C++ 常数函数指针优化

I am trying to implement an abstract interface in C using function pointers inside a struct.
Something like the following

typedef int (*fn_t)(int);
typedef struct
{
    int x;
    const fn_t fnp;
}struct_t;

__attribute__((optimize("O0"))) int square(int num) 
{
    return num * num;
}

static struct_t test = {.fnp = square};

int main(void)
{
    test.x = 1;

    int fnp_ret = test.fnp(3);

    return (fnp_ret);
}

当使用ARM—GCC—13.2.0 unknown—eabi使用—O3构建godbolt时，输出如下.

square:
        str     fp, [sp, #-4]!
        add     fp, sp, #0
        sub     sp, sp, #12
        str     r0, [fp, #-8]
        ldr     r3, [fp, #-8]
        mov     r2, r3
        mul     r2, r3, r2
        mov     r3, r2
        mov     r0, r3
        add     sp, fp, #0
        ldr     fp, [sp], #4
        bx      lr
main:
        mov     r1, #1
        ldr     r3, .L5
        mov     r0, #3
        ldr     r2, [r3, #4]
        str     r1, [r3]
        bx      r2
.L5:
        .word   .LANCHOR0

这里可以看到，在main()中，程序集发出，首先在 struct 中定位函数指针，然后取消引用它.我觉得这很奇怪，因为函数指针是const，所以我希望编译器应该弄清楚它总是指向square函数，这样就相当于直接调用square函数.显然这里不是这样.

在实验过程中，我注意到，如果语句test.x = 1;被注释掉，程序集通过直接调用square函数，

square:
        str     fp, [sp, #-4]!
        add     fp, sp, #0
        sub     sp, sp, #12
        str     r0, [fp, #-8]
        ldr     r3, [fp, #-8]
        mov     r2, r3
        mul     r2, r3, r2
        mov     r3, r2
        mov     r0, r3
        add     sp, fp, #0
        ldr     fp, [sp], #4
        bx      lr
main:
        mov     r0, #3
        b       square

What am I missing?
Is there any way to implement this reliably without paying the performance hit described above?