Addresses are unintentionally aligned

[pvdrz]

During the implementation of the intptrcast model we discovered that memory addresses are aligned even when miri::intptrcast::GlobalState::align_addr is not used.

Relevant code:

let x = (&5u8 as *const u8 as usize) * 2;
let y = (&6u16 as *const u16 as usize) * 2 / 2;
assert!(y % 2 == 1);

[RalfJung]

% should also cause force_bits, so you shouldn't need the * 2 stuff.

But also it is impossible to entirely avoid this. So maybe we should keep the "no int base addresses" mode... or have a mode where the base address is only used for ptr comparison, not anything else? That seems neat actually.

[oli-obk]

wait how is assert!(x % 2 == 1); passing if its value was multiplied by 2 before?

[pvdrz]

wait how is assert!(x % 2 == 1); passing if its value was multiplied by 2 before?

Oh I should had left a comment/remove it. I left it when I copied and pasted just after finishing doodling with it.

[pvdrz]

Adding @oli-obk's comment: We should stop wasting align bytes if we were already aligned
Edit: Solved in #795