C++ 为什么 C 风格的类会产生额外的指令

将C风格的 struct 与带有‘Members’函数的C++类进行比较，试图对C++开销进行建模，我怀疑下面的实现将通过包含相同数量的指令而大致等价.我看到当调用‘Members’函数时，C实现会导致额外的指令.

int main()
{
    uint32_t a;
    rectangle_t r;
    
    /* struct */
    r.set(2,3, &r);
    /* asm 
       ldr     r3, [r7, #12]
       adds    r2, r7, #4
       movs    r1, #3
       movs    r0, #2
       blx     r3
    */

    a = r.getArea(&r);
    /* asm 
       ldr     r3, [r7, #16]
       adds    r2, r7, #4
       mov     r0, r2
       blx     r3
       str     r0, [r7, #20]
       movs    r3, #0
    */

    # Class
    r.set(2, 3);
    /* asm 
       adds    r3, r7, #4
       movs    r2, #3
       movs    r1, #2
       mov     r0, r3
       bl      rectangle_t::set(unsigned int, unsigned int)
    */
    a = r.getArea();
    /* asm 
       adds    r3, r7, #4
       mov     r0, r3
       bl      rectangle_t::getArea()
       str     r0, [r7, #12]
       movs    r3, #0
    */
}

为什么在调用 struct ‘Members’而不是类成员时会有额外的LDR指令？

编译:ARM GCC 12.2.0(LINUX)

声明:

typedef struct rectangle rectangle_t;
struct rectangle
{
    uint32_t w;
    uint32_t l;
    void (*set)(uint32_t L, uint32_t W, rectangle_t *self);
    uint32_t (*getArea)(rectangle_t *self);    
};
void set(uint32_t L, uint32_t W, rectangle_t *self)
{
    self->w = W;
    self->l = L;
}

uint32_t getArea(rectangle_t *self)
{
    return self->l * self->w;
}

class rectangle_t
{
public:   

    uint32_t w;
    uint32_t l;  
    void set(uint32_t L, uint32_t W);
    uint32_t getArea(); 
};

void rectangle_t::set(uint32_t L, uint32_t W)
{
    w = W;
    l = L;
}

uint32_t rectangle_t::getArea()
{
    return l * w;
}