Avoid allocation of temporary zone lists when inserting representation changes.

Instead of allocating fresh temporary lists for every instruction, reuse
the same instance and reset it between instructions.

This reduces the amount of zone memory used for inserting the HChange
instructions roughly by half.

Review URL: http://codereview.chromium.org/6628079

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7094 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -1775,15 +1775,18 @@ int CompareConversionUses(HValue* a,
 }
 
 
-void HGraph::InsertRepresentationChanges(HValue* current) {
+void HGraph::InsertRepresentationChangesForValue(
+    HValue* current,
+    ZoneList<HValue*>* to_convert,
+    ZoneList<Representation>* to_convert_reps) {
   Representation r = current->representation();
   if (r.IsNone()) return;
   if (current->uses()->length() == 0) return;
 
   // Collect the representation changes in a sorted list.  This allows
   // us to avoid duplicate changes without searching the list.
-  ZoneList<HValue*> to_convert(2);
-  ZoneList<Representation> to_convert_reps(2);
+  ASSERT(to_convert->is_empty());
+  ASSERT(to_convert_reps->is_empty());
   for (int i = 0; i < current->uses()->length(); ++i) {
     HValue* use = current->uses()->at(i);
     // The occurrences index means the index within the operand array of "use"
@@ -1803,10 +1806,10 @@ void HGraph::InsertRepresentationChanges(HValue* current) {
     Representation req = use->RequiredInputRepresentation(operand_index);
     if (req.IsNone() || req.Equals(r)) continue;
     int index = 0;
-    while (to_convert.length() > index &&
-           CompareConversionUses(to_convert[index],
+    while (index < to_convert->length() &&
+           CompareConversionUses(to_convert->at(index),
                                  use,
-                                 to_convert_reps[index],
+                                 to_convert_reps->at(index),
                                  req) < 0) {
       ++index;
     }
@@ -1816,13 +1819,13 @@ void HGraph::InsertRepresentationChanges(HValue* current) {
              current->id(),
              use->id());
     }
-    to_convert.InsertAt(index, use);
-    to_convert_reps.InsertAt(index, req);
+    to_convert->InsertAt(index, use);
+    to_convert_reps->InsertAt(index, req);
   }
 
-  for (int i = 0; i < to_convert.length(); ++i) {
-    HValue* use = to_convert[i];
-    Representation r_to = to_convert_reps[i];
+  for (int i = 0; i < to_convert->length(); ++i) {
+    HValue* use = to_convert->at(i);
+    Representation r_to = to_convert_reps->at(i);
     InsertRepresentationChangeForUse(current, use, r_to);
   }
 
@@ -1830,6 +1833,8 @@ void HGraph::InsertRepresentationChanges(HValue* current) {
     ASSERT(current->IsConstant());
     current->Delete();
   }
+  to_convert->Rewind(0);
+  to_convert_reps->Rewind(0);
 }
 
 
@@ -1865,17 +1870,19 @@ void HGraph::InsertRepresentationChanges() {
     }
   }
 
+  ZoneList<HValue*> value_list(4);
+  ZoneList<Representation> rep_list(4);
   for (int i = 0; i < blocks_.length(); ++i) {
     // Process phi instructions first.
     for (int j = 0; j < blocks_[i]->phis()->length(); j++) {
       HPhi* phi = blocks_[i]->phis()->at(j);
-      InsertRepresentationChanges(phi);
+      InsertRepresentationChangesForValue(phi, &value_list, &rep_list);
     }
 
     // Process normal instructions.
     HInstruction* current = blocks_[i]->first();
     while (current != NULL) {
-      InsertRepresentationChanges(current);
+      InsertRepresentationChangesForValue(current, &value_list, &rep_list);
       current = current->next();
     }
   }

src/hydrogen.h

@@ -296,7 +296,9 @@ class HGraph: public HSubgraph {
   void InsertRepresentationChangeForUse(HValue* value,
                                         HValue* use,
                                         Representation to);
-  void InsertRepresentationChanges(HValue* current);
+  void InsertRepresentationChangesForValue(HValue* current,
+                                           ZoneList<HValue*>* value_list,
+                                           ZoneList<Representation>* rep_list);
   void InferTypes(ZoneList<HValue*>* worklist);
   void InitializeInferredTypes(int from_inclusive, int to_inclusive);
   void CheckForBackEdge(HBasicBlock* block, HBasicBlock* successor);