1 /*
  2  * Copyright (c) 1998, 2021, 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 "ci/ciMethod.hpp"
 27 #include "ci/ciMethodBlocks.hpp"
 28 #include "ci/ciStreams.hpp"
 29 #include "classfile/vmIntrinsics.hpp"
 30 #include "compiler/methodLiveness.hpp"
 31 #include "interpreter/bytecode.hpp"
 32 #include "interpreter/bytecodes.hpp"
 33 #include "memory/allocation.inline.hpp"
 34 #include "memory/resourceArea.hpp"
 35 #include "utilities/bitMap.inline.hpp"
 36 
 37 // The MethodLiveness class performs a simple liveness analysis on a method
 38 // in order to decide which locals are live (that is, will be used again) at
 39 // a particular bytecode index (bci).
 40 //
 41 // The algorithm goes:
 42 //
 43 // 1. Break the method into a set of basic blocks.  For each basic block we
 44 //    also keep track of its set of predecessors through normal control flow
 45 //    and predecessors through exceptional control flow.
 46 //
 47 // 2. For each basic block, compute two sets, gen (the set of values used before
 48 //    they are defined) and kill (the set of values defined before they are used)
 49 //    in the basic block.  A basic block "needs" the locals in its gen set to
 50 //    perform its computation.  A basic block "provides" values for the locals in
 51 //    its kill set, allowing a need from a successor to be ignored.
 52 //
 53 // 3. Liveness information (the set of locals which are needed) is pushed backwards through
 54 //    the program, from blocks to their predecessors.  We compute and store liveness
 55 //    information for the normal/exceptional exit paths for each basic block.  When
 56 //    this process reaches a fixed point, we are done.
 57 //
 58 // 4. When we are asked about the liveness at a particular bci with a basic block, we
 59 //    compute gen/kill sets which represent execution from that bci to the exit of
 60 //    its blocks.  We then compose this range gen/kill information with the normal
 61 //    and exceptional exit information for the block to produce liveness information
 62 //    at that bci.
 63 //
 64 // The algorithm is approximate in many respects.  Notably:
 65 //
 66 // 1. We do not do the analysis necessary to match jsr's with the appropriate ret.
 67 //    Instead we make the conservative assumption that any ret can return to any
 68 //    jsr return site.
 69 // 2. Instead of computing the effects of exceptions at every instruction, we
 70 //    summarize the effects of all exceptional continuations from the block as
 71 //    a single set (_exception_exit), losing some information but simplifying the
 72 //    analysis.
 73 
 74 MethodLiveness::MethodLiveness(Arena* arena, ciMethod* method)
 75 #ifdef COMPILER1
 76   : _bci_block_start(arena, method->code_size())
 77 #endif
 78 {
 79   _arena = arena;
 80   _method = method;
 81   _bit_map_size_bits = method->max_locals();
 82 }
 83 
 84 void MethodLiveness::compute_liveness() {
 85 #ifndef PRODUCT
 86   if (TraceLivenessGen) {
 87     tty->print_cr("################################################################");
 88     tty->print("# Computing liveness information for ");
 89     method()->print_short_name();
 90   }
 91 #endif
 92 
 93   init_basic_blocks();
 94   init_gen_kill();
 95   propagate_liveness();
 96 }
 97 
 98 
 99 void MethodLiveness::init_basic_blocks() {
100   int method_len = method()->code_size();
101   ciMethodBlocks *mblocks = method()->get_method_blocks();
102 
103   // Create an array to store the bci->BasicBlock mapping.
104   _block_map = new (arena()) GrowableArray<BasicBlock*>(arena(), method_len, method_len, NULL);
105 
106   _block_count = mblocks->num_blocks();
107   _block_list = (BasicBlock **) arena()->Amalloc(sizeof(BasicBlock *) * _block_count);
108 
109   // Used for patching up jsr/ret control flow.
110   GrowableArray<BasicBlock*>* jsr_exit_list = new GrowableArray<BasicBlock*>(5);
111   GrowableArray<BasicBlock*>* ret_list = new GrowableArray<BasicBlock*>(5);
112 
113   // generate our block list from ciMethodBlocks
114   for (int blk = 0; blk < _block_count; blk++) {
115     ciBlock *cib = mblocks->block(blk);
116      int start_bci = cib->start_bci();
117     _block_list[blk] = new (arena()) BasicBlock(this, start_bci, cib->limit_bci());
118     _block_map->at_put(start_bci, _block_list[blk]);
119 #ifdef COMPILER1
120     // mark all bcis where a new basic block starts
121     _bci_block_start.set_bit(start_bci);
122 #endif // COMPILER1
123   }
124   // fill in the predecessors of blocks
125   ciBytecodeStream bytes(method());
126 
127   for (int blk = 0; blk < _block_count; blk++) {
128     BasicBlock *current_block = _block_list[blk];
129     int bci =  mblocks->block(blk)->control_bci();
130 
131     if (bci == ciBlock::fall_through_bci) {
132       int limit = current_block->limit_bci();
133       if (limit < method_len) {
134         BasicBlock *next = _block_map->at(limit);
135         assert( next != NULL, "must be a block immediately following this one.");
136         next->add_normal_predecessor(current_block);
137       }
138       continue;
139     }
140     bytes.reset_to_bci(bci);
141     Bytecodes::Code code = bytes.next();
142     BasicBlock *dest;
143 
144     // Now we need to interpret the instruction's effect
145     // on control flow.
146     assert (current_block != NULL, "we must have a current block");
147     switch (code) {
148       case Bytecodes::_ifeq:
149       case Bytecodes::_ifne:
150       case Bytecodes::_iflt:
151       case Bytecodes::_ifge:
152       case Bytecodes::_ifgt:
153       case Bytecodes::_ifle:
154       case Bytecodes::_if_icmpeq:
155       case Bytecodes::_if_icmpne:
156       case Bytecodes::_if_icmplt:
157       case Bytecodes::_if_icmpge:
158       case Bytecodes::_if_icmpgt:
159       case Bytecodes::_if_icmple:
160       case Bytecodes::_if_acmpeq:
161       case Bytecodes::_if_acmpne:
162       case Bytecodes::_ifnull:
163       case Bytecodes::_ifnonnull:
164         // Two way branch.  Set predecessors at each destination.
165         dest = _block_map->at(bytes.next_bci());
166         assert(dest != NULL, "must be a block immediately following this one.");
167         dest->add_normal_predecessor(current_block);
168 
169         dest = _block_map->at(bytes.get_dest());
170         assert(dest != NULL, "branch desination must start a block.");
171         dest->add_normal_predecessor(current_block);
172         break;
173       case Bytecodes::_goto:
174         dest = _block_map->at(bytes.get_dest());
175         assert(dest != NULL, "branch desination must start a block.");
176         dest->add_normal_predecessor(current_block);
177         break;
178       case Bytecodes::_goto_w:
179         dest = _block_map->at(bytes.get_far_dest());
180         assert(dest != NULL, "branch desination must start a block.");
181         dest->add_normal_predecessor(current_block);
182         break;
183       case Bytecodes::_tableswitch:
184         {
185           Bytecode_tableswitch tableswitch(&bytes);
186 
187           int len = tableswitch.length();
188 
189           dest = _block_map->at(bci + tableswitch.default_offset());
190           assert(dest != NULL, "branch desination must start a block.");
191           dest->add_normal_predecessor(current_block);
192           while (--len >= 0) {
193             dest = _block_map->at(bci + tableswitch.dest_offset_at(len));
194             assert(dest != NULL, "branch desination must start a block.");
195             dest->add_normal_predecessor(current_block);
196           }
197           break;
198         }
199 
200       case Bytecodes::_lookupswitch:
201         {
202           Bytecode_lookupswitch lookupswitch(&bytes);
203 
204           int npairs = lookupswitch.number_of_pairs();
205 
206           dest = _block_map->at(bci + lookupswitch.default_offset());
207           assert(dest != NULL, "branch desination must start a block.");
208           dest->add_normal_predecessor(current_block);
209           while(--npairs >= 0) {
210             LookupswitchPair pair = lookupswitch.pair_at(npairs);
211             dest = _block_map->at( bci + pair.offset());
212             assert(dest != NULL, "branch desination must start a block.");
213             dest->add_normal_predecessor(current_block);
214           }
215           break;
216         }
217 
218       case Bytecodes::_jsr:
219         {
220           assert(bytes.is_wide()==false, "sanity check");
221           dest = _block_map->at(bytes.get_dest());
222           assert(dest != NULL, "branch desination must start a block.");
223           dest->add_normal_predecessor(current_block);
224           BasicBlock *jsrExit = _block_map->at(current_block->limit_bci());
225           assert(jsrExit != NULL, "jsr return bci must start a block.");
226           jsr_exit_list->append(jsrExit);
227           break;
228         }
229       case Bytecodes::_jsr_w:
230         {
231           dest = _block_map->at(bytes.get_far_dest());
232           assert(dest != NULL, "branch desination must start a block.");
233           dest->add_normal_predecessor(current_block);
234           BasicBlock *jsrExit = _block_map->at(current_block->limit_bci());
235           assert(jsrExit != NULL, "jsr return bci must start a block.");
236           jsr_exit_list->append(jsrExit);
237           break;
238         }
239 
240       case Bytecodes::_wide:
241         assert(false, "wide opcodes should not be seen here");
242         break;
243       case Bytecodes::_athrow:
244       case Bytecodes::_ireturn:
245       case Bytecodes::_lreturn:
246       case Bytecodes::_freturn:
247       case Bytecodes::_dreturn:
248       case Bytecodes::_areturn:
249       case Bytecodes::_return:
250         // These opcodes are  not the normal predecessors of any other opcodes.
251         break;
252       case Bytecodes::_ret:
253         // We will patch up jsr/rets in a subsequent pass.
254         ret_list->append(current_block);
255         break;
256       default:
257         // Do nothing.
258         break;
259     }
260   }
261   // Patch up the jsr/ret's.  We conservatively assume that any ret
262   // can return to any jsr site.
263   int ret_list_len = ret_list->length();
264   int jsr_exit_list_len = jsr_exit_list->length();
265   if (ret_list_len > 0 && jsr_exit_list_len > 0) {
266     for (int i = jsr_exit_list_len - 1; i >= 0; i--) {
267       BasicBlock *jsrExit = jsr_exit_list->at(i);
268       for (int i = ret_list_len - 1; i >= 0; i--) {
269         jsrExit->add_normal_predecessor(ret_list->at(i));
270       }
271     }
272   }
273 
274   // Compute exception edges.
275   for (int b=_block_count-1; b >= 0; b--) {
276     BasicBlock *block = _block_list[b];
277     int block_start = block->start_bci();
278     int block_limit = block->limit_bci();
279     ciExceptionHandlerStream handlers(method());
280     for (; !handlers.is_done(); handlers.next()) {
281       ciExceptionHandler* handler = handlers.handler();
282       int start       = handler->start();
283       int limit       = handler->limit();
284       int handler_bci = handler->handler_bci();
285 
286       int intersect_start = MAX2(block_start, start);
287       int intersect_limit = MIN2(block_limit, limit);
288       if (intersect_start < intersect_limit) {
289         // The catch range has a nonempty intersection with this
290         // basic block.  That means this basic block can be an
291         // exceptional predecessor.
292         _block_map->at(handler_bci)->add_exception_predecessor(block);
293 
294         if (handler->is_catch_all()) {
295           // This is a catch-all block.
296           if (intersect_start == block_start && intersect_limit == block_limit) {
297             // The basic block is entirely contained in this catch-all block.
298             // Skip the rest of the exception handlers -- they can never be
299             // reached in execution.
300             break;
301           }
302         }
303       }
304     }
305   }
306 }
307 
308 void MethodLiveness::init_gen_kill() {
309   for (int i=_block_count-1; i >= 0; i--) {
310     _block_list[i]->compute_gen_kill(method());
311   }
312 }
313 
314 void MethodLiveness::propagate_liveness() {
315   int num_blocks = _block_count;
316   BasicBlock *block;
317 
318   // We start our work list off with all blocks in it.
319   // Alternately, we could start off the work list with the list of all
320   // blocks which could exit the method directly, along with one block
321   // from any infinite loop.  If this matters, it can be changed.  It
322   // may not be clear from looking at the code, but the order of the
323   // workList will be the opposite of the creation order of the basic
324   // blocks, which should be decent for quick convergence (with the
325   // possible exception of exception handlers, which are all created
326   // early).
327   _work_list = NULL;
328   for (int i = 0; i < num_blocks; i++) {
329     block = _block_list[i];
330     block->set_next(_work_list);
331     block->set_on_work_list(true);
332     _work_list = block;
333   }
334 
335 
336   while ((block = work_list_get()) != NULL) {
337     block->propagate(this);
338   }
339 }
340 
341 void MethodLiveness::work_list_add(BasicBlock *block) {
342   if (!block->on_work_list()) {
343     block->set_next(_work_list);
344     block->set_on_work_list(true);
345     _work_list = block;
346   }
347 }
348 
349 MethodLiveness::BasicBlock *MethodLiveness::work_list_get() {
350   BasicBlock *block = _work_list;
351   if (block != NULL) {
352     block->set_on_work_list(false);
353     _work_list = block->next();
354   }
355   return block;
356 }
357 
358 
359 MethodLivenessResult MethodLiveness::get_liveness_at(int entry_bci) {
360   int bci = entry_bci;
361   bool is_entry = false;
362   if (entry_bci == InvocationEntryBci) {
363     is_entry = true;
364     bci = 0;
365   }
366 
367   MethodLivenessResult answer;
368 
369   if (_block_count > 0) {
370 
371     assert( 0 <= bci && bci < method()->code_size(), "bci out of range" );
372     BasicBlock *block = _block_map->at(bci);
373     // We may not be at the block start, so search backwards to find the block
374     // containing bci.
375     int t = bci;
376     while (block == NULL && t > 0) {
377      block = _block_map->at(--t);
378     }
379     guarantee(block != NULL, "invalid bytecode index; must be instruction index");
380     assert(bci >= block->start_bci() && bci < block->limit_bci(), "block must contain bci.");
381 
382     answer = block->get_liveness_at(method(), bci);
383 
384     if (is_entry && method()->is_synchronized() && !method()->is_static()) {
385       // Synchronized methods use the receiver once on entry.
386       answer.at_put(0, true);
387     }
388 
389 #ifndef PRODUCT
390     if (TraceLivenessQuery) {
391       tty->print("Liveness query of ");
392       method()->print_short_name();
393       tty->print(" @ %d : result is ", bci);
394       answer.print_on(tty);
395     }
396 #endif
397   }
398 
399   return answer;
400 }
401 
402 MethodLiveness::BasicBlock::BasicBlock(MethodLiveness *analyzer, int start, int limit) :
403          _entry(analyzer->arena(),          analyzer->bit_map_size_bits()),
404          _normal_exit(analyzer->arena(),    analyzer->bit_map_size_bits()),
405          _exception_exit(analyzer->arena(), analyzer->bit_map_size_bits()),
406          _gen(analyzer->arena(),            analyzer->bit_map_size_bits()),
407          _kill(analyzer->arena(),           analyzer->bit_map_size_bits()),
408          _last_bci(-1) {
409   _analyzer = analyzer;
410   _start_bci = start;
411   _limit_bci = limit;
412   _normal_predecessors =
413     new (analyzer->arena()) GrowableArray<MethodLiveness::BasicBlock*>(analyzer->arena(), 5, 0, NULL);
414   _exception_predecessors =
415     new (analyzer->arena()) GrowableArray<MethodLiveness::BasicBlock*>(analyzer->arena(), 5, 0, NULL);
416 }
417 
418 
419 
420 MethodLiveness::BasicBlock *MethodLiveness::BasicBlock::split(int split_bci) {
421   int start = _start_bci;
422   int limit = _limit_bci;
423 
424   if (TraceLivenessGen) {
425     tty->print_cr(" ** Splitting block (%d,%d) at %d", start, limit, split_bci);
426   }
427 
428   GrowableArray<BasicBlock*>* save_predecessors = _normal_predecessors;
429 
430   assert (start < split_bci && split_bci < limit, "improper split");
431 
432   // Make a new block to cover the first half of the range.
433   BasicBlock *first_half = new (_analyzer->arena()) BasicBlock(_analyzer, start, split_bci);
434 
435   // Assign correct values to the second half (this)
436   _normal_predecessors = first_half->_normal_predecessors;
437   _start_bci = split_bci;
438   add_normal_predecessor(first_half);
439 
440   // Assign correct predecessors to the new first half
441   first_half->_normal_predecessors = save_predecessors;
442 
443   return first_half;
444 }
445 
446 void MethodLiveness::BasicBlock::compute_gen_kill(ciMethod* method) {
447   ciBytecodeStream bytes(method);
448   bytes.reset_to_bci(start_bci());
449   bytes.set_max_bci(limit_bci());
450   compute_gen_kill_range(&bytes);
451 
452 }
453 
454 void MethodLiveness::BasicBlock::compute_gen_kill_range(ciBytecodeStream *bytes) {
455   _gen.clear();
456   _kill.clear();
457 
458   while (bytes->next() != ciBytecodeStream::EOBC()) {
459     compute_gen_kill_single(bytes);
460   }
461 }
462 
463 void MethodLiveness::BasicBlock::compute_gen_kill_single(ciBytecodeStream *instruction) {
464   // We prohibit _gen and _kill from having locals in common.  If we
465   // know that one is definitely going to be applied before the other,
466   // we could save some computation time by relaxing this prohibition.
467 
468   switch (instruction->cur_bc()) {
469     case Bytecodes::_nop:
470     case Bytecodes::_goto:
471     case Bytecodes::_goto_w:
472     case Bytecodes::_aconst_null:
473     case Bytecodes::_new:
474     case Bytecodes::_aconst_init:
475     case Bytecodes::_withfield:
476     case Bytecodes::_iconst_m1:
477     case Bytecodes::_iconst_0:
478     case Bytecodes::_iconst_1:
479     case Bytecodes::_iconst_2:
480     case Bytecodes::_iconst_3:
481     case Bytecodes::_iconst_4:
482     case Bytecodes::_iconst_5:
483     case Bytecodes::_fconst_0:
484     case Bytecodes::_fconst_1:
485     case Bytecodes::_fconst_2:
486     case Bytecodes::_bipush:
487     case Bytecodes::_sipush:
488     case Bytecodes::_lconst_0:
489     case Bytecodes::_lconst_1:
490     case Bytecodes::_dconst_0:
491     case Bytecodes::_dconst_1:
492     case Bytecodes::_ldc2_w:
493     case Bytecodes::_ldc:
494     case Bytecodes::_ldc_w:
495     case Bytecodes::_iaload:
496     case Bytecodes::_faload:
497     case Bytecodes::_baload:
498     case Bytecodes::_caload:
499     case Bytecodes::_saload:
500     case Bytecodes::_laload:
501     case Bytecodes::_daload:
502     case Bytecodes::_aaload:
503     case Bytecodes::_iastore:
504     case Bytecodes::_fastore:
505     case Bytecodes::_bastore:
506     case Bytecodes::_castore:
507     case Bytecodes::_sastore:
508     case Bytecodes::_lastore:
509     case Bytecodes::_dastore:
510     case Bytecodes::_aastore:
511     case Bytecodes::_pop:
512     case Bytecodes::_pop2:
513     case Bytecodes::_dup:
514     case Bytecodes::_dup_x1:
515     case Bytecodes::_dup_x2:
516     case Bytecodes::_dup2:
517     case Bytecodes::_dup2_x1:
518     case Bytecodes::_dup2_x2:
519     case Bytecodes::_swap:
520     case Bytecodes::_iadd:
521     case Bytecodes::_fadd:
522     case Bytecodes::_isub:
523     case Bytecodes::_fsub:
524     case Bytecodes::_imul:
525     case Bytecodes::_fmul:
526     case Bytecodes::_idiv:
527     case Bytecodes::_fdiv:
528     case Bytecodes::_irem:
529     case Bytecodes::_frem:
530     case Bytecodes::_ishl:
531     case Bytecodes::_ishr:
532     case Bytecodes::_iushr:
533     case Bytecodes::_iand:
534     case Bytecodes::_ior:
535     case Bytecodes::_ixor:
536     case Bytecodes::_l2f:
537     case Bytecodes::_l2i:
538     case Bytecodes::_d2f:
539     case Bytecodes::_d2i:
540     case Bytecodes::_fcmpl:
541     case Bytecodes::_fcmpg:
542     case Bytecodes::_ladd:
543     case Bytecodes::_dadd:
544     case Bytecodes::_lsub:
545     case Bytecodes::_dsub:
546     case Bytecodes::_lmul:
547     case Bytecodes::_dmul:
548     case Bytecodes::_ldiv:
549     case Bytecodes::_ddiv:
550     case Bytecodes::_lrem:
551     case Bytecodes::_drem:
552     case Bytecodes::_land:
553     case Bytecodes::_lor:
554     case Bytecodes::_lxor:
555     case Bytecodes::_ineg:
556     case Bytecodes::_fneg:
557     case Bytecodes::_i2f:
558     case Bytecodes::_f2i:
559     case Bytecodes::_i2c:
560     case Bytecodes::_i2s:
561     case Bytecodes::_i2b:
562     case Bytecodes::_lneg:
563     case Bytecodes::_dneg:
564     case Bytecodes::_l2d:
565     case Bytecodes::_d2l:
566     case Bytecodes::_lshl:
567     case Bytecodes::_lshr:
568     case Bytecodes::_lushr:
569     case Bytecodes::_i2l:
570     case Bytecodes::_i2d:
571     case Bytecodes::_f2l:
572     case Bytecodes::_f2d:
573     case Bytecodes::_lcmp:
574     case Bytecodes::_dcmpl:
575     case Bytecodes::_dcmpg:
576     case Bytecodes::_ifeq:
577     case Bytecodes::_ifne:
578     case Bytecodes::_iflt:
579     case Bytecodes::_ifge:
580     case Bytecodes::_ifgt:
581     case Bytecodes::_ifle:
582     case Bytecodes::_tableswitch:
583     case Bytecodes::_ireturn:
584     case Bytecodes::_freturn:
585     case Bytecodes::_if_icmpeq:
586     case Bytecodes::_if_icmpne:
587     case Bytecodes::_if_icmplt:
588     case Bytecodes::_if_icmpge:
589     case Bytecodes::_if_icmpgt:
590     case Bytecodes::_if_icmple:
591     case Bytecodes::_lreturn:
592     case Bytecodes::_dreturn:
593     case Bytecodes::_if_acmpeq:
594     case Bytecodes::_if_acmpne:
595     case Bytecodes::_jsr:
596     case Bytecodes::_jsr_w:
597     case Bytecodes::_getstatic:
598     case Bytecodes::_putstatic:
599     case Bytecodes::_getfield:
600     case Bytecodes::_putfield:
601     case Bytecodes::_invokevirtual:
602     case Bytecodes::_invokespecial:
603     case Bytecodes::_invokestatic:
604     case Bytecodes::_invokeinterface:
605     case Bytecodes::_invokedynamic:
606     case Bytecodes::_newarray:
607     case Bytecodes::_anewarray:
608     case Bytecodes::_checkcast:
609     case Bytecodes::_arraylength:
610     case Bytecodes::_instanceof:
611     case Bytecodes::_athrow:
612     case Bytecodes::_areturn:
613     case Bytecodes::_monitorenter:
614     case Bytecodes::_monitorexit:
615     case Bytecodes::_ifnull:
616     case Bytecodes::_ifnonnull:
617     case Bytecodes::_multianewarray:
618     case Bytecodes::_lookupswitch:
619       // These bytecodes have no effect on the method's locals.
620       break;
621 
622     case Bytecodes::_return:
623       if (instruction->method()->intrinsic_id() == vmIntrinsics::_Object_init) {
624         // return from Object.init implicitly registers a finalizer
625         // for the receiver if needed, so keep it alive.
626         load_one(0);
627       }
628       break;
629 
630 
631     case Bytecodes::_lload:
632     case Bytecodes::_dload:
633       load_two(instruction->get_index());
634       break;
635 
636     case Bytecodes::_lload_0:
637     case Bytecodes::_dload_0:
638       load_two(0);
639       break;
640 
641     case Bytecodes::_lload_1:
642     case Bytecodes::_dload_1:
643       load_two(1);
644       break;
645 
646     case Bytecodes::_lload_2:
647     case Bytecodes::_dload_2:
648       load_two(2);
649       break;
650 
651     case Bytecodes::_lload_3:
652     case Bytecodes::_dload_3:
653       load_two(3);
654       break;
655 
656     case Bytecodes::_iload:
657     case Bytecodes::_iinc:
658     case Bytecodes::_fload:
659     case Bytecodes::_aload:
660     case Bytecodes::_ret:
661       load_one(instruction->get_index());
662       break;
663 
664     case Bytecodes::_iload_0:
665     case Bytecodes::_fload_0:
666     case Bytecodes::_aload_0:
667       load_one(0);
668       break;
669 
670     case Bytecodes::_iload_1:
671     case Bytecodes::_fload_1:
672     case Bytecodes::_aload_1:
673       load_one(1);
674       break;
675 
676     case Bytecodes::_iload_2:
677     case Bytecodes::_fload_2:
678     case Bytecodes::_aload_2:
679       load_one(2);
680       break;
681 
682     case Bytecodes::_iload_3:
683     case Bytecodes::_fload_3:
684     case Bytecodes::_aload_3:
685       load_one(3);
686       break;
687 
688     case Bytecodes::_lstore:
689     case Bytecodes::_dstore:
690       store_two(instruction->get_index());
691       break;
692 
693     case Bytecodes::_lstore_0:
694     case Bytecodes::_dstore_0:
695       store_two(0);
696       break;
697 
698     case Bytecodes::_lstore_1:
699     case Bytecodes::_dstore_1:
700       store_two(1);
701       break;
702 
703     case Bytecodes::_lstore_2:
704     case Bytecodes::_dstore_2:
705       store_two(2);
706       break;
707 
708     case Bytecodes::_lstore_3:
709     case Bytecodes::_dstore_3:
710       store_two(3);
711       break;
712 
713     case Bytecodes::_istore:
714     case Bytecodes::_fstore:
715     case Bytecodes::_astore:
716       store_one(instruction->get_index());
717       break;
718 
719     case Bytecodes::_istore_0:
720     case Bytecodes::_fstore_0:
721     case Bytecodes::_astore_0:
722       store_one(0);
723       break;
724 
725     case Bytecodes::_istore_1:
726     case Bytecodes::_fstore_1:
727     case Bytecodes::_astore_1:
728       store_one(1);
729       break;
730 
731     case Bytecodes::_istore_2:
732     case Bytecodes::_fstore_2:
733     case Bytecodes::_astore_2:
734       store_one(2);
735       break;
736 
737     case Bytecodes::_istore_3:
738     case Bytecodes::_fstore_3:
739     case Bytecodes::_astore_3:
740       store_one(3);
741       break;
742 
743     case Bytecodes::_wide:
744       fatal("Iterator should skip this bytecode");
745       break;
746 
747     default:
748       tty->print("unexpected opcode: %d\n", instruction->cur_bc());
749       ShouldNotReachHere();
750       break;
751   }
752 }
753 
754 void MethodLiveness::BasicBlock::load_two(int local) {
755   load_one(local);
756   load_one(local+1);
757 }
758 
759 void MethodLiveness::BasicBlock::load_one(int local) {
760   if (!_kill.at(local)) {
761     _gen.at_put(local, true);
762   }
763 }
764 
765 void MethodLiveness::BasicBlock::store_two(int local) {
766   store_one(local);
767   store_one(local+1);
768 }
769 
770 void MethodLiveness::BasicBlock::store_one(int local) {
771   if (!_gen.at(local)) {
772     _kill.at_put(local, true);
773   }
774 }
775 
776 void MethodLiveness::BasicBlock::propagate(MethodLiveness *ml) {
777   // These set operations could be combined for efficiency if the
778   // performance of this analysis becomes an issue.
779   _entry.set_union(_normal_exit);
780   _entry.set_difference(_kill);
781   _entry.set_union(_gen);
782 
783   // Note that we merge information from our exceptional successors
784   // just once, rather than at individual bytecodes.
785   _entry.set_union(_exception_exit);
786 
787   if (TraceLivenessGen) {
788     tty->print_cr(" ** Visiting block at %d **", start_bci());
789     print_on(tty);
790   }
791 
792   int i;
793   for (i=_normal_predecessors->length()-1; i>=0; i--) {
794     BasicBlock *block = _normal_predecessors->at(i);
795     if (block->merge_normal(_entry)) {
796       ml->work_list_add(block);
797     }
798   }
799   for (i=_exception_predecessors->length()-1; i>=0; i--) {
800     BasicBlock *block = _exception_predecessors->at(i);
801     if (block->merge_exception(_entry)) {
802       ml->work_list_add(block);
803     }
804   }
805 }
806 
807 bool MethodLiveness::BasicBlock::merge_normal(const BitMap& other) {
808   return _normal_exit.set_union_with_result(other);
809 }
810 
811 bool MethodLiveness::BasicBlock::merge_exception(const BitMap& other) {
812   return _exception_exit.set_union_with_result(other);
813 }
814 
815 MethodLivenessResult MethodLiveness::BasicBlock::get_liveness_at(ciMethod* method, int bci) {
816   MethodLivenessResult answer(_analyzer->bit_map_size_bits());
817   answer.set_is_valid();
818 
819 #ifndef ASSERT
820   if (bci == start_bci()) {
821     answer.set_from(_entry);
822     return answer;
823   }
824 #endif
825 
826 #ifdef ASSERT
827   ResourceMark rm;
828   ResourceBitMap g(_gen.size(), false); g.set_from(_gen);
829   ResourceBitMap k(_kill.size(), false); k.set_from(_kill);
830 #endif
831   if (_last_bci != bci || trueInDebug) {
832     ciBytecodeStream bytes(method);
833     bytes.reset_to_bci(bci);
834     bytes.set_max_bci(limit_bci());
835     compute_gen_kill_range(&bytes);
836     assert(_last_bci != bci ||
837            (g.is_same(_gen) && k.is_same(_kill)), "cached computation is incorrect");
838     _last_bci = bci;
839   }
840 
841   answer.set_union(_normal_exit);
842   answer.set_difference(_kill);
843   answer.set_union(_gen);
844   answer.set_union(_exception_exit);
845 
846 #ifdef ASSERT
847   if (bci == start_bci()) {
848     assert(answer.is_same(_entry), "optimized answer must be accurate");
849   }
850 #endif
851 
852   return answer;
853 }
854 
855 #ifndef PRODUCT
856 
857 void MethodLiveness::BasicBlock::print_on(outputStream *os) const {
858   os->print_cr("===================================================================");
859   os->print_cr("    Block start: %4d, limit: %4d", _start_bci, _limit_bci);
860   os->print   ("    Normal predecessors (%2d)      @", _normal_predecessors->length());
861   int i;
862   for (i=0; i < _normal_predecessors->length(); i++) {
863     os->print(" %4d", _normal_predecessors->at(i)->start_bci());
864   }
865   os->cr();
866   os->print   ("    Exceptional predecessors (%2d) @", _exception_predecessors->length());
867   for (i=0; i < _exception_predecessors->length(); i++) {
868     os->print(" %4d", _exception_predecessors->at(i)->start_bci());
869   }
870   os->cr();
871   os->print ("    Normal Exit   : ");
872   _normal_exit.print_on(os);
873   os->print ("    Gen           : ");
874   _gen.print_on(os);
875   os->print ("    Kill          : ");
876   _kill.print_on(os);
877   os->print ("    Exception Exit: ");
878   _exception_exit.print_on(os);
879   os->print ("    Entry         : ");
880   _entry.print_on(os);
881 }
882 
883 #endif // PRODUCT