Method visitJumpInsn

src/jvm/clojure/asm/MethodWriter.java:1094–1198

(final int opcode, final Label label)

  }

  @Override
  public void visitJumpInsn(final int opcode, final Label label) {
    lastBytecodeOffset = code.length;
    // Add the instruction to the bytecode of the method.
    // Compute the 'base' opcode, i.e. GOTO or JSR if opcode is GOTO_W or JSR_W, otherwise opcode.
    int baseOpcode =
        opcode >= Constants.GOTO_W ? opcode - Constants.WIDE_JUMP_OPCODE_DELTA : opcode;
    boolean nextInsnIsJumpTarget = false;
    if ((label.flags & Label.FLAG_RESOLVED) != 0
        && label.bytecodeOffset - code.length < Short.MIN_VALUE) {
      // Case of a backward jump with an offset < -32768. In this case we automatically replace GOTO
      // with GOTO_W, JSR with JSR_W and IFxxx <l> with IFNOTxxx <L> GOTO_W <l> L:..., where
      // IFNOTxxx is the "opposite" opcode of IFxxx (e.g. IFNE for IFEQ) and where <L> designates
      // the instruction just after the GOTO_W.
      if (baseOpcode == Opcodes.GOTO) {
        code.putByte(Constants.GOTO_W);
      } else if (baseOpcode == Opcodes.JSR) {
        code.putByte(Constants.JSR_W);
      } else {
        // Put the "opposite" opcode of baseOpcode. This can be done by flipping the least
        // significant bit for IFNULL and IFNONNULL, and similarly for IFEQ ... IF_ACMPEQ (with a
        // pre and post offset by 1). The jump offset is 8 bytes (3 for IFNOTxxx, 5 for GOTO_W).
        code.putByte(baseOpcode >= Opcodes.IFNULL ? baseOpcode ^ 1 : ((baseOpcode + 1) ^ 1) - 1);
        code.putShort(8);
        // Here we could put a GOTO_W in theory, but if ASM specific instructions are used in this
        // method or another one, and if the class has frames, we will need to insert a frame after
        // this GOTO_W during the additional ClassReader -> ClassWriter round trip to remove the ASM
        // specific instructions. To not miss this additional frame, we need to use an ASM_GOTO_W
        // here, which has the unfortunate effect of forcing this additional round trip (which in
        // some case would not have been really necessary, but we can't know this at this point).
        code.putByte(Constants.ASM_GOTO_W);
        hasAsmInstructions = true;
        // The instruction after the GOTO_W becomes the target of the IFNOT instruction.
        nextInsnIsJumpTarget = true;
      }
      label.put(code, code.length - 1, true);
    } else if (baseOpcode != opcode) {
      // Case of a GOTO_W or JSR_W specified by the user (normally ClassReader when used to remove
      // ASM specific instructions). In this case we keep the original instruction.
      code.putByte(opcode);
      label.put(code, code.length - 1, true);
    } else {
      // Case of a jump with an offset >= -32768, or of a jump with an unknown offset. In these
      // cases we store the offset in 2 bytes (which will be increased via a ClassReader ->
      // ClassWriter round trip if it turns out that 2 bytes are not sufficient).
      code.putByte(baseOpcode);
      label.put(code, code.length - 1, false);
    }

    // If needed, update the maximum stack size and number of locals, and stack map frames.
    if (currentBasicBlock != null) {
      Label nextBasicBlock = null;
      if (compute == COMPUTE_ALL_FRAMES) {
        currentBasicBlock.frame.execute(baseOpcode, 0, null, null);
        // Record the fact that 'label' is the target of a jump instruction.
        label.getCanonicalInstance().flags |= Label.FLAG_JUMP_TARGET;
        // Add 'label' as a successor of the current basic block.
        addSuccessorToCurrentBasicBlock(Edge.JUMP, label);