Scala 2.9 optimizes for comprehensions way better!

Ok, I completely missed this. For comprehensions in Scala 2.9 was way better optimized with the parameter -optimize than they were before! Take this code:

class OptEx {
    def sum(l: Array[Int]) = {
        var acc = 0
        for (i <- 0 until l.length) acc += l(i)
        acc
    }
}

This is the java bytecode generated with Scala 2.8.1 for the method sum:

public int sum(int[]);
  Code:
   0:   new     #7; //class scala/runtime/IntRef
   3:   dup
   4:   iconst_0
   5:   invokespecial   #12; //Method scala/runtime/IntRef."":(I)V
   8:   astore_2
   9:   new     #14; //class scala/runtime/RichInt
   12:  dup
   13:  iconst_0
   14:  invokespecial   #15; //Method scala/runtime/RichInt."":(I)V
   17:  aload_1
   18:  arraylength
   19:  invokevirtual   #19; //Method scala/runtime/RichInt.until:(I)Lscala/collection/immutable/Range$ByOne;
   22:  new     #21; //class OptEx$$anonfun$sum$1
   25:  dup
   26:  aload_0
   27:  aload_1
   28:  aload_2
   29:  invokespecial   #24; //Method OptEx$$anonfun$sum$1."":(LOptEx;[ILscala/runtime/IntRef;)V
   32:  invokeinterface #30,  2; //InterfaceMethod scala/collection/immutable/Range$ByOne.foreach$mVc$sp:(Lscala/Functio
n1;)V
   37:  aload_2
   38:  getfield        #34; //Field scala/runtime/IntRef.elem:I
   41:  ireturn

And this is what Scala 2.9.0 does:

public int sum(int[]);
  Code:
   0:   new     #7; //class scala/runtime/IntRef
   3:   dup
   4:   iconst_0
   5:   invokespecial   #12; //Method scala/runtime/IntRef."":(I)V
   8:   astore  6
   10:  new     #14; //class scala/runtime/RichInt
   13:  dup
   14:  iconst_0
   15:  invokespecial   #15; //Method scala/runtime/RichInt."":(I)V
   18:  aload_1
   19:  arraylength
   20:  istore_3
   21:  astore_2
   22:  getstatic       #21; //Field scala/collection/immutable/Range$.MODULE$:Lscala/collection/immutable/Range$;
   25:  aload_2
   26:  invokevirtual   #25; //Method scala/runtime/RichInt.self:()I
   29:  iload_3
   30:  invokevirtual   #29; //Method scala/collection/immutable/Range$.apply:(II)Lscala/collection/immutable/Range;
   33:  dup
   34:  astore  8
   36:  invokevirtual   #34; //Method scala/collection/immutable/Range.length:()I
   39:  iconst_0
   40:  if_icmple       83
   43:  aload   8
   45:  invokevirtual   #37; //Method scala/collection/immutable/Range.last:()I
   48:  istore  4
   50:  aload   8
   52:  invokevirtual   #40; //Method scala/collection/immutable/Range.start:()I
   55:  istore  9
   57:  iload   9
   59:  iload   4
   61:  if_icmpne       89
   64:  iload   9
   66:  istore  5
   68:  aload   6
   70:  aload   6
   72:  getfield        #44; //Field scala/runtime/IntRef.elem:I
   75:  aload_1
   76:  iload   5
   78:  iaload
   79:  iadd
   80:  putfield        #44; //Field scala/runtime/IntRef.elem:I
   83:  aload   6
   85:  getfield        #44; //Field scala/runtime/IntRef.elem:I
   88:  ireturn
   89:  iload   9
   91:  istore  7
   93:  aload   6
   95:  aload   6
   97:  getfield        #44; //Field scala/runtime/IntRef.elem:I
   100: aload_1
   101: iload   7
   103: iaload
   104: iadd
   105: putfield        #44; //Field scala/runtime/IntRef.elem:I
   108: iload   9
   110: aload   8
   112: invokevirtual   #47; //Method scala/collection/immutable/Range.step:()I
   115: iadd
   116: istore  9
   118: goto    57

Time to take your old benchmarks out of the closet, people!