Add pointers to a VirtualFrame that keep track of the indexes of register...

src/virtual-frame-ia32.h

Index: src/virtual-frame-ia32.h
===================================================================
--- src/virtual-frame-ia32.h	(revision 1589)
+++ src/virtual-frame-ia32.h	(working copy)
@@ -337,6 +337,10 @@
   // used in the frame.
   RegisterFile frame_registers_;
 
+  // The index of the register frame element using each register, or
+  // kIllegalIndex if a register is not on the frame.
+  int register_locations_[kNumRegisters];
+
   // The index of the first parameter.  The receiver lies below the first
   // parameter.
   int param0_index() const { return 1; }
@@ -372,12 +376,13 @@
   }
 
   // Record an occurrence of a register in the virtual frame.  This has the
-  // effect of incrementing both the register's frame-internal reference
-  // count and its external reference count.
-  void Use(Register reg);
+  // effect of incrementing the register's external reference count and
+  // of updating the index of the register's location in the frame.
+  void Use(Register reg, int index);
 
   // Record that a register reference has been dropped from the frame.  This
-  // decrements both the register's internal and external reference counts.
+  // decrements the register's external reference count and invalidates the
+  // index of the register's location in the frame.
   void Unuse(Register reg);
 
   // Spill the element at a particular index---write it to memory if