Optimizing away unused function pointers - c

Question

I want gcc to optimize away unused function pointers. Ie remove the code completely from the final executable. So far I was not able to achieve this.
Here is updated code:
#include <stdio.h>
struct inner {
void (*fun)(void);
void (*fun2)(void);
};
struct inner2 {
void (*fun)(void);
};
struct foo {
struct inner in;
struct inner2 in2;
};
void lessfun(){
printf("lessfun\n");
}
void morefun(){
printf("morefun\n");
}
const struct foo inst = {
{ .fun = lessfun, .fun2 = morefun },
{ .fun = lessfun }
};
void test(struct foo *f){
f->in.fun();
}
int main(int argc, char *argv){
struct inner2 in = inst.in2;
inst.in.fun();
inst.in.fun2();
in.fun();
/////////////// alt1: nm out | grep morefun -> found
test(&inst);
///////////////
/////////////// alt2: nm out | grep morefun -> not found
struct inner in;
struct inner in2 = inst.in;
in = in2;
test(&in);
///////////////
}
compiler flags: -Os -fdata-sections -Wl,--relax,--gc-sections -ffunction-sections
link flags: -flto -Os -fdata-sections -Wl,--relax,--gc-sections
Compiler: arm-none-eabi-gcc
Here the compiler will include both method1 and method2 into the final program even if they are never used. It is the assignment that seems to make this happen. But if they are never called, it would be nice to completely remove the code to method1 and method2. This obviously happens because technically the function is in fact referenced in the assignment, but since the variable in the assignment is never user it should still be possible to determine that the method is never called.
Do I need to declare it const somehow? How?
How can I have gcc remove the unused functions?
EDIT: I was able to sort of make it work as you see above. But it only works if I do not make a copy of any members of the struct. If a direct copy is made and passed to a function, the compiler fails to optimize unused functions. I'm now 60% certain that this is some kind of optimizer bug.
EDIT2: you may not even reproduce the bug. But here is the scenario that creates it.
struct mydev dev;
struct dev_spi spi;
struct dev_spi sp2 = board.spi0;
sp2.writereadbyte(0);
spi = sp2;
//test(&cpu.spi0);
// using only this call results in correct optimization
// many unused methods pointed to by members of "board" var are gone.
mydev_init(&dev, &spi);
// using this version breaks optimization
// all methods referenced by "board" struct are included in final program
mydev_init(&dev, &sp2);
// this one breaks optimization as well
// same as above.
mydev_init(&dev, &board.spi0);
// there is no difference other than one passes variable directly to the init function
// and the other uses a temp variable.