local stack frame, so references should use negative offsets
in the range [−framesize, 0):
<code>x-8(SP)</code>, <code>y-4(SP)</code>, and so on.
On architectures with a real register named <code>SP</code>, the name prefix distinguishes
references to the virtual stack pointer from references to the architectural <code>SP</code> register.
That is, <code>x-8(SP)</code> and <code>-8(SP)</code> are different memory locations:
the first refers to the virtual stack pointer pseudo-register, while the second refe