Optimize pointer::is_aligned_to

[WaffleLapkin]

This PR replaces addr % align with addr & align - 1, which is correct due to align being a power of two.

Here is a proof that this makes things better: [godbolt].

This PR also removes assume(align != 0), with the new impl it does not improve anything anymore ([godbolt], [original concern]).

[rustbot]

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[rust-highfive]

r? @joshtriplett

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[workingjubilee]

Sanity checked these are numerically equivalent in the Playground:

use std::iter::successors;

fn main() {
    for addr in successors(Some(1u64), |x| x.checked_mul(2)) {
        let mut i = successors(Some(1u64), |x| x.checked_mul(2));
        while let Some(align) = i.next() && align <= addr {
            for addr in successors(Some(addr), |x| x.checked_add(addr)).take(256) {
                assert!(addr % align == addr & align - 1);
                assert!(addr & align -1 == 0);
            }
        }
    }
}

[workingjubilee]

@bors r+ rollup

[bors]

📌 Commit c195f7c has been approved by workingjubilee

It is now in the queue for this repository.

[lygstate]

self.cast::<u8>().addr() & (align - 1) == 0 are easier to understand