Opaque error error message if LLVM OOMs during full LTO

[matklad]

Starting today, I am seeing the following error in rust-analyzer's CI

   Compiling ide_ssr v0.0.0 (D:\a\rust-analyzer\rust-analyzer\crates\ide_ssr)
   Compiling ide v0.0.0 (D:\a\rust-analyzer\rust-analyzer\crates\ide)
fatal runtime error: Rust cannot catch foreign exceptions
error: could not compile `rust-analyzer`

Caused by:
  process didn't exit successfully: `rustc --crate-name rust_analyzer --edition=2018 crates\rust-analyzer\src/bin/main.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -C opt-level=3 -C lto -C debuginfo=1 -C metadata=79e139aff8fa11a3 --out-dir D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps --target x86_64-pc-windows-msvc -C linker=rust-lld -L dependency=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps -L dependency=D:\a\rust-analyzer\rust-analyzer\target\release\deps --extern always_assert=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libalways_assert-a5c3950cbac605c2.rlib --extern anyhow=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libanyhow-b92146a0e6d6413a.rlib --extern cfg=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libcfg-3451d2c1a2e1dd21.rlib --extern crossbeam_channel=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libcrossbeam_channel-8dc7041ff99977ca.rlib --extern dissimilar=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libdissimilar-a85bc727a6ef040f.rlib --extern env_logger=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libenv_logger-0c1b28edc895da2b.rlib --extern flycheck=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libflycheck-5a3d33ebf8982c91.rlib --extern hir=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libhir-f1c482a9f52ec024.rlib --extern hir_def=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libhir_def-84f9901156f3c37e.rlib --extern hir_ty=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libhir_ty-a9ff862504d19d8d.rlib --extern ide=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libide-aca7a6f5717b60fb.rlib --extern ide_db=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libide_db-30818be798bb4bd5.rlib --extern ide_ssr=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libide_ssr-25d0dd581c0a1f21.rlib --extern itertools=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libitertools-795925f20865e421.rlib --extern jod_thread=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libjod_thread-7b553ff844830aa9.rlib --extern log=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\liblog-d97217edfa7fa3e7.rlib --extern lsp_server=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\liblsp_server-1e7f9bab880d71c8.rlib --extern lsp_types=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\liblsp_types-55078c6e33798392.rlib --extern oorandom=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\liboorandom-fdca57d9670229c1.rlib --extern parking_lot=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libparking_lot-7574759f69a57d6d.rlib --extern proc_macro_srv=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libproc_macro_srv-14eb3c78110c3882.rlib --extern profile=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libprofile-4da50626cb505dfd.rlib --extern project_model=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libproject_model-54a1bf11492f68c6.rlib --extern rayon=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\librayon-0a74d6af60e18fd2.rlib --extern rust_analyzer=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\librust_analyzer-2fedc7074222fbbe.rlib --extern rustc_hash=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\librustc_hash-fd535a62a1631d92.rlib --extern serde=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libserde-aa69b9bf35e75485.rlib --extern serde_json=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libserde_json-d9c58ca21bdb469a.rlib --extern serde_path_to_error=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libserde_path_to_error-4c50a4fa3dc519a6.rlib --extern stdx=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libstdx-f1ad487878f200cc.rlib --extern syntax=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libsyntax-f7fcb85a088de37a.rlib --extern text_edit=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libtext_edit-b086ec402917223c.rlib --extern threadpool=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libthreadpool-88302915b8bc103a.rlib --extern toolchain=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libtoolchain-4dec8cd4ff032434.rlib --extern tracing=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libtracing-c63fa0ca38f03367.rlib --extern tracing_subscriber=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libtracing_subscriber-a3129190deedb9fe.rlib --extern tracing_tree=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libtracing_tree-700f7dfac6fdc792.rlib --extern vfs=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libvfs-0da9b6babb9c702b.rlib --extern vfs_notify=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libvfs_notify-09fa85939f13d34c.rlib --extern winapi=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libwinapi-a329bfbc416edc71.rlib --extern xflags=D:\a\rust-analyzer\rust-analyzer\target\x86_64-pc-windows-msvc\release\deps\libxflags-3011d41fb4019847.rlib -D warnings -W unreachable-pub` 
(exit code: 0xc0000409, STATUS_STACK_BUFFER_OVERRUN)
Error: command `cargo build --manifest-path ./crates/rust-analyzer/Cargo.toml --bin rust-analyzer --target x86_64-pc-windows-msvc --release` failed, exit code: 101
error: process didn't exit successfully: `target\debug\xtask.exe dist` (exit code: 1)
Error: Process completed with exit code 1.

This happens on windows builders, when compiling with --target x86_64-pc-windows-msvc or --target aarch64-pc-windows-msvc. The step which fails is compilation of the final binary crate. The binary is complied in --release mode with lto=true. I think the failure appeared after I added debug=1 as well.

So my theory is that maybe this is just some OOM in the linker, and not a problem with rustc per se? The error message is rather unhelpful though.

The relevant CI run: https://github.com/rust-analyzer/rust-analyzer/runs/2649419225?check_suite_focus=true#step:5:330

[ehuss]

I confirmed that rustc prints Rust cannot catch foreign exceptions when LLVM runs out of memory. Presumably it is raising bad_alloc, but AFAIK rust cannot catch C++ exceptions. I'm not sure if it could be caught on the C++ side, or if there is some LLVM build option to change the oom behavior.

rust-analyzer needs about 5 to 6 GB to build with LTO. I think GitHub Actions systems have 7GB of RAM, so it may be getting close to that limit. I might suggest using 'thin' LTO which should use substantially less memory.

[hameerabbasi]

Assigning P-high based on WG-prioritization discussion on Zulip and removing I-prioritize.

@rustbot modify labels -I-prioritize +P-high