Why does GCC move variables to a temporary location before assigning them?

When looking at some decompiled C code I saw this:

movl    -0xc(%rbp), %esi
movl    %esi, -0x8(%rbp)

This corresponds to this C code:

x = y;

This got me thinking: how come gcc moves y to %esi and then move %esi to x instead of just moving y to x directly?

This is the entire C and decompiled code, if it matters:

C

int main(void) {
    int x, y, z;

    while(1) {
        x = 0;
        y = 1;
        do {
            printf("%d\n", x);

            z = x + y;
            x = y;
            y = z;
        } while(x < 255);
    }
}

Decompiled

pushq    %rbp
movq     %rsp, %rbp
subq     $0x20, %rsp
movl     $0x0, -0x4(%rbp)

movl     $0x0, -0x8(%rbp) ; x = 0
movl     $0x1, -0xc(%rbp) ; y = 1

; printf
leaq     0x56(%rip), %rdi
movl     -0x8(%rbp), %esi
movb     $0x0, %al
callq    0x100000f78

; z = x + y
movl     -0x8(%rbp), %esi  ; x -> esi
addl     -0xc(%rbp), %esi  ; y + esi
movl     %esi, -0x10(%rbp) ; z = esi

; x = y
movl     -0xc(%rbp), %esi
movl     %esi, -0x8(%rbp)

; y = z
movl     -0x10(%rbp), %esi
movl     %esi, -0xc(%rbp)

movl     %eax, -0x14(%rbp) ; not sure... I believe printf return value?
cmpl     $0xff, -0x8(%rbp) ; x < 255
jl       0x100000f3d ; do...while(x < 255)
jmp      0x100000f2f ; while(1)