rustc 1.78.0 segfault on MacOS / M1

[dwrensha]

I get a segfault when I try to run cargo test on the following code:

# Cargo.toml

[package]

name = "rustc-segfault"
edition = "2021"

// src/lib.rs

#[repr(C, align(8))]
pub struct ConstantReader<T> {
    pub phantom: core::marker::PhantomData<T>,
    pub words: &'static [u64],
}

pub mod test_constants {
  pub static VOID_LIST_CONST: crate::ConstantReader<usize> = {
    pub static WORDS: [u64; 1] = [0];
    crate::ConstantReader {
      phantom: ::std::marker::PhantomData,
      words: &WORDS,
    }
  };
}

#[test]
fn test_constants() {
    let _ = test_constants::VOID_LIST_CONST.words.as_ptr();
}

 % rustc -vV
rustc 1.78.0 (9b00956e5 2024-04-29)
binary: rustc
commit-hash: 9b00956e56009bab2aa15d7bff10916599e3d6d6
commit-date: 2024-04-29
host: aarch64-apple-darwin
release: 1.78.0
LLVM version: 18.1.2

 % cargo test
   Compiling rustc-segfault v0.0.0 (/Users/dwrensha/Desktop/rustc-segfault)
error: could not compile `rustc-segfault` (lib test)

Caused by:
  process didn't exit successfully: `/Users/dwrensha/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustc --crate-name rustc_segfault --edition=2021 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=179 --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 -C split-debuginfo=unpacked --test -C metadata=47a41d92fd841df5 -C extra-filename=-47a41d92fd841df5 --out-dir /Users/dwrensha/Desktop/rustc-segfault/target/debug/deps -C incremental=/Users/dwrensha/Desktop/rustc-segfault/target/debug/incremental -L dependency=/Users/dwrensha/Desktop/rustc-segfault/target/debug/deps` (signal: 11, SIGSEGV: invalid memory reference)

I see the same behavior with the latest nightly rustc. I see no error with rustc 1.77.0 or earlier. It also works fine on Linux, and on an older Intel Macbook.

I also updated to the latest XCode to make sure all parts of my toolchain were up to date. Doing so did not make the segfault go away.

[dwrensha]

The problem disappears if I turn off incremental compilation by adding this to the Cargo.toml:

[profile.dev]
incremental = false

[lqd]

I believe this bisects to LLVM 18 from #120055 cc @nikic

[saethlin]

We are hitting an LLVM assertion:

Assertion failed: (N < NumContainedTys && "Element number out of range!"), function getElementType, file DerivedTypes.h, line 343.

[nikic]

Could someone please run cargo -v and then repeat the rustc command with -C save-temps and share the bitcode files?

[DianQK]

Could someone please run cargo -v and then repeat the rustc command with -C save-temps and share the bitcode files?

I can reproduce it, and I will try to reduce it.

[DianQK]

Upstream issue: llvm/llvm-project#92062
Reduced: https://llvm.godbolt.org/z/a4h1abfKc.

target triple = "arm64"

@p = external global { {}, { ptr } }

define void @foo() {
bb:
  %i1 = load ptr, ptr @p, align 8
  store ptr %i1, ptr null, align 8
  ret void
}

[DianQK]

It has already been backported to LLVM 18: llvm/llvm-project#92129.
@rustbot label +llvm-fixed-upstream