ICE in `check_mod_const_bodies` when compiling a modified libcore

[mzabaluev]

Code

In the Rust repository, modify libcore with this patch:

diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
index fa37ee4ffb2..136d048025d 100644
--- a/library/core/src/num/int_macros.rs
+++ b/library/core/src/num/int_macros.rs
@@ -2653,19 +2653,24 @@ pub const fn pow(self, mut exp: u32) -> Self {
             let mut base = self;
             let mut acc = 1;
 
-            while exp > 1 {
-                if (exp & 1) == 1 {
+            loop {
+                let n_zeros = exp.trailing_zeros();
+                for _ in 0..n_zeros {
+                    base = base * base;
+                }
+                exp >>= n_zeros;
+                let n_ones = exp.trailing_ones();
+                for _ in 0..(n_ones - 1) {
                     acc = acc * base;
+                    base = base * base;
+                }
+                acc = acc * base;
+                exp >>= n_ones;
+                if exp == 0 {
+                    return acc;
                 }
-                exp /= 2;
                 base = base * base;
             }
-
-            // since exp!=0, finally the exp must be 1.
-            // Deal with the final bit of the exponent separately, since
-            // squaring the base afterwards is not necessary and may cause a
-            // needless overflow.
-            acc * base
         }
 
diff --git a/library/core/src/num/uint_macros.rs b/library/core/src/num/uint_macros.rs
index 081a3c0b118..adbc48d3cd2 100644
--- a/library/core/src/num/uint_macros.rs
+++ b/library/core/src/num/uint_macros.rs
@@ -2439,19 +2439,24 @@ pub const fn pow(self, mut exp: u32) -> Self {
             let mut base = self;
             let mut acc = 1;
 
-            while exp > 1 {
-                if (exp & 1) == 1 {
+            loop {
+                let n_zeros = exp.trailing_zeros();
+                for _ in 0..n_zeros {
+                    base = base * base;
+                }
+                exp >>= n_zeros;
+                let n_ones = exp.trailing_ones();
+                for _ in 0..(n_ones - 1) {
                     acc = acc * base;
+                    base = base * base;
+                }
+                acc = acc * base;
+                exp >>= n_ones;
+                if exp == 0 {
+                    return acc;
                 }
-                exp /= 2;
                 base = base * base;
             }
-
-            // since exp!=0, finally the exp must be 1.
-            // Deal with the final bit of the exponent separately, since
-            // squaring the base afterwards is not necessary and may cause a
-            // needless overflow.
-            acc * base
         }
 

Changed settings in config.toml:

codegen-units-std = 1
incremental = false

Then build the library with ./x build library/core --stage 0

Meta

rustc version: 1.78.0-beta.1 (efd9d2d 2024-03-18)

Error output

error: internal compiler error: compiler/rustc_passes/src/check_const.rs:142:17: we should not have reached this point, since `.await` is denied earlier
    --> library/core/src/num/int_macros.rs:2658:17
     |
1    | /   macro_rules! int_impl {
2    | |       (
3    | |           Self = $SelfT:ty,
4    | |           ActualT = $ActualT:ident,
...    |
2658 | | /                 for _ in 0..n_zeros {
2659 | | |                     base = base * base;
2660 | | |                 }
     | | |_________________^
...    |
3533 | |       }
3534 | |   }
     | |___- in this expansion of `int_impl!` (#1)
     |
    ::: library/core/src/num/mod.rs:301:5
     |
301  |   /     int_impl! {
302  |   |         Self = i8,
303  |   |         ActualT = i8,
304  |   |         UnsignedT = u8,
...      |
319  |   |         bound_condition = "",
320  |   |     }
     |   |_____- in this macro invocation (#1)

thread 'rustc' panicked at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/compiler/rustc_middle/src/util/bug.rs:34:50:
Box<dyn Any>

rustc-ice-to-report.txt

Backtrace

   0:     0x7f38bdf8930f - std::backtrace_rs::backtrace::libunwind::trace::h539c03b0789a3163
                               at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/library/std/src/../../backtrace/src/backtrace/libunwind.rs:105:5
   1:     0x7f38bdf8930f - std::backtrace_rs::backtrace::trace_unsynchronized::h90a51b49b444fc01
                               at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f38bdf8930f - std::backtrace::Backtrace::create::h52a6c1d2ae0a3112
                               at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/library/std/src/backtrace.rs:331:13
   3:     0x7f38bdf89250 - std::backtrace::Backtrace::force_capture::h70557b27472ed963
                               at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/library/std/src/backtrace.rs:312:9
   4:     0x7f38bac2ccb7 - std[999bdecce25602ed]::panicking::update_hook::<alloc[5d2a9fe8278cb303]::boxed::Box<rustc_driver_impl[e6c4295f52574c92]::install_ice_hook::{closure#0}>>::{closure#0}
   5:     0x7f38bdfa3b50 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h8e05c89c9dfd827c
                               at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/library/alloc/src/boxed.rs:2034:9
   6:     0x7f38bdfa3b50 - std::panicking::rust_panic_with_hook::h6987b578e7dec23c
                               at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/library/std/src/panicking.rs:783:13
   7:     0x7f38bac55b94 - std[999bdecce25602ed]::panicking::begin_panic::<rustc_errors[17bedd29219f425c]::ExplicitBug>::{closure#0}
   8:     0x7f38bac52906 - std[999bdecce25602ed]::sys_common::backtrace::__rust_end_short_backtrace::<std[999bdecce25602ed]::panicking::begin_panic<rustc_errors[17bedd29219f425c]::ExplicitBug>::{closure#0}, !>
   9:     0x7f38bac525e6 - std[999bdecce25602ed]::panicking::begin_panic::<rustc_errors[17bedd29219f425c]::ExplicitBug>
  10:     0x7f38bac5f2b1 - <rustc_errors[17bedd29219f425c]::diagnostic::BugAbort as rustc_errors[17bedd29219f425c]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x7f38bb2d6c1c - <rustc_errors[17bedd29219f425c]::DiagCtxt>::span_bug::<rustc_span[ebf54beea9088bcf]::span_encoding::Span, alloc[5d2a9fe8278cb303]::string::String>
  12:     0x7f38bb2e844d - rustc_middle[f6bb74e4dd5a8f75]::util::bug::opt_span_bug_fmt::<rustc_span[ebf54beea9088bcf]::span_encoding::Span>::{closure#0}
  13:     0x7f38bb2e858a - rustc_middle[f6bb74e4dd5a8f75]::ty::context::tls::with_opt::<rustc_middle[f6bb74e4dd5a8f75]::util::bug::opt_span_bug_fmt<rustc_span[ebf54beea9088bcf]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  14:     0x7f38bb2e3178 - rustc_middle[f6bb74e4dd5a8f75]::ty::context::tls::with_context_opt::<rustc_middle[f6bb74e4dd5a8f75]::ty::context::tls::with_opt<rustc_middle[f6bb74e4dd5a8f75]::util::bug::opt_span_bug_fmt<rustc_span[ebf54beea9088bcf]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  15:     0x7f38bb2e24d4 - rustc_middle[f6bb74e4dd5a8f75]::util::bug::span_bug_fmt::<rustc_span[ebf54beea9088bcf]::span_encoding::Span>
  16:     0x7f38bcead8f1 - <rustc_passes[6fa7bc5fc5542eb4]::check_const::CheckConstVisitor>::const_check_violated
  17:     0x7f38b948bb28 - <rustc_passes[6fa7bc5fc5542eb4]::check_const::CheckConstVisitor as rustc_hir[121f359932e59ede]::intravisit::Visitor>::visit_expr
  18:     0x7f38b948bc6a - <rustc_passes[6fa7bc5fc5542eb4]::check_const::CheckConstVisitor as rustc_hir[121f359932e59ede]::intravisit::Visitor>::visit_expr
  19:     0x7f38bc084c42 - <rustc_passes[6fa7bc5fc5542eb4]::check_const::CheckConstVisitor as rustc_hir[121f359932e59ede]::intravisit::Visitor>::visit_block
  20:     0x7f38bc084b4d - <rustc_passes[6fa7bc5fc5542eb4]::check_const::CheckConstVisitor as rustc_hir[121f359932e59ede]::intravisit::Visitor>::visit_body
  21:     0x7f38bc081d46 - rustc_passes[6fa7bc5fc5542eb4]::check_const::check_mod_const_bodies
  22:     0x7f38bc081839 - rustc_query_impl[e29825a6f88888a7]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e29825a6f88888a7]::query_impl::check_mod_const_bodies::dynamic_query::{closure#2}::{closure#0}, rustc_middle[f6bb74e4dd5a8f75]::query::erase::Erased<[u8; 0usize]>>
  23:     0x7f38bc6528ca - rustc_query_system[3350c2d9ca0121e2]::query::plumbing::try_execute_query::<rustc_query_impl[e29825a6f88888a7]::DynamicConfig<rustc_query_system[3350c2d9ca0121e2]::query::caches::DefaultCache<rustc_span[ebf54beea9088bcf]::def_id::LocalModDefId, rustc_middle[f6bb74e4dd5a8f75]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[e29825a6f88888a7]::plumbing::QueryCtxt, false>
  24:     0x7f38bc65243f - rustc_query_impl[e29825a6f88888a7]::query_impl::check_mod_const_bodies::get_query_non_incr::__rust_end_short_backtrace
  25:     0x7f38bc655482 - rustc_interface[2cd87b402a7bbb07]::passes::analysis
  26:     0x7f38bc654f65 - rustc_query_impl[e29825a6f88888a7]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[e29825a6f88888a7]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[f6bb74e4dd5a8f75]::query::erase::Erased<[u8; 1usize]>>
  27:     0x7f38bcb01ba2 - rustc_query_system[3350c2d9ca0121e2]::query::plumbing::try_execute_query::<rustc_query_impl[e29825a6f88888a7]::DynamicConfig<rustc_query_system[3350c2d9ca0121e2]::query::caches::SingleCache<rustc_middle[f6bb74e4dd5a8f75]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[e29825a6f88888a7]::plumbing::QueryCtxt, false>
  28:     0x7f38bcb01949 - rustc_query_impl[e29825a6f88888a7]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7f38bc9a5894 - rustc_interface[2cd87b402a7bbb07]::interface::run_compiler::<core[75bed1c93f3984e1]::result::Result<(), rustc_span[ebf54beea9088bcf]::ErrorGuaranteed>, rustc_driver_impl[e6c4295f52574c92]::run_compiler::{closure#0}>::{closure#0}
  30:     0x7f38bccb1b2e - std[999bdecce25602ed]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[2cd87b402a7bbb07]::util::run_in_thread_with_globals<rustc_interface[2cd87b402a7bbb07]::interface::run_compiler<core[75bed1c93f3984e1]::result::Result<(), rustc_span[ebf54beea9088bcf]::ErrorGuaranteed>, rustc_driver_impl[e6c4295f52574c92]::run_compiler::{closure#0}>::{closure#0}, core[75bed1c93f3984e1]::result::Result<(), rustc_span[ebf54beea9088bcf]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[75bed1c93f3984e1]::result::Result<(), rustc_span[ebf54beea9088bcf]::ErrorGuaranteed>>
  31:     0x7f38bccb198a - <<std[999bdecce25602ed]::thread::Builder>::spawn_unchecked_<rustc_interface[2cd87b402a7bbb07]::util::run_in_thread_with_globals<rustc_interface[2cd87b402a7bbb07]::interface::run_compiler<core[75bed1c93f3984e1]::result::Result<(), rustc_span[ebf54beea9088bcf]::ErrorGuaranteed>, rustc_driver_impl[e6c4295f52574c92]::run_compiler::{closure#0}>::{closure#0}, core[75bed1c93f3984e1]::result::Result<(), rustc_span[ebf54beea9088bcf]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[75bed1c93f3984e1]::result::Result<(), rustc_span[ebf54beea9088bcf]::ErrorGuaranteed>>::{closure#1} as core[75bed1c93f3984e1]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  32:     0x7f38bdfad1e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h3b366b3d6b556d67
                               at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/library/alloc/src/boxed.rs:2020:9
  33:     0x7f38bdfad1e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h49756348eb63eea1
                               at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/library/alloc/src/boxed.rs:2020:9
  34:     0x7f38bdfad1e5 - std::sys::pal::unix::thread::Thread::new::thread_start::hdf802a7c2e3fdf20
                               at /rustc/efd9d2df12b5e17fac0b4d0fb89f612ecd79f259/library/std/src/sys/pal/unix/thread.rs:108:17

note: compiler flags: --crate-type lib -C opt-level=3 -C embed-bitcode=no -C codegen-units=1 -Z unstable-options -C symbol-mangling-version=legacy -Z unstable-options -Z unstable-options -Z macro-backtrace -C split-debuginfo=off -C prefer-dynamic -Z inline-mir -C link-args=-Wl,-z,origin -C link-args=-Wl,-rpath,$ORIGIN/../lib -C force-frame-pointers=yes -Z crate-attr=doc(html_root_url="https://doc.rust-lang.org/nightly/") -Z binary-dep-depinfo -Z force-unstable-if-unmarked

[oli-obk]

Is there an actual panic message? Your log starts at the backtrace, but the message, file, and line info is missing

[mzabaluev]

Is there an actual panic message? Your log starts at the backtrace, but the message, file, and line info is missing

@oli-obk I have added the error message to the description, HTH.

[oli-obk]

minimal repro:

#![feature(rustc_attrs)]
#![feature(effects)]
#![feature(const_for)]
#![feature(const_mut_refs)]
#![feature(const_trait_impl)]
#![feature(staged_api)]

#![stable(feature = "rust1", since = "1.0.0")]

#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_int_pow", since = "1.50.0")]
pub const fn pow() {
    for _ in 0..42 {}
}

basically what we want to prevent is the usage of unstable const features in a const_stable function. So instead of looking for missing globally set features, we actually need to look for rustc_allow_const_fn_unstable instead

cc @compiler-errors for the funny ICE message

[oli-obk]

I think we can close this issue by changing the ICE message and making it print more information so it can actually be debugged.