Prematurely resetting the stack pointer? Confusing assembly code

Question

Im trying to make sense of a small bit of assembly.

pushl %ebp
movl %esp,%ebp
movl 8(%ebp),%edx
movl 12(%ebp),%eax
movl %ebp,%esp
movl (%edx),%edx
addl %edx,(%eax)
movl %edx,%eax
popl %ebp
ret

Why is the sp being reset to the base pointer before the rest of the function? Why is the value in %edx being moved back into itself?

Answer 1

A shorter version of this would be:

mov 4(%esp), %eax
mov 8(%esp), %edx
mov (%edx), %edx
add  %edx, (%eax)
ret

or, a rough C equiv:

void add(int *from, int *to) {
  *to += *from;
}

The compiler likely plays with %ebp go ensure debug-able stack frames; and restoring %esp from %ebp does nothing -- they are the same value.