the stack pointer doesn't point to the top of the stack

Question

This is a basic C code for a basic function call:

int multiply(int num, int k) {
    return num * k;
}

int main(int argc, char** argv) {
    
    int k = multiply(5,2);
}

When I tried diassembling this code using the tool available at godbolt.org and picking the option for x86-64 clang 10.0.1, I got the following assembly instructions:

multiply:                               # @multiply
        push    rbp
        mov     rbp, rsp
        mov     dword ptr [rbp - 4], edi
        mov     dword ptr [rbp - 8], esi
        mov     eax, dword ptr [rbp - 4]
        imul    eax, dword ptr [rbp - 8]
        pop     rbp
        ret

main:                                   # @main
        push    rbp
        mov     rbp, rsp
        sub     rsp, 32
        mov     dword ptr [rbp - 4], edi
        mov     qword ptr [rbp - 16], rsi
        mov     edi, 5
        mov     esi, 2
        call    multiply
        xor     ecx, ecx
        mov     dword ptr [rbp - 20], eax
        mov     eax, ecx
        add     rsp, 32
        pop     rbp
        ret

However, the stack pointer doesn't seem to change with each (or even after) parameters are added to the stack from the registers edi and esi by the callee, and remains pointing to the location containing the old value of the base pointer register. Why does that happen?

Answer 1

The compiler plans all space needed for the function and adjusts the stack pointer once at the start of the function and once at the end instead of each time something is needed on the stack inside the function.