Compiled Factorial Example

Assume that translation of c, denoted [ [ c ] ], produces a boolean value on top of the stack

Then:

[[ If (c) sThen else sElse ]] =
       [[ c ]]
       if_eq nElse
       [[ sThen ]]
       goto nAfter
nElse: [[ sElse ]]
nAfter:

Translating

public static int test(boolean b) {
  if (b)
    return 13;
  else
    return 42;
}

Bytecode:

public static int test(boolean);
  Code:
   0:   iload_0
   1:   ifeq    7
   4:   bipush  13
   6:   ireturn
   7:   bipush  42
   9:   ireturn

When generating

if_eq nAfter

how do we know the offset nAfter?

1. generate symbolic labels
2. compute the values of labels when all instruction sizes are known (note: fixed size of jump instructions, regardless of their destination)
3. emit the code using appropriate values of labels