src/share/vm/opto/phaseX.cpp

*** 404,414 ****
  
  
  //=============================================================================
  //------------------------------PhaseRemoveUseless-----------------------------
  // 1) Use a breadthfirst walk to collect useful nodes reachable from root.
! PhaseRemoveUseless::PhaseRemoveUseless( PhaseGVN *gvn, Unique_Node_List *worklist ) : Phase(Remove_Useless),
    _useful(Thread::current()->resource_area()) {
  
    // Implementation requires 'UseLoopSafepoints == true' and an edge from root
    // to each SafePointNode at a backward branch.  Inserted in add_safepoint().
    if( !UseLoopSafepoints || !OptoRemoveUseless ) return;
--- 404,414 ----
  
  
  //=============================================================================
  //------------------------------PhaseRemoveUseless-----------------------------
  // 1) Use a breadthfirst walk to collect useful nodes reachable from root.
! PhaseRemoveUseless::PhaseRemoveUseless(PhaseGVN *gvn, Unique_Node_List *worklist, PhaseNumber phase_num) : Phase(phase_num),
    _useful(Thread::current()->resource_area()) {
  
    // Implementation requires 'UseLoopSafepoints == true' and an edge from root
    // to each SafePointNode at a backward branch.  Inserted in add_safepoint().
    if( !UseLoopSafepoints || !OptoRemoveUseless ) return;
*** 441,450 ****
--- 441,523 ----
        }
      }
    }
  }
  
+ //=============================================================================
+ //------------------------------PhaseRenumberLive------------------------------
+ // First, remove useless nodes (equivalent to identifying live nodes).
+ // Then, renumber live nodes.
+ //
+ // The set of live nodes is returned by PhaseRemoveUseless in the _useful structure.
+ // If the number of live nodes is 'x' (where 'x' == _useful.size()), then the
+ // PhaseRenumberLive updates the node ID of each node (the _idx field) with a unique
+ // value in the range [0, x).
+ //
+ // At the end of the PhaseRenumberLive phase, the compiler's count of unique nodes is
+ // updated to 'x' and the list of dead nodes is reset (as there are no dead nodes).
+ //
+ // The PhaseRenumberLive phase updates two data structures with the new node IDs.
+ // (1) The worklist is used by the PhaseIterGVN phase to identify nodes that must be
+ // processed. A new worklist (with the updated node IDs) is returned in 'new_worklist'.
+ // (2) Type information (the field PhaseGVN::_types) maps type information to each
+ // node ID. The mapping is updated to use the new node IDs as well. Updated type
+ // information is returned in PhaseGVN::_types.
+ //
+ // The PhaseRenumberLive phase does not preserve the order of elements in the worklist.
+ //
+ // Other data structures used by the compiler are not updated. The hash table for value
+ // numbering (the field PhaseGVN::_table) is not updated because computing the hash
+ // values is not based on node IDs. The field PhaseGVN::_nodes is not updated either
+ // because it is empty wherever PhaseRenumberLive is used.
+ PhaseRenumberLive::PhaseRenumberLive(PhaseGVN* gvn,
+                                      Unique_Node_List* worklist, Unique_Node_List* new_worklist,
+                                      PhaseNumber phase_num) :
+   PhaseRemoveUseless(gvn, worklist, RenumberLiveNodes ? Renumber_Live : Remove_Useless) {
+ 
+   assert(C->live_nodes() == _useful.size(), "the number of live nodes must match the number of useful nodes");
+   uint old_unique_count = C->unique();
+   uint live_node_count = C->live_nodes();
+   uint worklist_size = worklist->size();
+ 
+   // Storage for the updated type information.
+   Type_Array new_type_array(C->comp_arena());
+ 
+   // Iterate over the set of live nodes.
+   uint current_idx = 0; // The current new node ID. Incremented after every assignment.
+   for (uint i = 0; i < _useful.size(); i++) {
+     Node* n = _useful.at(i);
+     const Type* type = gvn->type_or_null(n);
+     new_type_array.map(current_idx, type);
+ 
+     bool in_worklist = false;
+     if (worklist->member(n)) {
+       in_worklist = true;
+     }
+ 
+     n->set_idx(current_idx); // Update node ID.
+ 
+     if (in_worklist) {
+       new_worklist->push(n);
+     }
+ 
+     current_idx++;
+   }
+ 
+   assert(worklist_size == new_worklist->size(), "the new worklist must have the same size as the original worklist");
+   assert(live_node_count == current_idx, "all live nodes must be processed");
+ 
+   // Replace the compiler's type information with the updated type information.
+   gvn->replace_types(new_type_array);
+ 
+   // Update the unique node count of the compilation to the number of currently live nodes.
+   C->set_unique(live_node_count);
+ 
+   // Set the dead node count to 0 and reset dead node list.
+   C->reset_dead_node_list();
+ }
+ 
  
  //=============================================================================
  //------------------------------PhaseTransform---------------------------------
  PhaseTransform::PhaseTransform( PhaseNumber pnum ) : Phase(pnum),
    _arena(Thread::current()->resource_area()),