1 /*
   2  * Copyright (c) 1999, 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 "c1/c1_Compilation.hpp"
  27 #include "c1/c1_FrameMap.hpp"
  28 #include "c1/c1_GraphBuilder.hpp"
  29 #include "c1/c1_IR.hpp"
  30 #include "c1/c1_InstructionPrinter.hpp"
  31 #include "c1/c1_Optimizer.hpp"
  32 #include "compiler/oopMap.hpp"
  33 #include "memory/resourceArea.hpp"
  34 #include "utilities/bitMap.inline.hpp"
  35 
  36 
  37 // Implementation of XHandlers
  38 //
  39 // Note: This code could eventually go away if we are
  40 //       just using the ciExceptionHandlerStream.
  41 
  42 XHandlers::XHandlers(ciMethod* method) : _list(method->exception_table_length()) {
  43   ciExceptionHandlerStream s(method);
  44   while (!s.is_done()) {
  45     _list.append(new XHandler(s.handler()));
  46     s.next();
  47   }
  48   assert(s.count() == method->exception_table_length(), "exception table lengths inconsistent");
  49 }
  50 
  51 // deep copy of all XHandler contained in list
  52 XHandlers::XHandlers(XHandlers* other) :
  53   _list(other->length())
  54 {
  55   for (int i = 0; i < other->length(); i++) {
  56     _list.append(new XHandler(other->handler_at(i)));
  57   }
  58 }
  59 
  60 // Returns whether a particular exception type can be caught.  Also
  61 // returns true if klass is unloaded or any exception handler
  62 // classes are unloaded.  type_is_exact indicates whether the throw
  63 // is known to be exactly that class or it might throw a subtype.
  64 bool XHandlers::could_catch(ciInstanceKlass* klass, bool type_is_exact) const {
  65   // the type is unknown so be conservative
  66   if (!klass->is_loaded()) {
  67     return true;
  68   }
  69 
  70   for (int i = 0; i < length(); i++) {
  71     XHandler* handler = handler_at(i);
  72     if (handler->is_catch_all()) {
  73       // catch of ANY
  74       return true;
  75     }
  76     ciInstanceKlass* handler_klass = handler->catch_klass();
  77     // if it's unknown it might be catchable
  78     if (!handler_klass->is_loaded()) {
  79       return true;
  80     }
  81     // if the throw type is definitely a subtype of the catch type
  82     // then it can be caught.
  83     if (klass->is_subtype_of(handler_klass)) {
  84       return true;
  85     }
  86     if (!type_is_exact) {
  87       // If the type isn't exactly known then it can also be caught by
  88       // catch statements where the inexact type is a subtype of the
  89       // catch type.
  90       // given: foo extends bar extends Exception
  91       // throw bar can be caught by catch foo, catch bar, and catch
  92       // Exception, however it can't be caught by any handlers without
  93       // bar in its type hierarchy.
  94       if (handler_klass->is_subtype_of(klass)) {
  95         return true;
  96       }
  97     }
  98   }
  99 
 100   return false;
 101 }
 102 
 103 
 104 bool XHandlers::equals(XHandlers* others) const {
 105   if (others == NULL) return false;
 106   if (length() != others->length()) return false;
 107 
 108   for (int i = 0; i < length(); i++) {
 109     if (!handler_at(i)->equals(others->handler_at(i))) return false;
 110   }
 111   return true;
 112 }
 113 
 114 bool XHandler::equals(XHandler* other) const {
 115   assert(entry_pco() != -1 && other->entry_pco() != -1, "must have entry_pco");
 116 
 117   if (entry_pco() != other->entry_pco()) return false;
 118   if (scope_count() != other->scope_count()) return false;
 119   if (_desc != other->_desc) return false;
 120 
 121   assert(entry_block() == other->entry_block(), "entry_block must be equal when entry_pco is equal");
 122   return true;
 123 }
 124 
 125 
 126 // Implementation of IRScope
 127 BlockBegin* IRScope::build_graph(Compilation* compilation, int osr_bci) {
 128   GraphBuilder gm(compilation, this);
 129   NOT_PRODUCT(if (PrintValueNumbering && Verbose) gm.print_stats());
 130   if (compilation->bailed_out()) return NULL;
 131   return gm.start();
 132 }
 133 
 134 
 135 IRScope::IRScope(Compilation* compilation, IRScope* caller, int caller_bci, ciMethod* method, int osr_bci, bool create_graph)
 136 : _compilation(compilation)
 137 , _callees(2)
 138 , _requires_phi_function(method->max_locals())
 139 {
 140   _caller             = caller;
 141   _level              = caller == NULL ?  0 : caller->level() + 1;
 142   _method             = method;
 143   _xhandlers          = new XHandlers(method);
 144   _number_of_locks    = 0;
 145   _monitor_pairing_ok = method->has_balanced_monitors();
 146   _wrote_final        = false;
 147   _wrote_fields       = false;
 148   _wrote_volatile     = false;
 149   _start              = NULL;
 150 
 151   if (osr_bci != -1) {
 152     // selective creation of phi functions is not possibel in osr-methods
 153     _requires_phi_function.set_range(0, method->max_locals());
 154   }
 155 
 156   assert(method->holder()->is_loaded() , "method holder must be loaded");
 157 
 158   // build graph if monitor pairing is ok
 159   if (create_graph && monitor_pairing_ok()) _start = build_graph(compilation, osr_bci);
 160 }
 161 
 162 
 163 int IRScope::max_stack() const {
 164   int my_max = method()->max_stack();
 165   int callee_max = 0;
 166   for (int i = 0; i < number_of_callees(); i++) {
 167     callee_max = MAX2(callee_max, callee_no(i)->max_stack());
 168   }
 169   return my_max + callee_max;
 170 }
 171 
 172 
 173 bool IRScopeDebugInfo::should_reexecute() {
 174   if (_should_reexecute) {
 175     return true;
 176   }
 177   ciMethod* cur_method = scope()->method();
 178   int       cur_bci    = bci();
 179   if (cur_method != NULL && cur_bci != SynchronizationEntryBCI) {
 180     Bytecodes::Code code = cur_method->java_code_at_bci(cur_bci);
 181     return Interpreter::bytecode_should_reexecute(code);
 182   } else
 183     return false;
 184 }
 185 
 186 // Implementation of CodeEmitInfo
 187 
 188 // Stack must be NON-null
 189 CodeEmitInfo::CodeEmitInfo(ValueStack* stack, XHandlers* exception_handlers, bool deoptimize_on_exception)
 190   : _scope_debug_info(NULL)
 191   , _scope(stack->scope())
 192   , _exception_handlers(exception_handlers)
 193   , _oop_map(NULL)
 194   , _stack(stack)
 195   , _is_method_handle_invoke(false)
 196   , _deoptimize_on_exception(deoptimize_on_exception) {
 197   assert(_stack != NULL, "must be non null");
 198 }
 199 
 200 
 201 CodeEmitInfo::CodeEmitInfo(CodeEmitInfo* info, ValueStack* stack)
 202   : _scope_debug_info(NULL)
 203   , _scope(info->_scope)
 204   , _exception_handlers(NULL)
 205   , _oop_map(NULL)
 206   , _stack(stack == NULL ? info->_stack : stack)
 207   , _is_method_handle_invoke(info->_is_method_handle_invoke)
 208   , _deoptimize_on_exception(info->_deoptimize_on_exception) {
 209 
 210   // deep copy of exception handlers
 211   if (info->_exception_handlers != NULL) {
 212     _exception_handlers = new XHandlers(info->_exception_handlers);
 213   }
 214 }
 215 
 216 
 217 void CodeEmitInfo::record_debug_info(DebugInformationRecorder* recorder, int pc_offset, bool maybe_return_as_fields) {
 218   // record the safepoint before recording the debug info for enclosing scopes
 219   recorder->add_safepoint(pc_offset, _oop_map->deep_copy());
 220   _scope_debug_info->record_debug_info(recorder, pc_offset, true/*topmost*/, _is_method_handle_invoke, maybe_return_as_fields);
 221   recorder->end_safepoint(pc_offset);
 222 }
 223 
 224 
 225 void CodeEmitInfo::add_register_oop(LIR_Opr opr) {
 226   assert(_oop_map != NULL, "oop map must already exist");
 227   assert(opr->is_single_cpu(), "should not call otherwise");
 228 
 229   VMReg name = frame_map()->regname(opr);
 230   _oop_map->set_oop(name);
 231 }
 232 
 233 // Mirror the stack size calculation in the deopt code
 234 // How much stack space would we need at this point in the program in
 235 // case of deoptimization?
 236 int CodeEmitInfo::interpreter_frame_size() const {
 237   ValueStack* state = _stack;
 238   int size = 0;
 239   int callee_parameters = 0;
 240   int callee_locals = 0;
 241   int extra_args = state->scope()->method()->max_stack() - state->stack_size();
 242 
 243   while (state != NULL) {
 244     int locks = state->locks_size();
 245     int temps = state->stack_size();
 246     bool is_top_frame = (state == _stack);
 247     ciMethod* method = state->scope()->method();
 248 
 249     int frame_size = BytesPerWord * Interpreter::size_activation(method->max_stack(),
 250                                                                  temps + callee_parameters,
 251                                                                  extra_args,
 252                                                                  locks,
 253                                                                  callee_parameters,
 254                                                                  callee_locals,
 255                                                                  is_top_frame);
 256     size += frame_size;
 257 
 258     callee_parameters = method->size_of_parameters();
 259     callee_locals = method->max_locals();
 260     extra_args = 0;
 261     state = state->caller_state();
 262   }
 263   return size + Deoptimization::last_frame_adjust(0, callee_locals) * BytesPerWord;
 264 }
 265 
 266 // Implementation of IR
 267 
 268 IR::IR(Compilation* compilation, ciMethod* method, int osr_bci) :
 269   _num_loops(0) {
 270   // setup IR fields
 271   _compilation = compilation;
 272   _top_scope   = new IRScope(compilation, NULL, -1, method, osr_bci, true);
 273   _code        = NULL;
 274 }
 275 
 276 
 277 void IR::optimize_blocks() {
 278   Optimizer opt(this);
 279   if (!compilation()->profile_branches()) {
 280     if (DoCEE) {
 281       opt.eliminate_conditional_expressions();
 282 #ifndef PRODUCT
 283       if (PrintCFG || PrintCFG1) { tty->print_cr("CFG after CEE"); print(true); }
 284       if (PrintIR  || PrintIR1 ) { tty->print_cr("IR after CEE"); print(false); }
 285 #endif
 286     }
 287     if (EliminateBlocks) {
 288       opt.eliminate_blocks();
 289 #ifndef PRODUCT
 290       if (PrintCFG || PrintCFG1) { tty->print_cr("CFG after block elimination"); print(true); }
 291       if (PrintIR  || PrintIR1 ) { tty->print_cr("IR after block elimination"); print(false); }
 292 #endif
 293     }
 294   }
 295 }
 296 
 297 void IR::eliminate_null_checks() {
 298   Optimizer opt(this);
 299   if (EliminateNullChecks) {
 300     opt.eliminate_null_checks();
 301 #ifndef PRODUCT
 302     if (PrintCFG || PrintCFG1) { tty->print_cr("CFG after null check elimination"); print(true); }
 303     if (PrintIR  || PrintIR1 ) { tty->print_cr("IR after null check elimination"); print(false); }
 304 #endif
 305   }
 306 }
 307 
 308 
 309 static int sort_pairs(BlockPair** a, BlockPair** b) {
 310   if ((*a)->from() == (*b)->from()) {
 311     return (*a)->to()->block_id() - (*b)->to()->block_id();
 312   } else {
 313     return (*a)->from()->block_id() - (*b)->from()->block_id();
 314   }
 315 }
 316 
 317 
 318 class CriticalEdgeFinder: public BlockClosure {
 319   BlockPairList blocks;
 320   IR*       _ir;
 321 
 322  public:
 323   CriticalEdgeFinder(IR* ir): _ir(ir) {}
 324   void block_do(BlockBegin* bb) {
 325     BlockEnd* be = bb->end();
 326     int nos = be->number_of_sux();
 327     if (nos >= 2) {
 328       for (int i = 0; i < nos; i++) {
 329         BlockBegin* sux = be->sux_at(i);
 330         if (sux->number_of_preds() >= 2) {
 331           blocks.append(new BlockPair(bb, sux));
 332         }
 333       }
 334     }
 335   }
 336 
 337   void split_edges() {
 338     BlockPair* last_pair = NULL;
 339     blocks.sort(sort_pairs);
 340     for (int i = 0; i < blocks.length(); i++) {
 341       BlockPair* pair = blocks.at(i);
 342       if (last_pair != NULL && pair->is_same(last_pair)) continue;
 343       BlockBegin* from = pair->from();
 344       BlockBegin* to = pair->to();
 345       BlockBegin* split = from->insert_block_between(to);
 346 #ifndef PRODUCT
 347       if ((PrintIR || PrintIR1) && Verbose) {
 348         tty->print_cr("Split critical edge B%d -> B%d (new block B%d)",
 349                       from->block_id(), to->block_id(), split->block_id());
 350       }
 351 #endif
 352       last_pair = pair;
 353     }
 354   }
 355 };
 356 
 357 void IR::split_critical_edges() {
 358   CriticalEdgeFinder cef(this);
 359 
 360   iterate_preorder(&cef);
 361   cef.split_edges();
 362 }
 363 
 364 
 365 class UseCountComputer: public ValueVisitor, BlockClosure {
 366  private:
 367   void visit(Value* n) {
 368     // Local instructions and Phis for expression stack values at the
 369     // start of basic blocks are not added to the instruction list
 370     if (!(*n)->is_linked() && (*n)->can_be_linked()) {
 371       assert(false, "a node was not appended to the graph");
 372       Compilation::current()->bailout("a node was not appended to the graph");
 373     }
 374     // use n's input if not visited before
 375     if (!(*n)->is_pinned() && !(*n)->has_uses()) {
 376       // note: a) if the instruction is pinned, it will be handled by compute_use_count
 377       //       b) if the instruction has uses, it was touched before
 378       //       => in both cases we don't need to update n's values
 379       uses_do(n);
 380     }
 381     // use n
 382     (*n)->_use_count++;
 383   }
 384 
 385   Values* worklist;
 386   int depth;
 387   enum {
 388     max_recurse_depth = 20
 389   };
 390 
 391   void uses_do(Value* n) {
 392     depth++;
 393     if (depth > max_recurse_depth) {
 394       // don't allow the traversal to recurse too deeply
 395       worklist->push(*n);
 396     } else {
 397       (*n)->input_values_do(this);
 398       // special handling for some instructions
 399       if ((*n)->as_BlockEnd() != NULL) {
 400         // note on BlockEnd:
 401         //   must 'use' the stack only if the method doesn't
 402         //   terminate, however, in those cases stack is empty
 403         (*n)->state_values_do(this);
 404       }
 405     }
 406     depth--;
 407   }
 408 
 409   void block_do(BlockBegin* b) {
 410     depth = 0;
 411     // process all pinned nodes as the roots of expression trees
 412     for (Instruction* n = b; n != NULL; n = n->next()) {
 413       if (n->is_pinned()) uses_do(&n);
 414     }
 415     assert(depth == 0, "should have counted back down");
 416 
 417     // now process any unpinned nodes which recursed too deeply
 418     while (worklist->length() > 0) {
 419       Value t = worklist->pop();
 420       if (!t->is_pinned()) {
 421         // compute the use count
 422         uses_do(&t);
 423 
 424         // pin the instruction so that LIRGenerator doesn't recurse
 425         // too deeply during it's evaluation.
 426         t->pin();
 427       }
 428     }
 429     assert(depth == 0, "should have counted back down");
 430   }
 431 
 432   UseCountComputer() {
 433     worklist = new Values();
 434     depth = 0;
 435   }
 436 
 437  public:
 438   static void compute(BlockList* blocks) {
 439     UseCountComputer ucc;
 440     blocks->iterate_backward(&ucc);
 441   }
 442 };
 443 
 444 
 445 // helper macro for short definition of trace-output inside code
 446 #ifdef ASSERT
 447   #define TRACE_LINEAR_SCAN(level, code)       \
 448     if (TraceLinearScanLevel >= level) {       \
 449       code;                                    \
 450     }
 451 #else
 452   #define TRACE_LINEAR_SCAN(level, code)
 453 #endif
 454 
 455 class ComputeLinearScanOrder : public StackObj {
 456  private:
 457   int        _max_block_id;        // the highest block_id of a block
 458   int        _num_blocks;          // total number of blocks (smaller than _max_block_id)
 459   int        _num_loops;           // total number of loops
 460   bool       _iterative_dominators;// method requires iterative computation of dominatiors
 461 
 462   BlockList* _linear_scan_order;   // the resulting list of blocks in correct order
 463 
 464   ResourceBitMap _visited_blocks;   // used for recursive processing of blocks
 465   ResourceBitMap _active_blocks;    // used for recursive processing of blocks
 466   ResourceBitMap _dominator_blocks; // temproary BitMap used for computation of dominator
 467   intArray       _forward_branches; // number of incoming forward branches for each block
 468   BlockList      _loop_end_blocks;  // list of all loop end blocks collected during count_edges
 469   BitMap2D       _loop_map;         // two-dimensional bit set: a bit is set if a block is contained in a loop
 470   BlockList      _work_list;        // temporary list (used in mark_loops and compute_order)
 471   BlockList      _loop_headers;
 472 
 473   Compilation* _compilation;
 474 
 475   // accessors for _visited_blocks and _active_blocks
 476   void init_visited()                     { _active_blocks.clear(); _visited_blocks.clear(); }
 477   bool is_visited(BlockBegin* b) const    { return _visited_blocks.at(b->block_id()); }
 478   bool is_active(BlockBegin* b) const     { return _active_blocks.at(b->block_id()); }
 479   void set_visited(BlockBegin* b)         { assert(!is_visited(b), "already set"); _visited_blocks.set_bit(b->block_id()); }
 480   void set_active(BlockBegin* b)          { assert(!is_active(b), "already set");  _active_blocks.set_bit(b->block_id()); }
 481   void clear_active(BlockBegin* b)        { assert(is_active(b), "not already");   _active_blocks.clear_bit(b->block_id()); }
 482 
 483   // accessors for _forward_branches
 484   void inc_forward_branches(BlockBegin* b) { _forward_branches.at_put(b->block_id(), _forward_branches.at(b->block_id()) + 1); }
 485   int  dec_forward_branches(BlockBegin* b) { _forward_branches.at_put(b->block_id(), _forward_branches.at(b->block_id()) - 1); return _forward_branches.at(b->block_id()); }
 486 
 487   // accessors for _loop_map
 488   bool is_block_in_loop   (int loop_idx, BlockBegin* b) const { return _loop_map.at(loop_idx, b->block_id()); }
 489   void set_block_in_loop  (int loop_idx, BlockBegin* b)       { _loop_map.set_bit(loop_idx, b->block_id()); }
 490   void clear_block_in_loop(int loop_idx, int block_id)        { _loop_map.clear_bit(loop_idx, block_id); }
 491 
 492   // count edges between blocks
 493   void count_edges(BlockBegin* cur, BlockBegin* parent);
 494 
 495   // loop detection
 496   void mark_loops();
 497   void clear_non_natural_loops(BlockBegin* start_block);
 498   void assign_loop_depth(BlockBegin* start_block);
 499 
 500   // computation of final block order
 501   BlockBegin* common_dominator(BlockBegin* a, BlockBegin* b);
 502   void compute_dominator(BlockBegin* cur, BlockBegin* parent);
 503   void compute_dominator_impl(BlockBegin* cur, BlockBegin* parent);
 504   int  compute_weight(BlockBegin* cur);
 505   bool ready_for_processing(BlockBegin* cur);
 506   void sort_into_work_list(BlockBegin* b);
 507   void append_block(BlockBegin* cur);
 508   void compute_order(BlockBegin* start_block);
 509 
 510   // fixup of dominators for non-natural loops
 511   bool compute_dominators_iter();
 512   void compute_dominators();
 513 
 514   // debug functions
 515   DEBUG_ONLY(void print_blocks();)
 516   DEBUG_ONLY(void verify();)
 517 
 518   Compilation* compilation() const { return _compilation; }
 519  public:
 520   ComputeLinearScanOrder(Compilation* c, BlockBegin* start_block);
 521 
 522   // accessors for final result
 523   BlockList* linear_scan_order() const    { return _linear_scan_order; }
 524   int        num_loops() const            { return _num_loops; }
 525 };
 526 
 527 
 528 ComputeLinearScanOrder::ComputeLinearScanOrder(Compilation* c, BlockBegin* start_block) :
 529   _max_block_id(BlockBegin::number_of_blocks()),
 530   _num_blocks(0),
 531   _num_loops(0),
 532   _iterative_dominators(false),
 533   _linear_scan_order(NULL), // initialized later with correct size
 534   _visited_blocks(_max_block_id),
 535   _active_blocks(_max_block_id),
 536   _dominator_blocks(_max_block_id),
 537   _forward_branches(_max_block_id, _max_block_id, 0),
 538   _loop_end_blocks(8),
 539   _loop_map(0),             // initialized later with correct size
 540   _work_list(8),
 541   _compilation(c)
 542 {
 543   TRACE_LINEAR_SCAN(2, tty->print_cr("***** computing linear-scan block order"));
 544 
 545   count_edges(start_block, NULL);
 546 
 547   if (compilation()->is_profiling()) {
 548     ciMethod *method = compilation()->method();
 549     if (!method->is_accessor()) {
 550       ciMethodData* md = method->method_data_or_null();
 551       assert(md != NULL, "Sanity");
 552       md->set_compilation_stats(_num_loops, _num_blocks);
 553     }
 554   }
 555 
 556   if (_num_loops > 0) {
 557     mark_loops();
 558     clear_non_natural_loops(start_block);
 559     assign_loop_depth(start_block);
 560   }
 561 
 562   compute_order(start_block);
 563   compute_dominators();
 564 
 565   DEBUG_ONLY(print_blocks());
 566   DEBUG_ONLY(verify());
 567 }
 568 
 569 
 570 // Traverse the CFG:
 571 // * count total number of blocks
 572 // * count all incoming edges and backward incoming edges
 573 // * number loop header blocks
 574 // * create a list with all loop end blocks
 575 void ComputeLinearScanOrder::count_edges(BlockBegin* cur, BlockBegin* parent) {
 576   TRACE_LINEAR_SCAN(3, tty->print_cr("Enter count_edges for block B%d coming from B%d", cur->block_id(), parent != NULL ? parent->block_id() : -1));
 577   assert(cur->dominator() == NULL, "dominator already initialized");
 578 
 579   if (is_active(cur)) {
 580     TRACE_LINEAR_SCAN(3, tty->print_cr("backward branch"));
 581     assert(is_visited(cur), "block must be visisted when block is active");
 582     assert(parent != NULL, "must have parent");
 583 
 584     cur->set(BlockBegin::backward_branch_target_flag);
 585 
 586     // When a loop header is also the start of an exception handler, then the backward branch is
 587     // an exception edge. Because such edges are usually critical edges which cannot be split, the
 588     // loop must be excluded here from processing.
 589     if (cur->is_set(BlockBegin::exception_entry_flag)) {
 590       // Make sure that dominators are correct in this weird situation
 591       _iterative_dominators = true;
 592       return;
 593     }
 594 
 595     cur->set(BlockBegin::linear_scan_loop_header_flag);
 596     parent->set(BlockBegin::linear_scan_loop_end_flag);
 597 
 598     assert(parent->number_of_sux() == 1 && parent->sux_at(0) == cur,
 599            "loop end blocks must have one successor (critical edges are split)");
 600 
 601     _loop_end_blocks.append(parent);
 602     return;
 603   }
 604 
 605   // increment number of incoming forward branches
 606   inc_forward_branches(cur);
 607 
 608   if (is_visited(cur)) {
 609     TRACE_LINEAR_SCAN(3, tty->print_cr("block already visited"));
 610     return;
 611   }
 612 
 613   _num_blocks++;
 614   set_visited(cur);
 615   set_active(cur);
 616 
 617   // recursive call for all successors
 618   int i;
 619   for (i = cur->number_of_sux() - 1; i >= 0; i--) {
 620     count_edges(cur->sux_at(i), cur);
 621   }
 622   for (i = cur->number_of_exception_handlers() - 1; i >= 0; i--) {
 623     count_edges(cur->exception_handler_at(i), cur);
 624   }
 625 
 626   clear_active(cur);
 627 
 628   // Each loop has a unique number.
 629   // When multiple loops are nested, assign_loop_depth assumes that the
 630   // innermost loop has the lowest number. This is guaranteed by setting
 631   // the loop number after the recursive calls for the successors above
 632   // have returned.
 633   if (cur->is_set(BlockBegin::linear_scan_loop_header_flag)) {
 634     assert(cur->loop_index() == -1, "cannot set loop-index twice");
 635     TRACE_LINEAR_SCAN(3, tty->print_cr("Block B%d is loop header of loop %d", cur->block_id(), _num_loops));
 636 
 637     cur->set_loop_index(_num_loops);
 638     _loop_headers.append(cur);
 639     _num_loops++;
 640   }
 641 
 642   TRACE_LINEAR_SCAN(3, tty->print_cr("Finished count_edges for block B%d", cur->block_id()));
 643 }
 644 
 645 
 646 void ComputeLinearScanOrder::mark_loops() {
 647   TRACE_LINEAR_SCAN(3, tty->print_cr("----- marking loops"));
 648 
 649   _loop_map = BitMap2D(_num_loops, _max_block_id);
 650 
 651   for (int i = _loop_end_blocks.length() - 1; i >= 0; i--) {
 652     BlockBegin* loop_end   = _loop_end_blocks.at(i);
 653     BlockBegin* loop_start = loop_end->sux_at(0);
 654     int         loop_idx   = loop_start->loop_index();
 655 
 656     TRACE_LINEAR_SCAN(3, tty->print_cr("Processing loop from B%d to B%d (loop %d):", loop_start->block_id(), loop_end->block_id(), loop_idx));
 657     assert(loop_end->is_set(BlockBegin::linear_scan_loop_end_flag), "loop end flag must be set");
 658     assert(loop_end->number_of_sux() == 1, "incorrect number of successors");
 659     assert(loop_start->is_set(BlockBegin::linear_scan_loop_header_flag), "loop header flag must be set");
 660     assert(loop_idx >= 0 && loop_idx < _num_loops, "loop index not set");
 661     assert(_work_list.is_empty(), "work list must be empty before processing");
 662 
 663     // add the end-block of the loop to the working list
 664     _work_list.push(loop_end);
 665     set_block_in_loop(loop_idx, loop_end);
 666     do {
 667       BlockBegin* cur = _work_list.pop();
 668 
 669       TRACE_LINEAR_SCAN(3, tty->print_cr("    processing B%d", cur->block_id()));
 670       assert(is_block_in_loop(loop_idx, cur), "bit in loop map must be set when block is in work list");
 671 
 672       // recursive processing of all predecessors ends when start block of loop is reached
 673       if (cur != loop_start && !cur->is_set(BlockBegin::osr_entry_flag)) {
 674         for (int j = cur->number_of_preds() - 1; j >= 0; j--) {
 675           BlockBegin* pred = cur->pred_at(j);
 676 
 677           if (!is_block_in_loop(loop_idx, pred) /*&& !pred->is_set(BlockBeginosr_entry_flag)*/) {
 678             // this predecessor has not been processed yet, so add it to work list
 679             TRACE_LINEAR_SCAN(3, tty->print_cr("    pushing B%d", pred->block_id()));
 680             _work_list.push(pred);
 681             set_block_in_loop(loop_idx, pred);
 682           }
 683         }
 684       }
 685     } while (!_work_list.is_empty());
 686   }
 687 }
 688 
 689 
 690 // check for non-natural loops (loops where the loop header does not dominate
 691 // all other loop blocks = loops with mulitple entries).
 692 // such loops are ignored
 693 void ComputeLinearScanOrder::clear_non_natural_loops(BlockBegin* start_block) {
 694   for (int i = _num_loops - 1; i >= 0; i--) {
 695     if (is_block_in_loop(i, start_block)) {
 696       // loop i contains the entry block of the method
 697       // -> this is not a natural loop, so ignore it
 698       TRACE_LINEAR_SCAN(2, tty->print_cr("Loop %d is non-natural, so it is ignored", i));
 699 
 700       BlockBegin *loop_header = _loop_headers.at(i);
 701       assert(loop_header->is_set(BlockBegin::linear_scan_loop_header_flag), "Must be loop header");
 702 
 703       for (int j = 0; j < loop_header->number_of_preds(); j++) {
 704         BlockBegin *pred = loop_header->pred_at(j);
 705         pred->clear(BlockBegin::linear_scan_loop_end_flag);
 706       }
 707 
 708       loop_header->clear(BlockBegin::linear_scan_loop_header_flag);
 709 
 710       for (int block_id = _max_block_id - 1; block_id >= 0; block_id--) {
 711         clear_block_in_loop(i, block_id);
 712       }
 713       _iterative_dominators = true;
 714     }
 715   }
 716 }
 717 
 718 void ComputeLinearScanOrder::assign_loop_depth(BlockBegin* start_block) {
 719   TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing loop-depth and weight"));
 720   init_visited();
 721 
 722   assert(_work_list.is_empty(), "work list must be empty before processing");
 723   _work_list.append(start_block);
 724 
 725   do {
 726     BlockBegin* cur = _work_list.pop();
 727 
 728     if (!is_visited(cur)) {
 729       set_visited(cur);
 730       TRACE_LINEAR_SCAN(4, tty->print_cr("Computing loop depth for block B%d", cur->block_id()));
 731 
 732       // compute loop-depth and loop-index for the block
 733       assert(cur->loop_depth() == 0, "cannot set loop-depth twice");
 734       int i;
 735       int loop_depth = 0;
 736       int min_loop_idx = -1;
 737       for (i = _num_loops - 1; i >= 0; i--) {
 738         if (is_block_in_loop(i, cur)) {
 739           loop_depth++;
 740           min_loop_idx = i;
 741         }
 742       }
 743       cur->set_loop_depth(loop_depth);
 744       cur->set_loop_index(min_loop_idx);
 745 
 746       // append all unvisited successors to work list
 747       for (i = cur->number_of_sux() - 1; i >= 0; i--) {
 748         _work_list.append(cur->sux_at(i));
 749       }
 750       for (i = cur->number_of_exception_handlers() - 1; i >= 0; i--) {
 751         _work_list.append(cur->exception_handler_at(i));
 752       }
 753     }
 754   } while (!_work_list.is_empty());
 755 }
 756 
 757 
 758 BlockBegin* ComputeLinearScanOrder::common_dominator(BlockBegin* a, BlockBegin* b) {
 759   assert(a != NULL && b != NULL, "must have input blocks");
 760 
 761   _dominator_blocks.clear();
 762   while (a != NULL) {
 763     _dominator_blocks.set_bit(a->block_id());
 764     assert(a->dominator() != NULL || a == _linear_scan_order->at(0), "dominator must be initialized");
 765     a = a->dominator();
 766   }
 767   while (b != NULL && !_dominator_blocks.at(b->block_id())) {
 768     assert(b->dominator() != NULL || b == _linear_scan_order->at(0), "dominator must be initialized");
 769     b = b->dominator();
 770   }
 771 
 772   assert(b != NULL, "could not find dominator");
 773   return b;
 774 }
 775 
 776 void ComputeLinearScanOrder::compute_dominator(BlockBegin* cur, BlockBegin* parent) {
 777   init_visited();
 778   compute_dominator_impl(cur, parent);
 779 }
 780 
 781 void ComputeLinearScanOrder::compute_dominator_impl(BlockBegin* cur, BlockBegin* parent) {
 782   // Mark as visited to avoid recursive calls with same parent
 783   set_visited(cur);
 784 
 785   if (cur->dominator() == NULL) {
 786     TRACE_LINEAR_SCAN(4, tty->print_cr("DOM: initializing dominator of B%d to B%d", cur->block_id(), parent->block_id()));
 787     cur->set_dominator(parent);
 788 
 789   } else if (!(cur->is_set(BlockBegin::linear_scan_loop_header_flag) && parent->is_set(BlockBegin::linear_scan_loop_end_flag))) {
 790     TRACE_LINEAR_SCAN(4, tty->print_cr("DOM: computing dominator of B%d: common dominator of B%d and B%d is B%d", cur->block_id(), parent->block_id(), cur->dominator()->block_id(), common_dominator(cur->dominator(), parent)->block_id()));
 791     // Does not hold for exception blocks
 792     assert(cur->number_of_preds() > 1 || cur->is_set(BlockBegin::exception_entry_flag), "");
 793     cur->set_dominator(common_dominator(cur->dominator(), parent));
 794   }
 795 
 796   // Additional edge to xhandler of all our successors
 797   // range check elimination needs that the state at the end of a
 798   // block be valid in every block it dominates so cur must dominate
 799   // the exception handlers of its successors.
 800   int num_cur_xhandler = cur->number_of_exception_handlers();
 801   for (int j = 0; j < num_cur_xhandler; j++) {
 802     BlockBegin* xhandler = cur->exception_handler_at(j);
 803     if (!is_visited(xhandler)) {
 804       compute_dominator_impl(xhandler, parent);
 805     }
 806   }
 807 }
 808 
 809 
 810 int ComputeLinearScanOrder::compute_weight(BlockBegin* cur) {
 811   BlockBegin* single_sux = NULL;
 812   if (cur->number_of_sux() == 1) {
 813     single_sux = cur->sux_at(0);
 814   }
 815 
 816   // limit loop-depth to 15 bit (only for security reason, it will never be so big)
 817   int weight = (cur->loop_depth() & 0x7FFF) << 16;
 818 
 819   // general macro for short definition of weight flags
 820   // the first instance of INC_WEIGHT_IF has the highest priority
 821   int cur_bit = 15;
 822   #define INC_WEIGHT_IF(condition) if ((condition)) { weight |= (1 << cur_bit); } cur_bit--;
 823 
 824   // this is necessery for the (very rare) case that two successing blocks have
 825   // the same loop depth, but a different loop index (can happen for endless loops
 826   // with exception handlers)
 827   INC_WEIGHT_IF(!cur->is_set(BlockBegin::linear_scan_loop_header_flag));
 828 
 829   // loop end blocks (blocks that end with a backward branch) are added
 830   // after all other blocks of the loop.
 831   INC_WEIGHT_IF(!cur->is_set(BlockBegin::linear_scan_loop_end_flag));
 832 
 833   // critical edge split blocks are prefered because than they have a bigger
 834   // proability to be completely empty
 835   INC_WEIGHT_IF(cur->is_set(BlockBegin::critical_edge_split_flag));
 836 
 837   // exceptions should not be thrown in normal control flow, so these blocks
 838   // are added as late as possible
 839   INC_WEIGHT_IF(cur->end()->as_Throw() == NULL  && (single_sux == NULL || single_sux->end()->as_Throw()  == NULL));
 840   INC_WEIGHT_IF(cur->end()->as_Return() == NULL && (single_sux == NULL || single_sux->end()->as_Return() == NULL));
 841 
 842   // exceptions handlers are added as late as possible
 843   INC_WEIGHT_IF(!cur->is_set(BlockBegin::exception_entry_flag));
 844 
 845   // guarantee that weight is > 0
 846   weight |= 1;
 847 
 848   #undef INC_WEIGHT_IF
 849   assert(cur_bit >= 0, "too many flags");
 850   assert(weight > 0, "weight cannot become negative");
 851 
 852   return weight;
 853 }
 854 
 855 bool ComputeLinearScanOrder::ready_for_processing(BlockBegin* cur) {
 856   // Discount the edge just traveled.
 857   // When the number drops to zero, all forward branches were processed
 858   if (dec_forward_branches(cur) != 0) {
 859     return false;
 860   }
 861 
 862   assert(_linear_scan_order->find(cur) == -1, "block already processed (block can be ready only once)");
 863   assert(_work_list.find(cur) == -1, "block already in work-list (block can be ready only once)");
 864   return true;
 865 }
 866 
 867 void ComputeLinearScanOrder::sort_into_work_list(BlockBegin* cur) {
 868   assert(_work_list.find(cur) == -1, "block already in work list");
 869 
 870   int cur_weight = compute_weight(cur);
 871 
 872   // the linear_scan_number is used to cache the weight of a block
 873   cur->set_linear_scan_number(cur_weight);
 874 
 875 #ifndef PRODUCT
 876   if (StressLinearScan) {
 877     _work_list.insert_before(0, cur);
 878     return;
 879   }
 880 #endif
 881 
 882   _work_list.append(NULL); // provide space for new element
 883 
 884   int insert_idx = _work_list.length() - 1;
 885   while (insert_idx > 0 && _work_list.at(insert_idx - 1)->linear_scan_number() > cur_weight) {
 886     _work_list.at_put(insert_idx, _work_list.at(insert_idx - 1));
 887     insert_idx--;
 888   }
 889   _work_list.at_put(insert_idx, cur);
 890 
 891   TRACE_LINEAR_SCAN(3, tty->print_cr("Sorted B%d into worklist. new worklist:", cur->block_id()));
 892   TRACE_LINEAR_SCAN(3, for (int i = 0; i < _work_list.length(); i++) tty->print_cr("%8d B%2d  weight:%6x", i, _work_list.at(i)->block_id(), _work_list.at(i)->linear_scan_number()));
 893 
 894 #ifdef ASSERT
 895   for (int i = 0; i < _work_list.length(); i++) {
 896     assert(_work_list.at(i)->linear_scan_number() > 0, "weight not set");
 897     assert(i == 0 || _work_list.at(i - 1)->linear_scan_number() <= _work_list.at(i)->linear_scan_number(), "incorrect order in worklist");
 898   }
 899 #endif
 900 }
 901 
 902 void ComputeLinearScanOrder::append_block(BlockBegin* cur) {
 903   TRACE_LINEAR_SCAN(3, tty->print_cr("appending block B%d (weight 0x%6x) to linear-scan order", cur->block_id(), cur->linear_scan_number()));
 904   assert(_linear_scan_order->find(cur) == -1, "cannot add the same block twice");
 905 
 906   // currently, the linear scan order and code emit order are equal.
 907   // therefore the linear_scan_number and the weight of a block must also
 908   // be equal.
 909   cur->set_linear_scan_number(_linear_scan_order->length());
 910   _linear_scan_order->append(cur);
 911 }
 912 
 913 void ComputeLinearScanOrder::compute_order(BlockBegin* start_block) {
 914   TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing final block order"));
 915 
 916   // the start block is always the first block in the linear scan order
 917   _linear_scan_order = new BlockList(_num_blocks);
 918   append_block(start_block);
 919 
 920   assert(start_block->end()->as_Base() != NULL, "start block must end with Base-instruction");
 921   BlockBegin* std_entry = ((Base*)start_block->end())->std_entry();
 922   BlockBegin* osr_entry = ((Base*)start_block->end())->osr_entry();
 923 
 924   BlockBegin* sux_of_osr_entry = NULL;
 925   if (osr_entry != NULL) {
 926     // special handling for osr entry:
 927     // ignore the edge between the osr entry and its successor for processing
 928     // the osr entry block is added manually below
 929     assert(osr_entry->number_of_sux() == 1, "osr entry must have exactly one successor");
 930     assert(osr_entry->sux_at(0)->number_of_preds() >= 2, "sucessor of osr entry must have two predecessors (otherwise it is not present in normal control flow");
 931 
 932     sux_of_osr_entry = osr_entry->sux_at(0);
 933     dec_forward_branches(sux_of_osr_entry);
 934 
 935     compute_dominator(osr_entry, start_block);
 936     _iterative_dominators = true;
 937   }
 938   compute_dominator(std_entry, start_block);
 939 
 940   // start processing with standard entry block
 941   assert(_work_list.is_empty(), "list must be empty before processing");
 942 
 943   if (ready_for_processing(std_entry)) {
 944     sort_into_work_list(std_entry);
 945   } else {
 946     assert(false, "the std_entry must be ready for processing (otherwise, the method has no start block)");
 947   }
 948 
 949   do {
 950     BlockBegin* cur = _work_list.pop();
 951 
 952     if (cur == sux_of_osr_entry) {
 953       // the osr entry block is ignored in normal processing, it is never added to the
 954       // work list. Instead, it is added as late as possible manually here.
 955       append_block(osr_entry);
 956       compute_dominator(cur, osr_entry);
 957     }
 958     append_block(cur);
 959 
 960     int i;
 961     int num_sux = cur->number_of_sux();
 962     // changed loop order to get "intuitive" order of if- and else-blocks
 963     for (i = 0; i < num_sux; i++) {
 964       BlockBegin* sux = cur->sux_at(i);
 965       compute_dominator(sux, cur);
 966       if (ready_for_processing(sux)) {
 967         sort_into_work_list(sux);
 968       }
 969     }
 970     num_sux = cur->number_of_exception_handlers();
 971     for (i = 0; i < num_sux; i++) {
 972       BlockBegin* sux = cur->exception_handler_at(i);
 973       if (ready_for_processing(sux)) {
 974         sort_into_work_list(sux);
 975       }
 976     }
 977   } while (_work_list.length() > 0);
 978 }
 979 
 980 
 981 bool ComputeLinearScanOrder::compute_dominators_iter() {
 982   bool changed = false;
 983   int num_blocks = _linear_scan_order->length();
 984 
 985   assert(_linear_scan_order->at(0)->dominator() == NULL, "must not have dominator");
 986   assert(_linear_scan_order->at(0)->number_of_preds() == 0, "must not have predecessors");
 987   for (int i = 1; i < num_blocks; i++) {
 988     BlockBegin* block = _linear_scan_order->at(i);
 989 
 990     BlockBegin* dominator = block->pred_at(0);
 991     int num_preds = block->number_of_preds();
 992 
 993     TRACE_LINEAR_SCAN(4, tty->print_cr("DOM: Processing B%d", block->block_id()));
 994 
 995     for (int j = 0; j < num_preds; j++) {
 996 
 997       BlockBegin *pred = block->pred_at(j);
 998       TRACE_LINEAR_SCAN(4, tty->print_cr("   DOM: Subrocessing B%d", pred->block_id()));
 999 
1000       if (block->is_set(BlockBegin::exception_entry_flag)) {
1001         dominator = common_dominator(dominator, pred);
1002         int num_pred_preds = pred->number_of_preds();
1003         for (int k = 0; k < num_pred_preds; k++) {
1004           dominator = common_dominator(dominator, pred->pred_at(k));
1005         }
1006       } else {
1007         dominator = common_dominator(dominator, pred);
1008       }
1009     }
1010 
1011     if (dominator != block->dominator()) {
1012       TRACE_LINEAR_SCAN(4, tty->print_cr("DOM: updating dominator of B%d from B%d to B%d", block->block_id(), block->dominator()->block_id(), dominator->block_id()));
1013 
1014       block->set_dominator(dominator);
1015       changed = true;
1016     }
1017   }
1018   return changed;
1019 }
1020 
1021 void ComputeLinearScanOrder::compute_dominators() {
1022   TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing dominators (iterative computation reqired: %d)", _iterative_dominators));
1023 
1024   // iterative computation of dominators is only required for methods with non-natural loops
1025   // and OSR-methods. For all other methods, the dominators computed when generating the
1026   // linear scan block order are correct.
1027   if (_iterative_dominators) {
1028     do {
1029       TRACE_LINEAR_SCAN(1, tty->print_cr("DOM: next iteration of fix-point calculation"));
1030     } while (compute_dominators_iter());
1031   }
1032 
1033   // check that dominators are correct
1034   assert(!compute_dominators_iter(), "fix point not reached");
1035 
1036   // Add Blocks to dominates-Array
1037   int num_blocks = _linear_scan_order->length();
1038   for (int i = 0; i < num_blocks; i++) {
1039     BlockBegin* block = _linear_scan_order->at(i);
1040 
1041     BlockBegin *dom = block->dominator();
1042     if (dom) {
1043       assert(dom->dominator_depth() != -1, "Dominator must have been visited before");
1044       dom->dominates()->append(block);
1045       block->set_dominator_depth(dom->dominator_depth() + 1);
1046     } else {
1047       block->set_dominator_depth(0);
1048     }
1049   }
1050 }
1051 
1052 
1053 #ifdef ASSERT
1054 void ComputeLinearScanOrder::print_blocks() {
1055   if (TraceLinearScanLevel >= 2) {
1056     tty->print_cr("----- loop information:");
1057     for (int block_idx = 0; block_idx < _linear_scan_order->length(); block_idx++) {
1058       BlockBegin* cur = _linear_scan_order->at(block_idx);
1059 
1060       tty->print("%4d: B%2d: ", cur->linear_scan_number(), cur->block_id());
1061       for (int loop_idx = 0; loop_idx < _num_loops; loop_idx++) {
1062         tty->print ("%d ", is_block_in_loop(loop_idx, cur));
1063       }
1064       tty->print_cr(" -> loop_index: %2d, loop_depth: %2d", cur->loop_index(), cur->loop_depth());
1065     }
1066   }
1067 
1068   if (TraceLinearScanLevel >= 1) {
1069     tty->print_cr("----- linear-scan block order:");
1070     for (int block_idx = 0; block_idx < _linear_scan_order->length(); block_idx++) {
1071       BlockBegin* cur = _linear_scan_order->at(block_idx);
1072       tty->print("%4d: B%2d    loop: %2d  depth: %2d", cur->linear_scan_number(), cur->block_id(), cur->loop_index(), cur->loop_depth());
1073 
1074       tty->print(cur->is_set(BlockBegin::exception_entry_flag)         ? " ex" : "   ");
1075       tty->print(cur->is_set(BlockBegin::critical_edge_split_flag)     ? " ce" : "   ");
1076       tty->print(cur->is_set(BlockBegin::linear_scan_loop_header_flag) ? " lh" : "   ");
1077       tty->print(cur->is_set(BlockBegin::linear_scan_loop_end_flag)    ? " le" : "   ");
1078 
1079       if (cur->dominator() != NULL) {
1080         tty->print("    dom: B%d ", cur->dominator()->block_id());
1081       } else {
1082         tty->print("    dom: NULL ");
1083       }
1084 
1085       if (cur->number_of_preds() > 0) {
1086         tty->print("    preds: ");
1087         for (int j = 0; j < cur->number_of_preds(); j++) {
1088           BlockBegin* pred = cur->pred_at(j);
1089           tty->print("B%d ", pred->block_id());
1090         }
1091       }
1092       if (cur->number_of_sux() > 0) {
1093         tty->print("    sux: ");
1094         for (int j = 0; j < cur->number_of_sux(); j++) {
1095           BlockBegin* sux = cur->sux_at(j);
1096           tty->print("B%d ", sux->block_id());
1097         }
1098       }
1099       if (cur->number_of_exception_handlers() > 0) {
1100         tty->print("    ex: ");
1101         for (int j = 0; j < cur->number_of_exception_handlers(); j++) {
1102           BlockBegin* ex = cur->exception_handler_at(j);
1103           tty->print("B%d ", ex->block_id());
1104         }
1105       }
1106       tty->cr();
1107     }
1108   }
1109 }
1110 
1111 void ComputeLinearScanOrder::verify() {
1112   assert(_linear_scan_order->length() == _num_blocks, "wrong number of blocks in list");
1113 
1114   if (StressLinearScan) {
1115     // blocks are scrambled when StressLinearScan is used
1116     return;
1117   }
1118 
1119   // check that all successors of a block have a higher linear-scan-number
1120   // and that all predecessors of a block have a lower linear-scan-number
1121   // (only backward branches of loops are ignored)
1122   int i;
1123   for (i = 0; i < _linear_scan_order->length(); i++) {
1124     BlockBegin* cur = _linear_scan_order->at(i);
1125 
1126     assert(cur->linear_scan_number() == i, "incorrect linear_scan_number");
1127     assert(cur->linear_scan_number() >= 0 && cur->linear_scan_number() == _linear_scan_order->find(cur), "incorrect linear_scan_number");
1128 
1129     int j;
1130     for (j = cur->number_of_sux() - 1; j >= 0; j--) {
1131       BlockBegin* sux = cur->sux_at(j);
1132 
1133       assert(sux->linear_scan_number() >= 0 && sux->linear_scan_number() == _linear_scan_order->find(sux), "incorrect linear_scan_number");
1134       if (!sux->is_set(BlockBegin::backward_branch_target_flag)) {
1135         assert(cur->linear_scan_number() < sux->linear_scan_number(), "invalid order");
1136       }
1137       if (cur->loop_depth() == sux->loop_depth()) {
1138         assert(cur->loop_index() == sux->loop_index() || sux->is_set(BlockBegin::linear_scan_loop_header_flag), "successing blocks with same loop depth must have same loop index");
1139       }
1140     }
1141 
1142     for (j = cur->number_of_preds() - 1; j >= 0; j--) {
1143       BlockBegin* pred = cur->pred_at(j);
1144 
1145       assert(pred->linear_scan_number() >= 0 && pred->linear_scan_number() == _linear_scan_order->find(pred), "incorrect linear_scan_number");
1146       if (!cur->is_set(BlockBegin::backward_branch_target_flag)) {
1147         assert(cur->linear_scan_number() > pred->linear_scan_number(), "invalid order");
1148       }
1149       if (cur->loop_depth() == pred->loop_depth()) {
1150         assert(cur->loop_index() == pred->loop_index() || cur->is_set(BlockBegin::linear_scan_loop_header_flag), "successing blocks with same loop depth must have same loop index");
1151       }
1152 
1153       assert(cur->dominator()->linear_scan_number() <= cur->pred_at(j)->linear_scan_number(), "dominator must be before predecessors");
1154     }
1155 
1156     // check dominator
1157     if (i == 0) {
1158       assert(cur->dominator() == NULL, "first block has no dominator");
1159     } else {
1160       assert(cur->dominator() != NULL, "all but first block must have dominator");
1161     }
1162     // Assertion does not hold for exception handlers
1163     assert(cur->number_of_preds() != 1 || cur->dominator() == cur->pred_at(0) || cur->is_set(BlockBegin::exception_entry_flag), "Single predecessor must also be dominator");
1164   }
1165 
1166   // check that all loops are continuous
1167   for (int loop_idx = 0; loop_idx < _num_loops; loop_idx++) {
1168     int block_idx = 0;
1169     assert(!is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx)), "the first block must not be present in any loop");
1170 
1171     // skip blocks before the loop
1172     while (block_idx < _num_blocks && !is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx))) {
1173       block_idx++;
1174     }
1175     // skip blocks of loop
1176     while (block_idx < _num_blocks && is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx))) {
1177       block_idx++;
1178     }
1179     // after the first non-loop block, there must not be another loop-block
1180     while (block_idx < _num_blocks) {
1181       assert(!is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx)), "loop not continuous in linear-scan order");
1182       block_idx++;
1183     }
1184   }
1185 }
1186 #endif // ASSERT
1187 
1188 
1189 void IR::compute_code() {
1190   assert(is_valid(), "IR must be valid");
1191 
1192   ComputeLinearScanOrder compute_order(compilation(), start());
1193   _num_loops = compute_order.num_loops();
1194   _code = compute_order.linear_scan_order();
1195 }
1196 
1197 
1198 void IR::compute_use_counts() {
1199   // make sure all values coming out of this block get evaluated.
1200   int num_blocks = _code->length();
1201   for (int i = 0; i < num_blocks; i++) {
1202     _code->at(i)->end()->state()->pin_stack_for_linear_scan();
1203   }
1204 
1205   // compute use counts
1206   UseCountComputer::compute(_code);
1207 }
1208 
1209 
1210 void IR::iterate_preorder(BlockClosure* closure) {
1211   assert(is_valid(), "IR must be valid");
1212   start()->iterate_preorder(closure);
1213 }
1214 
1215 
1216 void IR::iterate_postorder(BlockClosure* closure) {
1217   assert(is_valid(), "IR must be valid");
1218   start()->iterate_postorder(closure);
1219 }
1220 
1221 void IR::iterate_linear_scan_order(BlockClosure* closure) {
1222   linear_scan_order()->iterate_forward(closure);
1223 }
1224 
1225 
1226 #ifndef PRODUCT
1227 class BlockPrinter: public BlockClosure {
1228  private:
1229   InstructionPrinter* _ip;
1230   bool                _cfg_only;
1231   bool                _live_only;
1232 
1233  public:
1234   BlockPrinter(InstructionPrinter* ip, bool cfg_only, bool live_only = false) {
1235     _ip       = ip;
1236     _cfg_only = cfg_only;
1237     _live_only = live_only;
1238   }
1239 
1240   virtual void block_do(BlockBegin* block) {
1241     if (_cfg_only) {
1242       _ip->print_instr(block); tty->cr();
1243     } else {
1244       block->print_block(*_ip, _live_only);
1245     }
1246   }
1247 };
1248 
1249 
1250 void IR::print(BlockBegin* start, bool cfg_only, bool live_only) {
1251   ttyLocker ttyl;
1252   InstructionPrinter ip(!cfg_only);
1253   BlockPrinter bp(&ip, cfg_only, live_only);
1254   start->iterate_preorder(&bp);
1255   tty->cr();
1256 }
1257 
1258 void IR::print(bool cfg_only, bool live_only) {
1259   if (is_valid()) {
1260     print(start(), cfg_only, live_only);
1261   } else {
1262     tty->print_cr("invalid IR");
1263   }
1264 }
1265 
1266 
1267 typedef GrowableArray<BlockList*> BlockListList;
1268 
1269 class PredecessorValidator : public BlockClosure {
1270  private:
1271   BlockListList* _predecessors;
1272   BlockList*     _blocks;
1273 
1274   static int cmp(BlockBegin** a, BlockBegin** b) {
1275     return (*a)->block_id() - (*b)->block_id();
1276   }
1277 
1278  public:
1279   PredecessorValidator(IR* hir) {
1280     ResourceMark rm;
1281     _predecessors = new BlockListList(BlockBegin::number_of_blocks(), BlockBegin::number_of_blocks(), NULL);
1282     _blocks = new BlockList();
1283 
1284     int i;
1285     hir->start()->iterate_preorder(this);
1286     if (hir->code() != NULL) {
1287       assert(hir->code()->length() == _blocks->length(), "must match");
1288       for (i = 0; i < _blocks->length(); i++) {
1289         assert(hir->code()->contains(_blocks->at(i)), "should be in both lists");
1290       }
1291     }
1292 
1293     for (i = 0; i < _blocks->length(); i++) {
1294       BlockBegin* block = _blocks->at(i);
1295       BlockList* preds = _predecessors->at(block->block_id());
1296       if (preds == NULL) {
1297         assert(block->number_of_preds() == 0, "should be the same");
1298         continue;
1299       }
1300 
1301       // clone the pred list so we can mutate it
1302       BlockList* pred_copy = new BlockList();
1303       int j;
1304       for (j = 0; j < block->number_of_preds(); j++) {
1305         pred_copy->append(block->pred_at(j));
1306       }
1307       // sort them in the same order
1308       preds->sort(cmp);
1309       pred_copy->sort(cmp);
1310       int length = MIN2(preds->length(), block->number_of_preds());
1311       for (j = 0; j < block->number_of_preds(); j++) {
1312         assert(preds->at(j) == pred_copy->at(j), "must match");
1313       }
1314 
1315       assert(preds->length() == block->number_of_preds(), "should be the same");
1316     }
1317   }
1318 
1319   virtual void block_do(BlockBegin* block) {
1320     _blocks->append(block);
1321     BlockEnd* be = block->end();
1322     int n = be->number_of_sux();
1323     int i;
1324     for (i = 0; i < n; i++) {
1325       BlockBegin* sux = be->sux_at(i);
1326       assert(!sux->is_set(BlockBegin::exception_entry_flag), "must not be xhandler");
1327 
1328       BlockList* preds = _predecessors->at_grow(sux->block_id(), NULL);
1329       if (preds == NULL) {
1330         preds = new BlockList();
1331         _predecessors->at_put(sux->block_id(), preds);
1332       }
1333       preds->append(block);
1334     }
1335 
1336     n = block->number_of_exception_handlers();
1337     for (i = 0; i < n; i++) {
1338       BlockBegin* sux = block->exception_handler_at(i);
1339       assert(sux->is_set(BlockBegin::exception_entry_flag), "must be xhandler");
1340 
1341       BlockList* preds = _predecessors->at_grow(sux->block_id(), NULL);
1342       if (preds == NULL) {
1343         preds = new BlockList();
1344         _predecessors->at_put(sux->block_id(), preds);
1345       }
1346       preds->append(block);
1347     }
1348   }
1349 };
1350 
1351 class VerifyBlockBeginField : public BlockClosure {
1352 
1353 public:
1354 
1355   virtual void block_do(BlockBegin *block) {
1356     for ( Instruction *cur = block; cur != NULL; cur = cur->next()) {
1357       assert(cur->block() == block, "Block begin is not correct");
1358     }
1359   }
1360 };
1361 
1362 void IR::verify() {
1363 #ifdef ASSERT
1364   PredecessorValidator pv(this);
1365   VerifyBlockBeginField verifier;
1366   this->iterate_postorder(&verifier);
1367 #endif
1368 }
1369 
1370 #endif // PRODUCT
1371 
1372 void SubstitutionResolver::visit(Value* v) {
1373   Value v0 = *v;
1374   if (v0) {
1375     Value vs = v0->subst();
1376     if (vs != v0) {
1377       *v = v0->subst();
1378     }
1379   }
1380 }
1381 
1382 #ifdef ASSERT
1383 class SubstitutionChecker: public ValueVisitor {
1384   void visit(Value* v) {
1385     Value v0 = *v;
1386     if (v0) {
1387       Value vs = v0->subst();
1388       assert(vs == v0, "missed substitution");
1389     }
1390   }
1391 };
1392 #endif
1393 
1394 
1395 void SubstitutionResolver::block_do(BlockBegin* block) {
1396   Instruction* last = NULL;
1397   for (Instruction* n = block; n != NULL;) {
1398     n->values_do(this);
1399     // need to remove this instruction from the instruction stream
1400     if (n->subst() != n) {
1401       guarantee(last != NULL, "must have last");
1402       last->set_next(n->next());
1403     } else {
1404       last = n;
1405     }
1406     n = last->next();
1407   }
1408 
1409 #ifdef ASSERT
1410   SubstitutionChecker check_substitute;
1411   if (block->state()) block->state()->values_do(&check_substitute);
1412   block->block_values_do(&check_substitute);
1413   if (block->end() && block->end()->state()) block->end()->state()->values_do(&check_substitute);
1414 #endif
1415 }