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