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 /*

  * Copyright (c) 1999, 2012, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #include "precompiled.hpp"

 #include "c1/c1_Compilation.hpp"

 #include "c1/c1_FrameMap.hpp"

 #include "c1/c1_GraphBuilder.hpp"

 #include "c1/c1_IR.hpp"

 #include "c1/c1_InstructionPrinter.hpp"

 #include "c1/c1_Optimizer.hpp"

 #include "utilities/bitMap.inline.hpp"

 // Implementation of XHandlers

 //

 // Note: This code could eventually go away if we are

 //       just using the ciExceptionHandlerStream.

 XHandlers::XHandlers(ciMethod* method) : _list(method->exception_table_length()) {

   ciExceptionHandlerStream s(method);

   while (!s.is_done()) {

     _list.append(new XHandler(s.handler()));

     s.next();

   }

   assert(s.count() == method->exception_table_length(), "exception table lengths inconsistent");

 }

 // deep copy of all XHandler contained in list

 XHandlers::XHandlers(XHandlers* other) :

   _list(other->length())

 {

   for (int i = 0; i < other->length(); i++) {

     _list.append(new XHandler(other->handler_at(i)));

   }

 }

 // Returns whether a particular exception type can be caught.  Also

 // returns true if klass is unloaded or any exception handler

 // classes are unloaded.  type_is_exact indicates whether the throw

 // is known to be exactly that class or it might throw a subtype.

 bool XHandlers::could_catch(ciInstanceKlass* klass, bool type_is_exact) const {

   // the type is unknown so be conservative

   if (!klass->is_loaded()) {

     return true;

   }

   for (int i = 0; i < length(); i++) {

     XHandler* handler = handler_at(i);

     if (handler->is_catch_all()) {

       // catch of ANY

       return true;

     }

     ciInstanceKlass* handler_klass = handler->catch_klass();

     // if it's unknown it might be catchable

     if (!handler_klass->is_loaded()) {

       return true;

     }

     // if the throw type is definitely a subtype of the catch type

     // then it can be caught.

     if (klass->is_subtype_of(handler_klass)) {

       return true;

     }

     if (!type_is_exact) {

       // If the type isn't exactly known then it can also be caught by

       // catch statements where the inexact type is a subtype of the

       // catch type.

       // given: foo extends bar extends Exception

       // throw bar can be caught by catch foo, catch bar, and catch

       // Exception, however it can't be caught by any handlers without

       // bar in its type hierarchy.

       if (handler_klass->is_subtype_of(klass)) {

         return true;

       }

     }

   }

   return false;

 }

 bool XHandlers::equals(XHandlers* others) const {

   if (others == NULL) return false;

   if (length() != others->length()) return false;

   for (int i = 0; i < length(); i++) {

     if (!handler_at(i)->equals(others->handler_at(i))) return false;

   }

   return true;

 }

 bool XHandler::equals(XHandler* other) const {

   assert(entry_pco() != -1 && other->entry_pco() != -1, "must have entry_pco");

   if (entry_pco() != other->entry_pco()) return false;

   if (scope_count() != other->scope_count()) return false;

   if (_desc != other->_desc) return false;

   assert(entry_block() == other->entry_block(), "entry_block must be equal when entry_pco is equal");

   return true;

 }

 // Implementation of IRScope

 BlockBegin* IRScope::build_graph(Compilation* compilation, int osr_bci) {

   GraphBuilder gm(compilation, this);

   NOT_PRODUCT(if (PrintValueNumbering && Verbose) gm.print_stats());

   if (compilation->bailed_out()) return NULL;

   return gm.start();

 }

 IRScope::IRScope(Compilation* compilation, IRScope* caller, int caller_bci, ciMethod* method, int osr_bci, bool create_graph)

 : _callees(2)

 , _compilation(compilation)

 , _requires_phi_function(method->max_locals())

 {

   _caller             = caller;

   _level              = caller == NULL ?  0 : caller->level() + 1;

   _method             = method;

   _xhandlers          = new XHandlers(method);

   _number_of_locks    = 0;

   _monitor_pairing_ok = method->has_balanced_monitors();

   _wrote_final        = false;

   _start              = NULL;

   if (osr_bci == -1) {

     _requires_phi_function.clear();

   } else {

         // selective creation of phi functions is not possibel in osr-methods

     _requires_phi_function.set_range(0, method->max_locals());

   }

   assert(method->holder()->is_loaded() , "method holder must be loaded");

   // build graph if monitor pairing is ok

   if (create_graph && monitor_pairing_ok()) _start = build_graph(compilation, osr_bci);

 }

 int IRScope::max_stack() const {

   int my_max = method()->max_stack();

   int callee_max = 0;

   for (int i = 0; i < number_of_callees(); i++) {

     callee_max = MAX2(callee_max, callee_no(i)->max_stack());

   }

   return my_max + callee_max;

 }

 bool IRScopeDebugInfo::should_reexecute() {

   ciMethod* cur_method = scope()->method();

   int       cur_bci    = bci();

   if (cur_method != NULL && cur_bci != SynchronizationEntryBCI) {

     Bytecodes::Code code = cur_method->java_code_at_bci(cur_bci);

     return Interpreter::bytecode_should_reexecute(code);

   } else

     return false;

 }

 // Implementation of CodeEmitInfo

 // Stack must be NON-null

 CodeEmitInfo::CodeEmitInfo(ValueStack* stack, XHandlers* exception_handlers, bool deoptimize_on_exception)

   : _scope(stack->scope())

   , _scope_debug_info(NULL)

   , _oop_map(NULL)

   , _stack(stack)

   , _exception_handlers(exception_handlers)

   , _is_method_handle_invoke(false)

   , _deoptimize_on_exception(deoptimize_on_exception) {

   assert(_stack != NULL, "must be non null");

 }

 CodeEmitInfo::CodeEmitInfo(CodeEmitInfo* info, ValueStack* stack)

   : _scope(info->_scope)

   , _exception_handlers(NULL)

   , _scope_debug_info(NULL)

   , _oop_map(NULL)

   , _stack(stack == NULL ? info->_stack : stack)

   , _is_method_handle_invoke(info->_is_method_handle_invoke)

   , _deoptimize_on_exception(info->_deoptimize_on_exception) {

   // deep copy of exception handlers

   if (info->_exception_handlers != NULL) {

     _exception_handlers = new XHandlers(info->_exception_handlers);

   }

 }

 void CodeEmitInfo::record_debug_info(DebugInformationRecorder* recorder, int pc_offset) {

   // record the safepoint before recording the debug info for enclosing scopes

   recorder->add_safepoint(pc_offset, _oop_map->deep_copy());

   _scope_debug_info->record_debug_info(recorder, pc_offset, true/*topmost*/, _is_method_handle_invoke);

   recorder->end_safepoint(pc_offset);

 }

 void CodeEmitInfo::add_register_oop(LIR_Opr opr) {

   assert(_oop_map != NULL, "oop map must already exist");

   assert(opr->is_single_cpu(), "should not call otherwise");

   VMReg name = frame_map()->regname(opr);

   _oop_map->set_oop(name);

 }

 // Implementation of IR

 IR::IR(Compilation* compilation, ciMethod* method, int osr_bci) :

     _locals_size(in_WordSize(-1))

   , _num_loops(0) {

   // setup IR fields

   _compilation = compilation;

   _top_scope   = new IRScope(compilation, NULL, -1, method, osr_bci, true);

   _code        = NULL;

 }

 void IR::optimize_blocks() {

   Optimizer opt(this);

   if (!compilation()->profile_branches()) {

     if (DoCEE) {

       opt.eliminate_conditional_expressions();

 #ifndef PRODUCT

       if (PrintCFG || PrintCFG1) { tty->print_cr("CFG after CEE"); print(true); }

       if (PrintIR  || PrintIR1 ) { tty->print_cr("IR after CEE"); print(false); }

 #endif

     }

     if (EliminateBlocks) {

       opt.eliminate_blocks();

 #ifndef PRODUCT

       if (PrintCFG || PrintCFG1) { tty->print_cr("CFG after block elimination"); print(true); }

       if (PrintIR  || PrintIR1 ) { tty->print_cr("IR after block elimination"); print(false); }

 #endif

     }

   }

 }

 void IR::eliminate_null_checks() {

   Optimizer opt(this);

   if (EliminateNullChecks) {

     opt.eliminate_null_checks();

 #ifndef PRODUCT

     if (PrintCFG || PrintCFG1) { tty->print_cr("CFG after null check elimination"); print(true); }

     if (PrintIR  || PrintIR1 ) { tty->print_cr("IR after null check elimination"); print(false); }

 #endif

   }

 }

 static int sort_pairs(BlockPair** a, BlockPair** b) {

   if ((*a)->from() == (*b)->from()) {

     return (*a)->to()->block_id() - (*b)->to()->block_id();

   } else {

     return (*a)->from()->block_id() - (*b)->from()->block_id();

   }

 }

 class CriticalEdgeFinder: public BlockClosure {

   BlockPairList blocks;

   IR*       _ir;

  public:

   CriticalEdgeFinder(IR* ir): _ir(ir) {}

   void block_do(BlockBegin* bb) {

     BlockEnd* be = bb->end();

     int nos = be->number_of_sux();

     if (nos >= 2) {

       for (int i = 0; i < nos; i++) {

         BlockBegin* sux = be->sux_at(i);

         if (sux->number_of_preds() >= 2) {

           blocks.append(new BlockPair(bb, sux));

         }

       }

     }

   }

   void split_edges() {

     BlockPair* last_pair = NULL;

     blocks.sort(sort_pairs);

     for (int i = 0; i < blocks.length(); i++) {

       BlockPair* pair = blocks.at(i);

       if (last_pair != NULL && pair->is_same(last_pair)) continue;

       BlockBegin* from = pair->from();

       BlockBegin* to = pair->to();

       BlockBegin* split = from->insert_block_between(to);

 #ifndef PRODUCT

       if ((PrintIR || PrintIR1) && Verbose) {

         tty->print_cr("Split critical edge B%d -> B%d (new block B%d)",

                       from->block_id(), to->block_id(), split->block_id());

       }

 #endif

       last_pair = pair;

     }

   }

 };

 void IR::split_critical_edges() {

   CriticalEdgeFinder cef(this);

   iterate_preorder(&cef);

   cef.split_edges();

 }

 class UseCountComputer: public ValueVisitor, BlockClosure {

  private:

   void visit(Value* n) {

     // Local instructions and Phis for expression stack values at the

     // start of basic blocks are not added to the instruction list

     if (!(*n)->is_linked() && (*n)->can_be_linked()) {

       assert(false, "a node was not appended to the graph");

       Compilation::current()->bailout("a node was not appended to the graph");

     }

     // use n's input if not visited before

     if (!(*n)->is_pinned() && !(*n)->has_uses()) {

       // note: a) if the instruction is pinned, it will be handled by compute_use_count

       //       b) if the instruction has uses, it was touched before

       //       => in both cases we don't need to update n's values

       uses_do(n);

     }

     // use n

     (*n)->_use_count++;

   }

   Values* worklist;

   int depth;

   enum {

     max_recurse_depth = 20

   };

   void uses_do(Value* n) {

     depth++;

     if (depth > max_recurse_depth) {

       // don't allow the traversal to recurse too deeply

       worklist->push(*n);

     } else {

       (*n)->input_values_do(this);

       // special handling for some instructions

       if ((*n)->as_BlockEnd() != NULL) {

         // note on BlockEnd:

         //   must 'use' the stack only if the method doesn't

         //   terminate, however, in those cases stack is empty

         (*n)->state_values_do(this);

       }

     }

     depth--;

   }

   void block_do(BlockBegin* b) {

     depth = 0;

     // process all pinned nodes as the roots of expression trees

     for (Instruction* n = b; n != NULL; n = n->next()) {

       if (n->is_pinned()) uses_do(&n);

     }

     assert(depth == 0, "should have counted back down");

     // now process any unpinned nodes which recursed too deeply

     while (worklist->length() > 0) {

       Value t = worklist->pop();

       if (!t->is_pinned()) {

         // compute the use count

         uses_do(&t);

         // pin the instruction so that LIRGenerator doesn't recurse

         // too deeply during it's evaluation.

         t->pin();

       }

     }

     assert(depth == 0, "should have counted back down");

   }

   UseCountComputer() {

     worklist = new Values();

     depth = 0;

   }

  public:

   static void compute(BlockList* blocks) {

     UseCountComputer ucc;

     blocks->iterate_backward(&ucc);

   }

 };

 // helper macro for short definition of trace-output inside code

 #ifndef PRODUCT

   #define TRACE_LINEAR_SCAN(level, code)       \

     if (TraceLinearScanLevel >= level) {       \

       code;                                    \

     }

 #else

   #define TRACE_LINEAR_SCAN(level, code)

 #endif

 class ComputeLinearScanOrder : public StackObj {

  private:

   int        _max_block_id;        // the highest block_id of a block

   int        _num_blocks;          // total number of blocks (smaller than _max_block_id)

   int        _num_loops;           // total number of loops

   bool       _iterative_dominators;// method requires iterative computation of dominatiors

   BlockList* _linear_scan_order;   // the resulting list of blocks in correct order

   BitMap     _visited_blocks;      // used for recursive processing of blocks

   BitMap     _active_blocks;       // used for recursive processing of blocks

   BitMap     _dominator_blocks;    // temproary BitMap used for computation of dominator

   intArray   _forward_branches;    // number of incoming forward branches for each block

   BlockList  _loop_end_blocks;     // list of all loop end blocks collected during count_edges

   BitMap2D   _loop_map;            // two-dimensional bit set: a bit is set if a block is contained in a loop

   BlockList  _work_list;           // temporary list (used in mark_loops and compute_order)

   BlockList  _loop_headers;

   Compilation* _compilation;

   // accessors for _visited_blocks and _active_blocks

   void init_visited()                     { _active_blocks.clear(); _visited_blocks.clear(); }

   bool is_visited(BlockBegin* b) const    { return _visited_blocks.at(b->block_id()); }

   bool is_active(BlockBegin* b) const     { return _active_blocks.at(b->block_id()); }

   void set_visited(BlockBegin* b)         { assert(!is_visited(b), "already set"); _visited_blocks.set_bit(b->block_id()); }

   void set_active(BlockBegin* b)          { assert(!is_active(b), "already set");  _active_blocks.set_bit(b->block_id()); }

   void clear_active(BlockBegin* b)        { assert(is_active(b), "not already");   _active_blocks.clear_bit(b->block_id()); }

   // accessors for _forward_branches

   void inc_forward_branches(BlockBegin* b) { _forward_branches.at_put(b->block_id(), _forward_branches.at(b->block_id()) + 1); }

   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()); }

   // accessors for _loop_map

   bool is_block_in_loop   (int loop_idx, BlockBegin* b) const { return _loop_map.at(loop_idx, b->block_id()); }

   void set_block_in_loop  (int loop_idx, BlockBegin* b)       { _loop_map.set_bit(loop_idx, b->block_id()); }

   void clear_block_in_loop(int loop_idx, int block_id)        { _loop_map.clear_bit(loop_idx, block_id); }

   // count edges between blocks

   void count_edges(BlockBegin* cur, BlockBegin* parent);

   // loop detection

   void mark_loops();

   void clear_non_natural_loops(BlockBegin* start_block);

   void assign_loop_depth(BlockBegin* start_block);

   // computation of final block order

   BlockBegin* common_dominator(BlockBegin* a, BlockBegin* b);

   void compute_dominator(BlockBegin* cur, BlockBegin* parent);

   int  compute_weight(BlockBegin* cur);

   bool ready_for_processing(BlockBegin* cur);

   void sort_into_work_list(BlockBegin* b);

   void append_block(BlockBegin* cur);

   void compute_order(BlockBegin* start_block);

   // fixup of dominators for non-natural loops

   bool compute_dominators_iter();

   void compute_dominators();

   // debug functions

   NOT_PRODUCT(void print_blocks();)

   DEBUG_ONLY(void verify();)

   Compilation* compilation() const { return _compilation; }

  public:

   ComputeLinearScanOrder(Compilation* c, BlockBegin* start_block);

   // accessors for final result

   BlockList* linear_scan_order() const    { return _linear_scan_order; }

   int        num_loops() const            { return _num_loops; }

 };

 ComputeLinearScanOrder::ComputeLinearScanOrder(Compilation* c, BlockBegin* start_block) :

   _max_block_id(BlockBegin::number_of_blocks()),

   _num_blocks(0),

   _num_loops(0),

   _iterative_dominators(false),

   _visited_blocks(_max_block_id),

   _active_blocks(_max_block_id),

   _dominator_blocks(_max_block_id),

   _forward_branches(_max_block_id, 0),

   _loop_end_blocks(8),

   _work_list(8),

   _linear_scan_order(NULL), // initialized later with correct size

   _loop_map(0, 0),          // initialized later with correct size

   _compilation(c)

 {

   TRACE_LINEAR_SCAN(2, tty->print_cr("***** computing linear-scan block order"));

   init_visited();

   count_edges(start_block, NULL);

   if (compilation()->is_profiling()) {

     ciMethod *method = compilation()->method();

     if (!method->is_accessor()) {

       ciMethodData* md = method->method_data_or_null();

       assert(md != NULL, "Sanity");

       md->set_compilation_stats(_num_loops, _num_blocks);

     }

   }

   if (_num_loops > 0) {

     mark_loops();

     clear_non_natural_loops(start_block);

     assign_loop_depth(start_block);

   }

   compute_order(start_block);

   compute_dominators();

   NOT_PRODUCT(print_blocks());

   DEBUG_ONLY(verify());

 }

 // Traverse the CFG:

 // * count total number of blocks

 // * count all incoming edges and backward incoming edges

 // * number loop header blocks

 // * create a list with all loop end blocks

 void ComputeLinearScanOrder::count_edges(BlockBegin* cur, BlockBegin* parent) {

   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));

   assert(cur->dominator() == NULL, "dominator already initialized");

   if (is_active(cur)) {

     TRACE_LINEAR_SCAN(3, tty->print_cr("backward branch"));

     assert(is_visited(cur), "block must be visisted when block is active");

     assert(parent != NULL, "must have parent");

     cur->set(BlockBegin::linear_scan_loop_header_flag);

     cur->set(BlockBegin::backward_branch_target_flag);

     parent->set(BlockBegin::linear_scan_loop_end_flag);

     // When a loop header is also the start of an exception handler, then the backward branch is

     // an exception edge. Because such edges are usually critical edges which cannot be split, the

     // loop must be excluded here from processing.

     if (cur->is_set(BlockBegin::exception_entry_flag)) {

       // Make sure that dominators are correct in this weird situation

       _iterative_dominators = true;

       return;

     }

     assert(parent->number_of_sux() == 1 && parent->sux_at(0) == cur,

            "loop end blocks must have one successor (critical edges are split)");

     _loop_end_blocks.append(parent);

     return;

   }

   // increment number of incoming forward branches

   inc_forward_branches(cur);

   if (is_visited(cur)) {

     TRACE_LINEAR_SCAN(3, tty->print_cr("block already visited"));

     return;

   }

   _num_blocks++;

   set_visited(cur);

   set_active(cur);

   // recursive call for all successors

   int i;

   for (i = cur->number_of_sux() - 1; i >= 0; i--) {

     count_edges(cur->sux_at(i), cur);

   }

   for (i = cur->number_of_exception_handlers() - 1; i >= 0; i--) {

     count_edges(cur->exception_handler_at(i), cur);

   }

   clear_active(cur);

   // Each loop has a unique number.

   // When multiple loops are nested, assign_loop_depth assumes that the

   // innermost loop has the lowest number. This is guaranteed by setting

   // the loop number after the recursive calls for the successors above

   // have returned.

   if (cur->is_set(BlockBegin::linear_scan_loop_header_flag)) {

     assert(cur->loop_index() == -1, "cannot set loop-index twice");

     TRACE_LINEAR_SCAN(3, tty->print_cr("Block B%d is loop header of loop %d", cur->block_id(), _num_loops));

     cur->set_loop_index(_num_loops);

     _loop_headers.append(cur);

     _num_loops++;

   }

   TRACE_LINEAR_SCAN(3, tty->print_cr("Finished count_edges for block B%d", cur->block_id()));

 }

 void ComputeLinearScanOrder::mark_loops() {

   TRACE_LINEAR_SCAN(3, tty->print_cr("----- marking loops"));

   _loop_map = BitMap2D(_num_loops, _max_block_id);

   _loop_map.clear();

   for (int i = _loop_end_blocks.length() - 1; i >= 0; i--) {

     BlockBegin* loop_end   = _loop_end_blocks.at(i);

     BlockBegin* loop_start = loop_end->sux_at(0);

     int         loop_idx   = loop_start->loop_index();

     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));

     assert(loop_end->is_set(BlockBegin::linear_scan_loop_end_flag), "loop end flag must be set");

     assert(loop_end->number_of_sux() == 1, "incorrect number of successors");

     assert(loop_start->is_set(BlockBegin::linear_scan_loop_header_flag), "loop header flag must be set");

     assert(loop_idx >= 0 && loop_idx < _num_loops, "loop index not set");

     assert(_work_list.is_empty(), "work list must be empty before processing");

     // add the end-block of the loop to the working list

     _work_list.push(loop_end);

     set_block_in_loop(loop_idx, loop_end);

     do {

       BlockBegin* cur = _work_list.pop();

       TRACE_LINEAR_SCAN(3, tty->print_cr("    processing B%d", cur->block_id()));

       assert(is_block_in_loop(loop_idx, cur), "bit in loop map must be set when block is in work list");

       // recursive processing of all predecessors ends when start block of loop is reached

       if (cur != loop_start && !cur->is_set(BlockBegin::osr_entry_flag)) {

         for (int j = cur->number_of_preds() - 1; j >= 0; j--) {

           BlockBegin* pred = cur->pred_at(j);

           if (!is_block_in_loop(loop_idx, pred) /*&& !pred->is_set(BlockBeginosr_entry_flag)*/) {

             // this predecessor has not been processed yet, so add it to work list

             TRACE_LINEAR_SCAN(3, tty->print_cr("    pushing B%d", pred->block_id()));

             _work_list.push(pred);

             set_block_in_loop(loop_idx, pred);

           }

         }

       }

     } while (!_work_list.is_empty());

   }

 }

 // check for non-natural loops (loops where the loop header does not dominate

 // all other loop blocks = loops with mulitple entries).

 // such loops are ignored

 void ComputeLinearScanOrder::clear_non_natural_loops(BlockBegin* start_block) {

   for (int i = _num_loops - 1; i >= 0; i--) {

     if (is_block_in_loop(i, start_block)) {

       // loop i contains the entry block of the method

       // -> this is not a natural loop, so ignore it

       TRACE_LINEAR_SCAN(2, tty->print_cr("Loop %d is non-natural, so it is ignored", i));

       BlockBegin *loop_header = _loop_headers.at(i);

       assert(loop_header->is_set(BlockBegin::linear_scan_loop_header_flag), "Must be loop header");

       for (int j = 0; j < loop_header->number_of_preds(); j++) {

         BlockBegin *pred = loop_header->pred_at(j);

         pred->clear(BlockBegin::linear_scan_loop_end_flag);

       }

       loop_header->clear(BlockBegin::linear_scan_loop_header_flag);

       for (int block_id = _max_block_id - 1; block_id >= 0; block_id--) {

         clear_block_in_loop(i, block_id);

       }

       _iterative_dominators = true;

     }

   }

 }

 void ComputeLinearScanOrder::assign_loop_depth(BlockBegin* start_block) {

   TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing loop-depth and weight"));

   init_visited();

   assert(_work_list.is_empty(), "work list must be empty before processing");

   _work_list.append(start_block);

   do {

     BlockBegin* cur = _work_list.pop();

     if (!is_visited(cur)) {

       set_visited(cur);

       TRACE_LINEAR_SCAN(4, tty->print_cr("Computing loop depth for block B%d", cur->block_id()));

       // compute loop-depth and loop-index for the block

       assert(cur->loop_depth() == 0, "cannot set loop-depth twice");

       int i;

       int loop_depth = 0;

       int min_loop_idx = -1;

       for (i = _num_loops - 1; i >= 0; i--) {

         if (is_block_in_loop(i, cur)) {

           loop_depth++;

           min_loop_idx = i;

         }

       }

       cur->set_loop_depth(loop_depth);

       cur->set_loop_index(min_loop_idx);

       // append all unvisited successors to work list

       for (i = cur->number_of_sux() - 1; i >= 0; i--) {

         _work_list.append(cur->sux_at(i));

       }

       for (i = cur->number_of_exception_handlers() - 1; i >= 0; i--) {

         _work_list.append(cur->exception_handler_at(i));

       }

     }

   } while (!_work_list.is_empty());

 }

 BlockBegin* ComputeLinearScanOrder::common_dominator(BlockBegin* a, BlockBegin* b) {

   assert(a != NULL && b != NULL, "must have input blocks");

   _dominator_blocks.clear();

   while (a != NULL) {

     _dominator_blocks.set_bit(a->block_id());

     assert(a->dominator() != NULL || a == _linear_scan_order->at(0), "dominator must be initialized");

     a = a->dominator();

   }

   while (b != NULL && !_dominator_blocks.at(b->block_id())) {

     assert(b->dominator() != NULL || b == _linear_scan_order->at(0), "dominator must be initialized");

     b = b->dominator();

   }

   assert(b != NULL, "could not find dominator");

   return b;

 }

 void ComputeLinearScanOrder::compute_dominator(BlockBegin* cur, BlockBegin* parent) {

   if (cur->dominator() == NULL) {

     TRACE_LINEAR_SCAN(4, tty->print_cr("DOM: initializing dominator of B%d to B%d", cur->block_id(), parent->block_id()));

     cur->set_dominator(parent);

   } else if (!(cur->is_set(BlockBegin::linear_scan_loop_header_flag) && parent->is_set(BlockBegin::linear_scan_loop_end_flag))) {

     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()));

     // Does not hold for exception blocks

     assert(cur->number_of_preds() > 1 || cur->is_set(BlockBegin::exception_entry_flag), "");

     cur->set_dominator(common_dominator(cur->dominator(), parent));

   }

   // Additional edge to xhandler of all our successors

   // range check elimination needs that the state at the end of a

   // block be valid in every block it dominates so cur must dominate

   // the exception handlers of its successors.

   int num_cur_xhandler = cur->number_of_exception_handlers();

   for (int j = 0; j < num_cur_xhandler; j++) {

     BlockBegin* xhandler = cur->exception_handler_at(j);

     compute_dominator(xhandler, parent);

   }

 }

 int ComputeLinearScanOrder::compute_weight(BlockBegin* cur) {

   BlockBegin* single_sux = NULL;

   if (cur->number_of_sux() == 1) {

     single_sux = cur->sux_at(0);

   }

   // limit loop-depth to 15 bit (only for security reason, it will never be so big)

   int weight = (cur->loop_depth() & 0x7FFF) << 16;

   // general macro for short definition of weight flags

   // the first instance of INC_WEIGHT_IF has the highest priority

   int cur_bit = 15;

   #define INC_WEIGHT_IF(condition) if ((condition)) { weight |= (1 << cur_bit); } cur_bit--;

   // this is necessery for the (very rare) case that two successing blocks have

   // the same loop depth, but a different loop index (can happen for endless loops

   // with exception handlers)

   INC_WEIGHT_IF(!cur->is_set(BlockBegin::linear_scan_loop_header_flag));

   // loop end blocks (blocks that end with a backward branch) are added

   // after all other blocks of the loop.

   INC_WEIGHT_IF(!cur->is_set(BlockBegin::linear_scan_loop_end_flag));

   // critical edge split blocks are prefered because than they have a bigger

   // proability to be completely empty

   INC_WEIGHT_IF(cur->is_set(BlockBegin::critical_edge_split_flag));

   // exceptions should not be thrown in normal control flow, so these blocks

   // are added as late as possible

   INC_WEIGHT_IF(cur->end()->as_Throw() == NULL  && (single_sux == NULL || single_sux->end()->as_Throw()  == NULL));

   INC_WEIGHT_IF(cur->end()->as_Return() == NULL && (single_sux == NULL || single_sux->end()->as_Return() == NULL));

   // exceptions handlers are added as late as possible

   INC_WEIGHT_IF(!cur->is_set(BlockBegin::exception_entry_flag));

   // guarantee that weight is > 0

   weight |= 1;

   #undef INC_WEIGHT_IF

   assert(cur_bit >= 0, "too many flags");

   assert(weight > 0, "weight cannot become negative");

   return weight;

 }

 bool ComputeLinearScanOrder::ready_for_processing(BlockBegin* cur) {

   // Discount the edge just traveled.

   // When the number drops to zero, all forward branches were processed

   if (dec_forward_branches(cur) != 0) {

     return false;

   }

   assert(_linear_scan_order->index_of(cur) == -1, "block already processed (block can be ready only once)");

   assert(_work_list.index_of(cur) == -1, "block already in work-list (block can be ready only once)");

   return true;

 }

 void ComputeLinearScanOrder::sort_into_work_list(BlockBegin* cur) {

   assert(_work_list.index_of(cur) == -1, "block already in work list");

   int cur_weight = compute_weight(cur);

   // the linear_scan_number is used to cache the weight of a block

   cur->set_linear_scan_number(cur_weight);

 #ifndef PRODUCT

   if (StressLinearScan) {

     _work_list.insert_before(0, cur);

     return;

   }

 #endif

   _work_list.append(NULL); // provide space for new element

   int insert_idx = _work_list.length() - 1;

   while (insert_idx > 0 && _work_list.at(insert_idx - 1)->linear_scan_number() > cur_weight) {

     _work_list.at_put(insert_idx, _work_list.at(insert_idx - 1));

     insert_idx--;

   }

   _work_list.at_put(insert_idx, cur);

   TRACE_LINEAR_SCAN(3, tty->print_cr("Sorted B%d into worklist. new worklist:", cur->block_id()));

   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()));

 #ifdef ASSERT

   for (int i = 0; i < _work_list.length(); i++) {

     assert(_work_list.at(i)->linear_scan_number() > 0, "weight not set");

     assert(i == 0 || _work_list.at(i - 1)->linear_scan_number() <= _work_list.at(i)->linear_scan_number(), "incorrect order in worklist");

   }

 #endif

 }

 void ComputeLinearScanOrder::append_block(BlockBegin* cur) {

   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()));

   assert(_linear_scan_order->index_of(cur) == -1, "cannot add the same block twice");

   // currently, the linear scan order and code emit order are equal.

   // therefore the linear_scan_number and the weight of a block must also

   // be equal.

   cur->set_linear_scan_number(_linear_scan_order->length());

   _linear_scan_order->append(cur);

 }

 void ComputeLinearScanOrder::compute_order(BlockBegin* start_block) {

   TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing final block order"));

   // the start block is always the first block in the linear scan order

   _linear_scan_order = new BlockList(_num_blocks);

   append_block(start_block);

   assert(start_block->end()->as_Base() != NULL, "start block must end with Base-instruction");

   BlockBegin* std_entry = ((Base*)start_block->end())->std_entry();

   BlockBegin* osr_entry = ((Base*)start_block->end())->osr_entry();

   BlockBegin* sux_of_osr_entry = NULL;

   if (osr_entry != NULL) {

     // special handling for osr entry:

     // ignore the edge between the osr entry and its successor for processing

     // the osr entry block is added manually below

     assert(osr_entry->number_of_sux() == 1, "osr entry must have exactly one successor");

     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");

     sux_of_osr_entry = osr_entry->sux_at(0);

     dec_forward_branches(sux_of_osr_entry);

     compute_dominator(osr_entry, start_block);

     _iterative_dominators = true;

   }

   compute_dominator(std_entry, start_block);

   // start processing with standard entry block

   assert(_work_list.is_empty(), "list must be empty before processing");

   if (ready_for_processing(std_entry)) {

     sort_into_work_list(std_entry);

   } else {

     assert(false, "the std_entry must be ready for processing (otherwise, the method has no start block)");

   }

   do {

     BlockBegin* cur = _work_list.pop();

     if (cur == sux_of_osr_entry) {

       // the osr entry block is ignored in normal processing, it is never added to the

       // work list. Instead, it is added as late as possible manually here.

       append_block(osr_entry);

       compute_dominator(cur, osr_entry);

     }

     append_block(cur);

     int i;

     int num_sux = cur->number_of_sux();

     // changed loop order to get "intuitive" order of if- and else-blocks

     for (i = 0; i < num_sux; i++) {

       BlockBegin* sux = cur->sux_at(i);

       compute_dominator(sux, cur);

       if (ready_for_processing(sux)) {

         sort_into_work_list(sux);

       }

     }

     num_sux = cur->number_of_exception_handlers();

     for (i = 0; i < num_sux; i++) {

       BlockBegin* sux = cur->exception_handler_at(i);

       if (ready_for_processing(sux)) {

         sort_into_work_list(sux);

       }

     }

   } while (_work_list.length() > 0);

 }

 bool ComputeLinearScanOrder::compute_dominators_iter() {

   bool changed = false;

   int num_blocks = _linear_scan_order->length();

   assert(_linear_scan_order->at(0)->dominator() == NULL, "must not have dominator");

   assert(_linear_scan_order->at(0)->number_of_preds() == 0, "must not have predecessors");

   for (int i = 1; i < num_blocks; i++) {

     BlockBegin* block = _linear_scan_order->at(i);

     BlockBegin* dominator = block->pred_at(0);

     int num_preds = block->number_of_preds();

     TRACE_LINEAR_SCAN(4, tty->print_cr("DOM: Processing B%d", block->block_id()));

     for (int j = 0; j < num_preds; j++) {

       BlockBegin *pred = block->pred_at(j);

       TRACE_LINEAR_SCAN(4, tty->print_cr("   DOM: Subrocessing B%d", pred->block_id()));

       if (block->is_set(BlockBegin::exception_entry_flag)) {

         dominator = common_dominator(dominator, pred);

         int num_pred_preds = pred->number_of_preds();

         for (int k = 0; k < num_pred_preds; k++) {

           dominator = common_dominator(dominator, pred->pred_at(k));

         }

       } else {

         dominator = common_dominator(dominator, pred);

       }

     }

     if (dominator != block->dominator()) {

       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()));

       block->set_dominator(dominator);

       changed = true;

     }

   }

   return changed;

 }

 void ComputeLinearScanOrder::compute_dominators() {

   TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing dominators (iterative computation reqired: %d)", _iterative_dominators));

   // iterative computation of dominators is only required for methods with non-natural loops

   // and OSR-methods. For all other methods, the dominators computed when generating the

   // linear scan block order are correct.

   if (_iterative_dominators) {

     do {

       TRACE_LINEAR_SCAN(1, tty->print_cr("DOM: next iteration of fix-point calculation"));

     } while (compute_dominators_iter());

   }

   // check that dominators are correct

   assert(!compute_dominators_iter(), "fix point not reached");

   // Add Blocks to dominates-Array

   int num_blocks = _linear_scan_order->length();

   for (int i = 0; i < num_blocks; i++) {

     BlockBegin* block = _linear_scan_order->at(i);

     BlockBegin *dom = block->dominator();

     if (dom) {

       assert(dom->dominator_depth() != -1, "Dominator must have been visited before");

       dom->dominates()->append(block);

       block->set_dominator_depth(dom->dominator_depth() + 1);

     } else {

       block->set_dominator_depth(0);

     }

   }

 }

 #ifndef PRODUCT

 void ComputeLinearScanOrder::print_blocks() {

   if (TraceLinearScanLevel >= 2) {

     tty->print_cr("----- loop information:");

     for (int block_idx = 0; block_idx < _linear_scan_order->length(); block_idx++) {

       BlockBegin* cur = _linear_scan_order->at(block_idx);

       tty->print("%4d: B%2d: ", cur->linear_scan_number(), cur->block_id());

       for (int loop_idx = 0; loop_idx < _num_loops; loop_idx++) {

         tty->print ("%d ", is_block_in_loop(loop_idx, cur));

       }

       tty->print_cr(" -> loop_index: %2d, loop_depth: %2d", cur->loop_index(), cur->loop_depth());

     }

   }

   if (TraceLinearScanLevel >= 1) {

     tty->print_cr("----- linear-scan block order:");

     for (int block_idx = 0; block_idx < _linear_scan_order->length(); block_idx++) {

       BlockBegin* cur = _linear_scan_order->at(block_idx);

       tty->print("%4d: B%2d    loop: %2d  depth: %2d", cur->linear_scan_number(), cur->block_id(), cur->loop_index(), cur->loop_depth());

       tty->print(cur->is_set(BlockBegin::exception_entry_flag)         ? " ex" : "   ");

       tty->print(cur->is_set(BlockBegin::critical_edge_split_flag)     ? " ce" : "   ");

       tty->print(cur->is_set(BlockBegin::linear_scan_loop_header_flag) ? " lh" : "   ");

       tty->print(cur->is_set(BlockBegin::linear_scan_loop_end_flag)    ? " le" : "   ");

       if (cur->dominator() != NULL) {

         tty->print("    dom: B%d ", cur->dominator()->block_id());

       } else {

         tty->print("    dom: NULL ");

       }

       if (cur->number_of_preds() > 0) {

         tty->print("    preds: ");

         for (int j = 0; j < cur->number_of_preds(); j++) {

           BlockBegin* pred = cur->pred_at(j);

           tty->print("B%d ", pred->block_id());

         }

       }

       if (cur->number_of_sux() > 0) {

         tty->print("    sux: ");

         for (int j = 0; j < cur->number_of_sux(); j++) {

           BlockBegin* sux = cur->sux_at(j);

           tty->print("B%d ", sux->block_id());

         }

       }

       if (cur->number_of_exception_handlers() > 0) {

         tty->print("    ex: ");

         for (int j = 0; j < cur->number_of_exception_handlers(); j++) {

           BlockBegin* ex = cur->exception_handler_at(j);

           tty->print("B%d ", ex->block_id());

         }

       }

       tty->cr();

     }

   }

 }

 #endif

 #ifdef ASSERT

 void ComputeLinearScanOrder::verify() {

   assert(_linear_scan_order->length() == _num_blocks, "wrong number of blocks in list");

   if (StressLinearScan) {

     // blocks are scrambled when StressLinearScan is used

     return;

   }

   // check that all successors of a block have a higher linear-scan-number

   // and that all predecessors of a block have a lower linear-scan-number

   // (only backward branches of loops are ignored)

   int i;

   for (i = 0; i < _linear_scan_order->length(); i++) {

     BlockBegin* cur = _linear_scan_order->at(i);

     assert(cur->linear_scan_number() == i, "incorrect linear_scan_number");

     assert(cur->linear_scan_number() >= 0 && cur->linear_scan_number() == _linear_scan_order->index_of(cur), "incorrect linear_scan_number");

     int j;

     for (j = cur->number_of_sux() - 1; j >= 0; j--) {

       BlockBegin* sux = cur->sux_at(j);

       assert(sux->linear_scan_number() >= 0 && sux->linear_scan_number() == _linear_scan_order->index_of(sux), "incorrect linear_scan_number");

       if (!sux->is_set(BlockBegin::backward_branch_target_flag)) {

         assert(cur->linear_scan_number() < sux->linear_scan_number(), "invalid order");

       }

       if (cur->loop_depth() == sux->loop_depth()) {

         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");

       }

     }

     for (j = cur->number_of_preds() - 1; j >= 0; j--) {

       BlockBegin* pred = cur->pred_at(j);

       assert(pred->linear_scan_number() >= 0 && pred->linear_scan_number() == _linear_scan_order->index_of(pred), "incorrect linear_scan_number");

       if (!cur->is_set(BlockBegin::backward_branch_target_flag)) {

         assert(cur->linear_scan_number() > pred->linear_scan_number(), "invalid order");

       }

       if (cur->loop_depth() == pred->loop_depth()) {

         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");

       }

       assert(cur->dominator()->linear_scan_number() <= cur->pred_at(j)->linear_scan_number(), "dominator must be before predecessors");

     }

     // check dominator

     if (i == 0) {

       assert(cur->dominator() == NULL, "first block has no dominator");

     } else {

       assert(cur->dominator() != NULL, "all but first block must have dominator");

     }

     // Assertion does not hold for exception handlers

     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");

   }

   // check that all loops are continuous

   for (int loop_idx = 0; loop_idx < _num_loops; loop_idx++) {

     int block_idx = 0;

     assert(!is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx)), "the first block must not be present in any loop");

     // skip blocks before the loop

     while (block_idx < _num_blocks && !is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx))) {

       block_idx++;

     }

     // skip blocks of loop

     while (block_idx < _num_blocks && is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx))) {

       block_idx++;

     }

     // after the first non-loop block, there must not be another loop-block

     while (block_idx < _num_blocks) {

       assert(!is_block_in_loop(loop_idx, _linear_scan_order->at(block_idx)), "loop not continuous in linear-scan order");

       block_idx++;

     }

   }

 }

 #endif

 void IR::compute_code() {

   assert(is_valid(), "IR must be valid");

   ComputeLinearScanOrder compute_order(compilation(), start());

   _num_loops = compute_order.num_loops();

   _code = compute_order.linear_scan_order();

 }

 void IR::compute_use_counts() {

   // make sure all values coming out of this block get evaluated.

   int num_blocks = _code->length();

   for (int i = 0; i < num_blocks; i++) {

     _code->at(i)->end()->state()->pin_stack_for_linear_scan();

   }

   // compute use counts

   UseCountComputer::compute(_code);

 }

 void IR::iterate_preorder(BlockClosure* closure) {

   assert(is_valid(), "IR must be valid");

   start()->iterate_preorder(closure);

 }

 void IR::iterate_postorder(BlockClosure* closure) {

   assert(is_valid(), "IR must be valid");

   start()->iterate_postorder(closure);

 }

 void IR::iterate_linear_scan_order(BlockClosure* closure) {

   linear_scan_order()->iterate_forward(closure);

 }

 #ifndef PRODUCT

 class BlockPrinter: public BlockClosure {

  private:

   InstructionPrinter* _ip;

   bool                _cfg_only;

   bool                _live_only;

  public:

   BlockPrinter(InstructionPrinter* ip, bool cfg_only, bool live_only = false) {

     _ip       = ip;

     _cfg_only = cfg_only;

     _live_only = live_only;

   }

   virtual void block_do(BlockBegin* block) {

     if (_cfg_only) {

       _ip->print_instr(block); tty->cr();

     } else {

       block->print_block(*_ip, _live_only);

     }

   }

 };

 void IR::print(BlockBegin* start, bool cfg_only, bool live_only) {

   ttyLocker ttyl;

   InstructionPrinter ip(!cfg_only);

   BlockPrinter bp(&ip, cfg_only, live_only);

   start->iterate_preorder(&bp);

   tty->cr();

 }

 void IR::print(bool cfg_only, bool live_only) {

   if (is_valid()) {

     print(start(), cfg_only, live_only);

   } else {

     tty->print_cr("invalid IR");

   }

 }

 define_array(BlockListArray, BlockList*)

 define_stack(BlockListList, BlockListArray)

 class PredecessorValidator : public BlockClosure {

  private:

   BlockListList* _predecessors;

   BlockList*     _blocks;

   static int cmp(BlockBegin** a, BlockBegin** b) {

     return (*a)->block_id() - (*b)->block_id();

   }

  public:

   PredecessorValidator(IR* hir) {

     ResourceMark rm;

     _predecessors = new BlockListList(BlockBegin::number_of_blocks(), NULL);

     _blocks = new BlockList();

     int i;

     hir->start()->iterate_preorder(this);

     if (hir->code() != NULL) {

       assert(hir->code()->length() == _blocks->length(), "must match");

       for (i = 0; i < _blocks->length(); i++) {

         assert(hir->code()->contains(_blocks->at(i)), "should be in both lists");

       }

     }

     for (i = 0; i < _blocks->length(); i++) {

       BlockBegin* block = _blocks->at(i);

       BlockList* preds = _predecessors->at(block->block_id());

       if (preds == NULL) {

         assert(block->number_of_preds() == 0, "should be the same");

         continue;

       }

       // clone the pred list so we can mutate it

       BlockList* pred_copy = new BlockList();

       int j;

       for (j = 0; j < block->number_of_preds(); j++) {

         pred_copy->append(block->pred_at(j));

       }

       // sort them in the same order

       preds->sort(cmp);

       pred_copy->sort(cmp);

       int length = MIN2(preds->length(), block->number_of_preds());

       for (j = 0; j < block->number_of_preds(); j++) {

         assert(preds->at(j) == pred_copy->at(j), "must match");

       }

       assert(preds->length() == block->number_of_preds(), "should be the same");

     }

   }

   virtual void block_do(BlockBegin* block) {

     _blocks->append(block);

     BlockEnd* be = block->end();

     int n = be->number_of_sux();

     int i;

     for (i = 0; i < n; i++) {

       BlockBegin* sux = be->sux_at(i);

       assert(!sux->is_set(BlockBegin::exception_entry_flag), "must not be xhandler");

       BlockList* preds = _predecessors->at_grow(sux->block_id(), NULL);

       if (preds == NULL) {

         preds = new BlockList();

         _predecessors->at_put(sux->block_id(), preds);

       }

       preds->append(block);

     }

     n = block->number_of_exception_handlers();

     for (i = 0; i < n; i++) {

       BlockBegin* sux = block->exception_handler_at(i);

       assert(sux->is_set(BlockBegin::exception_entry_flag), "must be xhandler");

       BlockList* preds = _predecessors->at_grow(sux->block_id(), NULL);

       if (preds == NULL) {

         preds = new BlockList();

         _predecessors->at_put(sux->block_id(), preds);

       }

       preds->append(block);

     }

   }

 };

 class VerifyBlockBeginField : public BlockClosure {

 public:

   virtual void block_do(BlockBegin *block) {

     for ( Instruction *cur = block; cur != NULL; cur = cur->next()) {

       assert(cur->block() == block, "Block begin is not correct");

     }

   }

 };

 void IR::verify() {

 #ifdef ASSERT

   PredecessorValidator pv(this);

   VerifyBlockBeginField verifier;

   this->iterate_postorder(&verifier);

 #endif

 }

 #endif // PRODUCT

 void SubstitutionResolver::visit(Value* v) {

   Value v0 = *v;

   if (v0) {

     Value vs = v0->subst();

     if (vs != v0) {

       *v = v0->subst();

     }

   }

 }

 #ifdef ASSERT

 class SubstitutionChecker: public ValueVisitor {

   void visit(Value* v) {

     Value v0 = *v;

     if (v0) {

       Value vs = v0->subst();

       assert(vs == v0, "missed substitution");

     }

   }

 };

 #endif

 void SubstitutionResolver::block_do(BlockBegin* block) {

   Instruction* last = NULL;

   for (Instruction* n = block; n != NULL;) {

     n->values_do(this);

     // need to remove this instruction from the instruction stream

     if (n->subst() != n) {

       assert(last != NULL, "must have last");

       last->set_next(n->next());

     } else {

       last = n;

     }

     n = last->next();

   }

 #ifdef ASSERT

   SubstitutionChecker check_substitute;

   if (block->state()) block->state()->values_do(&check_substitute);

   block->block_values_do(&check_substitute);

   if (block->end() && block->end()->state()) block->end()->state()->values_do(&check_substitute);

 #endif

 }