[ICE]: broken MIR after phase change to runtime-optimized: invalid source scope

Code

   Compiling uuid v1.23.1
error: internal compiler error: broken MIR in Item(DefId(0:646 ~ uuid[e135]::{impl#0}::to_bytes_le)) (after phase change to runtime-optimized):
                                invalid source scope scope[131072]
   --> /home/ariel/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/uuid-1.23.1/src/lib.rs:849:5
    |
849 | /     pub const fn to_bytes_le(&self) -> Bytes {
850 | |         [
851 | |             self.0[3], self.0[2], self.0[1], self.0[0], self.0[5], self.0[4], self.0[7], self.0[6],
852 | |             self.0[8], self.0[9], self.0[10], self.0[11], self.0[12], self.0[13], self.0[14],
...   |
855 | |     }
    | |_____^


thread 'rustc' (539740) panicked at /rustc-dev/59807616e1fa2540724bfbac14d7976d7e4a3860/compiler/rustc_mir_transform/src/validate.rs:532:28:
Box<dyn Any>
stack backtrace:
   0:     0x76e248d9314b - <<std[e28293b1aa0f68bd]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[c1f1a4ba060b9bfa]::fmt::Display>::fmt
   1:     0x76e24941f408 - core[c1f1a4ba060b9bfa]::fmt::write
   2:     0x76e24a9683b6 - <std[e28293b1aa0f68bd]::sys::stdio::unix::Stderr as std[e28293b1aa0f68bd]::io::Write>::write_fmt
   3:     0x76e248d69238 - std[e28293b1aa0f68bd]::panicking::default_hook::{closure#0}
   4:     0x76e248d865b3 - std[e28293b1aa0f68bd]::panicking::default_hook
   5:     0x76e247d5cc30 - std[e28293b1aa0f68bd]::panicking::update_hook::<alloc[fdfd2bd8633a6659]::boxed::Box<rustc_driver_impl[e4ca9dd5dd6cf2a8]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x76e248d86892 - std[e28293b1aa0f68bd]::panicking::panic_with_hook
   7:     0x76e247d8d8b1 - std[e28293b1aa0f68bd]::panicking::begin_panic::<rustc_errors[795cd5cf46ddce51]::ExplicitBug>::{closure#0}
   8:     0x76e247d865c6 - std[e28293b1aa0f68bd]::sys::backtrace::__rust_end_short_backtrace::<std[e28293b1aa0f68bd]::panicking::begin_panic<rustc_errors[795cd5cf46ddce51]::ExplicitBug>::{closure#0}, !>
   9:     0x76e247d8643b - std[e28293b1aa0f68bd]::panicking::begin_panic::<rustc_errors[795cd5cf46ddce51]::ExplicitBug>
  10:     0x76e247d985a1 - <rustc_errors[795cd5cf46ddce51]::diagnostic::BugAbort as rustc_errors[795cd5cf46ddce51]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x76e2484d478c - <rustc_errors[795cd5cf46ddce51]::DiagCtxtHandle>::span_bug::<rustc_span[e3c9a1967c4921fd]::span_encoding::Span, alloc[fdfd2bd8633a6659]::string::String>
  12:     0x76e249feb4cb - <rustc_mir_transform[2be6bdc629d1da0e]::validate::Validator as rustc_mir_transform[2be6bdc629d1da0e]::pass_manager::MirPass>::run_pass
  13:     0x76e249409afa - rustc_mir_transform[2be6bdc629d1da0e]::run_optimization_passes
  14:     0x76e249b8edcf - rustc_mir_transform[2be6bdc629d1da0e]::optimized_mir
  15:     0x76e249b8ea1d - rustc_query_impl[b21371cac9e22a84]::query_impl::optimized_mir::invoke_provider_fn::__rust_begin_short_backtrace
  16:     0x76e249413368 - rustc_query_impl[b21371cac9e22a84]::execution::try_execute_query::<rustc_middle[9956b31dc9b62104]::query::caches::DefIdCache<rustc_middle[9956b31dc9b62104]::query::erase::ErasedData<[u8; 8usize]>>, false>
  17:     0x76e249412a4e - rustc_query_impl[b21371cac9e22a84]::query_impl::optimized_mir::execute_query_non_incr::__rust_end_short_backtrace
  18:     0x76e249cba98b - rustc_mir_transform[2be6bdc629d1da0e]::cross_crate_inline::cross_crate_inlinable
  19:     0x76e249976378 - rustc_query_impl[b21371cac9e22a84]::query_impl::cross_crate_inlinable::invoke_provider_fn::__rust_begin_short_backtrace
  20:     0x76e24997548e - rustc_query_impl[b21371cac9e22a84]::execution::try_execute_query::<rustc_middle[9956b31dc9b62104]::query::caches::DefIdCache<rustc_middle[9956b31dc9b62104]::query::erase::ErasedData<[u8; 1usize]>>, false>
  21:     0x76e249975058 - rustc_query_impl[b21371cac9e22a84]::query_impl::cross_crate_inlinable::execute_query_non_incr::__rust_end_short_backtrace
  22:     0x76e249a2374f - rustc_passes[6bf4acf08ac4e6d9]::reachable::reachable_set
  23:     0x76e24a642a9c - rustc_query_impl[b21371cac9e22a84]::query_impl::reachable_set::invoke_provider_fn::__rust_begin_short_backtrace
  24:     0x76e24a641f6e - rustc_query_impl[b21371cac9e22a84]::execution::try_execute_query::<rustc_middle[9956b31dc9b62104]::query::caches::SingleCache<rustc_middle[9956b31dc9b62104]::query::erase::ErasedData<[u8; 8usize]>>, false>
  25:     0x76e24a6429b9 - rustc_query_impl[b21371cac9e22a84]::query_impl::reachable_set::execute_query_non_incr::__rust_end_short_backtrace
  26:     0x76e249e6c9ed - <rustc_metadata[420ade231d97cbc6]::rmeta::encoder::EncodeContext>::encode_crate_root
  27:     0x76e24a8b0452 - <rustc_metadata[420ade231d97cbc6]::rmeta::encoder::encode_metadata::{closure#3} as core[c1f1a4ba060b9bfa]::ops::function::FnOnce<(rustc_middle[9956b31dc9b62104]::ty::context::TyCtxt, &std[e28293b1aa0f68bd]::path::Path)>>::call_once
  28:     0x76e24a8adb54 - rustc_metadata[420ade231d97cbc6]::rmeta::encoder::encode_metadata
  29:     0x76e24a3b87d9 - rustc_metadata[420ade231d97cbc6]::fs::encode_and_write_metadata
  30:     0x76e24a65b1eb - <rustc_interface[c8170c4b7b680ee8]::queries::Linker>::codegen_and_build_linker
  31:     0x76e24a6563e6 - rustc_interface[c8170c4b7b680ee8]::interface::run_compiler::<(), rustc_driver_impl[e4ca9dd5dd6cf2a8]::run_compiler::{closure#0}>::{closure#1}
  32:     0x76e24a62663e - std[e28293b1aa0f68bd]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[c8170c4b7b680ee8]::util::run_in_thread_with_globals<rustc_interface[c8170c4b7b680ee8]::util::run_in_thread_pool_with_globals<rustc_interface[c8170c4b7b680ee8]::interface::run_compiler<(), rustc_driver_impl[e4ca9dd5dd6cf2a8]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  33:     0x76e24a626ca0 - <std[e28293b1aa0f68bd]::thread::lifecycle::spawn_unchecked<rustc_interface[c8170c4b7b680ee8]::util::run_in_thread_with_globals<rustc_interface[c8170c4b7b680ee8]::util::run_in_thread_pool_with_globals<rustc_interface[c8170c4b7b680ee8]::interface::run_compiler<(), rustc_driver_impl[e4ca9dd5dd6cf2a8]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[c1f1a4ba060b9bfa]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  34:     0x76e24a627b2c - <std[e28293b1aa0f68bd]::sys::thread::unix::Thread>::new::thread_start
   Compiling rmp-serde v1.3.1
  35:     0x76e243e9caa4 - start_thread
                               at ./nptl/pthread_create.c:447:8
  36:     0x76e243f29c6c - clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78:0
  37:                0x0 - <unknown>

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 1.95.0 (59807616e 2026-04-14) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -C opt-level=3 -C panic=abort -C linker-plugin-lto -C codegen-units=1 -C strip=symbols

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [optimized_mir] optimizing MIR for `<impl at /home/ariel/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/uuid-1.23.1/src/lib.rs:467:1: 467:10>::to_bytes_le`
#1 [cross_crate_inlinable] whether the item should be made inlinable across crates
... and 1 other queries... use `env RUST_BACKTRACE=1` to see the full query stack
error: could not compile `uuid` (lib)

Caused by:
  process didn't exit successfully: `/home/ariel/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustc --crate-name uuid --edition=2021 /home/ariel/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/uuid-1.23.1/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=156 --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C panic=abort -C linker-plugin-lto -C codegen-units=1 --allow=unexpected_cfgs --check-cfg 'cfg(uuid_unstable)' --cfg 'feature="default"' --cfg 'feature="rng"' --cfg 'feature="serde"' --cfg 'feature="std"' --cfg 'feature="v7"' --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("arbitrary", "atomic", "borsh", "bytemuck", "default", "fast-rng", "js", "macro-diagnostics", "md5", "rng", "rng-getrandom", "rng-rand", "serde", "sha1", "slog", "std", "uuid-rng-internal-lib", "v1", "v3", "v4", "v5", "v6", "v7", "v8", "zerocopy"))' -C metadata=4677166967f1f8e5 -C extra-filename=-f6b35daa25e5ea2d --out-dir /home/ariel/remshell/target/x86_64-unknown-linux-musl/release/deps --target x86_64-unknown-linux-musl -C strip=symbols -L dependency=/home/ariel/remshell/target/x86_64-unknown-linux-musl/release/deps -L dependency=/home/ariel/remshell/target/release/deps --extern getrandom=/home/ariel/remshell/target/x86_64-unknown-linux-musl/release/deps/libge

Reproduce the ICE while compiling uuid-1.23.1 with the shown optimization and linker-plugin-LTO flags. Start in compiler/rustc_mir_transform/src/validate.rs at the reported validator panic and compare it with the MIR generated for uuid/src/lib.rs:849-855. Done means the compiler no longer reports broken MIR or panics for this build.