Warning fixes and 6.13 backport

[bonzini]

The 6.13 changes focused on fixing and enabling warnings, so do the same and make the standalone pinned-init warning-free. Similar changes are in #20.

[y86-dev]

Thanks a lot for the PR! I have one small comment/question, the rest looks good!

[y86-dev]

Is there a reason you changed the .cast to the indexing?
I checked with miri to see that this is allowed, but in my mind, this goes through the IndexMut trait, which would result in a dereference of the pointer... I am a bit confused, maybe that is wrong?

[bonzini]

I will check the MIR that's produced—I don't have the code at hand so I am not sure what is an intrinsic and what isn't. Certainly I can change it back.

[y86-dev]

I see, I tried this sample code

use std::ptr::addr_of_mut;

struct Buf {
    buf: [u8; 64],
}

fn foo(ptr: *mut Buf) -> *mut u8 {
    unsafe { addr_of_mut!((*ptr).buf).cast::<u8>() }
}

fn bar(ptr: *mut Buf) -> *mut u8 {
    unsafe { addr_of_mut!((*ptr).buf[0]) }
}

Unoptimized MIR:

fn foo(_1: *mut Buf) -> *mut u8 {
    debug ptr => _1;
    let mut _0: *mut u8;
    let mut _2: *mut [u8; 64];

    bb0: {
        _2 = &raw mut ((*_1).0: [u8; 64]);
        _0 = std::ptr::mut_ptr::<impl *mut [u8; 64]>::cast::<u8>(move _2) -> [return: bb1, unwind continue];
    }

    bb1: {
        return;
    }
}

fn bar(_1: *mut Buf) -> *mut u8 {
    debug ptr => _1;
    let mut _0: *mut u8;
    let _2: usize;
    let mut _3: usize;
    let mut _4: bool;

    bb0: {
        _2 = const 0_usize;
        _3 = const 64_usize;
        _4 = Lt(copy _2, copy _3);
        assert(move _4, "index out of bounds: the length is {} but the index is {}", move _3, copy _2) -> [success: bb1, unwind continue];
    }

    bb1: {
        _0 = &raw mut ((*_1).0: [u8; 64])[_2];
        return;
    }
}

Optimized MIR:

fn foo(_1: *mut Buf) -> *mut u8 {
    debug ptr => _1;
    let mut _0: *mut u8;
    let mut _2: *mut [u8; 64];

    bb0: {
        StorageLive(_2);
        _2 = &raw mut ((*_1).0: [u8; 64]);
        _0 = std::ptr::mut_ptr::<impl *mut [u8; 64]>::cast::<u8>(move _2) -> [return: bb1, unwind continue];
    }

    bb1: {
        StorageDead(_2);
        return;
    }
}

fn bar(_1: *mut Buf) -> *mut u8 {
    debug ptr => _1;
    let mut _0: *mut u8;

    bb0: {
        _0 = &raw mut ((*_1).0: [u8; 64])[0 of 1];
        return;
    }
}

I don't know if this makes a difference though...