Remove some more uses of subgraphs and more cleanup of the graph builder.

src/hydrogen-instructions.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 267 matching lines @@
 
 
 void HValue::SetOperandAt(int index, HValue* value) {
   ASSERT(value == NULL || !value->representation().IsNone());
   RegisterUse(index, value);
   InternalSetOperandAt(index, value);
 }
 
 
 void HValue::ReplaceAndDelete(HValue* other) {
-  ReplaceValue(other);
+  if (other != NULL) ReplaceValue(other);
   Delete();
 }
 
 
 void HValue::ReplaceValue(HValue* other) {
-  ZoneList<HValue*> start_uses(2);
   for (int i = 0; i < uses_.length(); ++i) {
-    HValue* use = uses_.at(i);
-    if (!use->block()->IsStartBlock()) {
-      InternalReplaceAtUse(use, other);
-      other->uses_.Add(use);
-    } else {
-      start_uses.Add(use);
-    }
+    HValue* use = uses_[i];
+    ASSERT(!use->block()->IsStartBlock());
+    InternalReplaceAtUse(use, other);
+    other->uses_.Add(use);
   }
-  uses_.Clear();
-  uses_.AddAll(start_uses);
+  uses_.Rewind(0);
 }
 
 
 void HValue::ClearOperands() {
   for (int i = 0; i < OperandCount(); ++i) {
     SetOperandAt(i, NULL);
   }
 }
 
 
@@ skipping 1165 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal