interpretedIC.cpp

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/* Copyright 1994 - 1996, LongView Technologies, L.L.C. $Revision: 1.34 $ */
/* Copyright (c) 2006, Sun Microsystems, Inc.
All rights reserved.

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# include "incls/_precompiled.incl"
# include "incls/_interpretedIC.cpp.incl"


// Implementation of Interpreter_PICs
//
// A simple free list manager for interpreted PICs.

class Interpreter_PICs : AllStatic {
 public:
  static objArrayOop free_list() { return Universe::pic_free_list(); }

  static objArrayOop allocate(int size) {
    oop first = free_list()->obj_at(size - 1);
    if (first == nilObj) {
      return objArrayKlass::allocate_tenured_pic(size*2);
    }
    free_list()->obj_at_put(size - 1, objArrayOop(first)->obj_at(1));

    objArrayOop result = objArrayOop(first);
    assert(result->is_objArray(),        "must be object array");
    assert(result->is_old(),             "must be tenures");
    assert(result->length() == size * 2, "checking size");
    return result;
  }

  static objArrayOop extend(objArrayOop old_pic) {
    int old_size = old_pic->length()/2;
    if (old_size >= size_of_largest_interpreterPIC) return NULL;
    objArrayOop result = allocate(old_size + 1);
    for (int index = 1; index <= old_size*2; index++) {
      result->obj_at_put(index, old_pic->obj_at(index));
    }
    return result;
  }

  static void deallocate(objArrayOop pic) {
    int entry = (pic->length()/2) - 1;
    oop first = free_list()->obj_at(entry);
    pic->obj_at_put(1, first);
    free_list()->obj_at_put(entry, pic);
  }

  static void set_first(objArrayOop pic, oop first, oop second) {
     pic->obj_at_put(1, first);
     pic->obj_at_put(2, second);
  }

  static void set_second(objArrayOop pic, oop first, oop second) {
     pic->obj_at_put(3, first);
     pic->obj_at_put(4, second);
  }

  static void set_last(objArrayOop pic, oop first, oop second) {
     int size = pic->length();
     pic->obj_at_put(size--, second);
     pic->obj_at_put(size,   first);
  }
};


// Implementation of InterpretedIC

void InterpretedIC::set(Bytecodes::Code send_code, oop first_word, oop second_word) {
  // Remember pics are allocated in new space and
  // require a store check when saved in the InlineCache
  // Note: If the second_word is a PIC, it has to be deallocated
  //       before using set!
  *send_code_addr() = send_code;
  Universe::store(first_word_addr(), first_word, first_word->is_new());
  Universe::store(second_word_addr(), second_word, second_word->is_new());
}


u_char* InterpretedIC::findStartOfSend(u_char* sel_addr) {
  u_char* p = sel_addr;                 // start of inline cache
  while (*--p == Bytecodes::halt) ;     // skip alignment bytes if there - this works only if the nofArgs byte != halt ! FIX THIS!
  if (*p < 128) --p;                    // skip nofArgs byte if there - this works only for sends with less than 128 args
                                        // and assumes that no send bytecodes is smaller than 128. FIX THIS!!!
  if (!Bytecodes::is_send_code(Bytecodes::Code(*p))) {
    return NULL;   // not a send
  }
  return p;
  // Clean solution:
  //
  // make all send bytecodes holding the no. of arguments,
  // use special filler value (e.g. restrict no of. args to 254).
  // not urgent (gri 1/29/96)
}


int InterpretedIC::findStartOfSend(methodOop m, int bci) {
  u_char* p = findStartOfSend(m->codes(bci));
  return (p == NULL) ? IllegalBCI : p - m->codes() + 1;
}


symbolOop InterpretedIC::selector() const {
  oop fw = first_word();
  if (fw->is_symbol()) {
    return symbolOop(fw);
  } else if (fw->is_method()) {
    return methodOop(fw)->selector();
  } else {
    jumpTableEntry* e = jump_table_entry();
    nmethod* nm = e->method();
    assert(nm != NULL, "must have an nmethod");
    return nm->key.selector();
  }
}


jumpTableEntry* InterpretedIC::jump_table_entry() const {
  assert(send_type() == Bytecodes::compiled_send ||
         send_type() == Bytecodes::megamorphic_send, "must be a compiled call");
  assert(first_word()->is_smi(), "must be smi");
  return (jumpTableEntry*) first_word();
}


int InterpretedIC::nof_arguments() const {
  u_char* p = send_code_addr();
  switch (Bytecodes::argument_spec(Bytecodes::Code(*p))) {
    case Bytecodes::recv_0_args: return 0;
    case Bytecodes::recv_1_args: return 1;
    case Bytecodes::recv_2_args: return 2;
    case Bytecodes::recv_n_args: {
      int n = selector()->number_of_arguments();
      assert(n = int(*(p+1)), "just checkin'..."); // send_code_addr()+1 must hold the number of arguments
      return n;
    }
    case Bytecodes::args_only: return selector()->number_of_arguments();
  }
  ShouldNotReachHere();
  return 0;
}


Bytecodes::SendType InterpretedIC::send_type() const {
  return Bytecodes::send_type(send_code());
}


Bytecodes::ArgumentSpec InterpretedIC::argument_spec() const {
  return Bytecodes::argument_spec(send_code());
}


void InterpretedIC::clear() {
  if (is_empty()) return;
  if (send_type() == Bytecodes::polymorphic_send) {
    // recycle PIC
    assert(second_word()->is_objArray(), "must be a pic");
    Interpreter_PICs::deallocate(objArrayOop(second_word()));
  }
  set(Bytecodes::original_send_code_for(send_code()), oop(selector()), smiOop_zero);
}


void InterpretedIC::replace(LookupResult result, klassOop receiver_klass) {
  // IC entries before modification - used for loging only
  Bytecodes::Code code_before  = send_code();
  oop             word1_before = first_word();
  oop             word2_before = second_word();
  int             transition   = 0;
  // modify IC
  guarantee(word2_before == receiver_klass, "klass should be the same");
  if (result.is_empty()) {
    clear();
    transition = 1;
  } else if (result.is_method()) {
    if (send_type() == Bytecodes::megamorphic_send) {
      set(send_code(), result.method(), receiver_klass);
      transition = 2;
    } else {
      // Please Fix this Robert
      // implement set_monomorphic(klass, method)
      clear();
      transition = 3;
    }
  } else {
    if (send_type() == Bytecodes::megamorphic_send) {
      set(send_code(), oop(result.entry()), receiver_klass);
      transition = 4;
    } else {
      assert(result.is_entry(), "must be jump table entry");
      // a jump table entry of a nmethod is found so let's update the current send
      set(Bytecodes::compiled_send_code_for(send_code()), oop(result.entry()), receiver_klass);
      transition = 5;
    }
  }
  // IC entries after modification - used for loging only
  Bytecodes::Code code_after  = send_code();
  oop             word1_after = first_word();
  oop             word2_after = second_word();
  // log modification
  LOG_EVENT3("InterpretedIC::replace: IC at 0x%x: entry for klass 0x%x replaced (transition %d)", this, receiver_klass, transition);
  LOG_EVENT3("  from (%s, 0x%x, 0x%x)", Bytecodes::name(code_before), word1_before, word2_before);
  LOG_EVENT3("  to   (%s, 0x%x, 0x%x)", Bytecodes::name(code_after ), word1_after , word2_after );
}


void InterpretedIC::cleanup() {
  if (is_empty()) return; // Nothing to cleanup

  switch (send_type()) {
    case Bytecodes::accessor_send:    // fall through
    case Bytecodes::primitive_send:   // fall through
    case Bytecodes::predicted_send:   // fall through
    case Bytecodes::interpreted_send:
      { // check if the interpreted send should be replaced by a compiled send   
        klassOop receiver_klass = klassOop(second_word());
        assert(receiver_klass->is_klass(), "receiver klass must be a klass");
        methodOop method = methodOop(first_word());
        assert(method->is_method(), "first word in interpreter IC must be method");
        if (!Bytecodes::is_super_send(send_code())) {
          // super sends cannot be handled since the sending method holder is unknown at this point.
          LookupKey key(receiver_klass, selector());
          LookupResult result = lookupCache::lookup(&key);
          if (!result.matches(method)) {
            replace(result, receiver_klass);
          }
        }
      }
      break;
    case Bytecodes::compiled_send:
      { // check if the current compiled send is valid
        klassOop receiver_klass = klassOop(second_word());
        assert(receiver_klass->is_klass(), "receiver klass must be a klass");
        jumpTableEntry* entry = (jumpTableEntry*) first_word();
        nmethod* nm = entry->method();
        LookupResult result = lookupCache::lookup(&nm->key);
        if (!result.matches(nm)) {
          replace(result, receiver_klass);
        }
      }
      break;
    case Bytecodes::megamorphic_send:
      // Note that with the current definition of is_empty()
      // this will not be called for normal megamorphic sends
      // since they store only the selector.
      { klassOop receiver_klass = klassOop(second_word());
        if (first_word()->is_smi()) {
          jumpTableEntry* entry = (jumpTableEntry*) first_word();
          nmethod* nm = entry->method();
          LookupResult result = lookupCache::lookup(&nm->key);
          if (!result.matches(nm)) {
            replace(result, receiver_klass);
          }
        } else {
          methodOop method = methodOop(first_word());
          assert(method->is_method(), "first word in interpreter IC must be method");
          if (!Bytecodes::is_super_send(send_code())) {
            // super sends cannot be handled since the sending method holder is unknown at this point.
            LookupKey key(receiver_klass, selector());
            LookupResult result = lookupCache::lookup(&key);
            if (!result.matches(method)) {
              replace(result, receiver_klass);
            }
          }
        }
      }
      break;
    case Bytecodes::polymorphic_send:
      {
        // %implementation note:
        //   when cleaning up we can always preserve the old pic since the
        //   the only transitions are:
        //     (compiled    -> compiled)
        //     (compiled    -> interpreted)
        //     (interpreted -> compiled)
        //   in case of a super send we do not have to cleanup because
        //   no nmethods are compiled for super sends. 
        if (!Bytecodes::is_super_send(send_code())) {
          objArrayOop pic = pic_array();
          for (int index = pic->length(); index > 0; index -= 2) {
            klassOop klass = klassOop(pic->obj_at(index));
            assert(klass->is_klass(), "receiver klass must be klass");
            oop first = pic->obj_at(index-1);
            if (first->is_smi()) {
              jumpTableEntry* entry = (jumpTableEntry*) first;
              nmethod* nm = entry->method();
              LookupResult result = lookupCache::lookup(&nm->key);
              if (!result.matches(nm)) {
                pic->obj_at_put(index-1, result.value());
              }
            } else {
              methodOop method = methodOop(first);
              assert(method->is_method(), "first word in interpreter IC must be method");
              LookupKey key(klass, selector());
              LookupResult result = lookupCache::lookup(&key);
              if (!result.matches(method)) {
                pic->obj_at_put(index-1, result.value());
              }
            }
          }
        }
      }
   }
}

void InterpretedIC::clear_without_deallocation_pic() {
  if (is_empty()) return;
  set(Bytecodes::original_send_code_for(send_code()), oop(selector()), smiOop_zero);
}


void InterpretedIC::replace(nmethod* nm) {
  // replace entry with nm's klass by nm (if entry exists)
  smiOop entry_point = smiOop(nm->jump_table_entry()->entry_point());
  assert(selector() == nm->key.selector(), "mismatched selector");
  if (is_empty()) return;

  switch (send_type()) {
    case Bytecodes::accessor_send:    // fall through
    case Bytecodes::primitive_send:   // fall through
    case Bytecodes::predicted_send:   // fall through
    case Bytecodes::interpreted_send:
      { // replace the monomorphic interpreted send with compiled send
        klassOop receiver_klass = klassOop(second_word());
        assert(receiver_klass->is_klass(), "receiver klass must be a klass");
        if (receiver_klass == nm->key.klass()) {
          set(Bytecodes::compiled_send_code_for(send_code()), entry_point, nm->key.klass());
        }
      }
      break;
    case Bytecodes::compiled_send:   // fall through
    case Bytecodes::megamorphic_send:
      // replace the monomorphic compiled send with compiled send
      set(send_code(), entry_point, nm->key.klass());
      break;
    case Bytecodes::polymorphic_send:
      { objArrayOop pic = pic_array();
        for (int index = pic->length(); index > 0; index -= 2) {
          klassOop receiver_klass = klassOop(pic->obj_at(index));
          assert(receiver_klass->is_klass(), "receiver klass must be klass");
          if (receiver_klass == nm->key.klass()) {
            pic->obj_at_put(index-1, entry_point);
            return;
          } 
        }
      }
      // did not find klass
      break;
    default: fatal("unknown send type");
  }
  LOG_EVENT3("interpreted IC at 0x%x: new nmethod 0x%x for klass 0x%x replaces old entry", this, nm, nm->key.klass());
}


void InterpretedIC::print() {
  std->print("Inline cache (");
  if (is_empty()) {
    std->print("empty");
  } else {
    std->print(Bytecodes::send_type_as_string(send_type()));
  }
  std->print(") ");
  selector()->print_value();
  std->cr();
  InterpretedIC_Iterator it(this);
  while (!it.at_end()) {
    std->print("\t- klass: ");
    it.klass()->print_value();
    if (it.is_interpreted()) {
      std->print(";\tmethod  %#x\n", it.interpreted_method());
    } else {
      std->print(";\tnmethod %#x\n", it.compiled_method());
    }
    it.advance();
  }
}

objArrayOop InterpretedIC::pic_array() {
  assert(send_type() == Bytecodes::polymorphic_send, "Must be a polymorphic send site");
  objArrayOop result = objArrayOop(second_word());  
  assert(result->is_objArray(), "interpreter pic must be object array");
  assert(result->length() >= 4, "pic should contain at least two entries");
  return result;
}

void InterpretedIC::update_inline_cache(InterpretedIC* ic, frame* f, Bytecodes::Code send_code, klassOop klass, LookupResult result) {
    // update inline cache
    if (ic->is_empty() && ic->send_type() != Bytecodes::megamorphic_send) {
      // fill ic for the first time
      Bytecodes::Code new_send_code = Bytecodes::halt;
      if (result.is_entry()) {

        methodOop method = result.method();
        if (UseAccessMethods && Bytecodes::has_access_send_code(send_code) && method->is_accessMethod()) {
          // access method found ==> switch to access send
          new_send_code = Bytecodes::access_send_code_for(send_code);
          ic->set(new_send_code, method, klass);

        } else if (UsePredictedMethods && Bytecodes::has_predicted_send_code(send_code) && method->is_special_primitiveMethod()) {
          // predictable method found ==> switch to predicted send
          // NB: ic of predicted send should be empty so that the compiler knows whether another type occurred or not
          // i.e., {predicted + empty} --> 1 class, {predicted + nonempty} --> 2 klasses (polymorphic)
          // but: this actually doesn't work (yet?) since the interpreter fills the ic on any failure (e.g. overflow)
          new_send_code = method->special_primitive_code();
          method = methodOop(ic->selector()); // ic must stay empty
          klass  = NULL;                     // ic must stay empty
          ic->set(new_send_code, method, klass);

        } else {
          // jump table entry found ==> switch to compiled send
          new_send_code = Bytecodes::compiled_send_code_for(send_code);
          ic->set(new_send_code, oop(result.entry()->entry_point()), klass);
        }
      } else {
        // methodOop found
        methodOop method = result.method();

        if (UseAccessMethods && Bytecodes::has_access_send_code(send_code) && method->is_accessMethod()) {
          // access method found ==> switch to access send
          new_send_code = Bytecodes::access_send_code_for(send_code);

        } else if (UsePredictedMethods && Bytecodes::has_predicted_send_code(send_code) && method->is_special_primitiveMethod()) {
          // predictable method found ==> switch to predicted send
          // NB: ic of predicted send should be empty so that the compiler knows whether another type occurred or not
          // i.e., {predicted + empty} --> 1 class, {predicted + nonempty} --> 2 klasses (polymorphic)
          // but: this actually doesn't work (yet?) since the interpreter fills the ic on any failure (e.g. overflow)
          new_send_code = method->special_primitive_code();
          method = methodOop(ic->selector()); // ic must stay empty
          klass  = NULL;                     // ic must stay empty

        } else if (UsePrimitiveMethods && method->is_primitiveMethod()) {
          // primitive method found ==> switch to primitive send
          new_send_code = Bytecodes::primitive_send_code_for(send_code);
          Unimplemented(); // take this out when all primitive send bytecodes implemented
        
        } else {
          // normal interpreted send ==> do not change
          new_send_code = send_code;
          assert(new_send_code == Bytecodes::original_send_code_for(send_code), "bytecode should not change");
        }
        assert(new_send_code != Bytecodes::halt, "new_send_code not set");
        ic->set(new_send_code, method, klass);
      }
    } else {
      // ic not empty
      switch (ic->send_type()) {
        // monomorphic send
        case Bytecodes::accessor_send   : // fall through
        case Bytecodes::predicted_send  : // fall through
        case Bytecodes::compiled_send   : // fall through
        case Bytecodes::interpreted_send: {
          // switch to polymorphic send with 2 entries
          objArrayOop pic = Interpreter_PICs::allocate(2);
          Interpreter_PICs::set_first(pic, ic->first_word(), ic->second_word());
          Interpreter_PICs::set_second(pic, result.value(), klass);
          ic->set(Bytecodes::polymorphic_send_code_for(send_code), ic->selector(), pic);
          break;
        }

        // polymorphic send
        case Bytecodes::polymorphic_send: {

          objArrayOop old_pic = ic->pic_array();
          objArrayOop new_pic = Interpreter_PICs::extend(old_pic); // add an entry to the PIC if appropriate
          if (new_pic == NULL) {
            // switch to megamorphic send
            if (Bytecodes::is_super_send(send_code)) {
              ic->set(Bytecodes::megamorphic_send_code_for(send_code), result.value(), klass);
            } else {
              ic->set(Bytecodes::megamorphic_send_code_for(send_code), ic->selector(), NULL);
            }
          } else {
            // still a polymorphic send, add entry and set ic to new_pic
            Interpreter_PICs::set_last(new_pic, result.value(), klass);
            ic->set(send_code, ic->selector(), new_pic);
          }
          // recycle old pic
          Interpreter_PICs::deallocate(old_pic);
          break;
        }

        // megamorphic send
        case Bytecodes::megamorphic_send: {
          if (Bytecodes::is_super_send(send_code)) {
            ic->set(send_code, result.value(), klass);
          }
          break;
        }

        default: ShouldNotReachHere();
      }
    }

    // redo send (reset instruction pointer)
    f->set_hp(ic->send_code_addr());
}


extern "C" bool have_nlr_through_C;

void InterpretedIC::does_not_understand(oop receiver, InterpretedIC* ic, frame* f) {
  // message not understood...
  BlockScavenge bs; // make sure that no scavenge happens
  klassOop msgKlass = klassOop(Universe::find_global("Message"));
  oop obj = msgKlass->klass_part()->allocateObject();
  assert(obj->is_mem(), "just checkin'...");
  memOop msg = memOop(obj);
  int nofArgs = ic->selector()->number_of_arguments();
  objArrayOop args = oopFactory::new_objArray(nofArgs);
  for (int i = 1; i <= nofArgs; i++) {
    args->obj_at_put(i, f->expr(nofArgs - i));
  }
  // for now: assume instance variables are there...
  // later: should check this or use a VM interface:
  // msg->set_receiver(recv);
  // msg->set_selector(ic->selector());
  // msg->set_arguments(args);
  msg->raw_at_put(2, receiver);
  msg->raw_at_put(3, ic->selector());
  msg->raw_at_put(4, args);
  symbolOop sel = oopFactory::new_symbol("doesNotUnderstand:");
  if (interpreter_normal_lookup(receiver->klass(), sel).is_empty()) {
    // doesNotUnderstand: not found ==> process error
    { ResourceMark rm;
      std->print("LOOKUP ERROR\n");
      sel->print_value(); std->print(" not found\n");
    }
    if (DeltaProcess::active()->is_scheduler()) {
      DeltaProcess::active()->trace_stack();
      fatal("lookup error in scheduler");
    } else {
      DeltaProcess::active()->suspend(::lookup_error);
    }
    ShouldNotReachHere();
  }
  // return marked result of doesNotUnderstand: message
  oop result = Delta::call(receiver, sel, msg);

  // Solution: use an nmethod-like stub-routine called from
  // within a (possibly one-element) PIC (in order to keep
  // the method selector in the IC. That stub does the
  // Delta:call and pops the right number of arguments
  // taken from the selector (the no. of arguments from
  // the selector can be optimized).
}


void InterpretedIC::trace_inline_cache_miss(InterpretedIC* ic, klassOop klass, LookupResult result) {
  std->print("InterpretedIC lookup (");
  klass->print_value();
  std->print(", ");
  ic->selector()->print_value();
  std->print(") --> ");
  result.print_short_on(std);
  std->cr();
}


// The following routine handles all inline cache misses in the interpreter
// by looking at the ic state and the send byte code issuing the send. The
// inline cache is updated and the send bytecode might be backpatched such
// that it corresponds to the inline cache contents.

void InterpretedIC::inline_cache_miss() {
  NoGCVerifier noGC;  

  // get ic info
  frame           f         = DeltaProcess::active()->last_frame();
  InterpretedIC*  ic        = f.current_interpretedIC();
  Bytecodes::Code send_code = ic->send_code();

  oop receiver = ic->argument_spec() == Bytecodes::args_only // Are we at a self or super send?
               ? f.receiver()                                //  yes: take receiver of frame
               : f.expr(ic->nof_arguments());                //  no:  take receiver pushed before the arguments

  // do the lookup
  klassOop klass = receiver->klass();
  LookupResult result = Bytecodes::is_super_send(send_code)
                      ? interpreter_super_lookup(ic->selector())
                      : interpreter_normal_lookup(klass, ic->selector());

  // tracing
  if (TraceMessageSend) std->print_cr("inline cache miss");
  if (TraceLookup)      trace_inline_cache_miss(ic, klass, result);

  // handle the lookup result
  if (!result.is_empty()) 
    update_inline_cache(ic, &f, send_code, klass, result);
  else {
    does_not_understand(receiver, ic, &f);
    // If the program continues we'll redo the inline_cache_miss
    if (!have_nlr_through_C) inline_cache_miss();
  }
}


// Implementation of InterpretedIC_Iterator

InterpretedIC_Iterator::InterpretedIC_Iterator(InterpretedIC* ic) {
  _ic = ic;
  init_iteration();
}


void InterpretedIC_Iterator::set_klass(oop k) {
  assert(k->is_klass(), "not a klass");
  _klass = klassOop(k);
}


void InterpretedIC_Iterator::set_method(oop m) {
  if (m->is_mem()) {
    assert(m->is_method(), "must be a method");
    _method = (methodOop)m;
    _nm = NULL;
  } else {
    jumpTableEntry* e = (jumpTableEntry*)m;
    _nm = e->method();
    _method = _nm->method();
  }
}


void InterpretedIC_Iterator::init_iteration() {
  _pic = NULL;
  _index = 0;
  // determine initial state
  switch (_ic->send_type()) {
    case Bytecodes::interpreted_send:
      if (_ic->is_empty()) {
        // anamorphic call site (has never been executed => no type information)
        _number_of_targets = 0;
        _info = anamorphic;
      } else {
        // monomorphic call site
        _number_of_targets = 1;
        _info = monomorphic;
        set_klass(_ic->second_word());
        set_method(_ic->first_word());
      }
      break;
    case Bytecodes::compiled_send   : 
      _number_of_targets = 1;
      _info = monomorphic;
      set_klass(_ic->second_word());
      assert(_ic->first_word()->is_smi(), "must have jumpTableEntry");
      set_method(_ic->first_word());
      assert(is_compiled(), "bad type");
      break;
    case Bytecodes::accessor_send   : // fall through
    case Bytecodes::primitive_send  :
      _number_of_targets = 1;
      _info = monomorphic;
      set_klass(_ic->second_word());
      set_method(_ic->first_word());
      assert(is_interpreted(), "bad type");
      break;
    case Bytecodes::megamorphic_send:
      // no type information stored
      _number_of_targets = 0;
      _info = megamorphic;
      break;
    case Bytecodes::polymorphic_send:
      // information on many types
      _pic = objArrayOop(_ic->second_word());
      _number_of_targets = _pic->length() / 2;
      _info = polymorphic;
      set_klass(_pic->obj_at(2));
      set_method(_pic->obj_at(1));
      break;
    case Bytecodes::predicted_send:
      if (_ic->is_empty() || _ic->second_word() == smiKlassObj) {
        _number_of_targets = 1;
        _info = monomorphic;
      } else {
        _number_of_targets = 2;
        _info = polymorphic;
      }
      set_klass(smiKlassObj);
      set_method(interpreter_normal_lookup(smiKlassObj, selector()).value());
      assert(_method != NULL && _method->is_mem(), "this method must be there");
      break;
    default: ShouldNotReachHere();
  }
  assert((number_of_targets() > 1) == (_info == polymorphic), "inconsistency");
}


void InterpretedIC_Iterator::advance() {
  assert(!at_end(), "iterated over the end");
  _index++;
  if (! at_end()) {
    if (_pic != NULL) {
      // polymorphic inline cache 
      int index = _index + 1;   // array is 1-origin
      set_klass (_pic->obj_at(2 * index));
      set_method(_pic->obj_at(2 * index - 1));
    } else {
      // predicted send with non_empty inline cache
      assert(_index < 2, "illegal index");
      set_klass(_ic->second_word());
      set_method(_ic->first_word());
    }
  }
}


methodOop InterpretedIC_Iterator::interpreted_method() const { 
  if (is_interpreted()) {
    methodOop m = (methodOop)_method;
#ifdef ASSERT
    assert(m->is_old(), "methods must be old");
    m->verify();
#endif
    return m; 
  } else {
    return compiled_method()->method();
  }
}


nmethod* InterpretedIC_Iterator::compiled_method() const { 
  if (!is_compiled()) return NULL;  
#ifdef ASSERT 
  if (!_nm->isNMethod()) fatal("not an nmethod"); // cheap test
  // _nm->verify();     // very slow
#endif
  return _nm; 
}


bool InterpretedIC_Iterator::is_super_send() const {
  return Bytecodes::is_super_send(_ic->send_code());
}


void InterpretedIC_Iterator::print() {
  std->print_cr("InterpretedIC_Iterator %#x for ic %#x (%s)", this, _ic, selector()->as_string());
}

  InterpretedIC* as_InterpretedIC(char* address_of_next_instr) {
    return (InterpretedIC*)(address_of_next_instr - InterpretedIC::size);
  }

---