How will i know whether inline function is actually replaced at the place where it is called or not?

Question

I know that inline function are either replaced where it is called or behave as a normal function.

But how will I know whether inline function is actually replaced a

Answer 1

There is a way to determine if a function is inline programmatically, without looking at the assembly code. This answer is taken from here.

Say you want to check if a specific call is inlined. You would go about like this. Compiler inlines functions, but for those functions that are exported (and almost all function are exported) it needs to maintain a non-inlined addressable function code that can be called from the outside world.

To check if your function my_function is inlined, you need to compare the my_function function pointer (which is not inlined) to the current value of the PC. Here is how I did it in my environment (GCC 7, x86_64):

void * __attribute__((noinline)) get_pc () { return _builtin_return_address(0); }

void my_function() {
    void* pc = get_pc();
    asm volatile("": : :"memory");
    printf("Function pointer = %p, current pc = %p\n", &my_function, pc);
}
void main() {
    my_function();
}

If a function is not inlined, difference between the current value of the PC and value of the function pointer should small, otherwise it will be larger. On my system, when my_function is not inlined I get the following output:

Function pointer = 0x55fc17902500, pc = 0x55fc1790257b

If the function is inlined, I get:

Function pointer = 0x55ddcffc6560, pc = 0x55ddcffc4c6a

For the non-inlined version difference is 0x7b and for the inlined version difference is 0x181f.