What Java code will force javac 1.6 to use the 'swap' and 'nop' opcodes?

问题

I'm working on an amateur JVM implementation, and I'm trying to make sure I have test coverage for all of the opcodes in the spec. I've gotten it down to the last few, but nop and swap have been eluding me. For example, here's a simple function that might use swap:

static int do_swap() {
  int a = 56;
  int b = 32;
  return b%a;
}

But the bytecode produced by javac 1.6 avoids swapping in lieu of local storage:

static int do_swap();
  Code:
   0:   bipush  56
   2:   istore_0
   3:   bipush  32
   5:   istore_1
   6:   iload_1
   7:   iload_0
   8:   irem
   9:   ireturn

Any ideas?

回答1:

None. The Java Language Specification does not provide such guarantees. You can just write your own Java bytecode using Jasmin (a bytecode assembler).

来源：https://stackoverflow.com/questions/9722421/what-java-code-will-force-javac-1-6-to-use-the-swap-and-nop-opcodes