Extend the enum check to pointer and union reads

[1c3t3a]

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This change extends the previously added enum discriminant check to enums read through a union or pointer. At the moment we only insert the check when transmuting to an enum. Although I hoped for it, this check isn't yet inserted for calls to MaybeUninit::assume_init, because the pass is running on polymorphic MIR and thus doesn't have the information yet to know whether the type that is read is an enum.

This is related to #143087.

r? @saethlin

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[saethlin]

CI doesn't pass, so I'm setting this to waiting on author. If that's wrong and you want help with getting CI to pass, give a shout.

[rustbot]

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @vakaras

This PR changes rustc_public

cc @oli-obk, @celinval, @ouz-a

[rustbot]

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rust-log-analyzer]

The job aarch64-gnu-llvm-20-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

REPOSITORY                                   TAG       IMAGE ID       CREATED       SIZE
ghcr.io/dependabot/dependabot-updater-core   latest    afc745c7535d   3 weeks ago   783MB
=> Removing docker images...
Deleted Images:
untagged: ghcr.io/dependabot/dependabot-updater-core:latest
untagged: ghcr.io/dependabot/dependabot-updater-core@sha256:faae3d3a1dedd24cde388bb506bbacc0f7ed1eae99ebac129af66acd8540c84a
deleted: sha256:afc745c7535da1bb12f92c273b9a7e9c52c3f12c5873714b2542da259c6d9769
deleted: sha256:64e147d5e54d9be8b8aa322e511cda02296eda4b8b8d063c6a314833aca50e29
deleted: sha256:5cba409bb463f4e7fa1a19f695450170422582c1bc7c0e934d893b4e5f558bc6
deleted: sha256:cddc6ebd344b0111eaab170ead1dfda24acdfe865ed8a12599a34d338fa8e28b
deleted: sha256:2412c3f334d79134573cd45e657fb6cc0abd75bef3881458b0d498d936545c8d
---
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_nounwind_fmt
   2: core::panicking::panic_misaligned_pointer_dereference
   3: <rustc_middle::mir::syntax::Rvalue>::ty::<rustc_middle::mir::Body>
   4: <rustc_borrowck::type_check::TypeChecker as rustc_middle::mir::visit::Visitor>::visit_statement
   5: <rustc_borrowck::type_check::TypeChecker as rustc_middle::mir::visit::Visitor>::visit_body
   6: rustc_borrowck::type_check::type_check
   7: rustc_borrowck::borrowck_collect_region_constraints
   8: <rustc_borrowck::root_cx::BorrowCheckRootCtxt>::do_mir_borrowck
   9: rustc_borrowck::mir_borrowck
      [... omitted 2 frames ...]
  10: rustc_mir_transform::mir_drops_elaborated_and_const_checked
      [... omitted 2 frames ...]
  11: rustc_mir_transform::mir_for_ctfe
      [... omitted 2 frames ...]
  12: rustc_mir_transform::optimized_mir
      [... omitted 2 frames ...]
  13: rustc_mir_transform::deduce_param_attrs::deduced_param_attrs
      [... omitted 2 frames ...]
  14: rustc_ty_utils::abi::fn_abi_new_uncached
  15: rustc_ty_utils::abi::fn_abi_of_instance
      [... omitted 2 frames ...]
  16: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeMachine> as rustc_middle::ty::layout::FnAbiOf>::fn_abi_of_instance
  17: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeMachine>>::eval_callee_and_args
  18: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeMachine>>::eval_terminator
  19: rustc_const_eval::const_eval::eval_queries::eval_static_initializer_provider
      [... omitted 2 frames ...]
  20: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}
  21: std::panicking::catch_unwind::<(), core::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures::sync::parallel::par_for_each_in<&rustc_span::def_id::LocalDefId, &[rustc_span::def_id::LocalDefId], <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}>::{closure#0}::{closure#1}::{closure#0}>>
  22: rustc_hir_analysis::check_crate
  23: rustc_interface::passes::analysis
      [... omitted 2 frames ...]
  24: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<<rustc_middle::ty::context::GlobalCtxt>::enter<rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}, core::option::Option<rustc_interface::queries::Linker>>::{closure#1}, core::option::Option<rustc_interface::queries::Linker>>::{closure#0}, core::option::Option<rustc_interface::queries::Linker>>
  25: <rustc_middle::ty::context::TyCtxt>::create_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}>
  26: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  27: std::panicking::catch_unwind::<(), core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}::{closure#0}>>
  28: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  29: rustc_span::create_session_globals_then::<(), rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}::{closure#0}>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
---
warning: the ICE couldn't be written to `/checkout/rustc-ice-2026-02-19T18_34_06-39467.txt`: Read-only file system (os error 30)

note: rustc 1.95.0-nightly (183457d66 2026-02-19) running on aarch64-unknown-linux-gnu

note: compiler flags: --crate-type bin -C opt-level=3 -C embed-bitcode=no -C debug-assertions=on -C symbol-mangling-version=v0 -Z annotate-moves -Z randomize-layout -Z unstable-options -Z macro-backtrace -C split-debuginfo=off -C link-arg=-L/usr/lib/llvm-20/lib -C llvm-args=-import-instr-limit=10 -C link-args=-Wl,-z,origin -C link-args=-Wl,-rpath,$ORIGIN/../lib -Z binary-dep-depinfo -Z force-unstable-if-unmarked

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

query stack during panic:
#0 [mir_borrowck] borrow-checking `prepare::<impl at compiler/rustc_codegen_cranelift/build_system/prepare.rs:69:1: 69:13>::github`
#1 [mir_drops_elaborated_and_const_checked] elaborating drops for `prepare::<impl at compiler/rustc_codegen_cranelift/build_system/prepare.rs:69:1: 69:13>::github`
#2 [mir_for_ctfe] caching mir of `prepare::<impl at compiler/rustc_codegen_cranelift/build_system/prepare.rs:69:1: 69:13>::github` for CTFE
#3 [optimized_mir] optimizing MIR for `prepare::<impl at compiler/rustc_codegen_cranelift/build_system/prepare.rs:69:1: 69:13>::github`
#4 [deduced_param_attrs] deducing parameter attributes for prepare::<impl at compiler/rustc_codegen_cranelift/build_system/prepare.rs:69:1: 69:13>::github
#5 [fn_abi_of_instance] computing call ABI of `prepare::<impl at compiler/rustc_codegen_cranelift/build_system/prepare.rs:69:1: 69:13>::github`
#6 [eval_static_initializer] evaluating initializer of static `abi_cafe::ABI_CAFE_REPO`
#7 [analysis] running analysis passes on crate `y`
end of query stack
thread caused non-unwinding panic. aborting.
[RUSTC-TIMING] y test:false 0.439
rustc exited with signal: 6 (SIGABRT) (core dumped)
error: could not compile `y` (bin "y")

Caused by:
  process didn't exit successfully: `/checkout/obj/build/bootstrap/debug/rustc /checkout/obj/build/bootstrap/debug/rustc --crate-name y --edition=2021 compiler/rustc_codegen_cranelift/build_system/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type bin --emit=dep-info,link -C opt-level=3 -C embed-bitcode=no -C debug-assertions=on --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("unstable-features"))' -C metadata=7254b91c94d9ae57 -C extra-filename=-fe9a244d40edbf17 --out-dir /checkout/obj/build/aarch64-unknown-linux-gnu/stage3-codegen/aarch64-unknown-linux-gnu/release/deps --target aarch64-unknown-linux-gnu -L dependency=/checkout/obj/build/aarch64-unknown-linux-gnu/stage3-codegen/aarch64-unknown-linux-gnu/release/deps -L dependency=/checkout/obj/build/aarch64-unknown-linux-gnu/stage3-codegen/release/deps -Csymbol-mangling-version=v0 -Zannotate-moves -Zrandomize-layout -Zunstable-options '--check-cfg=cfg(bootstrap)' -Zmacro-backtrace -Csplit-debuginfo=off -Clink-arg=-L/usr/lib/llvm-20/lib -Cllvm-args=-import-instr-limit=10 -Clink-args=-Wl,-z,origin '-Clink-args=-Wl,-rpath,$ORIGIN/../lib' -Z binary-dep-depinfo` (exit status: 254)
Command `/checkout/obj/build/aarch64-unknown-linux-gnu/stage0/bin/cargo run -Zwarnings --target aarch64-unknown-linux-gnu -Zbinary-dep-depinfo -j 4 -Zroot-dir=/checkout --locked --color=always --profile=release --manifest-path /checkout/compiler/rustc_codegen_cranelift/build_system/Cargo.toml -- test --download-dir /checkout/obj/build/cg_clif_download --out-dir /checkout/obj/build/aarch64-unknown-linux-gnu/stage2-codegen/cg_clif --no-unstable-features --use-backend cranelift --sysroot llvm --skip-test testsuite.extended_sysroot [workdir=/checkout/compiler/rustc_codegen_cranelift]` failed with exit code 101
Created at: src/bootstrap/src/core/build_steps/test.rs:3877:25
Executed at: src/bootstrap/src/core/build_steps/test.rs:3922:26

Command has failed. Rerun with -v to see more details.
Bootstrap failed while executing `--stage 2 test --skip tests --skip coverage-map --skip coverage-run --skip library --skip tidyselftest`
Build completed unsuccessfully in 0:24:45
  local time: Thu Feb 19 18:34:06 UTC 2026
  network time: Thu, 19 Feb 2026 18:34:07 GMT
##[error]Process completed with exit code 1.

[rust-bors]

☔ The latest upstream changes (presumably #153741) made this pull request unmergeable. Please resolve the merge conflicts.