ReferencePropagation MIR opt prevents partial initialisation in MIR

[cbeuw]

ReferencePropagation panics when a local of a composite type is initialised field-by-field (when the first assignment to this local is through a projection)

#![feature(custom_mir, core_intrinsics)]
extern crate core;
use core::intrinsics::mir::*;

#[custom_mir(dialect = "runtime", phase = "initial")]
pub fn fn0() {
    mir! (
        let x: (isize, );
        {
        x.0 = 1;
        Return()
        }
    )
}
pub fn main() {
    fn0();
}

% rustc +master -Zmir-opt-level=0 -Zmir-enable-passes=+ReferencePropagation repro.rs
thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `None`,
 right: `Some(_2)`', compiler/rustc_mir_transform/src/ssa.rs:276:9
stack backtrace:
   0:        0x104ad5abc - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h55f7d97045313ad5
   1:        0x104b25570 - core::fmt::write::h106bf26cb364358d
   2:        0x104acbcc8 - std::io::Write::write_fmt::hde7b4c7920e77eda
   3:        0x104ad5910 - std::sys_common::backtrace::print::h95b67084a837f60c
   4:        0x104ad8314 - std::panicking::default_hook::{{closure}}::hf4eb388f1c340bec
   5:        0x104ad811c - std::panicking::default_hook::h3e20c7e694225675
   6:        0x10cf358e4 - rustc_driver_impl[57ad0c21a6a9d990]::install_ice_hook::{closure#0}
   7:        0x104ad8928 - std::panicking::rust_panic_with_hook::h4a5e4d9762ea7797
   8:        0x104ad8724 - std::panicking::begin_panic_handler::{{closure}}::h1b5a6942462f6646
   9:        0x104ad5eb4 - std::sys_common::backtrace::__rust_end_short_backtrace::h0bb3d97a073dbb67
  10:        0x104ad84b0 - _rust_begin_unwind
  11:        0x104b502fc - core::panicking::panic_fmt::h1b9b804fde1edf71
  12:        0x104b50660 - core::panicking::assert_failed_inner::hf8ed417130b26580
  13:        0x1111d9084 - core[fa76fbc839568f1d]::panicking::assert_failed::<core[fa76fbc839568f1d]::option::Option<rustc_middle[28ddddcee064ee09]::mir::Local>, core[fa76fbc839568f1d]::option::Option<rustc_middle[28ddddcee064ee09]::mir::Local>>
  14:        0x10f6760b4 - <rustc_mir_transform[94137a30ce227c72]::ssa::SsaLocals>::new
  15:        0x10f7943c0 - <rustc_mir_transform[94137a30ce227c72]::ref_prop::ReferencePropagation as rustc_middle[28ddddcee064ee09]::mir::MirPass>::run_pass
  16:        0x10f731854 - rustc_mir_transform[94137a30ce227c72]::pass_manager::run_passes_inner
  17:        0x10f664490 - rustc_mir_transform[94137a30ce227c72]::optimized_mir
  18:        0x11007cca0 - rustc_query_system[c91188e96fcab682]::query::plumbing::try_execute_query::<rustc_query_impl[b54e71c67810b295]::queries::optimized_mir, rustc_query_impl[b54e71c67810b295]::plumbing::QueryCtxt>
  19:        0x1101e57d8 - rustc_query_impl[b54e71c67810b295]::get_query::optimized_mir
  20:        0x110cc34a8 - rustc_middle[28ddddcee064ee09]::ty::query::query_get_at::<rustc_query_system[c91188e96fcab682]::query::caches::DefaultCache<rustc_span[c6e86278ee0bafba]::def_id::DefId, rustc_middle[28ddddcee064ee09]::query::erase::Erased<[u8; 8usize]>>>
  21:        0x110cd6964 - <rustc_middle[28ddddcee064ee09]::ty::context::TyCtxt>::instance_mir
  22:        0x10f601db8 - rustc_monomorphize[2a7d102951d99f0f]::collector::collect_neighbours
  23:        0x10f600d70 - rustc_monomorphize[2a7d102951d99f0f]::collector::collect_items_rec
  24:        0x10f601074 - rustc_monomorphize[2a7d102951d99f0f]::collector::collect_items_rec
  25:        0x10f6217b8 - <core[fa76fbc839568f1d]::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures[11d1296fd85ed732]::sync::par_for_each_in<alloc[699e0727aa91b95d]::vec::Vec<rustc_middle[28ddddcee064ee09]::mir::mono::MonoItem>, rustc_monomorphize[2a7d102951d99f0f]::collector::collect_crate_mono_items::{closure#1}::{closure#0}>::{closure#0}::{closure#0}> as core[fa76fbc839568f1d]::ops::function::FnOnce<()>>::call_once
  26:        0x10f613ec4 - rustc_data_structures[11d1296fd85ed732]::sync::par_for_each_in::<alloc[699e0727aa91b95d]::vec::Vec<rustc_middle[28ddddcee064ee09]::mir::mono::MonoItem>, rustc_monomorphize[2a7d102951d99f0f]::collector::collect_crate_mono_items::{closure#1}::{closure#0}>
  27:        0x10f61c9c8 - <rustc_session[5a840e94703f904]::session::Session>::time::<(), rustc_monomorphize[2a7d102951d99f0f]::collector::collect_crate_mono_items::{closure#1}>
  28:        0x10f5ff484 - rustc_monomorphize[2a7d102951d99f0f]::collector::collect_crate_mono_items
  29:        0x10f6116ac - rustc_monomorphize[2a7d102951d99f0f]::partitioning::collect_and_partition_mono_items
  30:        0x1101480d4 - rustc_query_system[c91188e96fcab682]::query::plumbing::try_execute_query::<rustc_query_impl[b54e71c67810b295]::queries::collect_and_partition_mono_items, rustc_query_impl[b54e71c67810b295]::plumbing::QueryCtxt>
  31:        0x1101f99c0 - rustc_query_impl[b54e71c67810b295]::get_query::collect_and_partition_mono_items
  32:        0x10cff2428 - rustc_codegen_ssa[f92b5776b52308c8]::base::codegen_crate::<rustc_codegen_llvm[13255e5f9e066824]::LlvmCodegenBackend>
  33:        0x10d044814 - <rustc_codegen_llvm[13255e5f9e066824]::LlvmCodegenBackend as rustc_codegen_ssa[f92b5776b52308c8]::traits::backend::CodegenBackend>::codegen_crate
  34:        0x10cfe5554 - rustc_interface[a675cf37ce06623c]::passes::start_codegen
  35:        0x10cf5dcd8 - <rustc_middle[28ddddcee064ee09]::ty::context::GlobalCtxt>::enter::<<rustc_interface[a675cf37ce06623c]::queries::Queries>::ongoing_codegen::{closure#0}::{closure#0}, core[fa76fbc839568f1d]::result::Result<alloc[699e0727aa91b95d]::boxed::Box<dyn core[fa76fbc839568f1d]::any::Any>, rustc_span[c6e86278ee0bafba]::ErrorGuaranteed>>
  36:        0x10cfe8b90 - <rustc_interface[a675cf37ce06623c]::queries::Queries>::ongoing_codegen
  37:        0x10cf11a2c - <rustc_interface[a675cf37ce06623c]::interface::Compiler>::enter::<rustc_driver_impl[57ad0c21a6a9d990]::run_compiler::{closure#1}::{closure#2}, core[fa76fbc839568f1d]::result::Result<core[fa76fbc839568f1d]::option::Option<rustc_interface[a675cf37ce06623c]::queries::Linker>, rustc_span[c6e86278ee0bafba]::ErrorGuaranteed>>
  38:        0x10ced9dac - std[8c9422f4eb635902]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[a675cf37ce06623c]::util::run_in_thread_pool_with_globals<rustc_interface[a675cf37ce06623c]::interface::run_compiler<core[fa76fbc839568f1d]::result::Result<(), rustc_span[c6e86278ee0bafba]::ErrorGuaranteed>, rustc_driver_impl[57ad0c21a6a9d990]::run_compiler::{closure#1}>::{closure#0}, core[fa76fbc839568f1d]::result::Result<(), rustc_span[c6e86278ee0bafba]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[fa76fbc839568f1d]::result::Result<(), rustc_span[c6e86278ee0bafba]::ErrorGuaranteed>>
  39:        0x10cedbbe4 - <<std[8c9422f4eb635902]::thread::Builder>::spawn_unchecked_<rustc_interface[a675cf37ce06623c]::util::run_in_thread_pool_with_globals<rustc_interface[a675cf37ce06623c]::interface::run_compiler<core[fa76fbc839568f1d]::result::Result<(), rustc_span[c6e86278ee0bafba]::ErrorGuaranteed>, rustc_driver_impl[57ad0c21a6a9d990]::run_compiler::{closure#1}>::{closure#0}, core[fa76fbc839568f1d]::result::Result<(), rustc_span[c6e86278ee0bafba]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[fa76fbc839568f1d]::result::Result<(), rustc_span[c6e86278ee0bafba]::ErrorGuaranteed>>::{closure#1} as core[fa76fbc839568f1d]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  40:        0x104ae1290 - std::sys::unix::thread::Thread::new::thread_start::he87bdd6811d19cfc
  41:        0x1a89f7fa8 - __pthread_joiner_wake

error: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.71.0-nightly (25444e5a2 2023-05-10) running on aarch64-apple-darwin

note: compiler flags: -Z mir-opt-level=0 -Z mir-enable-passes=+ReferencePropagation

query stack during panic:
#0 [optimized_mir] optimizing MIR for `fn0`
#1 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack

This can only reproduced with Custom MIR as I do not find any way to make MIR building emit partial initialisations. Nonetheless I don't think it should break in this case.

cc @cjgillot

[saethlin]

FYI I think that this pattern is what we used to emit before #107267