org.objectweb.asm.Opcodes# DUP_X2 ( ) 源码实例Demo

private void genericSswap(String desc) {
	//caters for double, int on stack - to swap
	if(desc.equals("J") || desc.equals("D")){//long and double take up two slots insteead of 1
		super.visitInsn(Opcodes.DUP_X2);
		super.visitInsn(Opcodes.POP);
	}
	else{//1 slot each
		super.visitInsn(Opcodes.SWAP);
	}
}
 

public static int getDupXOpcode(Type dType, Type bType) {
	if (dType.getSize() == 1 && bType.getSize() == 1) {
		return Opcodes.DUP_X1;
	} else if (dType.getSize() == 1 && bType.getSize() == 2) {
		return Opcodes.DUP_X2;
	} else if (dType.getSize() == 2 && bType.getSize() == 1) {
		return Opcodes.DUP2_X1;
	} else if (dType.getSize() == 2 && bType.getSize() == 2) {
		return Opcodes.DUP2_X2;
	} else {
		throw new IllegalArgumentException(dType.toString() + " " + bType.toString());
	}
}
 

/**
 * NOTE:  All calls to instruction visitation routines are made against super, directly, since we do frame offset accounting within our overrides
 * and that offset only applies to incoming bytecodes, not outgoing ones.
 * 
 * @param opcode The opcode.
 * @param descriptor The type descriptor of the field to which the opcode is applied.
 */
private void checkInjectLazyLoad(int opcode, String descriptor) {
    // If this is a PUTFIELD or GETFIELD, we want to call "lazyLoad()":
    // -PUTIFELD:  DUP2, POP, INVOKEVIRTUAL
    // -GETIFELD:  DUP, INVOKEVIRTUAL
    if ((Opcodes.PUTFIELD == opcode) && ((null == this.tracker) || !this.tracker.isThisTargetOfPut(this.frameOffset))) {
        // We need to see how big this type is since double and long need a far more complex dance.
        if ((1 == descriptor.length()) && ((DescriptorParser.LONG == descriptor.charAt(0)) || (DescriptorParser.DOUBLE == descriptor.charAt(0)))) {
            // Here, the stack looks like: ... OBJECT, VAR1, VAR2 (top)
            // Where we need:  ... OBJECT, VAR1, VAR2, OBJECT (top)
            // This is multiple stages:
            // DUP2_X1: ... VAR1, VAR2, OBJECT, VAR1, VAR2 (top)
            super.visitInsn(Opcodes.DUP2_X1);
            // POP2: ... VAR1, VAR2, OBJECT (top)
            super.visitInsn(Opcodes.POP2);
            // DUP: ... VAR1, VAR2, OBJECT, OBJECT (top)
            super.visitInsn(Opcodes.DUP);
            // INOKE: ... VAR1, VAR2, OBJECT (top)
            super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, SHADOW_OBJECT_NAME, LAZY_LOAD_NAME, LAZY_LOAD_DESCRIPTOR, false);
            // DUP_X2: ... OBJECT, VAR1, VAR2, OBJECT (top)
            super.visitInsn(Opcodes.DUP_X2);
            // POP: ... OBJECT, VAR1, VAR2 (top)
            super.visitInsn(Opcodes.POP);
        } else {
            // Here, the stack looks like: ... OBJECT, VAR, (top)
            // Where we need:  ... OBJECT, VAR, OBJECT (top)
            // Stages:
            // DUP2: ... OBJECT, VAR, OBJECT, VAR (top)
            super.visitInsn(Opcodes.DUP2);
            // POP: ... OBJECT, VAR, OBJECT (top)
            super.visitInsn(Opcodes.POP);
            // INOKE: ... OBJECT, VAR (top)
            super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, SHADOW_OBJECT_NAME, LAZY_LOAD_NAME, LAZY_LOAD_DESCRIPTOR, false);
        }
    } else if ((Opcodes.GETFIELD == opcode) && ((null == this.tracker) || !this.tracker.isThisTargetOfGet(this.frameOffset))) {
        // Here, the stack looks like: ... OBJECT, (top)
        // Where we need:  ... OBJECT, OBJECT (top)
        super.visitInsn(Opcodes.DUP);
        super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, SHADOW_OBJECT_NAME, LAZY_LOAD_NAME, LAZY_LOAD_DESCRIPTOR, false);
    }
}