[jvm-l] Single return point important?

[Charles Oliver Nutter]

I was examining the bytecode output of Duby this morning, comparing it 
to javac output, and noticed that for fib() there's only one small 
difference: javac inserts an extra branch in order to have a single 
return instruction.

Is this useful? Necessary? Anyone know why javac does this, since it 
increases the bytecode size for this simple case?

Duby source:

def fib(a => :fixnum)
   if a < 2
     a
   else
     fib(a - 1) + fib(a - 2)
   end
end

Java source:

public static int fib(int a) {
   if (a < 2) {
     return a;
   } else {
     return fib(a - 1) + fib(a - 2);
   }
}

Duby bytecode:

public static int fib(int);
   Code:
    0:  iload_0
    1:  iconst_2
    2:  if_icmpge       7
    5:  iload_0
    6:  ireturn
    7:  iload_0
    8:  iconst_1
    9:  isub
    10: invokestatic    #2; //Method fib:(I)I
    13: iload_0
    14: iconst_2
    15: isub
    16: invokestatic    #2; //Method fib:(I)I
    19: iadd
    20: ireturn

Java bytecode:

public static int fib(int);
   Code:
    0:  iload_0
    1:  iconst_2
    2:  if_icmpge       9
    5:  iload_0
    6:  goto    22
    9:  iload_0
    10: iconst_1
    11: isub
    12: invokestatic    #11; //Method fib:(I)I
    15: iload_0
    16: iconst_2
    17: isub
    18: invokestatic    #11; //Method fib:(I)I
    21: iadd
    22: ireturn

Other than the branch-to-return, the two compilers output identical 
code. So I'm understandably curious if this is a difference I should be 
interested in.

- Charlie

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