debug assertion: Post-projection layout should be non-Ref, but it's...

[saethlin]

#![feature(custom_mir, core_intrinsics)]

use std::intrinsics::mir::*;

#[custom_mir(dialect = "runtime", phase = "initial")]
fn main() {
    mir!{
        let _49: (Adt24,);
        let _63: *const Adt24;
        {
            (*_63) = _49.0;
            Return()
        }
    }
}

enum Adt24 {
    Variant1 {
        fld0: f64,
    },
    Variant2 {
        fld0: u64,
    },
}

Will hit a debug assertion:

thread 'rustc' (3695161) panicked at /home/ben/rust/compiler/rustc_codegen_ssa/src/mir/analyze.rs:159:13:
Post-projection (_1.0: Adt24) layout should be non-Ref, but it's TyAndLayout { ty: Adt24, layout: Layout { size: Size(16 bytes), align: AbiAlign { abi: Align(8 bytes) }, backend_repr: Memory { sized: true }, fields: Arbitrary { offsets: [Size(0 bytes)], memory_index: [0] }, largest_niche: Some(Niche { offset: Size(0 bytes), value: Int(I64, false), valid_range: 0..=1 }), uninhabited: false, variants: Multiple { tag: Initialized { value: Int(I64, false), valid_range: 0..=1 }, tag_encoding: Direct, tag_field: 0, variants: [Layout { size: Size(16 bytes), align: AbiAlign { abi: Align(8 bytes) }, backend_repr: Memory { sized: true }, fields: Arbitrary { offsets: [Size(8 bytes)], memory_index: [0] }, largest_niche: None, uninhabited: false, variants: Single { index: 0 }, max_repr_align: None, unadjusted_abi_align: Align(8 bytes), randomization_seed: 1530056383329300088 }, Layout { size: Size(16 bytes), align: AbiAlign { abi: Align(8 bytes) }, backend_repr: Memory { sized: true }, fields: Arbitrary { offsets: [Size(8 bytes)], memory_index: [0] }, largest_niche: None, uninhabited: false, variants: Single { index: 1 }, max_repr_align: None, unadjusted_abi_align: Align(8 bytes), randomization_seed: 1530056379034332792 }] }, max_repr_align: None, unadjusted_abi_align: Align(8 bytes), randomization_seed: 4590169132808031073 } }

#144347 added the assertion.

[saethlin]

cc @scottmcm

[saethlin]

The small reproducer in the issue description is reduced from a large rustlantis output which crashes the compiler with a stack overflow in LLVM. Re-reducing without debug assertions enabled yields this:
Compile with -Copt-level=3 -Ccodegen-units=1 -Zmir-opt-level=1 -Zmir-enable-passes=+ScalarReplacementOfAggregates

#![feature(custom_mir, core_intrinsics)]

extern crate core;

use core::intrinsics::mir::*;

#[custom_mir(dialect = "runtime", phase = "initial")]
#[inline(never)]
fn fn5(mut _1: Adt59) {
    mir!{
        let _8: isize;
        let _9: *const [char; 1];
        let _10: f32;
        let _11: f64;
        let _13: bool;
        let _14: (i64, [char; 1], char, f32);
        let _17: f32;
        let _19: (i64, [char; 1], char, f32);
        let _20: (Adt19,);
        let _21: *mut i128;
        let _27: i16;
        let _29: i128;
        {
            Goto(bb5)
        }
        bb5 = {
            place!(Field::<u64>(Variant(_1, 2), 0)) = 10414447555494633067_u64;
            _20.0 = Adt19::Variant0 {
                fld0: false,
                fld1: Field::<u64>(Variant(_1, 2), 0),
                fld2: 0,
                fld3: 0,
                fld4: -11866_i16,
                fld5: -1130655031_i32,
                fld6: _10,
            };
            Goto(bb6)
        }
        bb6 = {
            place!(Field::<i16>(Variant(_20.0, 0), 4)) = 19324_i16;
            _21 = core::ptr::addr_of_mut!(place!(Field::<i128>(Variant(_20.0, 0), 2)));
            Goto(bb7)
        }
        bb7 = {
            (*_9) = _14.1;
            Goto(bb8)
        }
        bb8 = {
            _27 = Field::<i16>(Variant(_20.0, 0), 4);
            _11 = 1715794145_u32 as f64;
            match Field::<u64>(Variant(_20.0, 0), 1) {
                6021699284742575674_u64 => bb9,
                10414447555494633067_u64 => bb11,
                _ => bb5,
            }
        }
        bb9 = {
            _14 = (2935980720417225015_i64, (*_9), 'a', _17);
            Goto(bb6)
        }
        bb11 = {
            _10 = Field::<f32>(Variant(_20.0, 0), 6);
            Goto(bb13)
        }
        bb13 = {
            _9 = core::ptr::addr_of!(_19.1);
            match _27 {
                (- 3985_i16) => bb8,
                19324_i16 => bb23,
                _ => bb7,
            }
        }
        bb23 = {
            _20.0 = Adt19::Variant3 {
                fld0: _10,
                fld1: _11,
                fld2: _8,
                fld3: 2625443366_u32,
                fld4: _27,
                fld5: 863987309_i32,
                fld6: Field::<u64>(Variant(_1, 2), 0),
                fld7: _29,
            };
            match Field::<u64>(Variant(_1, 2), 0) {
                10414447555494633067_u64 => bb33,
                _ => bb29,
            }
        }
        bb29 = {
            (*_21) = 81952901669863362890427228537909870717_i128 & (-61186293297549817448741491219523149034_i128);
            Goto(bb8)
        }
        bb33 = {
            _1 = Adt59::Variant0 { fld0: _20.0 };
            _21 = core::ptr::addr_of_mut!(_29);
            place!(Field::<i32>(Variant(place!(Field::<Adt19>(Variant(_1, 0), 0)), 3), 5)) = _29 as i32;
            _20 = (Field::<Adt19>(Variant(_1, 0), 0),);
            match Field::<u64>(Variant(_20.0, 3), 6) {
                7494031543471311720_u64 => bb7,
                4508285487499475801_u64 => bb29,
                _ => bb33,
            }
        }
    }
}

fn main() {
    fn5(Adt59::Variant2 { fld0: 0 });
}

enum Adt19 {
    Variant0 {
        fld0: bool,
        fld1: u64,
        fld2: i128,
        fld3: i8,
        fld4: i16,
        fld5: i32,
        fld6: f32,
    },
    Variant1 {},
    Variant2 {},
    Variant3 {
        fld0: f32,
        fld1: f64,
        fld2: isize,
        fld3: u32,
        fld4: i16,
        fld5: i32,
        fld6: u64,
        fld7: i128,
    },
}

enum Adt24 {}

enum Adt59 {
    Variant0 {
        fld0: Adt19,
    },
    Variant1 {},
    Variant2 {
        fld0: u64,
    },
}