Speed up FastAsciiArrayJoin on ia32 by improving hand-written assembly code.

src/ia32/macro-assembler-ia32.h

Index: src/ia32/macro-assembler-ia32.h
===================================================================
--- src/ia32/macro-assembler-ia32.h	(revision 6301)
+++ src/ia32/macro-assembler-ia32.h	(working copy)
@@ -386,22 +386,13 @@
                                Register scratch2,
                                Label* gc_required);
 
-  // All registers must be distinct.  Only current_string needs valid contents
-  // on entry.  All registers may be invalid on exit.  result_operand is
-  // unchanged, padding_chars is updated correctly.
-  // The top of new space must contain a sequential ascii string with
-  // padding_chars bytes free in its top word.  The sequential ascii string
-  // current_string is concatenated to it, allocating the necessary amount
-  // of new memory.
-  void AppendStringToTopOfNewSpace(
-      Register current_string,  // Tagged pointer to string to copy.
-      Register current_string_length,
-      Register result_pos,
-      Register scratch,
-      Register new_padding_chars,
-      Operand operand_result,
-      Operand operand_padding_chars,
-      Label* bailout);
+  // Copy memory, byte-by-byte, from source to destination.  Not optimized for
+  // long or aligned copies.
+  // The contents of index and scratch are destroyed.
+  void CopyBytes(Register source,
+                 Register destination,
+                 Register length,
+                 Register scratch);
 
   // ---------------------------------------------------------------------------
   // Support functions.