1 /*
   2  * Copyright (c) 1998, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "interpreter/bytecodes.hpp"
  27 #include "interpreter/interpreter.hpp"
  28 #include "interpreter/rewriter.hpp"
  29 #include "memory/metaspaceShared.hpp"
  30 #include "memory/gcLocker.hpp"
  31 #include "memory/resourceArea.hpp"
  32 #include "oops/generateOopMap.hpp"
  33 #include "prims/methodHandles.hpp"
  34 
  35 // Computes a CPC map (new_index -> original_index) for constant pool entries
  36 // that are referred to by the interpreter at runtime via the constant pool cache.
  37 // Also computes a CP map (original_index -> new_index).
  38 // Marks entries in CP which require additional processing.
  39 void Rewriter::compute_index_maps() {
  40   const int length  = _pool->length();
  41   init_maps(length);
  42   bool saw_mh_symbol = false;
  43   for (int i = 0; i < length; i++) {
  44     int tag = _pool->tag_at(i).value();
  45     switch (tag) {
  46       case JVM_CONSTANT_InterfaceMethodref:
  47       case JVM_CONSTANT_Fieldref          : // fall through
  48       case JVM_CONSTANT_Methodref         : // fall through
  49         add_cp_cache_entry(i);
  50         break;
  51       case JVM_CONSTANT_String:
  52       case JVM_CONSTANT_MethodHandle      : // fall through
  53       case JVM_CONSTANT_MethodType        : // fall through
  54         add_resolved_references_entry(i);
  55         break;
  56       case JVM_CONSTANT_Utf8:
  57         if (_pool->symbol_at(i)->equals(vmSymbols::java_lang_invoke_MethodHandle()))
  58           saw_mh_symbol = true;
  59         break;
  60     }
  61   }
  62 
  63   // Record limits of resolved reference map for constant pool cache indices
  64   record_map_limits();
  65 
  66   guarantee((int)_cp_cache_map.length()-1 <= (int)((u2)-1),
  67             "all cp cache indexes fit in a u2");
  68 
  69   if (saw_mh_symbol)
  70     _method_handle_invokers.initialize(length, (int)0);
  71 }
  72 
  73 // Unrewrite the bytecodes if an error occurs.
  74 void Rewriter::restore_bytecodes() {
  75   int len = _methods->length();
  76   bool invokespecial_error = false;
  77 
  78   for (int i = len-1; i >= 0; i--) {
  79     Method* method = _methods->at(i);
  80     scan_method(method, true, &invokespecial_error);
  81     assert(!invokespecial_error, "reversing should not get an invokespecial error");
  82   }
  83 }
  84 
  85 // Creates a constant pool cache given a CPC map
  86 void Rewriter::make_constant_pool_cache(TRAPS) {
  87   ClassLoaderData* loader_data = _pool->pool_holder()->class_loader_data();
  88   ConstantPoolCache* cache =
  89       ConstantPoolCache::allocate(loader_data, _cp_cache_map,
  90                                   _invokedynamic_cp_cache_map,
  91                                   _invokedynamic_references_map, CHECK);
  92 
  93   // initialize object cache in constant pool
  94   _pool->initialize_resolved_references(loader_data, _resolved_references_map,
  95                                         _resolved_reference_limit,
  96                                         CHECK);
  97   _pool->set_cache(cache);
  98   cache->set_constant_pool(_pool());
  99 }
 100 
 101 
 102 
 103 // The new finalization semantics says that registration of
 104 // finalizable objects must be performed on successful return from the
 105 // Object.<init> constructor.  We could implement this trivially if
 106 // <init> were never rewritten but since JVMTI allows this to occur, a
 107 // more complicated solution is required.  A special return bytecode
 108 // is used only by Object.<init> to signal the finalization
 109 // registration point.  Additionally local 0 must be preserved so it's
 110 // available to pass to the registration function.  For simplicty we
 111 // require that local 0 is never overwritten so it's available as an
 112 // argument for registration.
 113 
 114 void Rewriter::rewrite_Object_init(methodHandle method, TRAPS) {
 115   RawBytecodeStream bcs(method);
 116   while (!bcs.is_last_bytecode()) {
 117     Bytecodes::Code opcode = bcs.raw_next();
 118     switch (opcode) {
 119       case Bytecodes::_return: *bcs.bcp() = Bytecodes::_return_register_finalizer; break;
 120 
 121       case Bytecodes::_istore:
 122       case Bytecodes::_lstore:
 123       case Bytecodes::_fstore:
 124       case Bytecodes::_dstore:
 125       case Bytecodes::_astore:
 126         if (bcs.get_index() != 0) continue;
 127 
 128         // fall through
 129       case Bytecodes::_istore_0:
 130       case Bytecodes::_lstore_0:
 131       case Bytecodes::_fstore_0:
 132       case Bytecodes::_dstore_0:
 133       case Bytecodes::_astore_0:
 134         THROW_MSG(vmSymbols::java_lang_IncompatibleClassChangeError(),
 135                   "can't overwrite local 0 in Object.<init>");
 136         break;
 137     }
 138   }
 139 }
 140 
 141 
 142 // Rewrite a classfile-order CP index into a native-order CPC index.
 143 void Rewriter::rewrite_member_reference(address bcp, int offset, bool reverse) {
 144   address p = bcp + offset;
 145   if (!reverse) {
 146     int  cp_index    = Bytes::get_Java_u2(p);
 147     int  cache_index = cp_entry_to_cp_cache(cp_index);
 148     Bytes::put_native_u2(p, cache_index);
 149     if (!_method_handle_invokers.is_empty())
 150       maybe_rewrite_invokehandle(p - 1, cp_index, cache_index, reverse);
 151   } else {
 152     int cache_index = Bytes::get_native_u2(p);
 153     int pool_index = cp_cache_entry_pool_index(cache_index);
 154     Bytes::put_Java_u2(p, pool_index);
 155     if (!_method_handle_invokers.is_empty())
 156       maybe_rewrite_invokehandle(p - 1, pool_index, cache_index, reverse);
 157   }
 158 }
 159 
 160 // If the constant pool entry for invokespecial is InterfaceMethodref,
 161 // we need to add a separate cpCache entry for its resolution, because it is
 162 // different than the resolution for invokeinterface with InterfaceMethodref.
 163 // These cannot share cpCache entries.  It's unclear if all invokespecial to
 164 // InterfaceMethodrefs would resolve to the same thing so a new cpCache entry
 165 // is created for each one.  This was added with lambda.
 166 void Rewriter::rewrite_invokespecial(address bcp, int offset, bool reverse, bool* invokespecial_error) {
 167   address p = bcp + offset;
 168   if (!reverse) {
 169     int cp_index = Bytes::get_Java_u2(p);
 170     if (_pool->tag_at(cp_index).is_interface_method()) {
 171       int cache_index = add_invokespecial_cp_cache_entry(cp_index);
 172       if (cache_index != (int)(jushort) cache_index) {
 173         *invokespecial_error = true;
 174       }
 175       Bytes::put_native_u2(p, cache_index);
 176     } else {
 177       rewrite_member_reference(bcp, offset, reverse);
 178     }
 179   } else {
 180     rewrite_member_reference(bcp, offset, reverse);
 181   }
 182 }
 183 
 184 
 185 // Adjust the invocation bytecode for a signature-polymorphic method (MethodHandle.invoke, etc.)
 186 void Rewriter::maybe_rewrite_invokehandle(address opc, int cp_index, int cache_index, bool reverse) {
 187   if (!reverse) {
 188     if ((*opc) == (u1)Bytecodes::_invokevirtual ||
 189         // allow invokespecial as an alias, although it would be very odd:
 190         (*opc) == (u1)Bytecodes::_invokespecial) {
 191       assert(_pool->tag_at(cp_index).is_method(), "wrong index");
 192       // Determine whether this is a signature-polymorphic method.
 193       if (cp_index >= _method_handle_invokers.length())  return;
 194       int status = _method_handle_invokers[cp_index];
 195       assert(status >= -1 && status <= 1, "oob tri-state");
 196       if (status == 0) {
 197         if (_pool->klass_ref_at_noresolve(cp_index)->equals(vmSymbols::java_lang_invoke_MethodHandle()) &&
 198             MethodHandles::is_signature_polymorphic_name(SystemDictionary::MethodHandle_klass(),
 199                                                          _pool->name_ref_at(cp_index))) {
 200           // we may need a resolved_refs entry for the appendix
 201           add_invokedynamic_resolved_references_entries(cp_index, cache_index);
 202           status = +1;
 203         } else {
 204           status = -1;
 205         }
 206         _method_handle_invokers[cp_index] = status;
 207       }
 208       // We use a special internal bytecode for such methods (if non-static).
 209       // The basic reason for this is that such methods need an extra "appendix" argument
 210       // to transmit the call site's intended call type.
 211       if (status > 0) {
 212         (*opc) = (u1)Bytecodes::_invokehandle;
 213       }
 214     }
 215   } else {
 216     // Do not need to look at cp_index.
 217     if ((*opc) == (u1)Bytecodes::_invokehandle) {
 218       (*opc) = (u1)Bytecodes::_invokevirtual;
 219       // Ignore corner case of original _invokespecial instruction.
 220       // This is safe because (a) the signature polymorphic method was final, and
 221       // (b) the implementation of MethodHandle will not call invokespecial on it.
 222     }
 223   }
 224 }
 225 
 226 
 227 void Rewriter::rewrite_invokedynamic(address bcp, int offset, bool reverse) {
 228   address p = bcp + offset;
 229   assert(p[-1] == Bytecodes::_invokedynamic, "not invokedynamic bytecode");
 230   if (!reverse) {
 231     int cp_index = Bytes::get_Java_u2(p);
 232     int cache_index = add_invokedynamic_cp_cache_entry(cp_index);
 233     int resolved_index = add_invokedynamic_resolved_references_entries(cp_index, cache_index);
 234     // Replace the trailing four bytes with a CPC index for the dynamic
 235     // call site.  Unlike other CPC entries, there is one per bytecode,
 236     // not just one per distinct CP entry.  In other words, the
 237     // CPC-to-CP relation is many-to-one for invokedynamic entries.
 238     // This means we must use a larger index size than u2 to address
 239     // all these entries.  That is the main reason invokedynamic
 240     // must have a five-byte instruction format.  (Of course, other JVM
 241     // implementations can use the bytes for other purposes.)
 242     // Note: We use native_u4 format exclusively for 4-byte indexes.
 243     Bytes::put_native_u4(p, ConstantPool::encode_invokedynamic_index(cache_index));
 244     // add the bcp in case we need to patch this bytecode if we also find a
 245     // invokespecial/InterfaceMethodref in the bytecode stream
 246     _patch_invokedynamic_bcps->push(p);
 247     _patch_invokedynamic_refs->push(resolved_index);
 248   } else {
 249     int cache_index = ConstantPool::decode_invokedynamic_index(
 250                         Bytes::get_native_u4(p));
 251     // We will reverse the bytecode rewriting _after_ adjusting them.
 252     // Adjust the cache index by offset to the invokedynamic entries in the
 253     // cpCache plus the delta if the invokedynamic bytecodes were adjusted.
 254     int adjustment = cp_cache_delta() + _first_iteration_cp_cache_limit;
 255     int cp_index = invokedynamic_cp_cache_entry_pool_index(cache_index - adjustment);
 256     assert(_pool->tag_at(cp_index).is_invoke_dynamic(), "wrong index");
 257     // zero out 4 bytes
 258     Bytes::put_Java_u4(p, 0);
 259     Bytes::put_Java_u2(p, cp_index);
 260   }
 261 }
 262 
 263 void Rewriter::patch_invokedynamic_bytecodes() {
 264   // If the end of the cp_cache is the same as after initializing with the
 265   // cpool, nothing needs to be done.  Invokedynamic bytecodes are at the
 266   // correct offsets. ie. no invokespecials added
 267   int delta = cp_cache_delta();
 268   if (delta > 0) {
 269     int length = _patch_invokedynamic_bcps->length();
 270     assert(length == _patch_invokedynamic_refs->length(),
 271            "lengths should match");
 272     for (int i = 0; i < length; i++) {
 273       address p = _patch_invokedynamic_bcps->at(i);
 274       int cache_index = ConstantPool::decode_invokedynamic_index(
 275                           Bytes::get_native_u4(p));
 276       Bytes::put_native_u4(p, ConstantPool::encode_invokedynamic_index(cache_index + delta));
 277 
 278       // invokedynamic resolved references map also points to cp cache and must
 279       // add delta to each.
 280       int resolved_index = _patch_invokedynamic_refs->at(i);
 281       for (int entry = 0; entry < ConstantPoolCacheEntry::_indy_resolved_references_entries; entry++) {
 282         assert(_invokedynamic_references_map[resolved_index+entry] == cache_index,
 283              "should be the same index");
 284         _invokedynamic_references_map.at_put(resolved_index+entry,
 285                                              cache_index + delta);
 286       }
 287     }
 288   }
 289 }
 290 
 291 
 292 // Rewrite some ldc bytecodes to _fast_aldc
 293 void Rewriter::maybe_rewrite_ldc(address bcp, int offset, bool is_wide,
 294                                  bool reverse) {
 295   if (!reverse) {
 296     assert((*bcp) == (is_wide ? Bytecodes::_ldc_w : Bytecodes::_ldc), "not ldc bytecode");
 297     address p = bcp + offset;
 298     int cp_index = is_wide ? Bytes::get_Java_u2(p) : (u1)(*p);
 299     constantTag tag = _pool->tag_at(cp_index).value();
 300     if (tag.is_method_handle() || tag.is_method_type() || tag.is_string()) {
 301       int ref_index = cp_entry_to_resolved_references(cp_index);
 302       if (is_wide) {
 303         (*bcp) = Bytecodes::_fast_aldc_w;
 304         assert(ref_index == (u2)ref_index, "index overflow");
 305         Bytes::put_native_u2(p, ref_index);
 306       } else {
 307         (*bcp) = Bytecodes::_fast_aldc;
 308         assert(ref_index == (u1)ref_index, "index overflow");
 309         (*p) = (u1)ref_index;
 310       }
 311     }
 312   } else {
 313     Bytecodes::Code rewritten_bc =
 314               (is_wide ? Bytecodes::_fast_aldc_w : Bytecodes::_fast_aldc);
 315     if ((*bcp) == rewritten_bc) {
 316       address p = bcp + offset;
 317       int ref_index = is_wide ? Bytes::get_native_u2(p) : (u1)(*p);
 318       int pool_index = resolved_references_entry_to_pool_index(ref_index);
 319       if (is_wide) {
 320         (*bcp) = Bytecodes::_ldc_w;
 321         assert(pool_index == (u2)pool_index, "index overflow");
 322         Bytes::put_Java_u2(p, pool_index);
 323       } else {
 324         (*bcp) = Bytecodes::_ldc;
 325         assert(pool_index == (u1)pool_index, "index overflow");
 326         (*p) = (u1)pool_index;
 327       }
 328     }
 329   }
 330 }
 331 
 332 
 333 // Rewrites a method given the index_map information
 334 void Rewriter::scan_method(Method* method, bool reverse, bool* invokespecial_error) {
 335 
 336   int nof_jsrs = 0;
 337   bool has_monitor_bytecodes = false;
 338 
 339   {
 340     // We cannot tolerate a GC in this block, because we've
 341     // cached the bytecodes in 'code_base'. If the Method*
 342     // moves, the bytecodes will also move.
 343     No_Safepoint_Verifier nsv;
 344     Bytecodes::Code c;
 345 
 346     // Bytecodes and their length
 347     const address code_base = method->code_base();
 348     const int code_length = method->code_size();
 349 
 350     int bc_length;
 351     for (int bci = 0; bci < code_length; bci += bc_length) {
 352       address bcp = code_base + bci;
 353       int prefix_length = 0;
 354       c = (Bytecodes::Code)(*bcp);
 355 
 356       // Since we have the code, see if we can get the length
 357       // directly. Some more complicated bytecodes will report
 358       // a length of zero, meaning we need to make another method
 359       // call to calculate the length.
 360       bc_length = Bytecodes::length_for(c);
 361       if (bc_length == 0) {
 362         bc_length = Bytecodes::length_at(method, bcp);
 363 
 364         // length_at will put us at the bytecode after the one modified
 365         // by 'wide'. We don't currently examine any of the bytecodes
 366         // modified by wide, but in case we do in the future...
 367         if (c == Bytecodes::_wide) {
 368           prefix_length = 1;
 369           c = (Bytecodes::Code)bcp[1];
 370         }
 371       }
 372 
 373       assert(bc_length != 0, "impossible bytecode length");
 374 
 375       switch (c) {
 376         case Bytecodes::_lookupswitch   : {
 377 #ifndef CC_INTERP
 378           Bytecode_lookupswitch bc(method, bcp);
 379           (*bcp) = (
 380             bc.number_of_pairs() < BinarySwitchThreshold
 381             ? Bytecodes::_fast_linearswitch
 382             : Bytecodes::_fast_binaryswitch
 383           );
 384 #endif
 385           break;
 386         }
 387         case Bytecodes::_fast_linearswitch:
 388         case Bytecodes::_fast_binaryswitch: {
 389 #ifndef CC_INTERP
 390           (*bcp) = Bytecodes::_lookupswitch;
 391 #endif
 392           break;
 393         }
 394 
 395         case Bytecodes::_invokespecial  : {
 396           rewrite_invokespecial(bcp, prefix_length+1, reverse, invokespecial_error);
 397           break;
 398         }
 399 
 400         case Bytecodes::_getstatic      : // fall through
 401         case Bytecodes::_putstatic      : // fall through
 402         case Bytecodes::_getfield       : // fall through
 403         case Bytecodes::_putfield       : // fall through
 404         case Bytecodes::_invokevirtual  : // fall through
 405         case Bytecodes::_invokestatic   :
 406         case Bytecodes::_invokeinterface:
 407         case Bytecodes::_invokehandle   : // if reverse=true
 408           rewrite_member_reference(bcp, prefix_length+1, reverse);
 409           break;
 410         case Bytecodes::_invokedynamic:
 411           rewrite_invokedynamic(bcp, prefix_length+1, reverse);
 412           break;
 413         case Bytecodes::_ldc:
 414         case Bytecodes::_fast_aldc:  // if reverse=true
 415           maybe_rewrite_ldc(bcp, prefix_length+1, false, reverse);
 416           break;
 417         case Bytecodes::_ldc_w:
 418         case Bytecodes::_fast_aldc_w:  // if reverse=true
 419           maybe_rewrite_ldc(bcp, prefix_length+1, true, reverse);
 420           break;
 421         case Bytecodes::_jsr            : // fall through
 422         case Bytecodes::_jsr_w          : nof_jsrs++;                   break;
 423         case Bytecodes::_monitorenter   : // fall through
 424         case Bytecodes::_monitorexit    : has_monitor_bytecodes = true; break;
 425       }
 426     }
 427   }
 428 
 429   // Update access flags
 430   if (has_monitor_bytecodes) {
 431     method->set_has_monitor_bytecodes();
 432   }
 433 
 434   // The present of a jsr bytecode implies that the method might potentially
 435   // have to be rewritten, so we run the oopMapGenerator on the method
 436   if (nof_jsrs > 0) {
 437     method->set_has_jsrs();
 438     // Second pass will revisit this method.
 439     assert(method->has_jsrs(), "didn't we just set this?");
 440   }
 441 }
 442 
 443 // After constant pool is created, revisit methods containing jsrs.
 444 methodHandle Rewriter::rewrite_jsrs(methodHandle method, TRAPS) {
 445   ResourceMark rm(THREAD);
 446   ResolveOopMapConflicts romc(method);
 447   methodHandle original_method = method;
 448   method = romc.do_potential_rewrite(CHECK_(methodHandle()));
 449   // Update monitor matching info.
 450   if (romc.monitor_safe()) {
 451     method->set_guaranteed_monitor_matching();
 452   }
 453 
 454   return method;
 455 }
 456 
 457 void Rewriter::rewrite_bytecodes(TRAPS) {
 458   assert(_pool->cache() == NULL, "constant pool cache must not be set yet");
 459 
 460   // determine index maps for Method* rewriting
 461   compute_index_maps();
 462 
 463   if (RegisterFinalizersAtInit && _klass->name()->equals(vmSymbols::java_lang_Object())) {
 464     bool did_rewrite = false;
 465     int i = _methods->length();
 466     while (i-- > 0) {
 467       Method* method = _methods->at(i);
 468       if (method->intrinsic_id() == vmIntrinsics::_Object_init) {
 469         // rewrite the return bytecodes of Object.<init> to register the
 470         // object for finalization if needed.
 471         methodHandle m(THREAD, method);
 472         rewrite_Object_init(m, CHECK);
 473         did_rewrite = true;
 474         break;
 475       }
 476     }
 477     assert(did_rewrite, "must find Object::<init> to rewrite it");
 478   }
 479 
 480   // rewrite methods, in two passes
 481   int len = _methods->length();
 482   bool invokespecial_error = false;
 483 
 484   for (int i = len-1; i >= 0; i--) {
 485     Method* method = _methods->at(i);
 486     scan_method(method, false, &invokespecial_error);
 487     if (invokespecial_error) {
 488       // If you get an error here, there is no reversing bytecodes
 489       // This exception is stored for this class and no further attempt is
 490       // made at verifying or rewriting.
 491       THROW_MSG(vmSymbols::java_lang_InternalError(),
 492                 "This classfile overflows invokespecial for interfaces "
 493                 "and cannot be loaded");
 494       return;
 495      }
 496   }
 497 
 498   // May have to fix invokedynamic bytecodes if invokestatic/InterfaceMethodref
 499   // entries had to be added.
 500   patch_invokedynamic_bytecodes();
 501 }
 502 
 503 void Rewriter::rewrite(instanceKlassHandle klass, TRAPS) {
 504   if (!DumpSharedSpaces) {
 505     assert(!MetaspaceShared::is_in_shared_space(klass()), "archive methods must not be rewritten at run time");
 506   }
 507   ResourceMark rm(THREAD);
 508   Rewriter     rw(klass, klass->constants(), klass->methods(), CHECK);
 509   // (That's all, folks.)
 510 }
 511 
 512 Rewriter::Rewriter(instanceKlassHandle klass, constantPoolHandle cpool, Array<Method*>* methods, TRAPS)
 513   : _klass(klass),
 514     _pool(cpool),
 515     _methods(methods)
 516 {
 517 
 518   // Rewrite bytecodes - exception here exits.
 519   rewrite_bytecodes(CHECK);
 520 
 521   // Stress restoring bytecodes
 522   if (StressRewriter) {
 523     restore_bytecodes();
 524     rewrite_bytecodes(CHECK);
 525   }
 526 
 527   // allocate constant pool cache, now that we've seen all the bytecodes
 528   make_constant_pool_cache(THREAD);
 529 
 530   // Restore bytecodes to their unrewritten state if there are exceptions
 531   // rewriting bytecodes or allocating the cpCache
 532   if (HAS_PENDING_EXCEPTION) {
 533     restore_bytecodes();
 534     return;
 535   }
 536 
 537   // Relocate after everything, but still do this under the is_rewritten flag,
 538   // so methods with jsrs in custom class lists in aren't attempted to be
 539   // rewritten in the RO section of the shared archive.
 540   // Relocated bytecodes don't have to be restored, only the cp cache entries
 541   int len = _methods->length();
 542   for (int i = len-1; i >= 0; i--) {
 543     methodHandle m(THREAD, _methods->at(i));
 544 
 545     if (m->has_jsrs()) {
 546       m = rewrite_jsrs(m, THREAD);
 547       // Restore bytecodes to their unrewritten state if there are exceptions
 548       // relocating bytecodes.  If some are relocated, that is ok because that
 549       // doesn't affect constant pool to cpCache rewriting.
 550       if (HAS_PENDING_EXCEPTION) {
 551         restore_bytecodes();
 552         return;
 553       }
 554       // Method might have gotten rewritten.
 555       methods->at_put(i, m());
 556     }
 557   }
 558 }