const-eval: always do full typed copies #149901

RalfJung · 2025-12-12T07:38:58Z

Perf experiment exploring alternatives to #148967.

This is the maximally naive version that just always does full typed copies. It may be possible to skip some of the validation work if all we care about is resetting padding -- though it's not obvious to me how to do that in a way that actually helps with performance. Also, typed copies at integer type technically do not preserve provenance, which could become relevant in const-eval for the same reason as provenance in padding (see #148470) -- so it's not like we can just skip all types without padding.

RalfJung · 2025-12-12T07:45:32Z

@bors try
@rust-timer queue

rust-timer · 2025-12-12T07:45:35Z

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

const-eval: always do full typed copies

rust-log-analyzer · 2025-12-12T08:10:55Z

The job x86_64-gnu-gcc failed! Check out the build log: (web) (plain enhanced) (plain)

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


---- [mir-opt] tests/mir-opt/pattern_types.rs stdout ----
------rustc stdout------------------------------

------rustc stderr------------------------------
warning: unused variable: `x`
##[warning] --> /checkout/tests/mir-opt/pattern_types.rs:9:9
  |
9 |     let x: pattern_type!(u32 is 1..) = unsafe { std::mem::transmute(2) };
  |         ^ help: if this is intentional, prefix it with an underscore: `_x`
  |
  = note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default

warning: unused variable: `y`
##[warning]  --> /checkout/tests/mir-opt/pattern_types.rs:11:9
   |
11 |     let y: pattern_type!(u32 is 1..) = unsafe { std::mem::transmute(0) };
   |         ^ help: if this is intentional, prefix it with an underscore: `_y`

warning: function `main` is never used
##[warning] --> /checkout/tests/mir-opt/pattern_types.rs:7:4
  |
7 | fn main() {
  |    ^^^^
  |
  = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default


thread 'rustc' (30735) panicked at compiler/rustc_const_eval/src/util/check_validity_requirement.rs:192:41:
called `Result::unwrap()` on an `Err` value: InterpErrorInfo(InterpErrorInfoInner { kind: UndefinedBehavior(ValidationError(ValidationErrorInfo { path: None, kind: OutOfRange { value: "0", range: 1..=4294967295, max_value: 4294967295 } })), backtrace: InterpErrorBacktrace { backtrace: None } })
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::result::unwrap_failed
   3: rustc_const_eval::util::check_validity_requirement::validate_scalar_in_layout
   4: <rustc_const_eval::provide::{closure#3} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_middle::ty::consts::int::ScalarInt, rustc_middle::ty::Ty)>>::call_once
   5: <rustc_middle::ty::print::pretty::FmtPrinter as rustc_middle::ty::print::pretty::PrettyPrinter>::pretty_print_const_scalar_int
   6: <rustc_middle::ty::print::pretty::FmtPrinter as rustc_middle::ty::print::pretty::PrettyPrinter>::pretty_print_const_scalar
   7: rustc_middle::mir::pretty::pretty_print_const_value_tcx
   8: <rustc_middle::mir::consts::Const as core::fmt::Display>::fmt
   9: core::fmt::write
  10: <rustc_middle::mir::VarDebugInfoContents as core::fmt::Debug>::fmt
  11: core::fmt::write
  12: <rustc_middle::mir::VarDebugInfo as core::fmt::Debug>::fmt
  13: core::fmt::write
  14: alloc::fmt::format::format_inner
  15: rustc_middle::mir::pretty::write_scope_tree
  16: rustc_middle::mir::pretty::write_scope_tree
  17: rustc_middle::mir::pretty::write_scope_tree
  18: <rustc_middle::mir::pretty::MirWriter>::write_mir_fn
  19: <rustc_middle::mir::pretty::MirDumper>::dump_mir_to_writer
  20: <rustc_middle::mir::pretty::MirDumper>::dump_mir
  21: rustc_mir_transform::pass_manager::run_passes_inner
  22: rustc_mir_transform::run_optimization_passes
  23: rustc_mir_transform::optimized_mir
      [... omitted 2 frames ...]
  24: <rustc_middle::ty::context::TyCtxt>::instance_mir
  25: 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_interface::passes::analysis::{closure#1}::{closure#0}>::{closure#0}>
  26: <rustc_session::session::Session>::time::<(), rustc_interface::passes::analysis::{closure#1}>
  27: rustc_interface::passes::analysis
      [... omitted 2 frames ...]
  28: <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}::{closure#0}, 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>>
  29: <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}::{closure#0}>
  30: <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} as core::ops::function::FnOnce<(&rustc_session::session::Session, rustc_middle::ty::context::CurrentGcx, alloc::sync::Arc<rustc_data_structures::jobserver::Proxy>, &std::sync::once_lock::OnceLock<rustc_middle::ty::context::GlobalCtxt>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_middle::arena::Arena>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_hir::Arena>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  31: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  32: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  33: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<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.

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

note: using internal features is not supported and expected to cause internal compiler errors when used incorrectly

note: rustc 1.94.0-nightly (3fc493712 2025-12-12) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z threads=1 -Z simulate-remapped-rust-src-base=/rustc/FAKE_PREFIX -Z translate-remapped-path-to-local-path=no -Z ignore-directory-in-diagnostics-source-blocks=/cargo -Z ignore-directory-in-diagnostics-source-blocks=/checkout/vendor -Z codegen-backend=gcc -C opt-level=1 -Z dump-mir=PreCodegen -Z validate-mir -Z lint-mir -Z dump-mir-exclude-pass-number -Z mir-include-spans=false --crate-type rlib -Z mir-opt-level=4 -Z mir-enable-passes=+ReorderBasicBlocks,+ReorderLocals -Z dump-mir-dir=/checkout/obj/build/x86_64-unknown-linux-gnu/test/mir-opt/pattern_types -C prefer-dynamic -C rpath -C debuginfo=0

query stack during panic:
#0 [optimized_mir] optimizing MIR for `main`
#1 [analysis] running analysis passes on crate `pattern_types`
end of query stack
warning: 3 warnings emitted


------------------------------------------

error: compilation failed!
status: exit status: 101
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/mir-opt/pattern_types.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "-Zcodegen-backend=gcc" "--target=x86_64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "-O" "-Copt-level=1" "-Zdump-mir=PreCodegen" "-Zvalidate-mir" "-Zlint-mir" "-Zdump-mir-exclude-pass-number" "-Zmir-include-spans=false" "--crate-type=rlib" "-Zmir-opt-level=4" "-Zmir-enable-passes=+ReorderBasicBlocks,+ReorderLocals" "-Zdump-mir-dir=/checkout/obj/build/x86_64-unknown-linux-gnu/test/mir-opt/pattern_types" "--emit" "mir" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/mir-opt/pattern_types" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0"
stdout: none
--- stderr -------------------------------
warning: unused variable: `x`
##[warning] --> /checkout/tests/mir-opt/pattern_types.rs:9:9
  |
9 |     let x: pattern_type!(u32 is 1..) = unsafe { std::mem::transmute(2) };
  |         ^ help: if this is intentional, prefix it with an underscore: `_x`
  |
  = note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default

warning: unused variable: `y`
##[warning]  --> /checkout/tests/mir-opt/pattern_types.rs:11:9
   |
11 |     let y: pattern_type!(u32 is 1..) = unsafe { std::mem::transmute(0) };
   |         ^ help: if this is intentional, prefix it with an underscore: `_y`

warning: function `main` is never used
##[warning] --> /checkout/tests/mir-opt/pattern_types.rs:7:4
  |
7 | fn main() {
  |    ^^^^
  |
  = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default


thread 'rustc' (30735) panicked at compiler/rustc_const_eval/src/util/check_validity_requirement.rs:192:41:
called `Result::unwrap()` on an `Err` value: InterpErrorInfo(InterpErrorInfoInner { kind: UndefinedBehavior(ValidationError(ValidationErrorInfo { path: None, kind: OutOfRange { value: "0", range: 1..=4294967295, max_value: 4294967295 } })), backtrace: InterpErrorBacktrace { backtrace: None } })
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::result::unwrap_failed
   3: rustc_const_eval::util::check_validity_requirement::validate_scalar_in_layout
   4: <rustc_const_eval::provide::{closure#3} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_middle::ty::consts::int::ScalarInt, rustc_middle::ty::Ty)>>::call_once
   5: <rustc_middle::ty::print::pretty::FmtPrinter as rustc_middle::ty::print::pretty::PrettyPrinter>::pretty_print_const_scalar_int
   6: <rustc_middle::ty::print::pretty::FmtPrinter as rustc_middle::ty::print::pretty::PrettyPrinter>::pretty_print_const_scalar
   7: rustc_middle::mir::pretty::pretty_print_const_value_tcx
   8: <rustc_middle::mir::consts::Const as core::fmt::Display>::fmt
   9: core::fmt::write
  10: <rustc_middle::mir::VarDebugInfoContents as core::fmt::Debug>::fmt
  11: core::fmt::write
  12: <rustc_middle::mir::VarDebugInfo as core::fmt::Debug>::fmt
  13: core::fmt::write
  14: alloc::fmt::format::format_inner
  15: rustc_middle::mir::pretty::write_scope_tree
  16: rustc_middle::mir::pretty::write_scope_tree
  17: rustc_middle::mir::pretty::write_scope_tree
  18: <rustc_middle::mir::pretty::MirWriter>::write_mir_fn
  19: <rustc_middle::mir::pretty::MirDumper>::dump_mir_to_writer
  20: <rustc_middle::mir::pretty::MirDumper>::dump_mir
  21: rustc_mir_transform::pass_manager::run_passes_inner
  22: rustc_mir_transform::run_optimization_passes
  23: rustc_mir_transform::optimized_mir
      [... omitted 2 frames ...]
  24: <rustc_middle::ty::context::TyCtxt>::instance_mir
  25: 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_interface::passes::analysis::{closure#1}::{closure#0}>::{closure#0}>
  26: <rustc_session::session::Session>::time::<(), rustc_interface::passes::analysis::{closure#1}>
  27: rustc_interface::passes::analysis
      [... omitted 2 frames ...]
  28: <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}::{closure#0}, 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>>
  29: <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}::{closure#0}>
  30: <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} as core::ops::function::FnOnce<(&rustc_session::session::Session, rustc_middle::ty::context::CurrentGcx, alloc::sync::Arc<rustc_data_structures::jobserver::Proxy>, &std::sync::once_lock::OnceLock<rustc_middle::ty::context::GlobalCtxt>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_middle::arena::Arena>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_hir::Arena>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  31: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  32: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  33: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<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.

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

note: using internal features is not supported and expected to cause internal compiler errors when used incorrectly

note: rustc 1.94.0-nightly (3fc493712 2025-12-12) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z threads=1 -Z simulate-remapped-rust-src-base=/rustc/FAKE_PREFIX -Z translate-remapped-path-to-local-path=no -Z ignore-directory-in-diagnostics-source-blocks=/cargo -Z ignore-directory-in-diagnostics-source-blocks=/checkout/vendor -Z codegen-backend=gcc -C opt-level=1 -Z dump-mir=PreCodegen -Z validate-mir -Z lint-mir -Z dump-mir-exclude-pass-number -Z mir-include-spans=false --crate-type rlib -Z mir-opt-level=4 -Z mir-enable-passes=+ReorderBasicBlocks,+ReorderLocals -Z dump-mir-dir=/checkout/obj/build/x86_64-unknown-linux-gnu/test/mir-opt/pattern_types -C prefer-dynamic -C rpath -C debuginfo=0

query stack during panic:
#0 [optimized_mir] optimizing MIR for `main`
#1 [analysis] running analysis passes on crate `pattern_types`
end of query stack

For more information how to resolve CI failures of this job, visit this link.

rust-bors · 2025-12-12T10:12:30Z

☀️ Try build successful (CI)
Build commit: db4e1d2 (db4e1d23234d93b5e96ecc768b35d9090c32cddf, parent: 5b150d238fbd4fe7bc2cd3140d8e6fb4406099fa)

rust-timer · 2025-12-12T10:12:34Z

Queued db4e1d2 with parent 5b150d2, future comparison URL.
There are currently 2 preceding artifacts in the queue.
It will probably take at least ~2.1 hours until the benchmark run finishes.

const-eval: always do full typed copies

8ee6155

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Dec 12, 2025

RalfJung mentioned this pull request Dec 12, 2025

const-eval: always do mem-to-mem copies if there might be padding involved #148967

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rust-bors bot added a commit that referenced this pull request Dec 12, 2025

Auto merge of #149901 - RalfJung:const-eval-typed, r=<try>

db4e1d2

const-eval: always do full typed copies

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Dec 12, 2025

traviscross added the I-lang-radar Items that are on lang's radar and will need eventual work or consideration. label Dec 12, 2025

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