Cache first hint operand while building live ranges.

src/lithium-allocator.h

Index: src/lithium-allocator.h
diff --git a/src/lithium-allocator.h b/src/lithium-allocator.h
index 0300212f3103bdc23f8f2372e8a51da3a86ad903..552ebdd1dedb8b3aaa8fa6a161dedc4068efb5b2 100644
--- a/src/lithium-allocator.h
+++ b/src/lithium-allocator.h
@@ -329,6 +329,10 @@ class LiveRange: public ZoneObject {
   }
   bool IsSpilled() const { return spilled_; }
 
+  LOperand* current_hint_operand() const {
+    ASSERT(current_hint_operand_ == FirstHint());
+    return current_hint_operand_;
+  }
   LOperand* FirstHint() const {
     UsePosition* pos = first_pos_;
     while (pos != NULL && !pos->HasHint()) pos = pos->next();
@@ -398,6 +402,8 @@ class LiveRange: public ZoneObject {
   // This is used as a cache, it doesn't affect correctness.
   mutable UseInterval* current_interval_;
   UsePosition* last_processed_use_;
+  // This is used as a cache, it's invalid outside of BuildLiveRanges.
+  LOperand* current_hint_operand_;
   LOperand* spill_operand_;
   int spill_start_index_;
 };