code: public InstructionHandle getPredecessorOf(InstructionHandle handle) {
          if (VERIFY_INTEGRITY && !containsInstruction(handle)) {
              throw new IllegalStateException();
          }
          return handle == firstInstruction ? null : handle.getPrev();
      }
docs: Get the predecessor of given instruction within the basic block.
  
  @param handle
  the instruction
  @return the instruction's predecessor, or null if the instruction is the
  first in the basic block