int visitFrameStart(final int offset, final int numLocal, final int numStack) {
        int frameLength = 3 + numLocal + numStack;
        if (currentFrame == null || currentFrame.length < frameLength) {
            currentFrame = new int[frameLength];
        }
        currentFrame[0] = offset;
        currentFrame[1] = numLocal;
        currentFrame[2] = numStack;
        return 3;
    }
Starts the visit of a new stack map frame, stored in {@link #currentFrame}.

@param offset   the bytecode offset of the instruction to which the frame corresponds.
@param numLocal the number of local variables in the frame.
@param numStack the number of stack elements in the frame.
@return the index of the next element to be written in this frame.
core/src/main/java/com/alibaba/fastjson2/internal/asm/MethodWriter.java