Broken MIR ICE with let chains

[est31]

Originally reported by @flip1995 in #99938 (comment) .

Code

#![feature(let_chains)]

struct F(Box<()>);

impl F {
    fn s(&self) -> Option<&str> {
        None
    }
}

fn cex() -> Option<F> {
    None
}

pub fn main() {
    if false
        && let Some(ce) = cex()
        && let Some(_ce) = ce.s()
    {
    }
}

Error output

error: internal compiler error: no errors encountered even though `delay_span_bug` issued

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:9 ~ a[8fb6]::main), const_param_did: None }) (after phase change to runtime-optimized) at bb3[0]:
                                use of local _1, which has no storage here
  --> /tmp/a.rs:21:1
   |
21 | }
   | ^
   |
   = note: delayed at compiler/rustc_const_eval/src/transform/validate.rs:88:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:9 ~ a[8fb6]::main), const_param_did: None }) (after phase change to runtime-optimized) at bb4[0]:
                                use of local _1, which has no storage here
  --> /tmp/a.rs:21:1
   |
21 | }
   | ^
   |
   = note: delayed at compiler/rustc_const_eval/src/transform/validate.rs:88:36

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1594:13

Backtrace

   0:     0x7f4776d010da - std::backtrace_rs::backtrace::libunwind::trace::h06e8f32b98d440be
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f4776d010da - std::backtrace_rs::backtrace::trace_unsynchronized::h8a56795adafc3159
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f4776d010da - std::sys_common::backtrace::_print_fmt::h7ba19acb3601abb5
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f4776d010da - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::ha37df576307c1a49
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f4772c6fbae - core::fmt::write::hd3f2e7e755b45b01
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/core/src/fmt/mod.rs:1208:17
   5:     0x7f4776cf53a5 - std::io::Write::write_fmt::hc1388e059aac0a41
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/io/mod.rs:1682:15
   6:     0x7f4776d00ea5 - std::sys_common::backtrace::_print::h429db1082d921ab8
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f4776d00ea5 - std::sys_common::backtrace::print::h8d611e0005d3ccb9
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f4776d0320f - std::panicking::default_hook::{{closure}}::h07380c607f829a79
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/panicking.rs:267:22
   9:     0x7f4776d02f4b - std::panicking::default_hook::h78998b3f3926502a
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/panicking.rs:286:9
  10:     0x7f4775f5b284 - <rustc_driver[153e38e44d5410f9]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[1d8afb50f4e7a45]::ops::function::FnOnce<(&core[1d8afb50f4e7a45]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f4776d03a0d - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hbe7c77b7cbfe1f21
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/alloc/src/boxed.rs:2032:9
  12:     0x7f4776d03a0d - std::panicking::rust_panic_with_hook::hda16cab0ff009a11
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/panicking.rs:692:13
  13:     0x7f4775f93ab1 - std[2b5db76a972e300f]::panicking::begin_panic::<rustc_errors[6e875e03adfb8e66]::ExplicitBug>::{closure#0}
  14:     0x7f4775f923e6 - std[2b5db76a972e300f]::sys_common::backtrace::__rust_end_short_backtrace::<std[2b5db76a972e300f]::panicking::begin_panic<rustc_errors[6e875e03adfb8e66]::ExplicitBug>::{closure#0}, !>
  15:     0x7f4775f8ab76 - std[2b5db76a972e300f]::panicking::begin_panic::<rustc_errors[6e875e03adfb8e66]::ExplicitBug>
  16:     0x7f4775f8e306 - std[2b5db76a972e300f]::panic::panic_any::<rustc_errors[6e875e03adfb8e66]::ExplicitBug>
  17:     0x7f4775465556 - <rustc_errors[6e875e03adfb8e66]::HandlerInner>::flush_delayed::<alloc[eb468f42ab80a7c0]::vec::Vec<rustc_errors[6e875e03adfb8e66]::diagnostic::Diagnostic>, &str>
  18:     0x7f477546485b - <rustc_errors[6e875e03adfb8e66]::HandlerInner as core[1d8afb50f4e7a45]::ops::drop::Drop>::drop
  19:     0x7f477521271e - core[1d8afb50f4e7a45]::ptr::drop_in_place::<rustc_session[729ed7505232e216]::parse::ParseSess>
  20:     0x7f47751cb42f - core[1d8afb50f4e7a45]::ptr::drop_in_place::<rustc_session[729ed7505232e216]::session::Session>
  21:     0x7f47751cb160 - core[1d8afb50f4e7a45]::ptr::drop_in_place::<rustc_interface[d2ac3f3b3bfa4614]::interface::Compiler>
  22:     0x7f47751ca26e - rustc_span[cdf434c68ce75247]::with_source_map::<core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>, rustc_interface[d2ac3f3b3bfa4614]::interface::run_compiler<core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>, rustc_driver[153e38e44d5410f9]::run_compiler::{closure#1}>::{closure#0}::{closure#1}>
  23:     0x7f47751c9ba5 - <scoped_tls[2ec6d95ce5fd8213]::ScopedKey<rustc_span[cdf434c68ce75247]::SessionGlobals>>::set::<rustc_interface[d2ac3f3b3bfa4614]::interface::run_compiler<core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>, rustc_driver[153e38e44d5410f9]::run_compiler::{closure#1}>::{closure#0}, core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>>
  24:     0x7f47751c9192 - std[2b5db76a972e300f]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[d2ac3f3b3bfa4614]::util::run_in_thread_pool_with_globals<rustc_interface[d2ac3f3b3bfa4614]::interface::run_compiler<core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>, rustc_driver[153e38e44d5410f9]::run_compiler::{closure#1}>::{closure#0}, core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>>
  25:     0x7f47751c8ea8 - <<std[2b5db76a972e300f]::thread::Builder>::spawn_unchecked_<rustc_interface[d2ac3f3b3bfa4614]::util::run_in_thread_pool_with_globals<rustc_interface[d2ac3f3b3bfa4614]::interface::run_compiler<core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>, rustc_driver[153e38e44d5410f9]::run_compiler::{closure#1}>::{closure#0}, core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[1d8afb50f4e7a45]::result::Result<(), rustc_errors[6e875e03adfb8e66]::ErrorGuaranteed>>::{closure#1} as core[1d8afb50f4e7a45]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  26:     0x7f4776d0ac43 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h0c8cfd64ff347c2f
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/alloc/src/boxed.rs:2000:9
  27:     0x7f4776d0ac43 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h5243ef33e0bc55ac
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/alloc/src/boxed.rs:2000:9
  28:     0x7f4776d0ac43 - std::sys::unix::thread::Thread::new::thread_start::h248bc665ee6b9bda
                               at /rustc/70f8737b2f5d3bf7d6b784fad00b663b7ff9feda/library/std/src/sys/unix/thread.rs:108:17
  29:     0x7f4772985ff2 - start_thread
  30:     0x7f4772a08bfc - clone3
  31:                0x0 - <unknown>

The ICE requires -O to be passed to rustc, or --release be passed to cargo, the param to validate MIR is not enough. It's also a regression, on nightly-2022-07-30 it does not reproduce.

cc #99938 and #99852 related issues with similar error messages, but they are fixed and this is reproducible.

@rustbot label E-needs-bisection

[est31]

@rustbot label F-let_chains

[lukas-code]

searched nightlies: from nightly-2022-07-20 to nightly-2022-11-23
regressed nightly: nightly-2022-10-20
searched commit range: a24a020...4b8f431
regressed commit: d7dd01f

bisected with cargo-bisect-rustc v0.6.4

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --end=2022-11-23 --regress=ice -- rustc -- -Zvalidate-mir -O 

[Noratrieb]

Looks like #103034 didn't fix everything after all..... @nathanwhit
this feature just keeps on giving

[est31]

@rustbot label -E-needs-bisection

[flip1995]

Thanks for opening an issue for this! I put that on my todo list, but my todo list is just way to long...