rustc hangs when generating very large arrays

[cdmistman]

I tried this code:

const VALUES: [usize; std::u32::MAX as usize] = {
    todo!();
  }

It seems that generating large arrays causes rustc to start using up a LOT of memory - eats up over 32gb for this.

Meta

rustc --version --verbose:

rustc 1.49.0 (e1884a8e3 2020-12-29)
binary: rustc
commit-hash: e1884a8e3c3e813aada8254edfa120e85bf5ffca
commit-date: 2020-12-29
host: x86_64-unknown-linux-gnu
release: 1.49.0

[jonas-schievink]

You are creating an array containing 4 billion elements, the compiler isn't too happy about that

[cdmistman]

Makes sense - still, clang is able to compile similar programs with no problem and much less memory usage.

[jyn514]

I think this is a duplicate of #81124.

[jyn514]

A similar program causes rustc to abort:

> rustc array-hang.rs 
warning: constant is never used: `VALUES`
 --> array-hang.rs:2:1
  |
2 | const VALUES: [usize; std::u32::MAX as usize] = [0; std::u32::MAX as usize];
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

memory allocation of 34359738360 bytes failed
Aborted

(gdb) where
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#1  0x00007ffff3239535 in __GI_abort () at abort.c:79
#2  0x00007ffff34a9ca7 in std::sys::unix::abort_internal ()
    at /home/joshua/rustc2/library/std/src/sys/unix/mod.rs:237
#3  0x00007ffff34743c6 in std::process::abort ()
    at /home/joshua/rustc2/library/std/src/process.rs:1772
#4  0x00007ffff345261e in std::alloc::rust_oom ()
    at /home/joshua/rustc2/library/std/src/alloc.rs:332
#5  0x00007ffff34fac87 in alloc::alloc::__alloc_error_handler::__rg_oom ()
    at /home/joshua/rustc2/library/alloc/src/alloc.rs:397
#6  0x00007ffff34fc767 in alloc::alloc::handle_alloc_error ()
    at /home/joshua/rustc2/library/alloc/src/alloc.rs:366
#7  0x00007ffff554b853 in alloc::raw_vec::RawVec<T,A>::allocate_in ()
    at /home/joshua/rustc2/library/alloc/src/raw_vec.rs:193
#8  0x00007ffff5388c3d in alloc::raw_vec::RawVec<T,A>::with_capacity_zeroed_in ()
    at /home/joshua/rustc2/library/alloc/src/raw_vec.rs:136
#9  <u8 as alloc::vec::spec_from_elem::SpecFromElem>::from_elem ()
    at /home/joshua/rustc2/library/alloc/src/vec/spec_from_elem.rs:39
#10 alloc::vec::from_elem () at /home/joshua/rustc2/library/alloc/src/vec/mod.rs:1963
#11 0x00007ffff52e8ca0 in rustc_middle::mir::interpret::allocation::Allocation<Tag>::uninit ()
    at /home/joshua/rustc2/compiler/rustc_middle/src/mir/interpret/allocation.rs:110
#12 0x00007ffff559cf08 in rustc_mir::interpret::memory::Memory<M>::allocate ()
    at /home/joshua/rustc2/compiler/rustc_mir/src/interpret/memory.rs:197
#13 0x00007ffff5206fd7 in rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::allocate ()
    at /home/joshua/rustc2/compiler/rustc_mir/src/interpret/place.rs:1022
#14 0x00007ffff4edea3f in rustc_mir::const_eval::eval_queries::eval_body_using_ecx ()
    at /home/joshua/rustc2/compiler/rustc_mir/src/const_eval/eval_queries.rs:49
#15 rustc_mir::const_eval::eval_queries::eval_to_allocation_raw_provider::{{closure}}
    () at /home/joshua/rustc2/compiler/rustc_mir/src/const_eval/eval_queries.rs:305
#16 core::result::Result<T,E>::and_then ()
    at /home/joshua/rustc2/library/core/src/result.rs:704
#17 rustc_mir::const_eval::eval_queries::eval_to_allocation_raw_provider ()
    at /home/joshua/rustc2/compiler/rustc_mir/src/const_eval/eval_queries.rs:305
#18 0x00007ffff4edacfb in rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::eval_to_allocation_raw>::compute ()
    at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:377
#19 0x00007ffff4fac027 in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl ()
--Type <RET> for more, q to quit, c to continue without paging--c
    at /home/joshua/rustc2/compiler/rustc_query_system/src/dep_graph/graph.rs:362
#20 0x00007ffff4fb209f in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task () at /home/joshua/rustc2/compiler/rustc_query_system/src/dep_graph/graph.rs:245
#21 0x00007ffff5038e63 in rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:607
#22 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:73
#23 stacker::maybe_grow () at /home/joshua/.local/lib/cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55
#24 rustc_data_structures::stack::ensure_sufficient_stack () at /home/joshua/rustc2/compiler/rustc_data_structures/src/stack.rs:16
#25 0x00007ffff500b4a2 in rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:73
#26 rustc_middle::ty::context::tls::enter_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#27 rustc_middle::ty::context::tls::set_tlv () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1696
#28 rustc_middle::ty::context::tls::enter_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#29 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:72
#30 rustc_middle::ty::context::tls::with_related_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1756
#31 rustc_middle::ty::context::tls::with_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1740
#32 rustc_middle::ty::context::tls::with_context_opt () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1729
#33 rustc_middle::ty::context::tls::with_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1740
#34 rustc_middle::ty::context::tls::with_related_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1753
#35 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:61
#36 rustc_query_system::query::plumbing::force_query_with_job::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:597
#37 rustc_query_system::query::plumbing::with_diagnostics () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:302
#38 rustc_query_system::query::plumbing::force_query_with_job () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:596
#39 0x00007ffff4fc8046 in rustc_query_system::query::plumbing::try_execute_query () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:426
#40 rustc_query_system::query::plumbing::get_query_impl::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:644
#41 <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/caches.rs:114
#42 rustc_query_system::query::plumbing::try_get_cached () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:379
#43 rustc_query_system::query::plumbing::get_query_impl () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:636
#44 0x00007ffff4edd0a5 in rustc_query_system::query::plumbing::get_query () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:738
#45 rustc_middle::ty::query::TyCtxtAt::eval_to_allocation_raw () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:487
#46 rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::eval_to_allocation_raw () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:448
#47 rustc_mir::const_eval::eval_queries::eval_to_const_value_raw_provider () at /home/joshua/rustc2/compiler/rustc_mir/src/const_eval/eval_queries.rs:238
#48 0x00007ffff4edadfb in rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::eval_to_const_value_raw>::compute () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:377
#49 0x00007ffff4fa4452 in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl () at /home/joshua/rustc2/compiler/rustc_query_system/src/dep_graph/graph.rs:362
#50 0x00007ffff4fb188f in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task () at /home/joshua/rustc2/compiler/rustc_query_system/src/dep_graph/graph.rs:245
#51 0x00007ffff5037023 in rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:607
#52 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:73
#53 stacker::maybe_grow () at /home/joshua/.local/lib/cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55
#54 rustc_data_structures::stack::ensure_sufficient_stack () at /home/joshua/rustc2/compiler/rustc_data_structures/src/stack.rs:16
#55 0x00007ffff5004218 in rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:73
#56 rustc_middle::ty::context::tls::enter_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#57 rustc_middle::ty::context::tls::set_tlv () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1696
#58 rustc_middle::ty::context::tls::enter_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#59 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:72
#60 rustc_middle::ty::context::tls::with_related_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1756
#61 rustc_middle::ty::context::tls::with_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1740
#62 rustc_middle::ty::context::tls::with_context_opt () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1729
#63 rustc_middle::ty::context::tls::with_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1740
#64 rustc_middle::ty::context::tls::with_related_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1753
#65 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:61
#66 rustc_query_system::query::plumbing::force_query_with_job::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:597
#67 rustc_query_system::query::plumbing::with_diagnostics () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:302
#68 rustc_query_system::query::plumbing::force_query_with_job () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:596
#69 0x00007ffff4fc4e56 in rustc_query_system::query::plumbing::try_execute_query () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:426
#70 rustc_query_system::query::plumbing::get_query_impl::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:644
#71 <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/caches.rs:114
#72 rustc_query_system::query::plumbing::try_get_cached () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:379
#73 rustc_query_system::query::plumbing::get_query_impl () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:636
#74 0x00007ffff4edcdf1 in rustc_query_system::query::plumbing::get_query () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:738
#75 rustc_middle::ty::query::TyCtxtAt::eval_to_const_value_raw () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:487
#76 rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::eval_to_const_value_raw () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:448
#77 rustc_mir::const_eval::eval_queries::eval_to_const_value_raw_provider () at /home/joshua/rustc2/compiler/rustc_mir/src/const_eval/eval_queries.rs:215
#78 0x00007ffff67cb8ec in rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::eval_to_const_value_raw>::compute () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:377
#79 0x00007ffff65aa4b5 in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl () at /home/joshua/rustc2/compiler/rustc_query_system/src/dep_graph/graph.rs:362
#80 0x00007ffff65d6adf in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task () at /home/joshua/rustc2/compiler/rustc_query_system/src/dep_graph/graph.rs:245
#81 0x00007ffff6895e63 in rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:607
#82 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:73
#83 stacker::maybe_grow () at /home/joshua/.local/lib/cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55
#84 rustc_data_structures::stack::ensure_sufficient_stack () at /home/joshua/rustc2/compiler/rustc_data_structures/src/stack.rs:16
#85 0x00007ffff699e365 in rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:73
#86 rustc_middle::ty::context::tls::enter_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#87 rustc_middle::ty::context::tls::set_tlv () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1696
#88 rustc_middle::ty::context::tls::enter_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#89 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:72
#90 rustc_middle::ty::context::tls::with_related_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1756
#91 rustc_middle::ty::context::tls::with_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1740
#92 rustc_middle::ty::context::tls::with_context_opt () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1729
#93 rustc_middle::ty::context::tls::with_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1740
#94 rustc_middle::ty::context::tls::with_related_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1753
#95 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:61
#96 rustc_query_system::query::plumbing::force_query_with_job::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:597
#97 rustc_query_system::query::plumbing::with_diagnostics () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:302
#98 rustc_query_system::query::plumbing::force_query_with_job () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:596
#99 0x00007ffff69467c0 in rustc_query_system::query::plumbing::try_execute_query () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:426
#100 rustc_query_system::query::plumbing::get_query_impl::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:644
#101 <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/caches.rs:114
#102 rustc_query_system::query::plumbing::try_get_cached () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:379
#103 rustc_query_system::query::plumbing::get_query_impl () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:636
#104 0x00007ffff67ab9c7 in rustc_middle::mir::interpret::queries::<impl rustc_middle::ty::context::TyCtxt>::const_eval_global_id () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:487
#105 0x00007ffff67ab594 in rustc_middle::mir::interpret::queries::<impl rustc_middle::ty::context::TyCtxt>::const_eval_poly () at /home/joshua/rustc2/compiler/rustc_middle/src/mir/interpret/queries.rs:22
#106 0x00007ffff5e7b6b2 in <rustc_lint::builtin::UnusedBrokenConst as rustc_lint::passes::LateLintPass>::check_item () at /home/joshua/rustc2/compiler/rustc_lint/src/builtin.rs:1497
#107 0x00007ffff5e94894 in <rustc_lint::BuiltinCombinedLateLintPass as rustc_lint::passes::LateLintPass>::check_item () at /home/joshua/rustc2/compiler/rustc_lint/src/passes.rs:115
#108 0x00007ffff3e53343 in <rustc_lint::late::LateContextAndPass<T> as rustc_hir::intravisit::Visitor>::visit_item::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:145
#109 rustc_lint::late::LateContextAndPass<T>::with_param_env () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:75
#110 <rustc_lint::late::LateContextAndPass<T> as rustc_hir::intravisit::Visitor>::visit_item::{{closure}} () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:144
#111 rustc_lint::late::LateContextAndPass<T>::with_lint_attrs () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:63
#112 <rustc_lint::late::LateContextAndPass<T> as rustc_hir::intravisit::Visitor>::visit_item () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:143
#113 rustc_hir::intravisit::Visitor::visit_nested_item () at /home/joshua/rustc2/compiler/rustc_hir/src/intravisit.rs:273
#114 0x00007ffff3e4513d in rustc_hir::intravisit::walk_mod () at /home/joshua/rustc2/compiler/rustc_hir/src/intravisit.rs:500
#115 0x00007ffff3e52e2c in rustc_lint::late::LateContextAndPass<T>::process_mod () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:81
#116 <rustc_lint::late::LateContextAndPass<T> as rustc_hir::intravisit::Visitor>::visit_mod () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:251
#117 0x00007ffff3e414ef in rustc_hir::intravisit::walk_crate () at /home/joshua/rustc2/compiler/rustc_hir/src/intravisit.rs:486
#118 0x00007ffff3e50a2f in rustc_lint::late::late_lint_pass_crate::{{closure}} () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:444
#119 rustc_lint::late::LateContextAndPass<T>::with_lint_attrs () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:63
#120 rustc_lint::late::late_lint_pass_crate () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:439
#121 rustc_lint::late::late_lint_crate () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:458
#122 0x00007ffff3e6fe38 in rustc_lint::late::check_crate::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:488
#123 rustc_data_structures::profiling::VerboseTimingGuard::run () at /home/joshua/rustc2/compiler/rustc_data_structures/src/profiling.rs:570
#124 rustc_session::utils::<impl rustc_session::session::Session>::time () at /home/joshua/rustc2/compiler/rustc_session/src/utils.rs:9
#125 0x00007ffff3e6a8c2 in rustc_lint::late::check_crate::{{closure}} () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:486
#126 rustc_data_structures::sync::join () at /home/joshua/rustc2/compiler/rustc_data_structures/src/sync.rs:159
#127 0x00007ffff3e72b20 in rustc_lint::late::check_crate () at /home/joshua/rustc2/compiler/rustc_lint/src/late.rs:484
#128 rustc_interface::passes::analysis::{{closure}}::{{closure}}::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/passes.rs:912
#129 rustc_data_structures::profiling::VerboseTimingGuard::run () at /home/joshua/rustc2/compiler/rustc_data_structures/src/profiling.rs:570
#130 rustc_session::utils::<impl rustc_session::session::Session>::time () at /home/joshua/rustc2/compiler/rustc_session/src/utils.rs:9
#131 0x00007ffff3de0c48 in rustc_interface::passes::analysis::{{closure}}::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/passes.rs:911
#132 core::ops::function::FnOnce::call_once () at /home/joshua/rustc2/library/core/src/ops/function.rs:227
#133 <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once () at /home/joshua/rustc2/library/std/src/panic.rs:322
#134 std::panicking::try::do_call () at /home/joshua/rustc2/library/std/src/panicking.rs:379
#135 std::panicking::try () at /home/joshua/rustc2/library/std/src/panicking.rs:343
#136 0x00007ffff3ebe4bd in std::panic::catch_unwind () at /home/joshua/rustc2/library/std/src/panic.rs:396
#137 rustc_interface::passes::analysis::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/passes.rs:898
#138 core::ops::function::FnOnce::call_once () at /home/joshua/rustc2/library/core/src/ops/function.rs:227
#139 <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once () at /home/joshua/rustc2/library/std/src/panic.rs:322
#140 0x00007ffff3de0c16 in std::panicking::try::do_call () at /home/joshua/rustc2/library/std/src/panicking.rs:379
#141 std::panicking::try () at /home/joshua/rustc2/library/std/src/panicking.rs:343
#142 0x00007ffff3e719ba in std::panic::catch_unwind () at /home/joshua/rustc2/library/std/src/panic.rs:396
#143 rustc_interface::passes::analysis::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/passes.rs:894
#144 rustc_data_structures::profiling::VerboseTimingGuard::run () at /home/joshua/rustc2/compiler/rustc_data_structures/src/profiling.rs:570
#145 rustc_session::utils::<impl rustc_session::session::Session>::time () at /home/joshua/rustc2/compiler/rustc_session/src/utils.rs:9
#146 0x00007ffff3e5a0be in rustc_interface::passes::analysis () at /home/joshua/rustc2/compiler/rustc_interface/src/passes.rs:893
#147 0x00007ffff3b6d232 in rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:377
#148 0x00007ffff3b75833 in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl () at /home/joshua/rustc2/compiler/rustc_query_system/src/dep_graph/graph.rs:362
#149 0x00007ffff3b77088 in rustc_query_system::dep_graph::graph::DepGraph<K>::with_eval_always_task () at /home/joshua/rustc2/compiler/rustc_query_system/src/dep_graph/graph.rs:418
#150 0x00007ffff3b94222 in rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:599
#151 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:73
#152 stacker::maybe_grow () at /home/joshua/.local/lib/cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55
#153 rustc_data_structures::stack::ensure_sufficient_stack () at /home/joshua/rustc2/compiler/rustc_data_structures/src/stack.rs:16
#154 0x00007ffff3b8f5cd in rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:73
#155 rustc_middle::ty::context::tls::enter_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#156 rustc_middle::ty::context::tls::set_tlv () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1696
#157 rustc_middle::ty::context::tls::enter_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#158 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:72
#159 rustc_middle::ty::context::tls::with_related_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1756
#160 rustc_middle::ty::context::tls::with_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1740
#161 rustc_middle::ty::context::tls::with_context_opt () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1729
#162 rustc_middle::ty::context::tls::with_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1740
#163 rustc_middle::ty::context::tls::with_related_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1753
#164 rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:61
#165 rustc_query_system::query::plumbing::force_query_with_job::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:597
#166 rustc_query_system::query::plumbing::with_diagnostics () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:302
#167 rustc_query_system::query::plumbing::force_query_with_job () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:596
#168 0x00007ffff3b8c955 in rustc_query_system::query::plumbing::try_execute_query () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:426
#169 rustc_query_system::query::plumbing::get_query_impl::{{closure}} () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:644
#170 <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/caches.rs:114
#171 rustc_query_system::query::plumbing::try_get_cached () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:379
#172 rustc_query_system::query::plumbing::get_query_impl () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:636
#173 0x00007ffff3b6d8a7 in rustc_query_system::query::plumbing::get_query () at /home/joshua/rustc2/compiler/rustc_query_system/src/query/plumbing.rs:738
#174 rustc_middle::ty::query::TyCtxtAt::analysis () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:487
#175 rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::analysis () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/query/plumbing.rs:448
#176 rustc_driver::run_compiler::{{closure}}::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_driver/src/lib.rs:440
#177 rustc_interface::passes::QueryContext::enter::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/passes.rs:742
#178 rustc_middle::ty::context::tls::enter_context::{{closure}} () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#179 rustc_middle::ty::context::tls::set_tlv () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1696
#180 rustc_middle::ty::context::tls::enter_context () at /home/joshua/rustc2/compiler/rustc_middle/src/ty/context.rs:1712
#181 rustc_interface::passes::QueryContext::enter () at /home/joshua/rustc2/compiler/rustc_interface/src/passes.rs:742
#182 0x00007ffff3b48413 in rustc_driver::run_compiler::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_driver/src/lib.rs:440
#183 rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter () at /home/joshua/rustc2/compiler/rustc_interface/src/queries.rs:418
#184 0x00007ffff3b7d000 in rustc_driver::run_compiler::{{closure}} () at /home/joshua/rustc2/compiler/rustc_driver/src/lib.rs:341
#185 rustc_interface::interface::create_compiler_and_run::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/interface.rs:197
#186 rustc_span::with_source_map () at /home/joshua/rustc2/compiler/rustc_span/src/lib.rs:787
#187 0x00007ffff3b49523 in rustc_interface::interface::create_compiler_and_run () at /home/joshua/rustc2/compiler/rustc_interface/src/interface.rs:191
#188 0x00007ffff3b7206b in rustc_interface::interface::run_compiler::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/interface.rs:213
#189 rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals::{{closure}}::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/util.rs:152
#190 scoped_tls::ScopedKey<T>::set () at /home/joshua/.local/lib/cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-1.0.0/src/lib.rs:137
#191 0x00007ffff3b7d773 in rustc_span::with_session_globals () at /home/joshua/rustc2/compiler/rustc_span/src/lib.rs:103
#192 0x00007ffff3b72f20 in rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/util.rs:150
#193 rustc_interface::util::scoped_thread::{{closure}} () at /home/joshua/rustc2/compiler/rustc_interface/src/util.rs:125
#194 std::sys_common::backtrace::__rust_begin_short_backtrace () at /home/joshua/rustc2/library/std/src/sys_common/backtrace.rs:125
#195 0x00007ffff3b9a1c6 in std::thread::Builder::spawn_unchecked::{{closure}}::{{closure}} () at /home/joshua/rustc2/library/std/src/thread/mod.rs:474
#196 <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once () at /home/joshua/rustc2/library/std/src/panic.rs:322
#197 std::panicking::try::do_call () at /home/joshua/rustc2/library/std/src/panicking.rs:379
#198 std::panicking::try () at /home/joshua/rustc2/library/std/src/panicking.rs:343
#199 0x00007ffff3bca18a in std::panic::catch_unwind () at /home/joshua/rustc2/library/std/src/panic.rs:396
#200 std::thread::Builder::spawn_unchecked::{{closure}} () at /home/joshua/rustc2/library/std/src/thread/mod.rs:473
#201 core::ops::function::FnOnce::call_once{{vtable-shim}} () at /home/joshua/rustc2/library/core/src/ops/function.rs:227
#202 0x00007ffff3473368 in <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once () at /home/joshua/rustc2/library/alloc/src/boxed.rs:1484
#203 <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once () at /home/joshua/rustc2/library/alloc/src/boxed.rs:1484
#204 0x00007ffff344e72a in std::sys::unix::thread::Thread::new::thread_start () at /home/joshua/rustc2/library/std/src/sys/unix/thread.rs:71
#205 0x00007fffee796fa3 in start_thread (arg=<optimized out>) at pthread_create.c:486
#206 0x00007ffff33104cf in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

[jyn514]

Relevant code:

rust/compiler/rustc_mir/src/const_eval/eval_queries.rs

Line 49 in c5a96fb

let ret = ecx.allocate(layout, MemoryKind::Stack);

[jyn514]

Not sure who to ping, maybe @oli-obk - would it be possible to only allocate places if they're something other than a constant value? Something like this:

enum MPlaceTy {
    Allocated(MemPlace, TyAndLayout),
    Constant(Constant, TyAndLayout),
}

[oli-obk]

cc @rust-lang/wg-const-eval we could delay the allocation of local _0 (return value) until its first use (and its only use, now that we have mir_for_ctfe). This would allow

const fn foo() -> [u8; u32::max_value() as usize] { panic!("hello") }

to actually show the panic and not run out of memory or hang when called

[RalfJung]

First of all, even if we end up supporting the case where the function panics, the OOM will still occur once you actually implement the function. So I'd say the benefit of supporting this is rather marginal.

On the cost side, the interpreter is already complicated enough as things are; every extra bit of complexity will increase the risk of bugs. If we do anything here, I think the right layer to do that is Allocation: we can delay actually allocating the Vec<u8> byte buffer until the first write.

const VALUES: [usize; std::u32::MAX as usize] = [0; std::u32::MAX as usize];

This program asks the compiler to allocate size_of::<usize>() * 4GB of RAM... I'd say if people want to shoot themselves into the foot we should let them. I don't see anything reasonable we can do about code like this.

[oli-obk]

This program asks the compiler to allocate size_of::<usize>() * 4GB of RAM... I'd say if people want to shoot themselves into the foot we should let them. I don't see anything reasonable we can do about code like this.

Specifically this example allocates an all-zero static allocation, which is guaranteed immutable. This kind of static allocation has custom support in LLVM and won't take up any memory until runtime. So if we can track this kind of information through the compiler, we can support that, too. But all of this is a big rabbit hole.

Related issues:

• Codegen for a large static array uses a lot of memory #30083
• static array of zeroes can take minutes to lint check #55795

A previous attempt for undef bytes: #62655

This issue is still actionable by itself, as just the action of allocating an all-undef array should not take very long. It should either OOM quickly or manage to allocate that array. It should only be marginally slower than vec![0_usize, u32::max_value() as usize] on the same machine at runtime. So we need to find out where exactly it is "stuck" on a machine with sufficient memory to actually show this.

@cdmistman can you run a rustc in gdb and give us a backtrace after a minute of compiling your example?

[RalfJung]

This is not an all-undef array though, it is an all-zero array. A lot more extra hackery is needed to add "lazy zeros" everywhere throughout CTFE. I assume writing all these zeros is what takes so much time.

[oli-obk]

The original issue

const VALUES: [usize; std::u32::MAX as usize] = { todo!() };

is an all undef array, because we create the array before running the initializer body. Otherwise I would agree with the assessment that interpreting 2^32 index + assignment ops (even if not in actual MIR ops, but just a loop in the interpreter) would be the issue here.

[tesuji]

Consider this Rust program (file named hang.rs):

pub const VALUES: [usize; u32::MAX as usize] = [0; u32::MAX as usize];

fn main() {}

Run rustc hang.rs. Then I have the following backtrace through gdb.

Backtrace

(gdb) bt
#0  0x00007fef25ec4772 in rustc_middle::mir::interpret::allocation::Allocation<Tag,Extra>::compress_uninit_range () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#1  0x00007fef25f59b85 in rustc_mir::interpret::memory::Memory<M>::copy_repeatedly () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#2  0x00007fef25f713f6 in rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::copy_op_no_validate () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#3  0x00007fef25f71970 in rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::copy_op_transmute () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#4  0x00007fef25f555f8 in rustc_mir::interpret::eval_context::InterpCx<M>::pop_stack_frame () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#5  0x00007fef25f73e46 in rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::run () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#6  0x00007fef25f33241 in rustc_mir::const_eval::eval_queries::eval_to_allocation_raw_provider () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#7  0x00007fef25f25f20 in rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::eval_to_allocation_raw>::compute () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#8  0x00007fef25ed0c52 in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#9  0x00007fef25f26e82 in rustc_data_structures::stack::ensure_sufficient_stack () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#10 0x00007fef25fce12a in rustc_query_system::query::plumbing::force_query_with_job () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#11 0x00007fef25fb6479 in rustc_query_system::query::plumbing::get_query_impl () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#12 0x00007fef25f32604 in rustc_mir::const_eval::eval_queries::eval_to_const_value_raw_provider () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#13 0x00007fef26aaeb80 in rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::eval_to_const_value_raw>::compute () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#14 0x00007fef26a713e6 in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#15 0x00007fef26ab1ca2 in rustc_data_structures::stack::ensure_sufficient_stack () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#16 0x00007fef26b05c18 in rustc_query_system::query::plumbing::force_query_with_job () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#17 0x00007fef26afee89 in rustc_query_system::query::plumbing::get_query_impl () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#18 0x00007fef25f3287a in rustc_mir::const_eval::eval_queries::eval_to_const_value_raw_provider () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#19 0x00007fef270214e7 in rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::eval_to_const_value_raw>::compute () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#20 0x00007fef2703c926 in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#21 0x00007fef26ee5106 in rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}} () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#22 0x00007fef26f979ce in rustc_query_system::query::plumbing::force_query_with_job () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#23 0x00007fef263ad230 in rustc_query_system::query::plumbing::get_query_impl () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#24 0x00007fef26407e20 in rustc_middle::mir::interpret::queries::<impl rustc_middle::ty::context::TyCtxt>::const_eval_global_id () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#25 0x00007fef26407c57 in rustc_middle::mir::interpret::queries::<impl rustc_middle::ty::context::TyCtxt>::const_eval_poly () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#26 0x00007fef261db740 in <rustc_lint::BuiltinCombinedLateLintPass as rustc_lint::passes::LateLintPass>::check_item () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#27 0x00007fef25a62b9a in rustc_hir::intravisit::Visitor::visit_nested_item () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#28 0x00007fef264d97d7 in rustc_hir::intravisit::walk_crate () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#29 0x00007fef264e6f3a in rustc_session::utils::<impl rustc_session::session::Session>::time () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#30 0x00007fef26504430 in <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#31 0x00007fef264e9134 in rustc_session::utils::<impl rustc_session::session::Session>::time () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#32 0x00007fef264ff156 in rustc_interface::passes::analysis () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#33 0x00007fef264a70c9 in rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#34 0x00007fef2649ad9e in rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#35 0x00007fef2649d687 in rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}} () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#36 0x00007fef264816d9 in rustc_query_system::query::plumbing::force_query_with_job () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#37 0x00007fef26480ab2 in rustc_query_system::query::plumbing::get_query_impl () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#38 0x00007fef264a74d1 in rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#39 0x00007fef2649cea4 in rustc_span::with_source_map () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#40 0x00007fef264a876a in rustc_interface::interface::create_compiler_and_run () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#41 0x00007fef2649d52e in rustc_span::with_session_globals () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#42 0x00007fef264a3473 in std::sys_common::backtrace::__rust_begin_short_backtrace () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#43 0x00007fef2648224a in core::ops::function::FnOnce::call_once{{vtable-shim}} () from /home/lzutao/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-844665e24828f0f2.so
#44 0x00007fef238ab68a in <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once () at /rustc/4253153db205251f72ea4493687a31e04a2a8ca0/library/alloc/src/boxed.rs:1484
#45 <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once () at /rustc/4253153db205251f72ea4493687a31e04a2a8ca0/library/alloc/src/boxed.rs:1484
#46 std::sys::unix::thread::Thread::new::thread_start () at /rustc/4253153db205251f72ea4493687a31e04a2a8ca0//library/std/src/sys/unix/thread.rs:71
#47 0x00007fef235e14a4 in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#48 0x00007fef22f17d0f in clone () from /lib/x86_64-linux-gnu/libc.so.6

[oli-obk]

Thanks, but that's the program that will actually initialize the bits with all zeros, if you replace the initializer body [0; u32::MAX as usize] with todo!(), does it also "hang"?

[tesuji]

Rustc doesn't hang in that case. I just have this error from rustc:

error: any use of this value will cause an error
 --> hang.rs:2:55
  |
2 | pub const VALUES: [usize; std::u32::MAX as usize] = { todo!() };
  | ------------------------------------------------------^^^^^^^---
  |                                                       |
  |                                                       the evaluated program panicked at 'not yet implemented', hang.rs:2:55
  |
  = note: `#[deny(const_err)]` on by default
  = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info

Also run through time -v I got:

Command exited with non-zero status 1
        Command being timed: "rustc hang.rs"
        User time (seconds): 1.24
        System time (seconds): 1.88
        Percent of CPU this job got: 99%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.12
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 4334640
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 908334
        Voluntary context switches: 2
        Involuntary context switches: 8
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 1

[oli-obk]

Oh, then I don't know what happened to the original example of @cdmistman Maybe your OS started using swap space and that slowed everything down?

I'm going to close this issue as not actionable then.

Thanks @lzutao for investigating

[RalfJung]

The original issue was

It seems that generating large arrays causes rustc to start using up a LOT of memory - eats up over 32gb for this.

So, it's about RAM usage, not hanging. [usize; 2^32] is indeed 32GB in size (on a 64bit system). So the fix here would be to make Allocation allocate its bytes lazily.

[oli-obk]

Oh... I read this as "start using.." -> "never stops"... But yea, that seems totally fine to me, as in the happy path you'd also use that much memory. I don't think we need to do anything here except for the discussed things in the actually successfully compiling path for which we already have issues.