SROA is incompatible with RFC 3943 semantics #163388

#![feature(custom_mir, core_intrinsics)]
#![allow(internal_features)]
use std::intrinsics::mir::*;
use std::mem::MaybeUninit;
#[custom_mir(dialect = "runtime")]
pub fn main() {
    mir! {
        let _1: (usize, MaybeUninit<usize>);
        let _2: MaybeUninit<usize>;
        {
            _1.0 = 0;
            _2 = _1.1;
            Return()
        }
    }
}

// WARNING: This output format is intended for human consumers only
// and is subject to change without notice. Knock yourself out.
// HINT: See also -Z dump-mir for MIR at specific points during compilation.
fn main() -> () {
    let mut _0: ();
    let mut _1: (usize, std::mem::MaybeUninit<usize>);
    let mut _2: std::mem::MaybeUninit<usize>;
    let mut _3: usize;
    let mut _4: std::mem::MaybeUninit<usize>;

    bb0: {
        _3 = const 0_usize;
        _2 = copy _4;
        return;
    }
}