1 /*
   2  * Copyright (c) 1999, 2022, 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   ciMethod* cur_method = scope()->method();
 175   int       cur_bci    = bci();
 176   if (cur_method != NULL && cur_bci != SynchronizationEntryBCI) {
 177     Bytecodes::Code code = cur_method->java_code_at_bci(cur_bci);
 178     return Interpreter::bytecode_should_reexecute(code);
 179   } else
 180     return false;
 181 }
 182 
 183 
 184 // Implementation of CodeEmitInfo
 185 
 186 // Stack must be NON-null
 187 CodeEmitInfo::CodeEmitInfo(ValueStack* stack, XHandlers* exception_handlers, bool deoptimize_on_exception)
 188   : _scope_debug_info(NULL)
 189   , _scope(stack->scope())
 190   , _exception_handlers(exception_handlers)
 191   , _oop_map(NULL)
 192   , _stack(stack)
 193   , _is_method_handle_invoke(false)
 194   , _deoptimize_on_exception(deoptimize_on_exception)
 195   , _force_reexecute(false) {
 196   assert(_stack != NULL, "must be non null");
 197 }
 198 
 199 
 200 CodeEmitInfo::CodeEmitInfo(CodeEmitInfo* info, ValueStack* stack)
 201   : _scope_debug_info(NULL)
 202   , _scope(info->_scope)
 203   , _exception_handlers(NULL)
 204   , _oop_map(NULL)
 205   , _stack(stack == NULL ? info->_stack : stack)
 206   , _is_method_handle_invoke(info->_is_method_handle_invoke)
 207   , _deoptimize_on_exception(info->_deoptimize_on_exception)
 208   , _force_reexecute(info->_force_reexecute) {
 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) {
 218   // record the safepoint before recording the debug info for enclosing scopes
 219   recorder->add_safepoint(pc_offset, _oop_map->deep_copy());
 220   bool reexecute = _force_reexecute || _scope_debug_info->should_reexecute();
 221   _scope_debug_info->record_debug_info(recorder, pc_offset, reexecute, _is_method_handle_invoke);
 222   recorder->end_safepoint(pc_offset);
 223 }
 224 
 225 
 226 void CodeEmitInfo::add_register_oop(LIR_Opr opr) {
 227   assert(_oop_map != NULL, "oop map must already exist");
 228   assert(opr->is_single_cpu(), "should not call otherwise");
 229 
 230   VMReg name = frame_map()->regname(opr);
 231   _oop_map->set_oop(name);
 232 }
 233 
 234 // Mirror the stack size calculation in the deopt code
 235 // How much stack space would we need at this point in the program in
 236 // case of deoptimization?
 237 int CodeEmitInfo::interpreter_frame_size() const {
 238   ValueStack* state = _stack;
 239   int size = 0;
 240   int callee_parameters = 0;
 241   int callee_locals = 0;
 242   int extra_args = state->scope()->method()->max_stack() - state->stack_size();
 243 
 244   while (state != NULL) {
 245     int locks = state->locks_size();
 246     int temps = state->stack_size();
 247     bool is_top_frame = (state == _stack);
 248     ciMethod* method = state->scope()->method();
 249 
 250     int frame_size = BytesPerWord * Interpreter::size_activation(method->max_stack(),
 251                                                                  temps + callee_parameters,
 252                                                                  extra_args,
 253                                                                  locks,
 254                                                                  callee_parameters,
 255                                                                  callee_locals,
 256                                                                  is_top_frame);
 257     size += frame_size;
 258 
 259     callee_parameters = method->size_of_parameters();
 260     callee_locals = method->max_locals();
 261     extra_args = 0;
 262     state = state->caller_state();
 263   }
 264   return size + Deoptimization::last_frame_adjust(0, callee_locals) * BytesPerWord;
 265 }
 266 
 267 // Implementation of IR
 268 
 269 IR::IR(Compilation* compilation, ciMethod* method, int osr_bci) :
 270   _num_loops(0) {
 271   // setup IR fields
 272   _compilation = compilation;
 273   _top_scope   = new IRScope(compilation, NULL, -1, method, osr_bci, true);
 274   _code        = NULL;
 275 }
 276 
 277 
 278 void IR::optimize_blocks() {
 279   Optimizer opt(this);
 280   if (!compilation()->profile_branches()) {
 281     if (DoCEE) {
 282       opt.eliminate_conditional_expressions();
 283 #ifndef PRODUCT
 284       if (PrintCFG || PrintCFG1) { tty->print_cr("CFG after CEE"); print(true); }
 285       if (PrintIR  || PrintIR1 ) { tty->print_cr("IR after CEE"); print(false); }
 286 #endif
 287     }
 288     if (EliminateBlocks) {
 289       opt.eliminate_blocks();
 290 #ifndef PRODUCT
 291       if (PrintCFG || PrintCFG1) { tty->print_cr("CFG after block elimination"); print(true); }
 292       if (PrintIR  || PrintIR1 ) { tty->print_cr("IR after block elimination"); print(false); }
 293 #endif
 294     }
 295   }
 296 }
 297 
 298 void IR::eliminate_null_checks() {
 299   Optimizer opt(this);
 300   if (EliminateNullChecks) {
 301     opt.eliminate_null_checks();
 302 #ifndef PRODUCT
 303     if (PrintCFG || PrintCFG1) { tty->print_cr("CFG after null check elimination"); print(true); }
 304     if (PrintIR  || PrintIR1 ) { tty->print_cr("IR after null check elimination"); print(false); }
 305 #endif
 306   }
 307 }
 308 
 309 
 310 static int sort_pairs(BlockPair** a, BlockPair** b) {
 311   if ((*a)->from() == (*b)->from()) {
 312     return (*a)->to()->block_id() - (*b)->to()->block_id();
 313   } else {
 314     return (*a)->from()->block_id() - (*b)->from()->block_id();
 315   }
 316 }
 317 
 318 
 319 class CriticalEdgeFinder: public BlockClosure {
 320   BlockPairList blocks;
 321   IR*       _ir;
 322 
 323  public:
 324   CriticalEdgeFinder(IR* ir): _ir(ir) {}
 325   void block_do(BlockBegin* bb) {
 326     BlockEnd* be = bb->end();
 327     int nos = be->number_of_sux();
 328     if (nos >= 2) {
 329       for (int i = 0; i < nos; i++) {
 330         BlockBegin* sux = be->sux_at(i);
 331         if (sux->number_of_preds() >= 2) {
 332           blocks.append(new BlockPair(bb, sux));
 333         }
 334       }
 335     }
 336   }
 337 
 338   void split_edges() {
 339     BlockPair* last_pair = NULL;
 340     blocks.sort(sort_pairs);
 341     for (int i = 0; i < blocks.length(); i++) {
 342       BlockPair* pair = blocks.at(i);
 343       if (last_pair != NULL && pair->is_same(last_pair)) continue;
 344       BlockBegin* from = pair->from();
 345       BlockBegin* to = pair->to();
 346       BlockBegin* split = from->insert_block_between(to);
 347 #ifndef PRODUCT
 348       if ((PrintIR || PrintIR1) && Verbose) {
 349         tty->print_cr("Split critical edge B%d -> B%d (new block B%d)",
 350                       from->block_id(), to->block_id(), split->block_id());
 351       }
 352 #endif
 353       last_pair = pair;
 354     }
 355   }
 356 };
 357 
 358 void IR::split_critical_edges() {
 359   CriticalEdgeFinder cef(this);
 360 
 361   iterate_preorder(&cef);
 362   cef.split_edges();
 363 }
 364 
 365 
 366 class UseCountComputer: public ValueVisitor, BlockClosure {
 367  private:
 368   void visit(Value* n) {
 369     // Local instructions and Phis for expression stack values at the
 370     // start of basic blocks are not added to the instruction list
 371     if (!(*n)->is_linked() && (*n)->can_be_linked()) {
 372       assert(false, "a node was not appended to the graph");
 373       Compilation::current()->bailout("a node was not appended to the graph");
 374     }
 375     // use n's input if not visited before
 376     if (!(*n)->is_pinned() && !(*n)->has_uses()) {
 377       // note: a) if the instruction is pinned, it will be handled by compute_use_count
 378       //       b) if the instruction has uses, it was touched before
 379       //       => in both cases we don't need to update n's values
 380       uses_do(n);
 381     }
 382     // use n
 383     (*n)->_use_count++;
 384   }
 385 
 386   Values* worklist;
 387   int depth;
 388   enum {
 389     max_recurse_depth = 20
 390   };
 391 
 392   void uses_do(Value* n) {
 393     depth++;
 394     if (depth > max_recurse_depth) {
 395       // don't allow the traversal to recurse too deeply
 396       worklist->push(*n);
 397     } else {
 398       (*n)->input_values_do(this);
 399       // special handling for some instructions
 400       if ((*n)->as_BlockEnd() != NULL) {
 401         // note on BlockEnd:
 402         //   must 'use' the stack only if the method doesn't
 403         //   terminate, however, in those cases stack is empty
 404         (*n)->state_values_do(this);
 405       }
 406     }
 407     depth--;
 408   }
 409 
 410   void block_do(BlockBegin* b) {
 411     depth = 0;
 412     // process all pinned nodes as the roots of expression trees
 413     for (Instruction* n = b; n != NULL; n = n->next()) {
 414       if (n->is_pinned()) uses_do(&n);
 415     }
 416     assert(depth == 0, "should have counted back down");
 417 
 418     // now process any unpinned nodes which recursed too deeply
 419     while (worklist->length() > 0) {
 420       Value t = worklist->pop();
 421       if (!t->is_pinned()) {
 422         // compute the use count
 423         uses_do(&t);
 424 
 425         // pin the instruction so that LIRGenerator doesn't recurse
 426         // too deeply during it's evaluation.
 427         t->pin();
 428       }
 429     }
 430     assert(depth == 0, "should have counted back down");
 431   }
 432 
 433   UseCountComputer() {
 434     worklist = new Values();
 435     depth = 0;
 436   }
 437 
 438  public:
 439   static void compute(BlockList* blocks) {
 440     UseCountComputer ucc;
 441     blocks->iterate_backward(&ucc);
 442   }
 443 };
 444 
 445 
 446 // helper macro for short definition of trace-output inside code
 447 #ifdef ASSERT
 448   #define TRACE_LINEAR_SCAN(level, code)       \
 449     if (TraceLinearScanLevel >= level) {       \
 450       code;                                    \
 451     }
 452 #else
 453   #define TRACE_LINEAR_SCAN(level, code)
 454 #endif
 455 
 456 class ComputeLinearScanOrder : public StackObj {
 457  private:
 458   int        _max_block_id;        // the highest block_id of a block
 459   int        _num_blocks;          // total number of blocks (smaller than _max_block_id)
 460   int        _num_loops;           // total number of loops
 461   bool       _iterative_dominators;// method requires iterative computation of dominatiors
 462 
 463   BlockList* _linear_scan_order;   // the resulting list of blocks in correct order
 464 
 465   ResourceBitMap _visited_blocks;   // used for recursive processing of blocks
 466   ResourceBitMap _active_blocks;    // used for recursive processing of blocks
 467   ResourceBitMap _dominator_blocks; // temproary BitMap used for computation of dominator
 468   intArray       _forward_branches; // number of incoming forward branches for each block
 469   BlockList      _loop_end_blocks;  // list of all loop end blocks collected during count_edges
 470   BitMap2D       _loop_map;         // two-dimensional bit set: a bit is set if a block is contained in a loop
 471   BlockList      _work_list;        // temporary list (used in mark_loops and compute_order)
 472   BlockList      _loop_headers;
 473 
 474   Compilation* _compilation;
 475 
 476   // accessors for _visited_blocks and _active_blocks
 477   void init_visited()                     { _active_blocks.clear(); _visited_blocks.clear(); }
 478   bool is_visited(BlockBegin* b) const    { return _visited_blocks.at(b->block_id()); }
 479   bool is_active(BlockBegin* b) const     { return _active_blocks.at(b->block_id()); }
 480   void set_visited(BlockBegin* b)         { assert(!is_visited(b), "already set"); _visited_blocks.set_bit(b->block_id()); }
 481   void set_active(BlockBegin* b)          { assert(!is_active(b), "already set");  _active_blocks.set_bit(b->block_id()); }
 482   void clear_active(BlockBegin* b)        { assert(is_active(b), "not already");   _active_blocks.clear_bit(b->block_id()); }
 483 
 484   // accessors for _forward_branches
 485   void inc_forward_branches(BlockBegin* b) { _forward_branches.at_put(b->block_id(), _forward_branches.at(b->block_id()) + 1); }
 486   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()); }
 487 
 488   // accessors for _loop_map
 489   bool is_block_in_loop   (int loop_idx, BlockBegin* b) const { return _loop_map.at(loop_idx, b->block_id()); }
 490   void set_block_in_loop  (int loop_idx, BlockBegin* b)       { _loop_map.set_bit(loop_idx, b->block_id()); }
 491   void clear_block_in_loop(int loop_idx, int block_id)        { _loop_map.clear_bit(loop_idx, block_id); }
 492 
 493   // count edges between blocks
 494   void count_edges(BlockBegin* cur, BlockBegin* parent);
 495 
 496   // loop detection
 497   void mark_loops();
 498   void clear_non_natural_loops(BlockBegin* start_block);
 499   void assign_loop_depth(BlockBegin* start_block);
 500 
 501   // computation of final block order
 502   BlockBegin* common_dominator(BlockBegin* a, BlockBegin* b);
 503   void compute_dominator(BlockBegin* cur, BlockBegin* parent);
 504   void compute_dominator_impl(BlockBegin* cur, BlockBegin* parent);
 505   int  compute_weight(BlockBegin* cur);
 506   bool ready_for_processing(BlockBegin* cur);
 507   void sort_into_work_list(BlockBegin* b);
 508   void append_block(BlockBegin* cur);
 509   void compute_order(BlockBegin* start_block);
 510 
 511   // fixup of dominators for non-natural loops
 512   bool compute_dominators_iter();
 513   void compute_dominators();
 514 
 515   // debug functions
 516   DEBUG_ONLY(void print_blocks();)
 517   DEBUG_ONLY(void verify();)
 518 
 519   Compilation* compilation() const { return _compilation; }
 520  public:
 521   ComputeLinearScanOrder(Compilation* c, BlockBegin* start_block);
 522 
 523   // accessors for final result
 524   BlockList* linear_scan_order() const    { return _linear_scan_order; }
 525   int        num_loops() const            { return _num_loops; }
 526 };
 527 
 528 
 529 ComputeLinearScanOrder::ComputeLinearScanOrder(Compilation* c, BlockBegin* start_block) :
 530   _max_block_id(BlockBegin::number_of_blocks()),
 531   _num_blocks(0),
 532   _num_loops(0),
 533   _iterative_dominators(false),
 534   _linear_scan_order(NULL), // initialized later with correct size
 535   _visited_blocks(_max_block_id),
 536   _active_blocks(_max_block_id),
 537   _dominator_blocks(_max_block_id),
 538   _forward_branches(_max_block_id, _max_block_id, 0),
 539   _loop_end_blocks(8),
 540   _loop_map(0),             // initialized later with correct size
 541   _work_list(8),
 542   _compilation(c)
 543 {
 544   TRACE_LINEAR_SCAN(2, tty->print_cr("***** computing linear-scan block order"));
 545 
 546   count_edges(start_block, NULL);
 547 
 548   if (compilation()->is_profiling()) {
 549     ciMethod *method = compilation()->method();
 550     if (!method->is_accessor()) {
 551       ciMethodData* md = method->method_data_or_null();
 552       assert(md != NULL, "Sanity");
 553       md->set_compilation_stats(_num_loops, _num_blocks);
 554     }
 555   }
 556 
 557   if (_num_loops > 0) {
 558     mark_loops();
 559     clear_non_natural_loops(start_block);
 560     assign_loop_depth(start_block);
 561   }
 562 
 563   compute_order(start_block);
 564   compute_dominators();
 565 
 566   DEBUG_ONLY(print_blocks());
 567   DEBUG_ONLY(verify());
 568 }
 569 
 570 
 571 // Traverse the CFG:
 572 // * count total number of blocks
 573 // * count all incoming edges and backward incoming edges
 574 // * number loop header blocks
 575 // * create a list with all loop end blocks
 576 void ComputeLinearScanOrder::count_edges(BlockBegin* cur, BlockBegin* parent) {
 577   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));
 578   assert(cur->dominator() == NULL, "dominator already initialized");
 579 
 580   if (is_active(cur)) {
 581     TRACE_LINEAR_SCAN(3, tty->print_cr("backward branch"));
 582     assert(is_visited(cur), "block must be visisted when block is active");
 583     assert(parent != NULL, "must have parent");
 584 
 585     cur->set(BlockBegin::backward_branch_target_flag);
 586 
 587     // When a loop header is also the start of an exception handler, then the backward branch is
 588     // an exception edge. Because such edges are usually critical edges which cannot be split, the
 589     // loop must be excluded here from processing.
 590     if (cur->is_set(BlockBegin::exception_entry_flag)) {
 591       // Make sure that dominators are correct in this weird situation
 592       _iterative_dominators = true;
 593       return;
 594     }
 595 
 596     cur->set(BlockBegin::linear_scan_loop_header_flag);
 597     parent->set(BlockBegin::linear_scan_loop_end_flag);
 598 
 599     assert(parent->number_of_sux() == 1 && parent->sux_at(0) == cur,
 600            "loop end blocks must have one successor (critical edges are split)");
 601 
 602     _loop_end_blocks.append(parent);
 603     return;
 604   }
 605 
 606   // increment number of incoming forward branches
 607   inc_forward_branches(cur);
 608 
 609   if (is_visited(cur)) {
 610     TRACE_LINEAR_SCAN(3, tty->print_cr("block already visited"));
 611     return;
 612   }
 613 
 614   _num_blocks++;
 615   set_visited(cur);
 616   set_active(cur);
 617 
 618   // recursive call for all successors
 619   int i;
 620   for (i = cur->number_of_sux() - 1; i >= 0; i--) {
 621     count_edges(cur->sux_at(i), cur);
 622   }
 623   for (i = cur->number_of_exception_handlers() - 1; i >= 0; i--) {
 624     count_edges(cur->exception_handler_at(i), cur);
 625   }
 626 
 627   clear_active(cur);
 628 
 629   // Each loop has a unique number.
 630   // When multiple loops are nested, assign_loop_depth assumes that the
 631   // innermost loop has the lowest number. This is guaranteed by setting
 632   // the loop number after the recursive calls for the successors above
 633   // have returned.
 634   if (cur->is_set(BlockBegin::linear_scan_loop_header_flag)) {
 635     assert(cur->loop_index() == -1, "cannot set loop-index twice");
 636     TRACE_LINEAR_SCAN(3, tty->print_cr("Block B%d is loop header of loop %d", cur->block_id(), _num_loops));
 637 
 638     cur->set_loop_index(_num_loops);
 639     _loop_headers.append(cur);
 640     _num_loops++;
 641   }
 642 
 643   TRACE_LINEAR_SCAN(3, tty->print_cr("Finished count_edges for block B%d", cur->block_id()));
 644 }
 645 
 646 
 647 void ComputeLinearScanOrder::mark_loops() {
 648   TRACE_LINEAR_SCAN(3, tty->print_cr("----- marking loops"));
 649 
 650   _loop_map = BitMap2D(_num_loops, _max_block_id);
 651 
 652   for (int i = _loop_end_blocks.length() - 1; i >= 0; i--) {
 653     BlockBegin* loop_end   = _loop_end_blocks.at(i);
 654     BlockBegin* loop_start = loop_end->sux_at(0);
 655     int         loop_idx   = loop_start->loop_index();
 656 
 657     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));
 658     assert(loop_end->is_set(BlockBegin::linear_scan_loop_end_flag), "loop end flag must be set");
 659     assert(loop_end->number_of_sux() == 1, "incorrect number of successors");
 660     assert(loop_start->is_set(BlockBegin::linear_scan_loop_header_flag), "loop header flag must be set");
 661     assert(loop_idx >= 0 && loop_idx < _num_loops, "loop index not set");
 662     assert(_work_list.is_empty(), "work list must be empty before processing");
 663 
 664     // add the end-block of the loop to the working list
 665     _work_list.push(loop_end);
 666     set_block_in_loop(loop_idx, loop_end);
 667     do {
 668       BlockBegin* cur = _work_list.pop();
 669 
 670       TRACE_LINEAR_SCAN(3, tty->print_cr("    processing B%d", cur->block_id()));
 671       assert(is_block_in_loop(loop_idx, cur), "bit in loop map must be set when block is in work list");
 672 
 673       // recursive processing of all predecessors ends when start block of loop is reached
 674       if (cur != loop_start && !cur->is_set(BlockBegin::osr_entry_flag)) {
 675         for (int j = cur->number_of_preds() - 1; j >= 0; j--) {
 676           BlockBegin* pred = cur->pred_at(j);
 677 
 678           if (!is_block_in_loop(loop_idx, pred) /*&& !pred->is_set(BlockBeginosr_entry_flag)*/) {
 679             // this predecessor has not been processed yet, so add it to work list
 680             TRACE_LINEAR_SCAN(3, tty->print_cr("    pushing B%d", pred->block_id()));
 681             _work_list.push(pred);
 682             set_block_in_loop(loop_idx, pred);
 683           }
 684         }
 685       }
 686     } while (!_work_list.is_empty());
 687   }
 688 }
 689 
 690 
 691 // check for non-natural loops (loops where the loop header does not dominate
 692 // all other loop blocks = loops with mulitple entries).
 693 // such loops are ignored
 694 void ComputeLinearScanOrder::clear_non_natural_loops(BlockBegin* start_block) {
 695   for (int i = _num_loops - 1; i >= 0; i--) {
 696     if (is_block_in_loop(i, start_block)) {
 697       // loop i contains the entry block of the method
 698       // -> this is not a natural loop, so ignore it
 699       TRACE_LINEAR_SCAN(2, tty->print_cr("Loop %d is non-natural, so it is ignored", i));
 700 
 701       BlockBegin *loop_header = _loop_headers.at(i);
 702       assert(loop_header->is_set(BlockBegin::linear_scan_loop_header_flag), "Must be loop header");
 703 
 704       for (int j = 0; j < loop_header->number_of_preds(); j++) {
 705         BlockBegin *pred = loop_header->pred_at(j);
 706         pred->clear(BlockBegin::linear_scan_loop_end_flag);
 707       }
 708 
 709       loop_header->clear(BlockBegin::linear_scan_loop_header_flag);
 710 
 711       for (int block_id = _max_block_id - 1; block_id >= 0; block_id--) {
 712         clear_block_in_loop(i, block_id);
 713       }
 714       _iterative_dominators = true;
 715     }
 716   }
 717 }
 718 
 719 void ComputeLinearScanOrder::assign_loop_depth(BlockBegin* start_block) {
 720   TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing loop-depth and weight"));
 721   init_visited();
 722 
 723   assert(_work_list.is_empty(), "work list must be empty before processing");
 724   _work_list.append(start_block);
 725 
 726   do {
 727     BlockBegin* cur = _work_list.pop();
 728 
 729     if (!is_visited(cur)) {
 730       set_visited(cur);
 731       TRACE_LINEAR_SCAN(4, tty->print_cr("Computing loop depth for block B%d", cur->block_id()));
 732 
 733       // compute loop-depth and loop-index for the block
 734       assert(cur->loop_depth() == 0, "cannot set loop-depth twice");
 735       int i;
 736       int loop_depth = 0;
 737       int min_loop_idx = -1;
 738       for (i = _num_loops - 1; i >= 0; i--) {
 739         if (is_block_in_loop(i, cur)) {
 740           loop_depth++;
 741           min_loop_idx = i;
 742         }
 743       }
 744       cur->set_loop_depth(loop_depth);
 745       cur->set_loop_index(min_loop_idx);
 746 
 747       // append all unvisited successors to work list
 748       for (i = cur->number_of_sux() - 1; i >= 0; i--) {
 749         _work_list.append(cur->sux_at(i));
 750       }
 751       for (i = cur->number_of_exception_handlers() - 1; i >= 0; i--) {
 752         _work_list.append(cur->exception_handler_at(i));
 753       }
 754     }
 755   } while (!_work_list.is_empty());
 756 }
 757 
 758 
 759 BlockBegin* ComputeLinearScanOrder::common_dominator(BlockBegin* a, BlockBegin* b) {
 760   assert(a != NULL && b != NULL, "must have input blocks");
 761 
 762   _dominator_blocks.clear();
 763   while (a != NULL) {
 764     _dominator_blocks.set_bit(a->block_id());
 765     assert(a->dominator() != NULL || a == _linear_scan_order->at(0), "dominator must be initialized");
 766     a = a->dominator();
 767   }
 768   while (b != NULL && !_dominator_blocks.at(b->block_id())) {
 769     assert(b->dominator() != NULL || b == _linear_scan_order->at(0), "dominator must be initialized");
 770     b = b->dominator();
 771   }
 772 
 773   assert(b != NULL, "could not find dominator");
 774   return b;
 775 }
 776 
 777 void ComputeLinearScanOrder::compute_dominator(BlockBegin* cur, BlockBegin* parent) {
 778   init_visited();
 779   compute_dominator_impl(cur, parent);
 780 }
 781 
 782 void ComputeLinearScanOrder::compute_dominator_impl(BlockBegin* cur, BlockBegin* parent) {
 783   // Mark as visited to avoid recursive calls with same parent
 784   set_visited(cur);
 785 
 786   if (cur->dominator() == NULL) {
 787     TRACE_LINEAR_SCAN(4, tty->print_cr("DOM: initializing dominator of B%d to B%d", cur->block_id(), parent->block_id()));
 788     cur->set_dominator(parent);
 789 
 790   } else if (!(cur->is_set(BlockBegin::linear_scan_loop_header_flag) && parent->is_set(BlockBegin::linear_scan_loop_end_flag))) {
 791     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()));
 792     // Does not hold for exception blocks
 793     assert(cur->number_of_preds() > 1 || cur->is_set(BlockBegin::exception_entry_flag), "");
 794     cur->set_dominator(common_dominator(cur->dominator(), parent));
 795   }
 796 
 797   // Additional edge to xhandler of all our successors
 798   // range check elimination needs that the state at the end of a
 799   // block be valid in every block it dominates so cur must dominate
 800   // the exception handlers of its successors.
 801   int num_cur_xhandler = cur->number_of_exception_handlers();
 802   for (int j = 0; j < num_cur_xhandler; j++) {
 803     BlockBegin* xhandler = cur->exception_handler_at(j);
 804     if (!is_visited(xhandler)) {
 805       compute_dominator_impl(xhandler, parent);
 806     }
 807   }
 808 }
 809 
 810 
 811 int ComputeLinearScanOrder::compute_weight(BlockBegin* cur) {
 812   BlockBegin* single_sux = NULL;
 813   if (cur->number_of_sux() == 1) {
 814     single_sux = cur->sux_at(0);
 815   }
 816 
 817   // limit loop-depth to 15 bit (only for security reason, it will never be so big)
 818   int weight = (cur->loop_depth() & 0x7FFF) << 16;
 819 
 820   // general macro for short definition of weight flags
 821   // the first instance of INC_WEIGHT_IF has the highest priority
 822   int cur_bit = 15;
 823   #define INC_WEIGHT_IF(condition) if ((condition)) { weight |= (1 << cur_bit); } cur_bit--;
 824 
 825   // this is necessery for the (very rare) case that two successing blocks have
 826   // the same loop depth, but a different loop index (can happen for endless loops
 827   // with exception handlers)
 828   INC_WEIGHT_IF(!cur->is_set(BlockBegin::linear_scan_loop_header_flag));
 829 
 830   // loop end blocks (blocks that end with a backward branch) are added
 831   // after all other blocks of the loop.
 832   INC_WEIGHT_IF(!cur->is_set(BlockBegin::linear_scan_loop_end_flag));
 833 
 834   // critical edge split blocks are prefered because than they have a bigger
 835   // proability to be completely empty
 836   INC_WEIGHT_IF(cur->is_set(BlockBegin::critical_edge_split_flag));
 837 
 838   // exceptions should not be thrown in normal control flow, so these blocks
 839   // are added as late as possible
 840   INC_WEIGHT_IF(cur->end()->as_Throw() == NULL  && (single_sux == NULL || single_sux->end()->as_Throw()  == NULL));
 841   INC_WEIGHT_IF(cur->end()->as_Return() == NULL && (single_sux == NULL || single_sux->end()->as_Return() == NULL));
 842 
 843   // exceptions handlers are added as late as possible
 844   INC_WEIGHT_IF(!cur->is_set(BlockBegin::exception_entry_flag));
 845 
 846   // guarantee that weight is > 0
 847   weight |= 1;
 848 
 849   #undef INC_WEIGHT_IF
 850   assert(cur_bit >= 0, "too many flags");
 851   assert(weight > 0, "weight cannot become negative");
 852 
 853   return weight;
 854 }
 855 
 856 bool ComputeLinearScanOrder::ready_for_processing(BlockBegin* cur) {
 857   // Discount the edge just traveled.
 858   // When the number drops to zero, all forward branches were processed
 859   if (dec_forward_branches(cur) != 0) {
 860     return false;
 861   }
 862 
 863   assert(_linear_scan_order->find(cur) == -1, "block already processed (block can be ready only once)");
 864   assert(_work_list.find(cur) == -1, "block already in work-list (block can be ready only once)");
 865   return true;
 866 }
 867 
 868 void ComputeLinearScanOrder::sort_into_work_list(BlockBegin* cur) {
 869   assert(_work_list.find(cur) == -1, "block already in work list");
 870 
 871   int cur_weight = compute_weight(cur);
 872 
 873   // the linear_scan_number is used to cache the weight of a block
 874   cur->set_linear_scan_number(cur_weight);
 875 
 876 #ifndef PRODUCT
 877   if (StressLinearScan) {
 878     _work_list.insert_before(0, cur);
 879     return;
 880   }
 881 #endif
 882 
 883   _work_list.append(NULL); // provide space for new element
 884 
 885   int insert_idx = _work_list.length() - 1;
 886   while (insert_idx > 0 && _work_list.at(insert_idx - 1)->linear_scan_number() > cur_weight) {
 887     _work_list.at_put(insert_idx, _work_list.at(insert_idx - 1));
 888     insert_idx--;
 889   }
 890   _work_list.at_put(insert_idx, cur);
 891 
 892   TRACE_LINEAR_SCAN(3, tty->print_cr("Sorted B%d into worklist. new worklist:", cur->block_id()));
 893   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()));
 894 
 895 #ifdef ASSERT
 896   for (int i = 0; i < _work_list.length(); i++) {
 897     assert(_work_list.at(i)->linear_scan_number() > 0, "weight not set");
 898     assert(i == 0 || _work_list.at(i - 1)->linear_scan_number() <= _work_list.at(i)->linear_scan_number(), "incorrect order in worklist");
 899   }
 900 #endif
 901 }
 902 
 903 void ComputeLinearScanOrder::append_block(BlockBegin* cur) {
 904   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()));
 905   assert(_linear_scan_order->find(cur) == -1, "cannot add the same block twice");
 906 
 907   // currently, the linear scan order and code emit order are equal.
 908   // therefore the linear_scan_number and the weight of a block must also
 909   // be equal.
 910   cur->set_linear_scan_number(_linear_scan_order->length());
 911   _linear_scan_order->append(cur);
 912 }
 913 
 914 void ComputeLinearScanOrder::compute_order(BlockBegin* start_block) {
 915   TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing final block order"));
 916 
 917   // the start block is always the first block in the linear scan order
 918   _linear_scan_order = new BlockList(_num_blocks);
 919   append_block(start_block);
 920 
 921   assert(start_block->end()->as_Base() != NULL, "start block must end with Base-instruction");
 922   BlockBegin* std_entry = ((Base*)start_block->end())->std_entry();
 923   BlockBegin* osr_entry = ((Base*)start_block->end())->osr_entry();
 924 
 925   BlockBegin* sux_of_osr_entry = NULL;
 926   if (osr_entry != NULL) {
 927     // special handling for osr entry:
 928     // ignore the edge between the osr entry and its successor for processing
 929     // the osr entry block is added manually below
 930     assert(osr_entry->number_of_sux() == 1, "osr entry must have exactly one successor");
 931     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");
 932 
 933     sux_of_osr_entry = osr_entry->sux_at(0);
 934     dec_forward_branches(sux_of_osr_entry);
 935 
 936     compute_dominator(osr_entry, start_block);
 937     _iterative_dominators = true;
 938   }
 939   compute_dominator(std_entry, start_block);
 940 
 941   // start processing with standard entry block
 942   assert(_work_list.is_empty(), "list must be empty before processing");
 943 
 944   if (ready_for_processing(std_entry)) {
 945     sort_into_work_list(std_entry);
 946   } else {
 947     assert(false, "the std_entry must be ready for processing (otherwise, the method has no start block)");
 948   }
 949 
 950   do {
 951     BlockBegin* cur = _work_list.pop();
 952 
 953     if (cur == sux_of_osr_entry) {
 954       // the osr entry block is ignored in normal processing, it is never added to the
 955       // work list. Instead, it is added as late as possible manually here.
 956       append_block(osr_entry);
 957       compute_dominator(cur, osr_entry);
 958     }
 959     append_block(cur);
 960 
 961     int i;
 962     int num_sux = cur->number_of_sux();
 963     // changed loop order to get "intuitive" order of if- and else-blocks
 964     for (i = 0; i < num_sux; i++) {
 965       BlockBegin* sux = cur->sux_at(i);
 966       compute_dominator(sux, cur);
 967       if (ready_for_processing(sux)) {
 968         sort_into_work_list(sux);
 969       }
 970     }
 971     num_sux = cur->number_of_exception_handlers();
 972     for (i = 0; i < num_sux; i++) {
 973       BlockBegin* sux = cur->exception_handler_at(i);
 974       if (ready_for_processing(sux)) {
 975         sort_into_work_list(sux);
 976       }
 977     }
 978   } while (_work_list.length() > 0);
 979 }
 980 
 981 
 982 bool ComputeLinearScanOrder::compute_dominators_iter() {
 983   bool changed = false;
 984   int num_blocks = _linear_scan_order->length();
 985 
 986   assert(_linear_scan_order->at(0)->dominator() == NULL, "must not have dominator");
 987   assert(_linear_scan_order->at(0)->number_of_preds() == 0, "must not have predecessors");
 988   for (int i = 1; i < num_blocks; i++) {
 989     BlockBegin* block = _linear_scan_order->at(i);
 990 
 991     BlockBegin* dominator = block->pred_at(0);
 992     int num_preds = block->number_of_preds();
 993 
 994     TRACE_LINEAR_SCAN(4, tty->print_cr("DOM: Processing B%d", block->block_id()));
 995 
 996     for (int j = 0; j < num_preds; j++) {
 997 
 998       BlockBegin *pred = block->pred_at(j);
 999       TRACE_LINEAR_SCAN(4, tty->print_cr("   DOM: Subrocessing B%d", pred->block_id()));
1000 
1001       if (block->is_set(BlockBegin::exception_entry_flag)) {
1002         dominator = common_dominator(dominator, pred);
1003         int num_pred_preds = pred->number_of_preds();
1004         for (int k = 0; k < num_pred_preds; k++) {
1005           dominator = common_dominator(dominator, pred->pred_at(k));
1006         }
1007       } else {
1008         dominator = common_dominator(dominator, pred);
1009       }
1010     }
1011 
1012     if (dominator != block->dominator()) {
1013       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()));
1014 
1015       block->set_dominator(dominator);
1016       changed = true;
1017     }
1018   }
1019   return changed;
1020 }
1021 
1022 void ComputeLinearScanOrder::compute_dominators() {
1023   TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing dominators (iterative computation reqired: %d)", _iterative_dominators));
1024 
1025   // iterative computation of dominators is only required for methods with non-natural loops
1026   // and OSR-methods. For all other methods, the dominators computed when generating the
1027   // linear scan block order are correct.
1028   if (_iterative_dominators) {
1029     do {
1030       TRACE_LINEAR_SCAN(1, tty->print_cr("DOM: next iteration of fix-point calculation"));
1031     } while (compute_dominators_iter());
1032   }
1033 
1034   // check that dominators are correct
1035   assert(!compute_dominators_iter(), "fix point not reached");
1036 
1037   // Add Blocks to dominates-Array
1038   int num_blocks = _linear_scan_order->length();
1039   for (int i = 0; i < num_blocks; i++) {
1040     BlockBegin* block = _linear_scan_order->at(i);
1041 
1042     BlockBegin *dom = block->dominator();
1043     if (dom) {
1044       assert(dom->dominator_depth() != -1, "Dominator must have been visited before");
1045       dom->dominates()->append(block);
1046       block->set_dominator_depth(dom->dominator_depth() + 1);
1047     } else {
1048       block->set_dominator_depth(0);
1049     }
1050   }
1051 }
1052 
1053 
1054 #ifdef ASSERT
1055 void ComputeLinearScanOrder::print_blocks() {
1056   if (TraceLinearScanLevel >= 2) {
1057     tty->print_cr("----- loop information:");
1058     for (int block_idx = 0; block_idx < _linear_scan_order->length(); block_idx++) {
1059       BlockBegin* cur = _linear_scan_order->at(block_idx);
1060 
1061       tty->print("%4d: B%2d: ", cur->linear_scan_number(), cur->block_id());
1062       for (int loop_idx = 0; loop_idx < _num_loops; loop_idx++) {
1063         tty->print ("%d ", is_block_in_loop(loop_idx, cur));
1064       }
1065       tty->print_cr(" -> loop_index: %2d, loop_depth: %2d", cur->loop_index(), cur->loop_depth());
1066     }
1067   }
1068 
1069   if (TraceLinearScanLevel >= 1) {
1070     tty->print_cr("----- linear-scan block order:");
1071     for (int block_idx = 0; block_idx < _linear_scan_order->length(); block_idx++) {
1072       BlockBegin* cur = _linear_scan_order->at(block_idx);
1073       tty->print("%4d: B%2d    loop: %2d  depth: %2d", cur->linear_scan_number(), cur->block_id(), cur->loop_index(), cur->loop_depth());
1074 
1075       tty->print(cur->is_set(BlockBegin::exception_entry_flag)         ? " ex" : "   ");
1076       tty->print(cur->is_set(BlockBegin::critical_edge_split_flag)     ? " ce" : "   ");
1077       tty->print(cur->is_set(BlockBegin::linear_scan_loop_header_flag) ? " lh" : "   ");
1078       tty->print(cur->is_set(BlockBegin::linear_scan_loop_end_flag)    ? " le" : "   ");
1079 
1080       if (cur->dominator() != NULL) {
1081         tty->print("    dom: B%d ", cur->dominator()->block_id());
1082       } else {
1083         tty->print("    dom: NULL ");
1084       }
1085 
1086       if (cur->number_of_preds() > 0) {
1087         tty->print("    preds: ");
1088         for (int j = 0; j < cur->number_of_preds(); j++) {
1089           BlockBegin* pred = cur->pred_at(j);
1090           tty->print("B%d ", pred->block_id());
1091         }
1092       }
1093       if (cur->number_of_sux() > 0) {
1094         tty->print("    sux: ");
1095         for (int j = 0; j < cur->number_of_sux(); j++) {
1096           BlockBegin* sux = cur->sux_at(j);
1097           tty->print("B%d ", sux->block_id());
1098         }
1099       }
1100       if (cur->number_of_exception_handlers() > 0) {
1101         tty->print("    ex: ");
1102         for (int j = 0; j < cur->number_of_exception_handlers(); j++) {
1103           BlockBegin* ex = cur->exception_handler_at(j);
1104           tty->print("B%d ", ex->block_id());
1105         }
1106       }
1107       tty->cr();
1108     }
1109   }
1110 }
1111 
1112 void ComputeLinearScanOrder::verify() {
1113   assert(_linear_scan_order->length() == _num_blocks, "wrong number of blocks in list");
1114 
1115   if (StressLinearScan) {
1116     // blocks are scrambled when StressLinearScan is used
1117     return;
1118   }
1119 
1120   // check that all successors of a block have a higher linear-scan-number
1121   // and that all predecessors of a block have a lower linear-scan-number
1122   // (only backward branches of loops are ignored)
1123   int i;
1124   for (i = 0; i < _linear_scan_order->length(); i++) {
1125     BlockBegin* cur = _linear_scan_order->at(i);
1126 
1127     assert(cur->linear_scan_number() == i, "incorrect linear_scan_number");
1128     assert(cur->linear_scan_number() >= 0 && cur->linear_scan_number() == _linear_scan_order->find(cur), "incorrect linear_scan_number");
1129 
1130     int j;
1131     for (j = cur->number_of_sux() - 1; j >= 0; j--) {
1132       BlockBegin* sux = cur->sux_at(j);
1133 
1134       assert(sux->linear_scan_number() >= 0 && sux->linear_scan_number() == _linear_scan_order->find(sux), "incorrect linear_scan_number");
1135       if (!sux->is_set(BlockBegin::backward_branch_target_flag)) {
1136         assert(cur->linear_scan_number() < sux->linear_scan_number(), "invalid order");
1137       }
1138       if (cur->loop_depth() == sux->loop_depth()) {
1139         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");
1140       }
1141     }
1142 
1143     for (j = cur->number_of_preds() - 1; j >= 0; j--) {
1144       BlockBegin* pred = cur->pred_at(j);
1145 
1146       assert(pred->linear_scan_number() >= 0 && pred->linear_scan_number() == _linear_scan_order->find(pred), "incorrect linear_scan_number");
1147       if (!cur->is_set(BlockBegin::backward_branch_target_flag)) {
1148         assert(cur->linear_scan_number() > pred->linear_scan_number(), "invalid order");
1149       }
1150       if (cur->loop_depth() == pred->loop_depth()) {
1151         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");
1152       }
1153 
1154       assert(cur->dominator()->linear_scan_number() <= cur->pred_at(j)->linear_scan_number(), "dominator must be before predecessors");
1155     }
1156 
1157     // check dominator
1158     if (i == 0) {
1159       assert(cur->dominator() == NULL, "first block has no dominator");
1160     } else {
1161       assert(cur->dominator() != NULL, "all but first block must have dominator");
1162     }
1163     // Assertion does not hold for exception handlers
1164     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");
1165   }
1166 
1167   // check that all loops are continuous
1168   for (int loop_idx = 0; loop_idx < _num_loops; loop_idx++) {
1169     int block_idx = 0;
1170     assert(!is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx)), "the first block must not be present in any loop");
1171 
1172     // skip blocks before the loop
1173     while (block_idx < _num_blocks && !is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx))) {
1174       block_idx++;
1175     }
1176     // skip blocks of loop
1177     while (block_idx < _num_blocks && is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx))) {
1178       block_idx++;
1179     }
1180     // after the first non-loop block, there must not be another loop-block
1181     while (block_idx < _num_blocks) {
1182       assert(!is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx)), "loop not continuous in linear-scan order");
1183       block_idx++;
1184     }
1185   }
1186 }
1187 #endif // ASSERT
1188 
1189 
1190 void IR::compute_code() {
1191   assert(is_valid(), "IR must be valid");
1192 
1193   ComputeLinearScanOrder compute_order(compilation(), start());
1194   _num_loops = compute_order.num_loops();
1195   _code = compute_order.linear_scan_order();
1196 }
1197 
1198 
1199 void IR::compute_use_counts() {
1200   // make sure all values coming out of this block get evaluated.
1201   int num_blocks = _code->length();
1202   for (int i = 0; i < num_blocks; i++) {
1203     _code->at(i)->end()->state()->pin_stack_for_linear_scan();
1204   }
1205 
1206   // compute use counts
1207   UseCountComputer::compute(_code);
1208 }
1209 
1210 
1211 void IR::iterate_preorder(BlockClosure* closure) {
1212   assert(is_valid(), "IR must be valid");
1213   start()->iterate_preorder(closure);
1214 }
1215 
1216 
1217 void IR::iterate_postorder(BlockClosure* closure) {
1218   assert(is_valid(), "IR must be valid");
1219   start()->iterate_postorder(closure);
1220 }
1221 
1222 void IR::iterate_linear_scan_order(BlockClosure* closure) {
1223   linear_scan_order()->iterate_forward(closure);
1224 }
1225 
1226 
1227 #ifndef PRODUCT
1228 class BlockPrinter: public BlockClosure {
1229  private:
1230   InstructionPrinter* _ip;
1231   bool                _cfg_only;
1232   bool                _live_only;
1233 
1234  public:
1235   BlockPrinter(InstructionPrinter* ip, bool cfg_only, bool live_only = false) {
1236     _ip       = ip;
1237     _cfg_only = cfg_only;
1238     _live_only = live_only;
1239   }
1240 
1241   virtual void block_do(BlockBegin* block) {
1242     if (_cfg_only) {
1243       _ip->print_instr(block); tty->cr();
1244     } else {
1245       block->print_block(*_ip, _live_only);
1246     }
1247   }
1248 };
1249 
1250 
1251 void IR::print(BlockBegin* start, bool cfg_only, bool live_only) {
1252   ttyLocker ttyl;
1253   InstructionPrinter ip(!cfg_only);
1254   BlockPrinter bp(&ip, cfg_only, live_only);
1255   start->iterate_preorder(&bp);
1256   tty->cr();
1257 }
1258 
1259 void IR::print(bool cfg_only, bool live_only) {
1260   if (is_valid()) {
1261     print(start(), cfg_only, live_only);
1262   } else {
1263     tty->print_cr("invalid IR");
1264   }
1265 }
1266 #endif // PRODUCT
1267 
1268 #ifdef ASSERT
1269 class EndNotNullValidator : public BlockClosure {
1270  public:
1271   virtual void block_do(BlockBegin* block) {
1272     assert(block->end() != NULL, "Expect block end to exist.");
1273   }
1274 };
1275 
1276 class XentryFlagValidator : public BlockClosure {
1277  public:
1278   virtual void block_do(BlockBegin* block) {
1279     for (int i = 0; i < block->end()->number_of_sux(); i++) {
1280       assert(!block->end()->sux_at(i)->is_set(BlockBegin::exception_entry_flag), "must not be xhandler");
1281     }
1282     for (int i = 0; i < block->number_of_exception_handlers(); i++) {
1283       assert(block->exception_handler_at(i)->is_set(BlockBegin::exception_entry_flag), "must be xhandler");
1284     }
1285   }
1286 };
1287 
1288 typedef GrowableArray<BlockList*> BlockListList;
1289 
1290 // Validation goals:
1291 // - code() length == blocks length
1292 // - code() contents == blocks content
1293 // - Each block's computed predecessors match sux lists (length)
1294 // - Each block's computed predecessors match sux lists (set content)
1295 class PredecessorAndCodeValidator : public BlockClosure {
1296  private:
1297   BlockListList* _predecessors; // Each index i will hold predecessors of block with id i
1298   BlockList*     _blocks;
1299 
1300   static int cmp(BlockBegin** a, BlockBegin** b) {
1301     return (*a)->block_id() - (*b)->block_id();
1302   }
1303 
1304  public:
1305   PredecessorAndCodeValidator(IR* hir) {
1306     ResourceMark rm;
1307     _predecessors = new BlockListList(BlockBegin::number_of_blocks(), BlockBegin::number_of_blocks(), NULL);
1308     _blocks = new BlockList(BlockBegin::number_of_blocks());
1309 
1310     hir->start()->iterate_preorder(this);
1311     if (hir->code() != NULL) {
1312       assert(hir->code()->length() == _blocks->length(), "must match");
1313       for (int i = 0; i < _blocks->length(); i++) {
1314         assert(hir->code()->contains(_blocks->at(i)), "should be in both lists");
1315       }
1316     }
1317 
1318     for (int i = 0; i < _blocks->length(); i++) {
1319       BlockBegin* block = _blocks->at(i);
1320       verify_block_preds_against_collected_preds(block);
1321     }
1322   }
1323 
1324   virtual void block_do(BlockBegin* block) {
1325     _blocks->append(block);
1326     collect_predecessors(block);
1327   }
1328 
1329  private:
1330   void collect_predecessors(BlockBegin* block) {
1331     for (int i = 0; i < block->end()->number_of_sux(); i++) {
1332       collect_predecessor(block, block->end()->sux_at(i));
1333     }
1334     for (int i = 0; i < block->number_of_exception_handlers(); i++) {
1335       collect_predecessor(block, block->exception_handler_at(i));
1336     }
1337   }
1338 
1339   void collect_predecessor(BlockBegin* const pred, const BlockBegin* sux) {
1340     BlockList* preds = _predecessors->at_grow(sux->block_id(), NULL);
1341     if (preds == NULL) {
1342       preds = new BlockList();
1343       _predecessors->at_put(sux->block_id(), preds);
1344     }
1345     preds->append(pred);
1346   }
1347 
1348   void verify_block_preds_against_collected_preds(const BlockBegin* block) const {
1349     BlockList* preds = _predecessors->at(block->block_id());
1350     if (preds == NULL) {
1351       assert(block->number_of_preds() == 0, "should be the same");
1352       return;
1353     }
1354     assert(preds->length() == block->number_of_preds(), "should be the same");
1355 
1356     // clone the pred list so we can mutate it
1357     BlockList* pred_copy = new BlockList();
1358     for (int j = 0; j < block->number_of_preds(); j++) {
1359       pred_copy->append(block->pred_at(j));
1360     }
1361     // sort them in the same order
1362     preds->sort(cmp);
1363     pred_copy->sort(cmp);
1364     for (int j = 0; j < block->number_of_preds(); j++) {
1365       assert(preds->at(j) == pred_copy->at(j), "must match");
1366     }
1367   }
1368 };
1369 
1370 class VerifyBlockBeginField : public BlockClosure {
1371 public:
1372   virtual void block_do(BlockBegin* block) {
1373     for (Instruction* cur = block; cur != NULL; cur = cur->next()) {
1374       assert(cur->block() == block, "Block begin is not correct");
1375     }
1376   }
1377 };
1378 
1379 class ValidateEdgeMutuality : public BlockClosure {
1380  public:
1381   virtual void block_do(BlockBegin* block) {
1382     for (int i = 0; i < block->end()->number_of_sux(); i++) {
1383       assert(block->end()->sux_at(i)->is_predecessor(block), "Block's successor should have it as predecessor");
1384     }
1385 
1386     for (int i = 0; i < block->number_of_exception_handlers(); i++) {
1387       assert(block->exception_handler_at(i)->is_predecessor(block), "Block's exception handler should have it as predecessor");
1388     }
1389 
1390     for (int i = 0; i < block->number_of_preds(); i++) {
1391       assert(block->pred_at(i) != NULL, "Predecessor must exist");
1392       assert(block->pred_at(i)->end() != NULL, "Predecessor end must exist");
1393       bool is_sux      = block->pred_at(i)->end()->is_sux(block);
1394       bool is_xhandler = block->pred_at(i)->is_exception_handler(block);
1395       assert(is_sux || is_xhandler, "Block's predecessor should have it as successor or xhandler");
1396     }
1397   }
1398 };
1399 
1400 void IR::expand_with_neighborhood(BlockList& blocks) {
1401   int original_size = blocks.length();
1402   for (int h = 0; h < original_size; h++) {
1403     BlockBegin* block = blocks.at(h);
1404 
1405     for (int i = 0; i < block->end()->number_of_sux(); i++) {
1406       if (!blocks.contains(block->end()->sux_at(i))) {
1407         blocks.append(block->end()->sux_at(i));
1408       }
1409     }
1410 
1411     for (int i = 0; i < block->number_of_preds(); i++) {
1412       if (!blocks.contains(block->pred_at(i))) {
1413         blocks.append(block->pred_at(i));
1414       }
1415     }
1416 
1417     for (int i = 0; i < block->number_of_exception_handlers(); i++) {
1418       if (!blocks.contains(block->exception_handler_at(i))) {
1419         blocks.append(block->exception_handler_at(i));
1420       }
1421     }
1422   }
1423 }
1424 
1425 void IR::verify_local(BlockList& blocks) {
1426   EndNotNullValidator ennv;
1427   blocks.iterate_forward(&ennv);
1428 
1429   ValidateEdgeMutuality vem;
1430   blocks.iterate_forward(&vem);
1431 
1432   VerifyBlockBeginField verifier;
1433   blocks.iterate_forward(&verifier);
1434 }
1435 
1436 void IR::verify() {
1437   XentryFlagValidator xe;
1438   iterate_postorder(&xe);
1439 
1440   PredecessorAndCodeValidator pv(this);
1441 
1442   EndNotNullValidator ennv;
1443   iterate_postorder(&ennv);
1444 
1445   ValidateEdgeMutuality vem;
1446   iterate_postorder(&vem);
1447 
1448   VerifyBlockBeginField verifier;
1449   iterate_postorder(&verifier);
1450 }
1451 #endif // ASSERT
1452 
1453 void SubstitutionResolver::visit(Value* v) {
1454   Value v0 = *v;
1455   if (v0) {
1456     Value vs = v0->subst();
1457     if (vs != v0) {
1458       *v = v0->subst();
1459     }
1460   }
1461 }
1462 
1463 #ifdef ASSERT
1464 class SubstitutionChecker: public ValueVisitor {
1465   void visit(Value* v) {
1466     Value v0 = *v;
1467     if (v0) {
1468       Value vs = v0->subst();
1469       assert(vs == v0, "missed substitution");
1470     }
1471   }
1472 };
1473 #endif
1474 
1475 
1476 void SubstitutionResolver::block_do(BlockBegin* block) {
1477   Instruction* last = NULL;
1478   for (Instruction* n = block; n != NULL;) {
1479     n->values_do(this);
1480     // need to remove this instruction from the instruction stream
1481     if (n->subst() != n) {
1482       guarantee(last != NULL, "must have last");
1483       last->set_next(n->next());
1484     } else {
1485       last = n;
1486     }
1487     n = last->next();
1488   }
1489 
1490 #ifdef ASSERT
1491   SubstitutionChecker check_substitute;
1492   if (block->state()) block->state()->values_do(&check_substitute);
1493   block->block_values_do(&check_substitute);
1494   if (block->end() && block->end()->state()) block->end()->state()->values_do(&check_substitute);
1495 #endif
1496 }