(), array->id());

     }

     // Ensure previous passes do not cause wrong state

     x->set_needs_null_check(true);

     x->set_explicit_null_check(NULL);

   }

   clear_last_explicit_null_check();

 }

 void NullCheckEliminator::handle_LoadIndexed(LoadIndexed* x) {

   Value array = x->array();

   if (set_contains(array)) {

     // Value is non-null => update AccessArray

     if (last_explicit_null_check_obj() == array) {

       x->set_explicit_null_check(consume_last_explicit_null_check());

       x->set_needs_null_check(true);

       if (PrintNullCheckElimination) {

         tty->print_cr("Folded NullCheck %d into LoadIndexed %d's null check for value %d",

                       x->explicit_null_check()->id(), x->id(), array->id());

       }

     } else {

       x->set_explicit_null_check(NULL);

       x->set_needs_null_check(false);

       if (PrintNullCheckElimination) {

         tty->print_cr("Eliminated LoadIndexed %d's null check for value %d", x->id(), array->id());

       }

     }

   } else {

     set_put(array);

     if (PrintNullCheckElimination) {

       tty->print_cr("LoadIndexed %d of value %d proves value to be non-null", x->id(), array->id());

     }

     // Ensure previous passes do not cause wrong state

     x->set_needs_null_check(true);

     x->set_explicit_null_check(NULL);

   }

   clear_last_explicit_null_check();

 }

 void NullCheckEliminator::handle_StoreIndexed(StoreIndexed* x) {

   Value array = x->array();

   if (set_contains(array)) {

     // Value is non-null => update AccessArray

     if (PrintNullCheckElimination) {

       tty->print_cr("Eliminated StoreIndexed %d's null check for value %d", x->id(), array->id());

     }

     x->set_needs_null_check(false);

   } else {

     set_put(array);

     if (PrintNullCheckElimination) {

       tty->print_cr("StoreIndexed %d of value %d proves value to be non-null", x->id(), array->id());

     }

     // Ensure previous passes do not cause wrong state

     x->set_needs_null_check(true);

   }

   clear_last_explicit_null_check();

 }

 void NullCheckEliminator::handle_NullCheck(NullCheck* x) {

   Value obj = x->obj();

   if (set_contains(obj)) {

     // Already proven to be non-null => this NullCheck is useless

     if (PrintNullCheckElimination) {

       tty->print_cr("Eliminated NullCheck %d for value %d", x->id(), obj->id());

     }

     // Don't unpin since that may shrink obj's live range and make it unavailable for debug info.

     // The code generator won't emit LIR for a NullCheck that cannot trap.

     x->set_can_trap(false);

   } else {

     // May be null => add to map and set last explicit NullCheck

     x->set_can_trap(true);

     // make sure it's pinned if it can trap

     x->pin(Instruction::PinExplicitNullCheck);

     set_put(obj);

     set_last_explicit_null_check(x);

     if (PrintNullCheckElimination) {

       tty->print_cr("NullCheck %d of value %d proves value to be non-null", x->id(), obj->id());

     }

   }

 }

 void NullCheckEliminator::handle_Invoke(Invoke* x) {

   if (!x->has_receiver()) {

     // Be conservative

     clear_last_explicit_null_check();

     return;

   }

   Value recv = x->receiver();

   if (!set_contains(recv)) {

     set_put(recv);

     if (PrintNullCheckElimination) {

       tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());

     }

   }

   clear_last_explicit_null_check();

 }

 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {

   set_put(x);

   if (PrintNullCheckElimination) {

     tty->print_cr("NewInstance %d is non-null", x->id());

   }

 }

 void NullCheckEliminator::handle_NewArray(NewArray* x) {

   set_put(x);

   if (PrintNullCheckElimination) {

     tty->print_cr("NewArray %d is non-null", x->id());

   }

 }

 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {

   set_put(x);

   if (PrintNullCheckElimination) {

     tty->print_cr("ExceptionObject %d is non-null", x->id());

   }

 }

 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {

   Value obj = x->obj();

   if (set_contains(obj)) {

     // Value is non-null => update AccessMonitor

     if (PrintNullCheckElimination) {

       tty->print_cr("Eliminated AccessMonitor %d's null check for value %d", x->id(), obj->id());

     }

     x->set_needs_null_check(false);

   } else {

     set_put(obj);

     if (PrintNullCheckElimination) {

       tty->print_cr("AccessMonitor %d of value %d proves value to be non-null", x->id(), obj->id());

     }

     // Ensure previous passes do not cause wrong state

     x->set_needs_null_check(true);

   }

   clear_last_explicit_null_check();

 }

 void NullCheckEliminator::handle_Intrinsic(Intrinsic* x) {

   if (!x->has_receiver()) {

     if (x->id() == vmIntrinsics::_arraycopy) {

       for (int i = 0; i < x->number_of_arguments(); i++) {

         x->set_arg_needs_null_check(i, !set_contains(x->argument_at(i)));

       }

     }

     // Be conservative

     clear_last_explicit_null_check();

     return;

   }

   Value recv = x->receiver();

   if (set_contains(recv)) {

     // Value is non-null => update Intrinsic

     if (PrintNullCheckElimination) {

       tty->print_cr("Eliminated Intrinsic %d's null check for value %d", x->id(), recv->id());

     }

     x->set_needs_null_check(false);

   } else {

     set_put(recv);

     if (PrintNullCheckElimination) {

       tty->print_cr("Intrinsic %d of value %d proves value to be non-null", x->id(), recv->id());

     }

     // Ensure previous passes do not cause wrong state

     x->set_needs_null_check(true);

   }

   clear_last_explicit_null_check();

 }

 void NullCheckEliminator::handle_Phi(Phi* x) {

   int i;

   bool all_non_null = true;

   if (x->is_illegal()) {

     all_non_null = false;

   } else {

     for (i = 0; i < x->operand_count(); i++) {

       Value input = x->operand_at(i);

       if (!set_contains(input)) {

         all_non_null = false;

       }

     }

   }

   if (all_non_null) {

     // Value is non-null => update Phi

     if (PrintNullCheckElimination) {

       tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());

     }

     x->set_needs_null_check(false);

   } else if (set_contains(x)) {

     set_remove(x);

   }

 }

 void Optimizer::eliminate_null_checks() {

   ResourceMark rm;

   NullCheckEliminator nce(this);

   if (PrintNullCheckElimination) {

     tty->print_cr("Starting null check elimination for method %s::%s%s",

                   ir()->method()->holder()->name()->as_utf8(),

                   ir()->method()->name()->as_utf8(),

                   ir()->method()->signature()->as_symbol()->as_utf8());

   }

   // Apply to graph

   nce.iterate(ir()->start());

   // walk over the graph looking for exception

   // handlers and iterate over them as well

   int nblocks = BlockBegin::number_of_blocks();

   BlockList blocks(nblocks);

   boolArray visited_block(nblocks, false);

   blocks.push(ir()->start());

   visited_block[ir()->start()->block_id()] = true;

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

     BlockBegin* b = blocks[i];

     // exception handlers need to be treated as additional roots

     for (int e = b->number_of_exception_handlers(); e-- > 0; ) {

       BlockBegin* excp = b->exception_handler_at(e);

       int id = excp->block_id();

       if (!visited_block[id]) {

         blocks.push(excp);

         visited_block[id] = true;

         nce.iterate(excp);

       }

     }

     // traverse successors

     BlockEnd *end = b->end();

     for (int s = end->number_of_sux(); s-- > 0; ) {

       BlockBegin* next = end->sux_at(s);

       int id = next->block_id();

       if (!visited_block[id]) {

         blocks.push(next);

         visited_block[id] = true;

       }

     }

   }

   if (PrintNullCheckElimination) {

     tty->print_cr("Done with null check elimination for method %s::%s%s",

                   ir()->method()->holder()->name()->as_utf8(),

                   ir()->method()->name()->as_utf8(),

                   ir()->method()->signature()->as_symbol()->as_utf8());

   }

 }