Speed up removing phi nodes.

src/hydrogen-instructions.cc

 // Copyright 2012 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 365 matching lines @@
 void HValue::SetOperandAt(int index, HValue* value) {
   RegisterUse(index, value);
   InternalSetOperandAt(index, value);
 }
 
 
 void HValue::DeleteAndReplaceWith(HValue* other) {
   // We replace all uses first, so Delete can assert that there are none.
   if (other != NULL) ReplaceAllUsesWith(other);
   ASSERT(HasNoUses());
-  // Clearing the operands includes going through the use list of each operand
-  // to remove this HValue, which can be expensive.  Instead, we mark this as
-  // dead and only check the first item in the use list of each operand.
-  // For the following items in the use lists we rely on the tail() method to
-  // skip dead dead items and remove them lazily.
-  SetFlag(kIsDead);
-  for (int i = 0; i < OperandCount(); ++i) {
-    HValue* operand = OperandAt(i);
-    HUseListNode* first = operand->use_list_;
-    if (first != NULL && first->index() == i && first->value() == this) {
-      operand->use_list_ = first->tail();
-    }
-  }
+  Kill();
   DeleteFromGraph();
 }
 
 
 void HValue::ReplaceAllUsesWith(HValue* other) {
   while (use_list_ != NULL) {
     HUseListNode* list_node = use_list_;
     HValue* value = list_node->value();
     ASSERT(!value->block()->IsStartBlock());
     value->InternalSetOperandAt(list_node->index(), other);
     use_list_ = list_node->tail();
     list_node->set_tail(other->use_list_);
     other->use_list_ = list_node;
   }
 }
 
 
-void HValue::ClearOperands() {
+void HValue::Kill() {
+  // Instead of going through the entire use list of each operand, we only
+  // check the first item in each use list and rely on the tail() method to
+  // skip dead items, removing them lazily next time we traverse the list.
+  SetFlag(kIsDead);
   for (int i = 0; i < OperandCount(); ++i) {
-    SetOperandAt(i, NULL);
+    HValue* operand = OperandAt(i);
+    HUseListNode* first = operand->use_list_;
+    if (first != NULL && first->index() == i && first->value() == this) {

[fschneider, 2012/02/24 08:42:03]

Maybe reorder the condition to:

if (first != NULL && first->value() == this && first->index() == i)

+      operand->use_list_ = first->tail();
+    }
   }
 }
 
 
 void HValue::SetBlock(HBasicBlock* block) {
   ASSERT(block_ == NULL || block == NULL);
   block_ = block;
   if (id_ == kNoNumber && block != NULL) {
     id_ = block->graph()->GetNextValueID(this);
   }
@@ skipping 1819 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal